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The earliest archaeological evidence for the use of the Greek abacus dates to the 5th century BC. Demosthenes 384 BC322 BC complained that the need to use pebbles for calculations was too difficult. A play by Alexis from the 4th century BC mentions an abacus and pebbles for accounting, and both Diogenes and Polybius use the abacus as a metaphor for human behavior, stating "that men that sometimes stood for more and sometimes for less" like the pebbles on an abacus. The Greek abacus was a table of wood or marble, preset with small counters in wood or metal for mathematical calculations. This Greek abacus saw use in Achaemenid Persia, the Etruscan civilization, Ancient Rome, and the Western Christian world until the French Revolution.
A tablet found on the Greek island Salamis in 1846 AD the Salamis Tablet dates to 300 BC, making it the oldest counting board discovered so far. It is a slab of white marble in length, wide, and thick, on which are 5 groups of markings. In the tablet's center is a set of |
5 parallel lines equally divided by a vertical line, capped with a semicircle at the intersection of the bottommost horizontal line and the single vertical line. Below these lines is a wide space with a horizontal crack dividing it. Below this crack is another group of eleven parallel lines, again divided into two sections by a line perpendicular to them, but with the semicircle at the top of the intersection; the third, sixth and ninth of these lines are marked with a cross where they intersect with the vertical line. Also from this time frame, the Darius Vase was unearthed in 1851. It was covered with pictures, including a "treasurer" holding a wax tablet in one hand while manipulating counters on a table with the other.
China
The earliest known written documentation of the Chinese abacus dates to the 2nd century BC.
The Chinese abacus, also known as the suanpan , lit. "calculating tray", is typically tall and comes in various widths, depending on the operator. It usually has more than seven rods. There |
are two beads on each rod in the upper deck and five beads each in the bottom one. The beads are usually rounded and made of hardwood. The beads are counted by moving them up or down towards the beam; beads moved toward the beam are counted, while those moved away from it are not. One of the top beads is 5, while one of the bottom beads is 1. Each rod has a number under it, showing the place value. The suanpan can be reset to the starting position instantly by a quick movement along the horizontal axis to spin all the beads away from the horizontal beam at the center.
The prototype of the Chinese abacus appeared during the Han Dynasty, and the beads are oval. The Song Dynasty and earlier used the 14 type or fourbeads abacus similar to the modern abacus including the shape of the beads commonly known as Japanesestyle abacus.
In the early Ming Dynasty, the abacus began to appear in a 15 ratio. The upper deck had one bead and the bottom had five beads. In the late Ming Dynasty, the abacus styles appeared in a |
25 ratio. The upper deck had two beads, and the bottom had five.
Various calculation techniques were devised for Suanpan enabling efficient calculations. Some schools teach students how to use it.
In the long scroll Along the River During the Qingming Festival painted by Zhang Zeduan during the Song dynasty 9601297, a suanpan is clearly visible beside an account book and doctor's prescriptions on the counter of an apothecary's Feibao.
The similarity of the Roman abacus to the Chinese one suggests that one could have inspired the other, given evidence of a trade relationship between the Roman Empire and China. However, no direct connection has been demonstrated, and the similarity of the abacuses may be coincidental, both ultimately arising from counting with five fingers per hand. Where the Roman model like most modern Korean and Japanese has 4 plus 1 bead per decimal place, the standard suanpan has 5 plus 2. Incidentally, this allows use with a hexadecimal numeral system or any base up to 18 which may h |
ave been used for traditional Chinese measures of weight. Instead of running on wires as in the Chinese, Korean, and Japanese models, the Roman model used grooves, presumably making arithmetic calculations much slower.
Another possible source of the suanpan is Chinese counting rods, which operated with a decimal system but lacked the concept of zero as a placeholder. The zero was probably introduced to the Chinese in the Tang dynasty 618907 when travel in the Indian Ocean and the Middle East would have provided direct contact with India, allowing them to acquire the concept of zero and the decimal point from Indian merchants and mathematicians.
Rome
The normal method of calculation in ancient Rome, as in Greece, was by moving counters on a smooth table. Originally pebbles calculi were used. Later, and in medieval Europe, jetons were manufactured. Marked lines indicated units, fives, tens, etc. as in the Roman numeral system. This system of 'counter casting' continued into the late Roman empire and in medie |
val Europe and persisted in limited use into the nineteenth century. Due to Pope Sylvester II's reintroduction of the abacus with modifications, it became widely used in Europe again during the 11th century This abacus used beads on wires, unlike the traditional Roman counting boards, which meant the abacus could be used much faster and was more easily moved.
Writing in the 1st century BC, Horace refers to the wax abacus, a board covered with a thin layer of black wax on which columns and figures were inscribed using a stylus.
One example of archaeological evidence of the Roman abacus, shown nearby in reconstruction, dates to the 1st century AD. It has eight long grooves containing up to five beads in each and eight shorter grooves having either one or no beads in each. The groove marked I indicates units, X tens, and so on up to millions. The beads in the shorter grooves denote fives five units, five tens, etc., essentially in a biquinary coded decimal system, related to the Roman numerals. The short groov |
es on the right may have been used for marking Roman "ounces" i.e. fractions.
India
The Abhidharmakoabhya of Vasubandhu 316396, a Sanskrit work on Buddhist philosophy, says that the secondcentury CE philosopher Vasumitra said that "placing a wick Sanskrit vartik on the number one ekka means it is a one while placing the wick on the number hundred means it is called a hundred, and on the number one thousand means it is a thousand". It is unclear exactly what this arrangement may have been. Around the 5th century, Indian clerks were already finding new ways of recording the contents of the abacus. Hindu texts used the term nya zero to indicate the empty column on the abacus.
Japan
In Japan, the abacus is called soroban , lit. "counting tray". It was imported from China in the 14th century. It was probably in use by the working class a century or more before the ruling class adopted it, as the class structure obstructed such changes. The 14 abacus, which removes the seldomused second and fifth bead became p |
opular in the 1940s.
Today's Japanese abacus is a 14 type, fourbead abacus, introduced from China in the Muromachi era. It adopts the form of the upper deck one bead and the bottom four beads. The top bead on the upper deck was equal to five and the bottom one is similar to the Chinese or Korean abacus, and the decimal number can be expressed, so the abacus is designed as a onefour device. The beads are always in the shape of a diamond. The quotient division is generally used instead of the division method; at the same time, in order to make the multiplication and division digits consistently use the division multiplication. Later, Japan had a 35 abacus called , which is now in the Ize Rongji collection of Shansi Village in Yamagata City. Japan also used a 25 type abacus.
The fourbead abacus spread, and became common around the world. Improvements to the Japanese abacus arose in various places. In China an aluminium frame plastic bead abacus was used. The file is next to the four beads, and pressing the "c |
learing" button put the upper bead in the upper position, and the lower bead in the lower position.
The abacus is still manufactured in Japan even with the proliferation, practicality, and affordability of pocket electronic calculators. The use of the soroban is still taught in Japanese primary schools as part of mathematics, primarily as an aid to faster mental calculation. Using visual imagery can complete a calculation as quickly as a physical instrument.
Korea
The Chinese abacus migrated from China to Korea around 1400 AD. Koreans call it jupan , supan or jusan . The fourbeads abacus 14 was introduced during the Goryeo Dynasty. The 51 abacus was introduced to Korea from China during the Ming Dynasty.
Native America
Some sources mention the use of an abacus called a nepohualtzintzin in ancient Aztec culture. This Mesoamerican abacus used a 5digit base20 system. The word Nephualtzintzin comes from Nahuatl, formed by the roots; Ne personal ; phual or phualli the account ; and tzintzin small simila |
r elements. Its complete meaning was taken as counting with small similar elements. Its use was taught in the Calmecac to the temalpouhqueh , who were students dedicated to taking the accounts of skies, from childhood.
The Nephualtzintzin was divided into two main parts separated by a bar or intermediate cord. In the left part were four beads. Beads in the first row have unitary values 1, 2, 3, and 4, and on the right side, three beads had values of 5, 10, and 15, respectively. In order to know the value of the respective beads of the upper rows, it is enough to multiply by 20 by each row, the value of the corresponding count in the first row.
The device featured 13 rows with 7 beads, 91 in total. This was a basic number for this culture. It had a close relation to natural phenomena, the underworld, and the cycles of the heavens. One Nephualtzintzin 91 represented the number of days that a season of the year lasts, two Nephualtzitzin 182 is the number of days of the corn's cycle, from its sowing to its har |
vest, three Nephualtzintzin 273 is the number of days of a baby's gestation, and four Nephualtzintzin 364 completed a cycle and approximated one year. When translated into modern computer arithmetic, the Nephualtzintzin amounted to the rank from 10 to 18 in floating point, which precisely calculated large and small amounts, although round off was not allowed.
The rediscovery of the Nephualtzintzin was due to the Mexican engineer David Esparza Hidalgo, who in his travels throughout Mexico found diverse engravings and paintings of this instrument and reconstructed several of them in gold, jade, encrustations of shell, etc. Very old Nephualtzintzin are attributed to the Olmec culture, and some bracelets of Mayan origin, as well as a diversity of forms and materials in other cultures.
Sanchez wrote in Arithmetic in Maya that another base 5, base 4 abacus had been found in the Yucatn Peninsula that also computed calendar data. This was a finger abacus, on one hand, 0, 1, 2, 3, and 4 were used; and on the other h |
and 0, 1, 2, and 3 were used. Note the use of zero at the beginning and end of the two cycles.
The quipu of the Incas was a system of colored knotted cords used to record numerical data, like advanced tally sticks but not used to perform calculations. Calculations were carried out using a yupana Quechua for "counting tool"; see figure which was still in use after the conquest of Peru. The working principle of a yupana is unknown, but in 2001 Italian mathematician De Pasquale proposed an explanation. By comparing the form of several yupanas, researchers found that calculations were based using the Fibonacci sequence 1, 1, 2, 3, 5 and powers of 10, 20, and 40 as place values for the different fields in the instrument. Using the Fibonacci sequence would keep the number of grains within any one field at a minimum.
Russia
The Russian abacus, the schoty , plural from , counting, usually has a single slanted deck, with ten beads on each wire except one wire with four beads for quarterruble fractions. Older model |
s have another 4bead wire for quarterkopeks, which were minted until 1916. The Russian abacus is often used vertically, with each wire running horizontally. The wires are usually bowed upward in the center, to keep the beads pinned to either side. It is cleared when all the beads are moved to the right. During manipulation, beads are moved to the left. For easy viewing, the middle 2 beads on each wire the 5th and 6th bead usually are of a different color from the other eight. Likewise, the left bead of the thousands wire and the million wire, if present may have a different color.
The Russian abacus was in use in shops and markets throughout the former Soviet Union, and its usage was taught in most schools until the 1990s. Even the 1874 invention of mechanical calculator, Odhner arithmometer, had not replaced them in Russia; according to Yakov Perelman. Some businessmen attempting to import calculators into the Russian Empire were known to leave in despair after watching a skilled abacus operator. Likewise, |
the mass production of Felix arithmometers since 1924 did not significantly reduce abacus use in the Soviet Union. The Russian abacus began to lose popularity only after the mass production of domestic microcalculators in 1974.
The Russian abacus was brought to France around 1820 by mathematician JeanVictor Poncelet, who had served in Napoleon's army and had been a prisoner of war in Russia. The abacus had fallen out of use in western Europe in the 16th century with the rise of decimal notation and algorismic methods. To Poncelet's French contemporaries, it was something new. Poncelet used it, not for any applied purpose, but as a teaching and demonstration aid. The Turks and the Armenian people used abacuses similar to the Russian schoty. It was named a coulba by the Turks and a choreb by the Armenians.
School abacus
Around the world, abacuses have been used in preschools and elementary schools as an aid in teaching the numeral system and arithmetic.
In Western countries, a bead frame similar to the Rus |
sian abacus but with straight wires and a vertical frame is common see image.
The wireframe may be used either with positional notation like other abacuses thus the 10wire version may represent numbers up to 9,999,999,999, or each bead may represent one unit e.g. 74 can be represented by shifting all beads on 7 wires and 4 beads on the 8th wire, so numbers up to 100 may be represented. In the bead frame shown, the gap between the 5th and 6th wire, corresponding to the color change between the 5th and the 6th bead on each wire, suggests the latter use. Teaching multiplication, e.g. 6 times 7, may be represented by shifting 7 beads on 6 wires.
The redandwhite abacus is used in contemporary primary schools for a wide range of numberrelated lessons. The twenty bead version, referred to by its Dutch name rekenrek "calculating frame", is often used, either on a string of beads or on a rigid framework.
Feynman vs the abacus
Physicist Richard Feynman was noted for facility in mathematical calculations. He wrote a |
bout an encounter in Brazil with a Japanese abacus expert, who challenged him to speed contests between Feynman's pen and paper, and the abacus. The abacus was much faster for addition, somewhat faster for multiplication, but Feynman was faster at division. When the abacus was used for a really difficult challenge, i.e. cube roots, Feynman won easily. However, the number chosen at random was close to a number Feynman happened to know was an exact cube, allowing him to use approximate methods.
Neurological analysis
Learning how to calculate with the abacus may improve capacity for mental calculation. Abacusbased mental calculation AMC, which was derived from the abacus, is the act of performing calculations, including addition, subtraction, multiplication, and division, in the mind by manipulating an imagined abacus. It is a highlevel cognitive skill that runs calculations with an effective algorithm. People doing longterm AMC training show higher numerical memory capacity and experience more effectively con |
nected neural pathways. They are able to retrieve memory to deal with complex processes. AMC involves both visuospatial and visuomotor processing that generate the visual abacus and move the imaginary beads. Since it only requires that the final position of beads be remembered, it takes less memory and less computation time.
Renaissance abacuses
Binary abacus
The binary abacus is used to explain how computers manipulate numbers. The abacus shows how numbers, letters, and signs can be stored in a binary system on a computer, or via ASCII. The device consists of a series of beads on parallel wires arranged in three separate rows. The beads represent a switch on the computer in either an "on" or "off" position.
Visually impaired users
An adapted abacus, invented by Tim Cranmer, and called a Cranmer abacus is commonly used by visually impaired users. A piece of soft fabric or rubber is placed behind the beads, keeping them in place while the users manipulate them. The device is then used to perform the mathem |
atical functions of multiplication, division, addition, subtraction, square root, and cube root.
Although blind students have benefited from talking calculators, the abacus is often taught to these students in early grades. Blind students can also complete mathematical assignments using a braillewriter and Nemeth code a type of braille code for mathematics but large multiplication and long division problems are tedious. The abacus gives these students a tool to compute mathematical problems that equals the speed and mathematical knowledge required by their sighted peers using pencil and paper. Many blind people find this number machine a useful tool throughout life.
See also
Chinese Zhusuan
Chisanbop
Logical abacus
Mental abacus
Napier's bones
Sand table
Slide rule
Soroban
Suanpan
Notes
Footnotes
References
Reading
External links
Tutorials
Min Multimedia
Abacus curiosities
Abacus in Various Number Systems at cuttheknot
Java applet of Chinese, Japanese and Russian abaci
An atomicscal |
e abacus
Examples of Abaci
Aztex Abacus
Indian Abacus
Mathematical tools
Chinese mathematics
Egyptian mathematics
Greek mathematics
Indian mathematics
Japanese mathematics
Roman mathematics |
An acid is a molecule or ion capable of either donating a proton i.e., hydrogen ion, H, known as a BrnstedLowry acid, or, capable of forming a covalent bond with an electron pair, known as a Lewis acid.
The first category of acids are the proton donors, or BrnstedLowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O and are known as Arrhenius acids. Brnsted and Lowry generalized the Arrhenius theory to include nonaqueous solvents. A Brnsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H.
Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals like calcium to form salts. The word acid is derived from the Latin acidusacre, meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referr |
ed to as "acid" as in "dissolved in acid", while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.
Common aqueous acids include hydrochloric acid a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes, acetic acid vinegar is a dilute aqueous solution of this liquid, sulfuric acid used in car batteries, and citric acid found in citrus fruits. As these examples show, acids in the colloquial sense can be solutions or pure substances, and can be derived from acids in the strict sense that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.
The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride BF3, whose |
boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia NH3. Lewis considered this as a generalization of the Brnsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons H into the solution, which then accept electron pairs. However, hydrogen chloride, acetic acid, and most other BrnstedLowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or BrnstedLowry acids. In modern terminology, an acid is implicitly a Brnsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid.
Definitions and concepts
Modern definitions are concerned with the fundamental chemical reactions common to all acids.
Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and |
BrnstedLowry definitions are the most relevant.
The BrnstedLowry definition is the most widely used definition; unless otherwise specified, acidbase reactions are assumed to involve the transfer of a proton H from an acid to a base.
Hydronium ions are acids according to all three definitions. Although alcohols and amines can be BrnstedLowry acids, they can also function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms.
Arrhenius acids
In 1884, Svante Arrhenius attributed the properties of acidity to hydrogen ions H, later described as protons or hydrons. An Arrhenius acid is a substance that, when added to water, increases the concentration of H ions in the water. Note that chemists often write Haq and refer to the hydrogen ion when describing acidbase reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion H3O or other forms H5O2, H9O4. Thus, an Arrhenius acid can also be described as a substance that increases |
the concentration of hydronium ions when added to water. Examples include molecular substances such as hydrogen chloride and acetic acid.
An Arrhenius base, on the other hand, is a substance which increases the concentration of hydroxide OH ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H2O molecules
H3O OH H2Oliq H2Oliq
Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it.
In an acidic solution, the concentration of hydronium ions is greater than 107 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7.
BrnstedLowry acids
While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, |
chemists Johannes Nicolaus Brnsted and Thomas Martin Lowry independently recognized that acidbase reactions involve the transfer of a proton. A BrnstedLowry acid or simply Brnsted acid is a species that donates a proton to a BrnstedLowry base. BrnstedLowry acidbase theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid CH3COOH, the organic acid that gives vinegar its characteristic taste
Both theories easily describe the first reaction CH3COOH acts as an Arrhenius acid because it acts as a source of H3O when dissolved in water, and it acts as a Brnsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia NH3, but does not relate to the Arrhenius definition of an acid because the reaction does not produce hydronium. Nevertheless, CH3COOH is both an Arrhenius and a BrnstedLowry acid.
BrnstedLowry theory can be used to describe reactions of molecular compounds in nonaqueous s |
olution or the gas phase. Hydrogen chloride HCl and ammonia combine under several different conditions to form ammonium chloride, NH4Cl. In aqueous solution HCl behaves as hydrochloric acid and exists as hydronium and chloride ions. The following reactions illustrate the limitations of Arrhenius's definition
H3O Cl NH3 Cl NHaq H2O
HClbenzene NH3benzene NH4Cls
HClg NH3g NH4Cls
As with the acetic acid reactions, both definitions work for the first example, where water is the solvent and hydronium ion is formed by the HCl solute. The next two reactions do not involve the formation of ions but are still protontransfer reactions. In the second reaction hydrogen chloride and ammonia dissolved in benzene react to form solid ammonium chloride in a benzene solvent and in the third gaseous HCl and NH3 combine to form the solid.
Lewis acids
A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acidbase characteristics that do not involve a proton |
transfer. A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor. Brnsted acidbase reactions are proton transfer reactions while Lewis acidbase reactions are electron pair transfers. Many Lewis acids are not BrnstedLowry acids. Contrast how the following reactions are described in terms of acidbase chemistry
In the first reaction a fluoride ion, F, gives up an electron pair to boron trifluoride to form the product tetrafluoroborate. Fluoride "loses" a pair of valence electrons because the electrons shared in the BF bond are located in the region of space between the two atomic nuclei and are therefore more distant from the fluoride nucleus than they are in the lone fluoride ion. BF3 is a Lewis acid because it accepts the electron pair from fluoride. This reaction cannot be described in terms of Brnsted theory because there is no proton transfer. The second reaction can be described using either theory. A proton is transferred from an u |
nspecified Brnsted acid to ammonia, a Brnsted base; alternatively, ammonia acts as a Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion. The species that gains the electron pair is the Lewis acid; for example, the oxygen atom in H3O gains a pair of electrons when one of the HO bonds is broken and the electrons shared in the bond become localized on oxygen. Depending on the context, a Lewis acid may also be described as an oxidizer or an electrophile. Organic Brnsted acids, such as acetic, citric, or oxalic acid, are not Lewis acids. They dissociate in water to produce a Lewis acid, H, but at the same time also yield an equal amount of a Lewis base acetate, citrate, or oxalate, respectively, for the acids mentioned. This article deals mostly with Brnsted acids rather than Lewis acids.
Dissociation and equilibrium
Reactions of acids are often generalized in the form , where HA represents the acid and A is the conjugate base. This reaction is referred to as protolysis. The pro |
tonated form HA of an acid is also sometimes referred to as the free acid.
Acidbase conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton protonation and deprotonation, respectively. Note that the acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as . In solution there exists an equilibrium between the acid and its conjugate base. The equilibrium constant K is an expression of the equilibrium concentrations of the molecules or the ions in solution. Brackets indicate concentration, such that H2O means the concentration of H2O. The acid dissociation constant Ka is generally used in the context of acidbase reactions. The numerical value of Ka is equal to the product of the concentrations of the products divided by the concentration of the reactants, where the reactant is the acid HA and the products are the conjugate base and H.
The stronger of two acids will have a higher Ka than |
the weaker acid; the ratio of hydrogen ions to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for Ka spans many orders of magnitude, a more manageable constant, pKa is more frequently used, where pKa log10 Ka. Stronger acids have a smaller pKa than weaker acids. Experimentally determined pKa at 25 C in aqueous solution are often quoted in textbooks and reference material.
Nomenclature
Arrhenius acids are named according to their anions. In the classical naming system, the ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as its anion, so the hydro prefix is used, and the ide suffix makes the name take the form hydrochloric acid.
Classical naming system
In the IUPAC naming system, "aqueous" is simply added to the name of the ionic compound. Thus, fo |
r hydrogen chloride, as an acid solution, the IUPAC name is aqueous hydrogen chloride.
Acid strength
The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely dissociates in water; in other words, one mole of a strong acid HA dissolves in water yielding one mole of H and one mole of the conjugate base, A, and none of the protonated acid HA. In contrast, a weak acid only partially dissociates and at equilibrium both the acid and the conjugate base are in solution. Examples of strong acids are hydrochloric acid HCl, hydroiodic acid HI, hydrobromic acid HBr, perchloric acid HClO4, nitric acid HNO3 and sulfuric acid H2SO4. In water each of these essentially ionizes 100. The stronger an acid is, the more easily it loses a proton, H. Two key factors that contribute to the ease of deprotonation are the polarity of the HA bond and the size of atom A, which determines the strength of the HA bond. Acid strengths are also often discussed in terms of the stability |
of the conjugate base.
Stronger acids have a larger acid dissociation constant, Ka and a more negative pKa than weaker acids.
Sulfonic acids, which are organic oxyacids, are a class of strong acids. A common example is toluenesulfonic acid tosylic acid. Unlike sulfuric acid itself, sulfonic acids can be solids. In fact, polystyrene functionalized into polystyrene sulfonate is a solid strongly acidic plastic that is filterable.
Superacids are acids stronger than 100 sulfuric acid. Examples of superacids are fluoroantimonic acid, magic acid and perchloric acid. Superacids can permanently protonate water to give ionic, crystalline hydronium "salts". They can also quantitatively stabilize carbocations.
While Ka measures the strength of an acid compound, the strength of an aqueous acid solution is measured by pH, which is an indication of the concentration of hydronium in the solution. The pH of a simple solution of an acid compound in water is determined by the dilution of the compound and the compound's Ka. |
Lewis acid strength in nonaqueous solutions
Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by CB plots. It has been shown that to define the order of Lewis acid strength at least two properties must be considered. For Pearson's qualitative HSAB theory the two properties are hardness and strength while for Drago's quantitative ECW model the two properties are electrostatic and covalent.
Chemical characteristics
Monoprotic acids
Monoprotic acids, also known as monobasic acids, are those acids that are able to donate one proton per molecule during the process of dissociation sometimes called ionization as shown below symbolized by HA
Ka
Common examples of monoprotic acids in mineral acids include hydrochloric acid HCl and nitric acid HNO3. On the other hand, for organic acids the term mainly indicates the presence |
of one carboxylic acid group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid HCOOH, acetic acid CH3COOH and benzoic acid C6H5COOH.
Polyprotic acids
Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic or dibasic acid two potential protons to donate, and triprotic or tribasic acid three potential protons to donate. Some macromolecules such as proteins and nucleic acids can have a very large number of acidic protons.
A diprotic acid here symbolized by H2A can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2.
Ka1
Ka2
The first dissociation constant is typically greater than the second i.e., Ka1 Ka2. For example, sulfuric acid H2SO4 can donate one proton to form the |
bisulfate anion HSO, for which Ka1 is very large; then it can donate a second proton to form the sulfate anion SO, wherein the Ka2 is intermediate strength. The large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid can lose one proton to form bicarbonate anion and lose a second to form carbonate anion CO. Both Ka values are small, but Ka1 Ka2 .
A triprotic acid H3A can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 Ka2 Ka3.
Ka1
Ka2
Ka3
An inorganic example of a triprotic acid is orthophosphoric acid H3PO4, usually just called phosphoric acid. All three protons can be successively lost to yield H2PO, then HPO, and finally PO, the orthophosphate ion, usually just called phosphate. Even though the positions of the three protons on the original phosphoric acid molecule are equivalent, the successive Ka values differ since it is energetically less favorable to lose a proton if the c |
onjugate base is more negatively charged. An organic example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion.
Although the subsequent loss of each hydrogen ion is less favorable, all of the conjugate bases are present in solution. The fractional concentration, alpha, for each species can be calculated. For example, a generic diprotic acid will generate 3 species in solution H2A, HA, and A2. The fractional concentrations can be calculated as below when given either the pH which can be converted to the H or the concentrations of the acid with all its conjugate bases
A plot of these fractional concentrations against pH, for given K1 and K2, is known as a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general n protic acid that has been deprotonated i times
where K0 1 and the other Kterms are the dissociation constants for the acid.
Neutralization
Neutralization is the reaction between an acid and a base, p |
roducing a salt and neutralized base; for example, hydrochloric acid and sodium hydroxide form sodium chloride and water
HClaq NaOHaq H2Ol NaClaq
Neutralization is the basis of titration, where a pH indicator shows equivalence point when the equivalent number of moles of a base have been added to an acid. It is often wrongly assumed that neutralization should result in a solution with pH 7.0, which is only the case with similar acid and base strengths during a reaction.
Neutralization with a base weaker than the acid results in a weakly acidic salt. An example is the weakly acidic ammonium chloride, which is produced from the strong acid hydrogen chloride and the weak base ammonia. Conversely, neutralizing a weak acid with a strong base gives a weakly basic salt e.g., sodium fluoride from hydrogen fluoride and sodium hydroxide.
Weak acidweak base equilibrium
In order for a protonated acid to lose a proton, the pH of the system must rise above the pKa of the acid. The decreased concentration of H in tha |
t basic solution shifts the equilibrium towards the conjugate base form the deprotonated form of the acid. In lowerpH more acidic solutions, there is a high enough H concentration in the solution to cause the acid to remain in its protonated form.
Solutions of weak acids and salts of their conjugate bases form buffer solutions.
Titration
To determine the concentration of an acid in an aqueous solution, an acidbase titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added. The titration curve of an acid titrated by a base has two axes, with the base volume on the xaxis and the solution's pH value on the yaxis. The pH of the solution always goes up as the base is added to the solution.
Example Diprotic acid
For each diprotic acid titration curve, from left to right, there are two midpoints, two equivalence points, and two buffer regions.
Equ |
ivalence points
Due to the successive dissociation processes, there are two equivalence points in the titration curve of a diprotic acid. The first equivalence point occurs when all first hydrogen ions from the first ionization are titrated. In other words, the amount of OH added equals the original amount of H2A at the first equivalence point. The second equivalence point occurs when all hydrogen ions are titrated. Therefore, the amount of OH added equals twice the amount of H2A at this time. For a weak diprotic acid titrated by a strong base, the second equivalence point must occur at pH above 7 due to the hydrolysis of the resulted salts in the solution. At either equivalence point, adding a drop of base will cause the steepest rise of the pH value in the system.
Buffer regions and midpoints
A titration curve for a diprotic acid contains two midpoints where pHpKa. Since there are two different Ka values, the first midpoint occurs at pHpKa1 and the second one occurs at pHpKa2. Each segment of the curve w |
hich contains a midpoint at its center is called the buffer region. Because the buffer regions consist of the acid and its conjugate base, it can resist pH changes when base is added until the next equivalent points.
Applications of acids
Acids exist universally in our lives. There are both numerous kinds of natural acid compounds with biological functions and massive synthesized acids which are used in many ways.
In industry
Acids are fundamental reagents in treating almost all processes in today's industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, which is also the mostproduced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batteries and dyes, as well as used in processing many products such like removing impurities. According to the statistics data in 2011, the annual production of sulfuric acid was around 200 million tonnes in the world. For example, phosphate minerals react with sulfuric acid to produce phosphoric acid for the pr |
oduction of phosphate fertilizers, and zinc is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning.
In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acid reacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can be esterified with alcohols, to produce esters.
Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuric acid in a car battery.
In food
Tartaric acid is an important component of some commonly used foods like unripened mangoes and tamarind. Natural fruits and vegetables also contain acids. Citric acid is present in oranges, lemon and other citrus fruits. Oxalic acid is present in tomatoes, spinach, and especially in carambola and rhubarb; rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid. Ascorbic acid |
Vitamin C is an essential vitamin for the human body and is present in such foods as amla Indian gooseberry, lemon, citrus fruits, and guava.
Many acids can be found in various kinds of food as additives, as they alter their taste and serve as preservatives. Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in daytoday life as vinegar. Citric acid is used as a preservative in sauces and pickles.
Carbonic acid is one of the most common acid additives that are widely added in soft drinks. During the manufacturing process, CO2 is usually pressurized to dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO2 at room temperature and pressure. Therefore, when bottles or cans of these kinds of soft drinks are opened, the soft drinks fizz and effervesce as CO2 bubbles come out.
Certain acids are used as drugs. Acetylsalicylic acid Aspirin is used as a pain killer and for bringing down fevers.
In human bodies
Acids |
play important roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for synthesis of proteins required for growth and repair of body tissues. Fatty acids are also required for growth and repair of body tissues. Nucleic acids are important for the manufacturing of DNA and RNA and transmitting of traits to offspring through genes. Carbonic acid is important for maintenance of pH equilibrium in the body.
Human bodies contain a variety of organic and inorganic compounds, among those dicarboxylic acids play an essential role in many biological behaviors. Many of those acids are amino acids which mainly serve as materials for the synthesis of proteins. Other weak acids serve as buffers with their conjugate bases to keep the body's pH from undergoing large scale changes which would be harmful to cells. The rest of the dicarboxylic acids also participate in the synthesis of various biologically important compo |
unds in human bodies.
Acid catalysis
Acids are used as catalysts in industrial and organic chemistry; for example, sulfuric acid is used in very large quantities in the alkylation process to produce gasoline. Some acids, such as sulfuric, phosphoric, and hydrochloric acids, also effect dehydration and condensation reactions. In biochemistry, many enzymes employ acid catalysis.
Biological occurrence
Many biologically important molecules are acids. Nucleic acids, which contain acidic phosphate groups, include DNA and RNA. Nucleic acids contain the genetic code that determines many of an organism's characteristics, and is passed from parents to offspring. DNA contains the chemical blueprint for the synthesis of proteins which are made up of amino acid subunits. Cell membranes contain fatty acid esters such as phospholipids.
An amino acid has a central carbon the or alpha carbon which is covalently bonded to a carboxyl group thus they are carboxylic acids, an amino group, a hydrogen atom and a variable grou |
p. The variable group, also called the R group or side chain, determines the identity and many of the properties of a specific amino acid. In glycine, the simplest amino acid, the R group is a hydrogen atom, but in all other amino acids it is contains one or more carbon atoms bonded to hydrogens, and may contain other elements such as sulfur, oxygen or nitrogen. With the exception of glycine, naturally occurring amino acids are chiral and almost invariably occur in the Lconfiguration. Peptidoglycan, found in some bacterial cell walls contains some Damino acids. At physiological pH, typically around 7, free amino acids exist in a charged form, where the acidic carboxyl group COOH loses a proton COO and the basic amine group NH2 gains a proton NH. The entire molecule has a net neutral charge and is a zwitterion, with the exception of amino acids with basic or acidic side chains. Aspartic acid, for example, possesses one protonated amine and two deprotonated carboxyl groups, for a net charge of 1 at physiologica |
l pH.
Fatty acids and fatty acid derivatives are another group of carboxylic acids that play a significant role in biology. These contain long hydrocarbon chains and a carboxylic acid group on one end. The cell membrane of nearly all organisms is primarily made up of a phospholipid bilayer, a micelle of hydrophobic fatty acid esters with polar, hydrophilic phosphate "head" groups. Membranes contain additional components, some of which can participate in acidbase reactions.
In humans and many other animals, hydrochloric acid is a part of the gastric acid secreted within the stomach to help hydrolyze proteins and polysaccharides, as well as converting the inactive proenzyme, pepsinogen into the enzyme, pepsin. Some organisms produce acids for defense; for example, ants produce formic acid.
Acidbase equilibrium plays a critical role in regulating mammalian breathing. Oxygen gas O2 drives cellular respiration, the process by which animals release the chemical potential energy stored in food, producing carbon d |
ioxide CO2 as a byproduct. Oxygen and carbon dioxide are exchanged in the lungs, and the body responds to changing energy demands by adjusting the rate of ventilation. For example, during periods of exertion the body rapidly breaks down stored carbohydrates and fat, releasing CO2 into the blood stream. In aqueous solutions such as blood CO2 exists in equilibrium with carbonic acid and bicarbonate ion.
It is the decrease in pH that signals the brain to breathe faster and deeper, expelling the excess CO2 and resupplying the cells with O2.
Cell membranes are generally impermeable to charged or large, polar molecules because of the lipophilic fatty acyl chains comprising their interior. Many biologically important molecules, including a number of pharmaceutical agents, are organic weak acids which can cross the membrane in their protonated, uncharged form but not in their charged form i.e., as the conjugate base. For this reason the activity of many drugs can be enhanced or inhibited by the use of antacids or |
acidic foods. The charged form, however, is often more soluble in blood and cytosol, both aqueous environments. When the extracellular environment is more acidic than the neutral pH within the cell, certain acids will exist in their neutral form and will be membrane soluble, allowing them to cross the phospholipid bilayer. Acids that lose a proton at the intracellular pH will exist in their soluble, charged form and are thus able to diffuse through the cytosol to their target. Ibuprofen, aspirin and penicillin are examples of drugs that are weak acids.
Common acids
Mineral acids inorganic acids
Hydrogen halides and their solutions hydrofluoric acid HF, hydrochloric acid HCl, hydrobromic acid HBr, hydroiodic acid HI
Halogen oxoacids hypochlorous acid HClO, chlorous acid HClO2, chloric acid HClO3, perchloric acid HClO4, and corresponding analogs for bromine and iodine
Hypofluorous acid HFO, the only known oxoacid for fluorine.
Sulfuric acid H2SO4
Fluorosulfuric acid HSO3F
Nitric acid HNO3
Phosphoric a |
cid H3PO4
Fluoroantimonic acid HSbF6
Fluoroboric acid HBF4
Hexafluorophosphoric acid HPF6
Chromic acid H2CrO4
Boric acid H3BO3
Sulfonic acids
A sulfonic acid has the general formula RSO2OH, where R is an organic radical.
Methanesulfonic acid or mesylic acid, CH3SO3H
Ethanesulfonic acid or esylic acid, CH3CH2SO3H
Benzenesulfonic acid or besylic acid, C6H5SO3H
pToluenesulfonic acid or tosylic acid, CH3C6H4SO3H
Trifluoromethanesulfonic acid or triflic acid, CF3SO3H
Polystyrene sulfonic acid sulfonated polystyrene, CH2CHC6H4SO3Hn
Carboxylic acids
A carboxylic acid has the general formula RCOOH, where R is an organic radical. The carboxyl group COOH contains a carbonyl group, CO, and a hydroxyl group, OH.
Acetic acid CH3COOH
Citric acid C6H8O7
Formic acid HCOOH
Gluconic acid HOCH2CHOH4COOH
Lactic acid CH3CHOHCOOH
Oxalic acid HOOCCOOH
Tartaric acid HOOCCHOHCHOHCOOH
Halogenated carboxylic acids
Halogenation at alpha position increases acid strength, so that the following acids are all stronger t |
han acetic acid.
Fluoroacetic acid
Trifluoroacetic acid
Chloroacetic acid
Dichloroacetic acid
Trichloroacetic acid
Vinylogous carboxylic acids
Normal carboxylic acids are the direct union of a carbonyl group and a hydroxyl group. In vinylogous carboxylic acids, a carboncarbon double bond separates the carbonyl and hydroxyl groups.
Ascorbic acid
Nucleic acids
Deoxyribonucleic acid DNA
Ribonucleic acid RNA
References
Listing of strengths of common acids and bases
External links
Curtipot AcidBase equilibria diagrams, pH calculation and titration curves simulation and analysis freeware
Acidbase chemistry |
Asphalt, also known as bitumen , , is a sticky, black, highly viscous liquid or semisolid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used. The word is derived from the Ancient Greek sphaltos. The largest natural deposit of asphalt in the world, estimated to contain 10 million tons, is the Pitch Lake located in La Brea in southwest Trinidad Antilles island located on the northeastern coast of Venezuela, within the Siparia Regional Corporation.
The primary use 70 of asphalt is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.
In material sciences and engineering, the terms "asphalt" and "bitumen" are often used interchangeably to mean both natural and manufactured forms of the substance, althoug |
h there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term "bitumen" for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, "bitumen" is the prevalent term in much of the world; however, in American English, "asphalt" is more commonly used. To help avoid confusion, the phrases "liquid asphalt", "asphalt binder", or "asphalt cement" are used in the U.S. Colloquially, various forms of asphalt are sometimes referred to as "tar", as in the name of the La Brea Tar Pits, although tar is a different material.
Naturally occurring asphalt is sometimes specified by the term "crude bitumen". Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at is sometimes referred to as "refined bitumen". The Canadian province of Alberta has most of the world's reserves of natural asphalt in the Athabasca oil sa |
nds, which cover , an area larger than England.
Asphalt properties change with temperature, which means that there is a specific range where viscosity permits adequate compaction by providing lubrication between particles during the compaction process. Low temperature prevents aggregate particles from moving, and the required density is not possible to achieve. Computer simulations of simplified model systems are able to reproduce some of asphalt's characteristic properties.
Terminology
Etymology
The word "asphalt" is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphalton, asphaltum, which is the latinisation of the Greek sphaltos, sphalton, a word meaning "asphaltbitumenpitch", which perhaps derives from , "not, without", i.e. the alpha privative, and sphallein, "to cause to fall, baffle, in passive err, in passive be balked of". The first use of asphalt by the ancients was in the nature of a cement for securing or joining together various objects, and it thus |
seems likely that the name itself was expressive of this application. Specifically, Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, and thence into French asphalte and English "asphaltum" and "asphalt". In French, the term asphalte is used for naturally occurring asphaltsoaked limestone deposits, and for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads.
The Latin source of the word "bitumen" is claimed by some to be originally gwitumen pertaining to pitch, and by others, pixtumens exuding or bubbling pitch, which was subsequently shortened to bitumen, thence passing via French into English. From the same root is derived the AngloSaxon word cwidu mastix, the German word Kitt cement or mastic and the old Norse word kvada.
Modern terminology
In British English, "bitumen" is used instead of "asphalt". The word "asphalt" is instead used t |
o refer to asphalt concrete, a mixture of construction aggregate and asphalt itself also called "tarmac" in common parlance. Bitumen mixed with clay was usually called "asphaltum", but the term is less commonly used today.
In Australian English, the word "asphalt" is used to describe a mix of construction aggregate. "Bitumen" refers to the liquid derived from the heavyresidues from crude oil distillation.
In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is also commonly used as a shortened form of "asphalt concrete" therefore equivalent to the British "asphalt" or "tarmac".
In Canadian English, the word "bitumen" is used to refer to the vast Canadian deposits of extremely heavy crude oil, while "asphalt" is used for the oil refinery product. Diluted bitumen diluted with naphtha to make it flow in pipelines is known as "dilbit" in the Canadian petroleum industry, while bitumen "upgraded" to synthetic crude oil is known as "syncrude", and syncrude blended with bitumen |
is called "synbit".
"Bitumen" is still the preferred geological term for naturally occurring deposits of the solid or semisolid form of petroleum. "Bituminous rock" is a form of sandstone impregnated with bitumen. The oil sands of Alberta, Canada are a similar material.
Neither of the terms "asphalt" or "bitumen" should be confused with tar or coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons primarily sourced from vegetation masses, whether fossilized as with coal, or freshly harvested. The majority of bitumen, on the other hand, was formed naturally when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenetic point, where the disorganized fatty hydrocarbon molecules joined together in long chains in the absence of oxygen. Bitumen occurs as a solid or highly viscous liquid. It may even be mixed in with coal deposits. Bitumen, and coal using the Bergius process, can be refined into petrol |
s such as gasoline, and bitumen may be distilled into tar, not the other way around.
Composition
Normal composition
The components of asphalt include four main classes of compounds
Naphthene aromatics naphthalene, consisting of partially hydrogenated polycyclic aromatic compounds
Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material
Saturated hydrocarbons; the percentage of saturated compounds in asphalt correlates with its softening point
Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
The naphthene aromatics and polar aromatics are typically the majority components. Most natural bitumens also contain organosulfur compounds, resulting in an overall sulfur content of up to 4. Nickel and vanadium are found at 10 parts per million, as is typical of some petroleum.
The substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and malt |
enes as the continuous phase. "It is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structure is extremely large".
Asphalt may be confused with coal tar, which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid20th century, when town gas was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of coal tar to macadam roads led to the word "tarmac", which is now used in common parlance to refer to roadmaking materials. However, since the 1970s, when natural gas succeeded town gas, asphalt has completely overtaken the use of coal tar in these applications. Other examples of this confusion include the La Brea Tar Pits and the Canadian oil sands, both of which actually contain natural bitumen rather than tar. "Pitch" is another term sometimes informally used at times to refer to a |
sphalt, as in Pitch Lake.
Additives, mixtures and contaminants
For economic and other reasons, asphalt is sometimes sold combined with other materials, often without being labeled as anything other than simply "asphalt".
Of particular note is the use of rerefined engine oil bottoms "REOB" or "REOBs"the residue of recycled automotive engine oil collected from the bottoms of rerefining vacuum distillation towers, in the manufacture of asphalt. REOB contains various elements and compounds found in recycled engine oil additives to the original oil and materials accumulating from its circulation in the engine typically iron and copper. Some research has indicated a correlation between this adulteration of asphalt and poorerperforming pavement.
Occurrence
The majority of asphalt used commercially is obtained from petroleum. Nonetheless, large amounts of asphalt occur in concentrated form in nature. Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae diatoms and oth |
er onceliving things. These natural deposits of bitumen have been formed during the Carboniferous period, when giant swamp forests dominated many parts of the Earth. They were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat above 50 C and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum.
Natural deposits of bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps occur in the La Brea Tar Pits and in the Dead Sea.
Bitumen also occurs in unconsolidated sandstones known as "oil sands" in Alberta, Canada, and the similar "tar sands" in Utah, US.
The Canadian province of Alberta has most of the world's reserves, in three huge deposits covering , an area larger than England or New York state. These bituminous sands contain of commercially established oil reserves, giving Canada the third largest oil reserves in the world. Although histo |
rically it was used without refining to pave roads, nearly all of the output is now used as raw material for oil refineries in Canada and the United States.
The world's largest deposit of natural bitumen, known as the Athabasca oil sands, is located in the McMurray Formation of Northern Alberta. This formation is from the early Cretaceous, and is composed of numerous lenses of oilbearing sand with up to 20 oil. Isotopic studies show the oil deposits to be about 110 million years old. Two smaller but still very large formations occur in the Peace River oil sands and the Cold Lake oil sands, to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80 has to be produced by oil wells using enhanced oil recovery techniques like steamassisted gravity drainage.
Much smaller heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, US. The Tar Sand Triangle deposit, f |
or example, is roughly 6 bitumen.
Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.
Bitumen is similar to the organic matter in carbonaceous meteorites. However, detailed studies have shown these materials to be distinct. The vast Alberta bitumen resources are considered to have started out as living material from marine plants and animals, mainly algae, that died millions of years ago when an ancient ocean covered Alberta. They were covered by mud, buried deeply over time, and gently cooked into oil by geothermal heat at a temperature of . Due to pressure from the rising of the Rocky Mountains in southwestern Alberta, 80 to 55 million years ago, the oil was |
driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands.
History
Ancient times
The use of natural bitumen for waterproofing, and as an adhesive dates at least to the fifth millennium BC, with a crop storage basket discovered in Mehrgarh, of the Indus Valley Civilization, lined with it. By the 3rd millennium BC refined rock asphalt was in use in the region, and was used to waterproof the Great Bath in Mohenjodaro.
In the ancient Middle East, the Sumerians used natural bitumen deposits for mortar between bricks and stones, to cement parts of carvings, such as eyes, into place, for ship caulking, and for waterproofing. The Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylon.
The long Euphrates Tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis c. 800 BC was reportedly constructed of burnt bricks covered with bitumen as a waterproofing agent.
|
Bitumen was used by ancient Egyptians to embalm mummies. The Persian word for asphalt is moom, which is related to the English word mummy. The Egyptians' primary source of bitumen was the Dead Sea, which the Romans knew as Palus Asphaltites Asphalt Lake.
In approximately 40 AD, Dioscorides described the Dead Sea material as Judaicum bitumen, and noted other places in the region where it could be found. The Sidon bitumen is thought to refer to material found at Hasbeya in Lebanon. Pliny also refers to bitumen being found in Epirus. Bitumen was a valuable strategic resource. It was the object of the first known battle for a hydrocarbon deposit between the Seleucids and the Nabateans in 312 BC.
In the ancient Far East, natural bitumen was slowly boiled to get rid of the higher fractions, leaving a thermoplastic material of higher molecular weight that when layered on objects became quite hard upon cooling. This was used to cover objects that needed waterproofing, such as scabbards and other items. Statuettes |
of household deities were also cast with this type of material in Japan, and probably also in China.
In North America, archaeological recovery has indicated that bitumen was sometimes used to adhere stone projectile points to wooden shafts. In Canada, aboriginal people used bitumen seeping out of the banks of the Athabasca and other rivers to waterproof birch bark canoes, and also heated it in smudge pots to ward off mosquitoes in the summer.
Continental Europe
In 1553, Pierre Belon described in his work Observations that pissasphalto, a mixture of pitch and bitumen, was used in the Republic of Ragusa now Dubrovnik, Croatia for tarring of ships.
An 1838 edition of Mechanics Magazine cites an early use of asphalt in France. A pamphlet dated 1621, by "a certain Monsieur d'Eyrinys, states that he had discovered the existence of asphaltum in large quantities in the vicinity of Neufchatel", and that he proposed to use it in a variety of ways "principally in the construction of airproof granaries, and in protec |
ting, by means of the arches, the watercourses in the city of Paris from the intrusion of dirt and filth", which at that time made the water unusable. "He expatiates also on the excellence of this material for forming level and durable terraces" in palaces, "the notion of forming such terraces in the streets not one likely to cross the brain of a Parisian of that generation".
But the substance was generally neglected in France until the revolution of 1830. In the 1830s there was a surge of interest, and asphalt became widely used "for pavements, flat roofs, and the lining of cisterns, and in England, some use of it had been made of it for similar purposes". Its rise in Europe was "a sudden phenomenon", after natural deposits were found "in France at Osbann BasRhin, the Parc Ain and the PuydelaPoix PuydeDme", although it could also be made artificially. One of the earliest uses in France was the laying of about 24,000 square yards of Seyssel asphalt at the Place de la Concorde in 1835.
United Kingdom
Among t |
he earlier uses of bitumen in the United Kingdom was for etching. William Salmon's Polygraphice 1673 provides a recipe for varnish used in etching, consisting of three ounces of virgin wax, two ounces of mastic, and one ounce of asphaltum. By the fifth edition in 1685, he had included more asphaltum recipes from other sources.
The first British patent for the use of asphalt was "Cassell's patent asphalte or bitumen" in 1834. Then on 25 November 1837, Richard Tappin Claridge patented the use of Seyssel asphalt patent 7849, for use in asphalte pavement, having seen it employed in France and Belgium when visiting with Frederick Walter Simms, who worked with him on the introduction of asphalt to Britain. Dr T. Lamb Phipson writes that his father, Samuel Ryland Phipson, a friend of Claridge, was also "instrumental in introducing the asphalte pavement in 1836".
Claridge obtained a patent in Scotland on 27 March 1838, and obtained a patent in Ireland on 23 April 1838. In 1851, extensions for the 1837 patent and fo |
r both 1838 patents were sought by the trustees of a company previously formed by Claridge. Claridge's Patent Asphalte Companyformed in 1838 for the purpose of introducing to Britain "Asphalte in its natural state from the mine at Pyrimont Seysell in France","laid one of the first asphalt pavements in Whitehall". Trials were made of the pavement in 1838 on the footway in Whitehall, the stable at Knightsbridge Barracks, "and subsequently on the space at the bottom of the steps leading from Waterloo Place to St. James Park". "The formation in 1838 of Claridge's Patent Asphalte Company with a distinguished list of aristocratic patrons, and Marc and Isambard Brunel as, respectively, a trustee and consulting engineer, gave an enormous impetus to the development of a British asphalt industry". "By the end of 1838, at least two other companies, Robinson's and the Bastenne company, were in production", with asphalt being laid as paving at Brighton, Herne Bay, Canterbury, Kensington, the Strand, and a large floor area |
in Bunhillrow, while meantime Claridge's Whitehall paving "continued in good order". The Bonnington Chemical Works manufactured asphalt using coal tar and by 1839 had installed it in Bonnington.
In 1838, there was a flurry of entrepreneurial activity involving asphalt, which had uses beyond paving. For example, asphalt could also be used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, both of which were also proliferating in the 19th century. On the London stockmarket, there were various claims as to the exclusivity of asphalt quality from France, Germany and England. And numerous patents were granted in France, with similar numbers of patent applications being denied in England due to their similarity to each other. In England, "Claridge's was the type most used in the 1840s and 50s".
In 1914, Claridge's Company entered into a joint venture to produce tarbound macadam, with materials manufactured through a subsidiary company called Clarmac Roads Ltd. Tw |
o products resulted, namely Clarmac, and Clarphalte, with the former being manufactured by Clarmac Roads and the latter by Claridge's Patent Asphalte Co., although Clarmac was more widely used. However, the First World War ruined the Clarmac Company, which entered into liquidation in 1915. The failure of Clarmac Roads Ltd had a flowon effect to Claridge's Company, which was itself compulsorily wound up, ceasing operations in 1917, having invested a substantial amount of funds into the new venture, both at the outset and in a subsequent attempt to save the Clarmac Company.
Bitumen was thought in 19th century Britain to contain chemicals with medicinal properties. Extracts from bitumen were used to treat catarrh and some forms of asthma and as a remedy against worms, especially the tapeworm.
United States
The first use of bitumen in the New World was by indigenous peoples. On the west coast, as early as the 13th century, the Tongva, Luiseo and Chumash peoples collected the naturally occurring bitumen that see |
ped to the surface above underlying petroleum deposits. All three groups used the substance as an adhesive. It is found on many different artifacts of tools and ceremonial items. For example, it was used on rattles to adhere gourds or turtle shells to rattle handles. It was also used in decorations. Small round shell beads were often set in asphaltum to provide decorations. It was used as a sealant on baskets to make them watertight for carrying water, possibly poisoning those who drank the water. Asphalt was used also to seal the planks on oceangoing canoes.
Asphalt was first used to pave streets in the 1870s. At first naturally occurring "bituminous rock" was used, such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphaltbased paving was used to pave Pennsylvania Avenue in Washington DC, in time for the celebration of the national centennial.
In the horsedrawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or tre |
nching often made streets difficult to pass, pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear and hazards for pedestrians. In the late 19th century with the rise of the popular bicycle, bicycle clubs were important in pushing for more general pavement of streets. Advocacy for pavement increased in the early 20th century with the rise of the automobile. Asphalt gradually became an ever more common method of paving. St. Charles Avenue in New Orleans was paved its whole length with asphalt by 1889.
In 1900, Manhattan alone had 130,000 horses, pulling streetcars, wagons, and carriages, and leaving their waste behind. They were not fast, and pedestrians could dodge and scramble their way across the crowded streets. Small towns continued to rely on dirt and gravel, but larger cities wanted much better streets. They looked to wood or granite blocks by the 1850s. In 1890, a third of Chicago's 2000 miles |
of streets were paved, chiefly with wooden blocks, which gave better traction than mud. Brick surfacing was a good compromise, but even better was asphalt paving, which was easy to install and to cut through to get at sewers. With London and Paris serving as models, Washington laid 400,000 square yards of asphalt paving by 1882; it became the model for Buffalo, Philadelphia and elsewhere. By the end of the century, American cities boasted 30 million square yards of asphalt paving, well ahead of brick. The streets became faster and more dangerous so electric traffic lights were installed. Electric trolleys at 12 miles per hour became the main transportation service for middle class shoppers and office workers until they bought automobiles after 1945 and commuted from more distant suburbs in privacy and comfort on asphalt highways.
Canada
Canada has the world's largest deposit of natural bitumen in the Athabasca oil sands, and Canadian First Nations along the Athabasca River had long used it to waterproof |
their canoes. In 1719, a Cree named WaPaSu brought a sample for trade to Henry Kelsey of the Hudson's Bay Company, who was the first recorded European to see it. However, it wasn't until 1787 that fur trader and explorer Alexander MacKenzie saw the Athabasca oil sands and said, "At about 24 miles from the fork of the Athabasca and Clearwater Rivers are some bituminous fountains into which a pole of 20 feet long may be inserted without the least resistance."
The value of the deposit was obvious from the start, but the means of extracting the bitumen was not. The nearest town, Fort McMurray, Alberta, was a small fur trading post, other markets were far away, and transportation costs were too high to ship the raw bituminous sand for paving. In 1915, Sidney Ells of the Federal Mines Branch experimented with separation techniques and used the product to pave 600 feet of road in Edmonton, Alberta. Other roads in Alberta were paved with material extracted from oil sands, but it was generally not economic. During th |
e 1920s Dr. Karl A. Clark of the Alberta Research Council patented a hot water oil separation process and entrepreneur Robert C. Fitzsimmons built the Bitumount oil separation plant, which between 1925 and 1958 produced up to per day of bitumen using Dr. Clark's method. Most of the bitumen was used for waterproofing roofs, but other uses included fuels, lubrication oils, printers ink, medicines, rust and acidproof paints, fireproof roofing, street paving, patent leather, and fence post preservatives. Eventually Fitzsimmons ran out of money and the plant was taken over by the Alberta government. Today the Bitumount plant is a Provincial Historic Site.
Photography and art
Bitumen was used in early photographic technology. In 1826, or 1827, it was used by French scientist Joseph Nicphore Nipce to make the oldest surviving photograph from nature. The bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the bitumen and made it insoluble, so that when it was |
subsequently rinsed with a solvent only the sufficiently lightstruck areas remained. Many hours of exposure in the camera were required, making bitumen impractical for ordinary photography, but from the 1850s to the 1920s it was in common use as a photoresist in the production of printing plates for various photomechanical printing processes.
Bitumen was the nemesis of many artists during the 19th century. Although widely used for a time, it ultimately proved unstable for use in oil painting, especially when mixed with the most common diluents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with other colors to render a darker tone resulted in the eventual deterioration of many paintings, for instance those of Delacroix. Perhaps the most famous example of the destructiveness of bitumen is Thodore Gricault's Raft of the M |
edusa 18181819, where his use of bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle.
Modern use
Global use
The vast majority of refined asphalt is used in construction primarily as a constituent of products used in paving and roofing applications. According to the requirements of the end use, asphalt is produced to specification. This is achieved either by refining or blending. It is estimated that the current world use of asphalt is approximately 102 million tonnes per year. Approximately 85 of all the asphalt produced is used as the binder in asphalt concrete for roads. It is also used in other paved areas such as airport runways, car parks and footways. Typically, the production of asphalt concrete involves mixing fine and coarse aggregates such as sand, gravel and crushed rock with asphalt, which acts as the binding agent. Other materials, such as recycled polymers e.g., rubber tyres, may be added to the asphalt to modify its properties accor |
ding to the application for which the asphalt is ultimately intended.
A further 10 of global asphalt production is used in roofing applications, where its waterproofing qualities are invaluable.
The remaining 5 of asphalt is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint. Asphalt is applied in the construction and maintenance of many structures, systems, and components, such as the following
Highways
Airport runways
Footways and pedestrian ways
Car parks
Racetracks
Tennis courts
Roofing
Damp proofing
Dams
Reservoir and pool linings
Soundproofing
Pipe coatings
Cable coatings
Paints
Building water proofing
Tile underlying waterproofing
Newspaper ink production
and many other applications
Rolled asphalt concrete
The largest use of asphalt is for making asphalt concrete for road surfaces; this accounts for approximately 85 of the asphalt consumed in the United States. There are about 4,000 asphalt concre |
te mixing plants in the US, and a similar number in Europe.
Asphalt concrete pavement mixes are typically composed of 5 asphalt cement and 95 aggregates stone, sand, and gravel. Due to its highly viscous nature, asphalt cement must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the asphalt and the aggregates, but warmmix asphalt technologies allow producers to reduce the temperature required.
The weight of an asphalt pavement depends upon the aggregate type, the asphalt, and the air void content. An average example in the United States is about 112 pounds per square yard, per inch of pavement thickness.
When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The asphalt in the removed material can be reactivated and put back to use in new pavement mixes. With some 95 |
of paved roads being constructed of or surfaced with asphalt, a substantial amount of asphalt pavement material is reclaimed each year. According to industry surveys conducted annually by the Federal Highway Administration and the National Asphalt Pavement Association, more than 99 of the asphalt removed each year from road surfaces during widening and resurfacing projects is reused as part of new pavements, roadbeds, shoulders and embankments or stockpiled for future use.
Asphalt concrete paving is widely used in airports around the world. Due to the sturdiness and ability to be repaired quickly, it is widely used for runways.
Mastic asphalt
Mastic asphalt is a type of asphalt that differs from dense graded asphalt asphalt concrete in that it has a higher asphalt binder content, usually around 710 of the whole aggregate mix, as opposed to rolled asphalt concrete, which has only around 5 asphalt. This thermoplastic substance is widely used in the building industry for waterproofing flat roofs and tanking u |
nderground. Mastic asphalt is heated to a temperature of and is spread in layers to form an impervious barrier about thick.
Asphalt emulsion
A number of technologies allow asphalt to be applied at mild temperatures. The viscosity can be lowered by emulsfying the asphalt by the addition of fatty amines. 225 is the content of these emulsifying agents. The cationic amines enhance the binding of the asphalt to the surface of the crushed rock.
Asphalt emulsions are used in a wide variety of applications. Chipseal involves spraying the road surface with asphalt emulsion followed by a layer of crushed rock, gravel or crushed slag. Slurry seal is a mixture of asphalt emulsion and fine crushed aggregate that is spread on the surface of a road. Coldmixed asphalt can also be made from asphalt emulsion to create pavements similar to hotmixed asphalt, several inches in depth, and asphalt emulsions are also blended into recycled hotmix asphalt to create lowcost pavements. Bitumen emulsion based techniques are known to |
be useful for all classes of roads, their use may also be possible in the following applications 1. Asphalts for heavily trafficked roads based on the use of polymer modified emulsions 2. Warm emulsion based mixtures, to improve both their maturation time and mechanical properties 3. Halfwarm technology, in which aggregates are heated up to 100 degrees, producing mixtures with similar properties to those of hot asphalts 4. High performance surface dressing.
Synthetic crude oil
Synthetic crude oil, also known as syncrude, is the output from a bitumen upgrader facility used in connection with oil sand production in Canada. Bituminous sands are mined using enormous 100ton capacity power shovels and loaded into even larger 400ton capacity dump trucks for movement to an upgrading facility. The process used to extract the bitumen from the sand is a hot water process originally developed by Dr. Karl Clark of the University of Alberta during the 1920s. After extraction from the sand, the bitumen is fed into a bitum |
en upgrader which converts it into a light crude oil equivalent. This synthetic substance is fluid enough to be transferred through conventional oil pipelines and can be fed into conventional oil refineries without any further treatment. By 2015 Canadian bitumen upgraders were producing over per day of synthetic crude oil, of which 75 was exported to oil refineries in the United States.
In Alberta, five bitumen upgraders produce synthetic crude oil and a variety of other products The Suncor Energy upgrader near Fort McMurray, Alberta produces synthetic crude oil plus diesel fuel; the Syncrude Canada, Canadian Natural Resources, and Nexen upgraders near Fort McMurray produce synthetic crude oil; and the Shell Scotford Upgrader near Edmonton produces synthetic crude oil plus an intermediate feedstock for the nearby Shell Oil Refinery. A sixth upgrader, under construction in 2015 near Redwater, Alberta, will upgrade half of its crude bitumen directly to diesel fuel, with the remainder of the output being sold |
as feedstock to nearby oil refineries and petrochemical plants.
Nonupgraded crude bitumen
Canadian bitumen does not differ substantially from oils such as Venezuelan extraheavy and Mexican heavy oil in chemical composition, and the real difficulty is moving the extremely viscous bitumen through oil pipelines to the refinery. Many modern oil refineries are extremely sophisticated and can process nonupgraded bitumen directly into products such as gasoline, diesel fuel, and refined asphalt without any preprocessing. This is particularly common in areas such as the US Gulf coast, where refineries were designed to process Venezuelan and Mexican oil, and in areas such as the US Midwest where refineries were rebuilt to process heavy oil as domestic light oil production declined. Given the choice, such heavy oil refineries usually prefer to buy bitumen rather than synthetic oil because the cost is lower, and in some cases because they prefer to produce more diesel fuel and less gasoline. By 2015 Canadian production |
and exports of nonupgraded bitumen exceeded that of synthetic crude oil at over per day, of which about 65 was exported to the United States.
Because of the difficulty of moving crude bitumen through pipelines, nonupgraded bitumen is usually diluted with naturalgas condensate in a form called dilbit or with synthetic crude oil, called synbit. However, to meet international competition, much nonupgraded bitumen is now sold as a blend of multiple grades of bitumen, conventional crude oil, synthetic crude oil, and condensate in a standardized benchmark product such as Western Canadian Select. This sour, heavy crude oil blend is designed to have uniform refining characteristics to compete with internationally marketed heavy oils such as Mexican Mayan or Arabian Dubai Crude.
Radioactive waste encapsulation matrix
Asphalt was used starting in the 1960s as a hydrophobic matrix aiming to encapsulate radioactive waste such as mediumactivity salts mainly soluble sodium nitrate and sodium sulfate produced by the re |
processing of spent nuclear fuels or radioactive sludges from sedimentation ponds. Bituminised radioactive waste containing highly radiotoxic alphaemitting transuranic elements from nuclear reprocessing plants have been produced at industrial scale in France, Belgium and Japan, but this type of waste conditioning has been abandoned because operational safety issues risks of fire, as occurred in a bituminisation plant at Tokai Works in Japan and longterm stability problems related to their geological disposal in deep rock formations. One of the main problems is the swelling of asphalt exposed to radiation and to water. Asphalt swelling is first induced by radiation because of the presence of hydrogen gas bubbles generated by alpha and gamma radiolysis. A second mechanism is the matrix swelling when the encapsulated hygroscopic salts exposed to water or moisture start to rehydrate and to dissolve. The high concentration of salt in the pore solution inside the bituminised matrix is then responsible for osmotic e |
ffects inside the bituminised matrix. The water moves in the direction of the concentrated salts, the asphalt acting as a semipermeable membrane. This also causes the matrix to swell. The swelling pressure due to osmotic effect under constant volume can be as high as 200 bar. If not properly managed, this high pressure can cause fractures in the near field of a disposal gallery of bituminised mediumlevel waste. When the bituminised matrix has been altered by swelling, encapsulated radionuclides are easily leached by the contact of ground water and released in the geosphere. The high ionic strength of the concentrated saline solution also favours the migration of radionuclides in clay host rocks. The presence of chemically reactive nitrate can also affect the redox conditions prevailing in the host rock by establishing oxidizing conditions, preventing the reduction of redoxsensitive radionuclides. Under their higher valences, radionuclides of elements such as selenium, technetium, uranium, neptunium and pluton |
ium have a higher solubility and are also often present in water as nonretarded anions. This makes the disposal of mediumlevel bituminised waste very challenging.
Different types of asphalt have been used blown bitumen partly oxidized with air oxygen at high temperature after distillation, and harder and direct distillation bitumen softer. Blown bitumens like Mexphalte, with a high content of saturated hydrocarbons, are more easily biodegraded by microorganisms than direct distillation bitumen, with a low content of saturated hydrocarbons and a high content of aromatic hydrocarbons.
Concrete encapsulation of radwaste is presently considered a safer alternative by the nuclear industry and the waste management organisations.
Other uses
Roofing shingles and roll roofing account for most of the remaining asphalt consumption. Other uses include cattle sprays, fencepost treatments, and waterproofing for fabrics. Asphalt is used to make Japan black, a lacquer known especially for its use on iron and steel, and it |
is also used in paint and marker inks by some exterior paint supply companies to increase the weather resistance and permanence of the paint or ink, and to make the color darker. Asphalt is also used to seal some alkaline batteries during the manufacturing process.
Production
About 40,000,000 tons were produced in 1984. It is obtained as the "heavy" i.e., difficult to distill fraction. Material with a boiling point greater than around 500 C is considered asphalt. Vacuum distillation separates it from the other components in crude oil such as naphtha, gasoline and diesel. The resulting material is typically further treated to extract small but valuable amounts of lubricants and to adjust the properties of the material to suit applications. In a deasphalting unit, the crude asphalt is treated with either propane or butane in a supercritical phase to extract the lighter molecules, which are then separated. Further processing is possible by "blowing" the product namely reacting it with oxygen. This step makes |
the product harder and more viscous.
Asphalt is typically stored and transported at temperatures around . Sometimes diesel oil or kerosene are mixed in before shipping to retain liquidity; upon delivery, these lighter materials are separated out of the mixture. This mixture is often called "bitumen feedstock", or BFS. Some dump trucks route the hot engine exhaust through pipes in the dump body to keep the material warm. The backs of tippers carrying asphalt, as well as some handling equipment, are also commonly sprayed with a releasing agent before filling to aid release. Diesel oil is no longer used as a release agent due to environmental concerns.
Oil sands
Naturally occurring crude bitumen impregnated in sedimentary rock is the prime feed stock for petroleum production from "oil sands", currently under development in Alberta, Canada. Canada has most of the world's supply of natural bitumen, covering 140,000 square kilometres an area larger than England, giving it the secondlargest proven oil reserves in |
the world. The Athabasca oil sands are the largest bitumen deposit in Canada and the only one accessible to surface mining, although recent technological breakthroughs have resulted in deeper deposits becoming producible by in situ methods. Because of oil price increases after 2003, producing bitumen became highly profitable, but as a result of the decline after 2014 it became uneconomic to build new plants again. By 2014, Canadian crude bitumen production averaged about per day and was projected to rise to per day by 2020. The total amount of crude bitumen in Alberta that could be extracted is estimated to be about , which at a rate of would last about 200 years.
Alternatives and bioasphalt
Although uncompetitive economically, asphalt can be made from nonpetroleumbased renewable resources such as sugar, molasses and rice, corn and potato starches. Asphalt can also be made from waste material by fractional distillation of used motor oil, which is sometimes otherwise disposed of by burning or dumping int |
o landfills. Use of motor oil may cause premature cracking in colder climates, resulting in roads that need to be repaved more frequently.
Nonpetroleumbased asphalt binders can be made lightcolored. Lightercolored roads absorb less heat from solar radiation, reducing their contribution to the urban heat island effect. Parking lots that use asphalt alternatives are called green parking lots.
Albanian deposits
Selenizza is a naturally occurring solid hydrocarbon bitumen found in native deposits in Selenice, in Albania, the only European asphalt mine still in use. The bitumen is found in the form of veins, filling cracks in a more or less horizontal direction. The bitumen content varies from 83 to 92 soluble in carbon disulphide, with a penetration value near to zero and a softening point ring and ball around 120 C. The insoluble matter, consisting mainly of silica ore, ranges from 8 to 17.
Albanian bitumen extraction has a long history and was practiced in an organized way by the Romans. After centuries of s |
ilence, the first mentions of Albanian bitumen appeared only in 1868, when the Frenchman Coquand published the first geological description of the deposits of Albanian bitumen. In 1875, the exploitation rights were granted to the Ottoman government and in 1912, they were transferred to the Italian company Simsa. Since 1945, the mine was exploited by the Albanian government and from 2001 to date, the management passed to a French company, which organized the mining process for the manufacture of the natural bitumen on an industrial scale.
Today the mine is predominantly exploited in an open pit quarry but several of the many underground mines deep and extending over several km still remain viable. Selenizza is produced primarily in granular form, after melting the bitumen pieces selected in the mine.
Selenizza is mainly used as an additive in the road construction sector. It is mixed with traditional asphalt to improve both the viscoelastic properties and the resistance to ageing. It may be blended with the |
hot asphalt in tanks, but its granular form allows it to be fed in the mixer or in the recycling ring of normal asphalt plants. Other typical applications include the production of mastic asphalts for sidewalks, bridges, carparks and urban roads as well as drilling fluid additives for the oil and gas industry. Selenizza is available in powder or in granular material of various particle sizes and is packaged in sacks or in thermal fusible polyethylene bags.
A lifecycle assessment study of the natural selenizza compared with petroleum asphalt has shown that the environmental impact of the selenizza is about half the impact of the road asphalt produced in oil refineries in terms of carbon dioxide emission.
Recycling
Asphalt is a commonly recycled material in the construction industry. The two most common recycled materials that contain asphalt are reclaimed asphalt pavement RAP and reclaimed asphalt shingles RAS. RAP is recycled at a greater rate than any other material in the United States, and typically con |
tains approximately 5 6 asphalt binder. Asphalt shingles typically contain 20 40 asphalt binder.
Asphalt naturally becomes stiffer over time due to oxidation, evaporation, exudation, and physical hardening. For this reason, recycled asphalt is typically combined with virgin asphalt, softening agents, andor rejuvenating additives to restore its physical and chemical properties.
For information on the processing and performance of RAP and RAS, see Asphalt Concrete.
For information on the different types of RAS and associated health and safety concerns, see Asphalt Shingles.
For information on inplace recycling methods used to restore pavements and roadways, see Road Surface.
Economics
Although asphalt typically makes up only 4 to 5 percent by weight of the pavement mixture, as the pavement's binder, it is also the most expensive part of the cost of the roadpaving material.
During asphalt's early use in modern paving, oil refiners gave it away. However, asphalt is a highly traded commodity today. Its pri |
ces increased substantially in the early 21st Century. A U.S. government report states
"In 2002, asphalt sold for approximately 160 per ton. By the end of 2006, the cost had doubled to approximately 320 per ton, and then it almost doubled again in 2012 to approximately 610 per ton."
The report indicates that an "average" 1mile 1.6kilometerlong, fourlane highway would include "300 tons of asphalt," which, "in 2002 would have cost around 48,000. By 2006 this would have increased to 96,000 and by 2012 to 183,000... an increase of about 135,000 for every mile of highway in just 10 years."
Health and safety
People can be exposed to asphalt in the workplace by breathing in fumes or skin absorption. The National Institute for Occupational Safety and Health NIOSH has set a recommended exposure limit of 5 mgm3 over a 15minute period.
Asphalt is basically an inert material that must be heated or diluted to a point where it becomes workable for the production of materials for paving, roofing, and other applications. |
In examining the potential health hazards associated with asphalt, the International Agency for Research on Cancer IARC determined that it is the application parameters, predominantly temperature, that affect occupational exposure and the potential bioavailable carcinogenic hazardrisk of the asphalt emissions. In particular, temperatures greater than 199 C 390 F, were shown to produce a greater exposure risk than when asphalt was heated to lower temperatures, such as those typically used in asphalt pavement mix production and placement. IARC has classified paving asphalt fumes as a Class 2B possible carcinogen, indicating inadequate evidence of carcinogenicity in humans.
In 2020, scientists reported that asphalt currently is a significant and largely overlooked source of air pollution in urban areas, especially during hot and sunny periods.
An asphaltlike substance found in the Himalayas and known as shilajit is sometimes used as an Ayurveda medicine, but is not in fact a tar, resin or asphalt.
See also
|
Asphalt plant
Asphaltene
Bioasphalt
Bitumenbased fuel
Bituminous rocks
Blacktop
Cariphalte
Cooper Research Technology
Duxit
Macadam
Oil sands
Pitch drop experiment
Pitch resin
Road surface
Tar
Tarmac
Sealcoat
Stamped asphalt
Notes
References
Sources
Barth, Edwin J. 1962, Asphalt Science and Technology, Gordon and Breach. .
External links
Pavement Interactive Asphalt
CSU Sacramento, The World Famous Asphalt Museum!
National Institute for Occupational Safety and Health Asphalt Fumes
Scientific American, "Asphalt", 20Aug1881, pp. 121
Amorphous solids
Building materials
Chemical mixtures
IARC Group 2B carcinogens
Pavements
Petroleum products
Road construction materials |
The American National Standards Institute ANSI is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.
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