ASPHALT

                ASPHALT

Asphalt is one of the important petroleum products which have various applications. The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called bitumen. Geological terminology often prefers the term bitumen. Common usage often refers to various forms of asphalt/bitumen as "tar", such as at the La Brea Tar Pits. Another term, mostly archaic, refers to asphalt/bitumen as "pitch". The pitch used in this mixture is sometimes found in natural deposits but usually made by the distillation of crude oil.

Naturally occurring asphalt/bitumen 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 525 °C (977 °F)] is sometimes referred to as "refined bitumen".

History

Naturally occurring deposits of asphalt/bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things. These remains 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 asphalt/bitumen, kerogen, or petroleum. Deposits at the La Brea Tar Pits are an example.

Natural deposits of asphalt/bitumen include lakes such as the Pitch Lake. Natural seeps of asphalt/bitumen occur in the La Brea Tar Pits and in the Dead Sea.

Asphalt/bitumen also occurs as impregnated sandstones known as bituminous rock and the similar "tar sands" such as in Athabasca, Canada and Utah, USA. The Athabasca tar sands are located in the McMurray Formation, Alberta. This Formation is of early Cretaceous age, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies attribute the oil deposits to be about 110 Ma old. Heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, USA. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen.

Asphalt/bitumen occurs in hydrothermal veins. An example of this is within the Uinta Basin of Utah, USA, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerisation and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.

There are structural similarities between asphalt/bitumen and the organic matter in carbonaceous meteorites. However, detailed studies have shown these materials to be distinct.

The use of asphalt/bitumen for waterproofing and as an adhesive dates at least to the fifth millennium B.C. in the early Indus community of Mehrgarh, where it was used to line the baskets in which they gathered crops.

In the ancient Middle East, the Sumerians used natural asphalt/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 asphalt/bitumen was used as mortar in the walls of Babylon.

In some versions of the Book of Genesis in the Bible, the name of the substance used to bind the bricks of the Tower of Babel is translated as bitumen (see Gen 11:3), while other translations use the word pitch. A one-kilometre tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis (ca. 800 B.C.) was reportedly constructed of burnt bricks covered with asphalt/bitumen as a waterproofing agent.

Asphalt/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 asphalt/bitumen was the Dead Sea, which the Romans knew as Palus Asphaltites (Asphalt Lake).

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 Judaicum Bitumen is better than others; that is reckoned the best, which doth shine like purple, being of a strong scent & weightie, but the black and fowle is naught for it is adulterated with Pitch mixed with it. It growes in Phoenice also, and in Sidon, & in Babylon, & in Zacynthum. It is found also moyst swimming upon wells in the country of the Agrigentines of Sicilie, which they use for lamps instead of oyle, and which they call falsely Sicilian oyle, for it is a kinde of moyst Bitumen."

The Sidon bitumen is thought to refer to asphalt/bitumen found at Hasbeya. Pliny refers also to asphalt/bitumen being found in Epirus. It was a valuable strategic resource; the object of the first known battle for a hydrocarbon deposit, between the Seleucids and the Nabateans in 312 B.C.

In the ancient Far East, natural asphalt/bitumen was slowly boiled to get rid of the higher fractions, leaving a material of higher molecular weight which is thermoplastic and 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 asphalt/bitumen was sometimes used to adhere stone projectile points to wooden shafts.

The Greek fire, which composition was a military secret of the Byzantine navy, contained, among other things, asphalt/bitumen as a component. 100 years after the fall of Constantinople in 1453, Pierre Belon described in his work Observations in 1553 that pissasphalto a mixture of pitch and bitumen was used in Dubrovnik for tarring of ships from where it was exported to a market place in Venice where it could be bought by anyone. 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 air-proof granaries, and in protecting, by means of the arches, the water-courses 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 it was generally neglected in France until the revolution of 1830. Then, 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 (l'Ain) and the Puy-de-la-Poix (Puy-de-Dome)", although it could also be made artificially.

Asphalt/bitumen was used in early photographic technology. In 1826 or 1827, it was used by French scientist Joseph Nicéphore Niépce to make the oldest surviving photograph from nature. The asphalt/bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the asphalt/bitumen and made it insoluble, so that when it was subsequently rinsed with a solvent only the sufficiently light-struck areas remained. Many hours of exposure in the camera were required, making asphalt/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.

Asphalt/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 dilutents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, asphalt/bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of asphalt/bitumen as a glaze to set in shadow or mixed with other colours to render a darker tone resulted in the eventual deterioration of a good many paintings, those of Delacroix being just one notable example. Perhaps the most famous example of the destructiveness of asphalt/bitumen is Théodore Géricault's Raft of the Medusa (1818-1819), where his use of asphalt/bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle.