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Bitumen is a mixture of organic liquids that are highly viscous, black, sticky, entirely soluble in carbon disulfide, and composed primarily of highly condensed polycyclic aromatic hydrocarbons.

Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum which is so thick and heavy that it must be heated or diluted before it will flow. At room temperature, it has a consistency much like cold molasses. Refined bitumen is the residual (bottom) fraction obtained by fractional distillation of crude oil. It is the heaviest fraction and the one with the highest boiling point, boiling at .

In British English, the word 'asphalt' refers to a mixture of mineral aggregate and bitumen (or tarmac in common parlance). The word 'tar' refers to the black viscous material obtained from the destructive distillation of coal and is chemically distinct from bitumen. In American English, bitumen is referred to as 'asphalt' or 'asphalt cement' in engineering jargon. In Australian English, bitumen is sometimes used as the generic term for road surfaces. 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 used to pave roads and manufacture roof shingles.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 as synbit.

Most bitumens contain sulfur and several heavy metals such as nickel, vanadium, lead, chromium, mercury and also arsenic, selenium, and other toxic elements. Bitumens can provide good preservation of plants and animal fossils.

Uses

is primarily used for paving roads. Its other uses are for bituminous waterproofing products, including the use of bitumen in the production of roofing felt and for sealing flat roofs.

Naturally occurring crude bitumen is the prime feed stock for petroleum production from tar 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 second largest proven oil reserves in the world. The Athabasca oil sandsmarker is 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 since 2003, upgrading bitumen to synthetic crude oil has become highly profitable. As of 2006 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 which could be extracted is estimated to be about , which at a rate of 4.4 million barrels per day would last about 200 years.
In the past, bitumen was used to waterproof boats, and even as a coating for buildings with some additives. The Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylonmarker. It is also possible that the city of Carthagemarker was easily burnt due to extensive use of bitumen in construction.

Vessels for the heating of bitumen or bituminous compounds are usually subject to specific conditions in public liability insurance policies, similar to those required for blow torches, welders, and flame-cutting equipment.

Bitumen was also used in early photographic technology. It was most notably used by Frenchmarker scientist Joseph Nicéphore Niépce in the first picture ever taken. The bitumen used in his experiments were smeared on pewter plates and then exposed to light, thus making a black and white image. It was similarly used to print millions of photochrom postcards.

Thin bitumen plates are sometimes used by computer enthusiasts for silencing computer cases or noisy computer parts such as the hard drive. Bitumen layers are baked onto the outside of high end dishwashers to provide sound insulation.

Bitumen also is used in paint and marker inks by some graffiti supply companies (primarily Molotow) to increase the weather resistance and permanence of the paint and/or ink, and to make the color much darker.

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, 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 a good many paintings, those of Delacroix being just one notable example.

Bitumen alternatives

Bitumen can now be made from non-petroleum based renewable resources such as sugar, molasses and rice, corn and potato starches. Bitumen can also be made from waste material by fractional distillation of used motor oils, which is sometimes disposed by burning or dumping into land fills. Non-petroleum based bitumen binders can be made light-colored. Roads made with lighter-colored pitch absorb less heat from solar radiation, and become less hot than darker surfaces, reducing their contribution to the urban heat island effect.

Geologic origin

Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae and other once-living things. When these organisms died, their remains were deposited in the mud on the bottom of the ocean or lake where they lived. Under the heat and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum.

As bitumens are also found in meteorites and Archean rocks it is possible that some bitumens are primordial material formed during accretion of the Earth and reworked by bacteria that consume hydrocarbons.

Grades of bitumen

The Paving Grades of bitumen are 30/40, 60/70 and 80/100.The grade 80/100 is commonly used in India and Bangladesh but for lower temperatures other grades are preferable.

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