Ewer from
Iran, dated 1180-1210CE. Composed of brass
worked in
repoussé and inlaid with silver and bitumen. NY Metropolitan
Museum.
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.
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 525 degrees Celsius.
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.
Most bitumens contain sulphur 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
Bitumen is primarily used for paving roads. Its other uses are for general waterproofing products, including the use of
bitumen in the production of roofing felt and for sealing flat roofs. It is also the prime
feed stock for petroleum production from tar sands currently under development in Alberta,
Canada. Bitumen from tar sands is projected to account for 80% of Canadian oil production by
2020.
In the past, bitumen was used to waterproof boats, and even as a coating for buildings. The
Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylon. [1] It is also possible that the
city of Carthage was easily burnt due to extensive use of bitumen in construction.
Vessels for the heating of bitumen or bituminous compounds are usually excluded from public liability insurance policies.
Most geologists believe that naturally occurring deposits of bitumen are formed from the
remains of ancient, microscopic algae and other once-living things. These organisms died and 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. Bitumens
are found also in meteorites, archean rocks, copper, zinc mineralizations, and caves. It is possible that bitumens are primordial
material formed during accretion of the earth and reworked by bacteria that consume hydrocarbons.
Bitumen was also used in early photography technology. It was most notably used by French scientist Joseph Nicephore Nipce in
the first picture ever taken. The bitumen used in his experiments were smeared on pweter plates and then exposed to light thus
making a black and white image.
Bitumen alternatives
The world has become increasingly concerned over the global climate change thought to
be caused by greenhouse gases, chief among them anthropogenic carbon dioxide which is released into the atmosphere from burning fossil fuels. This has led to the
introduction of bitumen alternatives that are more environmentally friendly and non toxic. 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 [1].
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. [2]
Notes
- ^ Herodotus, Book I, 179
See also
External links
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)