|
Asphalt ( or ,〔Merriam-Webster: ()〕〔Oxford Advanced Learner's Dictionary: ()〕 occasionally ), also known as bitumen (),〔Dictionary Reference: (bitumen )〕〔The Free Dictionary: (bitumen )〕 is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product; it is a substance classed as a pitch. Until the 20th century, the term asphaltum was also used.〔 Full text at Internet Archive (archive.org)〕 The word is derived from the Ancient Greek ἄσφαλτος ''ásphaltos'' (itself perhaps an Eastern word,〔Chambers English Dictionary〕 though see "Etymology" below). The primary use (70%) of asphalt/bitumen 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.〔Anja Sörensen and Bodo Wichert "Asphalt and Bitumen" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2009. 〕 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. Geologists often prefer the term ''bitumen''. Common usage often refers to various forms of asphalt/bitumen as "tar", such as at the La Brea Tar Pits. Another archaic term for asphalt/bitumen is "pitch". 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 is sometimes referred to as "refined bitumen". ==Composition== The components of asphalt are classified into four classes of compounds: *saturates, saturated hydrocarbons, the % saturates correlates with softening point of the material *Naphthene aromatics, consisting of partially hydrogenated polycyclic aromatic compounds. *Polar aromatics, consisting of high molecular weight phenols and carboxylic acids *Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds The naphthene aromatics and polar aromatics are typically the majority components. Additionally, most natural bitumens contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found in the <10 ppm level, 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 maltenes as the continuous phase. and "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".〔Muhammad Abdul Quddus (1992), p.99, in ch.5 pdf〕 Asphalt/bitumen can sometimes be confused with "coal tar", which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th 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 tar to macadam roads led to the word tarmac, which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, asphalt/bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include the asphalt/bitumen of the La Brea Tar Pits and the Canadian oil sands. Pitch is another term sometimes used at times to refer to asphalt/bitumen, as in Pitch Lake. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「asphalt」の詳細全文を読む スポンサード リンク
|