Carbon

Carbon (pronounced /kɑrbən/) is a chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5730 years.[7] Carbon is one of the few elements known to man since antiquity.[8][9] The name "carbon" comes from Latin language carbo, coal, and, in some Romance and Slavic languages, the word carbon can refer both to the element and to coal.

There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon.[10] The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials. All the allotropic forms are solids under normal conditions but graphite is the most thermodynamically stable.

All forms of carbon are highly stable, requiring high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and other transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil and methane clathrates. Carbon forms more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.[11]

Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known lifeforms, and in the human body, carbon is the second most abundant element by mass (about 18.5%) after oxygen.[12] This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.

カーボンとは炭素のことで元素記号はCで表す。炭素は地球上に１４番目に多く存在する原子で、 空や海には主に炭酸ガスとして、地中には主に岩石、石炭、石油として、そして生物の中には いろいろな有機物の形で存在している。単体（主に炭素原子だけが集まったもの）では 地中に天然黒鉛やダイヤモンドなどとして存在する。

我々カーボン業界で炭素とかカーボンというときは炭素の単体をさし、天然黒鉛や主にコークスから工業生産される 人造黒鉛や無定形炭素（炭素質カーボン）などがある。この他に炭素単体からなる製品としてはコークス、活性炭、 カーボンブラック、そして最近では炭素繊維などがある。

カーボンは熱的にも化学的にも極めて安定な物質で古くから使われてきたが、特に導電性があることが判ってから 様々な分野に用途が広がった。特に近年半導体、エレクトロニクス分野などで需要が高まっている。