The following uses for carbon are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
Carbon compounds are important in many facets of the petrotchemicals industry as the feedstock is carbon-based. Carbon is also the basis of fuels such as coal and oil since both coal and oil are rich in carbon.
Carbon as graphite is a good lubricant. Carbon is a key component of steel. The analysis of iron (ferrous) metals in industry is important and ideally achieved in the field with robust equipment. Portable analysers exist that give rapid semi-quantitative analysis and grade identification of metals on-site. Charge coupled device (CCD) technology drives portable emission spectrometers to measure the whole spectrum necessary for the analysis of all common metals including iron and important components such as carbon in steel.
A portable CCD emission spectrometer for the analysis of iron and carbon in metals. Image credit: Arun Technology.
Carbon combines with some metals to make carbides such as tungsten carbide. Tungsten carbide is very, very hard and durable. This makes it desirable as tips for cutting tools such as drill bits. Carbon as diamond is one of the hardest known materials and diamond is an excellent abrasive.
Pencil lead does not conain lead - it is a graphite clay mixture.
Activated carbon (also called activated charcoal) is a form of processed carbon that is extremely porous and with very large surface area available for adsorption or chemical reactions. Just one gram of activated carbon has a surface area in excess of 500 m2 (determined by nitrogen gas adsorption). Activated carbon is usually derived from charcoal but also from carbonaceous source materials like nutshells, peat, wood, coir, lignite, coal and petroleum pitch. Activated carbon filters are used extensively in air filters (including gas masks) or cleaners and also help to remove contaminants such as ozone, chlorine, or other halogen compounds. Charcoal itself is used in art and also as a barbecue fuel.
Carbon black, a very fine powdered carbon, is the pigment in black printing ink and India ink. It is also used in laser printer toner cartridges. Carbon black is also used in rubber products such as car tyres
Carbon-14 (14C) is radioactive and is produced in the upper atmosphere from nitrogen and cosmic rays but is present in very small amounts. It decays by β- emission. Living organisms take in carbon and so a little 14C is present in all of us while we live. The abundance of 14C in the atmosphere and living organisms is broadly constant (there is a dependence upon solar cycles). After death the 14C disappears with a half-life 5730 years. This means that the date of death may be determined by measuring the amount of 14C present in a deceased sample. Carbon dating in this way is considered reasonably reliable for samples younger than about 10 half-lives, that is, about 50000 years.