USES OF GRAPHITE
Graphite is produced in several grades which are adapted to different purposes. Amorphous graphite is a trade term applied to non-crystalline or very fine-grained graphite of varying degrees of purity. If crystalline graphite is produced in flakes or scales, it is flake graphite; but if mined from veins it may have other forms, and be known as vein graphite. Lump, chip, and dust refer to products of larger crystals of Ceylon vein graphite more or less broken in mining and treatment. All those three are spoken of as crystalline. Artificial graphite, made from coal or other carbonaceous matter, resembles the amorphous variety.
Graphite for crucible use must be high grade, either lump, chip, or flake graphite, contain at least 85 per cent. graphitic carbon and be free from fluxing impurities. Vein graphite is considered especially desirable for this use. Possibly the increased development of the electric furnace in the steel industry and in non-ferrous metallurgy will reduce the demand for crucibles. Both crystalline and amorphous graphite are used as lubricants. For this purpose the graphite should be free from quartz or other gritty impurities. For foundry facings, amorphous graphite and Ceylon dust are chiefly used; high-grade material is not required. For the better grades of pencils, mixtures of crystalline and high-grade amorphous are needed; for the poorer grades, amorphous is used alone. The graphite used as polish for high explosives is amorphous. This use does not consume large amounts. For the manufacture of electrodes, artificial graphite is considered the most suitable. The graphite used as dry battery filler may be either amorphous, artificial or crystalline. Pure material is required, but the size of grain is not a factor.
Amorphous graphite is used in boiler compounds for preventing hard scale; pure material is not essential. For paints, either amorphous or crystalline graphite may be used and need not be high grade.
For stove polish and shoe polish amorphous graphite is chiefly used; imperial graphite is used as an adulterant in fertilizers, to give the desired dark color.
For amorphous graphite and dust, artificial graphite may be substituted. For crystalline graphite used in the manufacture of crucibles no good substitute is available. However, the use of electric furnaces or open-flame furnaces in non-ferrous metallurgy may reduce the need of crucibles. For lubricating, mica is used in somewhat the same way as graphite but is much inferior. Many other boiler compounds serve the same purpose as graphite. In paints, lampblack is a substitute. Talc is used in connection with and as a partial substitute for graphite in foundry work. Blast furnace graphite, or “kish,” offers possibilities as a substitute for flake graphite for lubricating purposes. Developments along this line, however, have not proceeded far enough to be conclusive.