ABSTRACT
The large majority of inorganic crystalline ceramics are made in three steps: forming of a powder to the desired shape, partial drying, and firing. For certain applications of high value and limited sample numbers, various special techniques of ceramic manufacture are useful. However, control of crystalline particle size and size distribution of the clay and of impurities can improve properties and simplify processing. For special ceramics that must be pure and have controlled particle size and size distribution, precipitation from solution is a desirable method of preparing starting powders. Dental porcelains must be relatively translucent and have easier forming requirements, so a composition with more feldspar and less clay and sand is usual. Glass ceramics that contain a high density of fine crystals are white and opaque, resembling porcelain, because of light scattered by the crystals. Glassy carbon is produced by pyrolyzing cross-linked organic polymers such as cellulose, phenolformaldehyde, and polyfurfuryl alcohol under carefully controlled conditions.
