Vitreous ceramics

Sedimentary rocks (like sandstone) have a microstructure rather like that of a vitreous ceramic. Sandstone is made of particles of silica, bonded together either by more silica or by calcium carbonate (CaCOj). Like pottery, it is porous. The difference lies in the way the bonding phase formed it is precipitated from solution in ground water, rather than formed by melting. 

Vitreous ceramics are different. Clay, when wet, is hydroplastie the water is drawn between the clay particles, lubricating their sliding, and allowing the clay to be formed by hand or with simple machinery. When the shaped clay is dried and fired, one component in it melts and spreads round the other components, bonding them together. 

Vitreous ceramics are made waterproof and strengthened by glazing. A slurry of powdered glass is applied to the surface by spraying or dipping, and the part is refired at a lower temperature (typically 800°C). The glass melts, flows over the surface, and is drawn by capillary action into pores and microcracks, sealing them. 

Feng, X., Einziger, R. E. Eschenbach, R. C. 1997. A direct single-step plasma arc - vitreous ceramic process for stabilizing spent nuclear fuels, sludges, and associated wastes. Materials Research Society Symposium Proceedings, 465, 25-32. 

The term porcelain is used here in its European sense. In the USA, it is defined as vitreous ceramic whiteware for technical purposes (ASTM). whereas similar materials for non-technical applications (table ware, sanitary ware, art ware) made by somewhat different processes arc called china (also refer to the note on p. 311). 

China. BS 5416 specifies this to be pottery with water absorption 0.2% and tranlucency 0.75% (assessed by comparison with standard test pieces) See also bone china. In the USA, however, ASTM-C242 defines the word as any glazed or unglazed vitreous ceramic whiteware used for nontechnical purposes, e.g. dinnerware, sanitary-ware, and art-ware, provided that they are vitreous. The combined nomenclature (q.v.) equates this term with porcelain (q.v.). 

China Sanitary-ware. US term for vitreous ceramic sanitaryware. 

Jar Mill. A small ball mill (q.v.), the revolving cylinder being a vitreous ceramic jar such mills are used in the grinding of small batches of ceramic colours and vitreous enamels. 

Vitreous ceramics, which derive their name from the Latin word for glass, vitreus, are possibly the oldest and most widely used types of ceramic materials. Marco Polo introduced them in Western Europe in the fourteenth century, and European potters strove for decades to duplicate the quality of the Chinese porcelains. In addition to porcelain they include china, pottery, and brick. Typically, they are made fiom clays such as hydrous aluminosilicate mixed with other inert materials. Ware is formed when the clays are in the wet state, after which they are dried and fired. Various additives are used to provide desired properties. 

Norton has provided an excellent summary of the development of the vitreous ceramic industry in the United States and Europe. 

Alumina porcelains contain corundum and glass phases. Both phases are continuous at a composition corresponding to about 9 vol% glass. In such a case, the thermal conductivity value will be in between that of the two phases. Generally, the glass is continuous in vitreous ceramics. Therefore, the conductivity of these materials is closer to that of the glass phase. 

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