[Alumina reinforced porcelain jacket crown].
Aluminum oxides provide one of the most useful sources of high-strength and high-modulus crystals. New types of high alumina content glasses may replace feldspathic porcelains. Esthetics compare favorably.
Mechanisms Involved in Securing Dense, Vitrified Ceramics from Preshaped Partly Crystalline Bodies
The internal porosity of ceramics shaped before fusion has been improved by three firing techniques: (1) firing in vacuo, (2) firing in diffusible gas, and (3) finish firing and cooling under pressure. A method of measuring pore volume and texture has contributed to understanding the operating mechanics of these processes. This has led to recognition of the firing-process requirements for different porcelains depending on their crystalline content, matured viscosity, service conditions, and performance specifications.
Effect of Grinding and Firing Treatment on the Crystalline and Glass Content and the Physical Properties of Whiteware Bodies
The quantitative determination of the amount of quartz, mullite, and glass resulting from varying grinding and firing treatments was correlated with the physical properties of a whiteware body. The body composition selected contained 20% potash feldspar, 30% flint, 7.5%, ball clays, and 42.5% kaolins. The body mix was ground for 8−, 25−, and 100−hour periods, and, in addition, the flint and feldspar were preground for 25 and 100 hours. Special fluxes such as talc and nepheline syenite were also tried. All bodies were heated to cones 5, 7, and 9, and the fired porosity, modulus of rupture, and volume shrinkage after firing were determined. The amounts of quartz, mullite, and glass (by difference) were determined quantitatively with a Geiger-counter X-ray spectrometer, using a powdered sample with an internal standard. The results showed that the finer grinding of the body, flint, or the potash feldspar reduced the quartz content, increased slightly the mullite formation, and increased the amount of glass. The combination of finely ground feldspar and flint gave a much higher mullite formation and a lower quartz content. The results showed that an increase of talc is unfavorable to mullite formation. The transverse strength of the bodies investigated was proportional to the total mullite and glass content.