P-quartz glass-ceramics

Fig. 5. Relative change in length with temperature of P-quartz glass-ceramics designed for A, precision optics and B, cooktop panels. Curves for C, fused...

These P-quartz glass-ceramics are not only metastable at these temperatures but will... 

Further investigations regarding the optical effect of Cr " in mullite and P-quartz glass-ceramics were conducted by Reisfeld et al. (1984) and Kiselev et al. (1984). 

Glass-ceramics containing p-quartz or p-spodumene can be made from glass of the same composition by modifying its heat treatment p-quartz is formed by ceramming at or below 900°C, and p-spodumene by ceramming above 1000°C. 

Fig. 6. Microstructure of transparent p-quartz solid solution glass-ceramic as...

Alloys. Wood s metal, Rose s metal (see section on Alloys). Alloys of 40 parts Bi, 15 parts I, 25 parts Pb, 10 parts Sn and 10 parts Cd adhere e ecially well to glass. Pure indium metal (m.p. 155°C) and various indium alloys (for example, 50% In +50% Sn, m.p. 117°C) are suitable for joining metal to glass, quartz or ceramics. The surfaces of theparts must be very clean. Precautions should be taken with regard to the tenqierature ranges suitable for the various alloy cements and for the materials to be cemented. 

Ceramic crucibles may also be placed in glass, quartz or ceramic combustion tubes (one end open) so that the material may be in a vacuum or an inert gas atmosphere during the heating. Such an arrangement is shown in Fig. 272, p. 984. 

P-quartz. The P-quartz crystals are <0.1 pm in diameter. Crystal sizes below the wavelength of visible light (A. = 0.7-0.4 pm), a good match in refractive index between the glass and the crystal phase, coupled with a low birefringence result in high transparency. Table 26.4 lists the compositions and applications of some commercial transparent LAS glass-ceramics based on P-quartz. 

The low-pressure silica polymorphs include quartz, tridymite, and cristo-balite. The stable phase at room temperature is a-quartz or low quartz. This transforms to 3-quartz or high quartz at approximately 573°C at 1 bar. The transition from (3-quartz to tridymite occurs at 867°C and tridymite inverts to 3-cristobalite at 1470°C. P-Cristobalite melts to silica liquid at 1727 C. All three of these stable silica polymorphs experience displacive transformations that involve structural contraction with decreased temperature and all can be cooled stabily or metastabily to room temperature in glass-ceramics compositions. ... 

Findings from the theories of nucleation have also contributed to the optimization of these comprehensive experimental investigations. As a result, glass-ceramics with improved properties have been produced, specifically glass-ceramics with specific solid-solution limits like j3-spodumene and stuffed P-quartz or with stoichiometric compositions like cordierite and lithium disilicate. Initial results for the successfU application of the theory of nucleation to multicomponent glass-ceramics with a nonstoichiometric composition were achieved with mica and anosovite glass-ceramics. 

In the commercially important P-quartz solid solution glass-ceramics, values of 6-8 were achieved for n. These values improved the melting properties of the glasses and rendered the entire manufacturing process more economical (Beall 1986). 

The basic process development for the production of P-quartz solid solution glass-ceramics was conducted by Corning Glass Works. The key to the controlled crystallization of P-quartz solid solution was soon shown to be controlled nucleation, in other words, the correct selection of the nucleating agents and their concentration. 

The compositions of P-quartz solid solution glass-ceramics produced on a large scale for technical applications are summarized in Table 2-7. These glass-ceramics are called Vision , Zerodur , Narumi , Neoceram , Ceran , and Keraglas . Other products are Robax , which represents a col-... 

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