Of P-quartz solid solution glass-ceramics

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-... 

In the development of glass-ceramics of the P-quartz solid solution type, all three requirements were met similarity of the index of refraction between the glass matrix and the crystals, very small particle size, and low absorption. The solid-state reactions that are involved in the formation of P-quartz solid solution glass-ceramic are presented in Section 2.2.2. The chemical composition of different products are also discussed in this section. The special nanostructure of this glass-ceramic is described in Section 3.2.1. 

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

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). 

Figure 3-2 shows the cellular membrane microstructure of a P-quartz solid solution glass-ceramic. The individual phases are presented in connection with their effect on the different solid-state reactions to provide a better understanding of this microstructure. As described in Section 2.2.2, the nucleation of P-quartz solid-solution crystals is heterogeneously initiated by ZrTiO nucleating agents. These ZrHO crystals represent the nucleus of the... 

Glass-ceramics in which gahnite, Zn0 Al203, and P-quartz solid solution constitute the main crystal phase were introduced by Strnad (1986). The typical range of the chemical composition of P-quartz solid solution-gahnite glass-ceramics is shown below ... 

The formation of P-quartz solid solution and gahnite crystals in glass-ceramics from the Si02-Al203—ZnO allowed specific properties, such as translucency and even transparency, to be combined with variable coefficients of thermal expansion of... 

This type of cellular membrane microstructure can be developed in glass-ceramics that exhibit a very low coefficient of thermal expansion because of the precipitation of p-quartz solid-solution or P-spodumene crystals (Beall 1992). The glass matrix, which is very thin and surrounds the crystals, plays the part of the cellular membrane. As a result, the crystals are separated from each other. The membrane accounts for approximately 10 vol% of the micro-structure and can, for example, act as a diffusion barrier between the crystals. 

Beall (1992) attributes a great deal of importance to the glass matrix representing the cellular membrane in the solid-state reactions of P-quartz solid solution and P-spodumene solid solution glass-ceramics, the tenacious residual... 

The main crystal phase of the Zerodur glass-ceramic is composed of P-quartz solid solution This phase is produced by volume crystallization. Special thermal properties devdop as a result of the formation of very small crystallites and the simultaneous high crystallite count per unit of glass volume. 

The following formula is used by Petzoldt and Pannhorst (1991) and Petzoldt (1967) to describe the main crystal phase of the P-quartz solid solution type found in the Zerodur glass-ceramic ... 

This formula demonstrates that Li", Mg ", Zn, and Al ions are incorporated into the structure of P-quartz. As a result, the P-quartz is frozen in the structure of the glass-ceramic in a metastable state at room temperature. In addition, AlPO structural units are incorporated. These units are iso-morphous with Si02 and replace the [SiO J tetrahedra in the P-quartz solid solution structure. The microstructure of this glass-ceramic was studied by Maier and Muller (1987). It is evident that the P-quartz solid solution crystals measure approximately 100 nm. This microstructure was developed by heat treating the base glass at 700 C for 4 hours. Subsequently, the base glass was heat treated at 900°C for 10 minutes. Surprisingly, this relatively short heat treatment produced the fine crystals. 

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. 

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