Crystallization of glass

In ceramic materials for LTCCs, there are cases where crystals are actively precipitated in the glass to achieve the required characteristics, and cases where precipitation of crystals that are not required in the glass is hindered. In either case, it is necessary to fully understand the occurrence of crystallization of glass, and to control crystal precipitation. 

Glass coating (Corning) SiOi BjOj AI2O3 NajO K,0 MgO CaO PbO 

The dynamics of the process in which nucleation and crystal growth occur together are expressed by the Johnson-Mehl-Avrami (JMA) equation. 

A Constant, E Activation energy of crystal growth, N = Nr+ No/a, Nr is the number of crystal nuclei at the unit volume formed during heat treatment at nucleation temperature, and No/a is the number of crystal nuclei at the unit volume formed during the rise in temperature at speed a. 

If the temperature rises at the constant programming rate a, since k changes in accordance with the temperature or time, equation (2-2) is expressed as equation (2-4). 

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Matusita, K., and S. Sakka, Kinetics study of the crystallization of glass by differential scanning calorimetry, Phys. Chem. Glasses, 20, 81 (1979). 

Crystalline Silica. Quartz sand is of course the principal raw material for the production of glass (qv). Cristobalite and 3-quartz are used in glass ceramics (qv), ie, ceramics produced by the controlled crystallization of glass. Silica is a main constituent of ceramics (qv). For example, refractory silica brick containing small amounts of A O is used as roof brick for open-hearth furnaces at temperatures >1600° C (see Refractories). Silica sand or flour (ground quartz) is the raw material for soluble silicates, such as sodium silicate, which is consistently ranked as one of the top 50 U.S. industrial chemicals (98) (see Silicon compounds, synthetic inorganic silicates). 

Within the last decade several novel processing methods have been developed to overcome the limitations of traditional methods. For CMCs, these include chemical vapor infiltration [7-10] repeated infiltration/ pyrolysis of sols or polymers [77], crystallization of glass matrices [12-14] and the direct formation of a ceramic matrix by the directed oxidation of a... 

Applications of this camera will be in the area of time-resolved scattering on synthetic or biological supramolecular assemblies and in materials research (e.g. crystallization of glasses). The aims for the camera will be ... 

As single-phase substances are heated or cooled, they can undergo a number of polymorphic transformations. Polymorphs are different crystalline modifications of the same chemical substance. These transformations are quite common and include crystallization of glasses, melting, and many solid-solid phase transformations, some of which are described below. In general, there are two types of polymorphic transformations, displacive and reconstructive. 

Glass-ceramics are an important class of materials that have been commercially quite successful. They are polycrystalline materials produced by the controlled crystallization of glass and are composed of randomly oriented crystals with some residual glass, typically between 2 and 5 percent, with no voids or porosity. 

E. J. Muchin and N.G. Gutkina, Crystallization of Glasses, Oborongiz., Moscow, 1960. 

K. Matusita and S. Sakka, Kinetic-Study on Crystallization of Glass by Differential Thermal-Analysis - Criterion on Application of Kissinger Plot , J. Non-Cryst. Solids, 38-39, 741-46 (1980). 

M. R. Heslin, in Effect of Hydroxyl Ion Concentration on the Nucle-ation and Crystallization of Glasses, Ph.D. Thesis, Alfred University, 1993. 

The crystallization of glass is so well established that it is responsible for the development of a whole class of materials known as glass-ceramics. There is therefore a large body of literature on this subject. When glass is present in a GB, there is an additional constraint on the crystallization since a second nucleating interface is present. For example, it is possible that a glass that wiU crystallize on... 

Figure 21.11 Reprinted from Vogel, W (1971) Structure and Crystallization of Glasses The Leipzig Ed., Pergamon Press, Oxford, p. 150.

E Devaux, B Chabert. Non-isothermal crystallization of glass fibre reinforced polypropylene. Polymer Communications 31 391-394, 1990. 

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