The glass of a specific composition with or without a nucleating agent is subjected to crystallization heat treatment under controlled conditions, so that the original single glass phase forms a composite material having a uniform distribution of the microcrystalline phase and the glass phase. The difference between glass-ceramic and ordinary glass is that the former is partially crystalline and the latter is all amorphous. The surface of the glass-ceramics can be opaque with natural stone streaks and colors, while the glass is a transparent body of various colors and different procedures.
The comprehensive properties of glass-ceramics mainly determine three major factors: the composition of the original composition, the size and number of micro-crystals, and the nature and quantity of the residual glass phase.
The latter two factors are determined by the crystallisation crystallization heat treatment technique. The original composition of the glass-ceramics is different, and the types of crystal phases are also different, for example, β-wollastonite, β-quartz, fluorophlogopite, lithium disilicate, etc., various crystal phases impart different properties to the glass-ceramics, In the crystal phase, the β wollastonite crystal phase has the required properties of architectural glass-ceramics. For this reason, the CaO-Al2O3-SiO2 system is often used as the original composition system of architectural glass-ceramics. The general composition is shown in Table 1.
Table 1: Composition of CaO-Al2O3-SiO2 glass-ceramics
Color\Composition SiO2 Al2O3 B2O3 CaO ZnO BaO Na2O K2O Fe2O3 Sb2O3
White 59.0 7.0 1.0 17.0 6.5 4.0 3.0 2.0 0.5
Black 59.0 6.0 0.5 13.0 6.0 4.0 3.0 2.0 6.0 0.5
The main crystalline phase precipitated by the above glass component after the crystallization heat treatment is: β-wollastonite (β-CaO, SiO2).
Application of glass-ceramics in astronomical optics
Since the physical properties of the glass-ceramic are not easily affected by temperature, they can be applied to the primary and secondary mirrors of the astronomical telescope. This provides better heat balance adaptation time. A better optical surface can be processed due to its stable physical properties.
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