engleski

The influence of particle size on crystallization of Zno-Al2O3-SiO2 glass ceramics

Crystallization behavior of powder glass with various particle sizes from 63 μ m to 500 μ m and bulk glass (~5 mm), with the composition: 55.6 mol% SiO2, 22.8 mol% Al2O3, 17.7 mol% ZnO and with 3.84 mol% of TiO2 as nucleating agent, has been studied by differential thermal analysis (DTA) and X-ray diffraction (XRD). The DTA scans of all powder samples are characterized with two exothermal peaks, while bulk glass scan has one exothermal peak. Two crystalline phases: zinc-aluminosilicate s.s. with high-quartz structure, Znx/2AlxSi3-xO6, and gahnite, ZnAl2O4, are formed in powder samples after first peak. The ratio of these phases depends on particle sizes. As coarser the powder, more gahnite fraction is produced. Eventually, in bulk glass gahnite is the sole crystalline phase. As the temperature in powder samples increases the second DSC peak appears, due to the second step gahnite crystallization. Simultaneously, the amount of zinc aluminosilicate s.s. decreases and the quantity of zinc and aluminum incorporated in the structure reduce until almost pure high-quartz structure is formed. The activation energies of zinc-aluminosilicate s.s. and gahnite crystallization has been determined by non-isothermal method to be 510&plusmn ; ; 18 and 344&plusmn ; ; 17 kJmol-1, respectively.

activation energy; crystallization; gahnite; glass-ceramics; zinc-aluminosilicate

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