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NON-ISOTHERMAL STUDY OF CORUNDUM CERAMICS WITH A COMPLEX OXIDE ADDITIVE SINTERING

Dmitry Antonov

Abstract

Adjustment of compositions and processing techniques, mainly ? firing conditions, has been a key route for ceramics performance improvement. The present research addresses sintering process of alumina ceramics with an additive in system that was studied by non-isothermal method. Experimental samples shaped as cylinders 25 ? 6 mm in size were obtained and sintered by consequtive firings in air at heating rates q1 = 1,0 and q2 = 3,0 °?/min without curing and quenched in air. Linear shrinkage (? = ??/?, hereon ? ?) at two heating rates (q2 and q1) was plotted against temperature ? = f(T). To determine Arrhenius equation coefficient k0 following characteristic models F(?) were suggested: formal kinetic model (1); anti-Yander model (2); anti-Gistling (Wagner) model (3); and nucleation (Erofeev-Kolmogorov) model (4). Models 1 and 4 were also reduced to Z = 1 ? ?/?max. Models were verified in terms of squared Pirson correlation R2, where most adequate model had R2 > 1. Kinetic parameters for separate models were calculated, and two most adequate were anti-Yander and anti-Gistling (Wagner) models (R2 equals 0.952 and 0.913 respectively). Apparent sintering activation energy calculated from this model equals 183.7 kJ/mol. This suggests that the process corresponds to first order reaction, and sintering of ceramics with such additive may be described by liquid-phase sintering as well as nucleus formation in eutectic melt. It also proves that in case of a complex CaO ? ZnO ? Al2O3 ? SiO2 sintering aid the limiting stage of alumina sintering process is diffusion mass transfer through liquid phase, and sintering of ceramics with such additive may be intensified by technological means that reduce viscosity of the melt.

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