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Isothermal and nonisothermal sintering behaviors of glass-filled ceramics are compared in this paper. Equations developed to describe the kinetics of shrinkage for both techniques can be readily used to interpret the experimental data. It is shown that the kinetics of linear shrinkage of powder compacts during isothermal and nonisothermal constant rate of heating are consistent and can be described by the viscous flow of glass.

I. INTRODUCTION Kinetics and mechanism of sintering have always been approached by using the densification results obtained from isothermal rather than constant-rate heating, primarily because it provides the advantage of relative ease and simplicity in analyzing experimental data. In industrial operations, however, it has rarely been completely isothermal or constant-rate heating. As a matter of fact, a combination of constant-rate and isothermal heating is the most common practice in the manufacturing workplace. It is therefore necessary to understand the correlation in kinetic analysis for the experimental data obtained between isothermal and constant-rate heating before the sintering conditions are optimized. In this paper the sintering results gathered from isothermal and constant-rate heating are reported by using a glass-filled ceramic composite as the model system. Based upon those concepts proposed for kinetic analysis of nonisothermal chemical reactions1"3 and sintering of glasses,4'5 analytical expressions are developed to determine the mechanism and kinetics of sintering during isothermal and constant-rate heating. II. EXPERIMENTAL A. Sample preparation Samples used in this study were prepared by tapecasting and lamination processes. The inorganic and organic compositions used for tape casting were typical of those reported previously.6'7 The organic compositions contained binder, plasticizer, dispersant, and solvents. The total binder content was approximately 10—25 wt. % of inorganic powders. The inorganic compositions contained 40 vol. % low-softening borosilicate glass (BSG) and 60 vol. % high-softening ceramic fillers. The low-softening BSG had a composition of approximately 70-80 wt. % SiO 2 and 20-30 wt. % B 2 O 3 , and the high-softening ceramic filler had a SiO2 content of 95 wt. %. Experimental results for glass viscosity measurement8 showed that the borosilicate glass had a 3342 http://journals.cambridge.org

J. Mater. Res., Vol. 7, No. 12, Dec 1992 Downloaded: 14 Mar 2015

softening point of 700-750 °C and an activation energy of 220-240 kJ/mol at 700-1000 °C. The high-softening ceramic fillers had a softening point or melting point greater than 1500 °C. The particle sizes of inorganic powders were determined by sedimentation and had a median size of 2 - 4 /xm. The mixture of organic and inorganic compounds was ground in a ball mill for 16 h, de-aired, and tape-cast on cellulose acetate carrier. The tapes were very uniform and had a thickness of about 200 fim. Samples with a thickness of about 2000 /xm were made by placing 10-11 green tapes between two metal plates a