Liquid Phase Sintering in the Glass-Cordierite System - Effect of Melt Infiltration Distance
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LIQUID PHASE SINTERING IN THE GLASS-CORDIERITE SYSTEM - EFFECT OF MELT INFILTRATION DISTANCE
Jau-Ho Jean and Tapan K. Gupta Alcoa Electronic Packaging, Inc. Alcoa Center, PA 15069
ABSTRACT Effect of glass infiltration distance, controlled by particle sizes of glass and ceramic filler, and green density, on densification kinetics of glass-filled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing cordierite size, reducing glass size and increasing green density. The above results are attributed to both increased driving force of densification by reducing glass particle size, and decreased glass redistribution distance by either increasing green density of compacts or increasing the particle size ratio between cordierite and glass powders.
INTRODUCTION Liquid phase sintering has been phenomenologically classified into three stages including rearrangement, solution and precipitation, and solid state sintering [1]. For insoluble systems, such as W-Cu [2,3], W-Ag [3], A1203-glass [4,5], and cordierite-glass [6], the densification during liquid phase sintering is primarily achieved in the first stage. For the system with high viscosity melt, such as glass (>lxl05 N.s/m 2 ) in glass-ceramics, a combination of melt formation, melt redistribution and particle rearrangement processes are generally observed in the first stage of liquid phase sintering [6,7]. Important factors affecting the densification behavior of the initial stage of liquid phase sintering have been identified and extensively studied, such as contact angle of liquid on solid [2,3], liquid content [8-10], and particle morphology [9,10]. However, the effects of particle size and green density on the initial stage of liquid phase sintering have not been studied in detail, and are the major focus of this study. In our previous investigation [6], the effects of glass content, sintering temperature, time-dependent contact angle and glass viscosity on densification of borosilicate glass-cordierite system were studied. It has been found that the densification of the borosilicate glass-cordierite system mainly takes place in the initial stage of liquid phase sintering at 800900*C. Both densification and densification rate increase with increasing sintering temperature and glass content. Based on an activation energy analysis, the rate-controlling step during densification has been found to be viscous flow of glass with contributions arising from both viscous sintering of glass and glass redistribution kinetics. It is also observed from microstructural development, densification results, and contact angle-time data that the densification kinetics can be adequately described by the melt infiltration kinetics with a time-dependent contact angle. It is also found that a larger melt infiltration distance takes longer infiltration time to reach the same densification, which in turn reduces the densification rate or even the a
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