Sintering of Glass Powder Packings with Metal Inclusions
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Sintering of Glass Powder Packings with Metal Inclusions A. Jagota, E.D. Boyes, R.K. Bordia, The DuPont Company, Central Research, Experimental Station, P.O. Box 80356-347, Wilmington, Delaware 19880-0356. Abstract The sintering of glass powder packings with metal inclusions has been studied using (a) a loading dilatometer, and (b) an in-situ SEM hot-stage. The addition of a small volume fraction of metal particles unexpectedly increases the sintering rate of the composite. With a further increase in the volume fraction of inclusions the sintering rate decreases rapidly to zero at a well-defined threshold. The in-situ sintering experiments have been used to observe the sintering mechanisms and to determine the parameters that contribute to this phenomenon: to assess the distribution of inclusions, and the nature of inclusion-inclusion and matrix-inclusion interaction. Predictions of the effective sintering rate are computed using a truss model with randomly distributed inclusions. The computations capture accurately the decrease in sintering rate (beyond the initial increase) with increasing volume fraction of inclusions. The initial increase is attributed to a reduction in viscosity of the glass due to chemical interaction with the metal. lIntroduction The problem of sintering packings with stiff (i.e., rigid and non-sintering) inclusions is important in several technological applications, notably the sintering of ceramic substrates, and dielectric, resistor, or conductor films and tapes. It has received considerable attention in the literature recently and a review can be found in [1]. Experiments with crystalline matrices [2] show a strong reduction in sintering rate with small volume fractions of inclusions. This is related to percolation of contacting inclusions and the operation of coarsening processes, such as grain growth in the region between inclusions [3]. Previous experiments with glass matrices [4] show a much weaker effect of stiff inclusions on the sintering rate of the composite. Theoretical self-consistent and composite-spheres models of the effective sintering rate have been successful in predicting the experimental data for low volume fractions [5,6,7]. The formation of clusters of inclusions, and eventually percolation of contacting inclusions, causes these models to be inaccurate as the volume fraction is increased. This paper presents the results of an investigation of the sintering of packings of glass spheres with stiff metal inclusions. Bulk measurements of the sintering rate are carried out using a loading dilatometer. These reveal an unexpected increase in the sintering rate of the glass with small additions of metal inclusions. Further additions reduce the sintering rate, ultimately to zero at a well-defined threshold. Insitu observations during sintering in an SEM hot-stage are used to study the various parameters important in these phenomena. Theoretical predictions of the effective sintering rate using a truss model capture accurately the decrease in sintering rate. The initial increa
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