Abstract
The kinetics and the mechanism of material transport in sintering calcium fluoride was investigated. For this purpose spheres of hot-pressed calcium fluoride containing a fine dispersion of stabilized zirconia as markers were sintered for various times and at various temperatures to plates of the same composition. Both conventional sintering without application of an external load and sintering with an external load on the sphere were studied. The rate of growth of the neck between sphere and plate was determined by sectioning, polishing, and photographing the sintered samples. The photo-graphs of the neck regions were carefully examined in order to determine whether the marker particles extended throughout the diameter of the neck or whether a marker-free zone existed in the outer region of the neck. Only in samples sintered for long times (400–1000 hr) did the markers not extend through the entire neck regions, but left a marker-free zone near the ends of the neck. The extent of the marker-containing central region strongly depended upon the presence of an external load. With load the marker-containing region occupied a much larger percentage of the entire neck. From the strong influence of the external load upon the marker containing region of the neck it is concluded that material transport in sintering of calcium fluoride takes place by diffusional flow only in the later stages of sintering, where the stress due to surface tension forces becomes small. In the early stages of sintering, where the stress due to surface tension forces is higher, and particularly when an additional stress is supplied by an external load, material transport takes place by slip, i.e., dislocation motion. The range of stress which separates the two mechanisms is estimated to be in the neighborhood of 105 dyn/cm2 (1.4 psi).
This paper is based on a thesis submitted by A. R. Hingorany in partial fulfillment of the requirements for the Degree of Doctor of Philosophy to the Department of Materials Engineering, Rensselaer Polytechnic Institute.
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Hingorany, A.R., Lenel, F.V., Ansell, G.S. (1969). The Role of Plastic Flow by Dislocation Motion in the Sintering of Calcium Fluoride. In: Gray, T.J., Fréchette, V.D. (eds) Kinetics of Reactions in Ionic Systems. Materials Science Research. Springer, Boston, MA. https://doi.org/10.1007/978-1-4899-6461-8_21
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