Kinetics of Sintering of Sodium Chloride in the Presence of an Inert Gas

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Abstract
Direct observations of interfacial growth and the approach of centers between spheres of sodium chloride were made in an argon atmosphere and over a temperature range of 700 to 800°C. The rate law governing the increase of the contact area between spheres, the effect of changing size scale on this rate and the absence of a change in the center‐to‐center distance during sintering all indicate that the rate‐determining mechanism of material transport in this sintering process is evaporation‐condensation. A model is presented which considers Stefan flow to occur within a thin boundary layer in the gaseous phase adjacent to the condensing surface, the sintering rate being predominantly governed by the rate at which sodium chloride vapor diffuses through this boundary layer. The marked pressure‐dependence of the empirical relationship between contact area and sintering time for fixed temperature and sphere size is consistent with the proposed model.

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