Liquid-phase sintering of SmCo5

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Abstract
The initial sintering kinetics of stoichiometric SmCo5 powder containing a samarium‐rich sintering addition (60 wt% Sm plus 40 wt% Co) have been investigated as a function of amount of liquid phase, time, temperature, and particle size. The shrinkage as a function of time exhibits the classical three stages of liquid‐phase sintering, i.e., rearrangement, solution precipitation, and solid phase. The rate‐controlling step during the solution‐precipitation stage corresponds to a phase‐boundary (solid/liquid) reaction leading to dissolution. Evidence for this conclusion is partially based on the logarithm‐shrinkage—logarithm‐time slopes being equal to 1/2 instead of 1/3. A 1/3 slope is predicted by the liquid‐diffusion‐controlled sintering model while the phase‐boundary sintering model predicts a slope of 1/2. An activation energy of 52.8 kcal/mole was obtained for the temperature dependence, and this also suggests a phase‐boundary reaction rather than rate control by diffusion in the liquid phase. The rate of sintering follows an r−1 particle‐size dependence instead of an r−4/3 dependence, again suggesting that the solution‐precipitation stage of sintering of SmCo5 is controlled by a phase‐boundary reaction leading to dissolution.

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