Experimental and mathematical consideration of microstructural coarsening during liquid-phase sintering has resulted in kinetic laws which define grain size to the third power as being proportional to the isothermal sintering time. Despite those prior efforts, the situations typical to liquid-phase sintering are poorly treated by the current models because the models assume a structure consisting of widely separated spherical grains (zero contiguity). No experiment had been completed to quantify the effect of contiguityon the growth kinetics. In order to do this, the contiguity and growth rates of tungsten grains in a liquid matrix at 1,750K were measured in sintered heavy alloys of 78,83, 88, 93 and 98 wt. % W balanced with 70Ni-30Fe. The observed grain growth rates were compared with the theoretical predictions of the LSW theory and volume fraction modified theories. By modifying the volume fraction effect with a contiguity term, a model was produced that closely followed the experimental results.

Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300" to 1400°C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence three-dimensional grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature.All regressions between G" and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol. [

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