249As a final point, it is not considered likely that the present model will be of significance for pressureless sintering since the contribution of plastic flow mechanisms to densification under these conditions is believed to be limited.%
IV. ConclusionsA dependence of the sample density on the logarithm of the processing time during hot-pressing can be interpreted as a consequence of the dependence of the stress multiplication factor on porosity under conditions where densification is by dislocation creep and where rapid mass transport allows pores to retain their equilibrium configurations.The activation energy of the densification rate in hot-pressing will differ from the activation energy of the corresponding diffusion coefficient when the slope of the density vs log time plot changes with the temperature, say as the result of a dependence of the dihedral angle on temperature. Changes of the stress multiplication factor with temperature must accordingly be incorporated in the calculations.Low values of the dihedral angle of the material and control of deformation by a mechanism with a high value of the stress exponent are favorable conditions according to the present analysis for the observation of this form of densification kinetics in hot-pressing.This interpretation of the semilogarithmic law of densification is supported by observations of the hot-pressing of high-purity MgO.
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