Transformation kinetics from hexacelsian to celsian for powders having uniform particle size

Transformation kinetics from hexagonal to monoclinic form of celsian, which is an attractive material as a matrix of fiber-reinforced ceramics, were studied. Rate constants for nucleation and crystal growth were determined by isothermal transformation using classified powders having different ranges of particle size. Kinetics could be successfully analyzed by a modified first order equation. The activation energies for nucleation and growth were evaluated separately to be 407 and 228 kJ/mol from the temperature dependencies of the rate constants. The difference in the activation energies affected the change in shape of sigmoidal isotherms, and sluggishness of this phase transformation was attributed to a small value of the crystal growth rate.