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 s tudied. 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 analysed by a modified fi rst order equation. The activation energies for nucleation and growth were evaluated separately to be 407 and 228 kJ/mol from the temperature dependen cies of the rate constants. The difference in the activation energies affec ted the change in shape of sigmoidal isotherms, and sluggishness of this ph ase transformation was attributed to a small value of the crystal growth ra te. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.