In situ synchrotron XRD analysis of the kinetics of spodumene phase transitions

摘要

The phase transition by thermal activation of natural alpha-spodumene was followed by in situ synchrotron XRD in the temperature range 896 to 940 degrees C. We observed both beta- and gamma-spodumene as primary products in approximately equal proportions. The rate of the alpha-spodumene inversion is first order and highly sensitive to temperature (apparent activation energy similar to 800 kJ mol(-1)). The gamma-spodumene product is itself metastable, forming beta- spodumene, with the total product mass fraction ratio f(gamma)/f(beta) decreasing as the conversion of alpha-spodumene continues. We found the relationship between the product yields and the degree of conversion of alpha-spodumene to be the same at all temperatures in the range studied. A model incorporating first order kinetics of the alpha- and gamma-phase inversions with invariant rate constant ratio describes the results accurately. Theoretical phonon analysis of the three phases indicates that the gamma phase contains crystallographic instabilities, whilst the a and b phases do not.