| Catalysed phase transformations of silica were studied at
1400°C employing DTA method for determination of the
crystalline forms of silica. The consecutive transformation
of quartz to tridymite proceeded through metastable cristohalite
and intervening transition phases. The decomposition
of quartz in presence of mineralisers that produced liquid
phases proceeded with uniform radial velocity, while with
those acting in the solid state, the decomposition velocity
progressively decreased with time, and the conversion
kinetics were in approximate agreement with a phase
boundary-controlled and a diffusion-controlled process
respectively. The dependence of cristobalite formation rate
on the transition phase concentration suggested that development
of cristobalite occurred at the nuclca:ion centres
distributed inside the whole volume of the transition phase. |
