Differential thermal analysis studies on the crystallization of strontium tungstate melts

Kinetics of strontium tungstate crystallization from sodium tungstate melts were studied in platinum crucibles (by DTA) by continuous cooling from initial crystallization temperatures T0 = 800 to 1000 0C to below the eutetic temperature at cooling rates Rsub(T) = 0.67 to 3.3 0C/min. Heterogeneous nuclei first formed slowly onto metal platinate particles within the solution during induction periods; the main crystal growth then started after the development of some excess solute concentration at the induction temperature. The actual growth after that temperature was diffusion rate-controlled. The diffusion rate-constants for growth after the induction periods along the major axis were estimated; they increased with T0 and Rsub(T). These values were higher than those for diffusion-controlled crystal growth of strontium tungstate from sodium tungstate melts in alumina crucibles but much smaller than the real diffusion rate-constants. (author)