Differential thermal analysis studies on the crystallization of strontium tungstate melts. Variation of rate constants with crystallization temperatures and cooling rates |
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Authors: | B. N. Roy S. Appalasami A. K. Chatterji |
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Abstract: | 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° to below the eutectic temperature at cooling rates RT = 0.67° to 3.3° min−1. Heterogeneous nuclei first formed slowly onto metal platinate particles within the solution during induction periods (t ); the main crystal growth then started after the development of some exces solute concentration (ΔC ) at the induction temperature (T ). The actual growth after t was diffusion rate-controlled. The diffusion rate-constants (kDt) for growth after the induction periods along the major axis were estimated; the increased with T0 and RT. 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 (kDl)real. |
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