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|Title:||Volume Changes Accompanying the Melt-Crystal Transition in Binary Borate Melts|
|Author(s):||Richards, Elizabeth Ann|
|Department / Program:||Ceramics Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The volume changes accompanying the crystallization of PbB(,4)O(,7), BaB(,4)O(,7), Li(,2)B(,4)O(,7), Cs(,2)B(,6)O(,10) and Na(,2)B(,8)O(,13) were determined throughout the crystal growth range. The elevated temperature specific volumes of the crystals were calculated using x-ray unit cell densities and volume thermal expansion coefficients obtained by high-temperature x-ray diffraction analysis. Melt specific volumes had been previously determined.
Room temperature density measurements combined with glass thermal expansion measurements allowed the temperature dependence of the specific volumes of the glasses to be determined. In addition, the specific volume of noncrystalline Na(,2)B(,8)O(,13) was determined in the glass transformation range by a technique that involved measuring the density of the surface layers of quenched droplets.
A volume decrease of 30% accompanied the crystallization of PbB(,4)O(,7). Crystallization of Na(,2)B(,8)O(,13), Cs(,2)B(,6)O(,10) and Li(,2)B(,4)O(,7) involved a 12% volume decrease. The volume change accompanying the crystallization of BaB(,4)O(,7) was approximately 8%. (,)
Calculations based on the melt-crystal interface temperature rise indicate that the crystallization rates of binary borate crystals may be described by a model that combines heat transport kinetics and interface reaction kinetics. The crystallization of Li(,2)B(,4)O(,7) appears to be controlled by the rate of heat removal from the melt-crystal interface, while the growth of PbB(,4)O(,7) appears to be limited by the kinetics of attachment at the interface. The growth rates of Na(,2)B(,8)O(,13), BaB(,4)O(,7), and Cs(,2)B(,6)O(,10) can be described by a combination of heat transport and interface reaction control, with the interface reaction term predominating in the growth of Na(,2)B(,8)O(,13) and BaB(,4)O(,7) while the heat transport term predominates in the growth of Cs(,2)B(,6)O(,10). (,)
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-14|