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|Title:||The Effect of Nitrogen on The Crystallization Behavior of Barium-Silicon-Aluminum-Oxygen-Nitrogen Oxynitride Glasses (Phase Separation, Crystal Growth)|
|Author(s):||Tredway, William Kent|
|Department / Program:||Ceramics Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Engineering, Materials Science|
|Abstract:||Oxynitride glasses in the Ba-Si-Al-O-N system which were clear, homogeneous, and free of metallic inclusions were produced using gel-derived oxide glass batches and electronic-grade Si(,3)N(,4). Nitrogen was found to act as a nucleating agent in the oxynitride glasses by inducing separation into two distinct phases via a nucleation and growth mechanism, with the droplet phase being enriched in nitrogen. The droplet phase was the first to crystallize, followed by the growth of crystals into the matrix by an interface-controlled process. The final microstructure consisted mainly of interlocking clusters of lath-shaped crystals with some residual glass dispersed among the crystals. The crystalline phase was found to be a complex solid solution with the hexacelsian crystal structure whose composition can be given as BaAl(,2-(x+y))Si(,2+(x+y))O(,8-y)N(,y)(OH)(,x), where (x + y) (LESSTHEQ) 1.
Avrami kinetic analysis and electron microscopy indicated that crystallization was characterized by essentially one-dimensional crystal growth accompanied by the nucleation of new crystals. The effect of nitrogen on the kinetics of crystal growth was investigated using several different approaches. By applying Johnson-Mehl-Avrami transformation kinetics theory to the crystallization behavior observed in glasses differing in the ratio of nitrogen to oxygen, the rate of crystal growth was found to decrease with an increase in nitrogen content when analyzed as a function of temperature. The activation energy for crystallization as determined by DTA increased with increasing nitrogen content. At a given value of viscosity, the crystal growth rate was higher in glasses possessing a higher ratio of nitrogen to oxygen. These results suggested that while glass viscosity played a major role in determining the rate of crystal growth, a higher nitrogen content may actually lead to an increased reaction rate at the crystal/liquid interface.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1986.
|Date Available in IDEALS:||2014-12-16|