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Phase Transformations in Sol-Gel Yag Films

Published online by Cambridge University Press:  25 February 2011

R. S. Hay
R. S. Hay*
Affiliation:
Wright Laboratory, Materials Directorate WPAFB OH 45433
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Abstract

Diphasic yttrium-aluminum garnet (YAG) sols were gelled across TEM grids to make films. The films were heat-treated up to 300 hours between 800°C to 1150°C. Microstructure and phase evolution were observed by TEM. YAG fraction and grain size, matrix phases and grain size, nuclei/area, and film thickness were measured. Yttrium-aluminum monoclinic and transition alumina appeared at 800°C. YAG nucleated between 800°C and 950°C. Above 850°C nudeation was site-saturated. Final nuclei density averaged 0.3/μm3. Between 850°C and 1000°C YAG growth had ∼t1/2 dependence and Q ∼ 280 kJ/mole. Below 850°C nudeation was continuous and growth had ∼t0.85 dependence. Above 1000°C YAG growth had ∼t1/4 dependence and the matrix grains coarsened with ∼t1/4 dependence. Unreacted areas were more abundant in thinner films because the nuclei/area and reaction rate decreased. YAG growth was often accompanied by formation of 20 – 100 nm subgrains. Above 1100°C there was some readion to YAG by a different process.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 271: Symposium N – Better Ceramics Through Chemistry V , 1992 , 421
Copyright
Copyright © Materials Research Society 1992

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