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A phase transformation study in the BaO · Al2O3 · 2SiO2 (BAS)–Si3N4 system

Published online by Cambridge University Press:  03 March 2011

A. Bandyopadhyay  and
P.B. Aswath
A. Bandyopadhyay*
Affiliation:
Department of Mechanical and Aerospace Engineering and Materials Science and Engineering Program, University of Texas at Arlington, Arlington, Texas 76019–0031
P.B. Aswath
Affiliation:
Department of Mechanical and Aerospace Engineering and Materials Science and Engineering Program, University of Texas at Arlington, Arlington, Texas 76019–0031
*
a)Current address: Post Doctoral Fellow, Center for Ceramic Research, Rutgers University, P.O. Box 909, Piscataway, New Jersey 08855–0909.
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Abstract

A phase transformation study was carried out with barium aluminosilicate (BAS) forming powders (BaCO3, Al2O3, and SiO2) in a BAS-Si3N4 system. Powders were heat-treated in air at 1 atm pressure at different temperatures from 600 to 1150 °C at an interval of 50 °C to study the phase transformations during the formation of BAS. The phase transformations of α to β-Si3N4 is studied by heat-treating the powders at 1600 °C for different sintering times in a nitrogen environment at 1 atm pressure. Formation of different phases was identified by using powder x-ray diffraction. Formation of different forms of barium silicates occurs as an intermediate step between 650 and 950 °C and hexagonal BAS forms between 900 and 950 °C. The hexagonal form of BAS always forms first and persists as a metastable phase in the composites with no evidence of the monoclinic phase. An attempt made to fully transform hexagonal BAS to monoclinic BAS by using LiF as a mineralizer proved to be successful. The hexagonal form of BAS forms first when heat-treated at 1000 °C and is fully transformed to monoclinic BAS when heat-treated at 1100 °C.

Type
Articles
Information
Journal of Materials Research , Volume 10 , Issue 12 , December 1995 , pp. 3143 - 3148
Copyright
Copyright © Materials Research Society 1995

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References

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