Solid State Science and Technology, Vol.11, No.1 (2003) 9-15

MICROSTRUCTURAL CONTROL AND OXIDATION BEHAVIOUR OF Gd-SiAlON CERAMICS

 

M.H. Haji Jumali*, M.H. Lewis+ and R.J. Lumby+

* Physics Program, School of Applied Physics, Universiti Kebangsaan Malaysia

43600, Bangi, Selangor

+ Department of Physics, University of Warwick

Coventry, United Kingdom

 

ABSTRACT

 

The purpose of the present work are to investigate the possibility of controlling the microstructure of Gd α/β-SiAlON composite materials by controlling the starting composition and to study the oxidation behaviour of these ceramics. A series of Gd α/β-SiAlON composites were prepared by pressureless sintering at 1750 oC for 4 h. Additions of SiO2 were made to a selected composition to explore the potential mechanisms for controlling the microstructural development. Investigation on oxidation resistance of selected materials was carried out isothermally at 1350 oC in air. It was found that materials in the as-sintered state comprised a high proportion of equiaxed α phase and a small amount of β’ and AlN polytypoid. The additions of up to 5 wt% of SiO2  was found to be effective in promoting the development of β-SiAlON. The oxidation studies show that Gd α- SiAlON based materials exhibit greater oxidation resistance at 1350 oC compared to β+YAG material. The oxidation process of Gd α/β-SiAlONs was found to follow a parabolic relationship with respect to time. The parabolic rate constant for these materials is dependent on the microstructure of the ceramics.

 

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