|M.Sc Student||Ashuach Yechezkel|
|Subject||The Influence of Sintering Additives on the Microstructure|
and Properties of AION
|Department||Department of Materials Science and Engineering||Supervisor||Professor Wayne D. Kaplan|
g-aluminum oxynitride spinel (Al23O27N5) is a polycrystalline material in the AlN-Al2O3 system, which is an alternative to sapphire for applications requiring transparency and high strength and hardness. At the same time, the production of transparent AlON is extremely challenging because residual porosity must be reduced to an absolute minimum, beyond that required from conventional ceramic processing. Residual porosity is the critical microstructural parameter in defining the degree of transparency for polycrystalline optically isotropic AlON.
The main goal of the thesis research was to study the influence of dopants (magnesium, lanthanum and yttrium) on the microstructure and transparency of AlON. Towards this goal, a high temperature (2000°C) reaction sintering process was developed. Dopants were added to the Al2O3 and AlN starting powders, and the sintered microstructure was investigated as a function of dopant concentration, and sintering time and temperature. Typical grain sizes of the AlON samples were 100-150 mm, depending on the sintering parameters and dopants. Co-doping with Mg and La resulted in samples with the lowest porosity observed by SEM and the highest degree of translucency. Long sintering times (12 hours) were needed to achieve the highest density, very close to the theoretical density. Doping with Y was found to form relatively large pores. At the sintering temperature a very low dopant concentration cause the formation of a liquid phase, which assists densification.