Author: Stuart HampshirePublisher:
ISBN:
Category :
Languages : en
Pages : 96
Book Description
The objective was to study the effect on properties (such as microhardness, glass transition, crystallization temperature, viscosity, etc.) of replacing oxygen by nitrogen in sialon-based glasses containing rare-earth cations and to study the formation of glass-ceramics by controlled crystallization of these oxynitride glasses and to assess the effects of this on properties. Glasses were prepared by melting appropriate oxides and nitrides in boron nitride lined crucibles, melting at 1700 C under nitrogen and casting into preheated graphite moulds followed by annealing. Characterization of the glasses was carried out by differential thermal analysis (DTA) to ascertain the glass transition and crystallization temperatures and standard techniques used for microhardness and viscosity. Nitrogen increases the glass transition, microhardness and viscosity for constant cation ratio glasses and also inhibits crystallization. From DTA, suitable heat-treatment schedules were designed to produce fine-grain glass-ceramics. Optimization of these heat treatments was by measuring the changes (increases) in microhardness. Fully amorphous glasses can be prepared easily in large batches (approx. 100g) in many M-Si-Al-O-N systems. Work concentrated on Neodynium and Y-sialon glasses which undergo homogeneous nucleation at Tg+50 (C) followed by crystal growth at Tc-40 (C) each for 2.5 hours. (AW).