Lithium as a sintering aid for producing dense transparent Magnesium Aluminate Spinel

Reference	Presenter	Authors (Institution)	Abstract
09-012	Lorena Batista Caliman	Caliman, L.B.(Universidade de São Paulo); Gouvêa, D.(Universidade de São Paulo);	Nano-structured Magnesium Aluminate Spinel (MAS) brings together difficult-to-combine properties as transparency and elevate mechanical resistance, being used in extreme environments and applications such as transparent lightweight armor. MAS transparency is directly depended on the crystallite size, being most pronounced in the nano domain and as MAS is one of the difficult-to-sinter ceramics, new methods are always on the agenda to reduce costs and improve nano-MAS properties. As sintering in its basic definition is the substitution of gas-solid interfaces for solid-solid interfaces (pore elimination), the control of interface’s physical-chemical properties and stability can influence the sintering behaviour. One of the methods of interface energy modification is the additive interface segregation. In this context, MAS powders doped with different concentrations of lithium were synthesized by the polymeric precursors method and the lithium concentration in the different interfaces determined by selective lixiviation. The powders were sintered using a high-pressure SPS program (1.4 GPa) in different temperatures and the resulting pellet’s properties were related to the lithium concentration, grain size, transparency and densification. The best conditions for obtaining a transparent and dense pellet was 5%mol doping and maximum sintering temperature at 850°C. Final medium crystalline size was 25nm, Vickers hardness at 23.8 GPa, medium infrared and visible wavelengths transparency of ~51% and 100% of the theoretical density.
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