Monophase Ceramics

It was shown in [18] that practically monophase fine barium hexaaluminate can be obtained by mechanical activation of a mixture of barium oxide with Y-AI2O3, which exhibits acid properties to a larger extent than a-Al203, and by consequent thermal treatments at increased temperature. The product then is grinded in the presence of water. The synthesis was shown to proceed almost completely after activation for 5 min in the AGO-2 planetary mill and thermal treatment at 1300°C for 1 h. Mechanical activation of the mixture of aluminium hydroxide with barium oxide, followed by thermal treatment at 900°C, results in the formation of the final product and a-Al203 as an admixture which remains even at 1300°C. Mechanochemical synthesis helped also to synthesize barinm hexaaluminate in which a part of aluminium cations is replaced with manganese, iron, cobalt cations. Such compounds are nsed as active ceramics in catalysis [17]. 

The commercially important aluminosilicate ceramic mullite (Al6Si20i3) can readily be produced by heating either monophasic (homogeneous) or diphasic gel precursors. The reactivity and reaction paths of both types of mullite precursor have been... 

While it may be possible to form homogeneous monophase /5-alumina powders at temperatures below 1100°C, the feasibility of forming the desired 6"-alumina phase at low temperatures in any from of stabilization is remote, at best. Furthermore, most of these techniques involve expensive reactants, employ elaborate processing schemes, and have, in some cases, very low reaction yields, features that detract further from their viability in the large-scale fabrication of ceramic electrolytes. 

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