Synthesis of YAG powder by aluminum nitrate-yttrium nitrate-glycine reaction

摘要

Yttrium aluminum garnet (YAG) powders of controlled size distribution find application in the synthesis of optically transparent solid state laser components, advanced engineering materials and composites, etc. [1,2]. Solution combustion is one of the simple methods for synthesizing the powder. In this technique, from a very concentrated solution of the metal nitrates a very porous sponge-like oxide compounds is formed due to the evolution of a large amount of gaseous products formed in combustion reaction between an oxidizer (nitrate) and a fuel (urea, glycine etc.) present in the reactant system. The salient feature of combustion reaction is that it is exothermic and self sustaining. In this study the fuel, glycine, is chosen for formation of YAG since the amount of heat evolved and kinetics of the reaction are such that the combustion proceeds smoothly without bursting or spilling out of the product, a desirable aspect from the point of view of scaling up. The oxide formed is weakly agglomerated and needs to be ground into a fine powder before forming into shape. Formation of amorphous precursors for yttria-alumina compound phases by the nitrate-glycine reaction (with lean amount of fuel) and evolution of crystalline phases upon heat treatment has been studied by XRD [3]. However a study of the thermal evolution behavior by TG-DTA of the precursors formed by combustion to obtain temperature regimes of weight loss and heat effects (evolution/absorption) before and during crystallization of YAG is essential in obtaining conditions for formation of chemically pure YAG (Y_3Al_5O_(12) oxide compound). A study of the grinding behavior of the agglomerated mass formed is important from the point of view of its dispersion behavior, as the presence of coarse agglomerates reduces singterability and homogeneity of microstructure of the product formed. As no study on these aspects has been reported yet for the precursors formed by the nitrates-glycine reaction (with stoichiometric amount of fuel), a detailed investigation of the same has been carried out.