YAG (YAlO) as a Scavenger for Si and Ca
Kuru, Yener (2004) YAG (YAlO) as a Scavenger for Si and Ca. [Thesis]
General garnet structure (Ia3-d) is a forgiving host and can accommodate cations of varying sizes and valence states. Yttrium aluminate garnet (YAG, YAlO) forms with the substitution of yttrium for manganese in the original garnet mineral spessartite (MnAl(SiO)), if aluminum simultaneously substitute for silicon such that the charge neutrality is maintained. Studies on highly yttrium doped alumina ceramics with Si and Ca contamination indicated that YAG precipitates in the ceramic had a propensity to allow simultaneous incorporation of small amounts of Si and Ca impurities in their structure. In this study, using chemical synthesis techniques it was shown that YAG can accommodate up to approximately 10 cation % Si and Ca (i.e. Si/Y and Ca/Y) amount in YAG if they are incorporated together. Equilibrium conditions are established by calcining samples at 900ʻC for 2 hours and cooling the samples to room temperature in the furnace. Disappearing-phase method and EDS analysis were used to determine solubility and co-solubility limits. Beyond the solubility limit phase separation occured and three crystalline yttrium aluminate phases (YAG, YAP (yttrium aluminate perovskite, YAlO), YAM (yttrium aluminate monoclinic, YAlO)) were observed. It is believed that the excess Si and Ca above co-solubility limit precipitate out in the form of an x-ray amorphous anorthite like glass in the system.
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