Particle size effects on yttrium aluminum garnet (YAG) phase formation by solid-state reaction
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Scott Misturec) Department of Materials Science and Engineering, New York State College of Ceramics, Alfred University, Alfred, NY 14802, USA
Gary L. Messingd) Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA (Received 18 April 2014; accepted 21 July 2014)
The solid-state reaction of yttrium aluminum garnet (YAG, Y3Al5O12) during the heat treatment of Y2O3 and Al2O3 powder mixtures, differing in particle size and size ratio, was quantified using in situ high-temperature x-ray analysis and Rietveld refinement. Y2O3 particle size has the most profound effect on YAG formation. When the Y2O3 particle size was decreased from 5000 to 30 nm (on reaction with 270 nm Al2O3), the YAG formation rate increased from 20 to 48 vol% min1 over the temperature range of 1350–1450 °C. In this case, the final YAG content increased from 75 to 91 vol%. A simple model that includes the reactant particle coordination number, and thus particle size ratio, shows that when the size ratio (dA/dY) is .1 diffusion through the alumina powder is rate controlling whereas when the ratio is ,1, diffusion through the yttria, intermediate phases, and YAG is rate controlling. I. INTRODUCTION
YAG (Y3Al5O12) single crystals have been used for more than forty years for solid-state laser media because YAG has a relatively stable lattice and high thermal conductivity.1–3 It has been shown that the optical properties of transparent Nd:YAG ceramics are nearly equivalent to those of single crystals. Transparent YAG ceramics also have potential for transparent armor applications because of their higher hardness, and thus greater abrasion resistance, than most transparent oxide ceramics. Transparent ceramics are produced from either chemically synthesized powders or by solid-state reaction in which the metal oxides, including the fluorescing element oxide (e.g., Nd2O3, Yb2O3), are mixed and formed into a shape. Vacuum sintering of these solid-state mixtures at $1700 °C results in transparent ceramics.1 During the a)
Current address: Chulalongkorn University, Bangkok, Thailand Current address: Saint-Gobain R&D Center, Northboro, MA, USA c) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/jmr-editor-manuscripts/. d) Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/jmr-editor-manuscripts/. DOI: 10.1557/jmr.2014.224 b)
J. Mater. Res., Vol. 29, No. 19, Oct 14, 2014
http://journals.cambridge.org
Downloaded: 21 Oct 2014
reactive sintering approach, Y4Al2O9 (yttrium aluminum monoclinic, YAM), YAlO3 (yttrium aluminum perovskite, YAP), and YAG are formed in situ in the shaped part prior to densification. Incomplete reaction or nonYAG phases
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