Characterization of yttrium aluminate garnet precursors synthesized via precipitation using ammonium bicarbonate as the
- PDF / 1,004,820 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 230 Views
Stoichiometric yttrium aluminate garnet (Y3Al5O12) precursors with a wide range of chemical compositions were precipitated by dripping a mixed solution of ammonium aluminum sulfate and yttrium nitrate into ammonium bicarbonate solutions. The resultant precursors were characterized by chemical analysis, infrared spectroscopy, differential thermal analysis/thermogravimetry, x-ray diffractometry, and scanning electron microscopy. The effects of reaction temperature, precipitant concentration, dripping speed of the salt solution, and the molar ratio of precipitant/total-cations on the composition, thermal behavior, and particle morphology of the resultant precursors were investigated. The precipitation conditions that yield carbonate precursors composed of ammonium dawsonite [NH4Al(OH)2CO3] and yttrium normal carbonate [Y2(CO3)3 ⭈ 3H2O] were determined.
I. INTRODUCTION
Ceramics based on the Al2O3–Y2O3 system are promising materials for optical, electronic, and structural applications. The composition Y3Al5O12, commonly called yttrium aluminate garnet (YAG), adopts the cubic garnet structure and when doped with a transition or lanthanide element it is an important solid-state laser material widely used in luminescence systems and as window material.1– 4 In view of its high-temperature chemical stability (melting point at approximately 1970 °C) and exceptionally high creep resistance,5–7 YAG is also a promising structural material for high-temperature engineering. Considering such wide and diverse application potential of the YAG materials, it is highly desirable to develop new routes for the synthesis of high-purity, phase pure, and reactive YAG powders. Traditionally, YAG powders are produced by a solidstate reaction between the individual component oxide powders, which usually requires repeated mechanical mixing and lengthy heat treatment at high temperatures (>1600 °C) to eliminate yttrium aluminate monoclinic (YAM, Y4Al2O9) and yttrium aluminate perovskite (YAP, YAlO3) intermediate phases from the final product.8–11 The contamination during repeated mixing and the crystallite growth at high temperatures make it difficult to control powder properties.
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 11, Nov 2000
http://journals.cambridge.org
Downloaded: 22 Oct 2014
It is widely acknowledged that the wet-chemical processing of multication materials provides advantages of good mixing of the starting materials and excellent chemical homogeneity of the final products. Several kinds of wet-chemical processes or wet-chemicalassisted processes have been developed and successfully used in recent years for YAG synthesis, which include hydroxide coprecipitation,12–17 urea-based homogeneous precipitation,18–20 sol-gel processing,21–24 hydrothermal or glycothermal treatment,25,26 pyrolysis of metal nitrate or sulfate mixtures,27–29 combustion synthesis,30,31 and a modified Pechini process.33 These methods proved effective in lowering YAG formation temperature and in impro
Data Loading...
