Synthesis of sinteractive single-phase microstructure yttrium disilicate precursor powder using hydrothermal processing
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Synthesis of sinteractive single-phase microstructure yttrium disilicate precursor powder using hydrothermal processing P. A. Trustya) IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston, Birmingham B15 2T T, United Kingdom
K. C. Chan School of Metallurgy & Materials, The University of Birmingham, Edgbaston, Birmingham B15 2T T, United Kingdom
C. B. Ponton School of Metallurgy & Materials and IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston, Birmingham B15 2T T, United Kingdom (Received 3 January 1997; accepted 20 October 1997)
This paper is the first report of the synthesis of a sinteractive single-phase microstructure yttrium disilicate precursor powder using hydrothermal processing. The effect of the pH of the precursor chemicals on the ease of formation of a single-phase material was investigated using x-ray diffraction, TEM, and SEM. Under very acidic conditions (pH 1), the formation of yttrium chloride, in addition to the yttrium disilicate precursors, produced a powder that absorbed moisture, did not sinter well, and produced a two-phase interpenetrating microstructure after sintering. At pH 6, yttrium chloride no longer formed, but the interpenetrating network persisted after sintering. Only under basic conditions (pH 10) did single-phase yttrium disilicate form after sintering. This work is noteworthy because the calcination time of 1 h required for the formation of this ceramic at 1050 ±C is over an order of magnitude lower than the calcination times of over 100 h required when calcined in the temperature range 900 ±C to 1150 ±C, as reported previously by other workers.
I. INTRODUCTION
The synthesis of rare earth oxides, in particular oxides containing yttrium, has been of great interest since the early 1960s.1–6 Yttrium disilicate (Y2 Si2 O7 ) is a solid-solution ceramic which occurs naturally as yttrialite and is the basis of complex rare-earth silicates. It has been investigated for use as a cathode ray-tube phosphor when it acts as the host for cerium (Ce31 ) emitting ions.7 It has potential also for use as a material for high performance structural applications owing to the fact that it is one of the most refractory silicates with a melting point of 1775 ±C.8 Indeed, studies of silicon nitride using yttria as a sintering aid have highlighted the formation of a glassy yttrium disilicate phase at the grain boundaries. It has been shown that this amorphous material, upon crystallization, exhibits improved high temperature properties.9–12 The ultimate aim of this work is to use Y2 Si2 O7 as the matrix material in a woven fiber reinforced ceramic matrix composite (CMC). The fabrication of such CMC’s requires the woven fiber preform to be infiltrated initially with the Y2 Si2 O7 matrix material. One filtration technique that can be used is a)
Currently at Unilever Research, Colworth House, Sharnbrook, Bedford MK44 ILQ, United Kingdom. J. Mater. Res., Vol. 13, No. 11, Nov 199
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