Effect of LiYO 2 on the synthesis and pressureless sintering of Y 2 SiO 5
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nchun Zhoua) and Meishuan Li Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China (Received 16 March 2007; accepted 9 October 2007)
Y2SiO5 has potential applications as a high-temperature structural ceramic and environmental/thermal barrier coating. In this work, we synthesized single-phase Y2SiO5 powders utilizing a solid–liquid reaction method with LiYO2 as an additive. The reaction path of the Y2O3/SiO2/LiYO2 mixture with variation in temperatures and the role of the LiYO2 additive on preparation process were investigated in detail. The powders obtained by this method have good sinterability. Through a pressureless sintering process, almost fully dense Y2SiO5 bulk material was achieved with a very high density of 99.7% theoretical.
I. INTRODUCTION
Yttrium silicate (Y2SiO5) is an important laser crystal that has been synthesized since 1963.1 Most research activities are related to rare-earth (Ce3+, Eu3+, etc.)doped Y2SiO5 crystals to be used as blue phosphor or Cr4+-doped Y2SiO5 as a saturable absorber Q-switch laser.2–4 Although spectroscopic studies of doped Y2SiO5 have been widely performed, the fundamental properties of the host crystal itself are still lacking. Y2SiO5 is also recognized as a precipitated phase at the grain boundaries of sintered Si3N4 with Y2O3 or Y2O3+SiO2 sintering aids, and it is an important phase in the SiO2–Y2O3–Si3N4 phase diagram.5,6 The melting point of Y2SiO5 is 1950 °C, which renders it a potential high-temperature structural material.7 Y2SiO5 has good chemical stability, and its thermal expansion coefficient (8.36 × 10−6/K for polycrystalline sample) matches well with that of most non-oxide ceramics. For instance, a high-performance SiC/Y2SiO5 multilayer coating with good erosion resistance and low residual stress at the interface was developed recently.8 Moreover, the low evaporation rate of Y2SiO5 along with its low oxygen permeability constant at temperatures up to 1900 °C endows this material with excellent oxidation resistance.9 Y2SiO5 coatings can efficiently improve the hightemperature performance of silicon-based ceramics.9,10 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0085 732 J. Mater. Res., Vol. 23, No. 3, Mar 2008 http://journals.cambridge.org Downloaded: 11 Mar 2015
Unfortunately, preparation of single-phase Y2SiO5 is very difficult because a strict stoichiometric ratio of the starting Y2O3/SiO2 is needed.7 At present, the sol-gel process and powder-mixing route have been used for the synthesis of Y2SiO5 powders.10–12 In the sol-gel method, precursors of Y(NO3)3 and TEOS (tetraethyl orthosilicate) are put in ethanol to form a Y2O3/SiO2 gel, and then Y2SiO5 powders can be synthesized by calcining the gel above 900 °C. Because the stoichiometric ratio of the two precursors can be accurately controlled, pure Y2SiO5 can be obtained via this method. However, this method is not suitable for volume production. In addition,
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