Papers by Keyword: Rare Earth Silicate

Abstract: Silicon-based ceramics are among the main candidates for high temperature structural components in aeronautic applications. One key drawback of silicon-based ceramics for these applications is the volatilization of the protective silica scale, in moisture and the resulting ceramic recession. Therefore, the further use of these ceramics components depends on the development of external protection against water vapour attack. Some of the most promising materials seem to be rare earth silicates. Based on much richer data in the bibliography, the purpose of this work is to investigate the influence of two yttrium silicates elaboration processes on both the capability to crystallize and the corrosion resistance in an oxidative moist atmosphere at high temperature. Taking into account the material’s morphology, composition and degree of crystallization, the composition (Y2SiO5 or Y2Si2O7) and the preferable synthesis process are discussed.

Abstract: Corrosion experiments on a number of rare earth di-silicates containing Y, Yb and Lu have been conducted in flowing air with 30 vol.% H2O at 1500°C. Nominally the corrosion rate is slower by a factor 5 to 10 compared to silica. However, alumina impurity incorporation has a profound influence on the process of corrosion as it masks not only the gravimetric results but also changes the surface phase assemblages to contain rare earth garnets and liquid phases. It is presumed that silica loss occurs under those conditions via the liquid phase and does not necessarily follow the same kinetics as direct silicate corrosion. Furthermore, atmospheric silicon hydroxide saturation effects contribute to the corrosion process. Currently all determined corrosion rates of rare earth silicates are viewed as system specific only.