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Influence of Yb:Hf Ratio on Ytterbium Hafnate/Molten Silicate ( CMAS ) Reactivity
Author(s) -
Poerschke David L.,
Seward Gareth G. E.,
Levi Carlos G.
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.13964
Subject(s) - silicate , crystallization , mineralogy , aluminosilicate , ytterbium , materials science , chemistry , doping , biochemistry , organic chemistry , catalysis , optoelectronics
This study investigated the influence of YbO 1.5 concentration on the reactivity between YbO 1.5 –HfO 2 thermal barrier coating ( TBC ) materials and silicate melts [calcium–magnesium aluminosilicate ( CMAS ), specifically 33CaO–9MgO–13AlO 1.5 –45SiO 2 , all in mol%]. Three thermal barrier oxides ( TBO ) with YbO 1.5 concentration between 30 and 80 mol% were tested at 1300°C and 1500°C. Porous pellets were used to study reaction layer growth and the behavior within infiltrated porosity. Complementary experiments examined the phase equilibria in melts containing varying quantities of the candidate TBO s. The effectiveness of reactive crystallization to limit interaction depth increased with the YbO 1.5 concentration in the TBO . The results indicate that the TBO must contain sufficient YbO 1.5 to satisfy the equilibrium between the melt and HfO 2 ‐based fluorite phase before YbO 1.5 ‐bearing silicates can precipitate. Increasing the YbO 1.5 availability leads to the crystallization of apatite, garnet, silicocarnotite, and/or cuspidine (alumino)silicates. Apatite was observed at 1300°C and 1500°C, garnet and silicocarnotite only appeared at 1300°C, and cuspidine was only evident at 1500°C. The implications for the design of CMAS ‐resistant coatings are discussed in the context of the experimental results.