Hot corrosion Of gamma-Y2Si2O7 in strongly basic Na2CO3 molten salt environment

gamma-Y2Si2O7 is a promising candidate both for high temperature structural applications and as thermal barrier coatings due to its unique combination of properties, such as high melting point, good machinability, high thermal stability, low linear thermal expansion coefficient (3.9 x 10(-6) K-1, 25-1400 degrees C) and low thermal conductivity (< 3 W/m K above 300 degrees C). In this work, the hot corrosion behavior of gamma-Y2Si2O7 in strongly basic Na2CO3 molten salt at 850-1000 degrees C for 20 h in flowing air was investigated. In the employed conditions, multi-layer corrosion scales with total thickness less than 90 mu m were formed. At 850-900 degrees C, the outmost layer of the scale was composed of the reprecipitation Of Y2O3, the bottom of a Si-rich Na2O center dot xSiO(2) (x > 3.65) melt layer, and the middle of a NaYSiO4 layer. At 1000 degrees C, the corrosion products turned out to be a mixture of NaY9Si6O26 and Si-rich Na2O center dot xSiO(2) (x > 3.65). In all cases, a thin layer of protective SiO2 formed under the Na2O center dot XSiO2 melt and protected the bulk material from further corrosion. (c) 2007 Elsevier Ltd. All rights reserved.