Kinetics and mechanism of hot corrosion of γ-Y2Si2O7 in thin-film Na2SO4 molten salt

gamma-Y(2)Si(2)O(7) is a promising candidate material both for high-temperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9 x 10(-6)/K, 200 degrees-1300 degrees C), and low thermal conductivity (< 3.0 W/m.K above 300 degrees C). The hot corrosion behavior of gamma-Y(2)Si(2)O(7) in thin-film molten Na(2)SO(4) at 850 degrees-1000 degrees C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). gamma-Y(2)Si(2)O(7) exhibited good resistance against Na(2)SO(4) molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na(2)SO(4) and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of gamma-Y(2)Si(2)O(7) in Na(2)SO(4) molten salt with flowing air was evaluated to be 255 kJ/mol.