Corrosion products evolution and hot corrosion mechanisms of REPO4 (RE = Gd, Nd, La) in the presence of V2O5 + Na2SO4 molten salt

摘要

REPO4 (RE = Gd, Nd, La) ceramics with a monazite structure were fabricated by a chemical co-precipitation and calcination method. Hot corrosion tests were carried out in V2O5 + Na2SO4 molten salt at 800 degrees C, 900 degrees C and 1000 degrees C for 2 h and 10 h. The temperature and heat duration had little effect on the type of corrosion products in this study. However, GdPO4 and REPO4 (RE = Nd, La) revealed different hot corrosion behavior. Exposed to the molten salt, GdVO4 and Gd-4 (P2O7)(3) formed as the corrosion products for the GdPO4 case, while an RE(P,V)O-4 (RE = Nd, La) solid solution was generated for NdPO4 and LaPO4 cases. The formation of the solid solution had less damage to the original microstructure, which benefited the hot corrosion resistance of the ceramics. From the crystallographic characteristics of rare earth phosphates/vanadates and a thermodynamics perspective, the hot corrosion mechanisms of REPO4 (RE = Gd, Nd, La) are discussed.