Plasma spray-deposited lanthanum phosphate coatings for protection against molten uranium corrosion

Lanthanum phosphate is recommended as an effective barrier against molten uranium and its alloys. LaPO4 has a high melting point, is inert towards reactive metals and has low thermal conductivity, which make it an ideal candidate for corrosion barrier coatings in molten metal environment. Studies on plasma deposition of lanthanum phosphate, its characterization and interaction with molten uranium are reported in this paper. Lanthanum phosphate was synthesized by chemical route and the as-synthesized powder was converted to free flowing powder for plasma spray deposition. Lanthanum phosphate coatings were prepared on stainless steel substrates and the deposits were characterized for phase composition using X-ray diffraction (XRD), Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). Results showed that the coatings retained the monazite structure of LaPO4 precursor powder. Microstructure of the coatings and interface by scanning electron microscope (SEM) revealed good bonding between the phosphate layer and substrate. Porosity of the coatings was observed to decrease with the increase in deposition power from 10 kW to 20 kW. Adhesion strength of the coatings was found to increase with deposition power. Corrosion studies of coated LaPO4 in molten uranium showed that lanthanum phosphate does not chemically react with molten uranium and LaPO4 coating offers adequate resistance to the substrate against corrosion attack by molten uranium. (C) 2015 Elsevier B.V. All rights reserved.