Plasma Spray Deposition of Lanthanum Phosphate and Phase Structure of the Resultant Coatings

Plasma-sprayed lanthanum phosphate coatings were prepared on stainless steel substrates at different input powers from 16 to 24 kW. Coatings were characterized by x-ray diffraction, scanning electron microscopy, and Fourier transformed infrared spectroscopy. Results showed that the as-sprayed coatings consist of lanthanum ortho (LaPO 4 ), poly(La 2 P 4 O 13 ), and oxy(La 3 PO 7 ) phosphates. Subsequent heat treatment of the coatings resulted in the recombination of the La-polyphosphate and La-oxyphosphate to form LaPO 4 . SEM images of microstructure of the coatings and coating-substrate interface showed micro-cracks, voids, and porosity that were found to decrease with deposition power.