Synthesis and characterization of lanthanum phosphate sol for fibre coating

Various routes to synthesize lanthanum phosphate sets (LaPO4) were explored. Prepared lanthanum phosphate sols were characterized using differential thermal analysis/ thermogravimetric analysis (DTA/TGA) and powder X-ray diffraction (XRD) after heat treatments. Appreciable crystallization of lanthanum phosphate was observed above 400 degrees C and the average crystallite sizes were calculated to be 15 nm and 46 nm after heat treatment at 700 and 1100 degrees C, respectively. Sapphire fibres were dip coated in LaPO4 sol, and subsequently heated to 1100 degrees C. The thickness of the coating ranged from 60 to 150 nm depends upon the sol concentration and the number of times of dip coatings. XRD of coated fibres revealed the formation of LaPO4 after heat treatment above 700 degrees C.