SYNTHESIS OF LANTHANUM PYROCHLORE–LANTHANUM PHOSPHATE COMPOSITE POWDERS FOR THERMAL BARRIER COATING APPLICATIONS

Abstract

Thermal barrier coatings (TBCs) play a critical role in protecting metallic substrates from high-temperature degradation in aerospace and industrial applications. This study was undertaken to synthesize and evaluate a novel lanthanum phosphate zirconate (LaPZ) composite as a potential candidate for TBCs. The LaPZ composite was synthesized by a high-energy ball milling method followed by calcination, which allows precise control over the composition and microstructure. The synthesized LaPZ composite was characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal analysis. Lanthanum phosphate was prepared by precipitation method: calcined at 700 °C and further calcined at 1,200 °C for 2 h. LP-C was used for the preparation of composite powders. It was ball milled at 350 rpm for 8 h, wet milled with distilled water in a high energy planetary mill with zirconia media, and calcined at 1,300 °C for 4 h. X-ray diffraction analysis at 1,300 °C revealed LaPZ composite powders with a cubic pyrochlore structure of La₂Zr₂O₇ and monoclinic LaPO₄. To obtain the pyrochlore structure, LaP and zirconia were taken in two different molar ratios, namely 1 : 1 (LaPZ 1) and 1 : 2 (LaPZ 2). The coefficient of thermal expansion (CTE) of the LaPZ 1 coating was approximately 8.97 × 10^–6 K^–1. The LAPZ 2 coating exhibited a CTE of 9.15 × 10^–6 K^–1 when exposed to temperatures ranging from 0 to 1,400 °C. Samples maintained stable thermal expansion up to 1,400 °C, indicating the suitability of LaPZ for TBC applications.