Study of the core-shell structure MoSi2@ Al2O3 powder prepared by the sol-gel method in a low-vacuum atmosphere

Molybdenum disilicide (MoSi2) is a novel crack-healing material used in the traditional thermal barrier coating, which reacts with ZrO2 to attain a corresponding volume expansion of approximately 138%. However, the pre-oxidation of MoSi2 causes the "pesting" phenomenon, which degrades the microstructure and mechanical properties throughout the service. To address this issue, the aluminum oxide was fabricated on the MoSi2 surface using the sol-gel method and low-pressure post-heat treatment to prevent oxygen penetration. The orthogonal experiment investigated the effect of pH, temperature, and water amount on sol generation. Because the Zeta potential difference has reached its maximum value (about 27 mV) at pH 4, the aluminum sol was notably adsorbed on the MoSi2 particles. The modified MoSi2@Al2O3 particles were characterized to understand their morphologies, surface adsorption energy, and crystal structures. The oxygen adsorption energy on the MoSi2 (103) surface was lower than that on the Mo5Si3 (411) surface, which indicated that the oxidization process can be divided into two independent steps. The Al2O3 shell was uniformly formed on the MoSi2 particles, especially in the low-vacuum environment (10 MPa) for 3 h post-treatment. The dense core-shell structure can prevent oxygen penetration into the MoSi2 surface, thus prolonging the self-healing property of MoSi2.