Effect of Silica Sol on the Preparation and Oxidation Resistance of MoSi2@SiO2

The limited oxidation resistance of MoSi2 between 400 °C and 600 °C restricts its aerospace applications. This study develops a silica-sol derived core-shell MoSi2@SiO2 composite to enhance the low-temperature oxidation resistance of MoSi2. Acidic, neutral, and basic silica sols were systematically applied to coat MoSi2 powders through sol-adsorption encapsulation. Two pathways were used, one was ethanol-mediated dispersion, and the other was direct dispersion of MoSi2 particles in silica sol. Analysis demonstrated that ethanol-mediated dispersion significantly influenced the coating efficiency and oxidation resistance, exhibited significantly decreased coating weight gains (maximum 27%) and increased oxidation weight gains (10–20%) between 340 °C and 600 °C compared with direct dispersion of MoSi2 particles with silica sol, ascribe to the kinetic inhibition of hydroxyl group condensation and steric hindrance of MoSi2-silica sol interface interactions of ethanol. Systematic investigation of silica sol encapsulation of MoSi2 revealed critical correlations between colloid properties and oxidation resistance of MoSi2@SiO2. Basic silica sol coated MoSi2 (BS-MoSi2) exhibits the lowest coating efficiency (coating weight gain of 7.74 ± 0.06%) as well as lowest oxidation weight gain (18.45%) between 340 °C and 600 °C compared with those of acid and neutral silica sol coated MoSi2 (AS-MoSi2 and NS-MoSi2), arises from optimal gelation kinetics, enhanced surface coverage via reduced agglomeration, and suppressed premature nucleation through controlled charge interactions under alkaline conditions.