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.