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

TL;DR

This paper improves the oxidation resistance of MoSi2 by creating a silica-sol coated composite, which could be useful for aerospace applications.

Contribution

A novel silica-sol derived MoSi2@SiO2 composite is developed to enhance low-temperature oxidation resistance.

Findings

Ethanol-mediated dispersion improves coating efficiency and oxidation resistance compared to direct dispersion.

Basic silica sol coating shows the lowest oxidation weight gain due to optimal gelation and surface coverage.

Colloid properties significantly influence the oxidation resistance of MoSi2@SiO2 composites.

Abstract

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.

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