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Design of a phosphate-borate-boron nitride composite coating for graphite working at 800 °C in oxidative atmospheres
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DOI：10.1016/j.mseb.2026.119433.png)
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Abstract
En 中文
Graphite is highly susceptible to rapid oxidation at elevated temperatures in air, and this has severely restricted its industrial applications. To address this issue, a novel composite coating system composed of phosphate, borate, and boron nitride was developed in this study. The coating was synthesized through a two-step process, which has been optimized aiming at high-temperature oxidation-resistance. The optimal coating effectively sealed open pores of the graphite, reducing the average pore size from similar to 1000 nm to similar to 10 nm. The coated graphite exhibited exceptional oxidation-resistance with a mass loss of only 0.91% after 100 h of isothermal oxidation at 800 degrees C in static air. Furthermore, it showed outstanding thermal shock resistance, sustaining 32 cycles (320 h in total) of thermal cycling with a total mass loss below 8%. This protection mechanism is attributed to the formation of a structure combining a dense outer layer and an internal permeable layer through the infiltration-coating process, as well as the reaction between B2O3, generated from the oxidation of h-BN at high temperatures, and phosphates to form a low-viscosity borophosphate glass phase that continuously fills surface microcracks. Through the synergistic effects of physical barrier and chemical self-healing, this composite coating overcomes the volatility limitation of traditional phosphate coatings, offering a practical and industrially scalable strategy for improving the oxidation resistance of graphite in high-temperature environments.
Keywords:
Graphite
Protective coating
Phosphate-borate-boron nitride
Oxidation resistance
Thermal shock resistance
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