Effect of filler on adhesion characteristics of precursor ceramic coating against high-temperature molten ash

In view of the widespread high-temperature molten ash adhesion problem of heat exchanger surface in the chemical, power, metallurgy and other industries, precursor ceramic coating is proposed to reduce ash adhesion strength. Three ceramic coatings were obtained by adding hexagonal boron nitride (h-BN), zirconia (ZrO2) and aluminium oxide (Al2O3) inert fillers on TP347 steel sheets through the Czochralski method and high-temperature sintering. Results of the static contact angle test show that at 860°C, the contact angles of the molten ash on the coating surfaces of h-BN, ZrO₂ and Al₂O₃ are 58°, 54° and 53°, respectively, which are greater than that (39°) of the steel sheet sample. The spreading radiuses of the three coatings are significantly less than that of the bare sample, indicating a strong anti-adhesion performance, in which the h-BN coating is the best. Spreading dynamic analysis of the bare and h-BN coating samples reveals that the spreading dynamics of both sample surfaces is driven by a combination of reaction, dissolution and diffusion. The inert filler in the coating makes the reaction and dissolution of molten ash on the coating surface weaker than those of the steel sheet. The micromorphology of the melt ash-sample sheet cross-section shows that the melt ash binds closely to the steel sheet sample oxide layer, whereas the boundary with the coating is clear and obvious. This result indicates that the coating can effectively weaken the wetting and permeability of the molten ash. The research results provide new ideas for precursor ceramic coating to solve the high-temperature melting ash adhesion problem of the heat exchanger surface.