Slag Resistance Of Precursor-derived Ceramic Coatings:Mechanism And Performance

Targeted at the problem of slagging on the heating surface of coal-fired boiler generally,polysilazane was used as precursor,and ceramic coating was prepared on TP347 substrate by dip-coating method.In this paper,three different ceramic coatings were prepared by adding inert fillers such as hexagonal boron nitride（h-BN）,zirconia（ZrO₂）and alumina（Al₂O₃）on the basis of previous research on precursor-derived ceramic coatings.The experimental research and numerical simulation of the spreading and solidification characteristics of molten ash on the surface of the coating were carried out to explore the anti-slagging mechanism and performance of the coating.The main conclusions obtained in this paper are as follows:Experiments of adhesion characteristic shows that the contact angle of the molten ash on coatings is larger than steel sheet at the same temperature range from680°C to 860°C,which indicates that the wettability of fused ash on the surface of coatings is poor,wherein the h-BN coating exhibits the best lyophobic property,and the h-BN coating has excellent anti-slagging performance;The experiential power formula is used to analyze the wetting mechanism of molten ash between 760°C and860°C.The results show that the kinetic mechanism of molten ash on the steel sheet and h-BN coating is a mixed control model of reaction,dissolution and diffusion.The results of microscopic morphology and energy spectrum analysis show that h-BN coating can effectively prevent the penetration of molten ash and has good anti-slagging effect.Experiments of spreading solidification process shows that the contact angle of the molten ash on coating is larger than steel sheet,and the spreading coefficient is smaller than steel sheet.Moreover,on the surface of coating,the spreading equilibrium time is shorter,indicating that the coating weakens the wetting ability of the molten ash.Among the three coatings,the wettability of h-BN coating is worst,indicating that the addition of h-BN to the coating is better than the other two fillers.Comparing the results of the static adhesion characteristics experiments,it is known that the wettability time of the molten ash is significantly prolonged after the coating is applied on the surface of the sample.When the molten ash is spread and solidified on the surface of the coating,the spreading area is smaller than that of the steel sheet,so that the coated sample has better anti-slagging performance.In the numerical simulation,the simulated values of the contact angle and the spreading coefficient are in good agreement with the experimental values.After the droplets stop spreading,the simulated values of the contact angle of the steel sheet and the h-BN coating are different from the experimental values by 1.7°and 1°,respectively,and the simulated values of the spreading coefficient are different from the experimental values by 1.84%and 1.82%,respectively.It can be seen from the temperature field that at 7ms,solidification has almost been completed at the droplet/substrate interface,and the droplets are no longer spread.After 13s,the droplets completely solidified.