| In recent years,in the combustion process of boilers that burn high sodium coal(Xinjiang Zhundong),it is easy to cause serious high-temperature corrosion and fouling and slagging on the heating surface of the pipes,heat exchangers and water walls of coal-fired boilers.This resulted in the failure and destruction of boiler components,which seriously affected the safe operation of coal-fired boilers.In order to solve the high temperature corrosion problem of boilers,high temperature resistant organic silicon coatings had been developed and studied,which have important practical value.The main results obtained in the thesis are as follows:(1)In this thesis,benzyl silicone resin as the film material,xylene as the solvent,BN,SiC,ZrO2,Al2O3 and low-melting glass powder as fillers,and add a small amount of graphite and film-forming additives,using slurry spraying method to prepare high temperature resistant silicone coating.The effects of factors such as the ratio of resin to filler and different filler ratios and curing temperature on the heat resistance of high temperature resistant silicone coatings were studied by orthogonal experiments.The best optimized coating formulation was obtained as follows:the mass ratio of filler:resin:solvent was 1:1:1.3,the filler ratio was BN:SiC:ZrO2:Al2O3:glass powder=3:4:3:1:2;and curing conditions of 300?/2 h.(2)The coating was prepared under the best optimized process conditions.After curing at high temperature,the thickness is 87.60 ±10 ?m;the adhesion level is 0.After heat treatment at 400? and 500?,the coating surface is relatively dense and uniform,and it is well bonded to the substrate.At the same time,the addition of fillers such as BN,SiC,ZrO2,Al2O3 and glass powder can effectively improve the heat resistance of benzyl silicone resin at 500?.XRD showed that no phase transition and chemical transformation occurred in the filler.FTIR showed that compared with the side chain groups,the main chain of benzyl silicone resin still had part of undecomposed remains after heat treatment at 500?.The thermal shock test showed that after the 400?/100 cycles,the coating surface had no obvious cracks,and the average thermal cycle is about 46 times;according to the test of gradient heating method shows that when cracks or peeling occured,the average thermal cycle is 500?/7 times,when the peeling degree reaches 1/4 to 1/3 of the area,the average thermal cycle is 600?/17 times.After being corroded in sulfate environment at 400? and 500? for 15 days,compared with carbon steel substrate,the high temperature corrosion resistance of the coating was increased by nearly 2.0 and 3.1 times,respectively.After being oxidized in dry air at 400? and 500? for 15 days,compared with the carbon steel substrate,the oxidation resistance of the coating was increased by nearly 12.5 and 5.2 times,respectively.This shows that at 400?and 500?,the best optimized high temperature resistant silicone coating shows good heat resistance,thermal shock resistance,high temperature corrosion resistance and high temperature oxidation resistance.(3)Thermogravimetric analysis showed that the addition of fillers such as BN and SiC with high thermal conductivity increased the thermal conductivity of the coating and greatly reduced the decomposition temperature of the benzyl silicone resin.Low-melting glass powder can replace or repair the loose inorganic silica structure formed by the decomposition of benzyl silicone resin,and adhering the pigments and fillers together to form a new inorganic composite silicon and oxygen structure,that is "secondary film formation",which improved its heat resistance performance. |
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