Preparation Of Modified Phosphate Ceramic Coating And Its Application In High Temperature Boiler

Phosphate ceramic coating with excellent properties such as high temperature resistance,corrosion resistance,wear resistance,abrasion resistance and bond strength,has been widely used in high temperature industry.In view of the problem of corrosion of coal-fired boiler pipelines,in this paper,a slurry corrosion-resistant ceramic coating was selected as our research focus in which H₃PO₄,Al?OH?₃,MgO and ZnO were used as raw materials.The modified binders of aluminum magnesium phosphate,zinc aluminum phosphate and aluminum magnesium zinc phosphate were prepared by liquid-phase method.The effects of different metal atomic ratios in modified phosphate binders on the pH,curing temperature,micromorphology,crystal stability and thermal stability of the binders were investigated.A modified phosphate ceramic coating was prepared by mixing aluminum magnesium phosphate,zinc aluminum phosphate and aluminum magnesium zinc phosphate,respectively,with a certain amount of filler.The influence of different metal atoms in the adhesive on corrosion resistance,heat resistance,and thermal shock resistance of the coating was investigated.The binders of the three systems of aluminum magnesium phosphate,aluminum zinc phosphate,and aluminum magnesium zinc phosphate prepared in this paper are all acidic,with a pH between 0.7 and 1.2,and the pH is higher than that of aluminum dihydrogen phosphate.The three system phosphate binders all have the same curing characteristics.Before 300°C,the initial cure of the binder is complete and nearly 80wt%of the moisture has been removed.The stability of crystals of aluminum magnesium phosphate binder during sintering is obviously better than that of aluminum dihydrogen phosphate and magnesium dihydrogen phosphate,and the formed crystal grains are smaller.The aluminum zinc phosphate binder was amorphous overall after sintering,but there was also a small amount of Zn?PO₃?₂,Zn₃?PO₄?₂ and b-Al?PO₃?₃ crystals formed at high temperature.The addition of Mg and Zn atoms simultaneously in the aluminum phosphate binder increased the chaos of the system,and the binder crystals had good high temperature stability,and no crystal transformation during high temperature sintering.The main formation was Mg?PO₃?₂ and Zn₂?PO₃?₄ crystals.SEM shows that in the magnesium aluminum phosphate binder,with the increase of Mg atoms,the binder forms more crystals on the surface after sintering,and cracks and other defects are reduced.When the Mg atom content exceeds the critical value,the defects of the binder increase,and the surface morphology of the A1M2 binder is best.In the zinc aluminum phosphate binder,as the number of Zn atoms increases,more scaly crystalline material forms on the surface of the binder after sintering,and when Al/Zn=1:1 and Al/Zn=1:2,phosphoric acid Aluminum zinc binder is the most continuous and compact.The size of the scaly substance is not only related to the storage time of the binder,but also related to the Al/Zn ratio in the binder.The growth rate is slow at first,rapid at the end and tends to no longer increase at the end.The aluminum magnesium magnesium zinc phosphate binder has a continuous and dense surface with a small amount of visible crystals formed,and the adhesive has fewer defects,and the coating performance should be better.The test coating is resistant to acid liquid medium corrosion,high temperature molten salt corrosion and electrochemical corrosion.The results all indicate that the addition of Mg and Zn atoms can increase the corrosion resistance of the aluminum phosphate binder and the corrosion resistance of aluminum magnesium phosphate higher than the others,indicating that the degree of chaos in the high-entropy coating increases,and the corrosion resistance of the coating also increases.Test coating resistance to 700°C performance and thermal shock resistance,the results show that the addition of Mg,Zn atoms,can improve the aluminum phosphate binder heat resistance and thermal shock resistance.The wear resistance of the tested coatings was tested.The results showed that the wear resistance of the aluminum phosphate coating was improved by Mg atoms,but the friction and wear resistance of aluminum phosphate to aluminum phosphate was not improved.