Study On Preparation Technology Of Chemical Reactive Enamel Coating

Due to the effect of marine environment,reinforced concrete structures are confronted with serious corrosion problem.There are researches show that the chemical reactive enamel coated steel bar has excellent corrosion resistance and can be used in marine structures to improve the durability of reinforced concrete.But at present,the coating is still in the laboratory stage,electrostatic spraying technology is only used to spray CRE coating for a short period,the spraying process is still in the exploratory stage.It is of great significance to optimize the preparation technology of CRE coated steel bar through the study of relevant process parameters for subsequent relevant industry standard formulation and industrial production.In view of the purpose above,the preparation technology of CRE coating was optimized from three aspects of electrostatic spraying process,sintering time and auxiliary agent,and the performance changes of the coating were compared through a variety of test methods.The main test methods and conclusions of this paper are as follows:（1）Through comparing the adsorption capacity of CRE powder on steel plate under different spraying process parameters,it can be found out that with the increase of electrostatic voltage,the amount of powder on the substrate first increases and then remains unchanged;with the increase of spraying distance,the amount of powder on the substrate increases first and then decreases.The optimal electrostatic voltage is 70kv and the optimal spraying distance is between 150 mm and 200 mm.Preheating the CRE powder before spraying and reducing its humidity can significantly increase the amount of powder that adsorbed on the substrate.Through the analysis of the particle size of the CRE coating powder attached to the surface of the workpiece under the spraying parameters,it is determined that the ideal particle size of the coating powder should be less than 30.3μm,the adsorption rate of single spraying CRE powder can be improved by increasing the mesh number to 400 mesh.（2）SEM and EDS were used to compare the surface morphology of CRE coating and phase change of interfacial transition zone between the coating and the substrate in different sintering time.Combined SEM result with the impact test by drop hammer method,it was determined that prolonging the sintering holding time was helpful to the melting leveling of the coating and the growth of the interface transition zone,and the adhesion between the coating and the substrate was improved.However,too long sintering time will lead to the change of coating properties and the failure of dense layer.The optimum sintering time for preparing active enamel coating is 30 min.（3）The surface morphology and thermal shock resistance of CRE active glaze coatings with different Si3N4 contents were compared.It was found that with the increase of Si3N4 content,the apparent pores of the coating increased with the thermal shock resistance improved.Cracks appeared in the CRE coating without Si₃N₄ after 19 thermal shock cycles,on the contrary,CRE coating with more than 5%Si₃N₄ has excellent thermal shock resistance and can withstand 100 thermal shock cycles without cracking.（4）Through accelerated corrosion test by electrifying,it was found that the corrosion resistance of CRE coating is similar to that of stainless-steel bar and stainless steel clad rebar,weaker than epoxy coated steel bar and stronger than bare steel.Corrosion mainly occurs in the initial defect area of coating.The corrosion of the defect free position is not obvious.