Preparation And Properties Of High Corrosion Resistant Enamel Composite Coatings

Stainless steel pipeline,which is widely used in industrial and domestic piping systems,requires good molded performance,enameled properties,and resistance to acid and alkali corrosion.The inner wall of the pipeline is the main part that comes into contact with the fluid.The performance of the pipeline inner surface determines the quality of the pipeline.The environment used by industrial pipelines is often characterized by strong acids and alkalis corrosive environment,using in this environment is more likely to cause corrosion of the pipeline and lead to some problems like whether the pipeline's safety can be ensured.Therefore,aiming at the above issues,this article adjusts the parameters of the enamel coating by investigating the preparation technology of the composite enamel coating.Excellent enamel coatings were prepared on the surface of 304 and 321 stainless steel substrates and the enamel coating on different substrates'properties were evaluated.Combining with the microstructure of the steel and porcelain interface microscopic to characterize its characteristics.In addition,an anodized film was prepared on the surface of 321 stainless steel by anodizing the stainless steel surface to improve the enamel coating properties,such as enameled performance,thermal shock resistance performance,and corrosion resistance performance of the stainless steel.Finally,through coating the internal and external surfaces of 321 stainless steel bent pipes with different bent angle,we analyzed its mechanical properties before sintering and after sintering at 900?.It was combined with the flowability of the enamel fluidity and the microscopic interface combined morphology,the inner surface coating's effect of the elbow was evaluated.Two enamel powder with different chemical compositions are used:enamel powder-1and enamel powder-2.The main chemical composition of enamel powder is SiO₂-based oxides.After 900?reaction,the phase of the individual oxides in the enamel powder transformed into a network framework crystalline silicate;Observed from the macroscopic surface morphology after being enameled on 321 stainless steel between 800?and1000?,enamel powder-2 is significantly superior to enamel powder-1 enamel coatings prepared on 304 and 321 stainless steel surfaces.By comparing the enameled temperature of preparing the enamel coating,900?is the best enameled temperature.Based on the above experimental parameters,the best quality enamel surface coating can be prepared on the surface of 321 stainless steel using enamel powder-2 with a water content of 30wt%at sintering tenperture of 900?.Ranging from 800?to 850?,there is no characteristic interfacial bonding phenomenon at the steel-ceramic joint interface,within the temperature range of 875?-1000?,increasing by temperature,the steel-ceramic interface is combined under the thermal convection effect of Magnegny.The transition area gradually widens,the anchor joint area gradually expands and the number of joints increases,the enamel layer extends to the steel matrix,and the joint interface presents a tooth-shaped anchor structure.The chemical composition between the steel and the enamel layer:Si,Fe,Cr,etc.will have a mutual diffusion effect,indicating that the steel layer and enamel layer will tend to be in a more encrypted state,and the enamel layer can also be more stable attached to the surface of stainless steel.The thermal expansion coefficient curves of 304 and 321 stainless steel and the parameters of the enamel layer also tend to be consistent,which verifies that the enamel layer can be stably attached to the substrate surface.The electrochemical resistance and polarization curves of the enameled 321 stainless steel sample prepared by using the above optimal parameters were measured in 5 wt%HCl and 5 wt%NaOH solution.By comparing the parameters such as impedance value and self-corrosion current density,The results showed that the enameled stainless steel has excellent acid and alkali corrosion resistance,which proves that the application of enameling on the surface of the steel is conducive to improving the corrosion resistance of the stainless steel.On the surface of 321 stainless steel,an anodized film is pre-prepared.The macroscopic surface morphology of the anodized film is a relatively well-distributed and dense film layer.The microscopic morphology exists in the form of a cell and the main chemical composition is O,Cr,Fe,Ni,Mn-based.The prepared anodic oxide film is about2?m thick and uniform in thickness.After sintering at 900?,more anchor-bonded areas appear at the steel-ceramic interface,and some of the dendritic structures appear among the anodized film and it extended in the direction of the stainless steel layer.The compositional transition in this transitional region is also dominated by O,Fe,Si,and Cr elements.From the thermal shock resistance test,it can be observed that the anodized pretreated stainless steel has a good thermal shock resistance performance;Electrochemical tests in 5wt%HCl and NaOH solutions showed that the anodized samples had strongerr resistance to acid and alkali corrosion than other samples.The above results indicated that the stainless steel anodizing pretreatment can promote the stability and corrosion resistance performance of the enamel coating on the surface of stainless steel.The application of the enameled 321 stainless steel pipelines with different specifications were studied.The results showed that the fluidity of enamel glaze slurry with a viscosity value of 0.3555 Pa·s has a good enameling ability on the inner wall of the pipeline,the mechanical properties of 321 stainless before and after sintering on 900?were evaluated.The tensile strength and yield strength of the 321 stainless steel was decreased after 900?heat treatment,but its plasticity was improved.Normalizing treatment will reduce the internal stress of the stainless to enhance its corrosion resistance,and its microscopic interface combined morphology is still the main characteristics of the transition layer and the anchor node.These studies can serve as a reference for industrial enamel pipes.