Qingdong Zhong

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd(2)O(3) in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn(3)(PO(4))(2).4H(2)O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd(2)O(3) reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.

EFFECT OF GLASS POWDER ON ACID RESISTANCE OF ENAMEL COATING

Enamel glaze was added with glass powders of different sizes and masses and fired into enamel coatings on the surface of low-carbon steel. Acid resistance of the enamel coatings in H2SO4 solution was analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and mass loss of acid corrosion. As was discovered in research, the acid corrosion quantity in the enamel coatings decreased with the decrease in the particle size of the glass powder when the particle size of the additive glass powder reduced from 100μm to 1–2μm and heated the prepared enamel coatings in the H2SO4 solution until 80∘C and kept for 48h. When the additive amount of the glass powder increased from 5% to 20%, the surface of the enamel coating was smooth and flat with good glossiness and without defects like obvious bubbles and cracks, and the acid corrosion quantity decreased with increase in the additive amount of glass powder, which decreased from 43.24mg/cm2⋅d to 4.28mg/cm2.d, satisfying the acid-proof performance requirements of industrial enamel coatings.

MICROSTRUCTURE AND CORROSIVE BEHAVIOR OF ENAMEL COATING MODIFIED ON MILD STEEL

Due to the study of marine corrosion of mild steel, in order to simulate the corrosion conditions of enamel coatings in seawater, enamel coatings applied on mild steel were immersed in 3.5wt.% NaCl liquor and the related corrosion features and behavior of enamel were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and evaluated by electro-chemical method such as potentiodynamic polarization testing. Under the appropriate heat treatment system, the enamel coatings sintered on the same kind of mild steel at different temperatures were studied: all enamel samples were within the temperature range from 710∘C to 830∘C, the heat treating process at the microstructural level was evaluated and correlated with corrosion resistance properties. All the enamel coatings were characterized and it was observed that the enamel coatings that showed excellent corrosion resistance when sintered at a temperature of 810∘C can offer a better physical barrier than other temperatures because of their better bonding force and dense microstructure with less pores.