Papers by Author: Ping Zhao

Abstract: The effect of sulfate reducing bacteria (SRB) on the corrosion of Q235 steel has been investigated in the crevice under the simulated disbonded coating with aperture width of 1.0 and 0.5mm in the soil-extract solutions (SES) by using electrochemical methods. The results show that the existence of SRB in SES can cause corrosion potential of the working electrode to shift to a more negative value, and the formation of pitting on the surface of the electrode. Compared with the crevice width of 1.0mm, the corrosion potential of the electrode shows a little more positive at the crevice width of 0.5mm. The corrosion rate of the electrode increases with the increase of aperture width in the SES without SRB, however, decreases with the increase of aperture width in the SES with SRB. The results obtained indicate that either bio-film on the surface of the electrode formed by SRB in SES or aperture width has obvious influences on the crevice corrosion process of the carbon steel.

Abstract: Silane coupling agent is gradually concerns as a substitute for phosphate pre-treatment of painting. Ten kinds of silane solution such as the KH-450, KH-460, KH-470, KH-550, KH-560, KH-567, KH-578, 5501, 9810, BTSE were chosen as research objects in this paper. Corrosion resistance and adhesion of film were studied after silane treatment on A3 steel surface by copper sulfate drop test, alternate immersion in salt solution and adhesion experiments. These silane films were compared with uncoated A3 steel specimens. The results show that: silane treatment can improve the corrosion resistance of A3 steel in acid solution. KH-560, KH-5501 and KH-470 were ranked the top three in the corrosion resistance. KH-550, KH-560, KH-567 were fourth, fifth and sixth, respectively. Silane treatment can improve the corrosion resistance of A3 steel in neutral salt solution. KH-460, KH-560 and KH-567 have the best salt water corrosion resistance. KH-560 has better adhesion with paint film, following by KH-550 and KH460. When using ethanol and water as the hydrolysis solvent of silane, KH-450, KH-460, KH-470, KH-550, KH-560, KH-567, KH-578, 5501 have the better stability, but stability of 9810, BTSE are poor.

Abstract: The silane films are fabricated by dipping cast aluminum alloy in silane solution, then curing films. The corrosion resistance of single silane film, composite silane film is compared with phosphating film through acid dropping test, salt water immersion test and electrochemical impedance test (EIS), the results shows that the silane films are obviously superior to the phosphating films in terms of the corrosion resistance of acid solution and neutral salt solution, particularly the corrosion resistance of composite silane films is much better than sigle silane films; corrosion polarization curves show that the corrosion tendency of KH550+KH567 composite silane film is minimum, corrosion rate is yet minimal, corrosion process of this silane films is controled by diffusion step. The corrosion process of uncoated aluminum substrate, KH550 silane films, phosphating films are controlled by electrochemical step. The impedance of phosphate films are lower than the silane films. Appropriate silane treatment can effectively improve adhesion between the coating and the Al substrate. The adhesion between silane film and paint film is firmer than the phosphate film, so silane film is an excellent replacement to phosphate film for painting pre-treatment.

Abstract: The crevice corrosion behavior of Q235 carbon steel has been studied under the simulated disbonded coating with an aperture of 1.0mm in the soil-extract solution (SES) with and without sulfate-reducing bacteria (SRB) by using the electrochemical impedance spectroscopy (EIS). The surface morphologies of the steel after experiment were observed by scanning electron microscopy (SEM).The results showed that the capacitive arc of the Q235 steel electrode in SRB containing solution is smaller than that in the aseptic solution at the initial stage of test. However, after 19 days, the capacitive arc of the steel in bacteria containing solution becomes bigger than that in the aseptic solution, and corrosion rate of the steel was smaller in the SES with SRB than that without SRB. The degree of the corrosion on the surface of steel Q235 was more severe after 44 days in the SES without SRB than that with SRB. However, corrosion pits were found on the surface of Q235 steel in the SES with SRB.

Abstract: Aluminum alloy coatings for pretreatment are developed by sol-gel method. The adhesion between sol-gel film and the paint film was measured by scratching circles and corrosion resistance of sol-gel film was tested by salt spraying experiment. The adhesion between sol-gel film made by pure alumina sol and the paint film was so poor that it is unsuitable for ground coatings, but the composite sol which ultrafine Al₂O₃ powder was added to pure alumina sol can improve the adhesion and corrosion resistance. If the first layer film is made of pure alumina sol and the second layer is made of composite sol, the neutral salt spraying time of double layers film is longer than the single-layer composite sol-gel film. The adhesion for both double composite film and single-layer composite sol-gel film are first-grade. When solution of potessium dichromate is dropped on double combinatorial film for 100s, the solution will change in color. The gloss of paint film on double composite sol-gel film is 0.827, flexibility is 2×10mm and impact resistance is 1kg∙50cm. It is possible that composite sol-gel film or combinatorial sol-gel film replace dichromate salt conversion film on aluminum alloy using for painting pretreatment.

Abstract: Surface morphologies of sealed films on anodized aluminum alloy extraordinarily affect on their corrosion resistance. Two-dimensional surface morphologies and three-dimensional surface morphologies of sol sealing, sodium dichromate sealing, boiling water sealing and unsealed films were obtained by OLS3100 laser scanning confocal microscope (LSCM). The three-dimensional surface morphologies show that the amounts of pores are greatly reduced when anodized aluminum 2024 are sealed by these methods. Surface roughness of sealed anodized aluminum 2024 films is increased comparing with the unsealed films, especially the boiling water sealing film. The results of two-dimensional surface morphologies show that unsealed films have plenty of spherical particles; there are raised blocks on sol film; there are much round or chrysalis cavities inside sodium dichromate sealing and boiling water sealing film. Especially there are the most and the deepest cavities with the largest diameter on the boiling water sealing film.