Yuming Tang

Composition and corrosion resistance of palladium film on 316L stainless steel by brush plating

Abstract Palladium films with good adhesive strength were deposited on 316L stainless steel by brush plating. Scanning electronic microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), mass loss tests and electrochemical methods were used to study the properties of the films. The brush plated palladium film mainly consisted of palladium. XPS analysis indicated that palladium was present in the films as metal state. The palladium plated stainless steel samples showed excellent corrosion resistance in boiling 20% H 2 SO 4 solution and boiling acetic/formic acids with 0.005 mol/L Br − ions added. The corrosion rates of the palladium plated 316L stainless steel samples were about two orders of magnitude lower than those of the original 316L stainless steel samples. This method provides a possibility to prepare protective palladium films on stainless steel facilities with large areas in industrial sites.

Electrodeposition of multi-layer Pd–Ni coatings on 316L stainless steel and their corrosion resistance in hot sulfuric acid solution

Abstract Pd–Ni coating shows good corrosion resistance in strong corrosion environments. However, in complex aggressive environments, the performance of the coatings is limited and further improvement is necessary. The effects of the applied plating current density on the composition, structure and properties of Pd–Ni coatings were studied. By changing the current density in the same bath, multi-layer Pd–Ni coatings were prepared on 316L stainless steel. Scanning electronic microscopy, weight loss tests, adhesion strength, porosity and electrochemical methods were used to study the corrosion resistance of the films prepared by different coating methods. Compared with the single layer Pd–Ni coating, the multi-layer coatings showed higher microhardness, lower internal stress, lower porosity and higher adhesive strength. The multi-layer Pd–Ni coating showed obviously better corrosion resistance in hot sulfuric acid solution containing Cl−.

The adsorbing effect of calcined layered double hydroxide for chloride ions in simulated concrete pore solutions

The adsorbing effect of calcined layered double hydroxide (CLDH) for chloride ions in simulated concrete pore (SCP) solutions was investigated with the potentiodynamic polarization method, impedance measurement, ion selective electrode analysis and XRD. CLDH could effectively adsorb Cl− and increase pH value in SCP solutions containing NaCl. The chloride to hydroxyl ions ratio ([Cl−]/[OH−]) of the solution greatly decreased by CLDH treatment. In CLDH treated SCP solution with Cl−, the pitting potential of carbon steel notably increased, and the surface impedance was much higher, indicating strengthened passivation. The process of CLDH adsorbing chloride ions from SCP solutions was accompanied with the reconstruction of the layered structure.

Effect of Surface Roughness on Early Stage of Pitting Corrosion of 316L SS

The influence of the surface roughness(Ra) on the metastable pitting potential(Em) and the stable pitting potential(Eb) as well as on the growth mechanism of metastable pittings was studied by analyzing the current fluctuations at the early stages of pitting corrosion for 316 L stainless steel with three level of surface roughness. The results show that as lg Raincreases both Emand Eb values decrease linearly. With the increase in surface roughness, the average nucleation rate and lifetime of metastable pits decrease while its growth rate shows little change. But by the same growth rate the metastable pits on the steel with larger surface roughness has bigger sustained growth ability, which in combination with the accumulated corrosion damage resulted from high nucleation rate may be beneficial to the transformation of metastable pits into stable pits.

The influence of Ce(NO3)3·6H2O on the inhibitive effect of Ca(NO2)2 in simulated concrete pore solution

The effects of cerium nitrite on corrosion behaviors of carbon steel in simulated concrete pore solutions were studied with the methods of linear polarization, electrochemical impedance spectroscopy and surface analysis. In pore solutions in the presence of Ce(NO3)3·6H2O, the corrosion potential, polarization resistance and impedance of carbon steel obviously increased in contrast to the situation in the absence of cerium salts. The pore solution with [NO2−] / [Cl−] = 0.3 and 0.1% Ce(NO3)3·6H2O, carbon steel shows better corrosion resistance than that in the pore solution with [NO2−] / [Cl−] = 0.6, which indicates that a small amount of Ce(NO3)3·6H2O in pore solutions can effectively promote passivation of the steel and reduce the threshold [NO2−] / [Cl−] ratio for corrosion control. The surface layer formed in cerium salt containing pore solutions is more compact and smooth and 1.36%Ce is examined on the sample surface. The addition of 0.1% Ce(NO3)3· 6H2O in pore solutions can decrease the corrosion rate of steel in pore solutions and has little influence on pH change of the solutions. However, more cerium nitrate addition above 0.1% may result in pH decrease of the solution.

Influence of the C-S-H amount on [Cl - ]/[OH - ] ratio of simulated concrete SPS and the corrosion susceptibility of steel

Two kinds of simulated concrete pore solutions (SPSs) were treated with different amounts of synthetic calcium silicate hydrate (C-S-H). The variation of the [Cl-]/[OH-] ratio in SPS was measured and the corrosion susceptibility of carbon steel in the SPS was investigated with potentiodynamic polarization, EIS and weight lose tests. The experimental results showed that for the SPS at pH 12.5, as the amount of C-S-H increases, the [Cl-]/[OH-] ratio increases thereby causing an increase in the corrosion susceptibility of the steel. While for the SPS at pH 9.7, with increasing C-S-H amount, the drop amplitudes of both [Cl-]/[OH-] ratio and steel corrosion rate first decrease and then increase, and a 3% C-S-H addition shows the best inhibition effect. XPS results demonstrate that after C-S-H treating in pH 12.5 SPS the [Fe3+]/[Fe2+] ratio in the film on steel surface is reduced while in pH 9.7 SPS the [Fe3+]/[Fe2+] ratio is increased. The different effects of the C-S-H amount on the two SPSs and the steel corrosion behavior result from the influences of C-S-H on the SPS pH, which is related to the composition of the SPS.

Pitting Corrosion Behavior of Q235 Carbon Steel in NaHCO3+NaCl Solution under Strain

摘要:用动电位极化、EIS和XPS等方法研究了应变作用下Q235碳钢在NaHCO3+NaCl溶液中的孔蚀行为。结 果表明:在0.2 mol ·L NaHCO3+0.01 mol ·L NaCl溶液中,与无应变试样相比,8%的应变导致Q235碳钢的孔 蚀电位Eb升高;随溶液Cl-浓度升高,应变试样的Eb逐渐降低,当Cl-浓度增大到0.1 mol ·L时,应变试样的Eb值 降低到与无应变试样相同的水平。另一方面,应变导致Q235钢钝化膜中Fe/Fe比值减小,膜阻抗降低,电荷 转移电阻变小,钝化膜的稳定性有所降低。在实验条件下应变导致Eb升高的现象归因于溶液中HCO3的存在, 应变促进钢表面的阳极溶解,进而促进了HCO3在表面的优先吸附,一定程度上抑制了Cl促进孔蚀的作用。 随溶液中HCO3/Cl的比值降低,应变导致的Eb值变化逐渐减小直至消失。 关键词:Q235钢 孔蚀 应变 HCO3 钝化膜 中图分类号:TG172 文献标识码:A 文章编号:1005-4537(2016)03-0238-07

Correlation between microhardness and microstructure of anodic film on 2024 aluminum alloy

The correlation between the microhardness and microstructure features of anodic films on 2024 aluminum alloy formed in the mixed sulfuric acid/oxalic acid electrolyte was studied using micro-hardness tester and scanning electron microscope (SEM). The results show that the microhardness of the anodic film is influenced by the microstructure of the anodic film such as the film porosity, and the order and continuity of the hexagon columnar cells. The film microhardness increases as the porosity of the anodic film decreases and the order and continuity of the film cells increase. With the same current density, as the anodic film thickens with anodizing time, the film microhardness increases because the film porosity decreases and the order and continuity of the cells are also improved. Under the condition of the same anodizing time, as the current density increases, the film microhardness decreases due to the higher film porosity and the poorer order and continuity of the film cells. The film porosity increases because the increased current density can accelerate the oxidation reaction, strengthen the filed-assisted dissolution and the heating effect in the anodic film, resulting in decreased film order and continuity.

Performance of Aluminum Triphosphate and Ceria Modified Mg-rich Epoxy Coating on AZ91D Magnesium Alloy

A corrosion resistant coating for AZ91 D magnesium alloy was prepared by adding pure magnesium particles, aluminium triphosphate(SAP) and ceria in an epoxy coating. The performance of the coating in 3%Na Cl solution was studied with methods of Machu test, electrochemical impedance measurement and scanning electron microscope. The results show that the Mg-rich epoxy coating failed and the magnesium substrate was corroded after immersion for about 2000 h,while no corrosion was observed beneath the coating with SAP and ceria addition after immersion for 4448 h. Distinctly the added SAP and ceria can decrease the activity of magnesium particles in the Mg-rich epoxy and thereby prolong the life time of the coating. On the other hand, the compactness and the barrier property of the coating are improved as well.

Improvement of bonding strength of AZ31B magnesium alloy by anodizing and chromium-free conversion treatments

The influences of chromium-free chemical conversion treatment and anodizing treatment on bonding strength of AZ31 magnesium alloy were studied by lap-shear test, SEM and electrochemical methods. Both chemical conversion treatment and anodizing can increase the bonding strength. The anodizing treatment gives higher bonding strength and better corrosion resistance than chemical conversion treatment. The increase of bonding strength by the treatments may be attributed to the uneven surface structures with micro-pores, resulting in increased bonding areas and the embedding effect.