Xuhui Zhao

Hydroxyapatite Coatings on Titanium Prepared by Electrodeposition in a Modified Simulated Body Fluid

Abstract Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid. The configuration, structure and bioactivity of the coating were investigated with scanning electron microscopy (SEM), X-ray diffraction analyzer (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. The results demonstrated that pure and homogeneous hydroxyapatite coating can be obtained without any post-treatment. The prepared coating showed good bioactivity in simulated body fluid (SBF). The time required for a fully covered dense hydroxyapatite coatings was 4 days immersion in SBF.

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−.

Preparation and properties of Al-Ni composite anodic films on aluminum surface

Ni element was introduced to aluminum surface by a simple chemical immersion method, and Al-Ni composite anodic films were obtained by following anodizing. The morphology, structure and composition of the Al-Ni anodic films were examined by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and atomic force microscopy(AFM). The electrochemical behaviors of the films were studied by means of polarization measurement and electrochemical impedance spectroscopy (EIS). The experimental results show that the Al-Ni composite anodic film is more compact with smaller pore diameters than that of the Al anodic film. The introduction of nickel increases the impedances of both the barrier layer and the porous layer of the anodic films. In NaCl solutions, the Al-Ni composite anodic films show higher impedance values and better corrosion resistance.

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.

EIS evolution of anodised aluminium by cerium salt sealing in NaCl solution with exposure time

Abstract The sealing of porous anodic oxide film on aluminium 2024 involving immersion of the anodised aluminium in an aerated solution containing cerium salt under the application of pulse power at room temperature has been proposed as an alternative to dichromate sealing method. The sealing process shows some advantages. The corrosion behaviours of the anodised aluminium unsealed or sealed by dichromate and cerium salt respectively were investigated at different exposure times up to 30 days in 1M NaCl solution by means of electrochemical impedance spectroscopy, and the damage functions were calculated in this work. The results show that the damage functions of anodised aluminium sealed with cerium salt are lower than those unsealed or sealed with potassium dichromate. Cerium salt sealing provides a better corrosion resistance of anodised aluminium in NaCl solution for long exposure time than dichromate sealing.

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.

Electrochemical behaviors of anodic alumina sealed by Ce-Mo in NaCl solutions

Abstract The elimination of toxic materials in sealing methods for anodic films on 1070 aluminum alloy was studied. The new process uses chemical treatments in cerium solution and an electrochemical treatment in a molybdate solution. Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) were used to study the influences of sealing methods on the corrosion behavior of anodic films in NaCl solutions. The results show that the Ce-Mo sealing makes the surface structure and morphology of anodic films uniform and compact. Ce and Mo produce a cooperative effect to improve the corrosion resistance of anodic films. Anodic films sealed by Ce-Mo provide high corrosion resistance both in acidic and basic solutions.

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