平面叉指电极溶液阻抗的低频三角波测量

针对低浓度电解质溶液中生物细胞阻抗微弱变化过程的测量问题,研究了一种三角波电压激励结合主元分析(PCA)的测量方法。用三角波电压信号作为激励,采集单周期响应电流信号构成测量向量,由不同时刻所得测量向量组成测量矩阵,PCA处理后的载荷向量中即包含有溶液阻抗的变化信息。这种信号处理方式对阻抗变化过程的测量结果不依赖于等效阻抗模型的计算,同时可有效避免等效阻抗计算过程中的噪声问题。对低浓度氯化钾溶液中硅基底金电极、PCB基底铜电极和PCB基底镀金电极3种平面叉指电极进行了实验分析。实验结果表明,三角波激励结合PCA处理的方法可实现对溶液电导率微弱变化过程的有效检测。

Corrosion behavior of tinplate in NaCl solution

The corrosion process of tinplate in 0.5 mol/L NaCl solution was investigated using the electrochemical impedance spectroscopy（EIS）,and the morphology and structure of the corrosion products were characterized by scanning electron microscope（SEM）,scanning probe microscopy（SPM）,X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）.The results showed that the resistance of tin coating,Rc,was essentially constant but the charge transfer resistance,Rct,decreased by 2 orders of magnitude,which indicated that the tin coating was not seriously corroded while the carbon steel substrate was corroded continuously.The corrosion of tinplate in 0.5 mol/L NaCl solution was mainly the dissolution of carbon steel substrate because of the defects in the tin layer and the corrosion product was mainly γ-FeOOH.

Corrosion behavior of Hastelloy C22 coating produced by laser cladding in static and cavitation acid solution

The Hastelloy C22 coatings on Q235 steel substrate were produced by high power diode laser cladding technique. Their corrosion behaviors in static and cavitation hydrochloric, sulfuric and nitric acid solutions were investigated. The electrochemical results show that corrosion resistance of coatings in static acid solutions is higher than that in cavitation ones. In each case, coating corrosion resistance in descending order is in nitric, sulfuric and hydrochloric acid solutions. Obvious erosion-corrosion morphology and serious intercrystalline corrosion of coating are noticed in cavitation hydrochloric acid solution. This is mainly ascribed to the aggressive ions in hydrochloric acid solution and mechanical effect from cavitation bubbles collapse. While coating after corrosion test in cavitation nitric acid solution shows nearly unchanged surface morphology. The results indicate that the associated action of cavitation and property of acid solution determines the corrosion development of coating. Hastelloy C22 coating exhibits better corrosion resistance in oxidizing acid solution for the stable formation of dense oxide film on the surface.

Passivity Degradation of Alloy 800 in Simulated Crevice Chemistries

Passivity degradation of Alloy 800 in simulated crevice chemistries was systematically investigated using cyclic polarization curve, electrochemical impedance spectroscopy(EIS), Mott-Schottky analysis, Auger electron spectroscopy(AES)and atomic absorption spectrometry(AAS). Cyclic polarization showed that the pitting potential in a thiosulfate solution was much lower than in either a chloride solution or a sulfate-chloride solution. Mott-Schottky results revealed that passive films showed n-type semiconductivity, and the presence of thiosulfate in chloride solution led to an increased donor density in the passive film. EIS spectra indicated that thiosulfate enhanced the film dissolution rate in chloride solutions. Moreover, thiosulfate enhanced the pitting propagation rate in chloride solution by stabilizing the metastable pits and forming sulfide within the pits.

Influence of welding speed on corrosion behaviour of friction stir welded AA5086 aluminium alloy

The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA),the heat affected zone(HAZ),and the weld nugget zone(WNZ)of the joints were studied in 3.5%(mass fraction)aerated aqueous Na Cl solution by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min.However,the value of corrosion rate in the weldments is lower than that in the PA.Additionally,the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ.On the contrary,the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed.The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases.The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy.With increasing the welding speed,the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region.In the HAZ region,in addition to the pits in the corroded area,some cracks can be seen around the corroded areas,which confirms that intergranular corrosion is formed in this area.The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions.Crystallographic pits are observed within the weld regions.

The Study of the Varying Characteristics of Cathodic Regions for Defective Coating in 3.5% Sodium Chloride Solution by EIS and WBE

The current distributions over carbon steel under iron red alkyd primer exposed to 3.5% sodium chloride solution were mapped using the wire beam electrode （WBE）. The electrochemical impedance spectroscopy （EIS） of the WBE was carded out to analyze the performance of coating delamination and corrosion behavior of carbon steel beneath defective coating. The EIS data revealed that protective capability of coating decreased with immersion time and the degree of cathodic delamination showed a rapid rise. The current density distribution of WBE indicated that cathodic sites was located at the defect at the beginning of immersion and gradually spread into the intact coating. The cathodic regions were distinguished from the anodic area and distributed over the WBE. The changes of cathodic sites could reflect the deterioration process of defective coating. The cathodic area ratio was a more useful parameter than the cathodic delamination degree to evaluate the coating cathodic delamination. The polarity reversals of electrodes at the defect and beneath coating were observed. A simple discussion of relationship between the blister and the polarity reversal was made from a standpoint of electrochemical distribution. WBE method was able to map and record the changes of local cathodic sites beneath defective coating in real time, which could provide more detailed information about the local degradation of coating.

不同Cr含量的Ni基合金电化学腐蚀行为

利用电化学测试技术研究不同Cr含量的Ni基合金耐Cl^-离子水溶液腐蚀的能力。结果表明:Ni基合金耐Cl^-离子腐蚀性能随着合金中Cr含量的提高而增强,溶液中Cl^-离子浓度对Ni-9Cr、Ni-15Cr和Ni-20Cr合金有较大影响,特别是Ni-9Cr合金在0.6 mol/L NaCl溶液中腐蚀最为严重,而对于Ni-25Cr和Ni-30Cr合金的腐蚀不明显。通过采用XPS测试方法,对不同Cr含量的Ni基合金在0.6 mol/L NaCl溶液中形成的钝化膜表面进行成分分析,得到Ni-30Cr合金的钝化膜表面生成的Cr的氧化物和氢氧化物比例较大,分别为4.840%和4.130%,高于其它Ni-Cr合金;同时对Ni-Cr合金在不同浓度NaCl溶液中的点腐蚀机理进行了探讨。

Electrosynthsis of large polypyrrole films by multi-potential steps method

Polypyrrole (PPy) films were prepared by multi-potential steps polymerization in an aqueous pyrrole solution, with lithium perchlorate and oxalic acid as supporting electrolytes. Morphology and structure of PPy films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical behaviors of PPy films were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that multi-potential steps polymerization improves the conductivity of PPy films and large polymer films can be peeled off easily from the electrode without cracking. Lithium perchlorate and oxalic acid provide appropriate dopants for PPy polymerization. It was observed that the polymerization time and the current density have a crucial influence on the surface morphology of PPy films. Smooth and compact PPy films could be generated under long polymerization time and low current density. Multi-potential steps polymerization decreases the occurrence of peroxidation, which improves the conductivity of PPy films. The parameters for multi-potential steps polymerization have been optimized.