Evaluation of electroplated Co-Cu metallic coatings for intermediate-temperature solid oxide fuel cells

Co-Cu alloys have been co-deposited onto 430 ferritic stainless steels via electroplating with a citrate solution. At the initial oxidation stage, a three-layer scale composed of a thin CuO outer layer, a thick (Cu,Fe,Cr)-doped Co₃O₄ middle layer and a (Cu,Fe)-doped (Co,Cr)₃O₄ inner layer was formed on the coated steel. With extended oxidation, the (Co,Cr)₃O₄ inner layer has been transformed into a Cr-rich oxide inner layer. An obvious outward diffusion of Fe appeared, leading to the formation of an (Cu,Cr,Mn)-doped (Co,Fe)₃O₄ interaction zone between the Co₃O₄-based spinel and the chromia oxides. The Co-Cu coating effectively blocked the outward migration of Cr from the substrate. No Cr element could be found in the coupled La_0·8Sr_0·2MnO₃ (LSM) plate of the coated sample after oxidized at 800 °C in air for 500 h. The highly conductive coating with a structure of CuO/Co-based spinels significantly decreased the growth of the Cr-rich oxide scale, and thus a much lower scale area specific resistance (ASR). The electrical properties and the oxidation mechanism of the coated substrates were discussed.     

Preparation and performances of CuCo spinel coating on ferritic stainless steel for solid oxide fuel cell interconnect

A compact and adherent CoCu spinel coating on ferritic stainless steel was developed by electroplating a CoCu alloy layer followed by oxidation. The CoCu alloy was oxidized into a three-layer structure consisted of a thinner CuO outer layer, a middle thicker Cu_0.92Co_2.08O₄ layer and an inner Co₃O₄ layer after an oxidation treatment of 2 h at 800 °C in air. The three-layer oxide structure was transformed into a double-layer scale with a (Co,Cr,Cu,Mn,Fe)₃O₄ spinel outer layer and an inner Cr-rich oxide layer after an oxidation of 500 h at 800 °C in air. The CuCo coating enhanced the oxidation resistance of the alloy and served as a diffusion barrier against the outward migration of Cr elements. Meanwhile, the area specific resistance (ASR) of the scale for the CuCo coated alloy was significantly lower than that for the bare sample.     

Fabrication of three-dimensional nanoporous nickel films with tunable nanoporosity and their excellent electrocatalytic activities for hydrogen evolution reaction

Three-dimensional (3D) nanoporous nickel films were fabricated by a novel and facile method. The fabrication process involved the heat treatment of the electrodeposited zinc layer on nickel substrate and the subsequent electrochemical dealloying. The mutual diffusion of Ni and Zn during the heat treatment resulted in the formation of the Ni₂Zn₁₁ alloy surface film. The 3D nanoporous nickel films with open pores and interconnected ligaments were obtained by the electrochemical dealloying of relatively active zinc from the alloy surface film. As the electrodeposited zinc amount increased, the thickness, pore diameter and pore density of the nanoporous nickel films became larger. In our experimental range, the thickest nanoporous nickel film presented a thickness of 8 μm and an average pore diameter of 700 nm. The as-prepared 3D nanoporous nickel films exhibited much higher electrocatalytic activity for hydrogen evolution reaction (HER) than smooth nickel foil, and their electrocatalytic activities for HER enhanced with increase in the porosity and thickness. It was concluded that the enhanced electrocatalytic activity and excellent electrochemical stability for HER of the as-prepared 3D nanoporous nickel films can be ascribed to their unique nanostructured characteristics.     

2024-T3铝合金在模拟海洋大气环境中的腐蚀行为

通过循环盐雾腐蚀实验,模拟2024-T3铝合金在海洋大气环境中的腐蚀过程。采用腐蚀质量损失测试、扫描电镜(SEM)、X射线能谱(EDS)和电化学技术分别对腐蚀117、242、362、487和598 h的2024-T3铝合金试样进行测试分析,得到腐蚀动力学、腐蚀产物和点蚀坑的形貌、腐蚀产物的成分以及表面锈层的电化学特性,研究锈层对2024-T3铝合金大气腐蚀的影响。动力学分析表明,腐蚀过程中2024-T3铝合金的表面形成了具有较好保护性的锈层;电化学测试结果表明,锈层的保护性呈现随腐蚀时间的延长先增强后减弱然后再略增强的变化过程。     

红壤浸出液中X100管线钢微生物腐蚀特征

采用开路电位、线性极化曲线和阻抗谱等电化学手段,结合扫描电子显微镜研究了酸性红壤浸出液中硫酸盐还原菌对X100管线钢腐蚀的影响。研究结果如下:实验初期硫酸盐还原菌的存在降低了管线钢的自腐蚀电位,增加了管线钢腐蚀敏感性,促进了X100管线钢的腐蚀;实验中后期硫酸盐还原菌的生理活动改变了溶液中和X100管线钢表面的化学、电化学状态,抑制了腐蚀;硫酸盐还原菌的生理活动升高了酸性土壤浸出液的pH值,改变了X100管线钢表面膜层的结构,结合层出现了韦伯扩散,阻碍了腐蚀产物的扩散。     

Interfacial reaction between Co–Cr–Mo alloy and liquid Al

The interfacial reaction between Co–Cr–Mo alloy and liquid Al was investigated using immersion tests. Microstructure characterization indicated that the Co–Cr–Mo alloy was corroded by liquid Al homogeneously, with the formation of a (Co,Cr,Mo)₂Al₉ layer close to alloy matrix and “(Cr,Mo)₇Al₄₅ + Al” layer close to Al. Kinetics analysis showed that the corrosion of the Co–Cr–Mo alloy followed a linear relationship with the immersion duration. Compared with pure Co–liquid Al reaction system, the alloying of Cr and Mo changed the solid–liquid interface structure, but the corrosion of the solid metal was still dominated by the dissolution of an intermetallic layer.     

Polar Influence of the Organic Modifiers on the Structure of Montmorillonite in Epoxy Nanocomposites

The epoxy nanocomposites with similar amines （CH3（CH2）17NH2 and CH3（CH2）17N（CH3）301） treated montmorillonite clays have been investigated by wide-angle X-ray scattering, transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and thermal gravimetric analysis （TGA）. Different nanocomposite structures, intercalation and exfoliation were formed by the reaction of octadecyltrimethylammonium chloride-exchanged and octadecylamine-exchanged clays with epoxy resin and phenalkamine as the curing agent, respectively. Results showed that the exfoliated nanocomposite can be obtained when octadecylamine with the lower polarity was used as a modifier. However, the intercalated nanocomposite can be obtained when octadecyltrimethylammonium chloride with higher polarity was used as a modifier.     

Pitting mechanism on an austenite stainless steel nanocrystalline coating investigated by electrochemical noise and in-situ AFM analysis

The pitting corrosion behavior of an austenite stainless steel with polycrystalline (PC) and nanocrystalline (NC) microstructure in 3.5% NaCl solution was investigated by electrochemical noise (EN) and in-situ atomic force microscopy (AFM) under anodic potential. The power spectral density (PSD) and wavelet transform have been employed to analyze the EN data. The pitting corrosion resistance of the NC coating was much higher than that of the PC alloy, with different pitting mechanisms observed for both specimens; a slow metastable pit generation and healing for the PC alloy and a fast metastable pit initiation and death for the NC coating. There was good conformity between the EN and the in-situ AFM analysis. The pitting corrosion mechanism has been discussed according to the EN analysis and the in-situ AFM observations.     

Effect of Gold on the Corrosion Behavior of an Electroless Nickel/Immersion Gold Surface Finish

The performance of surface finishes as a function of the pH of the utilized plating solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. In addition, the surface finishes were examined by x-ray diffraction (XRD), and the contact angle of the liquid/solid interface was recorded. NiP films on copper substrates with gold coatings exhibited their highest coating performance at pH 5. This was attributed to the films having the highest protective efficiency and charge transfer resistance, lowest porosity value, and highest contact angle among those examined as a result of the strongly preferred Au(111) orientation and the improved surface wettability.     

Influence of cyclic frequency on oxidation behavior of K38 superalloy with yttrium additions at 1 273 K

Cyclic oxidation test is a fundamental method to assess lifetime of materials in high temperature environment.Cycle length or cyclic frequency is one important variable in cyclic oxidation testing.In present work,cyclic oxidation tests were performed on cast K38 alloys with 0 wt.%,0.1 wt.%,and 0.5 wt.% yttrium additions at 1 273 K respectively.Two cyclic frequencies were used to investigate the influence of cycle length (1 h vs.20 h) on the high temperature oxidation behavior of superalloy.The results showe...