Effect of rare earth Eu on anti-passivation of metal oxide anode coating

The anti passivation effect of metal oxide anode coating doped with rare earth element Eu was discussed. The morphology and the composition distribution of the metal oxide coating anode before and after electrolysis were studied by SEM and EDX analyses. The results show that the erosion of the electrolyte at the defects is the main cause for the failure of the coating. The erosion rate of the electrolyte is anisotropic. In area with high density of defects, the erosion rate is very fast and the failure of the coating is very quick. Moreover, the life time of the coating is prolonged by the doping of Eu. [

Electrochemical behavior of mesh and plate oxide coated anodes during zinc electrowinning

The catalytic performance of two oxides coated anodes （OCSs） meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 ℃. Their electrochemical behaviors were compared with that of a conventional Pb-0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential （OCP） and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/（IrO2-Ta2O5） mesh electrode is the lowest （3.37μA/cm^2） among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm^2and 38 ℃, the Ti/MnO2mesh anode has the highest potential （1.799 V）, followed by the Ti/（IrO2-Ta2O5） plate （1.775 V） and Ti/（IrO2-Ta2O5） mesh （1.705 V） anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/（IrO2-Ta2O5） mesh attains the lowest corrosion current density. The Ti/（IrO2-Ta2O5） mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb-Ag anode by about 245 mV.

Preparation and Corrosion Resistance of Anodic Oxidation Coatings on 2198 and 5A90 Al-Li Alloys

2198 and 5A90 Al-Li alloys were anodized with a constant DC potential in 18%H_2SO_4solution(Solu.A) and the mixture solution of 18%H_2SO_4+5%C_2H_2O_4(Solu.B) at room temperature. 12 and 11 V was optimized as the applied oxidation potential for 2198 and 5A90 alloys, respectively. Cross-sectional morphology, surface morphology and elements distribution of anodic oxidation coatings were observed by scanning electron microscope equipped with energy dispersive X-ray analysis(SEM/EDX). Corrosion resistance was tested by potentiodynamic polarization plot in 3.5%NaCl solution. The results showed that the thicknesses of coatings obtained at the selected potential in Solu.A and Solu.B were about 50 μm/110 μm for 2198 alloy and 80 μm/110 μm for 5A90 alloy. In both solutions, anodic oxidation coatings of 2198 alloy were primarily composed of Al oxides; those of 5A90 alloy were mainly consisted of Al oxides and a small amount of Mg oxides. The results of potentiodynamic polarization showed that anodic oxidation coatings of 2198 and 5A90 Al-Li alloys had better corrosion resistances than that of untreated alloys.

Improvement of stability of trivalent chromium electroplating of Ti based IrO_2+Ta_2O_5 coating anodes

The preparation process and properties of the thermally prepared Ti anodes coated with IrO2+Ta2O5 was studied. The structure and morphologies of the IrO2+Ta2O5 coatings were determined by XRD and SEM. Their electrochemical properties were studied by polarization curve and cyclic voltammetry. Trivalent chromium electroplating using Ti/IrO2+Ta2O5 anodes is carried out and the results were analyzed. Results show that this anode exhibits excellent electrochemical activity and stability in sulfate electrolysis. The electrocatalytic activity is determined not only by the content of IrO2 but also the structure and morphology of the anode coatings. The electroplating results indicats that Ti/IrO2+Ta2O5 anodes have excellent capabilities and merits in improving the stability of trivalent chromium electroplating in sulfate system.

Extended Anode Effect for Tube Inner Coating of Non-Conductive Ceramics by Pulsed Coaxial Magnetron Plasma

For uniform tube inner coating of non-conductive thin films, the double-ended coaxial magnetron pulsed plasma (DCMPP) method was investigated. In this study, coating of TiN and TiO2 was performed. It was clearly shown that the extended anode effect was strongly influenced by the electric resistance of the coated thin films on the inner surface of an insulator tube. Additionally, high frequency (100 kHz) was better for relatively high plasma density. On the other hand, in the case of titanium oxide deposition, negative ion productions drastically decrease the deposition rate and the shifting velocity of plasma main position for coated TiO2 films.

Preparation of Hydroxyapatite-titanium Dioxide Coating on Ti6Al4V Substrates using Hydrothermal-electrochemical Method

Ti6Al4V substrates were anodized in a 0.5 mol/L H_2SO_4 solution at applied voltages of 90-140 V.A hydroxyapatite-titanium oxide（HA-TiO2）coating was then deposited on the anodized Ti6Al4 V substrates via a hydrothermal-electrochemicalmethod at a constant current.The obtained films and coatings were characterized by X-ray diffraction,scanning electron microscopy,energy-dispersive X-ray spectroscopy,and Fourier-transform infrared spectrometry.The microstructures of the porous films on the Ti6Al4 V substrates were studied to investigate the effect of the anodizing voltage on the phase and morphology of the HATiO_2 coating.The results indicated that both the phase composition and the morphology of the coatings were significantly influenced by changes in the anodizing voltage.HA-TiO_2 was directly precipitated onto the surface of the substrate when the applied voltage was between 110 and 140 V.The coatings had a gradient structure and the HA exhibited both needle-like and cotton-like structures.The amount of cotton-like HA structures decreased with an increase in voltage from 90 to 120 V,and then increased slightly when the voltage was higher than 120 V.The orientation index of the（002）plane of the coating was at a minimum when the Ti6Al4 V substrate was pretreated at 120 V.

Development and Oxidation Behavior of Al-Cu-Fe Quasicrystalline Coating on Ti Alloy

An oxidation resistant Al-Cu-Fe quasicrystalline coating was fabricated on substrate of Ti alloy by low pressure plasma spraying (LPPS) method. As-sprayed Al-Cu-Fe coating has a rapidly solidified lamellar microstructure consisting of quasicrystalline phase and crystalline phase. The formation of quasicrystalline coating is related to the annealing. The results from the ox!dat!on experiments showed that Al-Cu-Fe quasicrystalline coating improved the oxidation resistance of Ti-base alloys. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al-Cu-Fe quasicrystalline coating after oxidation consisted of Al2O3. Oxidation occurs Ieading to a change of concentration and phase transformation in the coating surface. Selective oxidation of AI transforms the quasicrystalline phase into the phase.

Anodic Coating Characteristics of Different Aluminum Alloys for Spacecraft Materials Applications

Anodic oxide coatings on aluminum alloys are used for space environment applications. These provide specific thermo-optical properties to spacecraft surface. Fragments of these coatings lead to generate the contamination in satellites and affect the mission lifetime. The current work concerns studying of the anodic processes applied on aluminum and different groups of aluminum alloys as Al7075, Al2024 and Al6061. Experimental procedures are performed using sulfuric acid at different values of current density (1 - 2 A/dm2). The influence of the parameters of anodic film formation on the coating characteristics and layer thickness of aluminum alloys has been investigated. Reflectance and optical properties of the anodized aluminum alloy coatings are determined and found to be dependent on the alloying elements. Changes in anodic coating weight and film thickness of aluminium alloys with the process parameters as current density, temperature, time duration, acid concentration, and sealing system have been studied. Moreover, morphology and surface structure of the considered samples are carried out in attempt to understand the physical characteristics. The obtained results are compared and briefly outlined.

Chemical dissolution resistance of anodic oxide layers formed on aluminum

Chemically resistant anodic oxide layers were formed on pure aluminum substrates in oxalic acid-sulphuric acid bath.Acid dissolution tests of the obtained anodic layers were achieved in accordance with the ASTM B 680-80 specifications：35mL/L 85% H3PO4＋20g/L CrO3 at 38℃.Influence of oxalic acid concentration,bath temperature and anodic current density on dissolution rate and coating ratio was examined,when the sulphuric acid concentration was maintained at 160g/L.It was found that chemically resistant and compact oxide layers were produced under low operational temperature （5℃） and high current densities （3A/dm^2）.A beneficial effect was observed concerning the addition of oxalic acid （18g/L）.The morphology and the composition of the anodic oxide layer were examined by scanning electron microscopy （SEM）,atomic force microscopy （AFM） and glow-discharge optical emission spectroscopy （GDOES）.

INVESTIGATION OF SURFACE MORPHOLOGY, STRUCTURE AND ELECTROCATALYTIC PROPERTIES FOR O_2 EVOLUTION OF TITANIUM BASED IrO_2+Ta_2O_5 COATINGS

Titanium based IrO2 +Ta2O5 oxide anodes with different compositions and pyrolysis temperatures were prepared by termodecompoisition method. By using X-ray diffraction (XRD), the structure and texture coefficient of the coatings, TC(hkl), of IrO2 rutile crystal have been tested. It showed that, the crystallization processes of IrO2 and Ta2O5 in xIrO2 +(100-x) Ta2 O5 (x is in mol%) films affected and confined each other.In the mixed system, IrO2 rutile phase existed as a solid solution with Ta, and attained the maximum solubility when x=70mol%, i.e. for the coating of 70% IrO2 +Ta2O5.For the coatings of low iridium content or at low preparing tem pemture, (110) and (101) pwtered orientations were dominant. However, preferred growth of IrO2 weakened with increasing either iridium content or temperature. Three typical surface morphologies were observed by using scanning electron tnicroscopy(SEM). The crystallite size of the mixed oxide coatings were finest for the the film of 70%IrO2 +30%Ta2O5,and decreased with the pyrolysis tempemture. As the results of the finest crystallite segregating on sudece and the maxitnum solid solubility of Ir and Ta component in deposits, the coatings with the composition of 70%IrO2 +Ta2O5 prepared at 450℃ presented the mdrimutn electrocatalgtic activitg for O2 evolution in 0. 5M H2SO4 solution.UP to 550℃, Ti base suffered to oxidation resulting in decreasing anode conductivity,therefore, coatings performed a low activity.

Preparation and electrocatalytic properties of Ti/IrO_2-Ta_2O_5 anodes for oxygen evolution

The preparation and electrocatalytic activity for oxygen evolution of the thermally prepared Ti anodes coated with IrO2-Ta2O5 were studied. The structure and morphologies of the oxide films with different contents of IrO2 were determined by XRD and SEM respectively. Their electrochemical properties were studied by Linear Sweep Voltammetry, Tafel Plot and Cyclic Voltammetry. The results show that iridium and tantalum can form solid solution and the mutual solubility is affected by the ratio of Ir to Ta in coating solution. With increasing IrO2 content in the coatings, the amount of fine crystallites of IrO2 is increased and the electrocatalytic capability of oxygen evolution is strengthened. The coating adhesion and rigidity decrease, which affects electrochemical activity of the anode when the content of IrO2 is too high. The electrochemically active surface area is determined not only by the content of IrO2but also the structure and morphology of the anode coatings. It is probably due to the existence of proper quantities of inert Ta2O5 which results in a typical morphology of cracks and solid solution structure.

石墨烯增强冷喷涂-阳极氧化铝基复合涂层的微观组织及摩擦性能研究

目的增强冷喷涂铝合金-阳极氧化复合涂层的耐磨性能,充分利用二维层状石墨烯优异的润滑特性,探究石墨烯对复合涂层相关性能的作用机理。方法采用超声分散和磁力搅拌的方法,利用铝粉的还原性将氧化石墨烯原位还原为还原氧化石墨烯(rGO),将其包覆在7075Al合金颗粒的表面,通过冷喷涂和阳极氧化的复合工艺将铝合金的阳极氧化工艺“移植”到钢材表面,制备出7075Al-AAO和G/7075Al-AAO两种复合涂层。通过扫描电子显微镜SEM、X射线衍射、X射线能谱、拉曼光谱等手段分析涂层的形貌、成分、结构,开展涂层的硬度和摩擦磨损试验,最后通过SEM、3D激光共聚焦法观察磨痕形貌,并计算磨损率。结果7075Al-AAO涂层的硬度为208.1HV0.1,而G/7075Al-AAO涂层的硬度为319.1HV0.1,相较于经石墨烯改性前涂层的硬度提高了53.3%;G/7075Al-AAO涂层表现出更低的磨损率(4.42×10^(–4)mm^(3)·N^(–1)·m^(–1))和更小的摩擦因数(约为0.2),其磨损率相对于改性前涂层降低了近45%,摩擦因数仅为改性前涂层的1/2。结论经过石墨烯包覆改性与复合工艺处理后制备的G/7075Al-AAO涂层具有更高的硬度,更优异的减摩和耐磨性,这归因于原位转移并均匀分散于阳极氧化膜中的rGO增强了涂层的致密性和结合力,同时发挥了高强度和润滑减摩特性。石墨烯原位包覆改性及冷喷涂复合阳极氧化技术对高性能铝基耐磨涂层制备具有技术指导意义。

异种金属电偶腐蚀防护方法研究进展

铝合金、钛合金等轻质合金材料广泛应用于飞机、舰船等高端装备的管路系统中,用来传送水、油/气等工质并连接各种机械设备。在应用过程中,异种金属在电解液中接触而引起电化学反应并发生明显的电偶腐蚀现象,直接影响设备的结构完整性和服役安全性,必须采取措施预防此类电偶腐蚀的发生。介绍了电偶腐蚀发生的原理及影响因素,总结了近年来电偶腐蚀防护方法及绝缘防护涂层的研究现状,提出了电偶腐蚀防护值得关注的问题。

铝电解预焙阳极防氧化涂层材料的性能检测研究

本文针对纳米陶瓷基阳极防氧化涂层材料工业应用的特点,设计了该涂层材料的实验室性能检测流程,并对检测流程的各个步骤进行了详细说明及原因分析,确定了纳米陶瓷基阳极防氧化涂层材料检测的评判标准。

镁合金表面Ca-P涂层的制备及其耐蚀性研究

采用两步阳极氧化和化学沉积结合的方法,在钙/磷比为1.67的溶液中Mg-3wt%Zn-0.8wt%Zr合金表面制备了Ca-P生物涂层。分别采用XRD、SEM、划痕仪和光学显微镜表征分析涂层的物相成分、表面形貌、厚度和结合力,以及通过电化学工作站测定涂层材料的耐腐蚀性能。结果表明:Mg-Zn-Zr合金经过阳极氧化和化学沉积处理生成了Ca-P涂层,主要成分为磷酸氢钙(CaHPO_(4))、二水磷酸氢钙(CaHPO_(4)·2H_(2)O)和磷酸三钙(Ca_(3)(PO_(4))_(2));在沉积时间为48 h的条件下,形成的Ca-P涂层组织形貌致密均匀,与基体的结合力最好,且能使镁合金的腐蚀电位达到-1.181 V,腐蚀速率明显降低,达到了提高镁合金基体耐蚀性的目的。

Effects of Anodic Voltages on Microstructure and Properties of Plasma Electrolytic Oxidation Coatings on Biomedical NiTi Alloy

Plasma electrolytic oxidation （PEO） coatings, formed under various anodic voltages （320-440 V） on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during the PEO process under different anodic voltages was observed. The surface and cross-sectional morphologies, composition, bonding strength, wear resistance and corrosion resistance of the coatings were investigated by scanning electron microscopy （SEM）, thin-film X-ray diffraction （TF-XRD）, energy dispersive X-ray spectrometry （EDS）, surface roughness, direct pull-off test, ball-on-disk friction and wear test and potentiodynamic polarization test, respectively. The results showed that the evolution of discharging sparks during the PEO process directly influenced the microstructure of the PEO coatings and further influences the properties. When the anodic voltage increased from 320 V to 400 V, the corrosion resistance and wear resistance of the coatings slowly increased, and all the bonding strength was higher than 60 MPa; further increasing the anodic voltages, especially up to 440 V, although the thickness and γ-AI203 crystallinity of the coatings further increased, the microstructure and properties of the coatings were obviously deteriorated.

Formation and capacitance properties of Ti-Al composite oxide film on aluminum

Al specimens were covered with TiO2 film by sol-gel dip-coating and then anodized in ammonium adipate solution.The structure,composition and capacitance properties of the anodic oxide film were investigated by transmission electron microscopy (TEM),Auger electron spectroscopy (AES),X-ray diffractometry (XRD) and electrochemical impedance spectroscopy (EIS).It was found that an anodic oxide film with a dual-layer structure formed between TiO2 coating and Al substrate.The film consisted of an inner Al2O3 layer and an outer Ti-Al composite oxide layer.The thickness of layers varied with the number of times of sol-gel dip-coating.The capacitance of anodic oxide films formed on coated specimens was at most 80% higher than that without TiO2.In film formation mechanism,it was claimed that the formation of composite oxide film was mainly affected by the structure of micro-pores network in TiO2 coating which had an influence on Al3+ and O2? ions transport during the anodizing.

Ti/Ta_(2)O_(5)-IrO_(2)阳极在酸性体系的失效机理研究

钛基涂层阳极具有较低的析氧电位和较高的析氧电流效率,并且表现出良好的稳定性,广泛应用于电催化氧化处理废水领域。利用标准强化电解寿命试验,通过电化学分析和物相分析等手段系统地探讨了Ti/Ta_(2)O_(5)-IrO_(2)钛基涂层钛阳极在酸性环境中阳极寿命和阳极失效机制。结果表明,Ti/Ta_(2)O_(5)-IrO_(2)涂层钛阳极的电解失效机制是物理作用和化学作用的叠加,其在酸性体系中的强化电解并不是均匀的,根据槽压变化,可分为4个阶段。

纳米陶瓷基阳极防氧化涂层材料的应用

本文通过对纳米陶瓷基阳极防氧化涂层材料的大规模工业应用进行长期跟踪发现:该涂层材料的应用对降低噪声值、电耗、阳极毛耗和提升电流效率、原铝质量具有积极的效果;同时对应用结果进行汇总处理,得出了涂层材料对各生产指标影响的参考数据;并对各生产指标的影响原因进行了分析。

铝电解炭素阳极用防氧化保护涂料工业化应用研究

铝电解用炭素阳极容易在高温下发生氧化反应,造成炭素阳极的消耗量较大,生产成本较高。针对该情况利用纳米陶瓷基高温防氧化涂层材料在阳极炭块表面形成致密的抗氧化保护涂层,验证涂料对阳极炭块的保护作用,探索延长阳极炭块使用寿命,降低炭耗、CO_(2)排放的新路径。工业化试验结果表明该涂层的高温防氧化性较好,能有效实现对炭素阳极的保护。