BMCA-2.5型离子膜法单极槽膜极距改造

将单极式离子膜电解槽由常极距改造为膜极距,降低了槽电压.通过对比试验,说明使用新型阴极活性涂层更能有效抵抗Fe2+和反向电流对阴极的不利影响.     

膜极距电解运行的相关要求

新疆华泰重化工有限责任公司电解车间对窄极距电解槽进行了膜极距结构改造。针对膜极距改造后,阴极涂层对反向电流敏感、阴极极网对Fe3+敏感、阴极侧对反向压差敏感等对膜极距电解相关设备的特殊要求,采取了相应措施。     

C-DCDS开关在旭化成离子膜电解槽上的应用

介绍反向电流的产生、C-DCDS开关结构及使用等。通过在离子膜电解槽上加装C-DCDS开关,减小了反向电流对离子膜阴极涂层的影响。     

离子膜电解槽阴、阳极极片涂层调研

分析活性阴极失活原因及阳极涂层寿命的主要因素，提出离子膜电解槽对阳极、阳极涂层、阴极、阴极涂层的技术要求，结合天津化工厂2.5万t/a离子膜生产实际，对国内重涂电极与国外离子膜阴极涂层国内运行1年后阴极的槽压数据进行了对比。采用国内离子膜电解槽极片重涂技术，每年可节约电费约90万元。     

旧电解槽的升级改造方案分析

针对浙江善高化学有限公司电解槽的运行现状,经经济性计算,提出将M,自然循环单极槽改造为高电流密度自然循环电解槽。对NCS自然循环复极槽提出3种旧电解槽的升级改造方案：①不更换电极,膜继续运行;②更换同类型阳极,并根据阳极涂层决定是否更换阳极;③阴极零极距改造。认为阴极零极距改造方案可节电200kW·h／t,是最佳改造方案。     

膜极距电解槽新技术在电解槽改造中的应用

介绍了蓝星(北京)化工机械有限公司推出的膜极距电解槽新技术。该技术在电解槽改造中的应用包括:改进电解槽气液分离结构,改进电解槽循环结构,改进电解槽底网参数,优化电解槽弹性网的设计,改进槽阴极面网。给出该技术在不同槽上改造后的实际运行数据。从改造完的电解槽运行数据看,应用效果显著。电解槽气液分离结构的改进,使得上部气体和液体分布得更加均匀,减少了气体滞留量,延长了离子膜的使用寿命。电解槽内部循环结构的改变,使液体循环得更加充分,浓度和温度分布更加均匀。阴极网工艺参数的改进,使之更加适合在较高电流密度下运行,且耐腐蚀性更强,运行数据更加稳定。电解涂层技术的改进,不仅使电解槽电压越来越稳定,也使电解槽抗反向电流的能力进一步加强。     

旭化成离子膜复极电槽进口软管堵塞原因

旭化成离子膜复极电槽进口软管常被铁的氧化物和铁杂质、有机氯化物、盐、螯合树脂碎颗粒及其它机械杂质堵塞 ,单元槽流量减少甚至液位、槽压升高 ,槽温剧增 ,使膜受损 ,击穿极网。即使及早发现 ,也要停车清堵 ,造成巨大损失 ,严重影响生产。1　堵塞原因1 1　阴极阴极系统不锈钢阀门、管道、设备的碱腐蚀等 ;电解槽非活性焊点的腐蚀物—磁铁粉 (Ｆｅ3Ｏ4 ) ;镍活性涂层腐蚀及脱落 ,特别是电槽停车不及时排液及电流造成的涂层腐蚀尤为严重。1 2　阳极盐水精制助沉剂过量加入到电解系统形成有机氧化物 ;旭化成自然循环复极电槽单槽加酸 ,当…     

离子膜烧碱装置槽电压上升原因

分析旭化成复极式自然循环电解槽电压突然升高的原因，认为是由如下因素引起的：阴极网涂层脱落，阳极网腐蚀，涂层活性减弱，离子膜受污染和性能差，盐水或盐酸质量不合格及电流升高等。     

低电流密度离子膜电解槽零极距改造运行总结

对旭化成NCS电解槽进行改造的3种方案——①不更换电极,换膜;②更类阴极,根据涂层寿命决定是否更换阳极;③对阴极进行零极距改造,进行经济预算的对比,决定采用零极距改造。介绍了改造内容和操作控制部分,指出改造中需注意的问题。改造后约2.5年收回全部投资。     

离子膜电解槽部件使用效果的分析

总结了四期离子膜更换及运行情况，分析对比了不同阴、阳极涂层的使用效果，认为阴极涂层质量差导致槽电压上升，介绍了部分电解槽配件国产化改造情况及存在问题。     

Graphitic Carbon as Durable Cathode‐Catalyst Support for PEFCs

Long‐term deterioration in the performance of PEFCs is attributed largely to reduction in active area of the platinum catalyst at cathode, usually caused by carbon‐support corrosion. It is found that the use of graphitic carbon as cathode‐catalyst support enhances its long‐term stability in relation to non‐graphitic carbon. This is because graphitic‐carbon‐supported‐Pt (Pt/GrC) cathodes exhibit higher resistance to carbon corrosion in‐relation to non‐graphitic‐carbon‐supported‐Pt (Pt/Non‐GrC) cathodes in PEFCs during accelerated stress test (AST) as evidenced by chronoamperometry and carbon dioxide studies. The corresponding change in electrochemical surface area (ESA), cell performance and charge‐transfer resistance are monitored through cyclic voltammetry (CV), cell polarisation and impedance measurements, respectively. The degradation in performance of PEFC with Pt/GrC cathode is found to be around 10% after 70 h of AST as against 77% for Pt/Non‐GrC cathode. It is noteworthy that Pt/GrC cathodes can withstand even up to 100 h of AST with nominal effect on their performance. X‐ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy and cross‐sectional field‐emission scanning electron microscopy (FE‐SEM) studies before and after AST suggest lesser deformation in catalyst layer and catalyst particles for Pt/GrC cathodes in relation to Pt/Non‐GrC cathodes, reflecting that graphitic carbon‐support resists carbon corrosion and helps mitigating aggregation of Pt‐particles.     

Electrolytic preparation of cyclic multilayer Zn–Ni alloy coating using switching cathode current densities

Cyclic multilayer alloy (CMA) coating of Zn–Ni was developed on mild steel using single bath technique, by proper manipulation of cathode current densities. The thickness and composition of the individual layers were altered precisely and conveniently by cyclic modulation of cathode current densities. Multilayer coatings, having sharp change in compositions were developed using square current pulses. Gelatin and sulphanilic acid (SA) acid were used as additives. Laminar deposits with different configurations were produced, and their corrosion behaviors were studied, in 5% NaCl solution by electrochemical methods. It was observed that the corrosion resistance of CMA coating increased progressively with number of layers (up to certain optimal numbers) and then decreased. Cyclic voltammetry study demonstrated the role of gelatin and SA in multilayer coating. The coating configuration has been optimized for the peak performance against corrosion. The substantial decrease of corrosion rate, in the case of multilayer coatings was attributed to the changed intrinsic electric properties, evidenced by Electrochemical Impedance Spectroscopy (EIS) study. The surface morphology and its roughness were examined by Atomic Force Microscopy (AFM). The surface and cross-sectional view of coatings were examined, using Scanning Electron Microscopy (SEM). X-ray photoelectron spectrum (XPS) study was carried out for surface analysis. The relative performance of pure Zn, monolithic and CMA coatings were compared and discussed.     

The tribocorrosion behaviour of YSZ coating deposited on stainless steel substrate in 3.5 wt% NaCl solution

The YSZ coating was applied to 304 stainless steel substrate by atmospheric plasma spraying technology, and its electrochemical and tribological properties in 3.5 wt% NaCl solution were studied. In electrochemistry, under the action of cathode and anode potential, observe the changes of corrosion current density and EIS before and after wear. The results show that the YSZ coating has a very low corrosion current density during wear and corrosion compared to 304 stainless steel, and after the condition of the anode potential is applied, the effect of friction on the electrochemical impedance of the YSZ coating is very low, while the 304 stainless steel Impedance performance decreases; In terms of tribology, the friction coefficient of 304 stainless steel in 3.5 wt% NaCl solution is easily affected by potential, and the friction coefficient of YSZ coating relative to 304 stainless steel only changes under high potential. As the potential increases, the material volume loss of 304 stainless steel and YSZ coating increases linearly. From the data, the volume loss caused by the corrosion and wear of 304 stainless steel is much higher than that of YSZ coating.     

A reactive-sputter-deposited TiSiN nanocomposite coating for the protection of metallic bipolar plates in proton exchange membrane fuel cells

To meet the needs of corrosion resistance and electrically conductivity for metallic bipolar plates that are employed in proton exchange membrane fuel cells (PEMFCs), a TiSiN nanocomposite coating was fabricated on to a Ti–6Al–4V substrate using reactive sputter-deposition through the double cathode glow discharge plasma technique. The microstructure of the TiSiN coating comprised nanocrystallite TiN grains embedded in an amorphous Si₃N₄ matrix. Electrochemical measurements were employed to investigate the corrosion behavior of the TiSiN coating in the simulated operating environments of a PEMFC, specifically 0.5 M H₂SO₄ solution containing different HF concentrations (namely 2, 4 and 6 ppm) at 70 °C pumped with H₂ at the anode and air at the cathode. With increasing HF concentration, a higher corrosion current density and lower corrosion potential were observed from both the coating and the uncoated substrate, indicating that the addition of HF accelerated their corrosion rates under these conditions. Compared to the uncoated substrate, the TiSiN coating showed a markedly higher corrosion resistance at all HF concentrations. The passive film that formed on the TiSiN coating, with a resistance of the order of magnitude of ~10⁷ Ω cm², displayed good electrochemical stability and was less affected by changes in HF concentration. For the TiSiN coating, the values of interfacial contact resistance (ICR) were 14.7 mΩ cm⁻² and 18.3 mΩ cm⁻², respectively, before and after 2.5 h potentiostatic polarization with 6 ppm HF under cathodic conditions under a compaction pressure of 140 N cm⁻². Both values are much lower than those for the bare substrate. Moreover, the TiSiN coating was shown to improve the hydrophobicity of Ti–6Al–4V that would help facilitate water management in the PEMFC operating environment. This coating, which exhibited excellent corrosion resistance, electro-conductivity and hydrophobicity, is therefore a promising material for protecting metallic bipolar plates from corrosive attack.     

Improved corrosion resistance of pulse plated nickel through crystallisation control

When electrodeposition of nickel is used for corrosion protection of steel two aspects are important: the porosity of the coating and the resistance against corrosion provided by the coating itself. Using simple pulsed current (PC) plating, the size of the deposited crystals can be significantly smaller, thereby reducing porosity correspondingly. This usually also leads to improved hardness of the coating. Introducing pulse reversal (PR) plating, the most active crystals are continuously dissolved during the anodic pulse, providing a coating with improved subsequent corrosion resistance in almost any corrosive environment. This correlation between film texture and corrosion resistance will be discussed.     

双向脉冲电镀纳米级镍镀层耐腐蚀性能研究

用直流电沉积法制备了普通光亮镍镀层,同时用双向脉冲电镀制备了纳米级镍镀层。用X射线衍射(XRD)、扫描电镜(SEM)等方法研究了镀层的晶粒尺寸、组织结构和表面形貌,通过孔隙率测定、盐雾试验、静态浸泡腐蚀失重试验和电化学方法等测试了镀层的耐蚀性能。结果表明,采用双向脉冲电流制备的纳米级镍镀层的耐蚀性明显优于普通直流镍镀层。     

脉冲电沉积纳米镍-碳化硅复合镀层的性能

分别采用直流(DC)和换向脉冲电流(PRC)电沉积法制得纳米Ni-SiC复合镀层。采用X射线衍射仪、扫描电镜、能谱仪对比研究了纯Ni镀层和Ni-SiC复合镀层的微观结构、宏观残余应力、表面形貌及成分。用浸泡法研究了不同镀层在3.5%(质量分数)NaCl和10%(体积分数)H2SO4溶液中的腐蚀行为。结果表明,脉冲电沉积能改变镀层的微观结构,有效提高镀层硬度,降低宏观残余应力。脉冲电沉积所得到的纯Ni镀层和纳米Ni-SiC复合镀层在3.5%NaCl及10%H2SO4溶液中的耐蚀性均优于直流镀层。脉冲镀层在3.5%NaCl溶液中受腐蚀很轻,主要腐蚀形态为点蚀,而在10%H2SO4溶液中,SiC粒子作为增强相使镀层的耐腐蚀性进一步提高。     

Corrosion behavior of composition modulated multilayer Zn–Co electrodeposits produced using a single-bath technique

Composition modulated alloy (CMA) electrodeposits of Zn–Co were produced from acid chloride baths by the single-bath technique. Their corrosion behavior was evaluated as a function of the switched cathode current densities and the number of layers. The process was optimized with respect to the highest corrosion resistance. Enhanced corrosion resistance was obtained when the outer layer was slightly richer with cobalt. At the optimum switched current densities 40/55 mA cm⁻², a coating with 600 layers showed ~6 times higher corrosion resistance than monolithic Zn–Co electrodeposit having the same thickness. The CMA coating exhibited red rust only after 1,130 h in a salt-spray test. The increased corrosion resistance of the multilayer alloys was related to their inherent barrier properties, as revealed by Electrochemical Impedance Spectroscopy. The corrosion resistance was explained in terms of n-type semiconductor films at the interface as supported by Mott–Schottky plots.