Identification of structural entities in NdF3-LiF melts with cryoscopic method

Nd-F species in NdF3-LiF melts were studied using cryoscopic method.Liquidus temperatures of melts of various compositions were determined by differential thermal analysis(DTA).Based on the different model calculations,NdF4- was identified as the most likely Nd-F entity in the melts in which the mole fraction of NdF3 was lower than 20%,considering only one single Nd species in the melt,and which was formed in accordance with Temkin model or Flood model.Then,activities of different components in the melts were researched.The results show that activity of LiF decreases,and that of NdF3 increases with increasing the mole fraction of NdF3.The value of activity coefficient of NdF3 is higher than 1,and that of LiF is lower than 1.     

Anodic oxide films on nickel electrode in borate solutions

The effect of different concentrations of sodium borate, current densities, pH and temperature on the anodic oxidation of nickel was studied using galvanostatic polarization technique. The anodic potential-time curves showed four regions: the charging of the anodic double layer, an arrest corresponding to anodic dissolution and/or oxide film formation, linear rise in the potential due to the formation of barrier oxide film and finally deviation from linearity to reach steady-state potential value attributed to oxygen evolution reaction. The duration time of the arrest decreases with increasing current density and concentration of borate anion while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with increasing pH and temperature of the solution while the rate of oxide film formation decreases. Increasing the borate concentration and pH of the solution shifted the starting potential of the arrest towards more negative values. Linear relationships were obtained between the starting potential of the arrest and both borate concentration and pH.     

钕电解阳极产物的研究

用Orsat气体分析器和色谱－质谱联用仪研究了正常电解和发生阳极效应时钕电解的阳极气体成分,探讨了温度,阳极电流密度等对阳极气体组成的影响,计算了钕电解的总反应方程式,结果表明,正常电解时钕电解的阳极气体主要成分为CO,另有少量CO2,气体组成与铝电解有所不同,电解温度升高,CO的相对含量增多,电流密度增加,CO的相对含量减少,发生阳极效应时,利用色谱－质谱联用仪首次检测出阳极气体中所含氟碳化合物为CF4。     

计时电流法研究Pt/YSZ电极烧结条件对其性能的影响

借助计时电流法和扫描电镜,研究Pt/YSZ电极烧结条件对其性能的影响。结果表明,随着电极在850 ℃烧结时间的增加,电极孔隙减少,孔径增大,阳极电势阶跃极化后的稳定电流密度值先增大后减小,烧结时间为10 h时所制电极稳定电流密度值最大,活性最强;与烧结时间对电极性能的影响相似,当电极烧结时间为1 h时,烧结温度升高也会使得电极孔隙减少,孔径增大,阳极电势阶跃极化后的稳定电流密度值亦先增大后减小,烧结温度为1100 ℃时所制电极稳定电流密度值最大,性能最好。     

Nickel electrodeposition from leaching solution containing ammonia and chloride

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Corrosion of 304 stainless steel exposed to nitric acid-chloride environments

In an effort to examine the combined effect of HNO₃, NaCl, and temperature on the general corrosion behavior of 304 stainless steel (SS), electrochemical studies were performed. The corrosion response of 304 SS was bifurcated: materials were either continuously passive following immersion or spontaneously passivated following a period of active dissolution. Active dissolution was autocatalytic, with the corrosion rate increasing exponentially with time and potential. The period of active corrosion terminated following spontaneous passivation, resulting in a corrosion rate decrease of up to five orders of magnitude. The length of the active corrosion period was strongly dependent on the solution volume-to-surface area ratio. This finding, coupled with other results, suggested that spontaneous passivation arises solely from solution chemistry as opposed to changes in surface oxide composition. Increasing NaCl concentrations promoted pitting, active dissolution upon initial immersion, a smaller potential range for passivity, longer active corrosion periods, larger active anodic charge densities preceding spontaneous passivation, and larger corrosion current and peak current densities. In contrast, intermediate HNO₃ concentrations promoted active dissolution, with continuous passivity noted at HNO₃ concentration extremes. During active corrosion, increased HNO₃ concentrations increased the anodic charge density, corrosion current density, and peak current density. The time required for spontaneous passivation was greatest at intermediate HNO₃ concentrations. Susceptibility to pitting was also greatest at intermediate HNO₃ concentrations: the pit initiation and repassivation potentials decreased with increasing HNO₃ concentration until the HNO₃ concentration exceeded a critical concentration beyond which susceptibility to pitting was entirely eliminated. Increasing solution temperature increased the susceptibility to both pitting and active dissolution.     

Electrocatalysis of carbon anode in aluminium electrolysis

The anodic overvoltage of the carbon anode in aluminum electrolysis is of the order of 0.6 V at normal currem densities. However, it can be reduced somewhat by doping the anode carbon with various inorganic compounds. A new apparatus was designed to improve the precision of overvoltage measurements. Anodes were doped with MgAl2O4 and AlF3both by impregnation of the coke and by adding powder, and the measured overvoltage was compared with that of undoped samples. For prebake type anodes baked at around 1150℃, the anodic overvoltage was reduced by 40-60 mV,and for Soderberg type anodes, baked at 950 ℃, by 60-80 mV.     

Über den Einbau von Phosphor in Aluminiumhydroxide und anodische Aluminium-Oxidschichten

The Incorporation of Phosphorus into Aluminium Hydroxides and Anodic Aluminium Oxide Films The in corporation of phosphorus during the anodic oxidation of high purity aluminium in phosphoric acid solutions increases with formation voltage (20 V to 100 V) and formation temperature. There is a minimum of phosphorus incorporation at a current density of 5 mA/cm². For this case, a dependence of porous oxide layer formation and an impurity ion incorporation with current density is discussed. Aluminium covered with a hydroxide film produced by a pretreatment with hot water before anodic oxidation exhibits phosphorus contents independent of formation voltage and current density but increasing with temperature. Hence, it follows, that no porous layer is formed and that phosphorus is incorporated predominantly by chemical reaction of hydroxide and phosphoric acid. The concentration of phosphorus is determined by using the radiotracer method.     

铝阳极氧化膜的微观结构及沸水封闭处理对膜层显微硬度的影响

通过阳极氧化在铝合金表面获得稳定的阳极氧化膜,并对膜层进行沸水封闭处理,采用扫描电子显微镜(SEM)、电化学阻抗谱(EIS)等分析手段研究了氧化电流密度以及封闭处理对膜层显微硬度的影响。结果表明:随着电流密度的增加,铝合金阳极氧化膜的显微硬度先升高,后降低;沸水封闭会导致铝阳极氧化膜的显微硬度下降;铝阳极氧化膜表面形貌的优劣、多孔层的组织结构和屏蔽性与膜层显微硬度密切相关。     

Electrochemical behavior and the rate of general corrosion of NiAl intermetallic compound in the unbuffered sodium chloride solutions

Highly reproducible Tafel anodic and cathodic plots were obtained on NiAl intermetallic compound in the neutral and nearly neutral unbuffered NaCl solutions. The corrosion potentials and corrosion current densities were determined by the Tafel extrapolation technique at various pH values and concentrations of NaCl. The corrosion current density and Tafel slopes were determined by fitting the equation for the corrosion current density, which involves both anodic and cathodic reactions, to the experimental anodic and cathodic polarization curves in the pre-Tafel region of polarization curves. The results obtained by two methods are in good agreement.     

Wachstum und Auflösung anodisch erzeugter Oxidschichten auf Titan

Growth and dissolution of anodically obtained oxide layers on titanium Oxide films were grown by anodic polarization of titanium in various aqueous electrolytes. The field strength derived from film thickness and voltage is linearly related to the logarithm of the total current density. The current efficiency for film formation depends upon current density, pH-value, and film thickness. The dielectric constant of the film decreases with field strength from ε = 110 to ε = 7, but rises again at high field strengths and thick films. The dissolution rate of anodic oxide films on titanium was investigated as a function of pH-value, concentration of chloride, and temperature, respectively. Aging of the films in distilled water causes the dissolution rate to decrease by up to 3 order of magnitude.     

MEASUREMENT OF ANODIC OVERVOLTAGE BY AMODIFIED CURRENT INTERRUPTION METHOD IN CRYOLITE-ALUMINA MELTS

１ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｈｅｅｌｅｃｔｒｏｌｙｔｉｃｐｒｏｄｕｃｔｉｏｎｏｆａｌｕｍｉｎｉｕｍ，ｔｈｅｃｅｌｃｏｎｓｉｓｔｓｏｆａｃａｒｂｏｎａｎｏｄｅａｎｄａｎａｌｕｍｉｎｉｕｍｍｅｔａｌｃａｔｈｏｄｅ．Ｔｈｅｄｏｍｉｎａｎｔｐｏｔｅｎｔ...     

AlF3添加剂和焙烧温度对铝电解炭阳极过电位的影响

在实验室制备各类AlF3掺杂试验阳极，在测试其基本物理化学性能的基础上，采用“改进断电流法”进行阳极过电位测试，研究AlF3添加剂和阳极焙烧温度对阳极过电位的影响。结果表明：在一定条件下，阳极中添加AlF3既可降低阳极的空气／CO2反应活性，也可降低阳极过电位；受高温脱S等因素的影响，阳极的电化学活性及其空气／CO2反应活性并未随着焙烧温度的提高相应降低。     

Effect of phosphate ions on electrochemical behaviour of copper in sulphate solutions

Abstract

The effect of phosphate ions on the corrosion behaviour of copper in sulphate solutions was investigated at different temperatures (293, 313, 333, and 353 K) and at different pH values (pH = 2·1, 7·2, and 12·3). A three electrode electrochemical technique was used for the measurements, using a saturated calomel electrode (SCE) for reference purposes. Both anodic and cathodic polarisation curves were established, from which the anodic and cathodic Tafel constants were determined. Corrosion potentials were determined by extra trapolation of the anodic and cathodic Tafel lines to the point of zero current density. The results showed that for a pH value of 2·1, the corrosion rate of copper showed a marked tendency to increase with increasing temperature in solutions containing either sulphate alone or sulphate plus phosphate. However, at pH values of 7·2 and 12·3, this tendency became less pronounced in solutions containing sulphate alone and in solutions containing sulphate plus phosphate together, max imum corrosion rates were greatly reduced and showed less tendency to increase with increasing temperature. Anodic and cathodic reaction mechanisms are proposed to explain the observations for the corrosion of copper.     

Role of ClO4 in breakdown of tin passivity in NaOH solutions

The anodic behaviour of a tin electrode in NaOH solutions containing different concentrations of NaClO₄ was studied by employing potentiodynamic, potential transient under constant current density methods and complemented with scanning electron microscopy (SEM). In perchlorate-free NaOH solutions, the E/i response exhibits active/passive transition. The active region involves two anodic peaks corresponding to the formation of Sn(II) and Sn(IV) species respectively. The permanent passive layer is duplex and consists of SnO and SnO₂. Additions of NaClO₄ to the alkali solution, accelerates the active dissolution of tin and tends to breakdown the duplex passive layer at a certain breakdown potential. SEM examination confirms the occurrence of film breakdown. The breakdown potential decreases with an increase in ClO₄⁻ concentration, but increases with increasing both OH⁻ concentration and scan rate. The potential-time transients display that the incubation time for pit initiation decreases with increasing both ClO₄⁻ concentration and anodic current density.     

高压电子铝箔阳极电解扩孔行为

研究发孔铝箔在盐酸和硝酸溶液中的阳极极化行为与扩孔特性的关系。阳极扩孔的基本条件是将发孔箔的内、外表面都控制在钝化状态下。在盐酸溶液中,阳极极化时存在点蚀电位和一个较小的钝化电位区,当扩孔施加的电流密度大于临界点蚀电流密度时,铝箔表面发生二次发孔,导致形成孔蚀族与并孔,腐蚀箔厚度减薄,比电容显著降低。在硝酸溶液中,阳极极化时存在一个宽阔的钝化电位区,因此硝酸扩孔比盐酸扩孔容易控制,不会发生二次发孔。提高盐酸或硝酸浓度与温度均可以增大最大维钝电流密度,即增大扩孔的最大电流密度,提高扩孔的生产效率。     

不同电解温度下阳极氧化铝薄膜纳米孔的自组织过程

研究温度对阳极氧化铝薄膜纳米孔自组织过程的影响.使用环境扫描电镜(ESEM)研究了铝试样在硫酸、草酸、磷酸溶液中,于不同电解温度下阳极氧化形成的氧化铝薄膜形貌.通过分析阳极氧化时电流密度与时间关系曲线,研究了温度对阳极氧化铝薄膜纳米孔自组织过程的影响.提出降低电解温度能够缩短纳米孔自组织过程的时间,是由于降低电解温度增大了纳米孔内表面的表面张力.并且提出在不同的电解质溶液中,电解温度对纳米孔自组织过程的影响程度不同,电解温度对纳米孔自组织过程的影响以在硫酸溶液中最敏感,草酸次之,在磷酸溶液中的影响最小.     

Determination of ohmic/voltage drop and factors influencing anodic overvoltage of carbon anodes in Na_3AlF_6-Al_2O_3 based melts

1　INTRODUCTIONAlthoughtheanodicprocessandmeasurementofanodicovervoltageincryolite aluminameltshavebeenthesubjectsofnumerousinvestigations ,problemssuchasthereactionmechanismandtherate deter miningstepoftheanodereactionarestillcontrover sialandneedclarification .Theexperimentalinforma tionischaracterisedbymajordivergenceregardingthemagnitudeandthetypeofanodicovervoltage ,whichismostlikelycausedbythefollowingfac tors[16 ] :1)Theanodicovervoltagediffersamongtheva rietyofcarbonmaterials,sucha…     

The effect of shock deformation on the anodic polarization behavior of polycrystalline nickel in 1N sulphuric acid

The results of anodic potentiostatic polarization of shocked nickel polycrystals in 1N H₂SO₄ are reported. With increasing shock pressure, passivation and Flade potentials shift in the cathodic direction, the critical current density decreases, and the passive current density decreases. These effects are discussed in terms of substructural changes accompanying shock loading.     

Electrochemical corrosion of X65 pipe steel in oil/water emulsion

The electrochemical corrosion behavior of X65 pipeline steel in the simulated oil/water emulsion was investigated under controlled hydrodynamic and electrochemical conditions by rotating disk electrode technique. Results demonstrated that mass-transfer of oxygen plays a significant role in the cathodic process of steel in both oil-free and oil-containing solutions. Electrode rotation accelerates the oxygen diffusion and thus the cathodic reduction. The higher limiting diffusive current density measured in oil-containing solution is due to the elevated solubility of oxygen in oil/water emulsion. The anodic current density decreases with the increase of electrode rotating speed, which is attributed to the accelerated oxygen diffusion and reduction, enhancing the steel oxidation. Addition of oil decreases the anodic dissolution of steel due to the formation of a layer of oily phase on steel surface, increasing the reaction activation energy. The steel electrode becomes more active at the elevated temperature, indicating that the enhanced formation of oxide scale is not sufficiently enough to offset the effect resulting from the enhanced anodic dissolution reaction kinetics. The corrosion reaction mechanism is changed upon oil addition, and the interfacial reaction is activation-controlled, rather than mass-transfer controlled. When sand particles are added in oil/water emulsion, there is a significant increase of corrosion of the steel. The presence of sands in the flowing slurry would impact and damage the oxide film and oily film formed on the steel surface, exposing the bare steel to the corrosive solution.