The Electropolishing of Nickel in Urea-Ammonium Chloride Melts

Nickel may be electropolished in melts based on urea containing 5–20% w/w of ammonium chloride and 0–3·5% w/w of anhydrous nickel chloride, held at 120–135°C. The optimum applied potential difference across a cell with a vertical anode spaced 1 cm. from the cathode is 2·5–3 v., and the optimum current density is 0·15—0·4 amp./cm.². Considerably higher current densities also give polishing but lead to much gas evolution and increase the tendency to pitting; still higher current densities produce a grey film on the metal surface. The melts age with time, so that the optimum current density falls, and become useless after about three days at temperature; they are partially restored by the addition of fresh urea.

There is an induction period before polishing begins (shorter the higher the current density) during which the metal dissolves normally; the onset of polishing is determined by a rise of anode potential (1·5–1·8 v.) similar to that found in anodic passivation. The evidence suggests that the rise is due, as in passivation, to the formation on the anode surface of a compact film, which during the polishing process, however, dissolves at its outer surface as fast as it is formed. It is suggested that this mechanism is general in electro-polishing, and it is shown that it can account for the avoidance of etching characteristic of the process.     

Behaviour of different bare and anodised aluminium alloys in the atmosphere

Exposure tests in natural atmospheres are an indispensable means for determining the behaviour and durability of metallic materials in the atmosphere. The corrosion behaviour of bare aluminium and anodised aluminium with three different coating thicknesses has been evaluated for two years' exposure in two natural atmospheres of very different corrosivities: one urban and the other marine. Several techniques have been used to evaluate changes in the specimens during exposure, but special attention is paid to the direct measurement of corrosion by gravimetry and its indirect estimation by the comparatively much more sensitive electrochemical impedance spectroscopy (EIS) technique. The results show that if no demands are placed on the conservation of its appearance, aluminium may be used without protection even in atmospheres of medium or high corrosivity. The anodising and sealing of aluminium alloys, above an ill-defined minimum thickness threshold, is an appropriate solution to prevent localised corrosion of aluminium and to conserve its appearance, even in aggressive atmospheres.     

A comparative study of corrosion performance of sealed anodized layers of conventionally colored and interference-colored aluminium

The nanostructure of aluminium anodized layer was modified in phosphoric acid to induce light-interference colors through electrocoloring using nickel pigments. After a mixed sealing procedure, the corrosion performance of the interference-colored anodized layer was evaluated using Tafel polarization and electrochemical impedance spectroscopy. The results were compared with those obtained for conventionally colored anodized layer. The modification made the mixed sealing of subsequent colored layer less effective. The steam-sealing was found to be more effective for sealing the interference-colored anodized layer. For effectively sealed layers, the porous layer plays an additional role besides the barrier layer in determining the corrosion performance.     

Exfoliation corrosion and electrochemical impedance spectroscopy of an Al‐Li alloy in EXCO solution

The exfoliation corrosion and electrochemical impedance spectroscopy (EIS) of an Al‐2.8%Cu‐1.5%Li‐0.3%Mg‐0.3%Zn‐0.3%Mn‐0.15%Zr alloy with various aging states in EXCO solution were investigated. The equilibrium precipitates at grain boundaries are anodic to the alloy base at their adjacent periphery. With prolonging aging time, the amount and the size of the equilibrium precipitates at grain boundaries are increased, resulting in an enhanced susceptibility to exfoliation corrosion. At the beginning of immersion in EXCO solution, the EIS plot of the alloys is composed of a capacitive arc in the high frequency range and an inductive loop in the low frequency range. As immersion time is increased, two capacitive arcs appear in the high‐mediate and mediate‐low frequency ranges respectively and the appearance time of two capacitive arcs could be an indication of the speed of localized corrosion development in EXCO solution. The longer appearance time of two capacitive arcs of the under‐aged alloy indicates its slower localized corrosion development.     

The Activation and Metallisation of Plastic Components for Use as Mass Produced Electroforming Masters

A method of activating Medium Impact Polystyrene by using a plasma is described. The activated component is metallised by a chemical silver spray method, which has been shown to be more reliable than electroless metallisation for the continuous deposition of a metallic coating on a complex shaped component. It has been found that the thickness of the silver film is less than 0.2μm, and is deposited with an overall efficiency of less than 10%. Consideration is given to the plasma activation conditions as well as the mixing techniques and operating conditions of the silver spray solutions.     

Analysis of electrochemical noise obtained from pure aluminium in neutral chloride and alkaline solutions

The present work involves the analysis of electrochemical noise obtained from pure aluminium during breakdown of the oxide film in aqueous neutral chloride solution and hydrogen evolution in alkaline solution. Since the noise data involve information on such stochastic processes as uniform corrosion, breakdown of the oxide film and hydrogen evolution, they were analysed based upon a stochastic theory: the plot of the cumulative probability numerically calculated was first transformed from the domain of the frequency of events to the mean free time domain and then, the Weibull probability plot was constructed by fitting Weibull distribution function to the calculated cumulative probability. Finally, the conditional event generation rate was numerically determined as a function of time. From two linear regions in one Weibull probability plot, it was concluded that breakdown of the oxide film and hydrogen evolution, respectively, were clearly distinguished from uniform corrosion in the Weibull probability plot. In addition, the roles of anion additives in breakdown of the oxide film and hydrogen evolution were also discussed in terms of the distribution of the mean free time and the conditional event generation rate.     

Influence of interface chemistry and network density on interfacial ion transport kinetics for styrene/acrylate copolymer coated zinc and iron substrates

n-Butyl acrylate/styrene copolymer films were applied on iron and zinc surfaces. The kinetics of interfacial ion transport and cathodic delamination were tracked by in situ Scanning Kelvin Probe (SKP) measurements. A destabilisation of the interface was detected for latex network structures with an increased degree of cross-linking. In contrast, a reduction of the average macromolecular chain length resulted in films with higher resistance to interfacial ion transport. No comparable effect of the polymer structure was detectable when latex films were applied on zinc. Calculated coefficients for water diffusion through the bulk polymer partially supported the SKP results obtained on iron.     

Polyacrylic acid as a corrosion inhibitor for aluminium in weakly alkaline solutions. Part I: Weight loss, polarization, impedance EFM and EDX studies

This part is devoted to study the influence of three selected polyacrylic acids (PAAs) with different molecular weights (PAA1 = 1800, PAA2 = 11,000 and PAA3 = 14,000 g mol⁻¹) on the corrosion inhibition of Al in weakly alkaline solutions (pH 8 and 10) at 30 °C. Measurements were conducted under different experimental conditions using chemical (weight loss) and electrochemical (potentiodynamic polarization and impedance) techniques, complemented with ex situ energy dispersive X-ray (EDX) examinations of the electrode surface. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented here. The results demonstrated that these polymers inhibit the alkaline corrosion of Al. The inhibition effect of these polymers is due to their adsorption on Al surface. The isoelectric point (IEP) of aluminium oxide (pH 9) seems to be an important factor controlling corrosion inhibition and adsorption of the three polymers. The three polymers inhibit the corrosion reaction of aluminium excellently at pH 8, but less effectively at pH 10. Polarization measurements showed that the three polymers act as mixed-type inhibitors. The inhibition efficiencies of these polymers increase with increasing concentration, molecular weight and immersion time. Results obtained from the chemical and electrochemical measurements are in good agreements.     

Correlations Between Growth Kinetics and Microstructure for Scales Formed by High-Temperature Oxidation of Pure Nickel. I. Morphologies and Microstructures

The morphology and microstructure of NiO scales grown during oxidation of high-purity nickel were investigated. The oxidation tests performed between 450 and 1200°C in pure oxygen at atmospheric pressure were stopped at given scale thicknesses ranging from 1 to 70 m. The specific specimen preparation and test procedure used in this work led to very good test reproducibility. The morphological and microstructural evolution of NiO scales are described by temperature-thickness maps. The scale morphology can be faceted or cellular. In addition, the growth of NiO platelets was observed in a specific temperature-thickness range. The microstructure of oxide scales can be simplex compact, simplex porous, or duplex. An important effect of substrate orientation was also observed, independent of the test temperature and scale thickness.     

Flotation Separating Rutile from Calcium and Silicon Gangue Minerals

Rutile is an imPortant drineral in extractionmetal titanium and for mdeng titanium white(dioxide)[l]. Natural rutile comPoses of sea-shore placer and natural ores. Relatively, Chinais short of seashore placer which contains richrutile[2-], so it is very necessary to developand use the natural ores resource.There are always certain amounts of calciumand silicon gangue hanerals associated withnatural rutile ores, which is a vital restrictingfactor of raising the grade of rutile concentrates[5].…     

马来酸-丙烯酸共聚物络合超滤处理含锰废水(英文)

用马来酸-丙烯酸共聚物(PMA-100)作络合剂,采用PVB中空纤维膜,研究络合-超滤处理含锰废水。测定了高聚物的羧基含量以及Mn(II)与PMA-100的络合反应速率,研究聚合物与重金属质量比(P/M)、pH、外加盐浓度等因素对锰离子截留率(R)和膜通量(J)的影响。结果表明:高聚物中羧基含量为9.5 mmol/g,对Mn(II)质量浓度为10 mg/L的模拟废水,在pH=6.0时,Mn(II)与PMA-100的络合在5 min内基本可完成,络合率达99.6%。在一定P/M下,pH在2.5~7.0范围内,截留率和膜通量均随着pH的增加而增大;在一定pH下,截留率随着P/M的增加而增加,但膜通量基本不变。外加盐的存在使截留率下降,在同样离子强度下,CaCl2的影响远大于NaCl的。     

从炉灰、酸泥中回收并提取高纯铂、钯的工艺实验

通过对3批试料的生产实验,介绍了从炉灰、酸泥中回收和提取高纯铂、钯的工艺流程.实验过程中,经酸浸、置换、离子交换分离大部分杂质元素,再调整铂、钯化合价态,用氯化铵沉淀铂从而达到铂、钯的有效分离.实践证明,该工艺流程简单,实用性强,分离效果好,回收率高,产品质量稳定.     

野罂粟总生物碱对急性气管-支气管炎止咳效应的探索性临床研究

目的: 评价野罂粟总生物碱制剂对急性气管-支气管炎肺气上逆证的止咳效应。方法: 随机、双盲、安慰剂平行对照、叠加试验(add-on design) 设计。观察急性气管-支气管炎肺气上逆证共89 例, 其中野罂粟总生物碱组45 例, 安慰剂对照组44 例。结果: 试验组和安慰剂组服药后咳嗽明显减轻者分别占75.56 %和77.27 %(P=0.8487), 咳嗽明显减轻者的减轻时间分别为19.55±18.57 和25.27±19.60 h (P=0.1993);d 3 咳嗽消失率分别为33.33 %和36.36 %(P=0.7642);咳嗽记分值平均等级分别下降3.53 和4.16(P=0.2786) 。结论: 急性气管-支气管炎中度及重度咳嗽少痰肺气上逆证患者在使用头孢克洛缓释胶囊治疗的基础上, 野罂粟总生物碱制剂没有明显的止咳、平喘作用。