A Laboratory Technique for the Electrodeposition of Manganese on Other Metals

A technique for the deposition of bright smooth manganese plates is described, utilizing an electrolyte containing 112 g./l. of MnSO₄.4H₂O, 139 g./l. of (NH₄)₂SO₄, 1 g./l. of citric acid and small additions of hydroxylamine sulphate, in a divided cell with bagged carbon anodes. The best results were obtained at temperatures of 20–32°C, with a cathodic current density of about 23 amps./dm.²; moderate agitation of the catholyte, and water-cooling, are desirable. The initial pH of the solution is adjusted to 5; that of the catholyte rises to 8·5 during deposition.

Only α-manganese could be found in the deposits, which had hardness between 550 and 725 DPN. The deposits soon became tarnished with a brown film. Tests have shown that they give cathodic protection to steel and aluminium.     

Corrosion stability of electrodeposited cyclic multilayer Zn–Ni alloy coatings

Abstract

This paper reports on a study of electrodeposition and characterisation of cyclic multilayer coatings of Zn–Ni alloy from a sulphate bath. Cyclic multilayer alloy coatings were deposited on mild steel through the single bath technique by appropriate manipulation of cathode current densities. The thickness and composition of the individual layers of the CMA deposits were altered precisely and conveniently by cyclic modulation of the cathode current during electrodeposition. Multilayer deposits with sharp change in composition were developed using square current pulses, using thiamine hydrochloride and citric acid as additives. Laminar deposits with different configurations were produced and their corrosion behaviours were studied by AC and DC methods in 5%NaCl solution. It was observed that the corrosion resistance of the CMA coating increased progressively with the number of layers (up to certain optimal numbers) and then decreased. The decrease in corrosion resistance at high degree of layering was attributed to interlayer diffusion due to less relaxation time for redistribution of metal ions at cathode during deposition. The coating configurations have been optimised for peak performance of the coatings against corrosion. It was found that CMA coating developed at cyclic cathode current densities of 3·0/5·0 A dm^?2 with 300 layers showed the lowest corrosion rate (0·112×10^?2 mm/year) which is ～54 times better than that of monolithic Zn–Ni alloy, deposited from the same bath. The protection efficacy of CMA coatings is attributed to the difference in phase structure of the alloys in successive layers, deposited at different current densities, evidenced by X-ray diffraction analysis. The formation of multilayers and corrosion mechanism were examined by scanning electron microscopy.     

Preparation and properties of Os–Ir–Al alloy for impregnated tungsten cathodes

Os–Ir–Al alloy was fabricated by powder metallurgy technique.IrAl and OsIr interalloys were synthesized to reduce the Al evaporation and ensure the composition of the ternary alloy.Analysis on microstructures shows that each component is distributed homogeneously,and the green density reaches 94.9%.Ba–W cathodes with Os–Ir–Al alloy magnetic sputtered on the tips are prepared and directly current density tests are carried out on these cathodes.It is found that at 1,050℃,the average zero field emission density of the cathode reaches up to 20 Aácm-2.The improvements of cathodic current density and stability may indicate the prosperous application of Os–Ir–Al alloy on cathode.     

The Electrodeposition of Cobalt–Chromium Alloys from Sulfate–Oxalate Solutions

The kinetics of separate and concurrent discharge of cobalt and chromium ions from sulfate–oxalate solutions is studied. Cobalt–chromium alloys with the cobalt content of 4 to 94% and carbon content of 1 to 4% are obtained. At a concurrent discharge of chromium and cobalt ions, the deposition potential of chromium is shifted by 150 to 200 mV in the positive direction. The shift depends on the current density and cannot be accounted for by the energy of mixing of the components. The alloying of chromium with cobalt decreases the overpotential of the hydrogen discharge. The codeposition with chromium did not decelerate the reduction of cobalt ions in contrast to the electrodeposition of nickel. The main reasons for the difference between the effect the alloying with chromium produces on the electrochemical reduction of nickel and cobalt, which are similar in their properties, are considered.     

Electrochemical Properties of Pulse Plating Amorphous Ni-Mo-W Alloy Coating in Alkaline Medium

采用脉冲电镀技术获得了高活性Ni-Mo-W析氢合金阴极。以析氢反应过电位为考察指标,确定了脉冲镀Ni-Mo-W合金的最佳电镀条件,如Na2WO4·2H2O浓度、平均电流密度和占空比等。同时,系统研究了Mo和W含量对Ni-Mo-W合金镀层成分和组成的影响规律。结果表明,在二元合金中添加W能有效提高电极的析氢反应活性(η200＝80 mV);非晶态Ni-Mo-W合金的组织结构主要取决于Mo含量;与非晶态Ni-Mo合金镀层相比,Ni-Mo-W合金析氢阴极的电化学稳定性得到一定程度的提高。     

Ti_2Ni HYDRIDE COMPOSITE AS HYDROGEN CATHODE FOR ALKALINE WATER ELECTROLYSIS

1.IntroductionHydrogenasanenergyst0ragemediumhasattractedw0rldwideinterest,asitisacleanandfullyrecycleablesubstancewithapracticallyunlimitedsupplyThehydr0genenergy8ystemc0nsistsmainlyofthreepr0cesses:theproduction,transp0rt0rstorage,andutilizati0n0fhydr0gen.Large-scale,cheappr0duction0fhydr0genis0neofthekeylinksinthec0urseofdevel0pingthenovelhydr0genenergysystem.Waterelectrolysisisconsid-eredanimp0rtantmethodforlarge-scalepr0ducti0nofhydr0gent0day-However,loweringtheelectrolyticenergyconsumpt…     

The Electrodeposition of Iron-Zinc Alloys

Methods are given for depositing iron-zinc alloys of 3 to 90% zinc content from sulphate baths and attention is drawn to the useful properties of these deposits. Under a given set of plating conditions the iron-zinc ratio in the deposit is directly proportional to that in the bath. Lowering either the current density or the pH raises the zinc content of the deposit. Some baths have a levelling action, since bright deposits can be prepared from them on an etched surface. Examples of such baths are: (i) FeSO₄-7H₂O 248, ZnSO₄-7H₂O 8·8, (NHJ₄)₂SO₄ 118, KCl 10, citric acid 0·5 g./l., operated at pH 1·7, 50°G, 200 amps./ft.² and giving a 6% zinc alloy of 560 D.P.N, hardness;

(ii) FeSO₄-7H₂O 174, ZnSO₄-7H₂O 88, (NH₄)₂ SO₄ 118, KCl 10, citric acid 0·5 g., Teepol 0·4 ml./l., operated at pH 1·7, 50°C, 180 amps./ft.² and giving a 60% zinc alloy of 350 D.P.N, hardness.

The throwing power of the baths is comparable with that of a bright nickel bath. Pitting can be overcome by using a wetting agent (Teepol or Lubrol W) and operating at high temperature (80° C.) and low pH (<1·8). Under these conditions the deposits are usually matt and light grey in colour.

Alloys with zinc contents >ca. 30% have electrode potentials in N/10 KCl nearly equal to that of pure zinc. In the C.R.L. beaker test, the alloys with zinc contents between 30 and 90% are, in general, more corrosion resistant than pure zinc. Various applications of these alloys are proposed, including their use as an undercoat for paints and chromium plating and for decorative finishes indoors.

Deposition of iron-zinc alloys from chloride baths is dealt with briefly. A matt, corrosion-resistant alloy of 60% zinc content can be obtained, at pH 1·8, 50° C., and 50 amps./ft.², from a vigorously stirred bath of the following composition:—FeCl₂·4H₂O 177, ZnCl₂ 42, NH₄Cl 100, KCl 15, citric acid 0·5 g./l.

A colorimetrie method for the analysis of zinc in the presence of iron is described.     

Anodischer Schutz durch Lokalkathoden

Anodic protection through local cathodes If passivation-prone metals are brought into contact with local cathodes, it is possible to achieve an anodic passivation protection if the critical density of the passivating current is produced by the accelerated cathode process (e.g., accelerated reduction of H⁺ ions as a result of a reduction of the hydrogen over-potential). Particularly suitable local cathodes are the platinum metals but also carbon and semi-conducting oxides. Generally, small quantities of these are already sufficient. The cathodically acting components may be alloyed with the metal to be protected. But they may also be brought into contact with the metal surface from outside. Finally, it is also possible to add ions of electropositive metals to the corrosive agent. In this case, such ions initially act, because of their high redox potential, as oxidants and settle down on the surface after reduction so that the local cathode effect can commence. Anodic protection can also be obtained by contact with oxidant solids, e.g. manganese oxide. Particularly well suited metals or alloys are the stainless steels and titanium, but also lead.     

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.     

The Cleaning of Iron and Steel

The paper reviews the present state of development of a well established process for electro-brightening aluminium. The brightening operation is carried out in a solution containing 15% wt./vol. anhydrous sodium carbonate and 5% wt./vol. anhydrous trisodium phosphate at 80–82°C. After an initial etch for 10–30 seconds, 12V d.c. is applied between stainless steel cathodes and the aluminium anode, the anode current density falling rapidly from 35A/ft² at the start to about 20 A/ft². Treatment is for 5–15 minutes, after which the article is rapidly removed and rinsed in water.

The thin oxide film produced on the metal surface by this treatment is removed by immersion in a hot solution of phosphoric and chromic acids, since it forms an easily-marked outer layer on subsequent anodising, and the article is finally subjected to the normal protective anodic treatment in sulphuric acid, after which it is sealed and waxed. For certain decorative applications the anodic film may also be dyed.

The process works best with super purity aluminium (99·99% Al) and certain alloys made from this metal, particularly those containing small amounts of magnesium, but good results can also be obtained with 99·8% Al.

The treated surface has a high reflectivity for both light and radiant heat, and the process is extensively used in the production of aluminium reflectors, as well as for a wide range of decorative purposes.     

Electrochemical dissolution of cemented carbide scrap and electrochemical preparation of tungsten and cobalt metals

In this study, WC and WC-6 wt% Co scraps were utilized in molten salt state as two consumable anodes to circulate tungsten and cobalt during electrolysis. Because of poor dissolution of cemented carbide scrap in NaCl-KCl salt, tungsten trioxide was added to NaCl-KCl salt as active substance to improve the dissolution of the anode. Therefore, dissolutions of WC and WC-6 wt% Co anodes were studied at different tungsten trioxide contents. It was shown that addition of tungsten trioxide significantly increased dissolution of the anode. The addition of tungsten trioxide drastically reduced charge transfer impedance and accelerated the dissolution. The electrolyte resistance also reduced slightly. The electrolysis of WC anode was investigated at optimal tungsten trioxide content. Tungsten with single phase was obtained at current density of 0.1 A·cm⁻² for 8 h. The electrolysis of WC-6 wt% Co anode was also explored using same tungsten trioxide content. The data suggested that electrolysis time and current density greatly influenced the composition of cathode product. The preliminary conditions were determined for separation of tungsten and cobalt. Overall, the electrochemical preparations of cobalt and tungsten metal were achieved by two-step electrolysis processes.     

Advances in Thermionic Cathode of Tungsten and Molybdenum

Tungsten and motybdenum have been usedwidely in metallUrgy illumination and electfo-nics, astfonavig8tion and chemical fields due totheir high melting poillts and high hardness.They are imPoftam materials used in illumina-tion aPparatlls and electfon tubes. ln electron tu-bes, trigsten is used as thermonic cathode ma-terial, and molybdenum is mainly used as stand,anode, etc. Recently molybdenurn has beenused as thermonic cathode material for its goodperformance at high temPerthee. The aPplic…     

Normal and anomalous electrodeposition of tin–copper alloys from methanesulphonic acid bath containing perfluorinated cationic surfactant

Abstract

Sn–Cu alloys were deposited from a 12˙5 vol.-% (1˙93 mol dm^–3) methanesulphonic acid bath containing a perfluorinated, cationic surfactant at 296 K. Electrodeposition was carried out under controlled flow conditions, using rotating disc, rotating cylinder and rotating cylinder Hull cell electrodes. The influences of deposition current and potential, rotation speed, cupric ion concentration, stannous ion level and surfactant concentration on the deposited alloy composition have been investigated. The presence of surfactant resulted in a shift in the Cu deposition potential compared to that of Sn deposition. Both 'normal' deposition (Cu deposited at a more positive potential than Sn) and 'anomalous' deposition (Sn deposited at a more positive potential than Cu) could be achieved. A series of Sn–Cu alloys was electrodeposited over a wide range of operating conditions to produce matte grey through golden yellow to light brown, surface finishes. Golden yellow coloured bronze deposits, containing 70–80 wt-% Cu and 20–30 wt-%Sn could be obtained. When Sn was deposited preferentially, the Cu content of the alloy was typically in the range 3–9 wt-% along the cathode of the rotating cylinder Hull cell.     

Organic Additives: A Source of Hydrogen in Copper Cathodes

Increased quality requirements have been placed on electrolytically-refined copper cathodes for use as metal feed in the continuous casting and rolling processes. The presence of hydrogen in the copper is believed to be the most significant single impurity factor affecting the quality of the cast copper product. Hydrogen has a synergistic effect with grain boundary impurities which results in excessive cracking during hot rolling. This paper covers the effect of organic additives, mainly glue and thiourea, on the cathodic overpotential, and the relationship between the overpotential and the organic additive entrapment and the hydrogen content in the copper cathode.     

A Study into the Electrodeposition Mechanisms of Zinc-Nickel Alloys from an Acid-Sulphate Bath

Zinc-nickel alloys were electrodeposited under galvanostatic conditions from a sulphate based electrolyte. The effect of deposition current density on alloy composition was determined for an electrolyte containing 0.58 mol/l nickel and 0.92 mol/l zinc (as sulphates). At current densities exceeding 0.01 A/dm², a transition from normal deposition to anomalous co-deposition (ie where the less noble metal deposits preferentially) was observed and alloys rich in zinc were obtained. The transition current density was observed to increase with an increase in electrolyte temperature or a decrease in electrolyte pH.

The electrodeposition mechanism for zinc-nickel alloys in the transition regions was studied in detail using potentiodynamic cathodic polarisation techniques. The results were consistent with the suppression of nickel deposition due to the precipitation of zinc hydroxide on the cathode surface. This was supported by pH measurements made in the vicinity of the cathode where a rise in pH was detected as the transition current density was approached and exceeded the critical pH for zinc hydroxide precipitation.     

采用WC过渡层增加金刚石薄膜附着力的研究

在微波等离子体化学气相沉积装置中，以WC-8％Co为基体，采用氢等离子体脱碳、磁控溅射镀W、碳化等方法，制备了微晶WC过渡层。研究了金刚石薄膜与基体的附着力。结果表明，表面脱碳后再镀W膜，W填充了氢等离子体脱碳时刀具表面因钴蒸发而留下的空洞，形成过渡层，在随后的碳化中和基体WC连接较为紧密，能增加金刚石薄膜与基体附着力，克服单纯的氢等离子体脱碳还原法降低刀具基体硬度、不能完全消除钴的有害影响的缺点。     

THERMIONIC EMISSION OF CARBONIZED La-Mo CATHODE

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Calendar of Meetings

Abstract

Ethylene diamine was evaluated as a short-term inhibitor for aluminium alloys, 2S, 57Sand 65S in hydrochloric acid. At 43·5 ml/l concentration, it afforded complete protection to all the alloys in 1·0 N hydrochloric acid for up to three hours in the temperature range 35–55°c. At higher concentrations of hydrochloric acid, its efficiency was 97–99·5%. Ethylenediamine reduced the externalcathodic protective current, gave cathodic protection and inhibition by lowering the potential requirements and by increasing the anodic and cathodic polarisation characteristics of the metal surface. At concentrations up to 17·4 ml/l, ethylenediamine accelerated corrosion of the 2S alloy.     

Electrochemical behaviour of lead alloys as anodes in zinc electrowinning

Abstract

The electrochemical and corrosion properties of the ternary and quaternary lead alloys Pb–0·18Ag–0·012Co, Pb–0·2Ag–0·06Sn–0·03Co, and Pb–0·2Ag–0·12Sn–0·06Co (wt-%) have been investigated. The formation of oxide layers on the surface of these alloys was traced by cyclic voltammetric methods and the composition of the anodic oxide layers was determined by X-ray and SEM analyses. The cobalt inclusions reduce the anodic polarisation and improve the corrosion resistance of the alloy. The Pb–0·2Ag–0·12Sn–0·06Co alloy displays electrochemical and corrosion properties similar to those of Pb–1Ag and can be used as a substitute for the latter as a material for anodes in the electrowinning of zinc from sulphate electrolytes.     

钴盐沉淀法制备硬质合金混合料新工艺研究

以醋酸钴、WC粉和氨水为原料,以蒸馏水作为反应溶剂进行化学反应,反应物经氢气还原制得钨钴混合料,最后制得硬质合金,并与传统工艺制得的合金进行性能比较。结果表明,XRD图谱显示实验反应生成物是钴氧化物前驱体,面分析图谱显示新工艺制备的混合料元素分布更均匀,细碎WC颗粒更少,新工艺制备的硬质合金密度及硬度变化不大,强度提高了318N/mm2,韧性提高了0.2N·m/cm2。