Mild Steel Cathodes Research Articles

Recovery of Elemental Boron From Boron carbide Using KCl-KF-KBF4 Electrolyte in Fused Salt Electroextraction Process

Technology for extraction of elemental boron from boron carbide by fused salt electroextration using 70KCl-12KF-18KBF4 (in wt%) salt mixture as electrolyte was successfully demonstrated. The electrolytic cell was designed and fabricated suitably for using boron carbide as soluble anode, and boron was electroextracted on mild steel cathode plate. Initially, the salt mixture was characterized using differential thermal analysis (DTA) and thermogravimetry (TG) to understand the melting and evaporation behaviour of the salt. The electroextraction experiments were conducted at the optimized temperature of 860 °C applying a cathode current density (CCD) of 24.4 A dm−2 with varying times of 3, 7, 10, 12, and 24 h. High purity boron (∼98%) powder containing both rhombohedral and tetragonal crystals was successfully electroextracted. The morphology, composition and crystal structure of the electro-deposited boron was characterized using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction analysis. The kinetics of deposition of boron in cathode was found to be linear with an achievable current efficiency of 86.5%.

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm−3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., “green rust”, are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.Graphical

Synthesis and assessment of novel anticorrosive polyurethane coatings containing an amine-functionalized nanoclay additive prepared by the cathodic electrophoretic deposition method

Cathodic electrophoretic deposition (CEPD) was utilized to cover a mild steel cathode in an aqueous solution consisting of a newly synthesized two-component one-pack waterborne polyurethane resin.

Influence of CO2 Gas in the Electro-Carburisation Process of Mild Steel

In the attempt to develop a clean process, study has been conducted to determine the effect of absorbed CO2 gas as source of carbon to the case hardening of treated mild steels in the recently developed process of electro-carburisation in non-toxic molten carbonate salts. The concentration of CO2 in the process was varied by purging a CO2 and N2 mixture at flow rate ratios of CO2:N2 of 200:0, 150:50, 100:100, 50:150 and 0:200 mL.min -1 . Electro-carburisation was performed in two types of molten salt electrolyte i.e. a mixed anion Na2CO3-NaCl (mole ratio 4:1) and a pure carbonate Li2CO3-K2CO3 (1:1 mole ratio). A voltage of 2.5V was applied between mild steel cathode and an inert SnO2 anode at a carburisation temperature of 800 o C for 60 minutes. The results show that greater CO2 concentration produced samples with greater surface hardness and thicker case-hardening, attributed to the increased availability of the electro-active carbon source which was generated by absorption of CO2. Electro-carburisation in Li2CO3-K2CO3 and Na2CO3-NaCl gave surface hardness of 1075 ± 25 HV, however Li2CO3-K2CO3 (540 thickness) gave thicker case depth compared to Na2CO3-NaCl (500 thickness). This is thought to be due to the amount of carbon deposited in each salt; 12.70 wt.% C in Li2CO3-K2CO3 and 11.10 wt.% C in Na2CO3-NaCl.

Indirect electrochemical reduction of carbon dioxide to carbon nanopowders in molten alkali carbonates: Process variables and product properties

Carbon was deposited on a mild steel cathode during electrolysis in the molten mixture of Li2CO3 and K2CO3 (mole ratio: 62:38) under CO2 or mixed N2 and CO2 atmospheres at 3.0–5.0V and 540–700°C. In a three-electrode cell, cyclic voltammetry was applied on a platinum working electrode to study the reduction and deposition processes. A two-electrode cell helped correlate electrolysis variables, e.g. temperature and voltage, with the deposition rate, current efficiency, and properties of the deposited carbon powders. High current efficiency (>90%) and deposition rate (>0.11gcm−2h−1) were achieved in the study. Elemental analysis of the electro-deposits, following washing with HCl solutions (2.3–7.8molL−1), showed carbon as the dominant element (75–95wt.%) plus oxygen (5–10wt.%) and small amounts of other elements related to materials of the electrolytic cell. Thermogravimetry detected fairly low onset combustion temperatures (310–430°C), depending on the electrolysis and acid washing conditions. Amorphous and various nanostructures (sheet, rings and quasi-spheres) were revealed by electron microscopy in carbon samples deposited under different process conditions. The specific surface area of the carbon deposited at 5.0V and 540°C was as high as 585m2g−1. An analysis of the energy consumption suggests several ways for efficiency improvement so that the electrolytic carbon from CO2 will become commercially attractive.

Anodizing and corrosion behaviour of aluminium

In this study, aluminum was anodized in 0.4 M H2SO4 + 0.145 M H3BO3 solution by means of potentiostatic method. In first step, the most appropriate conditions (anodizing voltage and period) were determined. The voltage-current behavior was investigated between 0 to 30 V and oxide formation potential (15 V) was determined. Then chorono-amperometric measurement was obtained at this potential during 2 hours. Therefore, anodizing process was applied at 15 V between aluminium anode and mild steel cathode. In the second step, the corrosion performance of non-anodized (Al) and anodized samples (Al2O3) have been investigated in 3.5% NaCl solution by using electrochemical impedance spectroscopy and polarization techniques. The interface between metal and solution was modeled with the equivalent circuit successfully. The circuit’s elements were calculated with Ivium Soft fitting program. The polarization curves were obtained between −1.8 V and 0.5 V potential ranges. The experimental results proved that the thickness and quality of oxide film was improved with help of anodizing process. Thus the corrosion resistance of anodized aluminum is significantly increased.

Unusual kinetic behavior in cathodic H2 evolution from KF.2HF melts at mild-steel and alloy electrodes

Apart from its interest as a "model" process for kinetic studies of gas-evolving electrode reactions, the cathodic hydrogen evolution reaction (her) is involved in several processes that are of importance in applied electrochemistry, e.g., as the cathodic co-reactions in the commercial production of C12 and F2, in electrolyses for production of hydrogen, in electrochemical hydrogenation and, indirectly, as the partial process in corrosion of base metals in the absence of oxygen. The present paper reports several aspects of the unusual behavior of the her that is involved as the co-reaction to electrolytic production of F2 from KF/HF melts using carbon anodes and Fe or mild-steel cathodes. Anomalous anodic polarization behavior that arises in electrolytic generation of F2 from KF/HF melts at carbon electrodes is well known. It is characterized by very high Tafel slopes associated with "CF" film formation and by sluggish F2 bubble disengagement from the electrode. Interest in such effects has, however, tended to overshadow rather similar, so-called "hyper polarization" effects that also arise in the cathodic reaction, but for different reasons. The origins and nature of such effects are described and characterized in the present paper, and comparisons are made between behavior of Hz evolution from KF.2HF and that from the aquo-system analogue, KOH.2H2O. An important aspect is the very different interfacial behavior in KF/HF or KF.2HF melts from that in the corresponding aquo-system. Effects of As-species in HF feeds is investigated in terms of electro catalysis and poisoning effects on the her.

Ruthenium oxide for effective activation of aluminium sacrificial anodes: a new approach

Ruthenium oxide, one of the excellent electrocatalysts having high conductivity and high chemical and thermodynamic stability, has been coated onto the surface of an electrode made from a Al–5 wt-%Zn alloy. The activated aluminium ion was able to diffuse through the porous catalytic hydrophilic layer. Ruthenium oxide coated Al–Zn alloy anodes displayed high open circuit potential and high closed circuit potential during galvanic exposure with mild steel cathodes. A galvanic efficiency as high as 86% with an actual current capacity of 2573 A h kg-1 was achieved. The RuO2 film underwent very little deterioration and a considerable mass of the ruthenium oxide film persisted on the anode surface, even after the electrode size had been reduced to one third of its original size owing to galvanic dissolution. These electrodes are economically efficient, as convenient to prepare, install and use as other conventional electrodes, are tolerable of very aggressive media and highly efficient, even under high galvanic current loads.

Electrodeposition of Al–Ni intermetallic compounds from aluminum chloride- N-( n-butyl)pyridinium chloride room temperature molten salt

Electrodeposition of aluminum–nickel intermetallic compounds (particularly Ni 3Al) has been carried out onto platinum and mild steel cathodes from a 2:1 (mole ratio) aluminum(III) chloride- N-( n-butyl)pyridinium chloride (BPC) molten bath saturated with nickel(II) chloride at room temperature. A single phase of Al–Ni alloy is difficult to obtain by controlled-potential and controlled-current methods; however, it can be obtained by pulse current plating. The electrodeposition of nickel from an AlCl 3–BPC–NiCl 2 (6.14:3.07:0.09 mole ratio) molten bath occurs via an instantaneous nucleation mechanism in the very initial stage of the crystal growth. The deposition reaction mechanisms of nickel in this molten bath are revealed by electrochemical analysis. The experimental Tafel slope of 42 mV dec −1 and the calculated transfer coefficient α → c of 1.5 suggest that the rate determining step is a charge transfer reaction of an adsorbed bare monovalent cation to the metallic state. The effect of the cycle regime on the electrodeposition of Al–Ni alloys has been investigated. The current efficiency for the deposition of alloys is about 99%.

New Cathode Materials for Chlorate Electrolysis

Nanocrystalline Ti‐Ru‐O alloys of different composition were made by high‐energy ballmilling Ti and powders. Upon milling, reacted with Ti to form Ti oxides, Ru‐like hexagonal‐close‐packed (hcp) phase, and a cubic Ti‐Ru‐(O) alloy. After 40 h of milling, the final product was primarily a Ti‐Ru‐O alloy with iron impurities from the steel balls and crucible. A high ball‐to‐powder weight ratio resulted in higher impurity (iron) content. Most of the iron in the powder did not exist as α‐Fe particles but entered into the alloy lattice forming a Ti‐Ru‐(Fe)‐(O) cubic phase. The incorporation of iron did not affect the catalytic performance very much. The electrocatalytical activity of the studied cathode materials for the hydrogen evolution reaction (HER) in a chlorate electrolyte was investigated by measuring the overpotential at 250 mA/cm2 current density (η250). Good performance was found for ratios of 2:1 and 3:1. The HER η250 values for these electrodes were 300 mV lower than that for mild steel cathodes. The electrodes made of the new alloys were very stable in the chlorate electrolyte and had good resistance to poisoning from the solution. The origin of the catalytic activity resulted mainly from ruthenium, and the presence of titanium and oxygen in the alloys was indispensable for the stability of the electrodes.

Cyclizations. Part 3. Use of a mild-steel cathode in the electrochemical intramolecular cyclization of aryl halides

One electron reduction of aryl halides is known to generate the aryl radical and halide ion. These aryl radicals will cyclize onto an adjacent benzene ring in a reaction that is potentially useful in organic synthesis and which is well documented at a mercury cathode. 5-(2-Halophenyl)-1-(4-fluorophenyl)tetrazoles are used here as representative substrates and the cyclization reaction to 7-fluorotetrazolo[1,5-f]phenanthridine is developed at cathodes of cadmium, zinc and mild-steel. A high yield of the desired cyclization product is achieved using a mild-steel cathode and a sacrificial magnesium anode in an undivided cell with acetonitrile, 0.1 M tetraethyl ammonium tetrafluoroborate as electrolyte and under an air atmosphere.

Crystallographic Texture and Microstructure of Electrogalvanized Layer in Acid Sulfate Solution

The crystallographic texture and microstructure of electrogalvanized Zn layers on a mild steel cathode were studied with reference to the galvanizing variables including current density and chloride addition. Increasing the current density reduced the relative density of Zn basal planes parallel to the cathode surface. This phenomenon was attributed to the outgrowth of nonbasal planes within an ion‐depleted zone close to the metal substrate surface under high cathode overvoltage induced by the high current density. Chloride addition also affected the cathode overvoltage and subsequently the texture of the Zn layer. The effect depended on chloride concentration and temperature. Increasing the current density or adding chloride enhanced the hardness of the electrodeposited layer, as a result of grain size refinement and solid solution hardening.

Electrochemically induced radical cyclization reactions

A new route has been devised for intramolecular aryl radical cyclization reactions involving the electrochemical reduction of an ortho-halogenophenyl compound in acetonitrile at a mild steel cathode.

Nickel-based, binary-composite electrocatalysts for the cathodes in the energy-efficient industrial production of hydrogen from alkaline-water electrolytic cells

Ni-Mo, Ni-Zn, Ni-Co, Ni-W, Ni-Cr and Ni-Fe, binary-composite, codeposit surface coatings on mild-steel substrates were prepared by conventional electrodeposition techniques. The chemical compositions and the micrographic surface features of these coatings are reported. The utility of these coatings as cathodes in laboratory-scale alkaline-water electrolytic cells was assessed by polarisation techniques. The trend in their electrocatalytic activities ranks in this order: Ni-Mo>Ni-Zn>Ni-Co>Ni-W>Ni-Fe>Ni-Cr. The electrocatalytic activity of these coatings is very significant when compared with the data on conventional mild-steel cathodes currently used in industry. The results obtained experimentally are presented. A brief discussion is also included to highlight their utility.

A nickel molybdenite cathode for the hydrogen evolution reaction in alkaline media

The characteristics and mechanism of the hydrogen evolution reaction on a nickel sulphide electrode incorporating molybdenite particles are described. At 25°C the overpotential for the reaction is 300 mV lower than that of the mild steel cathodes used in unipolar electrolysers. The material shows good stability under long term operation.

Nickel based composite electrolytic surface coatings as electrocatalysts for the cathodes in the energy efficient industrial production of hydrogen from alkaline water electrolytic cells

The preparation of Ni - Mo - Fe, Ni - Mo - Cu, Ni - Mo - Zn, Ni - Mo - W, Ni - Mo - Co and Ni - Mo - Cr codeposit surface coatings on mild steel substrates by conventional electrodeposition techniques is carried out. The chemical composition and the micrographic surface features of these coatings are reported. The utility of these coatigs as cathodes in laboratory scale alkaline water electrolytic cells is assessed with polarization techniques. It is shown that the trend in their electrocatalytic activities follows this order: Ni - Mo - Fe > Ni - Mo - Cu > Ni - Mo - Zn > Ni - Mo - W - Ni - Mo - Co > Ni - Mo - Cr. The electrocatalytic activity of these coatings are very significant when compared with the data of performance realized on conventional mild steel cathodes used currently in industry. The results obtained experimentally are presented. A discussion in brief is also included to highlight their utility.

On the catalytic activity of NiMoFe composite surface coatings for the hydrogen cathodes in the industrial electrochemical production of hydrogen

Nickel-based composite surface coatings were assessed for their utility as catalytic hydrogen evolving cathodes in alkaline water electrolysers, chlor-alkali cells, chlorate cells, etc. Transition-metal-based hydrogen cathodes from metals, namely Ni, Mo, Cu, Fe, W, Co and Cr, obtained as thin electrolytic surface coatings on mild steel substrates were investigated in this laboratory. NiMoFe electrolytic ternary surface coatings had exhibited acceptable catalytic activity for the cathodic hydrogen evolution reaction (h.e.r.). The reduction in the hydrogen overpotential value (ν H 2) that could be practically realised by replacing the mild steel cathodes which are in use by convention, with the present NiMoFe coated cathodes, amounts to 0.3 V minimum at typical industrial operation conditions, namely 300 mA cm −2 and 353 K. A critical assessment of the catalytic application of NiMoFe composite for the h.e.r. had been carried out. The results of the range of examined conditions such as the ease of preparation of the NiMoFe surface coatings through electrolytic codeposition technique, the microstructural features of the coatings, the X-ray diffraction data, the influence of chloride on the polarisation characteristics, the effect of synthetic seawater treatment, the susceptibility to thermochemical reactions with oxygen and the welting agent in the PTFE binder at temperatures above 623 K and the effect of simulated application of asbestos separator on the catalytic activity of NiMoFe composite are presented. It is proposed that this new catalytic material does meet out the stability requirements. A laboratory size unit electrolytic cell assembled with catalytic electrodes working at 1.8 V, 300 mA cm −2 in 6M KOH is described. A discussion on the possible energy saving by employing the proposed NiMoFe catalyst for cathodes in the industrial production of hydrogen is also included.

ChemInform Abstract: Thermal/Mechanical Alterations of SAE 1008 Steel and Fe‐12ppmC vs. Hydrogen Overpotential in Alkaline Solution.

AbstractIt is demonstrated that alterations of the state of surface of mild steel or pure iron cathodes have a significant influence on the steady‐state electrocatalytic performance for the hydrogen evolution reaction (HER) and that the Tafel slope for HER can be reduced by appropriate thermomechanical processing.

ChemInform Abstract: KINETICS OF THE HYDROGEN EVOLUTION REACTION ON MILD STEEL AND NICKEL CATHODES IN CONCENTRATED SODIUM HYDROXIDE SOLUTIONS

AbstractDie H2‐Entwicklung wurde für glatte und aufgerauhte Elektrodenoberflächen in Abhängigkeit von der NaOH‐Elektrolytkonzentration (41‐50 Gew.‐%) und der Temp. (288‐358 K) bis zu Stromdichten von ca. 0.3 A/cm2 gemessen.

Kinetics of the Hydrogen Evolution Reaction on Mild Steel and Nickel Cathodes in Concentrated Sodium Hydroxide Solutions

Data are reported on the kinetics of the hydrogen evolution reaction on mild steel and nickel cathodes in sodium hydroxide electrolytes from 4 to 50 weight percent (1–26m) for temperatures of 288–358 K. Measurements were made for both smooth and roughened electrode surfaces up to current densities of about 0.3 A/cm2. Tafel plots for the nickel cathodes are linear over the whole current density range studied. The transfer coefficient, β, has an average value of 0.54 and is unaffected by varying either the caustic concentration, the temperature, or the surface roughness of the electrode. With the mild steel cathodes, the Tafel plots show two linear regions with the inflection point occurring at . In the lower overpotential region, β increases from about 0.5 to at least 1.4 with increasing caustic concentration and increasing temperature. This behavior is interpreted as being caused by a change in reaction mechanism and results from one of the reaction steps becoming reduced in rate. The ability of the caustic concentration or the temperature to affect the reaction mechanism is amplified by roughening the electrode surface. For the linear regions in the Tafel plots at high overpotentials, the slopes are almost invariant to changes in the caustic concentration, the temperature, or the surface roughness. The transition between the two Tafel regions appears to be caused by a change in the electrode surface resulting from the reduction of a surface oxide, possibly . The dependence of the inflection point potential on the experimental variables is analyzed in terms of this potential being equivalent to the equilibrium potential of the inferred surface redox reaction.