Inert Cathode Research Articles

Mathematical analysis of a batch electrocoagulation reactor

Electrocoagulation treats water by delivering coagulant from a sacrificial anode (aluminium) in an electrochemical cell. Hydrogen is evolved from the inert cathode. In the batch electrocoagulation reactor numerous interactions occur with settling and flotation identified as the dominant removal paths. Current determines both coagulant dosage and bubble production rate. The bubbles influence the mixing, and hence mass diffusion within the reactor. Rate of flotation and settling were experimentally determined for currents 0.25-2.0 A and pollutant loading 0.1-1.7 g/L. The performance of the electrocoagulation reactor was quantified by analysis of experimental results. First-order ordinary differential equations were developed to describe the pollutant's settling and flotation behaviour. Kinetic rate constants were calculated considering this pair of irreversible reactions. At low current (0.25A), sedimentation dominates with slow release of coagulant and gentle agitation provided by low bubble production. Removal is slow and hence the low rate constants calculated were appropriate. At high currents (1.0 and 2.0 A) faster removal occurs due to greater bubble density. This resulted in greater mass floated to the surface and higher rate constants were observed. Thus the developed rate equations successfully quantified the reactor's performance over a variety of conditions.

00/01894 A hybrid artificial neural network (ANN) and Ward equivalent approach for on-line power system voltage security assessment

An accelerating rate calorimeter (ARC) is used to measure the thermal stability of de-intercalated Li1+xMn2−xO4 in LiPF6 EC:DEC (33:67) electrolyte. Self-heating is detected well after the 80°C onset of self-heating measured for lithium intercalated mesocarbon microbead (MCMB) electrodes in LiPF6 EC:DEC (33:67) electrolyte. As a result, the initial self-heating measured in a practical carbon/Li1+xMn2−xO4 lithium-ion cell is caused by reactions at the anode. In previous work, we have proposed a model for the reactions that cause self-heating in MCMB electrodes in electrolyte. By assuming that a cell self-heats only because reactions occur at the anode, the model can be used to predict the power generated by the amount of MCMB in practical cells with an inert cathode. The calculated chemically generated power can be combined with power loss measurements, due to the transfer of heat to the environment, to predict the short-circuit behaviour and the oven exposure behaviour for a cell containing an MCMB anode and an inert cathode. The results agree qualitatively with short-circuit and oven exposure results measured on NEC Moli energy 18650 cells containing an Li1+xMn2−xO4 cathode.

Magnesium removal in the electrolytic zinc industry

Most electrolytic zinc plants have to deal with dissolved magnesium in their process liquors, as zinc sulphide concentrates contain small amounts of magnesium. Applied magnesium bleed methods are generally expensive and environmentally unfriendly. In this paper, a new approach is suggested and discussed in which magnesium fluoride is selectively precipitated from purified zinc sulphate solutions. The magnesium fluoride is contacted with sodium hydroxide solution and thus converted into magnesium hydroxide, which could be saleable product. It is shown that the resulting sodium fluoride solution can be electrolysed in a membrane cell consisting of a zinc anode and an inert cathode. This yields zinc fluoride and sodium hydroxide solutions, which both can be recycled to the magnesium removal process. Various experiments, which are discussed in this paper, confirm that the proposed process is possible.

Predicting electrical and thermal abuse behaviours of practical lithium-ion cells from accelerating rate calorimeter studies on small samples in electrolyte

Abstract An accelerating rate calorimeter (ARC) is used to measure the thermal stability of de-intercalated Li 1+ x Mn 2− x O 4 in LiPF 6 EC:DEC (33:67) electrolyte. Self-heating is detected well after the 80°C onset of self-heating measured for lithium intercalated mesocarbon microbead (MCMB) electrodes in LiPF 6 EC:DEC (33:67) electrolyte. As a result, the initial self-heating measured in a practical carbon/Li 1+ x Mn 2− x O 4 lithium-ion cell is caused by reactions at the anode. In previous work, we have proposed a model for the reactions that cause self-heating in MCMB electrodes in electrolyte. By assuming that a cell self-heats only because reactions occur at the anode, the model can be used to predict the power generated by the amount of MCMB in practical cells with an inert cathode. The calculated chemically generated power can be combined with power loss measurements, due to the transfer of heat to the environment, to predict the short-circuit behaviour and the oven exposure behaviour for a cell containing an MCMB anode and an inert cathode. The results agree qualitatively with short-circuit and oven exposure results measured on NEC Moli energy 18650 cells containing an Li 1+ x Mn 2− x O 4 cathode.

Development of a seawater battery for deep-water applications

Dissolved-oxygen seawater batteries rely on the corrosion of a reactive metal anode and the reduction of oxygen at an inert cathode to generate a potential of about 1 V when immersed in seawater. Because oxygen is not very soluble in seawater, such batteries are characterized by small cathodic current densities and are therefore most suitable for long-term low-power applications. A number of batteries have been built recently using sophisticated electrodes. The objective of this study was to evaluate the feasibility of building a seawater battery using cheap readily-available materials. The results show that magnesium anodes outperform aluminum. Although the cathodic current densities achieved in this study are markedly lower than reported previously, cathodes composed of copper (or stainless-steel) mesh perform reasonably well and facilitate the design of compact batteries with an open structure and large cathodic areas. Deep- and shallow water tests show that a battery occupying 1 m 3 could produce 5 W for a year or more in oxygen-saturated waters and 1–2 W in the oxygen-starved waters of the North Pacific seafloor. The energy density of such a battery including the flotation necessary for optimal performance and recovery is estimated to be 150–400 Wh kg −1.

Sea-water battery for subsea control systems

This paper describes a power source for the autonomous control system of a subsea well (SWACS) in the Ionian Sea. The unit was deployed in Jan. 1996 at a depth of 180 m. The 650 kWh sea-water battery uses anodes made from commercial magnesium alloys, sea-water as the electrolyte and oxygen dissolved in the sea-water as oxidant. The inert cathodes are made from carbon fibers. The system is composed of six, two-metre high sea-water cells integrated in a steel structure, a d.c./d.c. converter and a valve regulated lead-acid accumulator enclosed in a titanium container together with a monitoring unit which transfers data to the surface via an acoustic link.

Electrochemical extraction of samarium from mixture of rare earth metals

Electrochemical extraction of samarium from hydrochloric acid solutions of a mixture of semi-heavy rare earth metals has been developed. The kinetics of the process have been studied to control the electroreduction process of samarium on a solid inert (graphite) cathode. It has been established that the process proceeds in the diffusion kinetics zone. Optimum parameters for carrying out the electro-extraction of samarium from process solutions providing 80–85% samarium removal have been determined.

Impurities and grain boundaries in sintered titanium diboride

In conventional Al-electrolysis the electrodes suffer from degradation when used in the harsh environment of an aluminium electrolysis cell. The carbon cathode, which is placed at the cell bottom, is not well wetted by aluminium, and must be covered by a pad of liquid Al in order to establish a good electrical contact. To avoid short circuiting of the cell the anode-to-cathode distance (ACD) must be kept above 4-6 centimetres. Replacing the carbon cathode with a new, inert cathode, well wetted by liquid aluminium, would allow new cell designs where only a thin film of aluminium covers the cathode during cell operation, thereby allowing the ACD to be lowered. This in turn opens for substantial reductions in the energy consumption of an electrolysis cell, and combined with an inert anode the outlet of CO2 and fluorides harmful to the environment could be reduced.The most promising candidate for use as an inert cathode is titaniumdiboride (TiB2), a ceramic material which exhibits promising properties such as a high electrical conductivity, sufficient mechanical strength, good resistance to chemical attack and low solubility in liquid aluminium, and which is also well wetted by liquid aluminium.

Fluid Flow and Interpolar Resistance Measurements in Advanced Hall-Heroult Cells

Abstract This paper describes electrode design, velocity and interpolar resistance measurements in a physical model of advanced Hall-Heroult cells that use inert anodes and aluminum wcttable cathodes. The principal experimental tool has been a “water” model wherein gas generation was simulated by forcing compressed air through porous graphite and the fine bubbles characteristic of inert anodes were produced by adding butanol to water. Measurements were carried out with two different anode designs—one that is flat and the other that has grooves. The results show that energy-efficient operation of advanced Hall cells can be achieved by using grooved anodes that are fully submerged in the electrolyte in the near-horizontal electrode configuration.

Study of the deposition mechanism of neodymium on an iron consumable cathode and a molybdenum unconsumable cathode in NaCl + KCl (1:1) in the temperature range 700–850° C

With the intention of understanding processes involved in NdFe electrowinning better, the deposition processes of neodymium on inert cathodes (Mo and Ta) and consumable cathodes (Fe) have been investigated in molten NaCl + KCl (1:1) in the temperature range 700–850 °C by means of linear potential sweep voltammetry (LPSV), chronopotentiometry, X-ray diffraction and electronic microscope analysis of deposits at controlled potential. On inert cathodes the reduction of Nd 3+ was a single step process leading to Nd metal with characteristics close to reversibility. On the contrary, two steps were noticed for the deposition of neodymium on iron: a first step to form the alloy FeNd 2 and a second step where the deposition of pure neodymium was observed. The overall process had an irreversible behaviour due to the alloying properties of iron.

Formation of corrosion-resistant layers by electrodeposition of refractory metals or by alloy electrowinning in molten fluorides

The electrolytic treatment of less resistant metals such as iron, copper and nickel with tantalum or niobium has been carried out in K2TaF7-LiF-NaF or K2NbF7-LiF-NaF solutions in the 550 to 1050°C temperature range. Two kinds of experiments have been used. (i) At lower temperatures, electroplating with pure tantalum and niobium on inert cathodes was performed. The electrodeposition mechanism of each metal was studied and coherent electroplates were prepared which were tested in electrocatalytic applications. (ii) At higher temperatures (850–1050°C), using nickel cathodes, intermetallic compounds were obtained at more positive potentials than that for pure electrodeposition (Ta2Ni, TaNi, TaNi2, TaNi3, NbNi, NbNi3). The electrowinning of stable TaNi3 and NbNi3 layers was carried out by the metalliding process which makes these materials resistant to corrosion in various media. Further, a study of the kinetics of growth of the diffusion layer allowed a diffusion parameter to be determined which was in agreement with other results obtained by conventional methods.

Electroprecipitation treatment of acid mine wastewater

The utilization of electroprecipitation for the treatment of acid solutions associated with the non-ferrous mining industry on a laboratory scale is explored. The electrolytic couple involved in the active process includes a consumable metal anode and an inert cathode. Mechanistically, oxidation of the anode is matched by the reduction of dissolved hydrogen ion to H 2 gas resulting in a pH increase in solution. Heavy metal removal is accomplished by either precipitation of hydrous oxides or by adsorption. Reduction of the solution metal content of from 100% for Al 3+ to 25% for Mn 2− is accomplished using a stainless steel rod anode; final solution pH stabilizes at a value of 4.9. Stabilization of solution pH reflects the attainment of kinetic equilibrium with respect to the rates of oxidation at the anode and diffusion of the oxidized products to the cathode where they precipitate as the hydroxide. Zinc and lead sacrificial anodes are also studied.

Electrochemical processes in a high power Li-SO 2 source

Some factors defining the specific characteristics of a high power Li-SO 2 chemical current source have been studied. The solid-phase product of the cathodic reduction of SO 2 passivates the electrode surface, but it is gradually dissolved after de-energizing. Hence Perchlorate solutions have been compared with bromide solutions. The rate of the cathodic reduction of SO 2 is higher in perchlorate solutions. The The discharge capacity is higher in acetonitrile solutions as compared with those based on propylene carbonate. In this case the capacity increase is i The polarization curve obtained at a porous inert cathode during the reduction of SO 2 has areas of intrakinetic, intradiffusion, external kinetic a The anodic behaviour of a lithium electrode is determined by the properties of the film passivating its surface. Polarization resistance at anodic diss

Effect of reactive sputter etching of SiO 2 on the properties of subsequently formed MOS systems

We investigated the effects of reactive sputter etching (RSE) of SiO 2 on the electrical properties of the SiSiO 2 system using CHF 3 in a commercial apparatus. SIMS and Auger spectrometry revealed contamination of RSE-exposed Si surfaces with carbon and heavy metals. The generation of crystal defects during thermal reoxidation was observed to be closely related to the level of metal contamination. C- V, C- t and I- V measurements on subsequently formed MOS structures showed, that oxide charge, interface state and mobile ion densities are nearly unaffected by the RSE process. However, minority carrier lifetime in the Si substrate and isolation behavior of the oxide layer are strongly degraded; our results suggest, that both effects are mainly due to metallic impurities. The use of inert cathode materials like quartz reduces metal contamination, but a non-negligible contribution from the grounded metal surfaces of the reactor remains. Carrier lifetime and insulating properties reach the values obtained on wet chemically etched samples only after extended times of plasma excitation in the apparatus. This is attributed to a passivation of the grounded surfaces by the formation of polymer films. Taking advantage of this effect MOSFETs were fabricated by the use of RSE without deterioration of their electrical performance.

Demagging Processes for Aluminum Alloy Scrap

Demagging processes can be divided into three general categories: 1) chlorination processes, in which chlorine gas is bubbled into the molten aluminum to react preferentially with magnesium which is finally removed as magnesium chloride dross; 2) solid flux processes, in which a solid-flux (AlCl3, AlF3), is mixed into the molten aluminum to react with magnesium which is again removed as chloride or fluoride dross; and 3) electrochemical processes, in which magnesium is removed as metal on the cathode by passing a current between the molten aluminum anode covered with an electrolyte and an inert cathode dipped into the electrolyte. Of the processes reviewed, chlorination methods are the most widely practiced in the industry and seem reasonably efficient. However, most of the chlorination processes appear to have emission and waste generation (MgCl2 dross) problems. The electrochemical processes have been tested only on laboratory scale so far, but they look promising for commercial use. If successfully developed, the electrochemical processes would be pollution-free, and magnesium metal would be recovered as a by-product.

Kinetics of the initial stage of electrolytic deposition of metals III. Galvanostatic conditions

The kinetics of the initial stage of the electrolytic deposition of a thin metal film onto an inert cathode are considered for the case when the electric current flowing through the electrolytic cell is held constant with time. In studying the process the Gibbs-Thomson effect is taken into account and the cases of pure ohmic control, volume diffusion control and phase boundary transition control are examined separately. Expressions are derived for the radius of a single crystallite, the mean crystallite radius and the overvoltage as functions of time and current strength for each of the above types of growth control. Formulae are also obtained for the maximum overvoltage, the time taken to reach it and the maximum number of crystallites on the cathode as functions of the electric current. The analysis shows that the decrease in the maximum number of crystallites with decreasing current approximately obeys a power law and that there exists a critical value of the electric current, different for the different types of control, below which only one crystallite forms and grows on the cathode.

Kinetics of the initial stage of electrolytic deposition of metals I. General theory

The process of the electrolytic deposition of metals is considered as a particular case of heterogeneous phase formation. The basic set of kinetic equations describing the initial stage of formation of a thin metal film on an inert cathode is formulated in a general form. With the aid of these equations the mean crystallite radius, the overvoltage and the electric current flowing through the system can be found as functions of time if the total “ohmic” resistance of the electrolytic cell is known. Taking into account the Gibbs-Thomson effect of crystallite curvature, expressions are derived for this resistance in the particular cases when the crystallite growth is limited solely (i) by the specific electrical conductivity of the electrolyte, (ii) by volume diffusion of the metal ions from the bulk of the electrolyte towards the surface of the growing crystallites, and (iii) by impediments accompanying the transition of the metal ions through the crystallite/electrolyte interphase boundary. Finally, it is shown that electrodeposition processes characterized by other types of crystallite growth control can also be analysed by means of the basic set of kinetic equations if the total cell resistance is properly defined.

Kinetics of the initial stage of electrolytic deposition of metals: II. Potentiostatic conditions

The kinetics of the initial stage of electrolytic deposition of a thin metal film onto an inert cathode are considered with the assumptions that nucleation is completed and the overvoltage is kept constant with time. The process is studied separately in the cases of pure ohmic control, volume diffusion control and phase boundary transition control of the growth of the crystallites. Expressions are derived for the radius of a single crystallite, the mean crystallite radius and the strength of the electric current through the electrolytic cell as functions of time and overvoltage for each of the above types of growth control. The analysis shows that taking the Gibbs-Thomson effect of crystallite curvature into account leads to (i) the appearance of an intercept in the asymptotic linear dependences of the current and the crystallite radius on the square root of time for ohmic and volume diffusion control, and (ii) violation of the linear dependences on time of the square root of the current and of the crystallite radius for phase boundary transition control.

Study of the anodic profile in an electrolyser with rotating soluble anode floating on a flat inert cathode

The present investigation deals with the conditions of fluidodynamical and electrochemical equilibrium which develops in thinning metal disks in an electrolyser supplied with a flat inert cathode on which floats a rotating anode. These working conditions are characteristic of a new technique for the electrochemical thinning of metallic foils. The analytically simpler case of absence of rotation was considered first. Then the more complex case, in which the anode also participates in this movement, was examined. The two cases lead to film thickness profiles which are practically identical, at least as regards rotation speeds between zero and 300 rev min-1. The experimental data obtained in thinning tests on specimens of commercial steels previously subjected to thermic treatment of technological interest, and using as electrolyte solutions of HNO3 in low concentration were in good agreement with theoretical values. In particular we have seen that at the circular external rim of the specimen, where the equilibrium profile deviates in least degree from flatness, such a deviation is less than 20/00. A quantitative verification of the hypotheses on which this theoretical study was based has shown the validity of these hypotheses in the running conditions examined.

A Thermal Battery Based on the Reaction of Cadmium and Liquid Iodine

A thermal battery consisting of a cadmium anode, a solution of potassium iodide in liquid iodine, and an inert cathode was studied at 125°C. The solubilities of and as separate components and as mixtures in liquid iodine, the conductivities of these solutions, and their corrosion behavior toward cadmium were investigated. The conductivity of polycrystalline follows the expression in the range between 0° and 200°C. Current‐voltage dependence of the cell, efficiency and the importance of the formation of the complex salt are discussed. The cell exhibits a fairly flat discharge curve. It was not possible to recharge it. Corrosion of the cadmium anode was negligible at current densities above 35 ma/cm2.