Discharge In Electrolyte Research Articles

Effect of adding magnesium to lithium on the performance of discharge and hydrogen evolution of the lithium anode

The present study evaluates the effect of magnesium as an inhibitor on the performance of discharge and hydrogen evolution of lithium anode in alkaline electrolyte with additives. The electrochemical behaviors of lithium and lithium–magnesium alloy are assessed by hydrogen evolution rate, discharge current density, anodic potential, and potentiodynamic polarization. For these conditions, the results show that addition of magnesium to lithium enhances the current efficiency. Addition of 0.07 wt% Mg to lithium has minor effect on discharge current and anodic potential of lithium anode. The chemical composition and the morphology of the anode surfaces were evaluated by X-ray diffraction and scanning electron microscopy. The results show that the slow dissolution of lithium–magnesium alloy generates the formation of LiOH, LiOH·H2O, and Mg(OH)2. After discharge in saturated alkaline electrolyte with additives, the lithium–magnesium surface is less porous than lithium surface. Hydrogen evolution decrease, prompted by adding magnesium to lithium, is related to surface integrity enhanced by Mg(OH)2.

Preparation and characterization of three dimensionally ordered macroporous Li 4Ti 5O 12 anode for lithium batteries

Three dimensionally ordered macroporous (3DOM) Li 4Ti 5O 12 membrane (80 μm thick) was prepared by a colloidal crystal templating process. Colloidal crystal consisting of monodisperse polystyrene particles (1 μm diameter) was used as the template for the preparation of macroporous Li 4Ti 5O 12. A precursor sol consisting of titanium isopropoxide and lithium acetate was impregnated into the void space of template, and it was calcined at various temperatures. A macroporous membrane of Li 4Ti 5O 12 with inverse-opal structure was successfully prepared at 800 °C. The interconnected pores with uniform size (0.8 μm) were clearly observed on the entire part of membrane. The electrochemical properties of the three dimensionally ordered Li 4Ti 5O 12 were characterized with cyclic voltammetry and galvanostatic charge and discharge in an organic electrolyte containing a lithium salt. The 3DOM Li 4Ti 5O 12 exhibited a discharge capacity of 160 mA h g −1 at the electrode potential of 1.55 V versus Li/Li + due to the solid state redox of Ti 3+/4+ accompanying with Li + ion insertion and extraction. The discharge capacity was close to the theoretical capacity (167 mA h g −1), which suggested that the Li + ion insertion and extraction took place at the entire part of 3DOM Li 4Ti 5O 12 membrane. The 3DOM Li 4Ti 5O 12 electrode showed good cycle stability.

Electrochemical oxidation of titanium by pulsed discharge in electrolyte

We propose a high-voltage (>1000 V) pulsed discharge method of preparation of thin anodic films on valve metals under conditions of extremely high rates of the film growth. The peculiarities of this method have been demonstrated on the anodic oxidation of titanium in sulfuric acid solutions. A light flash at the electrode was generated upon the pulsed anodization of titanium. The emission spectra consist of narrow lines assigned to electronically excited O, H and Ti atoms, indicating that a hot plasma is created at the electrode surface. The current efficiency of TiO 2 anodic film formation exceeds markedly 100% for the pulsed Ti anodization. This non-faradaic yield was associated with the contribution of the plasma-generated high-energy radicals to the oxide growth processes. We applied various techniques to compare the composition, morphology, structure and semiconducting properties of the anodic films prepared by the high-voltage pulsed discharge and the conventional galvanostatic anodization. The anodic TiO 2 films prepared by the high-voltage pulsed discharge have nearly ideal stoichiometric composition and are more amorphous as compared to galvanostatically grown ones. Thin TiO 2 films (50–150 nm) formed in the pulsed regime exhibit significantly higher photocurrent quantum yields at λ < 310 nm and a significantly lower donor concentration.

Characterization of Oxide Coatings Deposited on Pure Titanium by Alternating-current Microarc Discharge in Electrolyte.

Microarc oxidation is an advanced coating process to deposit thick, hard ceramic oxide coatings on metal surfaces. In this paper, a ceramic oxide coating of 30 μm was prepared on TA2 pure titanium by alternating-current microarc oxidation in aluminate solution. Its morphology, composition and structure were characterized by scanning electron microscopy, X-ray diffractometry, Raman spectroscopy. The Al, Ti, O concentration profiles across the coating were determined by energy dispersive spectroscope. The outer layer of the coating is composed of a large amount of TiAl2O5 and a little rutile type TiO2 compounds. But the rutile contentin the inner layer is much higher than in the outer layer while the TiAl2O5 content decreases obviously in the inner layer. All of these oxides derive from a rapid solidification of the melt in microarc discharge zone. The Al atoms from the aqueous solution have diffused to the coating/titanium substrate interface, but are enriched in the outer layer. However, the oxygen and aluminum atoms have not diffused into the unoxidized titanium substrate, even near the coating/substrate interface. This facilitates maintaining mechanical properties of pure titanium substrate after microarc oxidation treatment on titanium surface.

Analyses of Microarc Oxidation Coatings Formed on Si-containing Cast Aluminum Alloy in Silicate Solution.

A dense ceramic coating up to 130μm thick was deposited on high silicon cast aluminum alloy by microarc discharge in silicate electrolyte. Its microstructure and composition were analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and phase identification was performed by X-ray diffraction (XRD). In addition, the distributions of hardness, H, and elastic modulus, E, across the ceramic coating were determined by nanoindentation method. The coating has a three-layer structure. The profiles of H and E in the coating are similar. From the surface to the inner layer of the coating, H and E gradually increase. The inner layer is dense and hard, in which the H and E can reach about 15 GPa and 250 GPa, respectively. This coating consists of mullite, γ-Al 2 O 3 , γ-Al 2 O 3 and amorphous SiO 2 phases. The surface layer enriched in Si element has a high fraction of amorphous SiO 2 , where the Si element comes mainly from the electrolyte rather than the alloy substrate. However, the Si element from Al-Si substrate enhances the formation of mullite phase in the coating.

Leclanché cell investigations. Part II: Zinc potential as a tool for studying intermittent discharge

R20 sized Leclanché cells containing EMD and traditional or ZnCl 2 electrolyte have been discharged through 4 Ω for 15, 30 and 60 min/day. Measurement of recuperated zinc electrode potential against a precisely-located KCl bridge/SCE reference electrode assembly has enabled the three major stages of discharge in traditional electrolyte to be demonstrated in a cell for the first time. Reasonable correspondence between the discharge data and calculations, based on the positive active mixture composition, have confirmed the overall discharge reactions taking place in stages 1 and 2. In ZnCl 2 electrolyte, zinc potential decreased more rapidly than would have been expected for a discharge product of ZnCl 2·4Zn(OH) 2·H 2O. The experimental behaviour could be explained if this product which has a layer structure, absorbed additional ZnCl 2 and possibly H 2O between the layers. The potential of the EMD/H insertion electrode confirmed data obtained previously on another EMD so the large decrease of potential with H insertion is again ascribed to independent mobility of inserted protons and electrons.

Ceramic material processing by electrical discharge in electrolyte

New ceramic materials receive a great deal of attention as machine components, but they are hard to work. So a hybrid processing which combines electrical discharge processing with grinding is proposed. In this study, in order to examine the possibility of this hybrid processing, the electrical discharge processing on four kinds of ceramics was carried out with a needle electrode. The ceramic materials were alumina and three kinds of silicon nitride series to which are added alumina (ASN), magnesia (MSN), yttria and alumina (YASN). The results obtained showed that a pit can be formed on any ceramic and the pit depth apparently varies with the ceramic material. The removal rates of ASN, alumina, YASN and MSN become low in turn, and are independent of their mechanical properties. In the case of the silicon nitride series, the removal rates depended on their sintering additives, and the higher the applied voltage, the greater was the volume removed. High removal rate and low electrode loss are obtained when the needle electrode is negative. The ceramic materials are mainly removed by etching the grain boundary in a high-temperature electrolyte during the discharging process.

On plasma composition of a pulsed discharge in electrolyte

The equilibrium plasma composition for a system containing H, O, N, Na, and Cu is determined for the temperature range between 5000–20,000 K. This corresponds to the pulsed discharge plasma in electrolyte with energy dissipation which is near threshold. For computing the plasma composition of the system based on the minimization of free energy, the method of steepest descent was used. The plasma composition was calculated for different electrolyte contents, conductivity, and various external pressures.

Effective conductivities of an FeS positive in LiCl-KCl eutectic electrolyte at different states of charge

The effective conductivities of an FeS positive electrode in an Li-Al/FeS cell were determined for different states of charge and discharge in LiCl-KCl eutectic electrolyte at 450° C. The data obtained experimentally were compared with those obtained in 67.4 mol% LiCl-KCl electrolyte and theoretically predicted profiles. The electrode resistance profiles indicate that precipitation of KC1, in addition to formation of Li2S, in the positive electrode causes high internal resistance and limits the discharge capacity.

電解放電加工の基礎的研究 ＩＩ 電解液中の短間げきパルス放電現象

Single pulse discharge phenomena in the electrode gap smaller than 0.1mm filled with NaCl or NaNO3 solution are studied to make clear the working mechanism of electro-chemical discharge machining (ECDM). Gap voltage and current in discharge process and marks remained on the anode surface are investigated. Besides, ECDM with a square wave pulse generator is tried to obtain the optimum pulse width in this process.Discharge in electrolyte between carbon rod cathode and steel plate anode gets a type of either spark or arc. Fine spark discharge occurrs through gas bubbles between electrode and electrolyte, and it has no effect of metal removal. Developed arc discharge takes place between two electrodes and makes crater on the work surface.The influences of electrolyte, electrode gap, applied voltage and pulse width to the discharge in electrolyte are discussed in view of ignition delay. It is remarkable that discharge occurrs more easily in the electrolyte of higher concentration. Working voltage wave form in ECDM with a square wave pulse generator is similar to that of the single pulse discharge. Metal removal rate of it shows maximum when the pulse width is about 10-15ms.

電解放電加工の基礎的研究 電解液中の放電現象および電解放電加工における電解除去量について

Electric discharge phenomena in electrolyte and the electro-chemical metal removal in electrochemical discharge machining (ECDM) are studied experimentally to make clear the working mechanism of ECDM. The results obtained are as follows:(1) Discharge in electrolyte has some appearances by various electrode voltages and the unstable arc discharge is utilized for ECDM.(2) When the electrode gap is rather wide (about 0.2mm and more) discharge takes place between the electrode and the electrolyte, but in the usual ECDM of small working gap (less than 0.1mm) discharge seems to occur between the two electrodes.(3) In the single discharge by a rectangular wave pulse current generator an ignition delay of long duration is found out which suggests that the discharge occurs after the electrode surface has been covered by the gas evoluted in the electrochemical process.(4) Chemical analysis of iron ion in the drainage of ECDM shows that electrochemical removal in ECDM is nearely equal to the maximum rate of electrochemical removal even if the total removal rate changes.