Electrodynamics applied to electrode potential and electrochemical kinetics

A key idea of the possibility of describing electrochemical systems and processes in terms of Maxwell’s electromagnetic theory is presented. This is an alternative to conventional Nernst-Tafel concept based on the Arrhenius hypothesis about electrolytic dissociation, which, despite of its minor heuristic value, is adhered to in many branches of chemistry for more than a century, thus, decelerating the progress. Fundamental laws of thermodynamics and electromagnetism enable us to use sufficiently elementary mathematical tools when quantitatively describing and predicting not only equilibrium states, but also transient processes with no use of model concepts.     

To the Tafel slopes at the anodic dissolution of iron in sulfuric electrolytes

Based on the hypothesis of the reversibility of an iron electrode, one can relatively easily explain the experimentally obtained Tafel slopes without multistage complex schemes involving hypothetic intermediate iron hydroxo compounds. On the other hand, the coincidence of the experimental slope with the slope following from the relation derived may be considered as a proof of the reversibility of the iron electrode. The Tafel slope is reproducible both on the clean and partially passivated iron surface. Original Russian Text ? Yu.P. Vishnevskaya, D.A. Tkalenko, M.V. Byk, V.A. Rupp, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 540–542.     

Atomic-topographic model of the electrochemical dissolution of a solid metal taking into account the effect of point lattice defects

A topokinetic model of a dissolving solid metal containing point defects, that is, either admixture atoms of a substantially more lowly or highly corrosion-resistant metal or the crystal lattice vacancies, is proposed. The model takes into account the mutual consistency of the atomic relief and the dissolution rate. Similarly to a defect-free crystal, the steady-state dissolution rate is determined by the elementary acts of transferring the base atoms to solution from step kinks whose amount substantially depends on the concentration of the point defects. Original Russian Text ? Yu. V. Alekseev, G.Yu. Alekseev, I.Yu. Alekseev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 479–487.     

Anodic dissolution of electrochemical chromium coatings in electrolytes for electrochemical machining: The dissolution rate and surface roughness

By the example of dissolution under conditions of controlled hydrodynamics (a rotating disk electrode), the distinctions of the surface formation after the anodic dissolution of electrolytic chromium films in electrolytes for electrochemical machining (ECM) (in chlorides and nitrates at current densities of 0.1–15 A/cm²) have been shown. The roughness of the produced surface was not considered intrinsic and correlated with the nature of the solution anion. In the chlorides, it was determined by the fracture formation due to the surface weakening and by the pitting formation, while, in nitrates, actually only by pitting formation. The influence of the current density and the surface heating at high current densities, along with the dimensions of the layers remaining after the chromium film dissolution, on the degree of the surface weakening and its roughness has been shown. The expedience of the nitrate solutions use at the high electrolyte flow rates during the electrochemical microprocessing of such surfaces has been demonstrated.     

The electrochemical dissolution of molybdenum in non-aqueous media

Electrochemical dissolution of molybdenum in 1.0 M solution of ammonium nitrate in liquid ammonia at − 35 °C was investigated. The electrolyte has good conductivity and it showed corrosive ability to great extent. The galvanostatic method was used to investigate the anodic dissolution of molybdenum in NH₄NO₃/NH₃ system with a cell potential difference of + 4.0 V. The dissolution efficiency of 79% was noted, while electrodeposition efficiency of molybdenum at parent cathode went up to 76%. No new molybdenum salt was added to the solution; only the dissolved molybdenum was redeposited on parent cathode. Later the residue left was analyzed for possible molybdenum complex and XRF analysis showed the presence of molybdenum in the residue. Cyclic voltammetry was used to investigate kinetic parameters of Mo in NH₄NO₃/NH₃ system. Electrochemical behavior of molybdenum in 1-butyl-3-methyl-imidazolium/trifluoromethansulfonat was also investigated and it was noticed that molybdenum dissolves in NH₄NO₃/NH₃ system at faster rates.     

Mechano-electrochemical dissolution of copper at reversible electrode potential

The mechano-electrochemical dissolution of copper during yielding at constant strain rate has been studied in acidic cupric sulphate solutions, restraining the electrode potential to the reversible potential by a potentiostat. It has been found that the mechano-electrochemical current undergoes a marked rise at the beginning of the plastic region and then shows an asymptotic tendency with increasing strain. It has been proved that the initial slope of the current-strain diagram is independent of strain rate and gives a direct measure of the anodic current density on the active surface formed by yielding. The initial slope increased with increasing either temperature or the concentration of cupric ion. It seems likely that slipping occurs at yielding, and the emerging active surface which has a high adatom activity provide an anodic dissolution at the reversible potential. The theory based on the model agrees well with the experimental results.     

Diffusion kinetics of a metal anodic dissolution with forming unstable charged products

Anodic dissolution of bivalent metal in binary electrolyte, through positively charged intermediates, is theoretically analyzed. The components’ concentrations and the electrical potential distributions in diffusion layer under the intermediate quasireversible decomposition are calculated. It is shown that the electrochemical process rate decreases when the products’ stability constant increases.     

Mathematical model of the local kinetics of a nickel oxide electrode

A new mathematical model of the local kinetics characteristic E = f(i, τ) for nickel oxide electrodes NiOOH/Ni(OH)₂ is presented. A flat crystal of active substance with thickness h that reconstructs a particle with a size of 2h is the sample for the studies. A mathematical model of the process is based on the conception considering the potential and polarization as a function of the concentration of the protons at the surface layer of the crystal. The polarization is considered as a sum of the concentration, activation, and ohmic components. The concept considers the coefficients of the protons activity and the proton vacancies in the crystal lattice. The potential of the electrode in the process of the discharge is determined by the changes in the surface concentration of protons. The coefficient of diffusion, the rate of the electromigration of protons, and the resistivity of the solid phase change over the thickness of the crystal in accordance with the changes in the concentration of the protons and the activity factors. The distribution of activity concentration of activity protons was determined by solving a one dimension problem of diffusive and electromigration transfer.     

Repassivation kinetics of zirconium alloys investigated by a scratching electrode technique

The repassivation behavior of zirconium alloys in a solution containing 0.1 M H₃BO₃ and 0.1 M LiOH was examined by means of a rapid scratching electrode technique. The repassivation behavior of the scratched surface of the alloys varied with time. The place exchange model reveals that at the initial stage of repassivation (within 10 ms) log i (t) is linearly proportional to q (t) with a slope of 1/K. The high field ion conduction model reveals that after 25 ms log i (t) is linearly proportional to 1/q(t) with a slope of cBV. The cBV value, in particular, which is a measure of the protectiveness and erosion resistance of an alloy, increases when there is an increase in the Nb content of the alloys, as well as in the applied potential and the solution temperature. This result suggests that these parameters can affect the repassivation rate of zirconium alloy.     

Regularities of electrochemical dissolution of Cu 62 Zn alloy in chloride solutions

The pattern of the electrochemical ionization and passivation of Cu 62 Zn brass in chloride solutions with different compositions is studied. The electrochemical dissolution of Cu 62 Zn alloy is shown to be controlled by ionization of the copper component in the alloy. The dissolution selectivity of the brass Cu 62 Zn components and the modification of the surface of the alloy during electrochemical etching in chloride solutions are studied. The uniform electrochemical dissolution of α-brass in an acid medium was found to occur in the presence of chlorine ions and an Fe³⁺ oxidizing agent.     

Suspended electrode kinetics of mechanically activated pyrite

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｃｈａｎｉｃａｌａｃｔｉｖａｔｉｏｎｉｓｗｉｄｅｌｙａｐｐｌｉｅｄｉｎｅｎ ｈａｎｃｉｎｇｍｅｔａｌｌｕｒｇｉｃａｌｐｒｏｃｅｓｓ[1～ 3] ａｎｄｃｈｅｍｉｃａｌｓｙｎ ｔｈｅｓｉｓ[4 ,5] .Ｓｏｆａｒｉｔｉｓｄｉｆｆｉｃｕｌｔｔ     

Kinetics of electrochemical process of galena electrode in diethyldithiocarbamate solution

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｉｅｔｈｙｌｄｉｔｈｉｏｃａｒｂａｍａｔｅ (ＤＤＴＣ)ｉｓｏｎｅｏｆｔｈｅｍｏｓｔｆｒｅｑｕｅｎｔｌｙｕｓｅｄｃｏｌｌｅｃｔｏｒｓｆｏｒｆｌｏｔａｔｉｏｎｏｆｈｅａｖｙ ｍｅｔａｌｓｕｌｆｉｄｅｍｉｎｅｒａｌｓ ,ｓｕｃｈａｓｇａｌｅｎａ ,ｃｈａｌｃｏｐｙｒｉｔｅａｎｄｊａｍｅｓｏｎｉｔｅ ,ａｎｄｉｔｓｈｏｗｓｓｔｒｏｎｇｓｅｌｅｃｔｉｖｉｔｙ[1] .ＷｈｅｎＤＤＴＣｗａｓｕｓｅｄｉｎｈｉｇｈｌｙａｌｋａｌｉｎｅ (ｐＨ >11.4 )ｆｏｒｓｅｐａｒａｔｉｎｇｇａｌｅｎａｆｒｏｍｓ…     

黄铜矿与斑铜矿在酸性细菌培养基中的电化学溶解对比(英文)

采用电化学测试和X射线光电子能谱(XPS)测试分析黄铜矿与斑铜矿在酸性细菌培养基中的电化学溶解过程。斑铜矿直接氧化反应比还原反应更容易发生,但黄铜矿既难被氧化,又难被还原。斑铜矿具有更高的氧化速率,从而比黄铜矿更容易被溶解。铜蓝(CuS)是黄铜矿与斑铜矿溶解过程的中间产物。因此,斑铜矿的溶解途径主要为直接氧化过程,中间产物铜蓝(CuS)可能限制其进一步溶解。黄铜矿的溶解途径包含了还原-氧化过程,其中,黄铜矿首先被还原为与斑铜矿类似的中间产物,再进一步被氧化,并产生铜蓝(CuS),而黄铜矿的最初还原过程是其溶解过程的主要限制步骤。     

Impedance of NiSi electrode in sulfuric acid in the active anodic dissolution range

Anodic behavior of NiSi electrode in 0.5 M H₂SO₄ in a potential range of active dissolution is studied. A conclusion about the selective dissolution of nickel from nickel silicide at a small anodic polarization (up to 0.15 V) is drawn based on the impedance data. The solid-phase diffusivity of nickel and the thickness of the diffusion zone are estimated.     

Computer processing of images when studying electrochemical dissolution of multiphase systems

The possibility of using a computer analysis of the surface images of a steel electrode upon polarization when studying the formation of anodic dissolution sites based on the brightness spectrum is illustrated. A numerical spectral parameter that characterizes the anodic dissolution sequence of separate structural constituents of an iron-carbon alloy is proposed.     

The kinetics of the anodic dissolution of copper in acid chloride solutions

The anodic dissolution of copper has been studied in different acid chloride solutions under potentiostatic conditions. A rotating disk electrode technique was employed.The results showed that the slow cuprous chloride complexes transferred towards the bulk is the r.d.s. all over the polarization range. Anodic limiting currents have been also observed and explained.     

氢氧化铝在苛性碱中溶解动力学研究

实验研究了氢氧化铝在苛性碱中溶解的表现动力学方程,在氢氧化铝溶解过程中存在着一对可逆过程,最终建立两相平衡体系.从动力学方程推测了氢氧化铝在苛性碱中溶解的机理,在溶解过程中没有发生化学反应.仅是氢氧化铝晶体的氢键断裂.氧化铝在苛性碱溶液中以Al(OH)3单分子形态存在.在溶解结束或者种分过程结束时,在苛性碱溶液中,液相中的Al(OH)3与固相通过氢键的生成或断裂构成的两相吸附平衡.实验得到了在平衡状态下,液相中氧化铝的平衡浓度与苛性碱浓度、温度以及固相量的关系,与经验公式数值吻合较好.     

Specifities of forming electrochemical dissolution zones at ferrite-cementite-structured alloys in sulfuric acid solutions

Specific features of the formation of electrochemical dissolution zones at steels C _T 20 and C _T 45 with a ferrite-cementite structure, were revealed by combining electrochemical and metallographic methods. A possibility of developing the self-dissolution process at the ferrite/cementite boundary is shown. A spontaneous sequence of the anodic dissolution of structural constituents of the alloys is found. Original Russian Text ? N.V. Tarasova, S.N. Saltykov, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 252–255.     

Potentials of electrochemical reactions and nature of singularities in electrode polarization dependences

The conditions of transition of the electrochemical polarization mode to a faradaic process are studied on the metal electrode within the framework of the microscopic approach when the value of polarization potential reaches the threshold value of the potential of the electrochemical reaction. It is suggested that the elementary act of electron transfer between the metal and redox electrolyte occurs at the interface under polarization bringing the local electron level of the reagent to the Fermi level of electrons of the metal. Discharge through the Helmholtz layer limited by electrons occurs due to resonance “lightening” of the potential barrier between the metal and localized redox state of the reagent. Estimates are obtained for the values of threshold potential and exchange current of the faradaic process. A method is suggested for consideration of the elementary act of the electrochemical reaction on the basis of the Hamiltonian describing the microscopic mechanism of Fermi edge singularities. Application of the known solutions allows the appearance of threshold singularities of polarization dependences in electrochemistry to be explained.