A. P. Khramov

Aluminum electrode for electrochemical studies in cryolite-alumina melts at 700–960°C

The paper presents the results of tests of different aluminum electrode designs for electrochemical studies in cryolite-alumina melts in the temperature range of 700–960°C. Their operation as regards stability and reproducibility of the potential and the highest activity of metallic aluminum is analyzed. The new design of the aluminum electrode is suggested that is characterized by a more stable and reproducible potential, as compared to the designs earlier suggested. Herewith, the activity of metallic aluminum is higher. It is shown that the suggested electrode is suitable for operation in cryolite-alumina melts in the temperature range from 700°C. The electrode can be used for a prolonged time. Herewith, its potential remains stable and reproducible.

Character of the corrosion destruction of inert anodes during electrolysis of cryolite alumina melt and the reasons for it

The behavior of inert anodes during the electrolysis of the cryolite alumina melt in a laboratory electrolyzer is investigated at 960°C. On the basis of the electrolysis tests of more than 150 anodes with various structures and compositions, the character of their corrosion and possible reasons for it are revealed. It is shown that the physical and physical-chemical processes of the interaction of the molten electrolyte and oxygen evolved from the anode material are the basis of the phenomena of the corrosion destruction of anodes. The requirements for increasing the corrosion stability of the structure of inert anodes are formulated.

Stationary anodic process at platinum in KF-NaF-AlF3-Al2O3 melts

The kinetics of the anodic process at platinum in KF-NaF-AlF3-Al2O3 melts in the temperature range 725–800°C is studied using potentiostatic polarization. Platinum is considered as an indifferent oxygen-evolving electrode, and a two-stage scheme is proposed for the anodic process on it. According to this scheme, primary charge transfer with the formation of adsorbed Oads particles is accompanied by their desorption according to a physical or an electrochemical mechanism. The polarization dependences of the anodic process on platinum are calculated under stationary conditions with allowance for the predominance of different stages of the process and a desorption mechanism. The calculated and experimental stationary anodic polarization dependences are compared.

Metal anodes oxidation rate forecasted by results of electrolysis

This work represented the results from electrolysis tests of low-melting cryolite-alumina melts at temperatures of 790 and 850°C using metal anodes based on Cu-Fe-Ni and Cu-Al. The duration of experiment was at least 72 h. With these results, oxide layer dissolution/erosion rate and anodic material oxidation depth was calculated in arbitrary units (alloy cm/year) with examples of extrapolated (forecasted) experimental data of oxidation depth and oxide layer thickness for a long period. The oxide layer formed on the anode surface by electrolysis of the studied materials was found to decelerate further oxidation all over the period of tests.

Reduction mechanism of oxides in calcium chloride melts

Alternative notions on the reduction mechanism of crystalline metal oxides during the electrolysis of CaCl2 melts, which has been actively discussed worldwide in scientific publications over the last 15 years, are described. It is shown based on the known experimental data on the nature of the Ca-CaCl2 solution and its reduction properties that metal oxides can reduce without direct contact with the cathode in the volume of a homogeneous Ca-CaCl2 salt near cathode, i.e., catholyte. The reducing agent is calcium dissolved in a form of Ca+ cations in this case. The reaction surface area multiply increases in this case, which favorably affects the course of heterophase chemical reactions. The method of introduction of Ca+ ions into the salt melt can be both by electrolysis of CaCl2 or due to the dissolution of metal calcium, and it does not vary the essence of our process model.

Effect of the cationic composition of cryolite-alumina melts on the anodic overvoltage

Steady-state polarization of anodes prepared from platinum or glassy carbon is studied in a laboratory cell in a cryolite-alumina melt containing small amounts of potassium and lithium fluorides and various alumina amounts. The surface area of the anodes reaches a few centimeters squared. An insignificant depolarization of the anodic process is discovered following the replacement of a fraction of sodium ions in the electrolyte by potassium ions in an amount of ∼3.9 mol % KF (∼4.1 wt %) and a noticeable depolarization, following the substitution of K+ in an amount of ∼7.1 mol % KF (∼7.6 wt %). Substituting lithium ions in an amount of ∼3.7 mol % LiF (∼1.8 wt %) for a fraction of sodium ions leads to an insignificant polarization. A significant effect of a general cryolite ratio on polarization is discovered. A noticeable increase in the anodic polarization is fixed at an alumina concentration equal to 5–5.5 wt %.

Kinetic Parameters of Silver Electrodeposition from Nitrate Melts

The system Ag/KNO3–NaNO3–AgNO3is studied in an open bath in air by various experimental methods. The limiting diffusion currents of the silver electrodeposition are determined by a galvanodynamic method at various linear current sweep rates. The diffusion coefficient of Ag+ions in equimolar KNO3–NaNO3melt is determined by a potentiodynamic method at linear potential sweep. The exchange currents on a silver support are determined by the method of two current pulses.

Хронопотенциометрия на платине в расплаве KF-NaF-AlF 3 -Al 2 O 3 А.В. Суздальцев, А.П, Храмов, Ю.П. Зайков О.В. Лимановская, В.Н. Некрасов

As a model of metabolic transformations of antiviral drug “Triazaverin” and its analogues‑2-alkylthio‑6-nitro‑1,2,4-triazolo[5,1-c][1,2,4]triazine‑7-ones 1a-d examined the oxidation of alkylthio groups to the corresponding sulfoxides 2a-d and sulfones 3a-d, as well as the process of nucleophilic substitution sulfonyloxy group of cysteine and cysteamine with the formation of compounds 5 and 6.In October 2015 marks 95 years of Chemical-technological faculty (HTF), Ural Polytechnic Institute named after S. M. Kirov (UPI), and now a Chemical-technological Institute (CTI) Ural Federal University named after first President of Russia B. N. Yeltsin (UrFU).I nstantaneous rate of aluminum corrosion in media with different acidity has been studied using a method of polarization and the electrical resistance. A resulting time series of instantaneous corrosion rate have been analyzed using the standardized range. As a result, it has been found that in all studied media corrosion process has a stochastic character, and time series of instantaneous rate are anti-persistent.

Anodic behavior of the NiO-Fe2O3-Cr2O3-Cu composite during the low-temperature electrolysis of aluminum

In order to fabricate oxide-metallic composites with the composition 25.3NiO-41.2Fe2O3-13.5Cr2O3-20.0Cu (wt %), the temperature and duration of sintering (1350°C, 30 min) that ensure the formation of the solid solution of chromium oxide in nickel ferrite have been determined. This material is tested as an anode for the electrolysis of the low-temperature solution with the composition 12.0NaF-36.8KF-51.2AlF3 (wt %), which was saturated with Al2O3 (t = 800°C). The amount of gaseous oxygen evolved on the anode was measured. It is shown that the main reaction on an anode at current density i = 0.015–1.0 A cm−2 is the oxidation of oxygen-containing anions from a melt with the formation of gaseous O2 and a substantial increase in the oxidation rate of the composite anode is observed at i > 1.0 A cm−2. The voltage across the electrolyzer (4.5 ± 0.5 V) and the anodic potential (2.43 ± 0.2 relative to the Al reference electrode) during a prolonged experiment (for 89 h, i = 0.4 A cm−2) indicate a stable and acceptable electrical conductivity of the material, while the dissolution rate, which was calculated by the weight loss (0.6 kg/yr) and volume loss (0.7 cm/yr), satisfy the requirements to inert anodes.

Rate of metallic anode oxidation in the course of electrolysis of cryolite-alumina melts. Derivation of basic equations

The well known oxidation law is offered as a basis for the new method that allowed predicting the service life of metallic anodes by extrapolation of the experimental results (time dependences of the substrate oxidation depth, oxide layer mass and its chemical composition) to a long-term period (a year). The suggested calculation technique allows predicting the steady state characterized by constant equal rates of metallic anode oxidation and erosion of its oxide layer and also the constant oxide layer thickness in the case when it features an ability to hinder further oxidation.