Voprosy khimii i khimicheskoi tekhnologii (Issues of Chemistry and Chemical Technology)

14-18

Authors: A.A. Kityk, Y.D. Rublova, N.G. Bannyk, V.S. Protsenko, F.I. Danilov

The paper describes the effect of electropolishing on the corrosion rate of mild steel in a deep eutectic solvent Ethaline (a eutectic mixture of choline chloride and ethylene glycol). Electrochemical polishing was carried out both in "pure" solvent Ethaline and in Ehtaline with the addition of water (10 vol.%). The rate of steel corrosion was measured using electrochemical impedance spectroscopy. It was shown that electropolishing of steel leads to a decrease in its corrosion rate. The influence of the polishing current density and bath temperature on the corrosion rate was determined. An analysis of the obtained results showed that the rate of corrosion was decreased both by reducing the true surface area of the samples and by reducing the reactivity of the metal surface in the anodic half-reaction. Optimal electropolishing conditions were established under which the highest reduction of the rate of corrosion of mild steel in Ethaline was achieved.

27-35

Authors: T. Luk'yanenko, A. Velichenko, V. Knysh, O. Shmychkova

It is shown that the process of lead dioxide electrodeposition can be described by a four-stage kinetic scheme in which the electroactive particles are methanesulfonate complexes of lead with different composition. The initial stage of the process is the electrooxidation of water with the formation of oxygen-containing particles of radical type OH•ads on the electrode surface. Considering the water concentration in aqueous solutions and the fact that the hydroxylation of the electrode surface occurs at much lower potentials than the processes of oxygen evolution and oxidation of lead compounds, this stage is fast. Then the chemical stage of oxidation of [Pb(CH3SO3)]n(2n)+ by oxygen-containing radicals OH•ads occurs with the formation of the unfixed on the electrode surface Pb(III) hydroxo complexes [Pb(CH3SO3)n(OH)](2-n)+, which are subsequently oxidized in the electrochemical stage of charge transfer. At low polarization, this stage is rate-determining. The extremal dependence of the reaction rate on the concentration of methanesulfonate ions observed in this case is due to the simultaneous action of two oppositely directed factors: a decrease in the charge of electroactive particles and the surface of the electrode on the one hand, and the effect of inhibition by specifically adsorbed methanesulfonate ions, on the other. In the last stage of the process, the hydroxo complexes of tetravalent lead decay by chemical mechanism with the formation of lead dioxide. At high polarization, the rate-determining step of the process is the delivery of lead complex ions to the electrode.

43-47

Authors: E.V. Potapenko, P.Y. Andreev, I.P. Isayenko

A process of catalytic oxidation of 4-nitrotoluene with ozone was studied in the system (CH3CO)2O – CCl3CO2H in the presence of Co(II) acetate. It is shown that 4-nitrobenzaldehyde can be obtained in the form of acylale at 20C with a yield of up to 78%. The kinetic parameters of the main stages of the catalytic cycle have been established and a reaction mechanism has been proposed according to which ozone initially reacts with Co(II) acetate, and the direct oxidation of the methyl group of the substrate occurs in the reaction with the oxidized form of the metal. The optimal ratio [ArCH3]/[Co (II)] = 2 was determined experimentally. A further increase in the concentration of the catalyst influences neither the rate of oxidation nor the selectivity of the reaction. The role of trichloroacetic acid is not limited to the catalysis of the acylation reaction of alcohols and aldehydes that are formed during the oxidation process, but significantly affects the reactivity of Co(III). An increase in temperature promotes a real increase in the selectivity of oxidation. However, there is an increase in the depth of oxidation under these conditions and the main product of the reaction is 4-nitrobenzoic acid.

59-68

Authors: O.Ya. Smirnova, I.P. Polyuzhyn, Yo.Yo. Yatchyshyn

This paper investigates the chromatographic characteristics of seven amino acid derivatives of 3-chloro-1,4-naphthoquinone under conditions of normal-phase thin-layer chromatography. The dependences of the retention parameters of compounds on the composition of the binary mobile phase are obtained; the mobile phase is based on benzene, and chloroform, acetone, acetonitrile, methanol and propan-2-ol are used to enhance the elution ability at concentrations ranging from 2.5 to 10% v/v. It is shown that the experimental data on the retention of the investigated compounds as functions of the concentration of the polar component in the eluent are well described in logarithmic coordinates of the linear Soczewinski equation. The slope of these dependencies satisfactorily correlates with the area occupied by the adsorbed analyte molecule on the stationary phase, and the intercept also depends on the nature of polar component of the mobile phase. The calculation of the area occupied by the adsorbed analyte molecule on the stationary phase is performed according to the Snyder scheme.

77-81

Authors: N.Yu. Strutynska, O.V. Livitska, N.S. Slobodyanik

The features of the formation of cesium-containing calcium phosphates were investigated in the course of their precipitation from aqueous solutions in the presence of sodium or potassium cations with the subsequent heating of the obtained samples at 700C to convert them to the form of ceramic materials. According to the results of energy dispersion X-ray spectroscopy, CHN analysis and powder X-ray diffraction, the formation of apatite-related Cs+, MI, CO32- -containing calcium phosphates (MI – Na, K) was observed. It was determined that the content of Cs+ cations in prepared samples increased with increasing the amount of carbonate ions and in the presence of potassium cations in the initial solutions. The results of the thermal analysis confirmed the stability of Cs+,K+,CO32--containing calcium phosphates as regards the losing of carbonate at their heating to 900C. The established conditions of the preparation of cesium-containing apatite-type phases can be assumed as a basis of the development of the processes of the removal of radioactive cesium from aqueous solutions and its immobilization into stable phosphate matrices.

92-96

Authors: V.I. Goleus, Y.S. Hordieiev, A.V. Nosenko

Low-melting lead borosilicate glasses are used in electrical engineering and instrument making to manufacture hermetic ceramic-metal junctions. Thus, there is a need for the development of glass cements to produce junction at temperatures lower than 450C. In this regard, the formation conditions and the properties of glasses were investigated, the content of the components was as follows (mol.%): PbO 30–56, ZnO 5–20, B2O3 15–40, and SiO2 5–25%. The glasses of this composition were melted in platinum crucibles at a temperature of 850–900C for 30 minutes. The initial materials included silica sand, boric acid, zinc oxide and lead oxide. Glasses obtained in this system possess physicochemical properties varying in a quite wide range. The dilatometric softening temperature of glass varied in the range of 290–430C, the coefficient of linear thermal expansion varied in the range of (78–117)10-7 К-1 and the density varied from 4.9 to 6.7 g/cm3. The generalization of the dependence of the properties of glasses on their chemical composition was carried out using additive formulas for which the partial contributions of oxides to the values of the corresponding properties have been determined by experimental and statistical methods. It was found that very good wettability and spreadability at temperatures of 450–500C on the surface of aluminum oxide ceramics are typical of the glasses with a dilatometric softening temperature of no more than 340C and with the lowest crystallization ability. The chemical composition of the glasses, which are the most promising for obtaining ceramic-metal junctions at a temperature of 450°C, is limited to the following contents (mol.%): PbO 48–55, ZnO 5–14, B2O3 25–35, and SiO2 5–15.

103-109

Authors: V.A. Kucherenko, Yu.V. Tamarkina, I.B. Frolova

The thermolysis (≤500C) of five anthracites ANs (C 94.6–95.6%) impregnated with hydroxides MOH (M = Li, Na, K, Rb, and Cs) at MOH/AN ratios of RМOH≤20 mmol/g was investigated. Using the thermoprogrammed gravimetry (5 deg/min, OD-103 MOM derivatograph), the weight loss (Δm) was determined as the yield of volatile products and the rate of their formation (ωm) was estimated. It has been established that the thermal dehydration (≤200°С) and the formation (>250°С) of volatile organic products (VOPs) are observed as a result of parallel thermal and alkaline destruction when heating AN and "AN-MOH" compounds. The thermodehydration does not depend on the AN type, but is influenced by MOH and manifested by three peaks at 82–92°C, 138–147°C and 158–160°C related to H2O associated with the following: (1) organic coal substance, (2) MOH molecules, and (3) complexes "M+--system of polyarene". For all ANs, the effect of MOH is observed at 250–500°C (RMOH≤2 mmol/g) and results in an increase in the VOPs yield (from 1% to 5–6%) and a decrease in the effective activation energy (from 230–250 to 110–170 kJ/mol). It was proposed to estimate the alkaline thermal destruction contribution as the following difference in rates: Δm=m(AN-MOH)–ωm(AN). The obtained data allowed drawing the following conclusions: (1) the alkali promotes thermal destruction, (2) the maximum of Δωm value and the beginning of the VOP formation decrease by 50–80°C, and (3) the alkali reactivity increases in the range: LiOH

120-128

Authors: N.V. Nikolenko, I.S. Samchileev, A.V. Dubenko

The kinetics of ammonical leaching of molybdenum from the spent iron-molybdenum catalyst of Perstorp Formox under mechanical and ultrasonic conditions is studied. The process is shown to proceed in the intradiffusion mode, as in a fixed-bed flow reactor. The mechanical influence on the catalyst particles was modeled by continuously mixing of the suspension by the propeller stirrer (with a surface area of 2 cm2) at a rotation speed of 300 min-1 in a round-bottomed flask. The flask was placed in an ultrasonic bath filled with water at a frequency of 22 kHz and an intensity of 0.4 W cm-2. We used the "shrinking core" model which was modified for low-dissociation reagents by us as a mathematical model of the investigated process. The rate-determining step of the leaching process is the diffusion of hydrated ammonia molecules through the layer of the reaction product, ferric hydroxide. To confirm this conclusion, the apparent activation energies of the leaching process were determined using ammonia, soda and alkali, which were 21.3, 6.0 and 1.5 kJ mol-1, respectively. The difference in the values of activation energies is well explained by the fact that the rate-determining step of the process is the diffusion of hydroxide ions in solutions of alkali and carbonate ions in soda solutions. The effect of increasing the time of complete conversion of the catalyst particles for concentrated ammonia solutions is established, which can be caused by decreasing the diffusion coefficient of ammonia molecules or increasing the molar density of the iron hydroxide film. According to this effect, we conclude that an increase in the concentration of ammonia solution at the decomposition of iron molybdate above 2 mol L-1 has no significant advantages. For example, when using 13.5 M ammonia solution, the total conversion time is 39 minutes. But when using 2 M solution, the time is 52 minutes, i.e. only 1.33 times more. Therefore, the use of highly concentrated solutions of ammonia is not rational for the leaching of molybdenum from a raw material containing ferric irons.

135-141

Authors: U.V. Khromyak, V.Ye. Levytskyi, K.V. Stepova, V.Y. Skorokhoda

The influence of monomer nature (vinyl acetate, methyl methacrylate and styrene), concentration factors, temperature and mixing rate on the kinetics of the emulsion polymerization of vinyl monomers in the presence of polyvinylpyrrolidone has been investigated. The rational technological parameters of copolymer synthesis have been established. It has been determined that the properties of emulsion polymerization of latexes (surface tension, pH and particle radius) depend on the conditions of the process; the ratio of monomer to aqueous phase, temperature, concentration of monomer and initiator, and also the amount of polyvinylpyrrolidone. The polyvinylpyrrolidone-grafted copolymers that have been synthesized by emulsion polymerization have been used as a polymer matrix for the preparation of methyl methacrylate-copolymer compositions. Block polymerization of methyl methacrylate in the presence of polyvinylpyrrolidone copolymers occurs at a high rate and, depending on the nature of the polymer matrix, the monomer conversion rate of 70–90% is achieved within 10–15 minutes. The highest polymerization rate and the maximum degree of conversion are observed when using a grafted copolymer of polyvinylpyrrolidone with methyl methacrylate. The modified materials obtained on the basis of the developed compositions are characterized by sufficiently high operational properties, such as surface hardness, heat resistance and strength of adhesive bonds to supports of different nature.

148-152

Authors: Ya.O. Shablovsky, V.V. Kiselevich

The possible solution of the classical problem of correct determining the glass transition temperature of polymers is proposed. The equation for the correlation between the glass transition temperature and the cooling rate of polymeric glass-forming media is suggested on the basis of combination of thermodynamic formalism and the ideas of relaxation kinetics. The parameters of that kinetic equation are determined and tabulated for a number of glass-forming substances covering sufficiently wide class of pure and modified polymers, in particular polyvinyls, polyesters, and polydienes. The possibility of the manifestation of an anomalous dependence of the glass transition temperature on the cooling rate is substantiated. It is suggested that the observable anomalies in the kinetics of the glass transition arise from considerable inertance of the segments of polymeric macromolecules, i.e. are of threshold nature.