卷 54, 编号 2 (2018)

The characteristics of Ni–P alloy electrodeposition from a methanesulfonate electrolyte have been investigated. It has been found that the phosphorus content of the alloy increases with increasing the concentration of sodium hypophosphite in the electrolyte and reducing the electrodeposition current density. A mechanism of codeposition of nickel and phosphorus has been suggested. It is shown that phosphorus was formed by electrochemical reduction of hypophosphite anions and their disproportionation at a catalytically active surface of a nickel cathode. It has been shown quantitatively that the most likely path for the formation of phosphorus through the electrochemical mechanism is the direct electrochemical reduction of a hypophosphite anion to atomic phosphorus. The rate of phosphorous formation from hypophosphite anions is dependent on the concentration of hydrogen ions in the near-electrode layer. Therefore, the phosphorus content of the coatings obtained from the methanesulfonate electrolyte is slightly decreased as compared with that from the sulfate electrolyte which exhibits higher buffering properties. It has been revealed that codeposition of nickel and phosphorus reduces the kinetic difficulties of electrochemical reduction of the nickel ions. This might be due to an increased near-electrode concentration of nickel hydroxyl complexes discharging at the cathode, which is the result of an increased near-electrode pH caused by the reactions involving hypophosphite anions and hydrogen ions.

The study considers heat exchange in a three-phase system: electrolyte solution—vapour-gas envelope (VGE)—a titanium workpiece. The temperature of a workpiece, current intensity, heat fluxes from the envelope to the electrolyte and the workpiece were measured in an aqueous solution of ammonium chloride with addition of ammonia and glycerol. Addition of ammonia and glycerol proved to decrease current intensity, heating temperature, total energy liberation and heat fluxes to the solution and the sample. Furthermore, it was found that heat shares passing to the electrolyte and the workpiece are not affected by ammonia and glycerol concentrations. The addition of ammonia and glycerol affect heat exchange, increasing the VGE thickness due to intense evaporation of these elements.

Regularities in the influence of processing time and discharge energy on the thickness, microhardness and roughness of carburized cases during electrospark graphite alloying of steel surfaces are studied and quantitative data on them are obtained. The thickness of the strengthened layer increases with gains in discharge energy and alloying time. Specimens of 40Kh, 38KhMYuA, 40KhN2MYuA, 30Kh13, Armco iron, 12Kh18N10T steels and 20 steel, as well as EGe-4 graphite are studied. The tests were carried out using the following devices: EILV-8А, EILV-9, Elitron-22А, and Elitron-52А, which provide discharge energy in the range from 0.1 to 6.8 J. Experiments show that case depth and microhardness under the same process conditions are differ significantly for various steel grades. Case depth increases with higher initial carbon contents in steel. The greater the discharge energy, the greater this difference is. Wear tests show that the method of nonabrasive ultrasonic finish processing after graphite electrospark alloying is effective, and it allows increases in the wear resistance of specimens by a factor of 7.8 for 40Kh steel and by a factor of 11.5 for 12Kh18N10T steel. Research confirms that the stage electrospark alloying of the surface of a specimen after carbonization with a graphite electrode effectively decreases roughness. Discharge energy is lowered at each stage. The stage graphite electrospark alloying of the 38KhMYuA steel case allowed decreases in the surface roughness from R_а = 11.9–14.0 μm to 0.8–0.9 μm. Industrial tests show that graphite electrospark alloying offers can accomplish a number of practical tasks.

The principle of operation of an electrohydrodynamic pump (EHDP) is explained. Research problems are formulated for the study of the patterns and peculiarities of the operation of the EHDP for the purpose of its optimization. The experimental facility is described and the peculiarities of the relaxation of the output characteristics of a single-stage EHDP are determined. The dependences of the pressure and current characteristics on the time and voltage (dc) supplied to the EHDP are presented. New results related to very long operation of EHDPs are revealed, e.g., the fact that the pressure characteristics are fluctuating time functions. A theoretical model of the electric current transfer in an EHDP is presented, which is based on an analog electrical circuit.

The objective of this study is to investigate the corrosion inhibition of API N80 steel pipelines in 1M HCl solution by a synthesized compound (N-(3-(dimethyl octyl ammonio) propyl) palmitamide bromide, subjected to four different modes of measurements. Weight loss (WL) was investigated at five different temperatures: 25–60°C, while potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) were tested at 25°C. The result showed that the synthesized inhibitor was good and its protection efficiency (%η) significantly increased by increasing both the dose and the temperature. The polarization curve revealed that the studied inhibitor acts as mixed-type of inhibitor. Adsorption of the investigated inhibitor led to a reduction in the double layer capacitance and an increase in the charge transfer resistance. The adsorption of this inhibitor was found to obey the Langmuir adsorption model. The thermodynamic parameters were calculated and discussed. A clear correlation was found between corrosion protection efficiency and theoretical parameters obtained using density functional theory.

The structure and the properties of oxide films formed on titanium in the diphosphate based electrolytes by plasma electrolytic oxidation in the spark-discharge regime at application of inter-electrode voltage 100 to 130 V have been studied. A possibility to obtain oxide layers containing alloying elements by the modification of the composition of electrolytes has been stated. It was found that the chemical and phase composition as well as the topography, the microstructure and the grain size of the formed layers depend on the electrolyte composition, applied current density and inter-electrode voltage. The effect of the chemical composition of the formed mixed oxide films on the corrosion resistance and catalytic activity has been discussed.

In this study, crude Tunisian kaolin clay (from the Tabarka region—North of Tunisia) was subjected to refluxing with phosphoric acid under different operating conditions. Acid activation was carried out with H₃PO₄ (28 and 54 wt % P₂O₅), at temperatures of 60 and 90°C, with the time of treatment ranging from 2 to 12 h. The structure of acid leached kaolinite clay was characterized by; the XRD, FTIR, SEM, ²⁹Si and ³¹P NMR techniques and the Brunauer Emmett Teller theory was uses as the base for respective calculations. The chemical composition was determined by ICP. The results of XRD show that the kaolin acid treatment at 90°C provoked a destruction of clay structure after 6 h with phosphoric acid 28 wt % P₂O₅ and after 4 h with phosphoric acid 54 wt % P₂O₅. Hereafter, the forming of an amorphous silica phase is detected, whose confirmation is effected by the ²⁹Si NMR analysis. FTIR studies indicate that acid treatment under reflux conditions leads to the removal of the octahedral Al³⁺ cations for the two types of phosphoric acid. In fact, the chemical analysis shows that the leaching of Al³⁺ ions increases progressively with severity and the time of the reaction. The acid treatment with H₃PO₄ 54 wt % P₂O₅ at 90°C, enlarged the surface area from 24 to 150 m²/g. Thus, the solids obtained by the acid treatments can be used as promising adsorbents and catalyst supports.