Oleg V. Belousov

Formation of bimetallic Au-Pd and Au-Pt nanoparticles under hydrothermal conditions and microwave irradiation.

The reduction of chlorocomplexes of gold(III) from muriatic solutions by nanocrystal powders of palladium and platinum at 110 and 130 °C under hydrothermal conditions and the action of microwave irradiation has been investigated. The structure and composition of the solid phase have been characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical methods. Bimetallic particles with a core-shell structure have been revealed. The obtained particles are established to have a core of the metal reductant covered with a substitutional solid (Au, Pd) solution in case of palladium, and isolated by a gold layer in the case of platinum. The main reason for such a difference is the ratio between the rates of aggregation and reduction. It has been shown by the example of the Au-Pd system that the use of microwave irradiation allows us not only to accelerate the synthesis of particles but also to obtain more homogeneous materials in comparison with conventional heating.

X-ray diffraction analysis of mesostructured materials by continuous density function technique

Abstract A continuous density function technique has been developed for X-ray diffraction (XRD) structural investigations of mesostructured materials. The technique is designed for the analysis of the density distribution in materials exhibiting nanoscale (2-50 nm) ordering of structural elements without atomic long-range order. The results of structure investigations of a series of silicate, metallosilicate and carbon mesostructured materials with hexagonal and cubic symmetry are presented.

The Dependence of the PdCl42−/Pd0 Electrode Potential on the Dispersity of Metallic Palladium

It was found that metastable equilibrium in the heterogeneous reaction PdCl42− + 2e = Pd0 + 4Cl− in H2PdCl4-hydrochloric acid solutions at 60°C depended on the dispersity of metallic palladium. It was shown experimentally that the dependence of the shift of the PdCl42− /Pd0 redox potential on the dispersity of palladium(0) was described by the Thomson equation.

The thermodynamic characteristics of aggregation of fine-dispersed palladium

The size-dependent effects of the heterogeneous reaction PdCl42− + 2e = Pd0 + 4Cl− were studied in hydrochloric acid solutions of H2PdCl4 at 40–70°C. Changes in the structural characteristics of palladium black were analyzed by transmission electron microscopy and X-ray diffraction. The temperature dependence of the redox potential of the PdCl42−/Pd0 pair was used to determine the thermodynamic characteristics of aggregation of fine-dispersed palladium. The heat effect of the reaction was in satisfactory agreement with direct differential scanning calorimetry measurements.

Behavior of platinum metal concentrates under autoclave conditions

Dressing processes of platinum metal concentrates (CP-1 and CP-2) in acid and alkaline media under autoclave conditions were studied. The optimal recovery conditions (time-, temperature-, and concentration-related) of impurity elements were found for the temperature range under study. It was demonstrated that the predominant changes occur during the first 30–60 min. Use of reducing agents can preclude transfer of noble metals into solution in leaching of impurity elements.

Interaction of ultrafine palladium and platinum powders with chlorocomplexes of gold(III) under hydrothermal conditions

Ultrafine Au-Pd and Au-Pt powders were synthesized under hydrothermal conditions, and their composition and structure were characterized.

Microstructure and the elemental and phase compositions of the diffusion joint of grade 45 steel through a powder layer

The microstructures of the transition zone and the powder layer, the concentration distribution of chemical elements across a diffusion joint, and the microhardness of the grade 45 steel-Ni powder layer-grade 45 steel layered composite materials fabricated by diffusion welding at various temperatures are studied. It is shown that the deposition of a nickel sublayer on steel and the application of a submicron nickel powder as an activating layer make it possible to form a high-quality diffusion joint at a temperature of 850°C, which is ~0.6 of the melting temperature of nickel (which has the lowest melting temperature in the given composite material). The sintering of a nickel powder and the formation of a transition zone between the nickel layer and steel occur simultaneously in a solid phase during diffusion joining. The transition zone consists of an α-Fe solid solution and the FeNi3 compound.

Refining of platinum–palladium concentrate under hydrothermal conditions

The possibility of refining platinum–palladium concentrates in alkaline and acid media by hydrothermal treatment under autoclave conditions was determined. The recovery parameters of impurity elements were found. Autoclave processing of platinum–palladium concentrate in alkaline media with sodium formate leads to recovery of the stable palladium oxide modification, which significantly improves opening of the concentrate in hydrochlorination.

Thermostimulated transformations of highly disperse powders of platinum group metals in an argon atmosphere

The behavior of palladium, rhodium, iridium, and platinum powders during their heating in an argon atmosphere was studied by differential scanning calorimetry (DSC). The DSC curves showed the exothermal peaks corresponding to the enlargement of the platinum group metal powders under study. Electron microscopy and XRD studies revealed that the particle size of highly disperse powders changed during the heating. Chemisorbed oxygen was removed from the powder surface above 800 K. During the heating of the mechanical mixture of highly disperse platinum and palladium powders, a solid solution formed with an exothermal effect.

Carbon-Supported Palladium–Gold Bimetallic Disperse Systems Formed in Aqueous Solutions at 110°С

Various palladium–carbon composites have been manufactured by autoclaving at 170°С to be used as precursors for manufacturing bimetallic particles. The morphology of the manufactured items was comprehensively studied by scanning electron microscopy; the ultrafine metal palladium was found to have particles sizes lying in the range 30–120 nm. The specifics of hydrothermal reduction of gold(III) chloro complexes by palladium–carbon composites at 110°С have been studied. An appreciable increase in gold(III) reduction rate was observed with the use of a palladium–carbon composite relative to the rate observed for ultrafine metallic palladium. Gold is reduced on a palladium–carbon composite to an individual metallic phase.