V. M. Krutskikh

Effect of doping nickel-boron alloys with rhenium, molybdenum, or tungsten on kinetics of partial reactions of chemical-catalytic reduction of metal ions

Catalytic activity, chemical composition, and structure of Ni-Re-B, Ni-Mo-B, and Ni-W-B alloys obtained by chemical-catalytic reduction of metal ions were studied. Introduction of a doping element into the nickel-boron alloy changes the catalytic activity of the alloy surface as regards concurrent partial reactions of heterogeneous hydrolysis of dimethylamine borane, reduction of nickel atoms, evolution of molecular hydrogen, boron, and carbon. The aim of the work was to elucidate the causes for nonlinear, bell-shaped dependence of partial rates of dimethylamine borane hydrolysis and hydrogen evolution on the concentration of the doping element in the alloy. The structure and uniformity of distribution of elements in the coatings were evaluated. Estimation of the grain size in the deposits based on the broadening of reflex (111) evidences the nanocrystalline structure of the obtained alloys. The minimum grain size (<20 nm) corresponds to the doping element concentration within the alloy with the maximum catalytic activity. Boron content in the alloys decreases at an increase in the doping element concentration. The observed acceleration of the heterogeneous reaction of dimethylamine borane hydrolysis is explained by a change in the catalytic activity of the coating surface as a result of the subsystem restructuring during the formation of an alloy between nickel and the doping element.

Structural characteristics and catalytic activities of nanocrystalline Ni-Mo-B coatings obtained by catalytic electroless reduction

The structures, chemical states of elements, and catalytic activities of Ni-Mo-B alloys with different molybdenum contents, which were obtained by catalytic electroless reduction of metal ions, were studied. The rates of the partial reactions (heterogeneous hydrolysis of dimethylamine borane, reduction of nickel ions, and evolution of molecular hydrogen) were found to make a bell-shaped curve when plotted versus the concentration of molybdate ions in solution.

Gaseous products of dimethylamine borane oxidation in chemically catalyzed deposition of nickel-rhenium-boron coatings

The gaseous products of the oxidation of hydride hydrogen of the dimethylamine borane (DMAB) (CH3)2NH · BH3 reducer used for depositing Ni-Re-B coatings and hydrolysis of DMAB on them were studied by mass spectrometry of the isotope composition of the gas. The oxidation level of hydride hydrogen of the DMAB reducer was found to depend on the catalytic activity of the Ni-Re-B alloy, on which heterogeneous hydrolysis takes place. For Ni-Re-B alloys with low rhenium concentrations (0–13 at %), the heterogeneous hydrolysis of DMAB proceeds with hydride hydrogen oxidation to the atomic state, as it does in the deposition of the Ni-B alloy. In contrast, at high rhenium concentrations (40–46 at %), the oxidation proceeds to the proton H+, leading to an antibatic dependence of the hydrolysis and alloy reduction rates. An analysis of the partial rates of the process and isotope composition of the evolved gas revealed two different mechanisms of the chemical-catalytic reduction of Ni-Re-B alloys at concentrations of potassium perrhenate of 0–4 and 4–16 mM in solution.

Formation mechanism and structure of nickel-molybdenum-boron chemical-catalytic coatings

Effect of molybdate-ions on the kinetics of partial reactions of dimethylamine-borane oxidation and nickel-and molybdate-ions reduction in the process of their chemical-catalytic reduction during the Ni-Mo-B-coatings deposition is studied. Molybdenum is deposited as metal only in the codeposition with nickel, yielding amorphous alloys. Adding of low concentration of the molybdate-ions to the nickel-plating solution increases the hydrogen evolution and alloy deposition rates as a result of the accelerating of dimethylamine-borane heterogeneous hydrolysis. At high molybdate-ion concentrations in the solution, a denser film of the molybdate reduction intermediate products forms at the electrode surface; this decreases the system’s catalytic activity as regards the dimethylamine-borane heterogeneous hydrolysis and thus decreases the hydrogen and nickel ions reduction rates.

Composition and structure of cobalt-molybdenum-boron alloys produced by chemical catalytic reduction with dimethylamine borane

The co-reduction of cobalt and molybdate ions with dimethylamine borane in pyrophosphate solutions is shown to produce Co-Mo-B alloy coatings. Molybdate is reduced concurrently with cobalt to metal forming a solid solution in cobalt matrix with a hexagonal lattice. The alloy deposits have a pronounced [001] texture with the easy magnetization direction normal to the coating surface. The composition of alloys is heterogeneous in their thickness. The alloys contain cobalt and molybdenum hydroxide admixtures, as well as intermediate products of molybdenum reduction, in the superficial layers.

Structure and chemical and phase composition of the thermal oxidation products of Ni-Mo-B coatings plated by chemical catalytic reduction

Morphology, phase composition, and chemical state of the elements in the superficial oxide layers on Ni-Mo-B alloy coatings obtained by chemical catalytic reduction of metal ions with dimethylamine borane are studied. The coatings were oxidized at 600°C and an air pressure of 2 × 104 Pa. The difference in the growth morphology of the oxide layers on freshly deposited coatings and those preliminarily heated in a vacuum is revealed. The oxide films are composed of the MoO2, Mo2C, as well as amorphous and nanocrystalline NiO, phases. Electron Auger spectroscopy has shown that boron in the form of B(OH)3 is present in segregations along spheroid boundaries. Upon the oxidation of freshly deposited coatings, pits are formed as a result of the “explosive” removal of water vapors from the coating.

Relaxation processes and kinetics of the thermal oxidation of Ni-Mo-B alloys obtained by chemical catalytic reduction

Kinetics of the high-temperature oxidation of Ni-Mo-B alloys containing 11 wt. % Mo (obtained by means of chemical catalytic reduction with the use of dimethylamine borane) is investigated. A strong dependence between the oxidation rate and the sublimation of volatile compounds on the prehistory of deposits is disclosed. Freshly obtained deposits exhibit an anomalous short-term weight loss caused by the “explosive” character of the removal of water vapors, evolved as a result of the reduction of molybdenum and boron oxides with hydrogen at heightened temperatures. Preliminarily heating the specimens in a vacuum decreases the intensity of or completely eliminates the anomalous phenomenon. When oxidizing the coatings in air at 600°C, two processes take place, namely, the oxidation of the coating components (a growth of the oxide layer) and the sublimation of volatile compounds.

Studies of chemical–catalytic formation of Ni–Re (Mo, W)–B alloys

The paper briefly reviews the studies of the processes of formation of Ni–Re–B, Ni–Mo–B, and Ni–W–B triple alloys using the method of chemical–catalytic reduction of metal ions and their properties.

Electroless deposition and properties of Co–Re–B alloys

The data on the mechanism of electroless (catalytic) deposition of Co–Re–B coatings are obtained by determining the donor capacitance of dimethylamine borane (DMAB) (CH3)2HN · BH3 reductant and the oxidation level of its hydride hydrogen. From the results of the study of isotopic composition of evolved hydrogen, it is concluded that the oxidation level of DMAB hydride hydrogen depends on the catalytic activity of the alloy. The alloys containing up to 46 at % rhenium were produced by the electroless deposition.