L. N. Vykhodtseva

Properties and preparation of amorphous chromium carbide electroplates

Abstract The electrochemical and corrosion behavior of chromium electroplates formed in sulfuric acid solutions of Cr(III) in the presence of oxalates was studied by measuring steady-state polarization curves in 0.5 M H 2 SO 4 solution. These electroplates demonstrate no active dissolution region and their open-circuit potentials are located in the passivity region, i.e. shifted substantially in the positive direction as compared with those of metallurgical chromium and electroplates from standard chrome-plating baths. The results of X-ray photoelectron spectroscopy (XPS) studies evidence that the passive metal surface layer several nanometers thick consists of chromium oxides with incorporated carbides formed during electroplating. It is supposed that the peculiarities of the corrosion and electrochemical behavior of the deposits under study can be attributed to the presence in them of chromium carbides, which operate as cathodic agents. At the same time, the formation of these carbide compounds during the cathodic deposition of chromium electroplates from sulfuric acid Cr(III) solutions in the presence of sodium oxalate is a result of electrocatalytic activity of metal chromium. The latter assumption is confirmed by XPS analysis of surface layers formed during the exposure of chromium to sulfuric acid solutions containing organic substances.

Cr local environment by valence-to-core X-ray emission spectroscopy.

Valence-to-core X-ray emission spectra have been measured for a number of chromium compounds such as oxides, carbides, borides, nitrides, phosphides etc. The experimental spectra are in good agreement with the calculated ones. They form the basis for a detailed analysis of the first coordination shell of Cr. The unique application of this technique for material chemistry and environmental science is illustrated by two very different examples. In the former case the presence of Cr–C bonds in the bulk structure of electrochemically deposited amorphous chromium coatings was confirmed. In the latter one we have shown that a contaminated soil sample most probably contains Cr carbides and/or phosphides from anthropogenic origin.

Structural features of the electrode/solution interface at the reduction of Cr3+(aq) cations on liquid mercury and solid indium electrodes in acidic media

AbstractCharacteristics of electroreduction of Cr3+ and Cr2+ ions on the dropping mercury (literature data) and indium cathodes are analyzed as a function of pH of the medium. A hypothesis that polymeric hydroxocompounds of chromium, which are present in different aggregate states, represent the main or partial reactants in the

Corrosion–Electrochemical Behavior of Chromium Deposits Obtained from Sulfuric Acid Solutions Containing Oxalates

Cr\left( {III} \right)\xrightarrow{{ + e}}Cr\left( {II} \right)\xrightarrow{{ + 2e}}Cr

Surface Layers on Chromium in Sulfuric Acid Solutions of Organic Substances: An X-ray Photoelectron Spectroscopy Study

stages is additionally substantiated.

Electrocatalytic Formation of Polymolecular Products at the Cathodic Polarization of Polycrystalline Chromium in Sulfuric Acid Solutions of Formic and Oxalic Acids

The studies on chrome-plating from sulfate–oxalate Cr(III) baths are generalized. It is shown that the metal is deposited from the mentioned baths at a current efficiency over 40% and forms deposits of any thickness. Chrome-plating may be carried out in the cells with undivided cathodic and anodic compartments, which reduces the current efficiency to 25–30%. The reflectivity and color of the deposits do not differ from those of the deposits from standard chrome-plating baths based on Cr(VI). Special attention is paid to the studies of the corrosion and electrochemical behavior of deposited layers. Steady-state polarization curves in a 0.5 M H2SO4indicate that the studied chromium deposits exhibit no active-dissolution range. The free corrosion–potential is shifted in the positive direction compared with coatings deposited from standard chrome-plating baths and falls into the passivity range. According to XPS method, the passive film is about several nanometers thick and, along with oxide compounds of chromium, includes its carbides formed during the electroplating.

Observation of Species of Intermediate Oxidation Degrees, Formed during Anodic Dissolution of Chromium, by the Rotating Ring–Disk Electrode Method

The corrosion–electrochemical behavior of chromium electrodeposits, which are formed in sulfuric acid solutions of Cr(III) containing oxalates, is studied by taking steady-state polarization measurements in a 0.5 M H2SO4 solution. No region of the metals active dissolution is observed for such coatings, and the open-circuit potential is localized in the passivity region, i.e. it is substantially displaced in the positive direction as compared with that for metallurgic chromium or the coatings deposited from standard chromium-plating electrolytes. According to XPS data, the surface layer of the passive metal a few nanometers thick includes oxide compounds of chromium and also carbides formed during the coating electrodeposition. Specific features of the corrosion–electrochemical behavior of the deposits are attributed to the presence of carbide compounds of chromium in them, with the compounds playing the role of a cathodic alloying agent.

Reduction of Trivalent Chromium Ions on Stationary Mercury Electrode in Concentrated LiCl Solutions

Using the valence-to-core version of X-ray emission spectroscopy (valence-to-core XES) together with X-ray diffraction analysis, the structure and the composition of nickel coatings deposited from solutions containing hypophosphite ions or dimethylaminoborane (DMAB) are studied. The diffraction patterns of prepared deposits are characterized by the presence of a wide “halo”. Annealing of crystallographically amorphous deposits at temperatures of 500°C and higher transforms these haloes into the spectra corresponding to metal nickel and its phosphides or borides present in the crystallized deposits. A result of fundamental importance obtained in the simultaneously conducted examination of the same deposits by the valence-to-core XES method is that both the binding energy and the intensities of Kβ satellite spectral lines of annealed samples remain unchanged as compared with original samples. Based on this comparison, it is concluded that phosphide and boride nickel compounds were already formed in the course of electrodeposition, whereas the thermal treatment of deposits (crystallization) leads only to aggregation of the metal and metal-metalloid nanoparticles.