V. I. Kichigin

Chemical Etching Technique for Investigations of a Structure of Annealed and Unannealed Proton Exchange Channel LiNbO3 Waveguides

The proton exchanged channel waveguides are actively used for different integrated-optic components. There is a problem of the channel waveguide characterization because the single-mode channel waveguides for infrared region have the cross section about several microns. The wet etching and noncontact profilometry were used to investigate phase composition in proton exchanged channel waveguide. It has been found the known phases of H x Li 1−x NbO 3 have noticeably different etching rates. So, obtained experimental data gives the possibility of phase composition identification for channels with cross-section down to ∼ 2 μm.

Kinetics of hydrogen evolution in acidic environments on pressed micrographite electrodes modified with carbon nanotubes. I. Polarization studies

The kinetics of cathodic hydrogen evolution on pressed micrographite electrodes containing up to 8 wt % multiwalled carbon nanotubes is studied. The effects of the potential scan rate, concentration of nanotubes, direction (forward or reverse) of polarization, acidity of environment, and electrode potential are discovered.

Electrochemical impedance spectroscopy of anodic processes on Co2Si electrode in sulfuric acid solutions

Frequency dependences of the impedance of Co2Si electrode in 0.5 M H2SO4 and 0.05 M H2SO4 + 0.45 M Na2SO4 solutions are measured in the ranges of the active dissolution, active-passive transition, passive state, and transpassivity. There are potential values in the active range when the impedance can be interpreted as the impedance of the selective cobalt dissolution. The impedance spectra in the passive range and in the beginning of the transpassive potential range are described with the use of an equivalent circuit taking into account the existence of an oxide layer on the electrode surface.

Electrical conductivity and IR spectra of molten benzoic acid

Impedance method was used to measure the electrical conductivity of benzoic acid melts, and the concentration of free protons in these melts was estimated. IR spectroscopic data are presented and the existence of benzoic acid in melts in the form of molecules is suggested.

Inhibition of corrosion and hydrogenation of carbon steel in media containing hydrogen sulfide and carbon dioxide with low concentrations of salts of oxyethylated amines

Impedance spectroscopy was used to study the protective action of salts of higher aliphatic oxyethylated amines as universal inhibitors of the hydrogen sulfide and carbon dioxide corrosion and hydrogenation of carbon steel.

A Study of Hydrogen Accumulation in Multiwall Carbon Nanotubes by Electrochemical Techniques

Accumulation of electrolytic hydrogen in alkaline medium (5 M KOH) by multiwall carbon nanotubes (MWCNTs) 20–60 nm in inner diameter and 2 μm in length obtained by catalytic pyrolysis of propane/butane mixture has been studied by means of the electrochemical diffusion technique, cyclic voltammetry, and impedance spectroscopy. MWCNTs were applied on a steel membrane and were encapsulated by a 10-nm electrolytic nickel layer. Cyclic voltammograms were recorded in the range of potentials from −1.2 to +0.2 V and contained a current peak in the cathode region corresponding to hydrogen absorption by nanotubes at −0.9 V and current peak in the anode region corresponding to oxidation of absorbed hydrogen at −0.6 V. Hydrogen storage capacity of MWCNTs varies from 4.6 to 6.5% depending on the amount of nanotubes according to electrochemical diffusion data. The electrochemical impedance data correlate with the results of the above methods.

Kinetics of hydrogen evolution from acidic solutions on pressed micro graphite electrodes modified with carbon nanotubes. II. Impedance studies

The kinetics of hydrogen evolution on pressed micro graphite electrodes modified with multi-walled carbon nanotubes (MWCNTs) is studied in chloride environments with a constant ionic strength equal to unity with the use of impedance spectroscopy. The impedance of electrodes containing from 0.1 to 8 wt % MWCNTs in solutions of a general composition x M HCl + (1 − x) M NaCl at a currentless potential and at E = −0.6 V (N.H.S.) is interpreted as impedance of porous electrodes. The data obtained indicate the absence of diffusion limitations of the processes that proceed at a currentless potential and of the hydrogen evolution reaction. When the content of MWCNTs in a micro graphite electrode increases to 8 wt % at E = −0.6 V (N.H.S.), the increase in the contribution of the double layer capacitance and the adsorption capacitance to the Faraday impedance is the most pronounced, which means that MWCNTs promote a specific interaction of the electrolyte ions and atomic hydrogen with the surface of the cathodically polarized electrode.

Use of method for chemical etching for identification of structure of proton exchange channel waveguides fabricated on Z-cut of lithium niobate crystal

It was established by chemical etching that proton exchange on the surface of LN +Z cut in the molten benzoic acid at the temperature of 190°…210°С during 1…4 h causes fabrication of channel waveguides, consisting of 3 proton exchange phases.

Aging effect in proton-exchanged optical waveguides based on lithium niobate crystals

The optical characteristics of planar waveguides produced by proton exchange in lithium niobate crystals in different acids (with and without additives) are unstable with time (“aging” effect). The aging effects in LiNbO3 optical waveguides are investigated at room and elevated (50, 60, or 70°C) temperatures. In all cases, variations in the refractive index of the waveguide layer with time, i.e., for two or three years at room temperature and for several weeks at elevated temperatures, are determined for waveguides prepared in different media. The dependences of the optical characteristics of waveguides on the nature of proton sources and the aging conditions are obtained experimentally.

Anodic behavior of cobalt silicides in potassium hydroxide solutions

Anodic behavior of a CoSi2 electrode in 0.1–4 M KOH solutions and a Co2Si electrode in 1 M KOH was studied in a range from the corrosion potential (Ecor) to the oxygen evolution potentials with the use of polarization and impedance measurements. A number of results indicate enrichment of electrode surface layers in cobalt. At potentials from Ecor to Etp transpassivation potential, impedance spectra correspond to the passive state of the silicides. At potentials from Etp to the onset potential of oxygen evolution, impedance spectra can be described taking into account the inclusion of hydroxide ions in the passivating film. Equivalent electric circuits are proposed for different electrode potential ranges.