I. V. Petukhov

Corrosion and electrochemical behavior of Ni-P coatings in 0.5 M H2SO4

An increase in the phosphorus content in Ni–P coatings (from 6.6 to 13.4%) is shown to be accompanied by amorphization of their structure and a decrease in the anodic dissolution rate (at low overvoltages) by two–three orders of magnitude, whereas the corrosion rate is decreased to a lesser degree. Polarization curves of the coatings measured in 0.5 M H2SO4 comprise two linear segments and no passive range. In the first segment, the ba coefficient is shown to be anomalously high (∼0.4–0.5 V for amorphous alloys), and the dissolution is controlled by transient volume diffusion of nickel and accompanied by surface accumulation of phosphorus. Being added as a stabilizer, thiourea reduces the corrosion resistance of the coatings and increases the dissolution currents, which can be to a considerable degree eliminated by increasing the phosphorus content in the coatings. The adverse effect of Pb incorporation into the coatings manifests itself as a substantial acceleration of their anodic dissolution.

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.

Obtaining of Ni–P–TiO2 Composite Coatings with TiO2 Sol and Surfactants and Their Properties

The influence of surfactants and TiO2 sol on mechanical, catalytic, and corrosive properties of electroless Ni–P coatings was investigated. Additives of the surfactants caused the decrease of internal stresses in the Ni–P coatings and smoothing of their surfaces. Incorporation of the TiO2 particles facilitated the rise of microhardness of the Ni–P coatings from 545 ± 11 Hv up to 614 ± 17 Hv. Additives of the surfactants accelerated hydrogen evolution reaction on the composite Ni–P–TiO2 coatings in acid and alkaline media, and increased photocatalytic activity in methylene blue decomposition. Incorporation of the TiO2 particles and application of the surfactants resulted in an improvement in the corrosion resistance of original Ni–P coatings in 0.5 M H2SO4.

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.

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.

Possible reasons for the appearance of metallic phase in electroless nickel plating solutions

The growth of Ni-P coatings was studied in the “stable” electroless nickel plating solution and in the “decomposed” solution containing in its bulk a sufficient amount of the metallic phase particles.

Structure and properties of proton exchange waveguides on Z cut of lithium niobate crystal fabricated in molten benzoic acid with the addition of lithium benzoate

Methods of chemical etching, non-contact profilometry, X-ray analysis and mode spectroscopy enabled to find out that proton exchange channel waveguides formed on Z cut of lithium niobate crystal in the molten benzoic acid with the addition of 3 mol.% of lithium benzoate at the temperature of 225°C were composed of κ2-phase and a thin layer of α-phase. Proton exchange on +Z and -Z faces of the lithium niobate crystal in benzoic acid (with or without the addition of lithium benzoate) occurs at the same rate.

Corrosion Degradation of Chromium Coatings on Steel in NaCl Concentrated Solution

Corrosion-electrochemical behavior of chromium coatings at steel substrates (40X, 20X13, and 12X18H10T) in concentrated (318 g/l) NaCl solution at elevated temperatures is studied, in particular, under conditions of friction against rubber (thus modeling the mine screw-driller rotor operation conditions). By and large, the chromium coatings in the studied solution have fairly good corrosion stability. However, when through pores occur in the coatings, chromium-steel galvanic couples are formed, in which chromium is the anode, and steel, the cathode. This causes intense corrosion damage to the coating in close proximity to the pores. Steel undergoes no corrosion here. It is the Cr-coating porosity that gives rise to its accelerated degradation under the friction, although friction as such does not accelerate the corrosion catastrophically.

Precipitation of lamellar phases in H: LiNbO3 layers

Structural defects in a surface layer of the proton-exchanged waveguide layer formed on a substrate prepared from an X-cut lithium niobate single crystal are revealed and investigated using scanning electron microscopy and optical interference profilometry in combination with selective etching. It is established that these structural defects, which are oriented along the [0 15 1] crystallographic direction and matched to the matrix (the β phase of the HxLi1 − xNbO3 solid solution) through a network of misfit dislocations, consist of one of the HxLi1 − xNbO3 phases precipitated in the form of lamellar regions ∼100 nm thick. Precipitation of lamellar phases precedes the destruction of the surface of the proton-exchanged layer. The presence of residual internal stresses in the LiNbO3 initial crystal favors the formation of the lamellar phases.