M. A. Petrunin

Vacuum oxidation of freshly deposited iron nanofilms

The interaction between freshly deposited iron films and oxygen at different evacuation degrees (from 10−5 to 760 mmHg) and room temperature is studied with the use of gravimetry (weighing with quartz nanobalance) and atomic force microscopy. According to data of atomic force microscopy, upon deposition of the metal on a glass substrate and during its subsequent oxidation, a metal-oxide composite film composed of metal-oxide nanoparticles with sizes of 20–30 nm where a metal core is covered with an oxide shell is formed. The reaction between freshly deposited iron and oxygen is shown to proceed quickly already at a pressure of 10−5 mmHg. An increase in the pressure is found to result in an increase in the bulk oxidation degree of the film. The growth kinetics of the film is two-stage. The initial oxidation stage can approximately be described with a linear-logarithmic dependence. The thinner the deposited iron nanolayer, the higher the bulk oxidation degree. The large value of the rate of initial oxidation of freshly deposited layer at a pressure of 10−5 mmHg, can be related to redox processes at the magnetite-hematite interfaces of multilayer nanoparticles that constitute the deposited nanocomposite layer. Upon passivation of the layer, the inherent nanoporosity makes the metal-oxide nanocomposite an adsorbent that can accumulate and store the adsorbed components of the environment (air).

The directional formation and protective effect of self-assembling vinyl siloxane nanolayers on copper surface

With the use of the electrochemical-quartz crystal microbalance technique, scanner-assisted electrochemical reflectometry, and X-ray spectral microanalysis, adsorption of vinyl triethoxysilane on a copper surface from an aqueous solution is studied and the possibilities of directional formation of self-assembling layers and their protective effect in corrosive chloride-containing electrolytes are determined. The greatest protective effect is observed at a thickness of 3.8 molecular layers when the most compact film, which hampers the adsorption of chloride ions and substantially decreases the rate of their interaction with the surface copper atoms, is formed.

Gravimetry, resistometry, and Fourier-transform infrared spectroscopy for monitoring the corrosivity of the atmosphere with the use of an iron-oxide nanocomposite sensor layer

The properties of a heterophase nanostructured metal-oxide layer produced by reactive sputtering in a vacuum followed by exposing to an oxidizing air environment at different evacuation degrees at 25°C are monitored with the use of diffuse reflectance Fourier transform infrared spectroscopy, resistometry, and gravimetry. According to the data of atomic force microscopy and infrared spectroscopy, as a result of the application of a metal to a glass substrate and subsequent oxidation, a metal-oxide nanocomposite film composed of metal-oxide nanoparticles with sizes of 20–30 nm covered with magnetite-hematite oxide shells is formed. It is shown that a metal-oxide nanocomposite layer can be used as a sensor in oxidizing environments. Gravimetric and resistometric sensor responses (the integral degree of oxidation) are almost proportional to the logarithmic rarefaction, which enables one to use metal-oxide sensors in broad ranges of pressure and rarefaction of the monitored atmosphere. Results of gravimetry and resistometry showed that the low-temperature oxidation of freshly sputtered iron films is accompanied by their partial oxide compaction. For overall monitoring of the formation of magnetite and its transformation into hematite, the above methods should be supplemented with a spectral method, such as Fourier-transform infrared spectroscopy.

Adsorption of vinyl trimethoxysilane and formation of vinyl siloxane nanolayers on zinc surface from aqueous solution

The method of quartz crystal microbalance is used to study adsorption of vinyl trimethoxysilane (VS) on the surface of zinc from an aqueous solution. Adsorption isotherms are obtained. Approaches corresponding to the known adsorption isotherms are used for interpretation of adsorption data: Langmuir, BET, Flory–Huggins, Langmuir multicenter, Temkin, and Langmuir–Freundlich. It is shown that silanes are adsorbed on the surface of thermally deposited zinc from aqueous solutions and displace adsorbed water from the surface by occupying more than six adsorption sites on the surface. It is found that monolayer coverage of the zinc surface is reached at a concentration of the VS solution of 1 × 10–4 M. The neighboring adsorbate molecules can interact, forming siloxane dimers and trimers bound to the metal surface by either covalent or hydrogen bonds. Adsorption heats are calculated using different adsorption models. It is shown that VS is chemosorbed on the surface of zinc. An increase in the concentration of the VS solution up to 0.1 M results in formation of polycondensed siloxane oligomers on the surface with polycondensation degree n = 8–12. Oligomer surface fragments are connected with each other by hydrogen bonds and are connected with the surface by Zn–O–Si bridge bonds. The overall thickness of such a layer is 10–12 nm or ten molecular layers.

Formation of metal (Iron)-oxide nanostructures and nanocomposites by reactive sputtering and low-temperature reoxidation

Morphology and composition of nanostructured metal-oxide coating prepared by iron reactive sputtering and subsequent low-temperature oxidation in air at 50°C were studied by atomic-force microscopy (with digital processing of images), X-ray diffraction, and resistance measurements. The growth kinetics of metal-oxide nanoparticles constituting the sputtered metal-oxide composite was evaluated by the direct processing of surface AMF-images. According to the results of morphological studies after the low-temperature oxidation, the surface layer has complicated structure: the metal nanoparticles surrounded by the α-Fe2O3 oxide phase merge to extended rod-like structures (globules) sized, on the average, 100–200 nm lengthwise, 20–30 nm in diameter. This structure allows explaining the coatings’ functional properties important for their applications.

Formation of organosilicon self–organizing nanolayers on an iron surface from vapor phase and their effect on corrosion behavior of metal

Quartz crystal microbalance technique is used to study adsorption of vinyl trimethoxysilane and γ-aminopropyl triethoxysilane on the surface of freshly sputtered iron from the vapor phase. Adsorption isotherms are obtained. Approaches corresponding to the known adsorption isotherms are used for interpretation of adsorption data: Langmuir, BET, Flory–Huggins, multicenter Langmuir, Temkin, Frumkin, and Freundlich. Surface orientation of adsorbed molecules is determined. Adsorption heats of silanes are calculated using various methods. It is shown that silanes are chemosorbed on the surface of iron.

Adsorption of alkoxysilanes on aluminum surface from aqueous solutions

Adsorption of vinyltriethoxysilane and γ-aminopropyltriethoxysilane on the surface of aluminum from an aqueous solution is studied with the use of a quartz-crystal microbalance. Upon adsorption of silanes, adsorbed water is found to be displaced from the surface. For the interpretation of adsorption data, Langmuir, Brunauer-Emmett-Teller, Flory-Huggins, multisite Langmuir, Temkin, Frumkin, and Freundlich adsorption isotherms were used. The surface orientation of adsorbed molecules is determined. The heat of adsorption of silanes is calculated in different ways. Silanes are found to be chemisorbed on the surface of aluminum.

The effect of self-organizing vinyl siloxane nanolayers on the corrosion behavior of aluminum in neutral chloride-containing solutions

The methods of quartz crystal microbalance, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier-transform IR spectroscopy, and X-ray structural microanalysis were is used to show that adsorption of vinyl silane on an aluminum surface from an aqueous solution results in formation of a uniform, self-organizing protective vinyl siloxane nanolayer covalently bound with surface metal groups. Its thickness can be controlled by variation of application conditions. The effect of a vinyl siloxane nanolayer on dissolution of aluminum is studied in chloride-containing solutions. It is found that an ordered vinyl siloxane nanolayer with a thickness of up to 5 molecular layers causes efficient inhibition of uniform and local corrosion of aluminum. It is shown that the vinyl siloxane nanolayer is preserved on the surface of aluminum after 10 days of corrosion tests, which indicates its stability at exposure to water and corrosive components.

Control of local corrosion and fracture of metals in optical models of narrow crevices, gaps and cracks using ellipsometry techniques

The method of laser polarization and optical monitoring is described for model studies of distributed and localized corrosion processes in optical models of gaps and cracks. It allows studying localized corrosion fracture of a surface (crevice corrosion; pitting; corrosion cracking; galvanic, selective, intercrystallite, or microbiological corrosion; etc.) in cases in which the process is nonuniformly distributed over the surface and is inaccessible for studies using the standard corrosion–electrochemical methods.

Local corrosion dissolution of steel in earth-simulating solutions

Methods of optical in situ microscopy and scanning reflectometry were used to determine that localized corrosion defects (pitting) emerging on a pipe steel in a neutral solution simulate a neutral underfilm solution. The initial stages of this process were studied. The density, mean radius,and dimensions of corrosion spots (or pits) were determined. It was shown that the defects grew mainly into a depth that exceeded 100 μm after several hours and attained 600 μm after 33 days of corrosion tests. Similar behavior may lead to corrosion cracking under the cyclic mechanical stresses. The stress intensity factors realizable in steel in the event of localized corrosion defects were calculated, and the possibility of determining the danger of corrosion cracking initiation under stress of pipe steel was determined on the basis of both optical and electrochemical data.