M. R. Kiselev

On the electrocontact oxidation of vacuum iron nanocondensates: II. Structural characteristics

Changes in the composition and morphology of thin-film conductors based on a nanostructured metal-oxide nanocomposite, which was obtained by the vacuum deposition of iron in an oxygen atmosphere at 10−5–10−3 mmHg on an amorphous glass substrate, induced by external electric current are studied using atomic force microscopy and Raman spectroscopy. The most pronounced zone of degradation is observed in the middle part of the conductor. Compared to the undistorted parts of the conductor, the degradation zone is characterized by an increased content of magnetite phase, which is formed as a result of the prevailing further oxidation of nanoparticles constituting the film. The surface morphology of the degraded part is characterized by the appearance of extended structures, some of which are nanoparticles and submicroparticles oriented in the direction of the applied electric current, which can be due to both the electric mass transfer of the metal and its electric oxidation. The other kind of extended structures are nanofibers composed of adjoining and coalesced metal-oxide nanoparticles, which can appear due to the electric oxidation in the electric contact areas between nanograins and leads to the coalescence of the neighboring nanograin chains into nanofibers. It is proposed that the electrocontact oxidation should be used as a method of creating fibrous metal-oxide nanocomposites based on vacuum deposits of iron or other metals.

Heat processes in mixtures of polymers with cyanuric acid after plastic deformation under high pressure according to calorimetric data

Mixtures of cyanuric acid with different polymers are subjected to plastic deformation under pressure of 1 GPa, and the DSC method is used to establish that endothermal processes with enthalpies that can reach 50 J g-1 occur in deformed mixtures under heating in the range of 50–250°C. The occurrence of endothermal processes is related to the destruction of intermolecular bonds formed at the acid–polymer interface and due to formation of double electric layers and appearance of interphase electrostatic attraction.

The effect of graphene oxide (GO) on biomineralization and solubility of calcium hydroxyapatite (HA)

Interaction between GO and the counterpart of the bone tissue, calcium hydroxyapatite Ca10(PO4)6(OH)2 (HA), is modeled in the course of synthesis of nanosize composite materials (CMs) based on graphene oxide (GO) and biocompatible HA with a GO content of 0.1, 1.0, 2.0, and 5.0 wt % GO from aqueous solutions in the system of Ca(OH)2–H3PO4–GO–H2O under native conditions (37°C). The effect of CM composition on the size and morphology of HA nanocrystals (HA NCs) is determined using the methods of physico-chemical analysis (chemical, XRD, IRS, DTA, TDG, SEM, TEM). The solubility of HA NC CMs by Ca2+ ions in distilled water is determined under in vitro conditions, and the possible results of interaction between GO and native calcified tissues are analyzed.

Thermal effects in mixtures of aluminum with polyvinyl chloride after plastic deformation under high pressure

PVC and mixtures of PVC with aluminum of different compositions were subjected to plastic deformation under a pressure of 0.5–3.0 GPa using setups of Bridgman anvil type. DSC data showed that ΔCp in the polymer was doubled and Tc increased by 20°C. Chemical reactions occurred on the interfaces of freshly opened metal surface/polymer phase under pressure treatment in the mixtures. They were accompanied by formation of volatile and soluble products. When metal-polymer mixtures were heated under pressure after deformation, chemical reactions occurred in them starting at 40°C and reaching the maximum intensity in the temperature range of polymer transition from the vitreous to highly elastic state. Thermogravimetric studies of mixture samples of different compositions were carried out.

Activation of Thermal Processes in Mixtures of Some Vanadium Compounds with LiOH as a Result of Plastic Deformation under High Pressure

V2O5, V2O3, HVO3, and mixtures of these compounds with 15% LiOH were subjected to plastic deformation at a pressure of 2 GPa and room temperature on high-pressure testing machines of the type of Bridgman anvils. The investigation of the samples was performed using differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis. The presence of LiOH in the mixtures decreased the thermal stability of vanadium compounds. During plastic deformation the LiV3O8 phase was formed in mixtures, the amount of which increased with heating the samples to 200°C. It is assumed that the ions that form by treatment under pressure can affect the structure formation processes in mix samples.

The formation of urchinlike nanostructures under thermal oxidation and depassivation of iron particles

Methods of scanning electron microscopy with an X-ray probe, Raman spectroscopy, and thermogravimetry are used to study the morphology and composition of metal–oxide nanostructures obtained by thermal oxidation of spherical microparticles of iron powder with a diameter of 1–3 μm. It is shown that unidimensional hematite nanoflakes and fibers grow under atmospheric annealing at 300°C and above in the radial direction from powder microparticles, which is accompanied by depassivation and acceleration of corrosion layer growth. An increase in temperature and oxidation time results in transformation of microparticles into urchinlike multilayer nanoparticles consisting of elongated crystalline α-Fe2O3 nanowhiskers growing normally to the surface of the particle consisting of an iron core and shells of the magnetite and hematite phases. Growth of hematite nanowhiskers continues until the metallic core is completely oxidized.

Heterophase activation of the growth processes of 1D hematite nanostructures under oxidation of plastically deformed iron powders

Methods of scanning electron microscopy with an X-ray probe, Raman spectroscopy, and thermogravimetry are used to study the morphology and composition of metal-oxide nanocomposites obtained by intense plastic deformation of iron powder and the further annealing in the TGA mode. It is shown that high-temperature annealing of activated powder deformation results in the formation of “hematite wood”—a layer of “nanoflakes” and “nanoleaves” growing vertically on the composite surface. In addition to its intrinsic functional (sensor, catalytic, semiconductor, adsorption) properties, this structure possesses pronounced primer properties for further formation of protective surface layers.

Thermogravimetric analysis of the aluminum-polypropylene mixtures after plastic deformation under high pressure

The thermogravimetric analysis of the aluminum-polypropylene mixture of varied composition was performed to determine the effect of plastic deformation under the high pressure. It was found that a loss of mass by the mixed samples up to 400°C is due to decomposition of a polymer and the mass gain above 500°C, due to aluminum oxidation.

A study of the mixtures of polystyrene and polyvinyl fluoride with aluminum after plastic deformation under high pressure using DSC and thermogravimetry

Mixtures of powdered polystyrene and polyvinyl fluoride with aluminum exposed to plastic deformation under pressure of 1 and 4 GPa, have been studied by DSC and thermogravimetry. It has been established that, in the deformed mixtures at temperatures up to 200°C, exothermal processes take place. Interaction between polymer decomposition products and aluminum has been studied, as have its oxidation and nitrogenation.

The effect of mechanical activation on the heat capacity of powdered tungsten

We have studied the heat capacity (Cp) of a mechanically activated tungsten powder. It is established that the mechanical processing leads to an increase in Cp of the metal powder at low temperatures and modifies the character of the temperature dependence of this parameter. The dependences of Cp and its heating-induced variation on the treatment duration have been determined. It is concluded that the observed effects are related to the accumulation of defects in the metal grain volume during mechanical activation and their annealing in the course of heating.