A. A. Vinokurov

The effect of Fe2O3 dopants on electrophysical and sorption properties of ZnO

The effect of Fe2O3 dopants (0–0.8 mol.%) on ZnO conductivity and its chlorine chemisorption ability has been studied in the temperature range of 20–250 °C. Introduction of dopants increases the activation energy of ZnO conductivity and decreases the conductivity. The effective charge of the chemisorbed chlorine species as well as the strength of their bonding to the surface in samples containing Fe2O3 are considerably lower than in initial ZnO, which leads to a decrease of reactivity of the doped catalysts in chlorination.

Chemisorption of hydrogen sulfide on lead sulfide

The hydrogen sulfide chemisorption on lead sulfide at 22–100°C is studied by static testing in a vacuum and by pulsed chromatography. It is established that H2S is sorbed in reversible and irreversible forms and that the process is accompanied by the sample charging. Irreversibly sorbed hydrogen sulfide is removed by heating the sample in a vacuum or in an inert-gas stream at temperatures exceeding the adsorption temperature by 30–50°C.

Formation of zirconium diboride nanoparticles as a result of reaction between zirconium tetrachloride and sodium borohydride

We have studied reaction between ZrCl4 and NaBH4 at temperatures between 300 and 725°C. The results demonstrate that single-phase zirconium diboride nanoparticles are formed starting at 575°C. According to electron microscopy data, the ZrB2 powder obtained at 575 and 725°C consists of variously shaped particles, some of which are almost spherical, ranging in diameter from ~10 to 20 and from 25 to 35 nm, respectively. These values agree with the equivalent particle diameters evaluated from the measured specific surface area of ZrB2, ~14 and ~32 nm, respectively, and with the crystallite size extracted from X-ray diffraction data: Dhkl ~ 13 and 28 nm.

The effect of platinum on the SnO2 sorption properties

Chemisorption of SO2 and O2 at Pt-modified SnO2 is studied by using the vacuum static method, with simultaneous recording of electrical conductivity, over the 22 to 300°C temperature range. The SnO2 surface modification results in the increasing of SO2 adsorption and weakening of the gas-surface bonding. The chemisorption enhances the samples’ electrical conductivity. The surface pretreatment with oxygen leads to the decreasing of the successive SO2 chemisorption.

Sorptive properties of antimony-doped In2O3

O2, Cl2, and SO2 chemisorption on the surface of nanocrystalline In2O3 doped with antimony (0.2 and 2.7 at %) has been studied at temperatures from 22 to 200°C. The results indicate that antimony prevents the formation of nonconducting indium chlorides on the surface of nanocrystalline In2O3 during Cl2 chemisorption. The logarithm of the conductivity of Sb-doped In2O3 is a nearly linear function of the surface coverage with chlorine, which makes it a candidate chlorine-sensing material. At the same time, antimony doping reduces the SO2 response of In2O3.

Effect of gallium oxide dopants on electrophysical and sorption properties of zinc oxide

The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S02 sorbed. Two forms of chemisorbed SO2 (donor and acceptor) are observed on the surface.

Special Features of Oxidation of Hafnium Diboride Nanoparticles of Different Dispersity

Products of oxidation of HfB2 particles with mean size 50–55 and 20–25 nm with air oxygen under polythermal and isothermal conditions have been studied by means of thermal analysis, scanning electron microscopy, X-ray energy-dispersive analysis, and elemental analysis. Rate constants of oxidation of the HfB2 nanoparticles have been determined.

Oxidation Behavior of Zirconium Diboride Nanoparticles

The products of oxidation of ZrB2 powders with average particle sizes of ~100 and ~30 nm by atmospheric oxygen under isothermal conditions and during heating have been characterized by thermal analysis, X-ray diffraction, scanning electron microscopy, IR frustrated total internal reflection spectroscopy, energy dispersive X-ray analysis, and elemental analysis. The oxidation onset has been observed at 594 and 396°C, respectively. Oxidation at temperatures of ≥800°C leads to the formation of boron oxide and monoclinic ZrO2, independent of the particle size of ZrB2. The reaction rate constants for the oxidation of ZrB2 nanoparticles ~100 and ~30 nm in size have been determined to be 0.03, 0.15, and 0.31 h–1 at 600, 650, and 700°C and 0.11, 0.35, and 0.81 h–1 at 500, 600, and 700°C, respectively. The apparent activation energies for the oxidation of the ZrB2 nanoparticles ~100 and ~30 nm in size are 161 ± 4 and 62 ± 3 kJ/mol, respectively, as evaluated from the temperature dependence of the rate constants at the above temperatures.

Behavior of titanium diboride nanofilms and nanopowders in hydrochloric acid solutions

We have studied the behavior of TiB2 nanofilms and nanopowders in HCl solutions of various concentrations (1.2 to 12.0 mol/L). The TiB2 films were grown by nonreactive magnetron sputtering in an additional magnetic field or without it. The TiB2 powder was prepared by reacting fine-particle titanium and boron in a Na2B4O7 ionic melt. The samples were characterized by X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, and atomic force microscopy. The reactions with the acid solutions were studied by atomic absorption spectroscopy. The results demonstrate that a magnetic field applied during the sputtering process improves the corrosion resistance of the films. Titanium diboride powders consisting of rounded particles are shown to have the highest resistance to dissolution in hydrochloric acid.

Physicochemical and functional properties of modified tin dioxide

Specimens of tin dioxide with modifying Sb and Pt additives are synthesized. Their physicochemical properties (specific surface area, porosity, and conductivity), chemisorption and catalytic activity in the model reaction of CO oxidation are studied. A considerable chemisorption of CO on SnO2 and SnO2-SbOx is observed at 150–180°C. The oxidation of CO in the flow of gases starts in the same temperature range. An addition of platinum leads to a significant increase in the rate of CO oxidation, the reaction starts at 80°C. It is proposed that the process proceeds at the SnO2/Pt interface.