I. I. Korobov

Fabrication and characterization of fluorinated single-walled carbon nanotubes

The optimum conditions for the fluorination of single-walled carbon nanotubes (SWCNT) in the atmosphere of gaseous fluorine with the nanotube structure remaining intact up to a stoichiometry of CFx, x ∼ 0.5 were determined. The kinetics of fluorination was examined. The fluorinated SWCNTs were characterized by various methods, including transmission electron microscopy, measurements of specific surface area and accessible internal volume, NMR spectroscopy, IR spectroscopy, X-ray absorption and photoelectron spectroscopies, thermal stability, and analysis of gaseous products by mass-spectrometry. The structure of fluorinated SWCNT was preserved up to brutto-composition CF0.5 but degree of fluorination of SWCNT bundles was decreased with distance from the SWCNT surface to its core. Such a decrease becomes evident at ∼1.5 nm distance. It means that the degree of fluorination depends on the degree of its dispersion.

Preparation of titanium diboride nanopowders of different particle sizes

Reactions between titanium and microcrystalline boron powders in a Na2B4O7 ionic melt at temperatures from 700 to 850°C and those between TiCl4 and NaBH4 at temperatures from 300 to 750°C and hydrogen pressures of up to 10 MPa, with no solvent, have been studied by X-ray diffraction, scanning electron microscopy, thermogravimetry, and elemental analysis. The results demonstrate that TiB2 formation occurs at t 〉 730°C and 550°C, respectively. According to scanning electron microscopy data, the TiB2 powder consists of particles 70–75 and 35–50 nm size, and the crystallite size evaluated from X-ray diffraction data is 55 and 30 nm, respectively, in agreement with the equivalent particle diameters obtained from the specific surface area of the TiB2 powders: 60 and 45 nm, respectively.

Chemical interaction between TiFe and ammonia

We have studied chemical interaction between the intermetallic compound TiFe and ammonia at temperatures from 150 to 500°C in the presence of NH4Cl as an activator of the process. We have derived schemes of the reactions involved and have shown that the use of ammonia for hydriding/nitriding enables the preparation of fine powders of TiFe and its hydride.

Synthesis of nanosized group IV borides in ionic melts of anhydrous sodium tetraborate

The preparation of nanosized Group IV metal diborides by reacting powdery titanium, zirconium, and hafnium with fine-grained boron in Na2B4O7 ionic melts in the temperature range 600–850°C has been studied. Nanosized titanium, zirconium, and hafnium diborides are formed at temperatures of at least 750°C.

Oxidation behavior of TiB2 micro- and nanoparticles

The oxidation of TiB2 particles (75 to 1500 nm in size) has been studied at temperatures of up to 1000°C by thermogravimetry, X-ray diffraction, X-ray photoelectron spectroscopy, IR frustrated total internal reflection spectroscopy, and energy dispersive X-ray analysis. The oxidation onset was observed between 210 and 475°C, depending on the particle size. This distinction can presumably be accounted for in terms of the deformation produced by the Laplace pressure. Oxidation at temperatures under 1000°C leads to the formation of the rutile phase of TiO2 and boron oxide (B2O3). Moreover, at a temperature of ≃ 1000°C titanium borate, TiBO3, was observed to form. Under all of the conditions examined, the oxidation reaction does not reach completion and the oxidation products contain unreacted TiB2.

Special features of preparation of nanosized hafnium diboride of different dispersity

X-ray diffraction analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, and elemental analysis have been applied to study the products of interaction of powder hafnium with fine-crystalline boron in the Na2B4O7 ionic melt at 600–850°C and of HfCl4 with NaBH4 at 300–700°C.

Preparation of hafnium diboride nanopowders in an anhydrous Na2B4O7 ionic melt

Reactions between hafnium powder and microcrystalline boron in a Na2B4O7 ionic melt have been studied at temperatures from 600 to 850°C. The results demonstrate that nanoparticulate hafnium diboride forms starting at 750°C. According to electron microscopy data, the HfB2 powder obtained at 850°C consists of nearly spherical particles 50–55 nm in diameter, which agrees with the equivalent particle diameter (≃ 60 nm) evaluated from the specific surface area of the HfB2 and with the crystallite size (≃55 nm) determined from X-ray diffraction data.

Corrosion resistance of nanostructured films of titanium diboride in mineral acid solutions

The reactions of nanostructured TiB2 films (mean grain size is 3.3 ± 1.1 nm) with mineral acids (HCl, H2SO4, H3PO4, and HNO3) of different concentrations have been studied. It is found that the dissolution of the films is a congruent process showing linear kinetics for the time periods in the range from 300 to 1500 min. The corrosion depth parameters of nanostructured TiB2 films in mineral acids are determined, and their corrosion resistance is graded on a ten-point scale. The studied films show the lowest corrosion resistance in their reaction with nitric acid solutions, and the highest resistance is observed in phosphoric acid solutions.

Hydriding of intermetallic compound Ti2Ni

Conditions of formation of the Ti2NiH3.3 hydride phase in the reaction of the Ti2Ni intermetallic compound with ammonia and hydrogen have been determined. The products of the reaction of the intermetallide with ammonia in the presence of the NH4Cl activator in the temperature range 100–500°C have been identified. It has been shown that the use of ammonia at temperatures >400°C leads to the formation of titanium nitride and nickel.

Chemical interaction of the Ti90Mg10 alloy with ammonia

We have studied the chemical interaction of the Ti90Mg10 alloy with ammonia in the presence of NH4Cl at temperatures from 150 to 500°C and identified conditions for the formation of fine-particle hydrides and nanocrystalline nitrides of titanium and magnesium.