A. G. Burlakova

Preparation of zirconium diboride nanopowders in a sodium tetraborate ionic melt

Reactions between zirconium powder 10–15 μm in particle size and microcrystalline boron 10–20 μm in particle size in an Na2B4O7 ionic melt have been studied at temperatures from 600 to 850°C and reaction times from 5 to 10 h. The results demonstrate that ZrB2 forms starting at 750°C. According to scanning electron microscopy data, the ZrB2 powder consists of particles 90–95 nm in average size. The crystallite size evaluated from X-ray diffraction data is 85 nm.

Activation of metallic aluminum by tin and gallium chlorides in oxidation with water

We have studied the effect of gallium chloride and tin chloride solutions on the water oxidation of aluminum at SnCl2 concentrations of 0.68 and 6.32 wt %, GaCl3 concentrations of 0.56 and 2.67 wt %, and MCln: Al(M = Sn, Ga; n = 2, 3) molar ratios from 0.017 to 0.3. The results indicate that, when aluminum is oxidized in the presence of these salts, the reaction rate and hydrogen yield increase with reaction temperature and salt concentration and reach the highest levels when a mixture of gallium and tin chlorides is used. The reaction products are identified and the likely mechanism of the processes involved in the oxidation of aluminum is discussed.

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.

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.

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.

Electron work function of intermetallic compounds in the cerium-cobalt system

The concentration dependences of the electron work function for lithium samples in the cobaltrich region of the state diagram of the Ce-Co binary mixture is studied by the contact potential difference method at 20°C. It is shown that the electron work function isotherm has the shape of a broken line with kinks corresponding to intermetallic compounds formed in the cerium-cobalt binary system.

Special features of preparation of nanosized zirconium diboride powders of various dispersity

Products of the zirconium powder reaction with amorphous boron in a Na2B4O7 ionic melt at 650–850°C and those of the ZrCl4 reaction with NaBH4 at 300–725°C have been studied by means of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, and elemental analysis. At temperature ≥750°C, single-phase ZrB2 with the particle size of 60–80 nm is formed in a Na2B4O7 ionic melt, whereas the ZrB2 powder obtained via the reaction of ZrCl4 with NaBH4 at temperature ≥575°C consists of particles differing in the shape, some of which are close to spherical with diameter of 10–35 nm.

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.

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.