S. P. Shilkin

Investigation of interactions in the TiH2-O2 system

Abstract Samples of the titanium oxyhydrides of composition TiH x O y , where x = 0.83–2.0, y = 0.1–1.4, were synthesized by interaction of titanium dihydride with oxygen at temperatures of 20–550 °C and pressures of 0.2–2.0 MPa and for each sample the electronic work function and the specific resistance were determined. It has been shown that the TiH 2 -O 2 system contains the suboxohydrides of compositions M 6 O, M 3 O and M 2 O, on the basis of the initial titanium dihydride lattice, where M is the initial titanium dihydride, analogous to the compositions which exist in the Ti-O 2 system.

Hydrogen absorption and electrocatalytic properties of ultrafine LaNi5 powders

Abstract The different conditions of milling LaNi 5 have been investigated. The hydrogen absorption characteristics and electrocatalytic properties of the ultrafine powders obtained are described and discussed. An anomalously high value of the exchange current in the reaction of hydrogen cathode deposition for some ultrafine powders has been observed.

Nanosized zirconium diboride: Synthesis and properties

The thermolysis of Zr(BH4)4 vapor at 573 and 623 K in a vacuum of 1.33 × 10−1 Pa was studied. Nanosized zirconium diboride was produced as an X-ray amorphous powder and a crystalline film. According to electron microscopy data, the X-ray amorphous zirconium diboride powder obtained at 573 or 623 K consists of spherical particles 30–40 nm in diameter, which is in quite a good agreement with the equivalent particle diameter (∼35 nm) calculated from the specific surface area of ZrB2. After annealing at 1273 K, the X-ray amorphous zirconium diboride powder crystallizes into a hexagonal lattice with the unit cell parameters a = 0.3159 nm and c = 0.3527 nm. The coherent scattering length Dhkl is ∼27 nm. The zirconium diboride film produced at 573 or 623 K crystallizes into a hexagonal lattice with the unit cell parameters a = 0.3163−0.3168 nm and c = 0.3524−0.3531 nm. The coherent scattering length Dhkl is ∼14 nm. The thickness of the ZrB2 film on quartz, glass ceramics, and stainless steel is 5–7 μm. The microhardness of the film on a stainless steel substrate under a load of 20 g is 17.8 GPa.

Synthesis of nano-sized titanium diboride in a melt of anhydrous sodium tetraborate

X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and elemental analysis were used to study the interaction of titanium powder with finely powdered boron of particle size 10–20 μm in Na2B4O7 ionic melt, in the temperature range 973–1088 K, at the 5–10 h contact duration. The TiB2 formation was shown to occur at the temperatures 1018 K or above, that is, at the borax melting temperature. According to the scanning electron microscopy, theTiB2 powder consists of the 70–75 nm particles, and its coherent scattering region calculated from the XRD data amounts to 55 nm.

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.

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.

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.