L. S. Volkova

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.

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.

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.

Synthesis of Mg2Ni nanoparticles in a KCl-NaCl-MgCl2 melt

The reaction between magnesium and nickel powders in a KCl-NaCl-MgCl2 ionic melt at 970 K (reaction time, 5 h) has been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and chemical analysis. According to scanning electron microscopy data, the synthesized Mg2Ni powder consists of particles 70–75 nm in size, in reasonable agreement with the equivalent particle diameter, ≃ 64 nm, determined from the specific surface area of the Mg2Ni powder and with the crystallite size, Dhkl ≃ 65 nm, evaluated from X-ray diffraction data. The hydrogen sorption properties of the Mg2Ni obtained in a KCl-NaCl-MgCl2 ionic melt are identical to those of Mg2Ni powder prepared by a standard method, but the former reacts with hydrogen far more rapidly.

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.

Synthesis of Mg2Cu and MgCu2 nanoparticles in a KCl-NaCl-MgCl2 melt

The reaction between magnesium and nickel powders in a KCl-NaCl-MgCl2 ionic melt at 973 K (reaction time, 5 h) has been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and chemical analysis. According to scanning electron microscopy data, the synthesized Mg2Cu and MgCu2 powders consist of particles ≃ 100 and ≃ 95 nm in size, respectively, in reasonable agreement with the equivalent particle diameters, ≃ 98 and ≃ 87 nm, determined from the specific surface area of the Mg2Cu and MgCu2 powders and with the crystallite sizes evaluated from X-ray diffraction data: Dhkl ≃ 90 and 84 nm, respectively. The Mg2Cu synthesized in the ionic melt reacts with hydrogen under milder conditions than do Mg2Cu samples prepared through standard melting of magnesium and copper in an electric arc or vacuum induction furnace.

Phase transformations of pseudo-alloys of tungsten with titanium in hydrogen atmosphere

The reaction of the caked pseudo-alloys of the composition Ti0.90–0.35W0.10–0.65 with hydrogen at 5 MPa, temperature 200°C, and the time of contact 40 min has been studied using the methods of X-ray diffraction, electron microscopy, elemental, thermogravimetric analyses, and differential scanning calorimetry. The hydrogenation is shown to result in destruction of the matrices of the original pseudo-alloys with the formation of a powder-like mixture of tungsten and titanium dihydride of composition TiH1.9.