Oxidation of gold metal particles supported on TiO<Subscript>2</Subscript>: an FTIR study by means of low-temperature CO adsorption

Two Au/TiO₂ samples with different gold loadings (0.7 and 4.0 wt.% Au) were prepared by deposition-precipitation with urea and calcined at 673 K. TEM revealed gold particles of 3.2 and 3.9 nm for the 0.7 and 4.0 wt.% samples, respectively. The samples were subjected to different red-ox treatments and then the state of gold was determined by the FTIR spectra of CO adsorbed at low temperature. Several kinds of gold carbonyl species were detected during the experiments: (i) Au⁰–CO at around 2107 cm⁻¹; (ii) Au⁺–CO at ca. 2175 cm⁻¹; (iii) Au^δ+–CO in the region of 2140–2137 cm⁻¹ and (iv) Au^δ′+–CO (δ^′ > δ) at around 2155 cm⁻¹. The 4.0 wt.% sample contained mainly metallic gold after evacuation at 673 K. Subsequent interaction with oxygen at 373 K leads to oxidation of a fraction of the surface metallic gold sites to Au^δ+ sites. These sites were considered as cations located on the surface of the metal particles with a partially positive charge δ+ (0 < δ < 1) because of electron transfer from the gold bulk. Evacuation at 673 K leads to back reduction of the Au^δ+ sites to metallic gold. The oxidation of gold particles was more efficient when performed with a NO + O₂ mixture. It resulted in creation of Au^δ′+ sites with a higher positive charge than that of the Au^δ+ sites. In this case the oxidation involved a higher number of Au⁰ sites. A similar treatment of the 0.7 wt.% Au sample, however, resulted in formation of “isolated” Au⁺ species. The results indicate that small metal particles are more easily oxidized by a NO + O₂ mixture. A model of the formation of the different sites, explaining well the experimental results, is proposed.     

Waveguide-dielectric resonator method for accurate measurement of parameters of materials at high frequencies

The theory is given, with an analysis and various examples, of the practical implementation of a method for measuring the relative permittivity ɛ^*=ɛ′−iɛ″ of materials in the 0.5–26-GHz frequency range. The results and experimental errors are given of measurements of ε′ in the range 2–200 and of tanδ in the range from 5·10⁻⁵ to 2·10⁻². Translated from Izmeritel'naya Tekhnika, No. 6, pp. 62–66, June, 1999.     

Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

Influence of Li<Superscript>+</Superscript> dopants on the properties of the ZnO piezoelectric films

ZnO piezoelectric films with the preferred 002-orientation were prepared by sol-gel method. The annealing temperature was 600^∘C and the resistivity of the ZnO film was 1 × 10⁶ Ω ⋅ cm. Li₂CO₃ and LiCl were added respectively into ZnO precursor as source of Li⁺-ion. The molar ratio of [Li⁺]/[Zn^{2 +}] was 0.05. It is observed that the annealing temperature for forming preferred 002-orientation of ZnO films decreases from 660 to 550^∘ C after Li₂CO₃ being doped. When Li₂CO₃ and LiCl are doped, the resistivity of ZnO films increases to 10⁸Ω ⋅ cm and 10⁹Ω ⋅ cm, respectively, with an annealing temperature of 550^∘ C. When annealing temperature is 600^∘ C, the resistivity of the ZnO film with LiCl dopant increases to 10⁷Ω cm. The influence mechanism of the two dopants on the properties of the ZnO films is analyzed.     

Production of high-current electron beams in an explosive-emission diode at gas pressures ∼ 10− 2–10−1 torr

Data on production of electron beams with ∼200 keV electrons and above ∼100 A beam current in a diode with an explosive-emission cathode at background gas pressures ∼10⁻²−10⁻¹ torr are presented. Discharge regimes with high-voltage stage duration up to 500–800 ns at 10⁻² torr and 80 ns at 10⁻¹ torr have been obtained. The duration of the electron beam behind a 50 μm thick titanium foil was equal to 200 and 400 ns, respectively, and was limited by the transmittance of the foil. Pis’ma Zh. Tekh. Fiz. 24, 88–92 (January 26, 1998)     

Specific Heat Capacity and Thermal Conductivity of Foam Glass (Type 150P) at Temperatures from 80 to 400 K1

Low-temperature specific heat capacities of foam glass (Type 150P) have been measured from 79 to 395 K by a precision automated adiabatic calorimeter. Thermal conductivities of the glass foams have been determined from 243 to 395 K with a flat steady-state heat-flow meter. Experimental results have shown that both the specific heat capacities and thermal conductivities of the 150P foam glass increased with temperature. Experimentally measured specific heat capacities have been fitted by a polynomial equation from 79 to 395 K: C _p /J · g⁻¹· K⁻¹=0.6889+0.3332x− 0.0578x ²+0.0987x ³+0.0521x ⁴− 0.0330x ⁵− 0.0629x ⁶, where x=(T/K − 273)/158. Experimental thermal conductivities as a function of temperature (T) have been fitted by another polynomial equation from 243 to 395 K: λ/ W · m⁻¹· K⁻¹=0.14433+0.00129T − 2.834 × 10⁻⁶ T ²+2.18 × 10⁻⁹ T ³. In addition, thermal diffusivities (a) of the form glass sample were calculated from the specific heat capacities and thermal conductivities and have been fitted by a polynomial equation as a function of temperature (T): a/m² · s⁻¹=−1.68285+0.01833T − 5.84891 × 10⁻⁵ T ²+8.11942 × 10⁻⁸ T ³ − 4.24975 × 10⁻¹¹ T ⁴.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Low temperature synthesis and characterisation of lecontite, (NH4)Na(SO4)·2H20

Lecontite, (NH₄)Na(SO₄).2H₂O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH₄)₂SO₄. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ₁ was observed around 2880 cm⁻¹, υ₂ around 1700 cm⁻¹ overlapping with water OH-bending modes, υ₃ around 3300 cm⁻¹ overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm⁻¹, and υ₄ around 1432, 1447 and 1462 cm⁻¹. The sulphate group in the crystal structure displays a decrease in symmetry from T_d as evidenced by the activation of the ν₁ mode at 982 cm⁻¹ and the ν₂ mode around 452 cm⁻¹ in the Infrared spectrum. The υ₃ mode shows clear splitting in the infrared spectra with a strong band at 1064 cm⁻¹ accompanied by two shoulders at 1107 and 1139 cm⁻¹. The Raman spectra show three weak bands at 1068, 1109 and 1135 cm⁻¹ with a shoulder at 1155 cm⁻¹. Similar splitting was observed for the υ₄ mode around 611 and 632 cm⁻¹ in the Infrared and Raman spectra, respectively.     

Molecular dynamics calculations of InSb nanowires thermal conductivity

Non-equilibrium molecular dynamics calculations were performed in order to obtain the thermal conductivity coefficients of InSb nanowires in comparison with the bulk system value. For bulk, the value obtained was 16 ± 2 Wm⁻¹ K⁻¹ which is in very good agreement with experimental value of 15 Wm⁻¹ K⁻¹, and the thermal conductivity of the nanowires were 0.54 ± 0.01 Wm⁻¹ K⁻¹ and 0.50 ± 0.01 Wm⁻¹ K⁻¹ for a 5 and 4 unit cells square cross-sectional nanowires, respectively, which is almost two orders of magnitude smaller. This result is in agreement with other simulations performed for other materials.     

Remote examination of radioactive wastes using γ-ray spectrometry

Places of location of some γ-ray sources on the site for temporary storage of solid radioactive wastes of SevRAO OF-2 Federal State Unitary Enterprise (Gremikha settlement, Murmansk oblast, Russia) were determined using a procedure for remote determination of radiation source coordinates with a Cartogam γ-imaging system. The γ-ray spectra from these radiation sources were recorded using the remote procedure with an ISOCS spectrometric complex. In particular, the isotope composition of γ-active containers Bet8, TK113, L18, and L20 was determined. The main technogenic γ-radiation from these objects is associated with the decay of ¹³⁷Cs and, to a lesser extent, with the decay of ⁶⁰Co, ¹⁵²Eu, and ¹⁵⁴Eu. For the Bet8 container, its activity content was estimated (∼10¹⁴ Bq). The dependence of the specific activity of the soil surface layer in the guard zone in front of the waste storage site on the distance from the site was determined with a 7 m step. The specific activity considerably decreases with an increase in the distance from the site (from 15–28 kBq kg⁻¹ at a distance of 3 m to 1–2.8 kBq kg⁻¹ at a distance of 10–24 m).     

Comparison of the fluoride,arsenate and nitrate anions water depollution potential of a calcined quintinite,a layered double hydroxide compound

The potential for removing anionic pollutants such as F⁻, HAsO₄²⁻, and NO₃⁻ from water by mixed oxides issued from the moderate thermal treatment of quintinite (Mg₄Al₂ LDH) has been studied. This compound shows good trapping properties for F⁻ and HAsO₄²⁻, and a low potential for NO₃⁻, due to the competition with OH⁻. The competition between these three anions and CO₃²⁻ has been envisaged and shows that CO₃²⁻ is able to easily replace F⁻ and NO₃⁻, making the mixed oxides issued from MgAl LDH an inappropriate trap for F⁻ and NO₃⁻. However, only small amounts of arsenic are released after the CO₃²⁻ introduction in water. Moreover, arsenates are able to replace carbonates even at lower concentrations. This means that HAsO₄²⁻ anions present a stronger affinity than CO₃²⁻ for the LDH structure. This makes mixed oxides issued from MgAl LDH very promising materials for the removal of arsenic in polluted waters.