High-pressure volume magnetostriction in the diluted magnetic semiconductor Cd1 ? xMnxGeAs2 (x = 0.06–0.3)

The specific volume of the diluted magnetic semiconductor Cd_{1 − x} Mn _x GeAs₂ (x = 0.06–0.3) has been determined for the first time by strain measurements at pressures of up to 7 GPa. From the pressure dependences of the relative specific volume, we evaluated the volume magnetostriction (spontaneous magnetization coefficient). A scaling relation was used to estimate the bulk modulus of the magnetically ordered and disordered phases.     

Crisis phenomena in metal hydride hydrogen storage facilities

We present the results of experimental studies of heat and mass transfer processes in a metal hydride reactor under absorption and release of pure hydrogen. The hydrogen absorption/release reaction is shown to proceed in three stages: (I) heating/cooling of the absorbing material bed up to the reaction temperature; (II) equilibrium absorption/release; and (III) reaction completion. The transition from the first stage to the second is accompanied by a sharp decrease in the hydrogen flow rate at the reactor input/output. The crisis is caused by the ineffective pick-up/application of hydrogen absorption/release heat from/to the absorbing material bed. The reactor charging/discharging operation modes balanced against heat transfer make it possible to avoid crisis and to proceed under a constant flow rate of hydrogen.     

Phase relations in the Nb-Cr-Sb and Nb-Mn-Sb systems

The 970-K phase relations in the Nb-Cr-Sb and Nb-Mn-Sb systems have been studied by X-ray diffraction. The systems contain no ternary compounds. There are substitutional solid solutions based on binary antimonides. The Nb₅Sb₄-based solid solution (Ti₅Te₄ structure) extends to the composition Nb_4.1Mn_0.9Sb₄; the Nb₃Sb-based solid-solution series (Cr₃Si structure) is bounded by the compositions Nb_2.6Cr_0.4Sb and Nb_2.4Mn_0.6Sb; the Cr_{1.04 − x} Sb_{0.96 + x} -based solution with x = 0.08 (NiAs structure) exists between the compositions Cr_0.94Nb_0.10Sb_0.96 and Cr_0.70Nb_0.30Sb_1.00; and the Mn_{1.00 + x} Sb_{1.00 − x} -based solution with x = 0.1 extends to the composition Mn_0.9Nb_0.2Sb_0.9. In addition, there is an interstitial solid solution (Ni₂In structure), which extends to MnNb_0.25Sb. The 970-K isothermal sections of the Nb-Cr-Sb and Nb-Mn-Sb phase diagrams are mapped out in the region 0–80 at % Sb.     

Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol by <Emphasis Type=Italic>tert</Emphasis>-butyl hydroperoxide over Pt/oxide catalysts

Heterogeneous oxidation of cyclohexane with tertiobutyl hydroperoxide was carried out on Pt/oxide (Al₂O₃, TiO₂ and ZrO₂) catalysts in the presence of different solvents (acetic acid and acetonitrile). The catalysts were prepared using Pt(NH₃)₂(NO₂)₂ as a precursor and characterized by chemical analysis using the ICP–AES method, XRD, TEM, FTIR and BET surface area determination. The oxidation reaction was carried out at 70°C under atmospheric pressure. The results showed the catalytic performance of Pt/Al₂O₃ as being very high in terms of turnover frequency.     

Interface-dependent resistance switching in Nd<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> ceramics

Interface-dependent electric-pulse-induced resistance switching effect (EPIR) in Nd_0.7Sr_0.3MnO₃ ceramics was studied. The results reveal that the EPIR effect originates from the interface between the electrodes and the bulk, and the EPIR ratio as well as the high and low resistance states can be strongly influenced by applying a large electrical field on the sample for different intervals. Also, the pulse parameters have great effect on the stability of EPIR and the optimal pulse width, pulse amplitude and read bias are obtained. Based on the space charge limited current mechanism together with the theory of interfacial charge-trapped state, the interface-dependent resistance switching effect is discussed.     

Study on conductivity and redox stability of iron orthovanadate

FeVO₄ was synthesised by conventional solid state technique. Impedance measurements using a silver electrode were unsuccessful due to a solid state reaction between FeVO₄ and Ag, forming α-AgVO₃ and α-Fe₂O₃ at the interface. Impedance measurements, with a platinum electrode, reaffirmed that FeVO₄ exhibits semiconductor behaviour in air. In a reducing atmosphere, 5% H₂/Ar, high electronic conductivity, from 1 S cm⁻¹ at 300 °C to 2 S cm⁻¹ at 700 °C, was observed with an activation energy of 0.13(1) eV. X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry data determined that the change in electronic conductivity was due to the degradation of the material into FeV₂O₄ and α-Fe₂O₃. It is believed that the conduction was due to electron hopping between vanadium d-orbitals. Neither FeVO₄ nor FeV₂O₄ are deemed suitable as anode materials for solid oxide fuel cells, due to redox instability.     

Measurement of the thermal properties of zirconium and tantalum carbides at high temperatures (up to and above the melting point)

Equipment and results of an investigation of the resistivity of zirconium and tantalum carbides in the solid and liquid states as a function of the specific energy employed are described. Estimates of the heat of fusion of the carbides are given. The investigation is carried out using pulsed electric heating of samples cut out of massive blocks, and film samples deposited on a substrate.     

Increasing the resolution and the stability of metrological characteristics of micromechanical accelerometers

Data on increased stability of the metrological characteristics of micromechanical accelerometers are presented. Prospects for expanded marketing of accelerometers with high stability and resolution for use in remote seismic warning systems in reactors and gravitational monitoring are discussed.     

Typical features of measurement of the flow rate of biological fluid in hemodialysis machines

We consider the typical features of application of the laser Doppler method for determination of blood flow rate in hemodialysis machines. We have analyzed the scattering characteristics of blood and blood flow in the blood tubing. We have obtained estimates of the basic parameters of the Doppler signal and we present the optical layout of the flowmeter.