A. S. Alikhanian

Effect of Au and NiO catalysts on the NO2 sensing properties of nanocrystalline SnO2

Nanocrystalline tin dioxide has been synthesized, and its surface has been modified with Au and NiO. Their distributions in the nanocrystalline tin dioxide have been examined by X-ray diffraction and transmission electron microscopy. The NO2 sensing properties of the materials have been studied in the range 100–1000 ppb. Both gold and nickel enhance the NO2 response of SnO2. Codoping with Au and NiO markedly enhances its sensing response and, in addition, lowers the peak response temperature. The observed effect of NO2 concentration in dry air on the sensing response of the SnO2〈Au, NiO〉 nanocomposite can be understood in terms of the sequence of processes that take place on the SnO2 surface upon nitrogen dioxide adsorption in the presence of chemisorbed oxygen.

Chemical interaction of fluoropolymers with transition metals

Chemical interaction of transition metals (Mo, W, Ta, Nb, and Ti) with a tetrafluoroethylene-vinylidene fluoride (TFE-VDF) copolymer (21 mol % TFE + 79 mol % VDF) has been studied by differential scanning calorimetry (DSC) and mass spectrometry. The DSC curves of mixtures of the fluoropolymer with Ta, Nb, and Ti showed exothermic peaks, and those of composites with W and Mo showed endothermic peaks. Mass spectrometric analysis indicated that the fluoropolymer reacted with the transition metals to form the higher fluorides TaF5, NbF5, TiF4, WF6, and MoF6. In addition, WOF4 and MoOF4 molecules were detected in the case of tungsten and molybdenum. At temperatures above 700 K, the mass spectra of all the systems showed ions corresponding to low-molecular hydrocarbon molecules.

High-temperature mass spectrometric vaporization study of the Bi-Sb-O system

The vapor composition in the Bi-Sb-O system has been determined by Knudsen cell mass spectrometry. We have calculated the individual mass spectra of the Bi3SbO6, Bi2Sb2O6, and BiSb3O6 molecules and determined the partial pressures of all the vapor species identified. Bi3SbO7 and BiSbO4 have been shown to sublime congruently. The results have been used to construct p-x sections for the pseudobinary oxide systems Bi2O3-BiSbO4 and BiSbO4-Sb2O4.

Phase diagram of the As-S system

Thermodynamic modeling of phase equilibria is used to consistent p-T-x phase diagram of the As-S system. Experimental evidence is presented that As2S5 is a metastable phase at moderate pressures. Analytical expressions are derived for the subsolidus phase equilibria in the As-S system. It is shown for the first time that crystalline As4S3 sublimes congruently and that two liquid-vapor azeotropes exist in the As-S system.

Chemical interaction of metallic titanium with a tetrafluoroethylene-vinylidene fluoride copolymer

Chemical interaction of Ti metal with a tetrafluoroethylene-vinylidene fluoride copolymer (29 and 71 mol %, respectively) has been studied by differential scanning calorimetry, mass spectrometry, and nuclear magnetic resonance. The results indicate the formation of titanium trifluoride, a nonvolatile compound. The CF2 groups surrounded by CH2 groups in the polymer are the most reactive with titanium. The solid defluorination product is an aliphatic polyene containing C=C=C and C≡C-C bonds.

Thermodynamic Properties of ZnTe–CdTe Solid Solutions

The pseudobinary system ZnTe–CdTe was studied at 899 K by Knudsen cell mass spectrometric measurements. The vapor composition and pressure, ZnTe and CdTe activities, and Gibbs energy of mixing were determined. The results demonstrate that the composition dependences of CdTe and ZnTe activities exhibit, respectively, positive and negative deviations from ideality and that the Gibbs energy of mixing is lower than that of an ideal solution. The p–xsection along the pseudobinary join is constructed. At 899 K, a continuous series of solid solutions exists in the ZnTe–CdTe system, with no miscibility gap, and sublimation is incongruent. The composition dependence of 780-K CdTe activity suggests some evidence of phase segregation.

Mass spectrometric study of the thermodynamic properties of mixed-ligand Mn(III) complexes

We have synthesized Mn(thd)3 (thd = dipivaloylmethane, or 2,2,6,6-tetramethyl-3,5-heptanedione) and evaluated its enthalpy of sublimation (89.0 ± 7.0 kJ/mol) and its saturated vapor pressure as a function of temperature from mass spectrometry data. Exchange reactions between Mn(acac)3 (acac = acetylacetonate, or 2,4-pentanedione) and Mn(thd)3 have been performed using an in situ technique. We have calculated the enthalpies of the exchange reactions and the enthalpies of formation of Mn(acac)2(thd) and Mn(acac)(thd)2 in the vapor phase: −1417.5 ± 15.0 and −1590.6 ± 15.0 kJ/mol, respectively.

Decomposition of aluminum oxynitride compounds in an air-vapor medium at 950°C

Aluminum oxynitride hydrolysis in wet air at a temperature of 950°C has been shown to lead to the formation of a phase whose composition lies beyond the Al2O3-AlN join in the Al-O-N system.

High-temperature mass spectrometric study of vaporization in nano- and microcrystalline Fe2O3-SnO2 and NiO-SnO2 oxide systems

Nano- and microcrystalline Fe2O3-SnO2 and NiO-SnO2 oxide systems have been studied by Knudsen cell mass spectrometry. The results demonstrate that the vaporization thermodynamics in these systems is independent of the particle size.

Heating-induced transformation of pseudoboehmite and a mixture of pseudoboehmite, aluminum nitride, and aluminum oxide

We have studied the heating-induced transformation of a mixture of pseudoboehmite and aluminum oxynitride and have shown that there is negligible chemical interaction between them up to 800–850℃ and that the weight loss of the mixture is only caused by the dehydration of the pseudoboehmite.