Inhibition of premixed methane flames by manganese and tin compounds

The first experimental measurements of the influence of manganese- and tin-containing compounds (MMT, TMT) on the burning velocity of methane/air flames are presented. Comparisons with Fe(CO)₅ and CF₃Br demonstrate that manganese and tin-containing compounds are effective inhibitors. The inhibition efficiency of MMT is about a factor of two less than that of iron pentacarbonyl, and that of TMT is about 26 times less effective, although TMT is still about twice as effective as CF₃Br. There exist conditions for which both MMT and TMT show a loss of effectiveness beyond that expected because of radical depletion, and the cause is believed to be particle formation. Kinetic models describing the inhibition mechanisms of manganese- and tin-containing compounds are suggested. Simulations of MMT- and TMT-inhibited flames show reasonable agreement with experimental data. The decomposition of the parent molecule for the tin and manganese species is found to have a small effect on the inhibition properties for the concentrations in this work. The inhibition effect of TMT is determined mostly by the rate of the association reaction H + SnO + M ↔ SnOH + M, and the catalytic recombination cycle is completed by the reactions SnOH + H ↔ SnO + H₂ and SnOH + OH ↔ SnO + H₂O. The inhibition mechanism by manganese-containing compounds includes the reactions: MnO + H₂O ↔ Mn(OH)₂; Mn(OH)₂ + H ↔ MnOH + H₂O, and MnOH + OH (or H) ↔ MnO + H₂O (or H₂), and the burning velocity is most sensitive to the rate of the reaction Mn(OH)₂ + H ↔ MnOH + H₂O.     

Formation of two-layer composite-on-insulator structures based on porous silicon and SnO x . Study of their electrical and gas-sensing properties

The objective of this work is to fabricate and study multilayer “composite-on-insulator” sensor structures based on porous silicon and nonstoichiometric tin oxide. Two-layer structures “macroporous silicon-mesoporous silicon” on single-crystal silicon with sharp geometrical boundaries are grown. Test “composite-on-insulator” structures are fabricated. Oxide on macroporous silicon walls and a buried layer of oxidized mesoporous silicon play the role of the insulator. Nonstoichiometric tin oxide deposited onto the extended surface of oxidized macroporous silicon by chemical vapor deposition (CVD) is the sensitive layer. The gas sensitivity is studied upon exposure to NO₂ and degassing in air at room temperature. The sensitivity of the por-Si/SnO _x composite structures is higher than the sensitivity of tin-oxide film samples.     

Composite electrodes for current sources based on graphene-like films in porous silicon

In this work, the results of formation of composite membranes with a thickness of about 200 μm with a high electric conduction based on porous silicon and graphene-like films have been presented. A method of CVD film synthesis that makes it possible to form a graphene-like coating on the inner surface of gradient-porous silicon with variable pore morphology across the thickness has been proposed. The pore sizes vary gradually from units of nanometers on the upper surface to several micrometers deep in silicon.     

High- and low-temperature X-ray diffraction studies of aluminate spinels in the CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript>–NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

Co _x Ni_1–x Al₂O₄ (x = 0, 0.25, 0.5, 0.75, 1) aluminate spinels have been prepared by solid-state reactions and their crystal structures have been refined by the Rietveld method. We have analyzed whether the results are consistent with theoretical relationships stemming from the hard sphere model. Using high- and low-temperature X-ray diffraction measurements, we have obtained the temperature dependences of the unit-cell parameters for the synthesized compounds and determined their thermal expansion coefficients. The rate of cation exchange reactions has been shown to be very slow at temperatures below 200°C.     

Ways to calculate electric fields in traction electric motor insulation by equivalent charge method

A procedure permitting one to calculate the electric fields in multilayer insulation based on the equivalent charge method is presented. Consideration of the new algorithm shows its fast response and proper accuracy.     

Vitrification of a simulator of Savannah River site (USA) wastes with high iron and aluminum content on bench and commercial facilities with a cold crucible

Bench and commercial-facility experiments have been performed on cold-crucible vitrification of a simulator of high-level wastes from the Savannah River site (USA). The wastes contained up to 29 mass% Fe₂O₃ and 26 mass% Al₂O₃. The specific product flow reached 1700 and 2450 kg/(m²·day) with specific energy consumption 14–16 and 9–10 kW·h/kg, respectively. The crucibles did not undergo any appreciable corrosion during the period of the work performed and are reusable. The product consisted of a borosilicate matrix, containing up to 10 vol.% crystalline phase of spinel. The method of induction melting in a cold crucible is especially effective for crucibles with a large diameter, since the specific productivity increases and the specific energy consumption on the vitrification of high-level wastes decreases. __________ Translated from Atomnaya énergiya, Vol. 104, No. 5, pp. 291–295, May, 2008.     

Wavy microstructures formed at the SiO2/Si interface under the action of high-power ion-beam pulses

The formation of wavy microstructures under the action of a nanosecond pulsed high-power ion beam on the surface of single-crystalline silicon covered with intrinsic oxide layers of various thickness has been studied. Morphological features of the observed structures depend on the oxide layer thickness and ion beam current density. Possible mechanisms of formation of these microstructures are considered.     

Synthesis and study of compounds of the general formula MITh2(VO4)3 (MI = Li, Na, Ag, K, Rb, Cs, Tl)

Double vanadates of thorium and univalent metals with r(M^I) < 1.6 Å were prepared by high-temperature solid-phase reactions. Representatives of this series with larger M^I atoms were prepared by the solgel method. The compounds crystallize in three structural types: zircon for Li and Na derivatives, scheelite for AgTh₂(VO₄)₃, and potassium thorium vanadate for the compounds containing K, Rb, Cs, and Tl. Thus, two morphotropic transitions are observed in the series of the compounds studied. The bands in the IR spectra were assigned, and the effect of the site symmetry of the VO₄ tetrahedra on the number of absorption bands was revealed. The incongruent melting points of the compounds were determined by differential scanning calorimetry.     

Thermodynamics of calcium uranosilicate

The standard enthalpy of formation at 298.15 K of crystalline α-Ca(HSiUO₆)₂ · 5H₂O (?6781.0 ± 9.5 kJ mol^?1) was determined by reaction calorimetry. The heat capacity in the range of 80–300 K was measured by adiabatic vacuum calorimetry, and the thermodynamic functions of this compound were evaluated. The standard entropy of formation (?1978.6±1.2 J mol^?1 K^?1) and the Gibbs free energy of formation (6191.0±10.0 kJ mol^?1) at 298.15 K were calculated. The standard thermodynamic functions of reactions of calcium uranosilicate synthesis were analyzed.