Thermochemical properties of dinitramidic acid salts

Enthalpies of formation and solution of hydrazinium, guanidinium, aminoguanidinium, and triaminoguanidinium salts of nitric and dinitramidic (HN(NO₂)₂, DN) acids were determined by combustion and solution calorimetry methods. Enthalpies of formation of respective cations in infinitely dilute aqueous solution were calculated using the enthalpy of formation of the nitrate ion. The enthalpy of formation of the DN acid anion was determined based on the enthalpy of formation and solution of the acid salts. The weight-average enthalpy of formation of the DN acid anion equal to 8.40±0.13 kcal mol⁻¹ was obtained. The enthalpy of solution of ammonium dinitramide (ADN) was measured (8.71±0.01 kcal mol⁻¹). From these data, the enthalpy of formation of ADN was calculated (−32.14±0.14 kcal mol⁻¹). The energy of combustion of ADN was measured by the calorimetry method, and the enthalpy of formation of ADN was calculated for a sample with purity above 99.9% (−32.20±0.19 kcal mol⁻¹). The weight-average enthalpy of formation of ADN equal to −32.16±0.11 kcal mol⁻¹ is recommended for use. Enthalpies of formation of sodium, potassium, and cesium salts of DN acid were determined.     

Influence of the particle size distribution of potassium heptafluorotantalate on the characteristics of sodium-reduced tantalum powders

Two versions of heterophase sodium-thermic reduction of potassium heptafluorotantalate were studied. One version implies initiation of the reaction in a homogeneous mixture of solid K₂TaF₇ and sodium flux, and the other, supply of solid K₂TaF₇ onto the surface of liquid sodium occurring above the molten halides. The surface area of the tantalum powder was correlated with the K₂TaF₇ particle size. The formation mechanisms for the tantalum powder particles were discussed for different reduction procedures. The conditions for preparation of powders with the specific surface area of ca. 4 m² g⁻¹ were identified.     

Diffusive–thermal oscillations of rich premixed hydrogen–air flames in a microflow reactor

In this paper the dynamics of rich hydrogen–air flames in a microflow reactor with controlled temperature of the walls is investigated numerically using the thermal-diffusion model with two-step kinetics in one spatial dimension. It is found that as the parameters of the system are varied the sequence of bifurcation occurs leading to the formation of complex spatio-temporal patterns. These include pulsating, chaotic, mixed-mode and FREI (Flames with Repetitive Extinction and Ignition) oscillations. The critical parameter values for the existence of different dynamical regimes are found in terms of equivalence ratio and flow velocity.     

The energy of the N→O bond in 3-nitroisoxazoline N-oxide

The enthalpy of combustion of 3-nitroisoxazoline has been determined as H _c ^298.15 =–414±0.3 kcal/mole and that of 3-nitroisoxazoline N-oxide as H _c ^298.15 =–406.6±0.5 kcal/mole. From the values for the heats of combustion and evaporation, the standard enthalpies of formation have been calculated and the energy of the NO bond has been evaluated at 64±3 kcal/mole.     

Open Resonators with Conducting Cylindrical Inserts. 2. Resonators with Finite-Length Mirrors

We present the results of experimental studies of controlling the spectrum and Q-factors of modes in an open resonator with a conducting cylindrical insert. The phenomenon of an increase in the diffraction Q-factor is experimentally observed for the fundamental TEM_00q mode for two resonant diameters of the conducting cylindrical insert located inside the open resonator. The features of excitation of modes in an open resonator with smooth cylindrical finite-length mirrors and in an open resonator with cutoff bevels at the mirror edges are studied. Prospects for using open resonators with conducting inserts in quasi-optical devices in the millimeter-wave range are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 684–691, August 2005.     

Fano resonance in quadratic waveguide arrays

We study resonant light scattering in arrays of channel optical waveguides in which tunable quadratic non-linearity is introduced as nonlinear defects by periodic poling of single (or several) waveguides in the array. We describe novel features of wave scattering that can be observed in this structure and show that it is a good candidate for observation of Fano resonance in nonlinear optics.     

Magnetostriction in porous nickel films

Conclusions A new type of magnetostriction has been found in porous metal-ceramic nickel films. The magnetostriction differs from that of compact nickel in that it is positive, does not saturate in fields up to 1400 Oe and exceeds ^s of nickel by several times.The existence of the negative magnetic charge striction and positive tensomagnetostriction proposed in this work was experimentally proved in model designed samples.It was proved experimentally that the magnetostriction of manufactured articles depends not only on ^s of the material, but also on the relative alignment and configuration of their parts.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 141–143, July, 1972.