Chemistry of Combustion Waves in Substances with a Complicated Structure of Reagent Molecules. 1. Structure of the Front of Rich Isopentane Flame

Results on the structure of the lowtemperature relaxation zone of the front of a laminar Bunsen flame of isoC₅H₁₂ (2methylbutane) under atmospheric pressure are presented. The flame of a premixed mixture isoC₅H₁₂ + O₂ + Ar with a fueltoair equivalence ratio of 1.7 is examined. The mass fluxes, total rates of reactions of matter consumption and expenditure, balance of substances, and profiles of bulk heatrelease rates are calculated on the basis of the experimental concentration and temperature profiles. The results obtained indicate that there is a vast region of lowtemperature conversion of isopentane in the flame front. It is found that only part of the products sampled by the microprobe from different points of the flame front results from transformations in the lowtemperature region, namely, oxygen, isopentane, water, carbon monoxide, propane, methane, and methanol. Ethylene, propylene, hydrogen dioxide, and formaldehyde are present in the lowtemperature zone in insignificant amounts; they are secondary products of conversion of methyl and propyl radicals. It is assumed that the observed feature is a result of the competing interaction of two mechanisms of fuelmixture conversion: selfcatalysis and thermal selfacceleration. Based on the previously suggested mechanism of oxidation pyrolysis by the scheme of intramolecular quadratic destruction, experimentally observed fragmentation of the isopentane molecule is demonstrated. In contrast to npentane, formation of methyl alcohol has been found in isopentane convection products.     

Selective deep catalytic cracking process (SDCC) of petroleum feedstocks for the production of light olefins. I. The Catlever effect obtained with a two reaction-zones system on the conversion of n-hexane

The n-hexane and steam gaseous mixture was first sent through a precatalytic zone containing quartz beads (temperature T₁), and then through a catalyst bed (T₂). The latter contained a ZSM5 zeolite or a zeolite-containing hybrid catalyst. By moderately increasing T₁ (T₂ being kept constant), significant increases in the total n-hexane conversion and in the total yield of light olefins were obtained. The ethylene/propylene product ratio could be varied widely, for instance, from 1.0 to 2.0 by varying T₁ from 660 to 720°C. Such temperature effect of zone I on the overall process performance was explained by the formation of selectivity modifiers such as diolefins. With the hybrid catalyst, the enhanced production of light olefins was also assigned to the formation of large olefins on the Cr–Al-containing cocatalyst.     

Effect of Mechanical Activation on the Combustion of Systems with Brittle Components (Using Mn–Si as an Example)

It has been shown experimentally that mechanical activation of a mixture of brittle dissimilar powders of manganese and silicon extends the concentration range of combustion, increases the burning rate and maximal temperature, decreases the initial temperature of combustion imitation, and leads to transition from oscillating combustion to steadystate combustion. These combustion features are related to agglomerate formation in the mixture of brittle powders; the agglomerates are regions of more solid silicon coated with a manganese layer with a distinct boundary between the components and a change in the heterogeneity scale.     

Aluminum Combustion in Nitrogen

The process of nitration of aluminum and aluminumcontaining mixtures in the regime of selfpropagating hightemperature synthesis with a high pressure (up to 300 MPa) of the reacting gas (nitrogen) is considered. The dependences of ignition temperatures and also burning temperatures and burning rates of these initial mixtures on test conditions (nitrogen pressure and composition of the initial mixture) are studied. The dependence of the burning rate of initial mixtures on factors affecting spreading of the liquid component (melt containing aluminum and nitrogen) over the surface of the second component (aluminum nitride or titanium diboride), such as the equilibrium wetting angle, interaction at the interface, and melting of the second component, is studied. The microstructure and some properties of materials obtained are examined. Based on these studies, the combustion mechanism is determined, a mechanism of phase formation in combustion of these mixtures is suggested, and the structure of the combustion wave is determined.     

Effect of Channel Geometry and Mixture Temperature on Detonation‐to‐Deflagration Transition in Gases

Results from theoretical and experimental studies of deflagrationtodetonation transition in hydrocarbon–air mixtures are reported. The effects of internal geometry, turbulence transition of the flow, and the temperature and fuel concentration in the unburned mixture on detonation initiation are considered.     

Mathematical Modeling of Chemical Conversion in Thin‐Layer Exothermic Mixtures under Periodic Electric‐Spark Discharges

The dynamics of coating production using a reaction mixture with thermoreactive electricspark strengthening is studied numerically. It is shown that the main parameter that determines the thermal regime of coating is the initial thickness of the mixture layer. The parameter ranges for the process in a combustion regime and in a quasivolume conversion regime are determined. The effect of discharge frequency and the thermal characteristics of the reaction mixture and the substrate being strengthened on coating time is investigated. It is established that for a particular reaction mixture, the characteristic conversion temperature can be controlled by varying the electric discharge power and, hence, the heat flux at the active stage of the process, and for coating formation at this characteristic temperature, it is necessary that the thickness of the active layer be lower than a certain critical value.     

On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity

The - and -phases of NiMoO₄ have been investigated with different techniques (X-ray diffraction, electrical conductivity, IR spectroscopy) in order to tentatively rationalise the different catalytic activities observed in the oxidative dehydrogenation of propane to propene. XRD analyses have shown that at 595 ° C, the -phase is already present but a temperature of 700 ° C is required to obtain a full conversion into a pure -phase. Electrical conductivity showed the presence of anionic vacancies. It is proposed that propene is formed by the reaction of propane with surface O^2- anions. The -phase is almost twice more selective in propene formation than the -phase for comparable conversion at identical temperatures. This could derive from different oxygen environments on the active catalytic site.     

Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils

The effectiveness of coastal superphosphate and two rock phosphate fertilizers was compared with the effectiveness of single superphosphate for pasture production on deep, humic, sandy podzols in high rainfall (> 800 mm annual average) areas of south-western Australia. The pastures were subterranean clover (Trifolium subterraneum) or mixed subterraneum clover and serradella (Ornithopus compressus). Coastal superphosphate was made by adding rock phosphate and elemental sulphur to superphosphate during manufacture, as it came out of the den before granulation. One rock phosphate was a 50% mixture of apatite rock phosphate from Nauru and Christmas Islands, and which was also used to make the single and coastal superphosphate used in this study, and superphosphate made in Western Australia at the time these experiments started. The other rock phosphate was Calciphos, the fertilizer produced by heating (calcining), at about 500 °C, Christmas Island C-grade ore, a calcium iron aluminium rock phosphate. There were two types of experiments. In the three Type 1 experiments, levels of each fertilizer were applied annually. In the two Type 2 experiments, levels of fertilizer were applied once only to new plots in different years. Coastal superphosphate was the most effective fertilizer in the Type 1 experiments, with both rock phosphates and single superphosphate being equally effective. All fertilizers were equally effective in the Type 2 experiments. There were large variations in fertiliser effectiveness values between yield measurements in the same or different years. It is known that P leaches from freshly-applied superphosphate in these soils. The extent of this leaching probably varies between yield measurements affecting effectiveness values determined for all fertilizers because the effectiveness values were calculated relative to the effectiveness of single superphosphate. The humic, sandy podzols remain wet during the growing season, are acidic, and are known from laboratory studies to possess adequate hydrogen ions to cause extensive dissolution of North Carolina rock phosphate so that rock phosphates are equally or more effective than single superphosphate in these soils. When elemental sulphur in coastal superphosphate is oxidized to SO₄ hydrogen ions are produced which in previous studies has been shown to enhance dissolution of rock phosphate in biosuper, a mixture of rock phosphate and elemental sulphur.     

Attraction of both sexes of Mexican fruit fly,Anastrepha ludens,to a mixture of ammonia,methylamine, and putrescine

Eight chemicals were evaluated in laboratory experiments as attractants for sugar-fed adult Mexican fruit flies. Ammonium bicarbonate, methylamine HCl, ethanolamine, pyrrolidine, putrescine, and monomethyl succinate were slightly attractive when tested singly. A mixture containing all eight chemicals was much more attractive than any of the individual chemicals. Through a series of experiments, a mixture of three of the chemicals was found that was at least as attractive as the original eight-component mixture. The final mixture consisted of ammonium bicarbonate, methylamine HCl, and putrescine in a 10101 ratio. Ratios were less important than actual concentrations of individual components over the range of component concentrations tested. The three-component mixture was equally attractive to male and female flies over at least a 1000-fold range of concentrations and was slightly more attractive thanTorula yeast over the upper 10-fold range in competing McPhail traps in a greenhouse flight chamber.     

Chemoionization and role of charged particles in ignition of monogermanate-oxygen mixtures

Chemoionization was detected in the ignition of monogermanate-oxygen mixtures at initial pressure above 0.25kPa and a temperature of 290K. The ranges of initial monogermanate concentrations and mixture pressures at which ignition and ionization occur are determined. The concentrations of charged particles (6.4·10¹¹ cm ³) and the effective activation energy (44kcal/mole) of the process that limits the ionization rate are estimated. The possible mechanisms of ionization of the reaction mixture were considered. The role of charges in the branching of chain carriers is shown to be negligible.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 13–18, July–August, 1996.     

Characteristics of Microscale Combustion in a Narrow Heated Channel

The characteristics of microscale combustion were investigated by using a microchannel heated by an external source. The inner diameter of the channel was 2 mm, which was slightly smaller than the quenching distance of the stoichiometric methane–air mixture under normal conditions. The effects of the equivalence ratio and the averaged flow velocity on the characteristics of combustion in the microchannel were examined. At a channelwall temperature of 1000°C, flames could be stabilized at equivalence ratios of 0.05–1.9 and mixture velocities up to 150 cm/sec in a Ushaped quartzglass channel. At moderate equivalence ratios and lower velocity conditions within the flammability region, oscillatory combustion was observed. A simple analytical model predicting flame oscillations on the basis of the linear analysis of steady solutions is proposed.     

New Carbon-Containing Refractories for the Lining of Steel-Teeming Ladles from the Kombinat Magnezit Joint-Stock Co.

Test results for new carbon-containing refractories for the lining of steel-teeming ladles — PUSK, PShUK, PShUP, PUPK, and ShPUP-grade, available from the Kombinat Magnezit JSC, are presented. The properties of refractory components (including heat resistance) in the as-received and subjected to coking condition are reported. The enhanced resistance of the new materials to thermal spalling under varying temperature conditions is noted. Results of the tests (carried out at the Magnitigorsk Iron-and-Steel Works and Oskol'skii Electrical ISW) provide the basis for an analysis of the economic feasibility of large-scale production of these materials.     

A Theoretical Analysis of the Formation of Nonstoichiometric Defects in Hexagonal Boron Nitride

Results of a theoretical analysis of the Schottky and anti-Frenkel defect formation in -BN carried out within the framework of an ionic model and quasi-chemical approximation are presented. Equations for describing of the -BN point defect formation as a function of the partial nitrogen pressure and temperature under different conditions of electrical neutrality are derived and solutions thereof are given. The equations derived allow prediction of any type of -BN defects in any range of the partial nitrogen pressure and temperature. It is suggested that nitrogen vacancies constitute the predominant type of nonstoichiometric point defect in -BN.     

Ionic conductivities and glass transition temperatures in poly(vinyl methyl ether)-salt mixtures

Summary The solubility of a number of salts in poly(vinyl methyl ether) (PVME) was tested, and several gave homogeneous solutions over a range of concentrations. When dissolution of the salts occurred, the glass transition temperature of the mixture tended to rise, reflecting the solvation of the cations by the ether oxygens which also leads to crosslinking. Ionic conductivities (/Scm^–1) were measured for some of the mixtures but the level at room temperature was low. A rise in with increase in temperature was observed reaching 10^–4 Scn^–1 at 430K for PVME/LiClO₄ mixtures at a [Li⁺]/[O] ratio of 0.25.     

Influence of static and cyclic compression on the electrical conductivity of FEF black-loaded rubbers

Summary The influence of static and cyclic compression on the temperature dependence of the electrical conductivity (T) of 100 phr FEF black-loaded rubber vulcanizates (SBR, NR, IIR, BR and NBR) has been studied. It was found that increases with static pressure for all rubber vulcanizates. The temperature coefficient of conductivity proved to be negative; its maximum value ranges between –0.1 and –0.01 deg^–1 depending upon the applied stress and type of rubber vulcanizate. The pressure coefficient of conductivity at room temperature varies with the static pressure from 0.78 to 0.04 (kg/cm²)^–1. Menwhile, a was found to decrease with the number and stress amplitude of the cyclic compressions, while increases with the number of compression cycles.     

Mechanism of Upper Temperature Limits in a Wave of Filtration Combustion of Gases

A physical mechanism is established, responsible for the experimentally observed strong deceleration of the growth rate of the maximum skeleton temperature in a wave of filtration combustion of gases with increasing flow rate. The maximum temperatures of the gas and skeleton become commensurable, and the length of the thermalrelaxation zone becomes much shorter. A classification of regimes based on the temperatureheterogeneity criterion ₁ is proposed. Explicit analytical solutions are obtained for the wave for ₁1 and ₁1. A correction to reverse reactions in combustion products is considered. The effect of composition on wave behavior is studied by means of numerical calculations with a detailed kinetic scheme. The activation energy for ultrarich and ultralean methane–air mixtures is evaluated. It is concluded that the limiting efficiency of the heatrecuperation cycle in the wave is reached as ₁1; methods for maximizing the efficiency are suggested.     

Relationship between the solubility of water vapour in caprolactam and its partial pressure and temperature

Conclusions It has been shown that the solubility of water vapour in a caprolactam melt decreases sharply with an increase in temperature, and also in the presence of acetic acid and a protective gas. Therefore, to increase the concentration of water in a caprolactam melt it is advantageous to use non-volatile molecular weight regulators and water vapour as the protective gas in the first section of a continuous polymerization tube.First communication in a series Investigation into the chemistry and technology of polycaproamide.Ivanov Chemical Technology Institute. Translated from Khimicheskie Volokna, No. 3, pp. 7–9, May–June, 1969.     

Some features of the oxidation of polycaproamide which is to be used for the synthesis of graft copolymers

Conclusions The mechanism of oxidation of PCA by atmospheric oxygen has been studied on a model low-molecular-weight compound — ethyl -acetylaminocaproate.It has been found that the oxidation of the low-molecular-weight compound takes place via the stage of formation of hydroperoxy groups at the methylene groups present in the -position to the NH group of the amide bond.The studies performed have made it possible to establish the chemical structure of the PCA graft polymers obtained. Activation and growth of the grafted chain is effected at the carbon atom present in the -position to the NH group of the amide bond in the PCA.Translated from Khimicheskie Volokna, No. 4, pp. 20–22, July–August, 1986.     

Partial oxidation of methane over platinum metal gauze

The partial oxidation of methane to synthesis gas has been studied over a platinum gauze catalyst. The experiments were carried out at atmospheric pressure with a single gauze in a quartz reactor heated in an electric furnace. The furnace temperature was varied in the range 200–900°C and the space time in the range 0.00021–0.00042 s. The feed consisted of a mixture of CH₄O₂Ar2110 and carbon oxides and water were the main products. Oxygen was only partly consumed and relatively small amounts of hydrogen were formed.     

Synthesis of polyethylene oxide macromers

Summary Anionic living polymerization of oxirane was shown to be efficient for the synthesis of polyethylene oxide macromers. The double bond at chainend was introduced either upon initiation or upon deactivation. The macromers obtained were characterized carefully to establish quantitatively the presence of the end-standing double bond. The species are well defined and of narrow molecular weight distribution.The authors are greatly indebted to Mr.E.Schuster and F.Isel for technical assistance.