Phenomenological characteristics of cool-flame oxidation of cyclohexane

The phenomenological characteristics of cool flames of cyclohexane are studied. It is shown that cyclohexane flames arise at lower temperatures (beginning at T ≈ 230°C) and lower pressures (lower than 10 torr at T = 290°C) than alkane and alkene flames. The temperature dependence of the lower pressure limit of the cool flame is determined. It is established that, depending on the conditions (p, T, and C₆H₁₂/O₂ ratio), cool-flame ignition is characterized by a rise and drop of the temperature ΔT or by several peaks imposed on each other. The dependence of the cool-flame structure (for ΔT) on the oxygen content in the reaction mixture is studied. It is shown that the cool flame resulting from cyclohexane oxidation is accompanied by ring opening and formation of products with a smaller number of carbon atoms. It is established that cool flames of cyclohexane are characterized by a negative temperature coefficient. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 26–28, January–February, 2008.     

Initiation of combustion of a CH<Subscript>4</Subscript>-O<Subscript>2</Subscript> mixture in a supersonic flow with excitation of O<Subscript>2</Subscript> molecules by an electric discharge

The possibility of intensification of ignition of a methane-oxygen mixture in a supersonic flow behind the front of an oblique shock wave by means of excitation of O₂ molecules to the states a ¹Δ_g and b ¹Σ_g⁺ in an electric discharge is discussed. Through numerical simulations, activation of O₂ molecules by an electric discharge is demonstrated to speed up chain reactions in the CH₄-O₂ mixture and to reduce the induction-zone length. Even a small amount of energy input to O₂ molecules in the discharge (≈3·0⁻² J/cm³) can reduce the ignition-delay length by a factor of hundreds and initiate combustion at distances of ≈1 m from the discharge zone at comparatively low temperatures of the gas behind the front (≈1000 K) and moderate pressures (≈10⁵ Pa). Excitation of O₂ molecules by an electric discharge is much more efficient than simple heating of the mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 3–16, May–June, 2008.     

Characterization of HETEs and related conjugated dienes by UV spectroscopy

Three distinct pairs of HETEs can be distinguished on the basis of their UV spectra. We used hydroxy-linoleates (hydroxy-octadeca-cis-trans-dienoates) as a base for comparisons; both the 9- and 13-hydroxy isomers have identical chromophores with λ_max near 234 nm. The presence of a double bond three carbons removed from the conjugated diene (the chromophore of 9- and 11-HETE) causes a shift in the observed λ_max to near 235 nm. A double bond β to the chromophore (5- and 15-HETE) gives a further shift of 1.5 nm, giving a λ_max between 236–236.5 nm. With double bonds in both these positions (8- and 12-HETE), the λ_max is observed near 237 nm. It is apparent that the exact λ_max of thecis-trans diene chromophore is influenced in a consistent way by the adjacent methylene interruptedcis double bonds. hydroxylinoleate, describes the two primary products of linoleate oxygenation, more properly named 9-hydroxy-octadeca-10trans,12cis-dienoate and 13-hydroxy-octadeca-9cis,11trans-dienoate. Hydroxylinoelaidate refers to the correspondingall-trans dienes. RH-HPLC, reversed-phase high pressure liquid chromatography; SP-HPLC, straight-phase high pressure liquid chromatography.     

Effect of a nanosecond gas discharge on deflagration to detonation transition

The possibility of using a high-voltage nanosecond discharge to initiate gaseous detonation was shown experimentally. The experiments were performed with C₃H₈ + 5O₂ and C₃H₈/C₄H₁₀ + 5O₂ + xN₂ (x = 0–10) mixtures at an initial pressure of 0.15–0.6 atm. The discharge was initiated by a voltage pulse of duration ≈60 nsec and amplitude 4–70 kV; the energy input was 0.07–12 J. Under the conditions of the experiment, three flame propagation regimes were observed: slow combustion, transient detonation, and Chapman—Jouguet detonation. For the initiation of the C₃H₈+ 5O₂ mixture in a tube of diameter 140 mm, the length of the deflagration to detonation transition was 130 mm at an initial pressure of 0.3 atm and an initiation energy of 70 mJ. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 80–90, March–April, 2006.     

The system SiC–W<Subscript>2</Subscript>B<Subscript>5</Subscript>–LaB<Subscript>6</Subscript>

Experiments and calculations have been applied to the structure of the triple eutectic system SiC–W₂B₅–LaB₆(T _eu = 1900 ± 40°C), composition in mol.%: 10 LaB₆, 44 SiC, 46 W₂B₅, error ±2–3%, which opens up prospects for making ceramic materials for various purposes.     

Recording local fluctuations of physicochemical parameters in a combustion wave in condensed systems

A method for recording fluctuations of physicochemical parameters in a combustion wave in condensed systems is proposed that makes it possible to estimate the frequency of these fluctuations experimentally. Experiments with a Zr+WO₃ pyrotechnic mixture using this method show that in the combustion wave there are fluctuation modes with frequencies ≈200 and ≈20 Hz corresponding to characteristic dimensions of heterogeneities of the system of order 0.1 and 1 mm, respectively. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 71–75, November–December 1999.     

Field Dependence of the Spin Relaxation Within a Film of Iron Oxide Nanocrystals Formed via Electrophoretic Deposition

The thermal relaxation of macrospins in a strongly interacting thin film of spinel-phase iron oxide nanocrystals (NCs) is probed by vibrating sample magnetometry (VSM). Thin films are fabricated by depositing FeO/Fe₃O₄ core–shell NCs by electrophoretic deposition (EPD), followed by sintering at 400°C. Sintering transforms the core–shell structure to a uniform spinel phase, which effectively increases the magnetic moment per NC. Atomic force microscopy (AFM) confirms a large packing density and a reduced inter-particle separation in comparison with colloidal assemblies. At an applied field of 25 Oe, the superparamagnetic blocking temperature is T _B^SP ≈ 348 K, which is much larger than the Néel-Brown approximation of T _B^SP ≈ 210 K. The enhanced value of T _B^SP is attributed to strong dipole–dipole interactions and local exchange coupling between NCs. The field dependence of the blocking temperature, T _B^SP(H), is characterized by a monotonically decreasing function, which is in agreement with recent theoretical models of interacting macrospins.     

Extension ratio of composite fibre fabricated from a polymer dispersion

The extension ratio of a composite fibre λ _t was calculated based on the mass balance using the values of the extension ratio of particles of disperse phase λ _f and polymer matrix λ _m and model concepts concerning the structure of the dispersion. Using the model composite PA-54—glass beads, it was experimentally demonstrated that the situation λ _m > λ _t is possible in deformation of the polymer dispersion. In deformation of the dispersions, the formation of matrix-fibril structures with “continuous” fibrils (φ _lf2 =1) is possible for λ _f /λ _m > 1 due to coalescence in the direction of flow. Kiev State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 3, pp. 44–47, May–June, 2000.     

Synthesis and properties of novel poly(aryl ether ketone)s containing imide linkages in the main chains

A new monomer containing imide linkages, bis[4-(p-phenoxybenzoyl)-1,2-benzenedioyl]-N,N,N′,N′-4,4′-diaminodiphenyl ether (BPBDADPE), was prepared by the Friedel–Crafts reaction of bis(4-chloroformyl-1,2-benzenedioyl)-N,N,N′,N′-4,4′-diaminodiphenyl ether (BCBDADPE) with diphenyl ether (DPE). Novel poly(aryl ether ketone)s containing imide linkages in the main chains (PEK-I) were synthesized by electrophilic Friedel–Crafts solution copolycondensation of terephthaloyl chloride (TPC) with a mixture of DPE and BPBDADPE. The polymers were characterized by different physico-chemical techniques. The polymers with 10–40 mol% BPBDADPE are semicrystalline and had increased T _gs over commercially available poly(ether ether ketone) (PEEK) and poly(ether ketone ketone) (PEKK) (70/30) due to the incorporation of imide linkages in the main chains. The polymers IV and V with 30–40 mol% BPBDADPE had not only high T _gs of 182–183 °C, but also moderate T _ms of 341–343 °C, having good potential for melt processing and exhibited high thermal stability and good resistance to common organic solvents.     

Critical diameter and critical thickness of an emulsion explosive

For a fine emulsion explosive, the dependence of the detonation velocity D on the cylindrical-charge diameter d and plane-layer thickness Δ is determined. It is shown that the emulsion explosive considered has low values of the critical diameter (d _cr ≈ 5 mm) and thickness (Δ_cr ≈ 2 mm). According to curved front theory, the relation D(d) ≈ (2Δ) is valid and the ratio d _cr/Δ_cr is 2.4–2.5. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 121–127, May–June, 2008.     

Synthesis and Characterization of New Biodiesels Derived From Oils of Plants Growing in Northern Wisconsin and Minnesota

We report on the preparation and selected properties of some new biodiesels which we synthesized from oils of plants growing in Northern Wisconsin and Minnesota. The composition and the low-temperature properties such as crystallization onset T _c and end of melting T _m investigated with the help of differential scanning calorimetry are presented. Some of these biodiesels exhibited remarkably good low-temperature characteristics. In order to further improve these properties, we use a variety of alcohols during the transesterification process, including isopropyl, 2-butyl, and isoamyl alcohols. Using several parameters such as oil content and crystallization onset temperature T _c, plant species that appear most promising have been identified, among those highbush cranberry (T _c ≈ −31 °C for its methyl esters, T _c ≈ −41 °C for its 2-butyl esters), dotted horsemint (T _c ≈ −17 °C for its methyl esters, T _c ≈ −40 °C for its 2-butyl esters), and American hazelnut (T _c ≈ −19 °C for its methyl esters, T _c  ≈ −30 °C for its 2-butyl esters).     

Reduced kinetic mechanism for combustion of synthesis gas at elevated temperatures and pressures

The key combustion reactions of synthesis gas at elevated initial temperatures (T ₀ = 500–700 K) and pressures (p = 10–30 atm) are identified by analyzing the kinetic mechanism. A reduced mechanism of the oxidation reactions of synthesis gas consisting of 14 elementary reactions involving 13 species is proposed which adequately describes the results of experimental data on the burning velocities of mixtures of synthesis gas with oxygen and inert diluents at T ₀ = 300–700 K, p = 10–30 atm, and ratios CO/H₂ = 0.05–0.95, and satisfactorily predicts the flame structure and the dependence of the flammability limits on the initial temperature at atmospheric pressure.     

Effect of Pre-Melting Time on Crystallization of Poly(ethylene terephthalate)

In this study poly(ethylene terephthalate) (PET) was melted at 300°C, approximately 46°C above the crystalline melting point, T _m, for different times, i.e., Δt _m,=5, 8, and 10 min, and then quenched to different isothermal crystallization temperatures, T _c, ranging from 190°C to 230°C. The effect of pre-melting time, Δt _m, at 300°C on the degree of crystallinity and on crystalline morphology were investigated by differential scanning calorimetry (DSC) and polarized-light microscopy (PLM). After crystallization at low T _c, PLM data revealed the PET contained usual, positive, and unringed spherulites. After crystallization at high T _c PET contained unusual, ringed, and double-extinction spherulites. The experimental results reveal that increasing the pre-melting time Δt _m at 300°C causes an increment in T _c for usual–unusual, unringed–ringed, and positive–double-extinction transitions of the PET spherulites. The experimental results also show that PET with a pre-melting time Δt _m=8 min had higher crystallinity than those with pre-melting times Δt _m=5 and 10 min. These crystallization phenomena were attributed to the different numbers of residual unmelted PET crystallites as a result of the variation in pre-melting time, Δt _m, at 300°C.     

Prediction of gaseous pollutants and heavy metals during fluidized bed incineration of dye sludge

This research provides an equilibrium model for predicting both the emission of gaseous pollutants and the fate of heavy metals during incineration of biologically treated dye sludge in a bench-scale fluidized bed incinerator. Major gaseous pollutants and hazardous trace heavy metals have been also measured under various operating conditions. The predicted values, which were derived by using a thermodynamic equilibrium model, can be used to determine the optimum operating parameters and the risk associated with hazardous waste incineration by means of verifying experimental data. However, prediction of NO_x emission using a thermodynamic equilibrium model during incineration of waste was not simple. The reason is that the variation of NO_x emission during incineration of waste was affected by the various operating parameters, such as air-fuel ratio(λ _T ), primary air factor(λ ₁ /λ _T ), combustor geometry, method of heat release, and preheating of combustion air. According to the distributions of Cr and Pb simulated by the equilibrium model, all of the Cr in the feed was retained in the ash as the solid phase of Cr₂CO₃. However, most Pb was retained in the ash during incineration as the solid phase of PbSO₄, or heterogeneously deposited onto the fly ash as PbO(g) when the combustion gas becomes cool. Presented at the Int’/Sym. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Catalytic Combustion of the Stoichiometric n-Butane/Air Mixture on Isothermally Heated Platinum Wire

The catalytic combustion of the stoichiometric n-butane–air mixture per se or diluted with N₂, on a platinum wire at different initial pressures (10–70 kPa) and temperatures (690–1,080 K) was studied. The chemical heat flow rate, dQ _r/dt, of the surface reaction was measured in isothermal and isobaric conditions and the overall kinetic parameters were evaluated for both steady state and initial transient catalytic combustion. At low total pressure (10 kPa), the temperature dependence of dQ _r/dt indicated a normal (Arrhenius) behavior for 690 < T < 900 K, while at higher temperatures, over 900 K, an anti-Arrhenius behavior was found. The obtained results are consistent with a diffusion-controlled process, accompanied by reactant depletion around the catalytic surface, at higher temperatures.     

Kinetics and mechanism of thermal decomposition of ammonium nitrate powder under the action of carbon black

It is shown that in the presence of carbon black, the decomposition rate of solid ammonium nitrate increases strongly (by more than seven orders of magnitude). The kinetic regularities of the decomposition in the temperature range 70–150°C are established. At relatively low temperatures, the process proceeds by a two-stage mechanism with corresponding acceleration at each stage. At elevated temperatures, the first stage is absent. The decomposition rate is proportional to the amount of carbon black in the mixture. The activation energy for the decomposition (≈30 kcal/mole) does not vary during transformation. Water decelerates the process. For a water content of ≈(4–5)%, an intermediate maximum of the deceleration is observed. The main gaseous decomposition product is N₂. The concurrent oxidation of carbon black is terminated by evolution of CO₂. The mechanism of the chemical transformations is discussed using the results obtained and information available on the kinetics of individual reactions. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 63–73, September–October, 2000.     

Estimation of critical conditions for the detonation-to-deflagration transition

An estimate is proposed for the critical Mach number of the shock wave that can ensure the deflagration-to-detonation transition (DDT): M_min ≈ 0.56M₀ for expanding waves and M_min ≈ 0.33M₀ for plane waves propagating in a constant-section straight tube (M₀ is the Mach number of an ideal Chapman—Jouguet detonation wave). The condition M > M_min ensures the DDT mode, whereas only laminar or turbulent burning without the DDT is observed for lower Mach numbers. The estimate is based on the equiprobable transition from the compressed state of the initial mixture both to the detonation and to the deflagration branch of the adiabat of reaction products (with respect to the initial state of the combustible mixture). __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 91–96, March–April, 2006.     

Hyperbranched azo polyurethane synthesized through A2 + B3 scheme

A hyperbranched azo polyurethane was synthesized by one-step polymerization of an A₂ type monomer diphenylmethane-4,4′-diisocyanate and a B₃ type monomer 4-(N,N′-bis(2-hydroxyethyl))amino-2′-hydroxyethoxyl-4′-nitro-azobenzene. The azo polymer was characterized by ¹H nuclear magnetic resonance (NMR), ultraviolet-visible (UV-Vis) spectrum and thermal analysis. The λ_max of the polymer in dimethylformamide (DMF) solution is 488 nm. The number average molecular weight (M_n) determined by GPC is 9,300 with a polydispersion index 1.9. The glass transition temperature (T _g) of the polymer is 131°C observed from DSC thermogram. The results show that the azo polyurethane has been successfully synthesized through this scheme. Surface-relief-gratings (SRGs) were fabricated on the polymer film after being irradiated by interference pattern of Ar⁺ laser beams for 1,000 s. The surface modulation depth and the grating space period measured by AMF are 67 and 770 nm, respectively. __________ Translated from Acta Polymerica Sinica, 2007, 1: 21–25 [译自: 高分子学报]     

Specific features of combustion of hydrocarbon gases in composite porous inserts

Results of an experimental study of combustion of propane-butane and methane with air in inserts made of a porous material with a pore size of ≈0.35 mm and a cellularporous material with a pore size of ≈3 mm, with the combustion zone being located at the junction between the materials, are presented. A comparison of the composition of the products and combustion efficiency with results calculated for equilibrium compositions in the range of the air-to-fuel ratio α = 0.4–2.5 reveals significant deviations of the experimental data from the equilibrium values (lower fraction of H₂ and NO, a greater value of the ratio CO/CO₂, elevated combustion efficiency at α = 0.6−0.7, and reduced combustion efficiency in the stoichiometric region) caused by intense radiative heat removal and radiative quenching of the composition of combustion products.     

Gas permeation properties of poly(2,5-dialkyl-p-phenyleneethynylene) membranes

Dipropynylbenzenes with alkyl groups (CH₃C ≡ CRC₆H₂RC≡CCH₃, R=n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, 1a–c, respectively) were polymerized with Mo(CO)₆ to afford solvent-soluble poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c). The polymers (2a–c) had high molecular weight over 3×10⁴, and gave free-standing membranes by solution casting method. According to thermogravimetric analysis (TGA), these poly(p-phenyleneethynylene)s showed high thermal stability (T₀ ≥380 °C). The densities of membranes of poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c) were 0.936–0.965, and their fractional free volume (FFV) were relatively large (ca. 0.14–0.15). The oxygen permeability coefficients (PO₂) of membranes of 2a–c were 4.88, 7.06, and 16.6 barrers, respectively.