Self-propagating high-temperature synthesis of porous Ti-Si-Al-C based materials

The pore formation process and the phase composition of the products of combustion of the Ti—Si—Al—C system were studied. The structure of Ti₅(Si,Al)₃C_0.6 single crystals formed in small amounts was determined. The dependences of the burning rate and elongation of the samples on their density and the gas pressure were determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 53–60, March–April, 2006.     

Activated combustion of a silicon—carbon mixture in nitrogen and SHS of Si3N4—SiC composite ceramic powders and silicon carbide

It is established that Si₃N₄—SiC composites with a mass content of SiC 5–60% and a dominating content of the β-modification of silicon nitride can be produced by interaction of the components in the Si—C—N₂ system in the combustion regime. It is found that the fraction of α-Si₃N₄ can be increased by diluting the starting mixture with the end products, but this leads to the occurrence of a certain amount of unreacted silicon in the products. It is shown that the use of chemical activation allows one to perform a single-stage synthesis of Si₃N₄—SiC composites with any contents of the individual components (from 0 to 100%), including pure carbide silicon. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 56–62, September–October, 2006.     

Flame propagation in mixtures of monogermane and oxygen. II. Peculiarities of flame propagation and the structure of combustion waves

Different flame propagation regimes, including a two-wave regime, are studied in a closed pipe with single ignition of GeH₄−O₂ mixtures. It is shown that, depending on the initial conditions and, in particular, on the composition of the initial mixtures, spatially separated chemical reaction waves for oxidation and decomposition of monogermane are observed in certain parts of the reaction vessel which lead to the formation of a two-layer deposit of GeO/Ge. The temporal sequence of the separated combustion wave and wave from which layers of solid products are deposited, as well as the location of the deposition zones in the reaction vessel, are determined by two interacting chain processes—the oxidation and decomposition of monogermane. The thermal relaxation kinetics of the reactive mixture after passage of the combustion waves is determined by the rate of conductive heat transfer from heated solid particles (reaction products) to the gaseous phase. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 77–84, January–February 1999.     

Deformation of nonfired refractories based on phosphate binders. 6. Deformation under heating and creep in corundum composites

The results of studying heating deformation and creep are described for two systems: electrocorundum — α-Al₂O₃ — phosphate binder and electrocorundum — pyrophyllite — phosphate binder. It is shown that composites with H₃PO₄ experience less deformation than composites with the alumochromium-phosphate binder, whereas using pyrophyllite instead of aluminum oxide increases creep deformation due to the presence of the liquid phase in the material. The effect of technological factors is investigated. __________ Translated from Novye Ogneupory, No. 6, pp. 58–62, June, 2007. Continuation. See beginning in Vol. 48, Nos. 1–2, 2007.     

Fumigant and Contact Toxicities of Monoterpenes to <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> (L.) and <Emphasis Type="Italic">Tribolium castaneum</Emphasis> (Herbst) and their Inhibitory Effects on Acetylcholinesterase Activity

A comparative study was conducted to assess the contact and fumigant toxicities of eleven monoterpenes on two important stored products insects—, Sitophilus oryzae, the rice weevil, and Tribolium castaneum, the rust red flour beetle. The monoterpenes included: camphene, (+)-camphor, (−)-carvone, 1-8-cineole, cuminaldehyde, (l)-fenchone, geraniol, (−)-limonene, (−)-linalool, (−)-menthol, and myrcene. The inhibitory effect of these compounds on acetylcholinesterase (AChE) activity also was examined to explore their possible mode(s) of toxic action. Although most of the compounds were toxic to S. oryzae and T. castaneum, their toxicity varied with insect species and with the bioassay test. In contact toxicity assays, (−)-carvone, geraniol, and cuminaldehyde showed the highest toxicity against S. oryzae with LC₅₀ values of 28.17, 28.76, and 42.08 μg/cm², respectively. (−)-Carvone (LC₅₀ = 19.80 μg/cm²) was the most effective compound against T. castaneum, followed by cuminaldehyde (LC₅₀ = 32.59 μg/cm²). In contrast, camphene, (+)-camphor, 1-8-cineole, and myrcene had weak activity against both insects (i.e., LC₅₀ values above 500 μg/cm²). In fumigant toxicity assays, 1-8-cineole was the most effective against S. oryzae and T. castaneum (LC₅₀ = 14.19 and 17.16 mg/l, respectively). Structure-toxicity investigations revealed that (−)-carvone—, a ketone—, had the highest contact toxicity against the both insects. 1-8-Cineole—, an ether—, was the most potent fumigant against both insects. In vitro inhibition studies of AChE from adults of S. oryzae showed that cuminaldehyde most effectively inhibited enzyme activity at the two tested concentrations (0.01 and 0.05 M) followed by 1-8-cineole, (−)-limonene, and (l)-fenchone. 1-8-Cineole was the most potent inhibitor of AChE activity from T. castaneum larvae followed by (−)-carvone and (−)-limonene. The results of the present study indicate that (−)-carvone, 1,8-cineole, cuminaldehyde, (l)-fenchone, and (−)-limonene could be effective biocontrol agents against S. oryzae and T. castaneum.     

Part 3. Phase Transformations within the Layer of a Dry Barrier Mixture for Aluminum Electrolysis Cells

It has been established that transformations within the layer of a dry barrier mixture (DBM) are selective in character and are mainly confined to the upper zones of the innermost part (core) of DBM. The DBM layer undergoes a solid-liquid sintering in these zones. The glass phase thus formed prevents the electrolysis products from penetration into the DBM layer. Modifier admixtures — titanium and iron oxides, products of electrolysis and degradation of the refractory layer AlF, SiF₄, and sodium oxide — decrease the viscosity of aluminosilicate melt. The grains of a disthene-sillimanite concentrate undergo cracking along the cleavage plane. Imperfections of the crystal lattice promote transformations in the grains of normal electrofused corundum. Oxyfluoride AlOF and an oxyfluoride of variable composition AlOF_{1 − x} are formed in the cathode lining of the electrolysis cell. For Parts 1 and 2, see Novye Ogneupory, Nos. 3 and 5, 2005. __________ Translated from Novye Ogneupory, No. 9, pp. 7 – 13, September, 2005.     

Anodic oxidation of organic pollutants on a Ti/SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> anode

A Ti/SnO₂–Sb₂O₄ electrode was prepared by alternate Sn and Sb electrodepositions using the thermo-electrochemical method. The chemical, electrochemical, and structural characterization of the electrode was performed and it was tested in the anodic oxidation of several pollutants, phenol, ibuprofen, acid orange 7 (AO7), and diclofenac, all in aqueous 0.035 M Na₂SO₄ solutions at current densities of 10 and 20 mA cm⁻². After the 24 h assay, removal of chemical oxygen demand, total organic carbon (TOC) and absorbance were very high, especially at the higher current density. TOC removals presented the lowest value. However, after 24 h at 20 mA cm⁻², TOC removals were: phenol—94%; ibuprofen—83%; AO7—88%; and diclofenac—73%. Combustion efficiency and instantaneous and mineralization current efficiencies were also determined.     

Chromium combustion in nitrogen

Results of investigation of chromium combustion in nitrogen are presented. It is shown that the combustion proceeds in the solid state. In the combustion wave, chromium reacts with nitrogen in steps. The first step—the formation of Cr₂N—proceeds in the separation regime. The maximum combustion temperature is limited by the temperature of dissociation of CrN. Afterburning is observed behind the combustion front. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 40–45, September–October 1999.     

Determination of the liquidus surface in the UO2 — ZrO2 — Fe(Cr, Ni)Oi system

Results of an experimental study of the interaction between corium melts of various compositions in the UO₂ — ZrO₂ — Fe(Cr, Ni)O_i system and the hard ZrO₂ wall of a cold crucible upon induction heating are presented. The conditions of heating, melting, and interaction with the hard wall and the heat balance in such a crucible are considered with allowance for the special features of the behavior of two-phase melts, when the melting occurs at a temperature ranging from liquidus to solidus. The notion of the effective liquidus temperature below which the binary system behaves as a solid body and above which it behaves as a liquid is suggested. The results of the analysis show that an unknown high-temperature (T_melt ≈ 2700 K) compound of composition close to 5UO₂ · 7ZrO₂ · 4Fe(Cr, Ni)O_i exists in the UO₂ — ZrO, — Fe(Cr, Ni)O_i system. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 11–22, March, 2000.     

Effect of structural defects formed in alloying of yttrium oxide by CeO2 and in heat treatment on phase transformations

X-ray methods are used for investigating the formation of substitutional — interstitial — subtractive solid solutions based on yttrium oxide alloyed by CeO₂ at 1900°C in an air medium. Single-phase solid solutions with disordered cubic structures of the C type are found in the region of dissolution of the CeO₂ alloying addition (0 – 10%). It is established that upon heating such specimens in the 25 – 1500°C range in an air medium the cubic C-phase is transformed into a monoclinic phase of type B₁. As a result of dissolution of the CeO₂ alloying addition anion vacancies forming in the yttrium oxide lattice and thermal vacancies forming at 1900°C influence strongly the temperature of the C - B₁ phase transformation and the temperature coefficients of linear expansion. Translated from Ogneupory, No. 9, pp. 8 – 10, September, 1995.     

Chemical reactions in the low-temperature zone of a laminar rich propane—air flame

The mechanism of chemical reactions in the low-temperature zone of a rich propane—air flame is considered. It is shown that at temperatures of 300–700 K, intense chemical reactions proceed with the formation of end products and that the water concentration reaches an intermediate equilibrium value even at a temperature of 685 K. In this zone of the front, the diffusion of atomic hydrogen from the high-temperature zone plays a determining role and water is formed mainly by the reactions H + O₂ + M ⇒ HO₂ + M, HO₂ + HO₂ ⇒ H₂O₂ + O₂, H₂O₂ (+M) ⇒ 2OH (+M), C₃H₈ + OH ⇒ C₃H₇ + H₂O. Propane reacts with active centers more effectively than molecular hydrogen. Its primary reactions are due to the interaction with OH and HO₂ radicals. Arguments are given in favor of the thermal-diffusion nature of the superadiabatic temperature phenomenon in rich propane—air flames. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 14–19, September–October, 2006.     

Comparative characterization of the distribution of biomarker hydrocarbons in the chemical transformation products of oxygen-containing precursors of petroleum

The distribution of biomarker hydrocarbons in the thermolysis and thermocatalysis products of oxygen-containing compounds (possible petroleum hydrocarbon precursors) was studied by gas chromatography-mass spectrometry. It was found that n-alkylcyclohexanes and steranes were generated in the course of thermolysis along with expected hydrocarbons—n-alkanes and isoprenes, which resulted from the loss of a functional group. In this case, the molecular-weight distributions of n-alkanes and n-alkylcyclohexanes correlated well with each other. In the course of thermocatalysis, the homologous series of n-alkanes and n-alkylcyclohexanes were also generated; however, an n-alkylcyclohexane distribution maximum had an even number of carbon atoms in the molecule (C₁₈). It was experimentally found that the sterane fragments of oxygen-containing compounds formed upon thermolysis were thermodynamically unstable; this was supported by the formation of biological C₂₇–C₂₉ 5α, 14α, 17α, 20S, and 20R and 5β, 14α, 17α, and 20R (coprostane) steranes as a result of thermolysis. Unlike thermolysis, all of the four epimers of regular C₂₇–C₂₉ (5α, 14α, 17α, 20S, and 20R and 5α, 14β, 17β, 20S, and 20R) steranes were formed as a result of thermocatalysis. It was found that the relative distribution of biomarker hydrocarbons in the thermolysis products of various oxygen-containing compounds largely reflected the structure of the parent organic substance, as compared with that upon thermocatalysis in the presence of active aluminosilicate.     

Thermal analysis of failed-batch palm oil by differential scanning calorimetry

Thermal behavior of palm oil samples drawn from the batch crystallizers that failed during crystallization and of a control oil that was drawn from a batch that produced good crystallization were analyzed by differential scanning calorimetry under constant heating and cooling conditions. Four polymorphs—β’₂, α, β’₁, and β₁—were observed, and their temperatures were tabulated. A rapid and sudden surge of heat demand was observed for samples from failed crystallizers. Less supercooling values were obtained from the control oil compared to the higher values for samples from failed crystallizers. In crystallization thermograms, a sharp high-temperature exotherm (high-T peak) and a broad low-temperature exotherm (low-T peak) were observed. Low-T peaks were found almost invariably stationary at −5.1 to −5.6°C, and high-T peaks varied depending on the saturation level of the oil. A new peak, sandwiched between the high-T and low-T peaks, was observed for the control oil.     

α-Oxidation of α-hydroxyfatty acids in rat brain. Possible involvement of an α-peroxylactone

Combine—but not individual—microsomal and supernatant fractions obtained from rat brains not only consume oxygen but also provoke emission from added chlorophyll. These results are consistent with literature data (Levis and Mead,J. Biol. Chem. 239, 77 [1964]) for trapping of radioactive¹⁴CO₂ following addition of α-hydroxy-[1-¹⁴C]stearic acid. The most plausible explanation for emission is the interaction of chlorophyll with an α-peroxylactone. An intermediary α-peroxylactone in α-oxidation is consistent with other available data (Salim-Hanna, Campa and Cilento,Photochem. Photobiol. 45, 849 [1987]; Campa, Salim-Hanna and Cilento,Photochem. Photobiol. 49, 349 [1989]) and, on chemical grounds, provides a feasible route to the final products.     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model. __________ Translated from Chemical Engineering (China), 2007, 35(10): 23–26 [译自: 化学工程]     

Biodiesel production by the transesterification of cottonseed oil by solid acid catalysts

Methyl esters (biodiesel) were produced by the transesterification of cottonseed oil with methanol in the presence of solid acids as heterogeneous catalysts. The solid acids were prepared by mounting H₂SO₄ on TiO₂ · nH₂O and Zr(OH)₄, respectively, followed by calcining at 823K. TiO₂-SO₄ ²⁻ and ZrO₂-SO₄ ²⁻ showed high activity for the transesterification. The yield of methyl esters was over 90% under the conditions of 230°C, methanol/oil mole ratio of 12:1, reaction time 8 h and catalyst amount (catalyst/oil) of 2% (w). The solid acid catalysts showed more better adaptability than solid base catalysts when the oil has high acidity. IR spectral analysis of absorbed pyridine on the samples showed that there were Lewis and Br?nsted acid sites on the catalysts. Translated from The Chinese Journal of Process Engineering, 2006, 6(4): 571–575 [译自: 过程工程学报]     

Dimorphism of water at 0‡c. refinement of the cluster-hygroscopic microstructure of water

The structural and physical behavior of water in the temperature range from 0 to 35‡C was examined. The possible enantiotropic mechanism of formation of two morphological modifications of (H₂O)₈ clusters at 0‡C (dimorphism of water) was demonstrated: liquid phase — body-centered cubic packing of the water molecules (bcc packing), ice — double tetrahedral (diamond) packing. The partial density of ice clusters at 0‡C is equal to 838 g/liter, and the maximum density of water is observed when (H₂O)₆ clusters predominate in the water. Translated fromKhimicheskie Volokna, No. 6. pp. 44–46, November–December, 1998.     

Polymorphism of stabilized and nonstabilized tristearin,pure and in the presence of food emulsifiers

The polymorphism of tristearin (SSS) was studied by means of differential scanning calorimetry and powder X-ray diffraction. The influence of 5% in weight of different food emulsifiers—i.e., 1-monostearin, sorbitan tristearate, and sugar monostearate—was also studied. Because polymorphism is sensitive to thermal treatment, two thermal conditionings were applied. According to the dynamic process (melting, quenching, and heating at 5°C/min), SSS showed three polymorphic forms: α, β′, and β₁. The presence of the emulsifiers hindered the β′→β transformation, and a destructured β₂ form was recorded. According to the stabilization process (stabilization at 57°C for various periods of time), SSS showed two β′ forms: β ₂ ^′ and β ₁ ^′ . Three hours of stabilization were necessary to recover the whole triglyceride under the β form. The emulsifiers slowed down the polymorphic transition rates. Indeed, after six hours of stabilization, mixtures of β′ and β were observed. Sugar monostearate seemed to have the most powerful effect on the transition kinetics because large amounts of α form were detected. Presented at the 86th AOCS Annual Meeting & Expo, in San Antonio, Texas, in May 1995.     

Development of glass ceramic coatings containing hydroxyapatite

Glass ceramic composites — to be used for coatings on titanium implants — based on leucite glass with elevated flux content and added hydroxyapatite or a mixture of hydroxyapatite and fluorite are examined. It is established that pastes containing no more than 30% hydroxyapatite in leucite glass are the best materials for denture coatings. Pastes with a higher content of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂(> 30%) are recommended for coatings on intramaxillary titanium implants. __________ Translated from Steklo i Keramika, No. 4, pp. 34–36, April, 2007.     

Combustion synthesis of lithium cobaltate

A feasibility of combustion synthesis of lithium cobaltate powders using oxide sources was investigated. Cobalt oxide Co₃O₄ and lithium carbonate Li₂CO₃ were used as starting reactants. Two different oxidizers were explored: (i) ammonia nitrate NH₄NO₃ and (ii) lithium nitrate LiNO₃. Some organic reducers (ORs)—such as CH-polymers, melamine, urotropine, etc.—were used as a fuel. Investigated was the effect of green composition/density and inert gas pressure on combustion parameters (burning velocity and combustion temperature) and product micro structure/composition. Best results were obtained for LiNO₃-Co₃O₄-OR blends. Relative green density ρ was found to have a crucial effect: good results might be obtained only for ρ > 65%. XRD data testified that the combustion products obtained in optimized conditions contained pure lithium cobaltate LiCoO₂. According to SEM data, the obtained powders had a mean particle size of 20 μm.