The effect of graphite nanoslabs on thermal oxidative destruction of polyethylene

The impact of graphite nanoslabs on thermal oxidation of polyethylene is studied via the methods of dynamic thermogravimetry and isothermal oxidation. Graphite nanoslabs are shown to exert an inhibiting effect on thermal oxidation of polyethylene, which leads to an increase in the induction period and in the oxygen-absorption rate. That there is an abnormal effect of the nanofiller content on the resistance to thermal oxidative destruction of composites, mainly for diffusion reasons, is established as well.     

The effect of mass diffusion in gas phase thermal lens experiments

The heat transfer equation is solved for a diffusive source which is undergoing energy relaxation and equilibration with a buffer gas. The resulting si     

Morphology of polytetrafluoroethylene coatings formed from the active gas phase and its thermal modification

Changes in the morphology and surface energy of polytetrafluoroethylene coatings in the course of their growth and after annealing were determined.     

Effect of magnesium nitrate vaporization on gas temperature in the graphite furnace

The vaporization of magnesium nitrate was observed in longitudinally-heated graphite atomizers, using pyrocoated and Ta-lined tubes and filter furnace, Ar or He as purge gas and 10–200-μg samples. A charge coupled device (CCD) spectrometer and atomic absorption spectrometer were employed to follow the evolution of absorption spectra (200–400 nm), light scattering and emission. Molecular bands of NO and NO₂ were observed below 1000°C. Magnesium atomic absorption at 285.2 nm appeared at approximately 1500°C in all types of furnaces. The intensity and shape of Mg atomization peak indicated a faster vapor release in pyrocoated than in Ta-lined tubes. Light scattering occurred only in the pyrocoated tube with Ar purge gas. At 1500–1800°C it was observed together with Mg absorption using either gas-flow or gas-stop mode. At 2200–2400°C the scattering was persistent with gas-stop mode. Light scattering at low temperature showed maximum intensity near the center of the tube axis. Magnesium emission at 382.9, 383.2 and 383.8 nm was observed simultaneously with Mg absorption only in the pyrocoated tube, using Ar or He purge gas. The emission lines were identified as Mg ³P°–³D triplet having 3.24 eV excitation energy. The emitting species were distributed close to the furnace wall. The emitting layer was thinner in He than in Ar. The experimental data show that a radial thermal gradient occurs in the cross section of the pyrocoated tube contemporaneously to the vaporization of MgO. This behavior is attributed to the reaction of the sample vapor with the graphite on the tube wall. The estimated variation of temperature within the cross section of the tube reaches more than 300–400°C for 10 μg of magnesium nitrate sampled. The increase of gas temperature above the sample originates a corresponding increase of the vaporization rate. Fast vaporization and thermal gradient together cause the spatial condensation of sample vapor that induces the light scattering.     

Properties of thermally expandable residual graphite nitrate formed in ambient air

The formation of residual graphite nitrate on keeping in air and the properties of this material were studied in relation to the amount of nitric acid taken for the graphite treatment. The dependence of the expansion ratio on temperature and on the extent of the graphite oxidation was examined. The acidity of the final product was studied in relation to the nitric acid consumption in the final step of the graphite oxidation.     

The effect of γ-irradiation on the thermal decomposition of strontium nitrate

The thermal decomposition of -irradiated strontium nitrate was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed by means of the Coats-Redfern method and were compared with those for the unirradiated salt. It has been suggested that NO₂ formed under irradiation catalyzes the decomposition.     

The effect of a magnetic field on the thermal destruction of cobalt formate

The thermal decomposition of cobalt formate in a flow of an inert gas led to the formation of cobalt nanoparticles in pores of various substrates (silica gel, alumina, activated carbon, and montmorillonite). Electron microscopic studies showed that the particle-size distribution of cobalt depended on the external magnetic field strength; the average particle size and distribution variance decreased as the field strength increased. It was assumed that the external magnetic field affected the nucleation constant of cobalt nanoparticles. Original Russian Text ? P.A. Chernavskii, V.I. Zaikovskii, G.V. Pankina, N.S. Perov, A.O. Turakulova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 586–589.     

The effect of gamma-irradiation on the thermal decomposition of anhydrous cadmium nitrate

The thermal decomposition of -irradiated anhydrous cadmium nitrate was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were calculated by the Coats-Redfern method and were compared with those of the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. The mechanism of the decomposition of unirradiated and irradiated anhydrous cadmium nitrate follows the Mampel equation: -ln(1-) for g() and the rate-controlling process is random nucleation with the formation of a nucleus on every particle.     

The effect of thermal sample pretreatment on the absorption signal in graphite furnace AAS

The origin of the unusual maxima observed in the decomposition curves for pure solutions of some elements has been investigated theoretically and experimentally. An increase in the atom residence time caused by longitudinal redistribution of the analyte in the tube during the pyrolysis step was found to be responsible. The effect can be observed only if the sample is atomized under gas-flow conditions. To prevent any influence on analytical results, atomization should be done in the gas-stop mode.     

Isomeric composition of ditolyls formed upon the thermal decomposition of an anionic Pt(IV) σ-tolyl chloride complex

Conclusion Heating a solution of PtCl₆ ^2– ions and toluene in CF₃CO₂H-H₂O leads to the formation of a platinum(IV) -tolyl complex which decomposes in the presence of free toluene to give 3,3-, 4,4-, 3,4-, 2,3- and 2,4-ditolyls.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 1986.This study was carried out in the framework of the Cooperation Program of Catalysis Scientists at the academies of sciences of the Socialist countries.     

Study of the composition of low-molecular products of the thermal oxidative destruction of atactic polypropylene by gas chromatography/mass spectrometry

The paper presents the results of studying the composition of low-molecular products of the thermal oxidative destruction of atactic polypropylene by gas chromatography/mass spectrometry. Special attention has been paid to the investigation of the mass spectra of compounds dominating in the composition of low-molecular products of the incomplete oxidative destruction of the original polymer, carried out for the synthesis of components for composite materials of the new generation. The most probable molecular structures of the studied compounds are determined on the basis of fragmentation patterns.     

A comparative study of graphene materials formed by thermal exfoliation of graphite oxide and chlorine trifluoride-intercalated graphite

Graphene 3D materials GM1 and GM2 obtained by explosive exfoliation of graphite oxide and graphite intercalated with chlorine trifluoride, respectively, have been studied by elemental analysis, X-ray photoelectron spectroscopy, mass spectrometry, infrared and Raman spectroscopy, and scanning electron microscopy. The specific surface area, the pore size, and electrical conductivity of the materials have been measured. A comparative study has shown that the gas mixture produced during the preparation of GM1 is less hazardous than that in the case of GM2. However, GM2 exhibits a higher conductivity and a larger size of graphene crystallites. The feasibility of isolation of a suspension of graphene nanosheets from the test 3D materials has been demonstrated. Possible applications of these materials are discussed.     

Investigation of cocrystallization of diamond and graphite from the gas phase

Conclusions A procedure was developed for separate determination of the rates of growth of diamond and graphite during their cocrystallization on diamond seed powders during thermal decomposition of methane, using the Kolmogorov theory for the change in the electric conductivity of the powder layer during growth.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 983–987, May, 1980.The authors thank Yu. N. Tolmachev and V. L. Bukhovets for carrying out the etching of the powders overgrown in the glow-discharge plasma.     

Application of thermal analysis in a phase composition study on by-product from semi-dry flue gas desulfurization system

DTA, TG and XRD methods were used for the determination of by-product - obtained during flue gas desulfurization by means of introduction of dehydration - resisting sludge from water decarbonization system. Analysis results enabled the development and application of sludge utilization technology by means of semi-dry flue gas desulfurization in 'Siersza' power plant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Computerized modeling of intermediate compounds formed during thermal decomposition of gadolinium nitrate hydrate

It was shown that after partial dehydration occurs a simultaneous condensation of four mol of initial monomer Gd(NO₃)₃ · 6H₂O into a tetramer Gd₄O₄(NO₃)₄. The heterocycle containing 4 gadolinium atoms gradually loses N₂O₅ and, through the formation of unstable oxynitrates, is transformed into Gd₂O₃. The interatomic distances and angles were calculated using the molecular mechanics method. The comparison of the potential energies of consecutive oxyphosphates permitted an evaluation of their stability. The models of intermediate oxynitrates represent a reasonably good approximation to the real structures and a proper interpretation of experimental data.     

The effect of ph and gas composition on the bubble fractionation of proteins

Studies were conducted to establish the effect of the variation of environmental factors on the separation occurring in protein systems, resulting from bubble fractionation in a bioreactor. The measure of separation was selected to be the separation ratio. This is defined to be the ratio of either the top or the middle position concentration in the vessel to the bottom concentration of the vessel. Invertase and α-amylase were the two “model” enzymes considered. It was observed that, under certain conditions, i.e., a combination of the nature of the sparging gas and the medium pH, varying degrees of protein separation were achieved. The pH of the system dramatically influenced the separation. It was found that the best separation occurred at a certain pH, assumed to be at or close to thepI of the protein in question. Furthermore, it was observed that systems sparged with CO₂ exhibited greater separation than systems sparged with air. In fact, in the case of invertase, almost threefold separation was observed at the top port when the solution was sparged with CO₂.     

The temperature dependence of the cage effect in the gas phase

The photodissociation of iodine has been studied in the gas phase by laser flash photolysis. The decrease of the quantum yield with increasing ethane and propane pressure has been interpreted in terms of the cage effect. As the temperature is increased a less pronounced cage effect is observed. The trends in the measured quantum yields with changing temperature and pressure agree with model calculations for dissociation in a viscous continuum. However the simple model applied is not useful for quantitative predictions. A small decrease of the second order rate constant for iodine atom recombination has been observed with increasing temperature.     

The thermal decomposition of diimide in the gas phase: Kinetics and stoichiometry

The kinetics and stoiehiometry of the decomposition of N₂H₂ and N₂D₂ have been studied as a function of sample size, pressure, and temperature. The reaction follows a single first order kinetic expression over most of its time course. It is suggested that the rate-determining step in the mechanism is a first-order homogeneous gas-phase isomerization of trans-diimide with rate constants:k = 1.8 exp (-4.2 kcal/mol/RT) sec^?1 and k = 1 exp (-4.4 kcal/mol/RT) sec^?1. The detailed mechanism of this isomerization, however, is not evident. At temperatures above room temperature, self-heating has been observed which leads to an initial fast decay. At room temperature the reaction exhibits autocatalysis with the rate increasing as the reaction proceeds. This has been attributed to enhancement by a surface decay process involving adsorbed hydrazine. The only significant products from the decomposition of N₂H₂ are N₂, H₂, and N₂H₄, and the results are interpreted in terms of two parallel reactions: The decomposition of N₂D₂ occurs almost completely by the single reaction giving N₂ + N₂D₄. No azide formation has been detected from either N₂D₂, or N₂D₂, and limits have been put on the yield of ammonia. Extinction coefficients at 365 nm of 3.9 ± 0.2 for N₂H₂ and 3.3 ± 0.1 for N₂D₂ have been measured. Both the rate of decay and the stoichiometry of products show pressure dependence below 150 torr, and this is suggested to be due to direct decomposition of cis-N₂H₂ on the surface.