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Gaseous Phase (gaseous + phase)
Selected AbstractsInteraction of a phosphorus-based FR, a nanoclay and PA6,Part 1: Interaction of FR and nanoclayFIRE AND MATERIALS, Issue 6 2009Alwar Ramani Abstract The thermal decomposition of organophosphorus fire-retardant (OP1311) and/ or organonanoclay (Cloisite 30B) is hereby investigated employing thermogravimetric analysis (TGA), to give an insight into their intrinsic behaviour and interaction in polymer nanocomposites for fire safety applications, because the addition of OP1311 and Cloisite 30B in Polyamide 6 (PA6) seems to have a synergistic effect on the thermal decomposition of PA6 (part 2 of the paper). An important objective of this research was to determine to what extent phosphorus components escape in the gaseous phase, which will affect the heat of combustion of the fire-retarded polymer. The decomposition products arising from pyrolysis and combustion are investigated by means of Fourier transform infrared spectroscopy. Under pyrolytic conditions, the inclusion of Cloisite 30B into OP1311 (FR) shows a synergistic effect on the initial mass loss at low temperature of ,280,420°C and leads to the acceleration of the thermal degradation process. While the DTG curve of Cloisite 30B shows two distinct degradation peaks (steps) that of OP1311 and OP1311 plus Cloisite 30B show four degradation steps. TGA measurements of OP1311 in nitrogen show more mass loss than in air, whereas Cloisite 30B gives similar amounts of mass loss in air and nitrogen. In nitrogen, the major evolved gaseous species from Cloisite 30B alone are hydrocarbons, 2-(diethylamino)ethanol and water, whereas the evolved gases from that of OP1311 at ,320°C are mainly water, at ,420°C, carbon dioxide, water and ammonia and at 480,570°C diethylphosphinic acid. Under thermo-oxidative conditions, the gases evolved are mainly carbon dioxide and water from both Cloisite 30B and OP1311. Copyright © 2009 John Wiley & Sons, Ltd. [source] Quantum chemical studies on molecular structural conformations and hydrated forms of salicylamide and O-hydroxybenzoyl cyanideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2005K. Anandan Abstract Ab initio and density functional theory (DFT) methods have been employed to study the molecular structural conformations and hydrated forms of both salicylamide (SAM) and O-hydroxybenzoyl cyanide (OHBC). Molecular geometries and energetics have been obtained in the gaseous phase by employing the Møller,Plesset type 2 MP2/6-311G(2d,2p) and B3LYP/6-311G(2d,2p) levels of theory. The presence of an electron-releasing group (SAM) leads to an increase in the energy of the molecular system, while the presence of an electron-withdrawing group (OHBC) drastically decreases the energy. Chemical reactivity parameters (, and ,) have been calculated using the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) obtained at the Hartree,Fock (HF)/6-311G(2d,2p) level of theory for all the conformers and the principle of maximum hardness (MHP) has been tested. The condensed Fukui functions have been calculated using the atomic charges obtained through the natural bond orbital (NBO) analysis scheme for all the optimized structures at the B3LYP/6-311G(2d,2p) level of theory, and the most reactive sites of the molecules have been identified. Nuclear magnetic resonance (NMR) studies have been carried out at the B3LYP/6-311G(2d,2p) level of theory for all the conformers in the gaseous phase on the basis of the method of Cheeseman and coworkers. The calculated chemical shift values have been used to discuss the delocalization activity of the electron clouds. The dimeric structures of the most stable conformers of both SAM and OHBC in the gaseous phase have been optimized at the B3LYP/6-311G(2d,2p) level of theory, and the interaction energies have been calculated. The most stable conformers of both compounds bear an intramolecular hydrogen bond, which gives rise to the formation of a pseudo-aromatic ring. These conformers have been allowed to interact with the water molecule. Special emphasis has been given to analysis of the intermolecular hydrogen bonds of the hydrated conformers. Self-consistent reaction field (SCRF) theory has been employed to optimize all the conformers in the aqueous phase (, = 78.39) at the B3LYP/6-311G(2d,2p) level of theory, and the solvent effect has been studied. Vibrational frequency analysis has been performed for all the optimized structures at MP2/6-311G(2d,2p) level of theory, and the stationary points corresponding to local minima without imaginary frequencies have been obtained for all the molecular structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Field experiments for the evaluation of pesticide spray-drift on arable cropsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 8 2005Isabelle Ravier Abstract Two distinct approaches were used to characterise spray-drift during the application of atrazine and alachlor to a maize crop. The first consisted in determining the quantities which did not reach their target. A first experiment was carried in 2001 to improve the sampling method. A second experiment in 2002 showed that losses represented 46 and 38% for atrazine and alachlor, respectively. The second approach was to follow the spatiotemporal evolution of the cloud formed during application. The concentrations observed near the application zone during spraying reached 4.5 µg m,3 for atrazine and 8.5 µg m,3 for alachlor. With alachlor these concentrations decreased rapidly when increasing distance from the plot or time following treatment, whereas in the case of atrazine they stabilised rapidly (between 0.5 and 0.3 µg m,3) both in space and in time. Deposits around the plot were light and slightly higher for alachlor (from 20 to 130 µg m,2). Alachlor was more rapidly diluted in space than atrazine, reflecting a differentiated evolution of physical form during the process. Alachlor, being more volatile than atrazine, is quickly transferred to the gaseous phase which was more rapidly dispersed than aerosols. Copyright © 2005 Society of Chemical Industry [source] FTIR Spectroscopic and Theoretical Study of the Photochemistry of Matrix-isolated CoumarinPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2007Nihal Ku The infrared spectrum of monomeric unsubstituted coumarin (C9H6O2; 2H -1-benzopyran-2-one), isolated in solid argon at 10 K is presented and assigned. The UV-induced (, > 200 nm) unimolecular photochemistry of the matrix-isolated compound was studied experimentally. Three main photoreactions were observed: (a) decarboxylation of the compound and formation of benzocyclobutadiene and CO2, with the Dewar form of coumarin as intermediate; (b) isomerization of the compound, leading to production of a conjugated ketene; and (c) decarbonylation, leading to formation of CO and benzofuran complex. Further decomposition of benzofuran to produce ethynol is suggested. Photochannels (a) and (b) correspond to those previously observed for matrix-isolated ,- pyrone and its sulfur analogs (Phys. Chem. Chem. Phys. 2004, 6, 929; J. Phys. Chem. A 2006, 110, 6415), while route (c) is similar to the UV-induced photochemistry of coumarin in the gaseous phase (J. Phys. Chem. A 2000, 104, 1095). Interpretation of the experimental data is supported by extensive calculations performed at the B3LYP/6-311++G(d,p), MP2/6-31G(d,p) and MP2/6-311++G(d,p) levels. [source] Phosphorus incorporation and activity in (100)-oriented homoepitaxial diamond layersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2009G. Frangieh Abstract In this work, we present a study about the homoepitaxial growth of phosphorus-doped diamond on (100) substrates. The growth was performed by microwave plasma assisted chemical vapor deposition (MPCVD) adding an organic precursor for phosphorus (tertiarybutylphosphine: TBP) in the gaseous phase. We show that phosphorus is incorporated in (100) chemical vapor deposition (CVD) diamond as proved by secondary ion mass spectrometry (SIMS). The recombination of excitons bound to phosphorus donors is observed by cathodoluminescence (CL) spectroscopy. The influence of the growth parameters on the phosphorus donor activity is investigated. We show that the [C*]/[H2] ratio is a key parameter for controlling the P-donor activity when diamond is grown on (100) surfaces. [source] Strain and wafer curvature of 3C-SiC films on silicon: influence of the growth conditionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007M. Zielinski Abstract We study the influence of the growth conditions on the residual strain and related optical and structural properties in the case of 3C-SiC films grown on (001) silicon substrates. We show that two possible mechanisms compete to manage the final sample bow: one is by controlling the composition of the gaseous phase (C/Si ratio) the other one by adjusting the growth temperature and duration (creep effect). In both cases, we compare the low temperature photoluminescence spectra of samples grown under tensile or compressive final stress. We show that better results can be obtained when using the creep effect. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermodynamic aspects of carbon incorporation into AlN epitaxial layers grown by MOVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005J. Leitner Abstract Thermodynamic aspects of carbon incorporation into AlN during the MOVPE growth are discussed. Under low potential in the gaseous phase, carbon dissolves in AlN substituting nitrogen atoms. A sublattice model has been proposed to describe the thermodynamic behavior of this pseudobinary solution AlN-C. When carbon potential increases, solid graphite is formed simultaneously to AlN. At V/III input ratio (V/III = x/x) lower than one, carbonitride Al5C3N as well carbide Al4C3 can be formed. The calculated results are compared with the composition of AlN layers growth by MOVPE. The serious discrepancies exist which can be explained by the crude nature of the solution model as well as by non-equilibrium conditions during the MOVPE growth and subsequent carbon supersaturation of the resulting layers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleationPOLYMER ENGINEERING & SCIENCE, Issue 2 2008Carlo Marrazzo The aim of this article was to investigate the nucleating ability of different nucleating agents for the foaming of poly(,-caprolactone), a biodegradable, semicrystalline polymer. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase has been compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semicrystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow interacting phenomena. Here, these two aspects have been evidenced and clarified. Foams were prepared by using a batch process with the pressure quench method, with nitrogen and carbon dioxide as the blowing agents. Conventional and novel nucleating agents were used: talc has been compared to several novel nanometric particles of different geometries and dimensions, such as titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Foam densities and morphologies, in terms of number of cells per initial unit volume, were measured and found to depend both on crystalline phase nucleation and gaseous phase nucleation. In fact, the different nucleating agents, depending on shape, dimension, and surface functionalization, selectively nucleated the crystallites and/or the bubbles, affecting, respectively, bubble growth (and, hence, final foam density) and bubble nucleation (and, hence, cell number density,morphology). POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source] Thermal Decomposition of NTO: An Explanation of the High Activation EnergyPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2007Valery Abstract Burning rate characteristics of the low-sensitivity explosive 5-nitro-1,2,4-triazol-3-one (NTO) have been investigated in the pressure interval of 0.1,40,MPa. The temperature distribution in the combustion wave of NTO has been measured at pressures of 0.4,2.1,MPa. Based on burning rate and thermocouple measurements, rate constants of NTO decomposition in the molten layer at 370,425,°C have been derived from a condensed-phase combustion model (k=8.08,1013,exp(,19420/T) s,1. NTO vapor pressure above the liquid (ln P=,9914.4/T+14.82) and solid phases (ln P=,12984.4/T+20.48) has been calculated. Decomposition rates of NTO at low temperatures have been defined more exactly and it has been shown that in the interval of 180,230,°C the decomposition of solid NTO is described by the following expression: k=2.9,1012,exp(,20680/T). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240,250,°C has been studied. Decomposition rate constants in the gaseous phase have been found to be comparable with rate constants in the solid state. Therefore, a partial decomposition in the gas cannot substantially increase the total rate. High values of the activation energy for solid-state decomposition of NTO are not likely to be connected with a sub-melting effect, because decomposition occurs at temperatures well below the melting point. It has been suggested that the abnormally high activation energy in the interval of 230,270,°C is a consequence of peculiarities of the NTO transitional process rather than strong bonds in the molecule. In this area, the NTO molecule undergoes isomerization into the aci -form, followed by C3-N2 heterocyclic bond rupture. Both processes depend on temperature, resulting in an abnormally high value of the observed activation energy. [source] Soil macrofauna research in ecosystems in UgandaAFRICAN JOURNAL OF ECOLOGY, Issue 2007M. J. N. Okwakol Abstract Soil is a living entity, comprising an inseparable mixture of solid, liquid and gaseous phases, and diverse fauna and flora, the below ground biodiversity. The macrofauna consists of animals longer than 4 mm or wider than 2 mm, which are easily located by the naked eye and include arthropods, molluscs and earthworms. This review is aimed at developing an inventory of the present knowledge about macrofauna in ecosystems in Uganda and identifying future priorities for research, application and capacity building. It is noted that there are a few assessments of soil macrofauna, diversity and abundance made for different habitats. Similarly, studies on their importance in ecosystems, distribution patterns, management, linkage with above ground biodiversity and effects of land use on them are deficient. Further, there is little documentation of farmers' knowledge and practices related to soil macrofauna management and conservation. It is also noted that the current gaps in the soil macrofauna data and information have been caused by lack of capacity and expertise to identify, evaluate and manage this resource. More research and training in the taxonomy, ecology, economic evaluation and management of this fauna are suggested. [source] | ||||||||||||||||