Showing papers on "Thermal decomposition published in 2004"

Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen.

Abstract: This review focuses on key aspects of the thermal decomposition of multinary or mixed hydride materials, with a particular emphasis on the rational control and chemical tuning of the strategically important thermal decomposition temperature of such hydrides, Tdec. An attempt is also made to predict the thermal stability of as-yet unknown, elusive or even unknown hydrides. The future of a particularly promising class of materials for hydrogen storage, namely the catalytically enhanced complex metal hydrides, is discussed. The predictions are supported by thermodynamics considerations, calculations derived from molecular orbital (MO) theory and backed up by simple chemical insights and intuition.

Easy Synthesis and Magnetic Properties of Iron Oxide Nanoparticles

Abstract: Easy preparation of iron oxide nanoparticles [5- and 11-nm maghemite (γ-Fe2O3) and 19-nm magnetite (Fe3O4)] by thermal decomposition of Fe(CO)5 in the presence of residual oxygen of the system and by consecutive aeration were investigated by TEM/HRTEM, XRD, and Mossbauer spectroscopy. Also, the magnetic properties of the nanoparticles were studied by SQUID magnetometer and optical microscopy. It was suggested that the intermediate iron oxide nanoparticles (before aeration) were formed by the competing processes of oxidation and crystal growth after decomposition of Fe(CO)5. At room temperature, the aerated 5-nm particles were superparamagnetic without interaction among the particles, whereas the 19-nm particles were ferrimagnetic. The 11-nm iron oxide nanoparticles were superparamagnetic with some interactions among the particles.

Physicochemical characterization of α-chitin, β-chitin, and γ-chitin separated from natural resources

Abstract: We isolated α-chitin, β-chitin, and γ-chitin from natural resources by a chemical method to investigate the crystalline structure of chitin. Its characteristics were identified with Fourier transform infrared (FTIR) and solid-state cross-polarization/magic-angle-spinning (CP–MAS) 13C NMR spectrophotometers. The average molecular weights of α-chitin, β-chitin, and γ-chitin, calculated with the relative viscosity, were about 701, 612, and 524 kDa, respectively. In the FTIR spectra, α-chitin, β-chitin, and γ-chitin showed a doublet, a singlet, and a semidoublet at the amide I band, respectively. The solid-state CP–MAS 13C NMR spectra revealed that α-chitin was sharply resolved around 73 and 75 ppm and that β-chitin had a singlet around 74 ppm. For γ-chitin, two signals appeared around 73 and 75 ppm. From the X-ray diffraction results, α-chitin was observed to have four crystalline reflections at 9.6, 19.6, 21.1, and 23.7 by the crystalline structure. Also, β-chitin was observed to have two crystalline reflections at 9.1 and 20.3 by the crystalline structure. γ-Chitin, having an antiparallel and parallel structure, was similar in its X-ray diffraction patterns to α-chitin. The exothermic peaks of α-chitin, β-chitin, and γ-chitin appeared at 330, 230, and 310, respectively. The thermal decomposition activation energies of α-chitin, β-chitin, and γ-chitin, calculated by thermogravimetric analysis, were 60.56, 58.16, and 59.26 kJ mol−1, respectively. With the Arrhenius law, ln β was plotted against the reciprocal of the maximum decomposition temperature as a straight line; there was a large slope for large activation energies and a small slope for small activation energies. α-Chitin with high activation energies was very temperature-sensitive; β-Chitin with low activation energies was relatively temperature-insensitive. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3423–3432, 2004

Thermal decomposition, combustion and fire‐retardancy of polyurethanes—a review of the recent literature

Abstract: An overview is presented of the literature on thermal decomposition, combustion and fire-retardancy of polyurethane (PU) elastomers, PU-based coatings, rigid and flexible PU foams. A brief overview of the structure of PU polymeric networks is helpful for a better understanding of the thermal decomposition and combustion phenomena. Literature sources were mostly taken from the publications of 1995 and later; however, for a basic description of the structural and thermal decomposition principles, older publication have also been cited. New developments in the efficient halogen-containing additives and reactive copolymers are described. However, major progress in the area of flame-retardant PUs in recent years is found in the field of phosphorus- or silicon-containing products, especially reactive ones. Inorganic additives remain of great interest, especially in PU-based intumescent coatings.

Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions

Abstract: Dinuclear ruthenium complex, with a bridging carbide and a hydride ligand, and methyltricyclohexylphosphonium chloride result from thermal decomposition of olefin metathesis catalyst, (ImesH_2)(PCy)_3)(Cl)_2Ru CH_2. Involvement of dissociated phosphine in the decomposition is proposed. The dinuclear complex has catalytic olefin isomerization activity, which can be responsible for competing isomerization processes in certain olefin metathesis reactions.

Thermal behavior of alginic acid and its sodium salt

Abstract: An evaluation of hydration and thermal decomposition of HAlg and its sodium salt is described using thermogravimetry (TG) and differential scanning calorimetry (DSC). TG curves in N2 and air, were obtained for alginic acid showed two decomposition steps attributed to loss of water and polymer decomposition respectively. The sodium alginate decomposed in three steps. The first attributed to water loss, followed by the formation of a carbonaceous residue and finally the Na2CO3. DSC curves presented peaks in agreement with the TG data. In the IR alginic acid presented bands at 1730 and 1631 cm-1, while sodium alginate presented a doublet at 1614 e 1431 cm-1, evidencing the presence of salified carboxyl groups.

One-Pot Reaction to Synthesize Water-Soluble Magnetite Nanocrystals

Abstract: Water-soluble magnetite nanocrystals of different sizes have been prepared by a one-pot reaction through thermal decomposition of ferric triacetylacetonate in 2-pyrrolidone.

Preparation and characterization of nano-structured silica from rice husk

Abstract: Uniformly sized ultrafine silica powder can be obtained by nonisothermal decomposition of rice husk in an oxidizing atmosphere. The properties of reactant and product including morphology, particle size, surface area, pore volume and pore distribution, have been investigated by TEM, SEM, XRD, FTIR, ICP-MS, and EA. At a heating rate of 5 K/min, the specific surface area of the silica powder was 235 m 2 /g, the average pore diameter was 5.4 nm, and the average particle size was 60 nm. The products obtained from various heating rates were all amorphous. By using a thermogravimetric analysis technique, a mechanism including two reaction stages was observed for the thermal decomposition of rice husk in air. The activation energy was found to be 166±10 kJ/mol. This method can conveniently provide preparation of silica of high surface area and nanometer grade.

Decomposition of Urea into NH3 for the SCR Process

Abstract: The thermal and catalytic decomposition of urea over a fixed-bed flow reactor system has been examined for the selective catalytic reduction (SCR) of NOx from mobile sources. The conversion of urea into NH3 and HNCO, the two major products from the thermal decomposition of urea, increased with the reaction temperature and the reactor space time. Urea was completely decomposed into NH3 and HNCO at 350 °C when the residence time was longer than 0.1 s. As the reaction temperature increased to 400 °C or higher, complete decomposition of urea was possible at a much shorter residence time of the feed gas stream. The simultaneous thermal and catalytic decomposition of urea was also examined in a dual-reactor system in which the first reactor was for thermal decomposition and the second was for catalytic decomposition, specifically over copper exchanged ZSM5 catalyst. The role of the catalyst in the decomposition of urea into NH3 and HNCO was negligible; urea decomposition occurs mainly by the thermal reaction. H...

β-Nickel Hydroxide Nanosheets and Their Thermal Decomposition to Nickel Oxide Nanosheets

Abstract: Powders of single-crystalline β-nickel hydroxide (β-Ni(OH)2) nanosheets with the hexagonal structure have been successfully synthesized by the hydrothermal method at 200 °C using nickel acetate as the nickel source and aqueous ammonia as both an alkaline and complexing reagent The yields of β-Ni(OH)2 nanosheet powders were higher than 924% This method is simple and low-cost for large-scale production of powders of single-crystalline β-Ni(OH)2 nanosheets Single-crystalline nickel oxide (NiO) nanosheets have been synthesized by thermal decomposition method at 400 °C for 2 h using single-crystalline β-Ni(OH)2 nanosheets as the precursor The sheet shape of β-Ni(OH)2 was sustained after thermal decomposition to NiO The as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TG)

Structure of organoclays—an X-ray diffraction and thermogravimetric analysis study

Abstract: X-ray diffraction has been used to study the changes in the surface properties of a montmorillonitic clay through the changes in the basal spacings of montmorillonite (SWy-2) and surfactant-intercalated organo-clays. Variation in the d-spacing was found to be a step-function of the surfactant concentration. High resolution thermogravimetric analysis (HRTG) was used to study the thermal decomposition surfactant modified SWy-2-MMTs modified with the surfactant octadecyltrimethylammonium bromide. High resolution thermogravimetry shows the decomposition takes place in 4 steps. A mass loss step is observed at room temperature and is attributed to dehydration of adsorption water. A second mass loss step is observed over the 87.9 to 135.5 degrees Celsius temperature range and is also attributed to dehydration of water hydrating metal cations such as Na+ . The third mass loss occurs from 178.9 to 384.5 degrees Celsius and is assigned to a loss of surfactant. The fourth mass loss step is ascribed to the loss of OH units through dehydroxylation over the 556.01 to 636.35 degrees Celsius temperature range.

Low‐Fired (Zn,Mg)TiO3 Microwave Dielectrics

Abstract: A dielectric ceramic comprised of (Zn1-xMgx)TiO3 (x= 0 to x= 0.5) with low sintering temperature and promising microwave properties was prepared by applying a semichemical synthesis route and a microbeads milling technique. X-ray diffractometry and thermal analyses results indicated that the phase stability region of the hexagonal (Zn,Mg)TiO3 extended to higher temperatures as the amount of magnesium increased. The dielectric properties in this system exhibited a significant dependence on the sintering conditions, especially near the phase decomposition temperature. From 950°C, the temperature compensation characteristics occurred as the phase composition changed from hexagonal (Zn,Mg)TiO3 to two phases: (Zn,Mg)2TiO4 and rutile. The magnesium content for zero temperature coefficient (tauf) was ~3 mol% at 950°C; however, tauf increased with the sintering temperatures because of the shift of the decomposition temperature.

Preparation and Characterization of Antimony-Doped Tin Dioxide Electrodes. Part 1. Electrochemical Characterization

Abstract: Antimony and antimony-platinum doped tin dioxide electrodes supported on titanium have been prepared by thermal decomposition. Ti/SnO2-Sb electrodes have a cracked-mud structure, typical of oxide electrodes prepared by thermal decomposition. The introduction of platinum in the oxide layer has a packing effect in the coating morphology. The electrochemical characterization of these electrodes has been performed in acid medium, and a relation between the roughness factor (measured from electrode capacitance) and electrochemical porosity (related to the voltammetric charge) has been established. The mechanism for the oxygen evolution reaction has been determined by Tafel measurements indicating that the electrodes prepared are nonactive electrodes. The electrocatalytic activity strongly depends on geometric factors, since the activity toward oxygen evolution increases with the electrochemical porosity. Anodic stability of Ti/SnO 2 electrodes has been checked with accelerated service life tests. The introduction of platinum in the oxide coating increases the service life by 2 orders of magnitude.

A review on thermal decomposition and combustion of thermoplastic polyesters

Abstract: An overview is presented of the literature on the thermal decomposition and combustion of thermoplastic polyesters, especially commercially important poly(ethylene terephthalate) (PET) and poly(1,4-butylene terephthalate) (PBT) Although the literature is not clear as to whether heterolytic or homolytic scission of aliphatic fragments is the first step in the thermal decomposition of polyesters, in any case volatilization of light aliphatic fragments make polyesters easily ignitable polymers Despite the presence of benzene groups in the main polymer chain, thermoplastic polyesters show very limited tendency to char, but instead, aromatic-containing polymer fragments volatilize and feed the flame Fire retardant additives, although they usually facilitate decomposition of the polyesters at lower temperature, also usually promote charring and therefore suppress combustion Copyright © 2004 John Wiley & Sons, Ltd

Effects of Nanometer Ni, Cu, Al and NiCu Powders on the Thermal Decomposition of Ammonium Perchlorate

Abstract: A study of the decomposition behaviour for Ammonium Perchlorate(AP) was carried out by differential thermal analysis and the two decomposition peaks were observed. The high temperature peak was found to shift to lower temperatures, but the corresponding shift in the low temperature peak was smaller due to the effect of nanometer metal powders. Results shows that Cu and NiCu nanopowders decreased both the high and low decomposition temperature, while Ni and Al nanopowders just decreased the high decomposition temperature and increased the low decomposition temperature. Metal micron-sized powders show catalytic effects on the thermal decomposition of AP, but their effects are less than that of nanometer metal powders. With the increase in content, nanometer metal powders enhanced their catalytic effect on the high temperature decomposition of AP, however their effect was weakened on the low temperature decomposition.

Proton conductive polyimide electrolytes containing fluorenyl groups: Synthesis, properties, and branching effect

Abstract: Novel sulfonated polyimide copolymers as electrolytes for high-temperature fuel cell applications are reported. A series of sulfonated polyimide copolymers (SPIH-X; X refers to molar percentage of fluorenyl content) containing 0−60 mol % of fluorenyl groups as hydrophobic component were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). High-molecular-weight copolymers with good film-forming capability were obtained. Thermal stability with decomposition temperature of ca. 280 °C and no glass transition temperature was confirmed for the copolymers. SPIH shows unique water uptake behavior with the maximum value of 57 wt % at X = 30. Water molecules absorbed in the electrolyte membrane with this specific composition do not evaporate easily so that the high proton conductivity of 1.67 S cm-1 was obtained at 120 °C and 100% RH. The branching and cross-linking of SPIH-30 were carried out by applying 2 mol % of trifunctional monomer (m...

Suppression of Toxic Compounds Produced in the Decomposition of Lithium-Ion Battery Electrolytes

Abstract: Liquid electrolytes typically used in commercial lithium-ion batteries are comprised of lithium hexafluorophosphate in carbonate solvents. This electrolyte undergoes thermal decomposition at moderately elevated temperatures (80-100°C), encountered in the normal operation of these rechargeable power sources, to quantitatively generate highly toxic alkylfluorophosphates. The decomposition occurs via an autocatalytic mechanism initiated by trace impurities of water or alcohol. The thermal decomposition is inhibited in the presence of lithium metal oxides frequently used as the cathode of lithium-ion batteries or Lewis basic additives.