Showing papers on "Thermal decomposition published in 2003"

Nanocrystalline Chalcopyrite Materials (CuInS2 and CuInSe2) via Low-Temperature Pyrolysis of Molecular Single-Source Precursors

Abstract: Nanometer-sized particles of the chalcopyrite compounds CuInS2 and CuInSe2 were synthesized by thermal decomposition of molecular single-source precursors (PPh3)2CuIn(SEt)4 and (PPh3)2CuIn(SePh)4, respectively, in the noncoordinating solvent dioctyl phthalate at temperatures between 200 and 300 °C. The nanoparticles range in size from 3 to 30 nm and are aggregated to form roughly spherical clusters of about 500 nm in diameter. X-ray diffraction of the nanoparticle powders shows greatly broadened lines, indicative of very small particle sizes, which is confirmed by TEM. Peaks present in the XRD can be indexed to reference patterns for the respective chalcopyrite compounds. Optical spectroscopy and elemental analysis by energy dispersive spectroscopy support the identification of the nanoparticles as chalcopyrites.

Synthesis of Monodisperse Palladium Nanoparticles

Abstract: We have synthesized monodisperse Pd nanoparticles with particle sizes of 3.5, 5, and 7 nm from the thermal decomposition of a Pd−surfactant complex. The particle size of Pd nanoparticles was controlled by varying the concentration of stabilizing surfactant.

Synthesis and optical properties of colloidal tungsten oxide nanorods.

Abstract: Thermal decomposition of W(CO)6 in oleylamine in the presence of mild oxidant Me3NO·2H2O produces tungsten oxide nanorods with diameters ranging from 3 to 6 nm. The size of nanorods can be easily varied by the employed surfactant ratio or reaction temperature. The prepared tungsten oxide nanorods exhibit strong photoluminescence (PL) peaks in 300−500 nm, which show a weak size dependency.

Dimensional Control of Cobalt-hydroxide-carbonate Nanorods and Their Thermal Conversion to One-Dimensional Arrays of Co3O4 Nanoparticles

Abstract: We report a detailed investigation on the formation of cobalt-basic-carbonate compounds [Co(OH)x(CO3)05(2-x)·nH2O] with dimensional and morphological controls Two complementary precipitation methods developed in this work produce cobalt-basic-carbonate in the form of nanorods across a wide diameter span from 2 to 200 nm and a length up to 5 μm Various controlling parameters were examined, such as anions in starting reagents, reaction temperature, aging time, and chemical compositions between the solid products and starting reagents The resultant solids were characterized using XRD, FTIR, CHN, and TGA/DrTGA methods with respect to their formation process and thermal decomposition More importantly, morphological aspects of the Co(OH)x(CO3)05(2-x)·nH2O and their heat-treated product Co3O4 were investigated with TEM/ED methods It has been found that the Co(OH)x(CO3)05(2-x)·nH2O nanorods are grown along the [010] direction (orthorhombic) Upon thermal decomposition at ≥300 °C, the above nanorods self-a

Thermal Decomposition of Metal Nitrates in Air and Hydrogen Environments

Abstract: The decomposition of metal nitrates in air has been systematically studied by thermogravimetry. Observed temperatures of decomposition (Td) have been inversely correlated to the charge densities (CD) of the metal cations. Due to a back-donation of electronic cloud from the nitrate to an unfilled d-orbital of transition and noble metals, their nitrates generally exhibited lower Tds ( 850 K). The thermal stability/reducibility of metal nitrates in an hydrogen atmosphere has also been studied by temperature-programmed reduction (TPR). Observed reduction temperatures (Tr) for nitrates of the base metals and the noble metals are lower than their Td, i.e., Tr < Td. The lowering of Tr might be attributed to a spillover of hydrogen to a nitrate moiety through heterolytic (ionic) and homolytic (atomic) dissociation of hydrogen on the respective base and noble metals. The stoichiometry of hydrogen consumption, quantitatively measured from TPR, varied with the group of metal ca...

Urea thermolysis and NOx reduction with and without SCR catalysts

Abstract: Urea–selective catalytic reduction (SCR) has been a leading contender for removal of nitrogen oxides (deNOx) from diesel engine emissions Despite its advantages, the SCR technology faces some critical detriments to its catalytic performance such as catalyst surface passivation (caused by deposit formation) and consequent stoichiometric imbalance of the urea consumption Deposit formation deactivates catalytic performance by not only consuming part of the ammonia produced during urea decomposition but also degrading the structural and thermal properties of the catalyst surface We have characterized the urea thermolysis with and without the urea-SCR catalyst using both spectroscopic (DRIFTS and Raman) and thermal techniques (thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)) to identify the deposit components and their corresponding thermal properties Urea thermolysis exhibits two decomposition stages, involving ammonia generation and consumption, respectively The decomposition after the second stage leads to the product of melamine complexes, (HNCNH)x(HNCO)y, that hinder catalytic performance The presence of catalyst accompanied with a good spray of the urea solution helps to eliminate the second stage In this work, kinetics of the direct reduction of NOx by urea is determined and the possibility of using additives to the urea solution in order to rejuvenate the catalyst surface and improve its performance will be discussed

Covalent Sidewall Functionalization of Single Wall Carbon Nanotubes

Abstract: Alkyllithium reagents may be used to attach alkyl groups to the sidewalls of fluoro nanotubes. Thermal gravimetric analysis combined with UV-vis-Nir spectroscopy has been used to provide a quantitative measure of the degree of functionalization. SWNTs prepared using the HiPco process exhibit a higher degree of alkylation than SWNTs from the laser-oven method, indicating that the smaller diameter fluoro tubes are alkylated more readily. The spectral signature of the pristine SWNTs can be regenerated when the alkylated SWNTs are heated in Ar at 500 °C, demonstrating that dealkylation occurs at this temperature. TGA-MS analysis using a sample of n-butylated h-SWNTs showed that 1-butene and n-butane are formed during thermolysis.

Catalysis of intumescent flame retardancy of polypropylene by metallic compounds

Abstract: Divalent and multivalent metallic compounds catalyze the flame retardancy performance of intumescent systems based on ammonium polyphosphate (APP) and pentaerythritol (petol) in poly(propylene) (PP). The catalytic effect is shown by increases in the oxygen index (OI) and UL-94 ratings. The effect is exerted by small concentrations of the metallic compounds in the range of 0.1–2.5 wt% of the compositions. The effect increases with the concentration of the catalyst until a maximum is reached. At higher concentrations of the catalyst a decrease in the flame retardancy parameters is observed, accompanied in several cases by a degradation and discoloration of the composition. The catalyst replaces melamine in intumescent systems. Catalytic effectiveness is defined and calculated for a number of compounds. Thermogravimetric parameters, such as initial decomposition temperature, temperature of the transition point and residue-after-transitions (RAT) change in parallel with the catalytic effect of the metal compound concentration. Metal compounds investigated include oxides, acetates, acetyl acetonates, borates and sulfates of Mn, Zn, Mg, Al, Ca, Ba, V, Co, Ni, Cu, Mo, Zr, and Cr. Mechanistic considerations on the activity of the catalysts are presented. Copyright © 2003 John Wiley & Sons, Ltd.

Thermal and Hydrolytic Decomposition of Urea for Automotive Selective Catalytic Reduction Systems: Thermochemical and Practical Aspects

Abstract: An energetic analysis of the thermal decomposition of solid urea and urea solutions is presented, and the results are discussed in view of urea selective catalytic reduction (SCR) for automotive DeNOx systems. Various types of decomposition reactors are possible which differ in their effectiveness to produce ammonia from urea. For reasons of simplicity, the decomposition is usually performed by atomizing urea solutions directly into the hot exhaust. However, this technique suffers from short residence times, leading to incomplete decomposition into ammonia and isocyanic acid and causing a significant performance loss of the SCR catalyst. The thermal decomposition out of the main exhaust stream allows much increased residence times for the process of urea decomposition. A reactor utilizing a partial stream of the exhaust seems particularly promising, especially if such a reactor includes a hydrolyzing catalyst, leading to ammonia practically free from isocyanic acid.

Growth of bismuth sulfide nanowire using bismuth trisxanthate single source precursors

Abstract: Crystalline Bi2S3 nanorods, nanotapes, and nanocrystals were obtained from the solvent thermalysis of bismuth trisxanthate precursors and related bismuth dithiocarbamate species in ethylene glycol at 197 °C. Precursors with different structural motifs were designed to produce compounds with different thermal decomposition temparatures, i.e., the dimeric motif of Bi(S2COR)3 when R = methyl and ethyl was found to have a lower decomposition temperature compared to precursors adopting the polymeric structure, so that solvothermalysis of the former gave rise to short nanocrystals; while in the case of the latter, long nanofibers were produced instead. Chemical vapor deposition on silicon substrates yielded well-defined nanorods of various lengths and diameters for almost all precursors. Internal microstructure of the nanorods was studied by high-resolution transmission electron microscopy.

Relations between synthesis and microstructural properties of copper/zinc hydroxycarbonates.

Abstract: Cu/Zn Hydroxycarbonates obtained by co-precipitation of Cu(2+) and Zn(2+) with Na(2)CO(3) have been investigated regarding phase formation and thermal decomposition in two series with varying Cu/Zn ratios prepared according to the decreasing pH and constant pH method. Hydrozincite, aurichalcite and (zincian)-malachite were found to form at differing Cu/Zn ratios for both series. For the constant pH preparation the Cu/Zn ratio in zincian-malachite was close to the nominal values whereas excess values were found for the decreasing pH samples. The degree of crystallinity as well as the thermal decomposition temperatures were lower for the constant pH series. All samples containing aurichalcite revealed an unexpected decomposition step at high temperatures evolving exclusively CO(2). The differences in composition and microstucture were traced back to the different pathways of solid formation for the two preparation methods. Substantial changes were observed during the post-precipitation processes of ageing and washing. The effects were studied in detail on samples with a cation ratio of Cu/Zn 70:30 mol %. Ageing of the precipitates in their own solutions is accompanied by a spontaneous crystallization of the initially amorphous solids. The decreasing pH sample develops from a hydroxy-rich material comprising basic copper nitrate (gerhardtite) as an intermediate. Only small changes in the chemistry of the samples were detected for the constant pH precipitation. The findings are summarised into a scheme of solid formation processes that explains the phenomenon of a "chemical memory" of the precipitates when they are converted into Cu/ZnO model catalysts.

Structure of synthetic K-rich birnessite obtained by high-temperature decomposition of KMnO4. I. two-layer polytype from 800 °C experiment

Abstract: The structure of a synthetic potassium birnessite (KBi) obtained as a finely dispersed powder by thermal decomposition of KMnO4 at 800 °C was for the first time studied by single-crystal X-ray diffraction (XRD). It is shown that KBi has a two-layer cell with a = 2.840(1) A and c = 14.03(1) A and space group P63/mmc. In contrast to the structure model proposed by Kim et al. (Chem. Mater. 1999, 11, 557−563), the refined model demonstrates the sole presence of Mn4+ in the octahedral layers, the presence of 0.12 vacant layer sites per octahedron being responsible for the layer charge deficit. In agreement with X-ray absorption spectroscopy result, this layer charge deficit is compensated (1) by the presence of interlayer Mn3+ above or below vacant layer octahedra sharing three Olayer atoms with neighboring Mnlayer octahedra to form a triple-corner surface complex (VITC sites) and (2) by the presence of interlayer K in prismatic cavities located above or below empty tridentate cavities, sharing three edges wit...

Thermal Decomposition and Combustion of Explosives and Propellants

Abstract: INTRODUCTION KINETIC PROBLEMS OF DECOMPOSITION OF EXPLOSIVES AND PROPELLANTS References GENERAL REGULARITIES OF THERMAL DECOMPOSITION OF HIGH-ENERGY COMPOUNDS Gas Phase Reactions Liquid Phase Reactions Decomposition In The Solid State References ALIPHATIC NITROCOMPOUNDS Gas Phase Decomposition By The Molecular Mechanism Gas Phase Decomposition By The Radical Mechanism Competition Of The Radical And Molecular Mechanisms Reactions In The Condensed State References AROMATIC NITROCOMPOUNDS Gas Phase Decomposition By The Radical Mechanism Molecular Mechanism Of Decomposition Decomposition In The Liquid State Decomposition In The Solid State References SECONDARY NITROAMINES First Stage Of Decomposition Secondary Reactions Kinetic Data References ORGANIC AZIDES Aliphatic Azides Aromatic And Heterocyclic Azides References ORGANIC DIFLUOROAMINO COMPOUNDS References HETEROCYCLIC COMPOUNDS Thermal Decomposition Of Furazanes And Furoxanes Stability Of Tetrazoles References NITROESTERS References COMPOUNDS WITH MIXED FUNCTIONS References GENERAL REGULARITIES OF THERMAL DECOMPOSITION OF ONIUM SALTS, NITRIC AND PERCHLORIC ACIDS, DINITRAMIDE General Regularities Nitric Acid Perchloric Acid Ninitramide References AMMONIUM NITRATE General Regularities Influence Of Water, Acid, And Ammonia On The Decomposition Rate The Heat And Macrokinetic Regularities Of Decomposition Thermal Decomposition Below The Melting Temperature Influence Of Additives On The Rate Of Thermal Decomposition AMMONIUM PERCHLORATE Kinetics Of The Low-Temperature Decomposition Kinetics Of The High-Temperature Decomposition Influence Of Excessive Acids And Bases Topochemical Peculiarities Of Thermal Decomposition Influence Of The Preliminary Irradiation And Additives Thermal Decomposition Of Composite Ap-Based Systems References AMMONIUM DINTRAMIDE Decomposition In The Melt Decomposition In The Solid Phase References THE SALTS OF HYDRAZINIUM, HYDROXYLAMMONIUM, AND NITRONIUM Hydrazinium Nitrate And Chloride Hydrazine Iodide Hydrazinium Azide Hydrazinium Perchloriate And Diperchlorate Hydroxyl Mmonium Sulphate And Phosphate Hydroxylammonium Chloride Hydroxylammonium Perchlorate And Its Hydroxylamine Complex Hydroxylammonium Nitrate Nitronium Perchlorate References METAL PERCHLORATES AND NITRATES, METAL SALTS OF DINITRAMIDE Metal Perchlorates Metal Nitrates Metal Salts Of Ninitramide Decomposition Of Potassium Salt In The Liquid State Decomposition Of Potassium Salt In The Solid Phase Dinitramide Salts Of Other Metals References BASIC ASPECTS OF THE COMBUSTION MECHANISM COMBUSTION OF PURE SUBSTANCES: REACTIONS IN THE CONDENSED PHASE The Model With Dispersion Of The Solid Substance The Model With Foaming Of The Reacting Substance The Model With Evaporation Or Sublimation References COMBUSTION OF PURE SUBSTANCES: REACTIONS IN THE GAS PHASE References COMBUSTION OF PURE SUBSTANCES: REACTIONS IN THE CONDENSED AND GAS PHASES References COMBUSTION OF CONDENSED COMPOSITE SYSTEMS Quasihomogenous Composites Layered Systems Composite Propellants References

FTIR analysis of storage behavior and sulfur tolerance in barium-based NOx storage and reduction (NSR) catalysts

Abstract: A series of NO x storage and reduction (NSR) catalysts containing platinum, BaO, and iron supported on γ-Al 2 O 3 has been studied using FTIR spectroscopy. CO adsorption studies at room temperature have shown that the BaO phase can chemisorb large quantities of CO, and that platinum sites can become encapsulated by BaO, following a reducing pretreatment. Exposure of the catalysts to fuel-lean and fuel-rich conditions has revealed that the species that participates in the storage is a surface nitrite complex (prevalent below 350 °C), which is converted to a surface monodentate nitrate species above 350 °C. Both of these species have also been identified at room temperature and are bonded to the surface through BaO lattice oxygen atoms. A mechanism has been proposed to describe the storage and reduction process in which NO reacts directly with the BaO surface to form nitrite and monodentate nitrate. The role of platinum is to adsorb O 2 under lean conditions and reducing gases (H 2 or hydrocarbons) under rich conditions. Once adsorbed, the oxygen and reducing agents spill over onto nearby BaO sites and react with the adsorbed NO. The oxidation of NO to NO 2 on platinum does not appear in this work to be a critical step, in contrast to previous studies. Sulfur tolerance studies using SO 2 have confirmed the previous observation that promotion with iron increases the durability of NSR catalysts. However, FTIR results show that the improvement is caused by the formation of a previously unobserved bulk nitrate species and not to a decrease in the sulfate decomposition temperature.

Chemical Synthesis of Magnetic Nanoparticles

Abstract: Recent advances in the synthesis of various magnetic nanoparticles using colloidal chemical approaches are reviewed. Typically, these approaches involve either rapid injection of reagents into hot surfactant solution followed by aging at high temperature, or the mixing of reagents at a low temperature and slow heating under controlled conditions. Spherical cobalt nanoparticles with various crystal structures have been synthesized by thermally decomposing dicobalt octacarbonyl or by reducing cobalt salts. Nanoparticles of Fe–Pt and other related iron or cobalt containing alloys have been made by simultaneously reacting their constituent precursors. Many different ferrite nanoparticles have been synthesized by the thermal decomposition of organometallic precursors followed by oxidation or by low-temperature reactions inside reverse micelles. Rod-shaped iron nanoparticles have been synthesized from the oriented growth of spherical nanoparticles, and cobalt nanodisks were synthesized from the thermal decomposition of dicobalt octacarbonyl in the presence of a mixture of two surfactants.

Studies on cl-20: the most powerful high energy material

Abstract: CL-20 is an attractive HEM having density (>2 g cm-3) and velocity of detonation (9400 m s-1) superior to HMX (1.9 g cm-3 and 9100 m s-1). During this study, CL-20 was synthesized to establish viability of efficient synthesis method. The compound synthesized at HEMRL was characterized by FTIR, 1H NMR and elemental analysis. Thermal studies (dynamic DSC and isothermal TG) were undertaken to determine kinetic parameters and understand the decomposition patterns. An attempt is made to explain the mechanism of decomposition of CL-20 on the basis of the data obtained by the authors and findings of other researchers. The activation energy values obtained during this work by adopting various approaches are close to the values reported for N-NO2 bond cleavage suggesting that it is global rate determining process rather than the collapse of cage structure. Mass spectra also provides evidences in this regard. Monitoring of decomposition products at high temperature supports these findings and brings out that NO2 initiates secondary decomposition processes because of entrapment in cage structure.