Showing papers on "Thermal decomposition published in 1993"

CVD of silicon-based ceramic materials on internal surface of a reactor

Abstract: In order to reduce the rate of coke formation during the industrial pyrolysis of hydrocarbons, the interior surface of a reactor is coated with a thin layer of a ceramic material, the layer being deposited by thermal decomposition of a non-oxygen containing silicon-nitrogen precursor in the vapor phase, in an inert or reducing gas atmosphere in order to minimize the formation of oxide ceramics.

Homogeneous Free Radical Polymerizations in Supercritical Carbon Dioxide: 2. Thermal Decomposition of 2,2′-Azobis(isobutyronitrile)

Abstract: The thermal decomposition of 2,2'-azobis(isobutyronitrile) (AIBN) in supercritical CO 2 was investigated by using UV/vis spectroscopic methods. The measured solvent strength of supercritical CO 2 aided in the interpretation of the observed effects of density on the decomposition kinetics. Analysis of the decomposition products indicated that supercritical CO 2 is an acceptable medium to conduct free radical reactions. The decomposition rate and initiation efficiency of AIBN in supercritical CO 2 as a function of pressure and temperature were determined and modeled using Kirkwood solution theory. The initiation efficiency of AIBN in supercritical CO 2 was shown to be ca. 1.5 times higher than that measured in benzene and was found to be invariant with pressure

Deposition of crystalline binary nitride films of tin, copper, and nickel by reactive sputtering

Abstract: Crystalline binary nitride films of tin, copper, and nickel were prepared by reactive sputtering in a nitrogen plasma generated in a dc glow discharge. The chemical composition and thermal behavior of the films were established. The films were characterized by additional physicochemical techniques. Tin nitride, Sn3N4 has an electrical resistivity of 0.02 Ω cm and decomposes into the elements at a maximum rate at 615 °C. The thermal decomposition of Cu3N takes place at 465 °C, while Ni3N decomposes at 405 °C in a stepwise fashion through an intermediate stage at 305 °C. Tin, copper, and nickel nitride decompose into the elements. Nickel nitride crystallized in a new cubic phase with a lattice parameter of 0.446 nm.

Preparation of Silicon Carbonitrides from an Organosilicon Polymer: I, Thermal Decomposition of the Cross-linked Polysilazane

Abstract: The conversion of a solid copolymer (ViSiHNH)x─(MeSiHNH)y into a ceramic was studied in the 20–1450°C temperature range under different atmospheres (inert or oxidative). The ceramic yield, the ceramic composition, and the gaseous evolution directly depend on the heating rate, the pyrolysis atmosphere, and the duration of pyrolysis. The implications of these observations to the pyrolysis mechanism are discussed. The silicon carbonitride obtained after pyrolysis is amorphous up to 1400°C with high carbon content. It will be shown in Parts II and III that either SiC or Si3N4 could be selectively crystallized depending upon processing conditions.

The use of pattern decomposition to study the combined X-ray diffraction effects of crystallite size and stacking faults in ex-oxalate zinc oxide

Abstract: The microstructure of ZnO powder, obtained from thermal decomposition of the oxalate and studied previously by electron microscopy and adsorption calorimetry, was investigated by means of X-ray powder diffraction pattern decomposition. A Williamson–Hall plot revealed that some lines were broadened solely due to the effects of crystallite size, whereas other breadths included a contribution due to stacking faults. Spherical and cylindrical models are used to describe the form of the crystallites and procedures are presented for separating 'size' effects from `mistake' broadening. This leads to estimates of the mean dimensions of the crystallites and the stacking-fault probability. The analysis demonstrates that, with good-quality data for a large number of reflections, a considerable amount of detailed information can be obtained about microstructure. On the other hand, it reveals some of the limitations of current procedures for modelling diffraction line profiles.

Kinetic study of the thermolysis of anisole in a hydrogen atmosphere

Abstract: The gas-phase thermal decomposition of anisole diluted in a 10-fold excess of hydrogen has been studied at atmospheric pressure in a tubular flow reactor over the temperature range 793-1020 K. In the overall process the unimolecular decomposition PhOCH 3 →PhO . +CH 3 . (1) plays a prominent role. The rate constant k 1 was separately determined between 790 and 875 K, employing a large (85-fold) excess of p-fluorotoluene as a carrier, and found to obey 10 15.3(±0.2) exp[(-63.6(±0.7) kcal mol -1 )/RT] (s -1 )

Thermal decomposition of Mg, Al-hydrotalcite material

Abstract: The effect of by-products obtained during the low-temperature synthesis of Mg, Al- hydrotalcite on further thermal decomposition of hydrotalcite material was studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and infrared spectroscopy. By-products, which thermally decomposed below 450°C, led to the formation of α-Al2O3 and MgO; by-products which completely decomposed above 500°C resulted in the formation of MgAl2O4 and a sharp increase in MgO dispersity.

NO2-sensitive LaFeO3film prepared by thermal decomposition of the heteronuclear complex, {La[Fe(CN)6]·5H2O}x

Abstract: Phase pure perovskite-type LaFeO3 powders have been prepared by the thermal decomposition of a cyanidebridged heteronuclear complex. Formation of the perovskite was confirmed for the sample sintered in air at 300 °C for 1 h. The mean particle diameter and the specific surface area were 200 nm and 5 m2 g–1, respectively, (sample density = 6.67 g cm–3) for the LaFeO3 obtained by calcining at 1000 °C. The conductivity of an LaFeO3 thick film formed by sintering at 1000 °C, increased when the measuring atmosphere was changed from air to NO2, and returned to the original level after NO2 was removed above 350 °C. The mechanical strength of the film was improved by sintering with glass resin.

Kinetics of silicon carbide CVD: surface decomposition of silacyclobutane and methylsilane

Abstract: Silicon carbide thin films have been deposited on Si(100) from the single-source reagents silacyclobutane (SCB, c-C 3 H 6 SiH 2 ) and methylsilane (MeSiH 3 ). Thermal decomposition kinetics were studied in a low-pressure (50 mTorr), cold-wall CVD reactor over the temperature range 600-1150 o C. Partial pressure analyses based on mass spectrometry indicate the dominant decomposition channels for SCB and MeSiH 3 are consistent with the formation of the isomeric intermediates H 2 Si=CH 2 and HSiCH 3 , respectively. Deposition rates using the two reagents were comparable at all temperatures, reaching 80 A/s at 1050 o C

Novel synthetic method for the catalytic use of thermally stable zirconia: thermal decomposition of zirconium alkoxides in organic media

Abstract: Thermal treatment of zirconium n-propoxide in glycol at 300°C yielded microcrystalline tetragonal zirconia (ZrO2). The crystallite size of the product depended on the carbon number of the glycol and increased in the following order (carbon number of glycol): 2

Chemistry of 1-iodopropane on copper(110): formation, bonding, and reactions of adsorbed propyl groups

Abstract: The adsorption and thermal decomposition of 1-iodopropane on Cu(110) has been investigated under ultrahigh vacuum conditions using temperature-programmed desorption/reaction spectroscopy and reflection-Adsorption infrared spectroscopy. Adsorption is molecular at 100 K, but at 110 K the 1-iodopropane decomposes to form surface-bound propyl groups and coadsorbed iodine and the propyl groups assume an orientation such that the methyl group is upright. The subsequent chemistry of the propyl moieties is dominated by the evolution of propylene at 200-230 K and H 2 at 315 K

Film properties of CVD titanium nitride deposited with organometallic precursors at low pressure using inert gases, ammonia, or remote activation

Abstract: Chemical vapor deposited (CVD)-TiN layers are required as interdiffusion barriers for the fabrication of microelectronic devices. The deposition of CVD-TiN from a metallorganic precursor, tetrakis-(dimethylamido)-titanium (IV),Ti[N(CH[sub 3])[sub 2]][sub 4] has been investigated and compared using three different experimental approaches: the thermal decomposition of the precursor, its thermal reaction with ammonia, and its reaction with H[sub 2]/N[sub 2] mixtures which have been activated in a remote microwave plasma (2.46 GHz). The experiments have been carried out at moderate temperatures of 250--500 C and pressures between 0.5 and 5 Torr. Mass spectrometric analysis of the effluent gases have been performed and reaction mechanisms for the different experimental conditions are postulated based on these investigations. The application of remote plasma activated H[sub 2]/N[sub 2] mixtures instead of ammonia is a major breakthrough in controlling the reactivity of the chemical partners and is proposed to be also used during CVD-TiN formation from TiCl[sub 4].

Neopentylcobalamin (neopentylB12) cobalt-carbon bond thermolysis products, kinetics, activation parameters, and bond dissociation energy: a chemical model exhibiting 106 of the 1012 enzymic activation of coenzyme B12's cobalt-carbon bond

Abstract: A quantitative study of the thermolysis of neopentylcobalamin (NpB 12 ) in ethylene glycol is reported, studies aimed at providing a well-defined chemical model for the 10 12 enzymic rate acceleration observed for AdoB 12 's (coenzyme B 12 's) Co-C bond homolysis. First, the mild 25-45 o C thermolysis of >98% pure NpB 12 in anaerobic ethylene glycol solutions containing ≥1 equiv of the nitroxide free-radical trap TEMPO (2,2,6,6,-tetramethylpiperidinyl-1-oxy) is reported, a clean reaction (5 UV-visible isosbestic points) which proceeds quantitatively to 98±2% neopentyl-TEMPO (trapped neopentyl radicals) and 99±2% Co(II)B 12 .

The thermal decomposition of the new energetic material ammoniumdinitramide (NH4N(NO2)2) in relation to Nitramide (NH2NO2) and NH4NO3

Abstract: This qualitative study examines the response of the novel energetic material ammonium dinitramide (ADN), NH4N(NO2)2, to thermal stress under low heating rate conditions in a new experimental apparatus. It involved a combination of residual gas mass spectrometry and FTIR absorption spectroscopy of a thin cryogenic condensate film resulting from deposition of ADN pyrolysis products on a KCl window. The results of ADN pyrolysis were compared under similar conditions with the behavior of NH4NO3 and NH2NO2 (nitramide), which served as reference materials. NH4NO3 decomposes into HNO3 and NH3 at 182°C and is regenerated on the cold cryostat surface. HNO3 undergoes presumably heterogeneous loss to a minor extent such that the condensed film of NH4NO3 contains occluded NH3. Nitramide undergoes efficient heterogeneous decomposition to N2O and H2O even at ambient temperature so that pyrolysis experiments at higher temperatures were not possible. However, the presence of nitramide can be monitored by mass spectrometry at its molecular ion (m/ℯ 62). ADN pyrolysis is dominated by decomposition into NH3 and HN(NO2)2 (HDN) in analogy to NH4NO3, with a maximum rate of decomposition under our conditions at approximately 155°C. The two vapor phase components regenerate ADN on the cold cryostat surface in addition to deposition of the pure acid HDN and H2O. Condensed phase HDN is found to be stable for indefinite periods of time at ambient temperature and vacuum conditions, whereas fast heterogeneous decomposition of HDN at higher temperature leads to N2O and HNO3. The HNO3 then undergoes fast (heterogeneous) decomposition in some experiments. Gas phase HDN also undergoes fast heterogeneous decomposition to NO and other products, probably on the internal surface (ca. 60°C) of the vacuum chamber before mass spectrometric detection. © 1993 John Wiley & Sons, Inc.