Thermal Decomposition Rate Research Articles

Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature

The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ∼780–790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth (0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N∼1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ∼1016 cm−3 for all films attribute further to the significant benefits of the high-temperature growth regime.

Catalytic and Autocatalytic Mechanisms of Acid Amplifiers for Use in EUV Photoresists

Twelve fluorinated acid amplifiers (AAs) were synthesized and studied for use in photoresists exposed to 13.5 nm, extreme ultraviolet (EUV) light. Acid amplifiers are compounds that decompose in the presence of acid to generate more acid via catalytic or autocatalytic mechanisms. These AAs are composed of a body, trigger, and an acid precursor. Thermal decomposition rates of solutions of the AAs in C6D6/m-ethylphenol (50/50 wt %) at 100 °C were monitored by 19F NMR with and without 1.2 equiv. of 2,4,6-tri-t-butylpyridine. All of the AAs in the presence of base decompose according to first-order kinetics with rate constants kBase. The rate constants, kBase, at various temperatures yielded the activation parameters ΔH‡, ΔS‡, and ΔG‡. The enthalpy of activation, ΔH,‡, was in a narrow range of 16.6−19.1 (kcal/mol), whereas the entropy of activation, ΔS‡, spanned from 0 to −12 (cal/(mol K)). When acid is allowed to build up in solution (in the absence of base), six of the AAs with tertiary triggers (Body-3) decompose autocatalytically, but the six with secondary triggers (Body-2) are unaffected. Although Body-2 AAs do not decompose autocatalytically, nonaflate acid does catalyze their decomposition. Lithographic evaluation showed that some AAs are capable of simultaneously improving the resolution, line-edge-roughness, and sensitivity of a control EUV photoresist. This simultaneous improvement was quantified using the Z-Parameter. The AAs investigated here were found to improve the Z-Parameter by as much as a factor of 3.

Ablation and Thermal Response Property ModelValidation for Phenolic Impregnated Carbon Ablator

Phenolic Impregnated Carbon Ablator was the heatshield material for the Stardust probe and is also a candidate heatshield material for the Orion Crew Module. As part of the heatshield qualification for Orion, physical and thermal properties were measured for newly manufactured material, included emissivity, heat capacity, thermal conductivity, elemental composition, and thermal decomposition rates. Based on these properties, an ablation and thermal-response model was developed for temperatures up to 3500 K and pressures up to 100 kPa. The model includes transversely isotropic and pressure-dependent thermal conductivity. In this work, model validation is accomplished by comparison of predictions with data from many arcjet tests conducted over a range of stagnation heat flux and pressure from 107 W/cm 2 at 2.3 kPa to 1100 W/cm 2 at 84 kPa. Over the entire range of test

Kinetics modeling of dynamic pyrolysis of bagasse fibers

The thermal decomposition mechanism of raw and treated bagasse fibers was modeled with three parallel independent first-order reactions. The kinetic parameters and pseudo components which best fit the experimental dynamic pyrolysis rate of bagasse was determined by means of the Matlab program using the least-square method. The calculated rate of thermal decomposition for each bagasse sample was consistent with experimental pyrolysis rate very well. A method was adopted to calculate the contents of cellulose, hemicelluloses, and lignin for bagasse fiber based on the dynamic pyrolysis model. The calculated contents of the untreated bagasse fiber agreed very well with some reported values from the literature. The effect of treatment conditions on the bagasse fiber compositions was also studied. From the three-dimensional plot for each of the three components, it could be observed that bagasse fibers treated under the intermediate alkaline condition could achieve the higher content of cellulose.

The Intrinsic Kinetics and Heats of Reactions for Cellulose Pyrolysis and Char Formation

The Intrinsic Kinetics and Heats of Reactions for Cellulose Pyrolysis and Char Formation

Shock Tube Study on the Thermal Decomposition of CH3OH

H atom produced in the thermal decomposition of CH(3)OH highly diluted in Ar (0.48-10 ppm) was monitored behind reflected shock waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (+/-10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of approximately 1 x 10(11) atoms/cm(3) and enables us to determine the branching fraction for the direct H atom production channel, CH(3)OH --> CH(2)OH + H (channel 1c ) in a mixture of 1 ppm CH(3)OH. Channel 1c is confirmed to be minor, that is, branching fraction for channel 1c is expressed by Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02), which corresponds to k(1c)/k(1) < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH(3)OH with (100-1000) ppm H(2), the total decomposition rate k(1) for CH(3)OH --> products is measured from the time dependence of H atom, where the radical products of main channels 1a and 1b , that is, OH, CH(3), and CH(2), were converted rapidly into H atoms. The experimental result is summarized as Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction: (3)CH(2) + H(2) --> CH(3) + H (reaction 3 ). The rate is given by k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T(2.3) exp (-3699/T). This result is used for numerical simulations to evaluate k(1). Present experimental results on the thermal decomposition rate of CH(3)OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH(3)OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.

PREPARATION AND STUDY OF PHOTO-THERMAL DEGRADATION FOR THE COMPOUND BIS(P-DITHIOCHLOROTO)SE(II)

Preparation and photo degradation have been studied for compound of Bis(pdithiochloroto) selenium(II) (C14H10CL2S4Se) . Two wavelengths of (253.7,356.0)nm for different periods time (5,10,15,….,120)min. have been used . The thermal degradation has been studied for the compound with different period's temperatures (283,293,303,313,323)K at periods of (2, 4, 6, 8, and 10) hour. Many experimental reaction have been done to determine the effective factors for degradation of the compound. Photo and thermal decomposition rates were estimated by using the change in (pH) values. The results showed that the photo decomposition for compound of Bis(p-dithiochloroto)Se(II) increased by increasing irradiation time. The (pH) values decreases to reach its minimum value at (25)min. then it increased as irradiation continues because the number of the released hydrogen ion will be high in the beginning of the reaction. The study showed a little effects on thermal decomposition at low temperature (283,293) K as indicated by (pH). However there was a decrease in pH values at high temperatures (283,313,323)oK and early periods due to a released Hydrogen ions. The (pH) values increased by increasing temperature and period of time.Different techniques such as UV-Visible spectrophotometry and Infrared spectrophotometry have been used to analyze final product. Also qualitative analytical methods have been used to identify the final products. The techniques showed that the final degradation is that dithio P-chloro benzoic acid (C7H5S2Cl

Effect of biopretreatment on thermogravimetric and chemical characteristics of corn stover by different white-rot fungi

The thermogravimetric and chemical characterization of corn stover biopretreated by three different species of white-rot fungi have been studied in this research. Results indicated that biopretreatment can optimize the thermal decomposition, decrease the reaction temperature and reduce the gas contamination (SO x ), making the biomass pyrolysis more efficient and environmentally friendly. Biopretreatment can decrease the activation energy and reacting temperature of the hemicellulose and cellulose pyrolysis (up to 36 °C), shorten the temperature range of the active pyrolysis (up to 14 °C), and increase the thermal decomposition rate, greatly promoting the reaction and making the biomass pyrolysis easier to start and carry on. On the other hand, by biopretreatment, the sulphur content can decrease up to 46.15%, which can considerably reduce the inventory of SO x emission. Moreover, the mechanism of the biopretreatment was also explored that the deconstruction and depolymerization of the recalcitrant linkages of lignin and cellulose by biopretreatment can make the structure of biomass incompact and easier to be pyrolyzed.

An improved method to measure the rate of vaporisation and thermal decomposition of high boiling organic and ionic liquids by thermogravimetrical analysis

The vapour pressure and the thermal stability of liquids are important material properties. For high boiling organic and ionic liquids (ILs), the determination of these properties is laborious and it is not easy to discriminate between evaporation and thermal decomposition. In this work, a simple but accurate method is presented to determine the parameters of decomposition and evaporation by thermogravimetrical analysis (TGA). The mass transfer coefficient was calculated based on a new correlation for the Sherwood number for cylindrical crucibles in overflow of a carrier gas. This correlation is valid for any diameter-to-height ratio and for any filling degree of the crucible and was derived from numerical simulations and proven by experiments with hexadecane, dodecane, and anthracene. The TGA analysis of two ILs was conducted. [EMIM][EtSO(4)] decomposes at ambient pressure without a measurable contribution of evaporation. To the contrary, [BMIM][NTf(2)] is relatively volatile. The vapour pressure of [BMIM][NTf(2)] and the kinetics of decomposition of both ILs were determined.

Degradation Behavior and Biocompatibility of PEG/PANI-Derived Polyurethane Co-polymers

A series of polyurethane (PU) co-polymers with designable molecular weight between cross-linking dots was synthesized by a hydrogen transfer polymerization route from polyaniline (PANI), poly(ethylene glycol) (PEG), various curing agents and chain extenders using dibutyltin dilaurate as a catalyst. Their swelling, hydrophilicity, degradation and biocompatibility were inspected and assessed based on different degrees of polymerization of PANI and PEG, and their component proportion. Fourier transformation infrared spectrometry (FT-IR), 1H-NMR spectroscopy, scanning electron microscopy (SEM), gel-permeation chromatography (GPC) and goniometry were used to characterize the structure and surface morphology of the synthesized PEG/PANI-based PU co-polymers, PU residues after degradation and degraded polymers at different time periods of hydrolysis. The thermal properties, aggregate structure and surface microstructure were examined by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM). Hemolysis, static platelet adhesion, dynamic clotting measurements and MTT assays were adopted to evaluate the hemo- or cytocompatibility. The experimental results indicated that these polymers exhibit various degrees of micro-phase separation, depending on the concentration and degree of polymerization of PANI, molecular weight of PEG, type of curing agent and chain extender, which further influence their swelling, hydrophilicity, degradable properties and biological performances in vitro. The incorporation of PANI and PANI* in co-polymers led to decreased thermal stability but slower decomposition rates than typical PEG-based PUs. The stress–strain tests showed that the as-prepared PU co-polymers possessed increased tensile strength and modulus, and decreased toughness in comparison with the blank PEG-based PU. These co-polymers are expected to find specific applications in tissue engineering or controlled drug release.

Critical Rate of Thermal Decomposition of Pure and Impregnated Lignocellulosic Materials

Critical Rate of Thermal Decomposition of Pure and Impregnated Lignocellulosic MaterialsContribution deals with monitoring the impact of airflow velocity around the sample, the oven temperature during thermal decomposition and nature of the sample for the minimum mass flux rate needed to initiate flame combustion. We used the samples of lignocellulosic materials, particularly spruce wood, pure cellulose, flax, cellulose impregnated by 5%, 10%, 15% water solution of KHCO3 and by 5%, 10%, 15% water solution of (NH4)2HPO4.

Characterization of the Combustion Process of Flame Resistant Thermal Protective Textiles in the Presence of Oily Contaminants: Effects of Contamination and Decontamination

This paper reports two experimental studies wherein the combustion process of flame resistant (FR) thermal protective textiles is characterized in terms of thermal decomposition and heat release parameters before and after contamination and in terms of heat release parameters after contamination and decontamination. Aramid and FR cotton/nylon decomposed at higher and aramid/FR viscose at lower temperature in the presence of oil. Oil interferes with thermally induced interactions between aramid and FR viscose, altering the thermal decomposition rates and formation of char, and thereby increasing the effectiveness of the flame retardant present in the viscose. It is apparent that oily contaminants present in FR fabrics affect the initiation of the thermal degradation and formation of char. All contaminated FR fabrics showed significantly higher peak heat release rate (PHRR), total heat release (THR) and effective heat of combustion (EHC) compared to uncontaminated ones. Oily specimens laundered with no detergent or prewash product had higher PHRR, THR and EHC compared to other treatments regardless of the fabric type or number of contamination/decontamination cycles. Heat release increased with increased number of contamination/decontamination cycles for most laundry treatments for all FR fabrics. FR cotton/nylon had the highest and aramid had the lowest PHRR and THR whether specimens were uncontaminated, contaminated or decontaminated. In this study heat release from FR fabrics increased with increased oily contamination.

Wplyw antypirenow na stabilnosc termiczna i palnosc usieciowanych kauczukow nitrylowych

Flammability of peroxide vulcanizates of acrylonitrile-butadiene rubber NBR 18, containing various flame retardants has been determined by thermal analysis (Table 1, Fig. 1—5). A clear relation between thermal decomposition rate of cured elastomer and its flammability, determined as oxygen index OI and combustion time in an air, was found (Table 2—7). The effects of particular flame retardants on the formation of a boundary layer (between a flame and a sample) and on the reactions in gas phase during combustion were discussed. The formation of liquid products of thermal decomposition during combustion of cured elastomer containing phosphoro-organic Disflamoll is the reason of easy combustion of these vulcanizates in an air. The most effective flame retardants appeared to be pentabromotoluene and mixtures of antimony oxide with chloroparaffin.

Pressure-Dependent Decomposition Kinetics of the Energetic Material HMX up to 3.6 GPa

The effect of pressure on the global thermal decomposition rate of the energetic material HMX was studied. HMX was precompressed in a diamond anvil cell (DAC) and heated at various rates. The parent species population was monitored as a function of time and temperature using Fourier transform infrared (FTIR) spectroscopy. Global decomposition rates were determined by fitting the fraction reacted to the extended-Prout-Tompkins nucleation-growth model and the Friedman isoconversional method. The results of these experiments and analysis indicate that pressure accelerates the decomposition at low-to-moderate pressures (i.e., between ambient pressure and 0.1 GPa) and decelerates the decomposition at higher pressures. The decomposition acceleration is attributed to pressure-enhanced autocatalysis, whereas the deceleration at high pressures is attributed to pressure-inhibiting bond homolysis step(s), which would result in an increase in volume. These results indicate that both the beta- and delta-polymorphs of HMX are sensitive to pressure in the thermally induced decomposition kinetics.

A New Study on Combustion Behavior of Pine Sawdust Characterized by the Weibull Distribution

An isothermal operation is implemented by employing a thermogravimetric analyzer (TGA) for simulating the thermal decomposition behavior of 58 μm pine sawdust in air atmosphere. An independent parallel reaction model is adopted in this study to describe the thermal decomposition mechanism. The Weibull distribution function is used to record and analyze the weight loss during isothermal decomposition at different temperatures (500, 600, 700, and 800°C). The total weight loss of the pine sawdust is assumed as a linear combination of individual weight loss from three components, including the char and two volatile matters. The plot of the thermal decomposition rate curve leads to kinetic parameters such as the reaction rate constants and the reaction order. The results show that the Weibull distribution function successfully represents decomposition curves of three components, and fits the experimental data very well. Therefore, this study provides a simple way to evaluate the decomposition rate of biomass combustion in a real combustor.

In situ Gravimetric Monitoring of Thermal Decomposition and Hydrogen Etching Rates of 6H-SiC(0001) Si Face

The thermal decomposition and hydrogen etching of a 6H-SiC(0001) Si-face were directly monitored using an in situ gravimetric monitoring system. The monitoring of the weight change of the 6H-SiC Si-face using this system clarified the dependences of the thermal decomposition and hydrogen etching rates on the substrate temperature. Although the thermal decomposition of the 6H-SiC Si-face above 1400 °C generated a graphite layer since only the Si atom directly desorbs from the surface, the etching of the 6H-SiC Si-face by hydrogen did not form this layer, and both Si and C atoms react with hydrogen. Moreover, the surface reaction of the 6H-SiC Si face with H2 and the resultant surface morphology were found to change at approximately 1250 °C.

Studies of the rates of thermal decomposition of glycine, alanine, and serine

Rates of thermal decomposition of glycine, alanine, and serine are described by the equation of first order reaction in the temperature range 200–300°C. Apparent rate constants and apparent activation energies of decomposition of α-amino acids were evaluated. It was found that the main gaseos reaction product is carbon dioxide.

Physical properties of polyhedral oligomeric silsesquioxanes–cycloolefin copolymer nanocomposites

AbstractProperties of cycloolefin copolymer (COC)–polyhedral oligomeric silsesquioxanes (POSS) nanocomposites, prepared by melt compounding, have been investigated. Composites retained the optical transparency of the matrix up to a nanofiller content of 5 wt %. whereas for higher percentages the formation of a crystalline phase, due to the presence of agglomerated nanoparticles, was revealed by X‐Ray diffraction (XRD). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) evidenced a significant decrease of the glass transition temperature (Tg) and of the thermal decomposition rate, with the POSS content. Similarly, at increasing filler content, both quasi‐static tensile tests in the solid state and rheological measurements on melts showed a decrease of measured parameters (elastic modulus, ultimate elongation, loss and storage shear modulus, viscosity). These results were attributed to the formation of a soft interphase at the nanoparticles/polymer boundary due to the presence of isobutylic groups on POSS nanoparticles that limited the stress transfer process and acted in the COC matrix as a molecular lubricant agent. A small increase of the receding contact angle with the nanofiller content was also detected from dynamic contact angle (DCA) measurements. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Laboratory simulations of prebiotic molecule stability in the jarosite mineral group; end member evaluation of detection and decomposition behavior related to Mars sample return

Recently, the prebiotic amino acid glycine has been found associated with natural jarosite samples from locations around the world. Since the discovery of jarosite on Mars, extensive research focuses on linking this mineral group with possible detection of biosignatures in the geologic record on Earth and Mars. Multiple analytical methods, including extraction and mass spectrometry techniques, have identified glycine and other biomolecules in jarosite samples. The jarosite end members jarosite (sensu stricto-potassium jarosite), natrojarosite (sodium jarosite), and ammoniojarosite (ammonium jarosite) have different thermodynamic stabilities, decompose at different rates, and have potentially different susceptibilities to substitution. The relationship between the thermodynamic stability of the jarosite end members and the effect that glycine has on the thermal decomposition behavior of each end member was investigated using thermal gravimetric analysis. Introducing glycine into the synthesis procedure (75 ppm) of the potassium, sodium, and ammonium jarosite end member has elucidated the effects that glycine has on the thermal stability of the mineral group. Potassium jarosite appears to be the least susceptible to the effects of glycine, with the sodium and ammonium end members showing marked changes in thermal decomposition behavior and decomposition rates. These results suggest that the sodium and ammonium jarosites are more suitable targets for identifying signs of prebiotic or biotic activity on Mars and Earth than the potassium jarosites. These results have implications for current in situ investigations of the martian surface and future sample return missions.

Kinetics of thermal decomposition of sulfur-containing amino acids

Rates of thermal decomposition of sulfur-containing amino acids such as D,L-methionine, L-cysteine, and L-cystine are studied. It is established that the amino acids decompose at 190–240°C to give the gaseous and liquid decomposition products in the polyphasic system formed. The rate of summary process is described by the first order kinetic equation up to 30–50% conversion. In spite of close values of the effective activation energies of thermal decomposition of D,L-methionine, L-cysteine, and L-cystine (195, 193, and 184 kJ mol−1 respectively) the effective rate constants at one and the the same temperature differ by one or two orders of magnitude in the above-mentioned series. Sulfur-containing compounds prevail in the gaseous decomposition products, while in the liquid phase the nitrogen-containing ones are accumulated.