Thermal Decomposition Rate Research Articles

Effects of organo-modified montmorillonite on the tribology performance of bismaleimide-based nanocomposites

Abstract Poly(allyl condensed polynuclear aromatic-bismaleimide) (ACOPNA–BMI) with different loadings of an organo-modified montmorillonite (OMMT) nanocomposites were successfully prepared via in situ suspension polymerization. Exfoliation/intercalation phenomena were detected using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Positive effects of the exfoliated platelets on the wearable and thermal behaviours were achieved by varying the OMMT load. The lowest friction coefficient of ACOPNA–BMI/2.0 wt.% OMMT was 0.46 at a wear rate of 0.508 × 10− 6 mm3/Nm, which was superior to that of pure ACOPNA–BMI copolymer resin. The thermostabilities of the materials were assessed by thermogravimetric analysis (TGA). The temperature at the maximum rate of thermal decomposition of ACOPNA–BMI/3 wt.% OMMT was 480 °C, which was much higher than that of the pure ACOPNA–BMI copolymer (436 °C). The nanocomposite obtained, which is a suitable wearable material, can be widely used for protecting drilling tools in petroleum engineering applications due to its thermostability and good self-lubrication properties.

Computational fluid dynamic modeling of the flame spray pyrolysis process for silica nanopowder synthesis

A computational fluid dynamic model that couples the fluid dynamics with various processes involving precursor droplets and product particles during the flame spray pyrolysis (FSP) synthesis of silica nanopowder from volatile precursors is presented. The synthesis of silica nanopowder from tetraethylorthosilicate and tetramethylorthosilicate in bench- and pilot-scale FSP reactors, with the ultimate purpose of industrial-scale production, was simulated. The transport and evaporation of liquid droplets are simulated from the Lagrangian viewpoint. The quadrature method of moments is used to solve the population balance equation for particles undergoing homogeneous nucleation and Brownian collision. The nucleation rate is computed based on the rates of thermal decomposition and oxidation of the precursor with no adjustable parameters. The computed results show that the model is capable of reproducing the magnitude as well as the variations of the average particle diameter with different experimental conditions using a single value of the collision efficiency factor α for a given reactor size.

Predicting the indicators characterizing the water decarbonization efficiency when using atmospheric-pressure thermal deaerators without subjecting water to steam bubbling in the deaerator tank

The results obtained from combined numerical and experimental investigations of the water decarbonization process carried out in atmospheric-pressure deaerators without subjecting water to steam bubbling in the deaerator tank are presented. More exact values of the hydrocarbonate thermal decomposition rate have been obtained, and the hypothesis about a change of the process governing mechanism in shifting to low total alkalinity values of deaerated water has been proven in the course of these investigations. A procedure for predicting the indicators characterizing the water decarbonization efficiency in using deaerators is proposed based on the obtained study results. The developed procedure features the maximally possible accuracy that can be achieved at the metrological characteristics of the standard alkalinity measurement methods.

Substituent effect on the rate of thermal decomposition of 5-(R-phenyl)-2-methyl-1,2,3,4-tetrazoles

Thermal decomposition of substituted 2-methyl-5-phenyltetrazoles in solution has been studied by manometric method with chromatographic determination of the evolved nitrogen. A relation has been found between the rate of thermal decomposition and nature of the substituent in the benzene ring. Effects of solvent and temperature on thermal decomposition of substituted tetrazoles have been revealed.

Kinetics of Propargyl Radical Dissociation

Due to the prominent role of the propargyl radical for hydrocarbon growth within combustion environments, it is important to understand the kinetics of its formation and loss. The ab initio transition state theory-based master equation method is used to obtain theoretical kinetic predictions for the temperature and pressure dependence of the thermal decomposition of propargyl, which may be its primary loss channel under some conditions. The potential energy surface for the decomposition of propargyl is first mapped at a high level of theory with a combination of coupled cluster and multireference perturbation calculations. Variational transition state theory is then used to predict the microcanonical rate coefficients, which are subsequently implemented within the multiple-well multiple-channel master equation. A variety of energy transfer parameters are considered, and the sensitivity of the thermal rate predictions to these parameters is explored. The predictions for the thermal decomposition rate coefficient are found to be in good agreement with the limited experimental data. Modified Arrhenius representations of the rate constants are reported for utility in combustion modeling.

Thermal Decomposition Behavior of Loblolly Pine Stemwood, Bark, and Limbs/Foliage Using TGA And DSC Techniques

<abstract> A standing tree before harvest has three primary components: bark, limbs/foliage, and stemwood. For a variety of reasons, most of the development work on forest biomass energy potential has used stemwood (also known as clean chips) as the feedstock. However, the amount of bark and limbs/foliage in a tree is significant (around 25% on mass basis) and may influence the economics of the forest-to-bioenergy process. In this study, the rate and kinetics of thermal decomposition of these three primary components were studied at heating rates of 5°C to 20°C min^-1 in both nitrogen and air atmospheres. The average mass fractions of the components were 74.6% stemwood, 18.2% limbs/foliage, and 7.2% bark. The stemwood component significantly had the lowest ash (0.32%, d.b.) and highest volatile matter (85.6%, d.b.) contents. Major loss in sample mass (40% to 60% of original mass depending on sample type) of each component occurred between 150°C and 425°C when the samples were thermally decomposed in nitrogen atmosphere. In air atmosphere, virtually all of the non-ash component of each sample was volatilized within the temperature range of 150°C to 600°C. The activation energies of stemwood were at least 20% lower than those of the low volatile matter content bark and limbs/foliage. The activation energies for the samples thermally decomposed in air atmosphere were higher than the corresponding values for nitrogen atmosphere.

Influence of Bark on the Physical and Thermal Decomposition Properties of Short-Rotation Eucalyptus

Highly productive short-rotation woody crops is one group of biomass feedstocks that has been identified as having the potential of meeting the goal of reducing the world’s reliance on crude oil. The goal of this project is to quantify the influence of bark on the physical properties, moisture sorption properties, and thermal decomposition of short-rotation (3 years old) Eucalyptus—the most widely planted short-rotation hardwood grown in the world. Results obtained from the study show that the physical properties of ground samples were significantly different between “no-bark” and “with-bark” samples with the bulk density of the with-bark samples decreasing by up to 20 % with a corresponding increase in compressibility of up to 75 %. The moisture sorption rate and the equilibrium moisture relations of the two samples were also significantly different. The susceptibility of no-bark sample to microbial degradation was higher. Thermal decomposition rate and peak temperatures for cellulose and hemicellulose were not affected by the presence of bark. The information obtained from this study will be important in the design and selection of systems for handling, storage, transporting, and thermochemical conversion of short-rotation Eucalyptus.

Kinetic analysis on the non-isothermal degradation of plum stone waste by thermogravimetric analysis and integral master-plots method.

In this study, pyrolysis of plum stone was investigated by thermogravimetric analysis in a nitrogen atmosphere at heating rates of 5, 10, 20 and 40 °C min(-1). Pyrolysis characteristics and the thermal-decomposition rate were significantly affected by variation in the heating rate. However, the heating rate slightly affected the total yield of the volatile matters. Activation energy of the pyrolysis reaction was evaluated by model-free methods, Friedman and Kissingere-Akahirae-Sunose. Results of the Master-Plots method indicated that the most probable reaction model function was the nth order reaction model function as f(x) = (1-x) (3.11), A = 8.02x10(12) under a mean activation energy of 150.61 kJ mol(-1). Proximate and ultimate analysis showed that plum stone can be considered as a favourable source for energy production owing to its low moisture and ash content, and high volatile matter ratio and moderate heating value.

Ignition of Wood (5) On the Thermal Decomposition Rate of Wood.

Ignition of Wood (5) On the Thermal Decomposition Rate of Wood.

Experimental and theoretical study on the thermal decomposition of C3H6 (propene).

The mechanism of the thermal unimolecular decomposition of C3H6 (propene) is studied both theoretically and experimentally. The potential energy surfaces for possible reaction pathways are investigated by CBS-QB3 level of quantum chemical calculations, and RRKM/master-equation calculation is performed for the main channels. The time evolutions of H atoms are observed experimentally by using a highly sensitive detection technique (ARAS, detection limit ≈ 10(11) atoms cm(-3)) behind reflected shock waves (0.5-1.0 ppm C3H6 diluted in Ar, 1450-1710 K at 2.0 atm). The objective of this study is to examine the main product channels by combining the experimental and theoretical investigations on the yield and the rates of H atom production. Present quantum chemical calculations identify reactions (1a-1d) as the candidates of product channels: C3H6 → aC3H5 (allyl radical) + H (1a), C3H6 → CH3 + C2H3 (vinyl radical) (1b), C3H6 → CH4 + :CCH2 (singlet vinyldene radical) (1c), and C3H6 → C3H4 (allene) + H2 (1d). The RRKM calculations reveal the branching fractions for (1a), (1b), and (1c) to be approximately 0.8, 0.2, and 0.01, respectively. Reaction (1d) and other product channels are negligible (< 0.1 %), and the pressure dependence of the branching fraction is small under the present experimental conditions. The experimental yield of H atoms (1.7-2.0) is consistent with the theoretical branching fractions considering the H-atom production from the rapid subsequent thermal decomposition of a C3H5 and C2H3. From the observed time profiles of H atoms, the rate of overall thermal decomposition of C3H6 can be evaluated as Ln(k1/s(-1)) = (38.05 ± 1.18) - (48.91 ± 1.85) × 10(3) K/T, which is in excellent agreement with the theoretical prediction.

Crystallization properties and thermal stability of polypropylene composites filled with wollastonite

The influence of wollastonite (CaSiO3) content on the crystallization properties and thermal stability of polypropylene (PP) composites was investigated. The results showed that the crystallization temperature, crystallization end temperature and crystallization temperature interval, as well as the degree of crystallinity of the composites, were higher than those of the unfilled PP resin, while the crystallization onset temperature was little changed from that of the unfilled PP resin. The increase of degree of crystallinity for the composites could be attributed to the heterogeneous nucleation of the CaSiO3 in the PP matrix. The thermal stability increased with increasing filler weight fraction (ϕf); the thermal decomposition rate decreased nonlinearly with increasingϕf. Finally, the dispersion of the filler particles in the matrix was observed, and the mechanisms of thermal stability and crystallizing behavior were discussed.

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (Tg), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.

A Study on the Pyrolysis of Peanut Shells at Different Isothermal Conditions and Determination of the Kinetic Parameters

The pyrolysis process, which is applied for the aim of producing energy and raw materials which are implemented for the chemical industry from biomass sources, is a thermal conversion process. Determination of the pyrolysis kinetic parameters are important In order to suitable equipment and process design. In this target, in the study the pyrolysis of peanut shells was conducted in a muffle furnace at static atmosphere with temperatures ranging from 300-700 °C. The effects of various parameters on the rate of thermal decomposition rate and the solid yield were determined. The parameters of interest were temperature 300-700 °C, particle size 4-50 mesh, pelletizing, and pelletizing pressure 1.103-5.103 kgf/cm2. Regression coefficients for the total decomposition step were obtained using the thermographs were obtained as a result of the pyrolysis of the peanut shells, and 20 different theoretical model equations that represented the degradation by the Coast-Redfern method. According to regression coefficients of the theoretical model equations, we determined the kinetic model that best represented the degradation. Using this model to represent the degradation, the activation energy (Ea) and Arhenius frequency factor ln(A) for the total reaction were calculated to be 38.245 kJ/mol and 8.124, respectively.

Model-free rate expression for thermal decomposition processes: The case of microcrystalline cellulose pyrolysis

We explore the possibility to derive a completely model-free rate expression using isoconversional methods. The Friedman differential method (Friedman, 1964) and the incremental integral method by Vyazovkin (2001) were both extended to allow for an estimation of not only the apparent activation energy but also the effective kinetic prefactor, defined as the product of the pre-exponential factor and the conversion function. Analyzing experimental thermogravimetric data for the pyrolytic decomposition of microcrystalline cellulose, measured at six different heating rates and three different initial sample masses (1.5–10mg), revealed the presence of secondary char forming reactions and thermal lag, both increasing with increased sample mass. Conditioning of the temperature function enables extraction of more reliable prefactors and we found that the derived kinetic parameters show weak dependence on initial sample mass. Finally, by successful modeling of quasi-isothermal experimental curves, we show that the discrete rate expression estimated from linear heating rate experiments enables modeling of the thermal decomposition rate without any assumptions regarding the chemical process present. These findings can facilitate the design and optimization of industrial isothermal biomass fed reactors.

Antimicrobial regenerated cellulose/nano-silver fiber without leaching

The formation of antimicrobial regenerated cellulose fibers using an ionic liquid solvent, 1-butyl-3-methylimidazolium chloride, and silver nanoparticles was studied. The cellulose preparation and dispersion efficiency of the silver nanoparticles in the solvent were evaluated via scanning electron microscope and transmission electron microscopy in terms of different processing conditions. The influence of silver nanoparticles on regenerated cellulose fiber crystallization and strength was examined using a wide angle X-ray diffractometry and tensiometry, respectively. The bioactive efficacy of the cellulose/nano-silver fiber was tested in accordance with the standard method of ASTM E 2149-10. The cellulose/nano-silver fibers were bioactive and killed Escherichia coli almost completely without any leaching problems. The addition of nano-silver significantly increased the cellulose fiber tensile strength and modulus with an insignificant reduction in fiber elongation, and a slower thermal decomposition rate, evidenced by increased fiber crystallinity. Higher processing temperatures improved the nano-silver dispersion efficiency. The final nano-silver suspension in the regenerated cellulose matrix was composed of scattered clusters with an average size of 700 nm and a distribution density of 14,098 mm−2.

A molecular based kinetic study on the thermal decomposition of poly-α-methyl styrene

Solid polymer thermal decomposition involves complex physical and chemical processes that are closely related to the microscopic molecular information (chemical structure, physical configuration, etc.). However, some important molecular information such as molecular weight is seldom involved in previous solid thermal decomposition studies due to the complexity of solid polymer itself. This work proposes a kinetic equation to study solid polymer thermal decomposition in which the influence of molecular weight to the decomposition is included based on an independent identical particle (IIP) model. Applications of this equation to the thermal decomposition of solid poly-α-methyl styrene (PαMS) show that: 1) there is good agreement between experimental and theoretical thermal decomposition rates; 2) molecular weight can affect not only the activation energy but also the pre-exponential factor of the thermal decomposition kinetic equation; 3) the higher the molecular weight is, the faster the PαMS decomposes in the main decomposition temperature range.

Thermal Decomposition Behaviors and Burning Characteristics of AN/Nitramine-Based Composite Propellant

Ammonium nitrate (AN) has attracted much attention due to its clean burning nature as an oxidizer. However, an AN-based composite propellant has the disadvantages of low burning rate and poor ignitability. In this study, we added nitramine of cyclotrimethylene trinitramine (RDX) or cyclotetramethylene tetranitramine (HMX) as a high-energy material to AN propellants to overcome these disadvantages. The thermal decomposition and burning rate characteristics of the prepared propellants were examined as the ratio of AN and nitramine was varied. In the thermal decomposition process, AN/RDX propellants showed unique mass loss peaks in the lower temperature range that were not observed for AN or RDX propellants alone. AN and RDX decomposed continuously as an almost single oxidizer in the AN/RDX propellant. In contrast, AN/HMX propellants exhibited thermal decomposition characteristics similar to those of AN and HMX, which decomposed almost separately in the thermal decomposition of the AN/HMX propellant. The ignitability was improved and the burning rate increased by the addition of nitramine for both AN/RDX and AN/HMX propellants. The increased burning rates of AN/RDX propellants were greater than those of AN/HMX. The difference in the thermal decomposition and burning characteristics was caused by the interaction between AN and RDX.

Effects of dry method esterification of starch on the degradation characteristics of starch/polylactic acid composites

Maleic anhydride esterified corn starch was prepared by dry method. Esterified starch/polylactic acid (PLA) biodegradable composite was produced via melt extrusion method with blending maleic anhydride esterified corn starch and PLA. The influence of the dry method esterification of starch on the degradation characteristics of starch/PLA composites was investigated by the natural aging degradation which was soil burial method. Test results of mass loss rate showed that the first 30 days of degradation was mainly starch degradation, and the degradation rate of esterified starch/PLA (ES/PLA) was slower than that of native starch/PLA (NS/PLA). Therefore, the damage degree of ES/PLA on the surface and inside was smaller than that of NS/PLA, and the infrared absorption peak intensities of CO, CO and CH were stronger than that of NS/PLA. With the increasing time of soil burial degradation, the damage degree of NS/PLA and ES/PLA on the exterior and interior were gradually increased, whereas the infrared absorption peak intensities of CO, CO and CH were gradually decreased. The XRD diffraction peak intensity of PLA in composites showed an increased trend at first which was then followed by a decreased one along with the increasing time of soil burial degradation, indicating that the degradation of amorphous regions of PLA was earlier than its crystalline regions. When the soil burial time was the same, the diffraction peak intensity of PLA in ES/PLA was stronger than that of NS/PLA. If the degradation time was the same, T0, Ti and residual rate of thermal decomposition of NS/PLA were larger than those of ES/PLA. The tensile strength and bending strength of composites were decreased gradually with soil burial time increasing. Both the tensile strength and bending strength of ES/PLA were stronger than those of NS/PLA.

Thermal Decomposition of the Froth Flotation Mineral Sulfide Concentrates Under Argon Atmosphere in the Presence and Absence of Carbon

Thermal decomposition of the mineral sulfide concentrates derived from froth flotation was studied in the temperature range between 1073 K and 1473 K. The experiments were carried out by heating the mineral sulfide concentrates under inert (argon) atmosphere and, in the presence and absence of carbon. The thermal decomposition of the mineral sulfide concentrates were analyzed by plotting the weight loss of the sample against the reaction time which were obtained from the thermogravimeric analysis (TGA) and characterizing the reacted samples by X-ray diffraction (XRD) and microscopic techniques. The extent and rate of thermal decomposition of the samples were temperature dependent. The high sulfur minerals (CuFeS2 and FeS2) were decomposed to low sulfur and stable phases (Cu1.1Fe1.1S2, Cu5FeS4, and FeS). However, the thermal decomposition of the mineral sulfides were complex because of liquid phase formation at high temperature such that the low sulfur phases appear to have precipitated from the liquid phase during cooling of the sample. Metallic copper was produced in the mineral concentrates containing hydrated and carbonated compounds. It was concluded that the formation of copper cannot occur in the absence of internal oxidation in the sample, when the mineral concentrates are heated under inert atmosphere. The phases were compared with the thermodynamic predictions.

Thermal Stability of n‐Acyl Peroxynitrates

ABSTRACTPeroxynitrates (RO2NO2), in particular acyl peroxynitrates (R = R′C(O) with R′ = alkyl), are prominent constituents of polluted air. In this work, a systematic study on the thermal decomposition rate constants of the first five members of the series of homologous R′C(O)O2NO2 with R′ = CH3 ( =PAN), C2H5, n‐C3H7, n‐C4H9, and n‐C5H11 is undertaken to verify the conclusions from previous laboratory data (Grosjean et al., Environ. Sci. Technol. 1994, 28, 1099–1105; Grosjean et al., Environ. Sci. Technol. 1996, 30, 1038–1047; Bossmeyer et al., Geophys. Res. Lett. 2006, 33, L18810) that the longer chain peroxynitrates may be considerably more stable than PAN. Experiments are performed in a temperature‐controlled, evacuable 200 L‐photoreactor made from quartz. n‐Acyl peroxynitrates are generated by stationary photolysis of mixtures of molecular bromine, O2, NO2, and the corresponding parent aldehydes, highly diluted in N2. Thermal decomposition of R′C(O)O2NO2 is initiated by the addition of an excess of NO. First‐order decomposition rate constants k1 of the reactions R′C(O)O2NO2 (+M) → R′C(O)O2 + NO2 (+M) are derived at 298 K and a total pressure of 1 bar from the measured loss rates of R′C(O)O2NO2, correcting for wall loss of R′C(O)O2NO2 and several percentages of reformation of R′C(O)O2NO2 by the reaction of R′C(O)O2 radicals with NO2. With increasing chain length of R′, k1(298 K) slightly decreases from 4.4 × 10−4 s−1 (R′ = CH3) to 3.7 × 10−4 s−1 (R′ = C2H5), leveling off at (3.4 ± 0.1) × 10−4 s−1 for R′ = n‐C3H7, n‐C4H9, and n‐C5H11. Temperature dependencies of k1 were measured for CH3C(O)O2NO2 and n‐C5H11C(O)O2NO2 in the temperature range 289–308 K, resulting in the same activation energy within the statistical error limits (2σ) of 0.9 and 1.5 kJ mol−1, respectively. A few experiments on n‐C6H13C(O)O2NO2, n‐C7H15C(O)O2NO2, and n‐C8H17C(O)O2NO2 were also performed, but the results were considered to be unreliable due to strong wall loss of the peroxynitrate and possible complications caused by radical‐sinitiated side reactions.