Thermal Decomposition Kinetics Research Articles

Thermal decomposition of n-hexane in organic Rankine cycle: a study combined ReaxFF reactive molecular dynamic and density functional theory

The thermal decomposition mechanism of n-hexane is investigated by using density functional theory and ReaxFF force field. The initial decomposition reactions, the effect of temperature on thermal decomposition and first-order kinetics are analyzed. The results show that the C-C bonds in n-hexane molecule are more easily decomposed than that of C-H bonds, and the breakage of C3-C4 bond is the main initial decomposition reaction. The main decomposition products of n-hexane are H2, CH4, C2H2, C2H4, C2H6, and C3H6. The decomposition rate of n-hexane is accelerated by temperature. The apparent activation energy and pre-exponential factor of n-hexane thermal decomposition are 209.8 kJ mol−1 and 1.1 × 1013 s−1, respectively.

Thermal stability of levopimaric acid and its oxidation products

Biofuels are renewable alternatives to fossil fuels. Levopimaric acid‒base biofuels have attracted increasing attention. However, their stability remains a critical issue in practice. Thus, there is a strong impetus to evaluate the thermal stability of levopimaric acid. Through thermogravimetry (TG) and a custom-designed mini closed pressure vessel test (MCPVT) operating under isothermal and stepped temperature conditions, we investigated thermal oxidation characteristics of levopimaric acid under oxygen atmosphere. Thin-layer chromatography (TLC) and iodimetry were used to measure the hydrogen peroxides generated by levopimaric acid oxidation. A high pressure differential scanning calorimeter (HPDSC) was used to assess hydroperoxide thermal decomposition characteristics. Gas chromatography-mass spectrometry (GC-MS) was used to characterize the oxidation products. The thermal decomposition kinetics of levopimaric acid were thus elucidated, and a high peroxide value was detected in the levopimaric acid. The decomposition heat (QDSC) and exothermic onset temperature (Tonset) of hydroperoxides were 338.75 J g−1 and 375.37 K, respectively. Finally, levopimaric acid underwent a second-stage oxidation process at its melt point (423.15 K), resulting in complex oxidation products. Thermal oxidation of levopimaric acid could yield potential thermal hazards, indicating that antioxidants must be added during levopimaric acid application to protect against such hazardous effects.

Thermodynamic Analysis and Pyrolysis Mechanism of 4,4'-Azobis-1,2,4-triazole.

The nonisothermal thermal decomposition kinetics of 4,4'-azobis-1,2,4-triazole (ATRZ) at different heating rates (5, 10, 15, and 20 °C·min-1) were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) studies. The thermal decomposition kinetic parameters such as apparent activation energy (E) and pre-exponential factor (A) were calculated by the Kissinger, Ozawa, and Šatava-Šestak methods. The E and A values calculated by the above three methods are very close, which are 391.1 kJ·mol-1/1034.92 s-1, 381.1 kJ·mol-1/1034.30 s-1, and 393.4 kJ·mol-1/1035.76 s-1, respectively. Then, the decomposition mechanism function of ATRZ is analyzed by the calculated results. The results show that the decomposition temperature of ATRZ is about 300 °C and the exothermic decomposition speed is fast. The decomposition pathway of ATRZ was analyzed by pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS). The thermal decomposition kinetic equation of the ATRZ was deduced.

The Influence of Ti + TiC Additive on Thermal Stability and Decomposition Kinetics of Nanosized MgH2 Phase in Mg-Based Mechanical Alloys

The Influence of Ti + TiC Additive on Thermal Stability and Decomposition Kinetics of Nanosized MgH2 Phase in Mg-Based Mechanical Alloys

Thermal decomposition mechanism and kinetics of bastnaesite in suspension roasting process: A comparative study in N2 and air atmospheres

To investigate the thermal decomposition behavior and reaction kinetics of bastnaesite in suspension roasting, the gas and solid products of bastnaesite roasted in N2 and air atmospheres were examined using a gas analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Subsequently, the kinetic parameters of bastnaesite in the suspension roasting process were derived and calculated using the isothermal method. The results show that the decomposition product of bastnaesite in N2 is CeOF. However, once the roasting temperature exceeds 600 °C, CO is generated in addition to CO2, and all the XRD diffraction peaks of CeOF are shifted to the right, indicating that CO2 can oxidize CeOF and lead to the transformation of Ce(III) into Ce(IV). When roasted in air, the decomposition product CeOF can be completely converted to CeF3 and Ce7O12 as it easily oxidizes. Additionally, the reaction rate of bastnaesite in air is higher than that of N2, and the starting reaction temperature is lower than that of N2. A large number of irregular cracks and holes appear on the surface of solid-phase products following suspension roasting, which are due to the thermal decomposition of bastnaesite that produces CO2 as well as the reconstruction of the lattice of the solid-phase products. The reaction kinetic model of bastnaesite roasted in N2 (temperature range 600–750 °C) and air (temperature range 500–575 °C) conforms to the A3/2 model with the mechanism function G(α)=–ln(1–α)2/3, and the reaction activation energy is 59.78 kJ/mol and lnA is 1.65 s−1 in N2 atmosphere. In air, the reaction activation energy is 100.30 kJ/mol and lnA is 9.63 s−1.

A study on the preparation of Cr2O3 from (NH4)2Cr2O7 based on thermal decomposition including the thermal decomposition temperature effect, mechanism and kinetics

In this study, the thermal decomposition process of (NH4)2Cr2O7, including the effect of thermal decomposition temperature on the physicochemical properties of products, thermal decomposition mechanism, and kinetics, was studied in detail. The phase compositions, crystal structures, and micromorphology of thermal decomposition products were determined based on XRD and SEM analysis. The effect of thermal decomposition temperature on particle size, specific surface area, and chromaticity was investigated systematically. The lowest thermal decomposition temperature was determined, and the reaction equations were conjectured. The thermal decomposition mechanism of (NH4)2Cr2O7 was further revealed at the molecular level using FT-IR analysis and DFT calculation. At last, Kissinger and Kissinger-Crane methods calculated the kinetic parameters of (NH4)2Cr2O7 thermal decomposition, and the rate equation was established.

Thermal hazards assessment of three azo nitrile compounds

Commercially available azo radical compounds provide efficient initiation of many chemical reactions. However, such energetic azo group initiators have thermal stability issues at ambient or even sub-ambient temperatures. Azo decomposition initiated by heat and/or light can generate significant amounts of nitrogen gas with rapid pressure increases, presenting a safety challenge for shipping, storage and usage. In this study, three azo nitrile compounds were examined using various thermal calorimetry techniques with only 5 mg to 1 g scale samples. We obtained calorimetric data on exothermic activity and gas generation. The testing results were subsequently analyzed by using differential iso-conversional methods to obtain key decomposition kinetics parameters, including activation energy and pre-exponential factor. The model was then validated and utilized for prediction of several key safety parameters for scale-up applications, including Self-Accelerating Decomposition Temperature (SADT), Time to Maximum Rate (TMR), temperature profiles at iso- or non-isothermal conditions for shelf-life evaluation, adiabatic temperature rise, and rate of pressure increase. For compounds such as 2,2’-azobis-(2,4-dimethylvaleronitrile) and 1,1’-azobis(cyclohexane-1-carbonitrile) which went through phase transitions associated with thermal decomposition, the thermal decomposition behavior of liquid and solid state was found to differ in characteristic. This methodology for thermal decomposition kinetics assessment enables safe storage, handling, and scale-up process preparation.

Thermal decomposition kinetic study on one-pack formulations of epoxy resin cured with novel phosphorus-containing flame retardant latent curing agents

Several phosphorous-containing flame retardant latent curing agents newly derived from 4,4-diamino diphenyl sulfone (DDS) and 4,4-diamino diphenyl methane (DDM) were designed to cure epoxy resin alongside dicyandiamide (Dicy). The thermal decomposition and kinetics of cured one-packed systems were investigated in detail. The epoxy systems were studied under a nitrogen atmosphere by using thermal gravimetric analysis at different heating rates. The kinetics of thermal decomposition was evaluated by Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink methods. The correlation coefficient for all systems obtained by the three above methods was almost equal to one, indicating that these three methods were correctly chosen. The results demonstrated that the activation energy of epoxy/Dicy blended with different phosphorous-containing DDS- and DDM-derived curing agents at a lower degree of conversion decreased by incorporation of the agents while increasing at a higher degree of conversion. The thermodynamic parameters (ΔH*, ΔG*, and ΔS*) of the studied systems were calculated by the obtained activation energy via three kinetics methods. It was found that as the conversion degree and the enthalpy increased, the Gibbs free energy decreased, while entropy changed from negative to positive values.

Experimental and theoretical studies on the kinetics of thermal decomposition and decomposition mechanism of CF3I in oxidizing environments

CF3I, as a novel “Halon” replacement fire-extinguishing agent, has the characteristics of low fire-extinguishing concentration, high efficiency, and safety. However, there are still some gaps in its thermal decomposition studies when it is released into the high-temperature fire, so the thermal decomposition of CF3I in oxidizing environments was studied to simulate its diffusive decomposition. The decomposition of CF3I was demonstrated to be accelerated by O2 through experiments in the temperature range of 100°C-800°C in air and N2 atmosphere. The effects of initial concentration, temperature, and residence time on the decomposition rate of CF3I and decomposition characteristics were investigated by tube furnace simulation. The kinetics of thermal decomposition was calculated using the Arrhenius equation in which activation energy Ea is 15.18 kJ/mol and pre-exponential factor (A) is 13.87s−1. Additionally, the thermal decomposition products were examined by GC-MS and FTIR. The experimental results showed that the pyrolysis gas products were mainly CF4, C2F6, and CF2O. Using quantum chemistry and density flooding theory (DFT) calculations, it was concluded that the main decomposition pathway was the reaction of CF3I with singlet oxygen. The reaction pathway of the thermal decomposition of CF3I under a high-temperature fire oxidation environment was proposed based on the products.

Preparation, characterization, and thermal decomposition kinetics of high test peroxide gel

High test peroxide gel was prepared by low temperature freezing under the action of calcium ion compound with sodium alginate as a gelling agent. The High test peroxide gel was characterized by ultra depth of field microscope, Fourier infrared spectrometer, rheometer, synchronous thermal analyzer, and electron microscope scanner. The thermal decomposition behavior and reaction kinetics of the gel were investigated. The effective content of H2O2 in the gel before and after aging was also analyzed by KMnO4 titration. The results show that the content of sodium alginate and the concentration of calcium ion compound directly affect the gelling and rheological properties of high test peroxide gel, and the gel with low sodium alginate content had a more uniform tissue structure. The Eα and lg(A/s−1) of the high test peroxide gel decomposition reaction are 69.10 kJ mol−1 and 9.13, respectively. Na2O, CaO, CaCl2 and CaSO4 are the main components of the high test peroxide gel thermal decomposition condensate products. After ignition, a boron-based high test peroxide gel propellant can produce a steady combustion. After being stored at 263 K for 20 days, the effective content of H2O2 in the gel is 96.50%, and the decomposition rate is only 0.63%.

Thermal properties of CL‐20/HMX‐Am‐GO composites

AbstractThe thermal decomposition of Hexanitrohexaazaisowurtzitane CL‐20/HMX‐ammonium formate functionalized graphene oxide (Am‐GO) composites was studied using an isothermal decomposition dynamics research instrument to explore the effects of Am‐GO on the stability of CL‐20/HMX co‐crystal. The gas pressure‐time curve generated by thermal decomposition reaches the decomposition inflection point at a decomposition degree of 85 %. Compared with CL‐20/HMX co‐crystal, the decomposition extent corresponding to the inflection point of the thermal decomposition curve of the composites increases. The activation energies of the composites before and after the inflection point of the pressure‐time curve were 161.3 kJ/mol and 171.0 kJ/mol, respectively. The residual substances produced by the thermal decomposition of the composites were characterized by HPLC and FTIR. Results showed that CL‐20 and HMX were decomposed before the inflection point of the decomposition pressure‐time curve. However, the decomposition of CL‐20 was completed before the inflection point, whereas that of HMX ran through the thermal decomposition process. The calculation results of thermal decomposition kinetics show that the addition of coating material increases the activation energy of co‐crystal and stabilizes CL‐20/HMX co‐crystal.

Preparation and Properties of Ultra-fine HNS-IV

Ultra-fine 2,2’,4,4’,6,6’- Hexanitrostilbene (HNS-IV) was obtained by HNS-II by vibration cavity comminute. This method uses only alcohol and deionized water, which can be viewed as a green technology. The morphology, particle size, specific surface area, thermal decomposition property and the threshold energy for slapper detonator were compared between HNS-IV and HNS-II in this paper. Results show that after HNS pulverizing, the particle size decreased from 27.18μm to 1.44μm, the specific surface area increased from 0.73m2•g−1 to 9.10m2•g−1. DSC analysis shows that the decomposition peak temperature Td decreases and the melting temperature Tm increases after pulverizing. It is speculated that in the explosive reaction with very high heating rate, the enthalpy of decomposition will be increased by pulverizing, which will be more conducive to detonation growth and explosive reaction. According to the calculation of thermal decomposition kinetics, the decomposition and activation energy Ea of HNS decreases after pulverizing, and the thermal decomposition reaction rate of HNS-IV increases when the temperature is less than 409.6°C. The initiation threshold test of the impact plate shows that the 50% initiation threshold energy of HNS- II is 1.242J, and the 50% initiation threshold energy of HNS-IV is 0.558J, and the initiation threshold for slapper detonatorer is significantly reduced by 55%. This means that the ultra-fine HNS-IV is very suitable as the main ingredient in the booster in the EFI initiation.

Thermal decomposition kinetics, reaction mechanism, and hazard evaluation of the hydroxylamine sulfate solution doping Fe3+

To study the stability of hydroxylamine sulfate (HAS) when mixed with metal ions (especially Fe3+), the effect of Fe3+ doping on the thermal decomposition of HAS was studied by differential scanning calorimeter. The results indicate that HAS decomposes at 365–376 K and average thermal effect of P1 and P2 are approximately 632.6 J/g and 66.9 J/g, respectively. Fe3+ increases thermal effect of P1 and P2, but it decreases the initial decomposition temperature (To) of P1, and delays the To of P2. The density functional theory calculations results reveal a detailed 8-step reaction model of HAS decomposition with the formation of NH3OH+ as the key step. Notably, Fe3+ affects the thermal decomposition process of HAS by forming a coordination compound Fe(NH2OH)63+ with NH2OH. In addition, model-free method prediction shows that Fe3+ reduces the kinetic parameters and the thermal hazard parameters.

Performance of Thermal-Oxidative Aging on the Structure and Properties of Ethylene Propylene Diene Monomer (EPDM) Vulcanizates.

A thermal-oxidative aging test at 120 °C was conducted on ethylene propylene diene monomer (EPDM) vulcanizates of the semi-efficient vulcanization system. The effect of thermal-oxidative aging on EPDM vulcanizates was systematically studied by curing kinetics, aging coefficient, crosslinking density, macroscopic physical properties, contact angle, Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric analysis (TGA) and thermal decomposition kinetics. The results show that the content of hydroxyl and carbonyl groups as well as the carbonyl index increased with increasing aging time, indicating that EPDM vulcanizates were gradually oxidized and degraded. As a result, the EPDM vulcanized rubber chains were crosslinked with limited conformational transformation and weakened flexibility. The thermogravimetric analysis demonstrates that the thermal degradation of EPDM vulcanizates had competitive reactions of crosslinking and degradation, and the thermal decomposition curve can be divided into three stages; meanwhile, the thermal stability of EPDM vulcanizates gradually decreased with increasing aging time. The introduction of antioxidants in the system can promote the crosslinking speed and reduce the crosslinking density of EPDM vulcanizates while inhibiting the surface thermal and oxygen aging reaction. This was attributed to the fact that the antioxidant can reduce the thermal degradation reaction level, but it is not conducive to the formation of a perfect crosslinking network structure and reduces the activation energy of thermal degradation of the main chain.

Preparation and characterization of Al@TKX-50@NC composite microspheres by electrospray

Micro-nano composite energetic materials have attracted extensive attention from researchers due to their excellent properties. Electrostatic spray drying, as an emerging composite material preparation technology, has an important impact on the assembly and energy release regulation of energetic materials. In this paper, NC with excellent mechanical properties was selected as the energetic binder. The uniform assembly of TKX-50 and Al was achieved by electrostatic spraying technology, and Al@TKX-50@NC micro-nano composite energetic material microspheres were prepared. The structure and composition of the composite were characterized, and its thermal decomposition kinetics and thermodynamics were calculated and analyzed. At the same time, its ignition and combustion performance were tested. It is found that the samples prepared by electrostatic spray are regular spherical, and the particle size is about 1–6 μm. Compared with the physical mixture samples, the Al@TKX-50@NC composite microspheres not only have a more complete oxidation reaction but also have better ignition and combustion performance. The results show that the electrostatic spray method is very effective in improving the energy release of composite energetic materials.

Formation mechanism and thermal decomposition properties of hydration products of superfine tailings cemented paste backfill

Filling mining with solid waste resources as aggregates is an important development direction for cleaner production in mines. The hydration products have an important effect on the mechanical properties of superfine tailings cemented paste backfill (SCPB). This paper investigates the mechanism of hydration product formation and thermal decomposition properties of SCPB by a series of experiments combined with thermal decomposition kinetics. Also, to optimize the mechanical properties of SCPB, the effect of Nano SiO2 (NS) on the related properties of SCPB is investigated. The results show that there are two main stages of the thermal decomposition of SCPB, and the kinetic models of these two stages are both reaction order models. After adding NS, the kinetic model of the second stage of thermal decomposition of SCPB is changed to random nucleation and growth model. The substances that undergo thermal decomposition reactions in the first stage are mainly hydration products such as ettringite and C-S-H, while the substances that undergo thermal decomposition reactions in the second stage are carbonates. The activation energy E and pre-exponential factor A of the first stage of thermal decomposition of SCPB with NS added are significantly improved, which indicates a more stable structure of its hydration products. The microscopic test results show that NS can promote the hydrolysis of C3S and gypsum and increase the production of hydration products, which in turn improves the strength of SCPB. In addition, the addition of NS to SCPB decreases the Ca/Si and increases the average silica chain length of C-S-H gels, while the H2O/Si decreases and the silica group increases, resulting in the enhancement of the structure of C-S-H gels.

Statistical Copolymers of N-Vinylpyrrolidone and 2-Chloroethyl Vinyl Ether via Radical RAFT Polymerization: Monomer Reactivity Ratios, Thermal Properties, and Kinetics of Thermal Decomposition of the Statistical Copolymers.

The radical statistical copolymerization of N-vinyl pyrrolidone (NVP) and 2-chloroethyl vinyl ether (CEVE) was conducted using the Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization technique, employing [(O-ethylxanthyl)methyl]benzene (CTA-1) and O-ethyl S-(phthalimidylmethyl) xanthate (CTA-2) as the Chain Transfer Agents (CTAs), leading to P(NVP-stat-CEVE) products. After optimizing copolymerization conditions, monomer reactivity ratios were estimated using various linear graphical methods, as well as the COPOINT program, which was applied in the framework of the terminal model. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the monomers' mean sequence lengths. Thermal properties of the copolymers were studied by Differential Scanning Calorimetry (DSC) and kinetics of their thermal degradation by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), applying the isoconversional methodologies of Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS).

Thermal Decomposition of Synthetic Cage Hydrocarbons and Their Mixtures

The kinetics of thermal decomposition of cage hydrocarbons, specifically exo-tricyclo[5.2.1.02.6]decane (exo-TCD) and exo,endo-tetracyclo[5.3.1.02,6.08,10]undecane (TCU-1, a monocyclo­propanated analog of exo-TCD), as well as their mixture (1 : 3 w/w) has been investigated. These compounds were compared in terms of thermal stability. The molar concentrations of the resultant gaseous products were determined experimentally. The equilibrium composition of the decomposition products was quantified, and the thermal effects of the thermal decomposition under thermodynamic and kinetic reaction control were identified.

Analysis on the thermal decomposition kinetics and storage period of biomass-based lycorine galanthamine.

As global ageing deepens and galanthamine is the preferred clinical drug for the treatment of mild to moderate Alzheimer's disease, it will be valuable to examine the behaviour and mechanism of galanthamine's thermal decomposition for its quality control, formulation process, evaluation of thermal stability, and expiry date in production. In order to study the pyrolysis of galanthamine hydrobromide with nitrogen as the carrier gas, a thermogravimetric-differential thermogravimetric technique (TG-DTG) was applied at a temperature rise rate of 10Kmin-1 and a volume flow rate of 35mLmin-1. The apparent activation energy E a and the prefactor A (E a = 224.45kJmol-1 and lnA = 47.40) of the thermal decomposition reaction of galanthamine hydrobromide were calculated according to the multiple heating rate method (Kissinger and Ozawa) and the single heating rate method (Coats-Redfern and Achar), and the most probable mechanism function was derived, and then the storage period was inferred from E a and E. A three-dimensional diffusion mechanism was suggested to control the thermal decomposition of galanthamine hydrobromide in accordance with the Jander equation, random nucleation and subsequent growth control, corresponding to the Mample one-way rule and the Avrami-Erofeev equation. As a result, the thermal decomposition temperature of galanthamine hydrobromide gradually increased with the rate of temperature rise. From Gaussian simulations and thermogravimetric data, galanthamine hydrobromide decomposed at the first stage (518.25-560.75K) to release H2O, at the second stage (563.25-650.75K) to generate CO, CO2, NH3 and other gases, and finally at the third stage (653.25-843.25K) to release CO2. After 843.25K, the residual molecular skeleton is cleaved to release CO2 and H2O. According to the E a and A presenting in the first stage of thermal decomposition, it is assumed that the storage life of galanthamine hydrobromide at room temperature 298.15K is 4-5years.

Study on the thermal stability and combustion performance of polyurethane foams modified with manganese phytate

Abstract A new environmental friendly flame retardant manganese phytate (MnPa) was prepared by a direct precipitation method and the polyurethane foam (PUF) modified with MnPa was obtained by a one-step all-water foaming method. The thermal stability and combustion performance of the MnPa-modified PUF (MnPUF) were investigated by using thermogravimetric (TG), thermal decomposition kinetics, smoke density characterization, limiting oxygen index (LOI) and UL-94 horizontal combustion test. The results indicated that the addition of MnPa significantly improved the thermal stability and combustion performance of the modified PUF. On the basis of the thermogravimetric analysis, Flynn-Wall-Ozawa method, Kissinger method and Coats Redfern method, it could be concluded that PUF with 7.5 wt% MnPa (MnPUF3) had the highest activation energy and the best thermal stability. Smoke density analysis, LOI and horizontal combustion analysis also showed that the addition of MnPa was positively correlated with smoke suppression, LOI value and burning time. The current research results can provide a reference for the subsequent flame retardant modification of PUF.