Probable Mechanism Function Research Articles

The kinetics research of thermochemical energy storage system Ca(OH)2/CaO

Summary As one of the most promising thermochemical energy storage medium, research on the Ca(OH)2/CaO system provides an important way of understanding energy storage/release rates of the entire energy storage system. In this paper, a high-precision thermogravimetric analysis is adopted to investigate thermal decomposition processes of the Ca(OH)2 samples in pure N2 atmosphere at different heating rates. The results demonstrate that during the thermal decomposition process, two weight loss processes respectively occur during 623.15 ~ 773.15 and 873.15 ~ 973.15 K, and the weight loss rates are close to 21% and 2% severally. Multi-heating rate methods are applied to the study of thermal decomposition dynamics. Findings show that the obtained kinetic parameters are related to reaction conversion, heating rate, and the chosen model-methods. To further understand the decomposition mechanism of Ca(OH)2, differential method, integral method, and multiple scanning method are used to deal with the experimental data. Through the most probable mechanism function analysis, under certain experimental conditions, thermal decomposition kinetics model of Ca(OH)2 accords well with the shrinking cylinder mechanism. These conclusions provide theoretical bases for applying the Ca(OH)2/CaO system to the thermochemical energy storage field. Copyright © 2016 John Wiley & Sons, Ltd.

Solid-State Thermal Reaction of a Molecular Material and Solventless Synthesis of Iron Oxide

Solid-state thermal decomposition reaction of a molecular material $$\{\hbox {As}(\hbox {C}_{6}\hbox {H}_{5})_{4}[\hbox {Fe}^{\mathrm{II}}\hbox {Fe}^{\mathrm{III}} (\hbox {C}_{2}\hbox {O}_{4})_{3}]\}_{\mathrm{n}}$$ has been studied using non-isothermal thermogravimetry (TG) in an inert atmosphere. By analyzing the TG data collected at multiple heating rates in 300 K–1300 K range, the kinetic parameters (activation energy, most probable reaction mechanism function and frequency factor) are determined using different multi-heating rate analysis programs. Activation energy and the frequency factor are found to be strongly dependent on the extent of decomposition. The decomposed material has been characterized to be hematite using physical techniques (FT-IR and powder XRD). Particle morphology has been checked by TEM. A solid-state reaction pathway leading the molecular precursor to hematite has been proposed illustrating an example of solventless synthesis of iron oxides utilizing thermal decomposition as a technique using innocuous materials.

Research on the Thermal Decomposition Reaction Kinetics and Mechanism of Pyridinol-Blocked Isophorone Diisocyanate.

A series of pyridinol-blocked isophorone isocyanates, based on pyridinol including 2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine, was synthesized and characterized by 1H-NMR, 13C-NMR, and FTIR spectra. The deblocking temperature of blocked isocyanates was established by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and the CO2 evaluation method. The deblocking studies revealed that the deblocking temperature was increased with pyridinol nucleophilicity in this order: 3-hydroxypyridine > 4-hydroxypyridine > 2-hydroxypyridine. The thermal decomposition reaction of 4-hydroxypyridine blocked isophorone diisocyanate was studied by thermo-gravimetric analysis. The Friedman–Reich–Levi (FRL) equation, Flynn–Wall–Ozawa (FWO) equation, and Crane equation were utilized to analyze the thermal decomposition reaction kinetics. The activation energy calculated by FRL method and FWO method was 134.6 kJ·mol−1 and 126.2 kJ·mol−1, respectively. The most probable mechanism function calculated by the FWO method was the Jander equation. The reaction order was not an integer because of the complicated reactions of isocyanate.

Thermal Dynamics and a Comparison of the Thermal Stability of Various Non-Wood Pulps

Specialty paper products made using natural pulps is an attractive field for the paper industry and for researchers. Studying the thermal dynamics of plant pulps is an important step toward improving the thermal stability of papers. This study has the aim of gaining detailed insight into the thermal properties of softwood, hardwood, flax, hemp, mulberry, bamboo, bagasse, and esparto pulps. Chemical composition and thermogravimetric analyses of these non-wood pulps were performed to find the correlations between the chemical, structural, and thermal properties of these pulps. In addition, the Malek model for kinetics of the thermo-decomposition process of pulps is proposed. The kinetics of the most probable mechanism function for G(α) = 1-(1-α) 1/2 of the thermo-decomposition process of plant fibers from 200 to 400 °C is deduced using the Malek model. This study also provides a method to help select the most promising pulps for specialty materials.

Thermal decomposition kinetics of polypropylene composites filled with graphene nanoplatelets

Three polypropylene (PP) composites filled separately with different sizes of graphene nano-platelets (GNPs) were prepared using a melt blending method. Thermal gravimetric analysis of the samples was conducted to investigate the effects of the GNP size on the thermal decomposition behavior. Some probable thermal decomposition mechanism parameters were determined through the Malek method, and then the most probable thermal decomposition mechanism functions of these composite systems were obtained using the Achar and Coats–Redfern methods. The thermal decomposition kinetics equation with integral form of the thermal degradation mechanism function for these composites was g(α)=1−(1−α)1/3. The thermal degradation mechanism was a phase boundary controlled reaction (contracting volume). The calculated activation energies of the three composites were, respectively, 277.4, 283.1 and 300.5 kJ/mol. This indicated that the GNPs could improve the activation energy of PP composites, and the activation energy increased with increasing the GNP lateral dimension. Moreover, the thermal decomposition was simulated by applying the thermal decomposition kinetics equation and the determined function parameters; good agreement was found between the simulations and the experimental values.

Maghemite nanosorbcats for methylene blue adsorption and subsequent catalytic thermo-oxidative decomposition: Computational modeling and thermodynamics studies

In this study methylene blue (MB) has been investigated for its adsorption and subsequent catalytic thermo-oxidative decomposition on surface of maghemite (γ-Fe2O3) nanoparticles. The experimental adsorption isotherm fit well to the Freundlich model, indicating multi-sites adsorption. Computational modeling of the interaction between the MB molecule and γ-Fe2O3 nanoparticle surface was carried out to get more insights into its adsorption behavior. Adsorption energies of MB molecules on the surface indicated that there are different adsorption sites on the surface of γ-Fe2O3 confirming the findings regarding the adsorption isotherm. The catalytic activity of the γ-Fe2O3 nanoparticles toward MB thermo-oxidative decomposition has been confirmed by subjecting the adsorbed MB to a thermo oxidation process up to 600°C in a thermogravimetric analyzer. The experimental results showed a catalytic activity for post adsorption oxidation. The oxidation kinetics were studied using the Ozawa–Flyn–Wall (OFW) corrected method. The most probable mechanism functions were fifth and third orders for virgin MB and MB adsorbed onto γ-Fe2O3 nanoparticles, respectively. Moreover, the results of thermodynamic transition state parameters, namely changes in Gibbs free energy of activation (ΔG‡), enthalpy of activation (ΔH‡), and entropy of activation (ΔS‡), emphasized the catalytic activity of γ-Fe2O3 nanoparticles toward MB oxidation.

The effect of particle size on the kinetics of thermal decomposition of Co(C2O4)·2H2O nanopowders under non-isothermal conditions

Cobalt oxalate dihydrate nanopowders have been prepared by precipitation method. The crystal size of Co(C2O4)·2H2O obtained in the absence and presence of CTAB surfactant was 30 and 60 nm, respectively. The effect of particle size on the thermal decomposition of Co(C2O4)·2H2O powders in air was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG). Non-isothermal studies revealed that the decomposition occurred in two main stages: removal of water and next decomposition of CoC2O4 to Co3O4. Both oxalate and the final decomposition residue were characterized by means of XRD, FT-IR and TEM techniques. The kinetic parameters of the two decomposition steps were evaluated from TG to DTG data by several integral and differential calculation methods. Based on the iterative isoconversional calculation procedure, the activation energy values Eit associated with the decomposition steps were evaluated. Kinetic parameters are given, and the most probable mechanism functions are suggested. The results show that the decomposition increases with decreasing the particle size.

Solid State Reaction Mechanisms of the LiMnPO4 Formation Using Special Function and Thermodynamic Studies

LiMnPO4 was successfully synthesized via thermal decomposition processes of the synthesized MnHPO4·3H2O precursor. Thermogravimetry/differential thermal gravimetry/differential thermal analysis, Fourier transform infrared, atomic absorption spectrophotometry, X-ray diffraction, and scanning electron microscopy techniques were employed for the characterization of the samples. Three thermal decomposition steps in the sequence of dehydration, polycondensation, and decarbonization were observed. The iterative Kissinger–Akahira–Sunose method was used to calculate the exact Eα values. Regions I and II of the first, second, and final steps were confirmed to be single-step kinetic processes with the unique kinetic triplets. The most probable mechanism functions were found to be R3, R2, A2, and P4 corresponding to contracting sphere, contracting cylinder, assumed random nucleation (its subsequent growth), and nucleation processes, respectively. The pre-exponential factors, A, were calculated using Eα and g(α). The...

Thermal decomposition kinetics of poly(3,3′-bisazidomethyl oxetane-3-azidomethyl-3′-methyl oxetane)

Poly(3,3′-bisazidomethyl oxetane-3-azidomethyl-3′-methyl oxetane) [P(BAMO/AMMO)] energetic thermoplastic elastomer (ETPE) is one of the most promising binders for the propellant and explosive formulations. It is synthesized with different content of hard segment and molar ratio of PBAMO and PAMMO. The results of mechanical test show that with higher content of hard segment and larger content of PBAMO, the ETPEs obtain higher tensile strength and lower breaking elongation. The thermal kinetics of the first decomposition stage of P(BAMO/AMMO) is investigated and the calculated apparent activation energy (E a) is about 169 kJ mol−1 by multi-heating rate method. In the single-heating rate study, f(α) = 1 − α is found to be the most probable mechanism function. Kinetic compensation effects are studied for the validation of the most probable mechanism function, and the results show that f(α) = 1 − α is quite suitable at a lower extent of conversion (α), but $$ f(\alpha ) = \frac{2}{3}\left( {1 - a} \right)\left[ { - { \ln }\left( {1 - a} \right)} \right]^{{ - \frac{1}{2}}} $$ is more fit when α is larger. P(BAMO/AMMO) ETPE was prepared, and the thermal decomposition kinetic of the first decomposition stage (mainly the thermal decomposition of –N3 group) was investigated. f(α) = 1 − α was a fitting mechanism function at a lower α, and $$ f(\alpha ) = \frac{2}{3}(1 - a)[ - \ln (1 - a)]^{{ - \frac{1}{2}}} $$ was more suitable when α was higher.

Studies of thermal decomposition kinetics and temperature dependence of thermodynamic functions of the new precursor LiNiPO4·3H2O for the synthesis of olivine LiNiPO4

The olivine LiNiPO4 was synthesized via the calcination of the new precursor LiNiPO4·3H2O at 600 °C. The precursor was obtained from low-temperature (50 °C) wet chemical reaction. The results from XRD, FTIR, AAS/AES and TG/DTG/DTA techniques confirmed the formula of the title compounds. The SEM results indicated the morphologies of the hydrate precursor as thin plate particles and the calcined product as small bead particles. The BET surface area of the final calcined product at 600 °C is much higher (5.807 m2 g−1) than that reported in the literature (0.25 m2 g−1). The kinetic triplet [activation energy, E, pre-exponential factor, A, and the most probable mechanism function, g(α)] and the thermodynamic functions of activated complexes (ΔS ≠, ΔH ≠ and ΔG ≠) for the dehydration step of LiNiPO4·3H2O were determined and discussed. The mechanism of the dehydration process is the single-step A3/2 (assumed random nucleation and its subsequent growth). New information, namely the isobaric molar heat capacity, experimental entropy, enthalpy and Gibbs energy changes as function of temperature (K) of LiNiPO4·3H2O and LiNiPO4, was evaluated from the DSC data by third-order polynomial fitting and reported for the first time. The calculated corresponding thermodynamic functions from kinetic parameters are compared and discussed.

Pyrolysis kinetics of tannin–phenol–formaldehyde resin by non-isothermal thermogravimetric analysis

The interest of using tannin–phenol–formaldehyde (TPF) resin as adhesive for industrial and building material application is growing fast. Because of copolymerization among tannin, phenol, and formaldehyde molecules, TPF resin has better thermal stability than phenolic resin. The goal of this paper is to investigate the thermal degradation behavior of TPF resin by thermogravimetric analysis and to summarize and verify the favorable pyrolysis kinetics model corresponding to bio-based phenolic resin. For this purpose, a comprehensive study was conducted to reveal the thermal behavior of TPF resin. Firstly, a model containing three pseudo-components was used to describe the overall pyrolysis process performed at three constant heating rates. Then, bi-Gauss method, an asymmetric multi-peak fitting function was applied to separate the overlapping peaks. Kinetic parameters and kinetic mechanism of each separated peak were determined by model-free isoconversional method and y(α) and z(α) master plots, respectively. Finally, the pyrolysis kinetics model was validated to prove its prediction ability. With results of the apparent activation energies, pre-exponential factors, and the most probable kinetic mechanism functions, the simulated data of reaction model agreed with experimental data well. Therefore, these procedures and results can help improve the industrial performance of TPF resin.

Kinetic analysis for spontaneous combustion of sulfurized rust in oil tanks

In order to evaluate the spontaneous combustion hazards of sulfurized rust in oil tanks, one kind of rust was obtained from respiratory valve inner cavity of a crude oil tank in a petrochemical company. The rust was sulfurized in sulfuration experimental apparatus. The production was analyzed by X-ray energy dispersive spectrometry (EDS), scanning electron microscopy (SEM) and then thermo-gravimetric analysis (TGA). The EDS result shows that the main substances are FeS and FeS2 which are liable to spontaneous combustion. The sulfurized rust gives a short length of side and diamond appearance, and a large pore size in structure based on X-ray Diffraction (XRD). The whole oxidation process has three complex stages. The corresponding apparent activation energy values, most probable mechanism functions and pre-exponential factor values were calculated by Madhusudanan–Krishnan–Ninan method and the master plot method. The results indicate that the first and third stages of mass loss are up to the power function mechanism, but the second stage accords with the nucleation and nucleus growth mechanism. The values of apparent activation energy increase successively from the first stage to the third stage. The second stage has the maximum pre-exponential factor value, while the first has the minimum. With the obtained parameters above, the oxidation process of sulfurised rust could be simulated, which would benefit for monitoring and early warning of oil tanks.

Pyrolytic and kinetic characteristics of Platycodon Grandiflorum peel and its cellulose extract

The pyrolytic and kinetic characteristics of a biomass waste material, namely Platycodon grandiflorum A. DC (P. G.) peel and its cellulose extract were studied at heating rates of 10, 30 and 50°C/min under a nitrogen flow atmosphere. The most probable mechanism function and activation energy pre-exponential factors were calculated by using the Popescu, FWO and KAS methods. The three stages appeared during pyrolysis include: moisture evaporation, primary devolatilization and residual decomposition. Significant differences in the average activation energy, thermal stability, final residuals and reaction rates of the P. G. peel and its cellulose extract were observed. Stage II of the P. G. peel and its cellulose extract could be described by the function Avrami–Erofeev [−ln(1−α)]3 and the function chemical reaction (1−α)−0.5, respectively. The average activation energy of P. G. peel and its cellulose extract were 157 and 196kJ/mol, respectively. Kinetic compensation effects of the pre-exponential factors and activation energy were also observed.

The Most Probable Mechanism Function of PVC Thermal Decomposition

The most probable mechanism function of non-isothermal kinetics about polyvinyl chloride thermal decomposition process was studied by the differential method (A-B-S)-integral method (C-R). The results show that the most probable mechanism function accorded with the mechanism function A1.5 when the heating rate of was 5 °C/min and the decomposition rate was 0.01-0.10.

Kinetics Study with Rigorous Nonlinear Methods for Thermal Decomposition of Polysaccharide Iron Complex

The advanced isoconversional and nonlinear model-fitting methods were used to calculate the activation energies of the thermal process of polysaccharide iron complex (PIC). The results of TG/TDG indicate that the processing temperature of the food should not exceed 223 °C when PIC is used as a food additive. The calculated results indicated the decomposition process involved two stages. The region I in stage II is a kinetically complex process, while stage I and region II of stage II are all single-step processes. The most probable mechanisms for stage I and region II of stage II are chemical reaction and contracting sphere. Meanwhile, the most probable mechanism functions for region I of stage II were determined by using nonlinear model-fitting method. The results of nonlinear model-fitting method showed the most probable mechanism of the parallel reactions for region I of stage II were nucleation and branching nuclei.

Thermolysis parameter and kinetic research in copolyamide 66 containing 2-carboxyethyl phenyl phosphinic acid

Polyamide 66 (PA66) containing phosphorus with flame-retardant property (FR-PA66) was synthesized with adipic acid hexamethylene salt and 2-carboxyethyl phenyl phosphinic acid as raw materials. The thermal degradation kinetics of FR-PA66 and PA66 were measured using a thermogravimetric analyzer, and the data obtained were analyzed with Flynn–Wall–Ozawa and Coast–Redfern methods. The results show that the activation energy ( Ea) of PA66 fabricated under different conditions will be different, while the mechanism functions of thermal decomposition remain the same. Comparing the limit Ea value of PA66 with FR-PA66 at different stages of thermolysis, FR-PA66 keeps the initial thermolysis Ea almost unchanged, reduces the middle thermolysis Ea to 139.1 kJ mol−1, and increases the last thermolysis Ea to 454 kJ mol−1, that is 223 kJ mol−1 higher than that of PA66 with 231 kJ mol−1. This result may be explained by the first cleavage of P–C bond and the formation of the carbonized protective layer. In addition, the most probable kinetic mechanism functions ( F( α)) of thermolysis of FR-PA66 in three different stages were when the rate of decomposition ( α) is lower than 0.4, F( α) = −ln(1 − α); when α is between 0.4 and 0.65, F( α) = [−ln(1 − α)]; and when α is beyond 0.65, F( α) = [−ln(1 − α)].

Synthesis, non-isothermal kinetic and thermodynamic studies of the formation of LiMnPO4 from NH4MnPO4·H2O precursor

NH4MnPO4·H2O was successfully synthesized by precipitating method. The LiMnPO4 was successfully generated through solid state reaction between synthesized NH4MnPO4·H2O precursor and Li2CO3. The morphologies were observed to depend on the reaction temperatures. The thermal decomposition of NH4MnPO4·H2O and the formation process of LiMnPO4 were confirmed by TG/DTG/DTA, FTIR, AAS/AES, XRD and SEM methods. The average crystallite size of NH4MnPO4·H2O, Mn2P2O7 and LiMnPO4 were found to be around 51.2, 44.9 and 48.1 nm, respectively. The non–isothermal kinetic parameters (kinetic triplet: Eα, A, g(α)) of the formation process of LiMnPO4 were evaluated from TG data by using Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose methods. The iterative methods of both equations were carried out to determine the exact values of Eα. The Coats–Redfern equation and kinetic compensation effects were successfully applied to confirm the activation energy and the most probable mechanism functions of the formation of LiMnPO4. The thermodynamic functions (ΔH≠, ΔS≠, ΔG≠) of the transition state complexes of the formation of LiMnPO4 were calculated from the kinetic parameters for the first time.

Estimation of the kinetic parameters for thermal decomposition of HNIW and its adiabatic time-to-explosion by Kooij formula

Abstract A differential/integral method to estimate the kinetic parameters (apparent activation energy Ea and pre-exponential factor A) for thermal decomposition reaction of energetic materials based on Kooij formula are applied to study the nonisothermal decomposition reaction kinetics of hexanitrohexaazaisowurtzitane (HNIW) by analyzing nonisothermal DSC curve data. The apparent activation energy (Ea) obtained by the integral isoconversional non-isothermal method based on Kooij formula is used to check the constancy and validity of apparent activation energy by the differential/integral method based on Kooij formula. The most probable mechanism function of thermal decomposition reaction of HNIW is determined by a logical choice method. The equations for calculating the critical temperatures of thermal explosion (Tb) and adiabatic time-to-explosion (tTIad) based on Kooij formula are used to calculate the values of Tb and tTIad to evaluate the thermal safety and heat-resistant ability of HNIW. All the original data needed for analyzing the kinetic parameters are from nonisothermal DSC curves. The results show that the kinetic model function in differential form and the values of Ea and A of decomposition reaction of HNIW are 3(1 − α)[−ln(1 − α)]2/3, 152.73 kJ mol−1 and 1011.97 s−1, respectively, and the values of self-accelerating decomposition temperature (TSADT), Tb and tTIad are 486.55 K, 493.11 K and 52.01 s, respectively.

Thermal kinetics and decomposition mechanism of 1-amino-1,2,3-triazolium nitrate

The thermal decomposition kinetics of 1-amino-1,2,3-triazolium nitrate(ATZ-NO3) was investigated by non-isothermal TG-DTG at various heating rates(2, 5, 10, 15 and 20 °C/min). The results show that the thermal decomposition of ATZ-NO3 consist of two stages corresponding to the losing of nitrate anion, substituent group and the splitting of triazole ring respectively. The kinetic triplets of the two stages were described by a three-step method. First, the differential Kissinger and intergral Ozawa methods were used to calculate the apparent activation energies(E) and pre-exponential factors(A) of the two decomposition stages. Second, two calculation methods(intergral Satava-Sestak and differential Achar methods) were used to obtain several probable decomposition mechanism functions. Third, three judgment methods(average, double-extrapolation and Popescu methods) were used to confirm the most probable decomposition mechanism functions. Both reaction models of the two stages were random-into-nucleation and random-growth mechanisms with n=3/2 for the first stage and n=1/3, m=3 for the second stage. The kinetic equations for the two decomposition stages of ATZ-NO3 may be expressed as \(\frac{{da}} {{dt}} = 10^{13.60} \times e^{ - \frac{{128970}} {{RT}}} (1 - a)\left[ { - \ln (1 - a)} \right]^{ - \frac{1} {2}}\) and \(\frac{{da}} {{dt}} = 10^{11.41} \times e^{ - \frac{{117370}} {{RT}}} (1 - a)\left[ { - \ln (1 - a)} \right]^{\frac{2} {3}}\). The thermodynamic parameters including Gibbs free energy of activation(ΔG ≠), entropy of activation(ΔS ≠) and enthalpy of activation(ΔH ≠), for the thermal decomposition reaction were also derived.

大型海藻绿潮浒苔的热解特性及其催化热解研究

以海洋生物质绿潮浒苔为研究对象，并以玉米秸秆(草类生物质)和锯末(木质类生物质)为对比研究对象，采用热重分析得到三种生物质的热解特性。研究结果表明，与玉米秸秆和锯末等典型陆生生物质相比，浒苔的热稳定性最低。采用Coats-Redfern法分别计算该三种生物质的动力学参数，并得到了较可能的几个反应机理函数以及各自活化能数值。并以碳酸钠作为催化剂，用热重分析法分析了三种生物质的热解过程以及催化剂在不同浓度下对其热解效果的影响。其结果表明，Na2CO3能显著降低三种生物质的初始热解温度和最大失重速率所对应的温度。从对初始热解温度和最大失重速率所对应温度的降低程度而言，Na2CO3对陆生生物质锯末和玉米秸秆的催化效果优于对海洋生物质浒苔的催化效果。Pyrolysis characteristics of Enteromorpha prolifera, cornstalk (grass biomass) and sawdust (woody biomass) were investigated with thermogravimetric analysis (TGA) method. The results showed that Enteromorpha prolifera has lower thermostability compared with cornstalk and sawdust. The kinetics parameters including activation energy and the most probable mechanism functions of the three biomasses were calculated by Coats-Redfren method. Moreover, using sodium carbonate as catalyst impregnated biomass, the pyrolysis process of the three kinds of biomass and the effect of the catalyst with different concentrations were studied with thermogravimetric analysis. The results show that sodium carbonate can decrease the initial decomposition temperature and the maximum weight loss temperature. It has a stronger catalytic effect on cornstalk and sawdust on Enteromorpha prolifera as far as the decrease extent of the temperature is concerned.