Coats-Redfern Integral Method Research Articles

Non-isothermal decomposition kinetics of FeC2O4·2H2O prepared by solid-state method aiming at the formation of Fe2O3

The thermal decomposition of FeC2O4·2H2O prepared by solid-state method was investigated in air using TG-DTG/DSC. The precursor and its decomposition products formed at various temperatures were characterized by FT-IR and XRD. As evidenced by the results, the thermal decomposition proceeds in two steps with DSC peaks closely corresponding to the mass loss. The decomposition of FeC2O4·2H2O and the kinetic analysis of the second step were performed under non-isothermal conditions, and the activation energies were estimated by the Ozawa integral method and the Coats–Redfern integral method. In order to make the kinetic calculation much more accurate, the temperature was risen by variable acceleration in the different stages of the decomposition to help distinguish the two steps from each other, and this is an innovation point that is deserved to be mentioned in this study. After calculation and comparison, the decomposition conforms to the nucleation and growth model and the physical interpretation is summarized. The activation energy and kinetic mechanism function were determined to be 113.90 kJ mol−1 and G(α) = [−ln(1 − α)]2/3, respectively .

Study on the synergistic co-pyrolysis behaviors of mixed rice husk and two types of seaweed by a combined TG-FTIR technique

An investigation by TG-FTIR analysis was undertaken of the pyrolysis of five samples, three pure samples; Enteromorpha clathrata(EN), Sargassum fusiforme(SA) and rice husk(HU), and two blended 50/50 by weight of Enteromorpha clathrata with rice husk and Sargassum fusiforme with rice husk. The pyrolysis of each pure and each blended sample was divided into four stages; evaporation, depolymerization, devolatilization and carbonization. Differential calorimetry analysis showed that pyrolysis of the rice husk was mainly endothermic, pyrolysis of the blended seaweed and rice husk was exothermic and that the seaweed and rice husk were syergistic coupled during pyrolysis. Comparison of experimental data and theoretical data for calculated DTG curves in the pyrolysis of the blended sample of seaweed and rice husk showed that during the process of the main volatiles being precipitated, the thermal weight-loss rate was improved. The components of the blended sample pyrolised synergistically. The FTIR analysis of volatile gases in the pyrolysis process indicated that oxysulfide and nitrogen gases were released from Enteromorpha clathrata and Sargassum fusiforme, the main components in seaweed being protein and soluble polysaccharides. Due to the blending, some differences were found. The strength of CO and SO precipitation peaks were enhanced in the FTIR spectrum of the blend of EN and HU. However, the precipitated carbonyl peaks were weaked in the FTIR spectrum of the mixture of SA and HU. Kinetic analysis using the Coats-Redfern integral method showed that the pyrolysis activation energy in the blended sample was lower than in the seaweed biomass. Kinetic model functions for the blended samples at high temperature and at low temperature respectively, conformed to the second order rate equation and the Avrami–Erofeev (n=1) equation.

Effects of additives on carbon gasification

In this study, the effect of different additives on the kinetics of carbon gasification was studied by nonisothermal thermogravimetric analysis. The results showed that the carbon gasification comprised slow and fast gasification stages. Moreover, the carbon gasification was exothermic and endothermic in the low- and high-temperature regions, respectively. The nonisothermal kinetics of the carbon gasification was studied by the modified Coats-Redfern integration method. In the low-temperature region, the activation energy of the carbon gasification decreased by using B4C and SiO2 and increased by using MgO, Al2O3, and SiC. In the high-temperature region, B4C increased the activation energy, and Al2O3, MgO, SiC, and SiO2 decreased the activation energy.

Dielectric characteristics and thermal behaviour of terbium fumarate heptahydrate crystals

Dielectric properties, ac conductivity and thermal characteristics of terbium fumarate heptahydrate crystals grown by gel diffusion method have been carried out. The real part of dielectric constant, dielectric loss and ac conductivity of the material have been measured as a function of temperature and frequency of the applied electric field. Dielectric constant, dielectric loss and ac conductivity of the title compound were systematically investigated, showing a hump at about 85 °C, which could be attributed to water molecules in the crystal boundary. The dielectric anomaly exhibited by the material has been correlated with its thermal behaviour. The ac conductivity of the material obeys the Jonscher's power law relation; σ(ω) = σ o + Aω s , with the temperature dependent power exponent s < 1. The ac conductivity of the compound has been found to increase with the increase in frequency. The material is suggested to show protonic conduction. The non-isothermal kinetics was used to evaluate the activation energy for the dehydration step of thermal decomposition of terbium fumarate heptahydrate by using the Coats–Redfern integral method. • Terbium fumarate heptahydrate shows dielectric anomaly due to dehydration. • Dielectric dispersion obeys the well known Universal Power Law(Jonshers power law). • AC conductivity study shows that the material exhibits protonic conductivity.

Effect of Heating Rate on the Deinking Sludge Pyrolysis Character

In this paper, the thermogravimetic (TG) and differential thermogravimetric (DTG) curves of deinking sludge from Huatai Group Co., Ltd were derived from tests of thermal gravimetric analyzer (TGA). Pyrolysis character and kinetics of deinking sludge were investigated using thermalanalysis. The result showed that the pyrolysis process was composed of three stages: water lose stage, organic decomposition and decomposition of residues. The dynamical model of this pyrolysis process could be expressed by three first-order parallel reaction. The kinetic parameters of pyrolysis reaction were calculated respectively by Coats-Redfern integration method, the effect of heating rate on the deinking sludge pyrolysis characteristics was discussed.

Syntheses, structures and properties of three metal–organic complexes containing 2,2′-dipyridyl-5,5′-dicarboxylate ligands

Three new metal–organic complexes Cu[Hbpdc]2 (1), [Ni(bpdc)(H2O)]·H2O (2) and [Ni(H2bpdc)(H2O)2]SO4 (3) (H2bpdc=2,2′-bipyridyl-5,5′-dicarboxylic acid) have been hydrothermally prepared and structurally characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. 1 is a 3-D supramolecular architecture formed by hydrogen bonding interactions between carboxyl O atoms and strong face-to-face π⋯π stacking interactions between bipyridyl rings of Hbpdc− ligands, 2 exhibits an intriguing 2-D sheet constructed from [Ni(bpdc)(H2O)] units and 3 displays an infinite 1-D chain built by {[Ni(H2bpdc)(H2O)2]2+} fragments through SO42−. Moreover, thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of 3 have been conducted and the TG curve shows two-stage weight loss between 300 and 950K and the corresponding apparent activation energies are calculated by Ozawa–Flynn–Wall (OFW) method and Friedman method. The most probable kinetic model function of the dehydration reaction of 3 has been estimated by Coats–Redfern integral method and Achar–Bridly–Sharp differential method.

Pyrolysis characteristics of the mixture of printed circuit board scraps and coal powder

Thermogravimetric (TG) analysis and infrared spectroscopy were used to analyze the pyrolysis characteristics of printed circuit board scraps (PCBs), coal powder and their mixtures under nitrogen atmosphere. The experimental results show that there is a large difference between waste PCBs and coal powder in pyrolysis processing. The pyrolysis properties of the mixing samples are the result of interaction of the PCBs and coal powder, which is influenced by the content of mixture. The degree of pyrolysis and pyrolysis properties of the mixture are much better than that of the single component. The TG and the differential thermogravimetric (DTG) curves of the PCBs mixed with coal powder move towards the high-temperature zone with increasing amount of coal powder and subsequently the DTG peak also becomes wider. The Coats–Redfern integral method was used to determine the kinetic parameters of pyrolysis reaction mechanism with the different proportion of mixture. The gas of pyrolysis mainly composes of CO2, CO, H2O and some hydrocarbon. The bromide characteristic absorption peak has been detected obviously in the pyrolysis gas of PCBs. On the contrary, the absorption peak of the bromide is not obvious in pyrolysis gas of the PCBs samples adding 40% coal powder.

The study of thermal decomposition kinetics of zinc oxide formation from zinc oxalate dihydrate

This study is devoted to the thermal decomposition of ZnC2O4·2H2O, which was synthesized by solid-state reaction using C2H2O4·2H2O and Zn(CH3COO)2·2H2O as raw materials. The initial samples and the final solid thermal decomposition products were characterized by Fourier transform infrared and X-ray diffraction. The particle size of the products was observed by transmission electron microscopy. The thermal decomposition behavior was investigated by thermogravimetry, derivative thermogravimetric and differential thermal analysis. Experimental results show that the thermal decomposition reaction includes two stages: dehydration and decomposition, with nanostructured ZnO as the final solid product. The Ozawa integral method along with Coats–Redfern integral method was used to determine the kinetic model and kinetic parameters of the second thermal decomposition stage of ZnC2O4·2H2O. After calculation and comparison, the decomposition conforms to the nucleation and growth model and the physical interpretation is summarized. The activation energy and the kinetic mechanism function are determined to be 119.7 kJ mol−1 and G(α) = −ln(1 – α)1/2, respectively.

A study of combustion characteristics of pulverized coal in O2/H2O atmosphere

Oxy-steam combustion technology in which the mixtures of oxygen and steam are used as oxidizer instead of air is a new generation oxy-fuel combustion technology. The combustion characteristics of SH and PDS pulverized coal in O2/H2O mixtures are studied using non-isothermal thermogravimetric analysis technology in this paper. The effect of combustion atmosphere, oxygen concentration, heating rate and particle size on the combustion characteristics of SH and PDS pulverized coal in O2/H2O mixtures are analyzed based on the combustion profiles and kinetic analysis. The results show that replacing the inert N2 gas in the oxidizer with steam delayed the burning process of SH and PDS pulverized coal. With the increasing of the oxygen concentration, the ignition Ti and burnout temperature Th decrease and the comprehensive combustibility index S increases both in O2/H2O and O2/N2 atmosphere. In O2/H2O atmosphere, the combustion of SH and PDS coal occur in a higher temperature region as the heating rate increases, but the increase in heating rate can enhance the coal combustion property. As the particle size decreases, the maximum mass loss rate increases and the ignition and burnout temperature decrease. The results of kinetic analysis indicate that the combustion reactions of SH and PDS pulverized coal in O2/H2O mixtures follow the first-order kinetics through linear fitting of experimental data using Coats–Redfern integral method, and compensation effect exists between apparent activation energy and pre-exponential factor in different oxygen concentrations during coal combustion in O2/H2O mixtures.

Regeneration dynamics of potassium-based sediment sorbents for CO2 capture

Simulating regeneration tests of Potassium-Based sorbents that supported by Suzhou River Channel Sediment were carried out in order to obtain parameters of regeneration reaction. Potassium-based sediment sorbents have a better morphology with the surface area of 156.73 m2·g−1, the pore volume of 357.5×10−3 cm3·g−1 and the distribution of pore diameters about 2–20 nm. As a comparison, those of hexagonal potassium-based sorbents are only 2.83 m2g−1, 7.45×10−3 cm3g−1 and 1.72–5.4 nm, respectively. TGA analysis shows that the optimum final temperature of regeneration is 200 and the optimum loading is about 40%, with the best heating rate of 10 °C·min−1. By the modified Coats-Redfern integral method, the activation energy of 40% KHCO3 sorbents is 102.43 kJ·mol−1. The results obtained can be used as basic data for designing and operating CO2 capture process.

PLLA‐HA vs. PLGA‐HA characterization and comparative analysis

The chemical, thermal, thermo‐mechanical, and morphology properties of poly(L‐lactide) (PLLA) and poly(D,L Lactide‐co‐glycolide) (PLGA) composites with 30% hydroxyapatite (HA) were evaluated. The composites were prepared employing the solvent casting technique. The degradation kinetic parameters were obtained using the Coats–Redfern integral method for the reaction order and the E2 function methodology to calculate the activation energy (Ea). The addition of HA to these polymers matrices increased their glass transition temperature. This was confirmed by differential scanning calorimetery and dynamic–mechanical–thermal analysis. Also, the presence of HA increased the crystallization temperature of PLLA, implying a nucleation effect. The PLLA‐HA and PLGA‐HA composites exhibited better thermal stability, higher decomposition temperature, and higher activation energy for the decomposition process than the neat polymers. Morphology and dispersion of the filler are highly responsible for the thermal and mechanical properties of the composites, the PLGA‐HA composites showed a well dispersion but no improvement on storage modulus was found. On the other hand, the storage modulus (E′) of PLLA‐HA was enhanced, with respect to the neat polymer, mainly at temperatures above the glass transition. POLYM. COMPOS., 34:1433–1442, 2013. © 2013 Society of Plastics Engineers

Thermal stability, thermal decomposition and mechanism analysis of cycloaliphatic epoxy/4,4′-dihydroxydiphenylsulfone/aluminum complexes latent resin systems

The thermal stability of latent resin systems, cycloaliphatic epoxy/4,4′-dihydroxydiphenylsulfone/aluminum complexes, was investigated by dynamic differential scanning calorimetry (DSC) analysis. Experiments were conducted under non-isothermal condition in a nitrogen atmosphere at the heating rate of 10, 20, 30 and 40 °C/min, respectively. TG curves showed that, in the temperature range of 25 to 600 °C, the stability of the resin systems could be enhanced by increasing the length of the aliphatic chain in the initiator. Both the Kissinger method and the Ozawa-Flynn-Wall method were employed to calculate activation energies of the decomposition reaction, and the values obtained from the two methods were compared. Moreover, the corresponding reaction mechanism was identified by the Achar differential method and the Coats-Redfern integral method. The experimental results showed that these four methods were reliable and effective to study the kinetics of the thermal decomposition reaction; and the most probable thermal decomposition mechanism of the resin systems we proposed was found to comply with Mampel power law (m=1).

The kinetics model and pyrolysis behavior of the aqueous fraction of bio-oil

The pyrolysis behavior and kinetics of the aqueous fraction of bio-oil were studied through thermogravimetric (TG) analysis. Based on the experimental data, activation energies and kinetic parameters were calculated by the Achar differential method and the Coats–Redfern integral method, then the most probable mechanism functions and kinetics model were obtained at last. The results show that the pyrolysis of bio-oil aqueous fraction can be divided into three stages, that is, the volatilization of volatile fractions, the decomposition stage of heavy fractions and char combustion. The experimental results show that the activation energy of volatilization is higher than that of the decomposition stage. The first stage was expressed as the first order reaction and the second stage the second order reaction. The correlation coefficient between the two stages illustrates that the reactions are in well conformity with each other and the calculated value of conversion is consistent with the experimental results.

Synthesis, characterization and thermal decomposition kinetics as well as evaluation of luminescent properties of several 3D lanthanide coordination polymers as selective luminescent probes of metal ions

A series of 3D isomorphous and isostructural coordination polymers, namely, {[Ln4(PDA)6(H2O)6]·H2O}∞ (Ln=La, Nd, Sm and Gd; corresponding as-synthesized products are denoted as 1, 2, 3, and 4, respectively; PDA2−=pyridine-2,6-dicarboxylate anion), were synthesized under hydrothermal conditions and characterized by means of elemental analyses, infrared spectrometry, thermal analysis and single crystal X-ray diffraction. In the meantime, the thermal decomposition kinetics of the as-synthesized complexes was investigated under non-isothermal conditions using the Achar differential method and the Coats–Redfern integral method. The room-temperature luminescent properties of the metal-organic frameworks (MOFs) of the lanthanide coordination polymers were measured. It has been found that Ln(III) centers in the complexes adopt eight-coordinated and nine-coordinated modes with N1O7 and N2O7 donors to construct distorted triangular dodecahedral and tricapped trigonal prism configurations, respectively. Based on the building block of tetranuclear homometallic La4C4O8 unit (16-membered ring), lanthanide coordination polymers 1–4 are connected into highly ordered two-dimensional corrugated layers via O—C—O linkers and further assembled into 3D architectures through hydrogen bonds. Besides, lanthanide contraction effect exists in as-synthesized coordination polymers; and the lanthanide coordination polymers possess good selectivity toward metal ions such as Mg2+, Cu2+ and Pb2+, showing promising potential as selective luminescent probes of those metal ions.

Thermal degradation behaviour of some metal chelate polymer compounds with bis(bidentate) ligand by TG/DTG/DTA

Seven novel divalent transitional metal chelate polymers compounds (commonly known as chelate compounds or metal coordination complexes or polymer complexes) have been characterized by thermogravimetry (TG), differential thermal gravimetry (DTG) and differential thermal analysis (DTA) methods. Thermal decomposition behaviour of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) polymers with terphthaoyl-bis(p-methoxyphenylcarbamide) has been investigated by thermogravimetric analysis (TGA) at heating rate 10 °C min−1 under nitrogen atmosphere. TG/DTA of chelate compounds were shown to be a stable compound against thermal decomposition which was measured on the basis of final decomposing temperature, but it is observed in some curves that decomposition takes place at low temperature due to the lattice water, which is always placed at outer coordination sphere of the central metal ion. The presence of both lattice and coordinated water were noteworthy investigated in Co(II), Ni(II) and Cu(II) chelate polymer compounds, whereas lattice water found in Zn(II), Cd(II) and Hg(II). However, Mn(II) showed only coordinated water. Thermal stabilities for release of lattice water, coordinated water and organic moiety that occur in sequential decomposition of chelate compounds are explained on the basis of ionic size effect and electronegativity. The processes of thermal degradation taking place in seven chelate polymers were studied comparatively by TG/DTG/DTA curves which indicating the difference in the thermal decomposition. Coats–Redfern integral method is used to determine the kinetic parameters for the successive steps in the decomposition sequence of TG curves. Scanning electron microscope images of some chelate polymers were shown in previous publication revealed that particle sizes of chelate polymers were found to be of nanomaterial level therefore, resulting chelate compounds might be called as nanomaterial.

Thermal Analysis of Plastic Contained Decorative Materials under Different Oxygen Concentration

The combustion characteristics of decorative materials were studied by thermal analysis. The experiments were performed in three kind of oxygen concentration (7%, 14%, 21%), the heating rate were 15°C/min and 30°C/min respectively. The ignition point and maximum weight loss rated were analyzed. Based on the Coats-Redfern integral method, the results show that the combustion process were first order reaction.

Thermal decomposition kinetics of light-weight composite NaNH2–NaBH4 hydrogen storage materials for fuel cells

Pristine and Co–B doped NaNH2–NaBH4 (2/1 molar rate) hydrogen storage materials were synthesized via a ball milling method. The kinetic parameters, especially the activation energies were calculated by the Achar differential and the Coats–Redfern integral methods, based on the thermogravimetry curves of the decomposition processes of the hydrogen storage materials. The as-obtained activation energy for the pristine NaNH2–NaBH4 (2/1) is 159.6 kJ/mol, while that for the Co–B doped NaNH2–NaBH4 (2/1) is 70 kJ/mol, only 43.9% of the former, which indicates the Co–B catalyst can dramatically promote the hydrogen generation reaction. The structural evolution and the hydrogen releasing performance of the Co–B doped NaNH2–NaBH4 (2/1) were investigated by X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). Then, the catalytic mechanism of NaNH2–NaBH4 (2/1) decomposition promoted by Co–B was discussed and illustrated. It implies that the existence of Co–B catalyst can promote the loss of electron from H−, thus improve the kinetics and accelerate the formation of H2 upon heating.

Reaction Mechanism Study on Combustion of Micro Nanometer Iron Powder

Thermogravimetric curves of micro nanometer iron powder’s combustion were studied in different heating rates that were 10K/min, 20 K/min, 30 K/min and 40 K/min, and the particle sizes of iron were 100nm and 20μm. The iron’s kinetic parameters of combustion reaction were calculated by Coats-Redfern integral, differential and Kissinger methods, then the kinetic model was determined and the most probable mechanism function was verified by Popescu method. The results show that different heating rates, particle sizes and calculations can affect kinetic parameters and reaction mechanism. The activation energy of 100nm and 20μm iron powder’s combustion is 122.48 KJ/mol and 161.64 KJ/mol respectively. The combustion reaction of micro nanometer iron powder is controlled by random nucleation and subsequent growth model which is in agreement with Avrami-Erofeev equation. Rational control for the temperature and reaction time are conducive to optimize the combustion reaction of micro nanometer iron powder.

Effect of Heating Rate on the Municipal Sewage Sludge Pyrolysis Character

In this paper, the TG and DTG curve of sewage sludge from Xi’an Business Water Limited Corporation were derived from tests of thermogravimetric analyzer. Pyrolysis characteristics and kinetics of dried sludge were investigated using thermalanalysis. The result showed that there are three temperature ranges in which the sludge lost weight in the process of pyrogenation. Kinetic fitting equation of the second pyrolysis reaction stage were founded and the kinetic parameters of pyrolysis reaction were calculated respectively by Coats-Redfern integration method, and the effect of heating rate on the sludge pyrolysis characteristics was discussed.

Combustion of sewage sludge as alternative fuel for cement industry

The combustion of sewage sludge and coal was studied by thermogravimetric analysis. Both differential scanning calorimetric analysis and derivative thermogravimetric profiles showed differences between combustion of sewage sludge and coal, and non-isothermal kinetics analysis method was applied to evaluate the combustion process. Based on Coats-Redfern integral method, some reaction models were tested, the mechanism and kinetics of the combustion reaction were discussed. The results show that the combustion of sewage sludge is mainly in the low temperature stage, meanwhile the ignition temperature and Arrhenius activation energy are lower than that of coal. The combustion of sewage sludge has the advantage over coal in some aspects, thus sewage sludge can partly replace coal used as cement industry fuel.