Average Value Of Activation Energy Research Articles

Dynamic strain aging and recrystallization mechanisms in laser powder bed melt printing of highly textured Hastelloy X

Hastelloy X (HX) is used in a wide range of aerospace applications due to its excellent high-temperature properties, Dynamic strain aging (DSA) and Dynamic recrystallization (DRX) are of great interest as they affect the mechanical behavior at high temperatures. In this study, the serrated flow behavior of highly textured Hastelloy X fabricated by laser powder bed fusion (LPBF) is investigated during uniaxial straining over a wide range of temperatures (20–800 °C) and strain rates (5×10−2 s−1 to 5×10−4 s−1). The alloy exhibits different types of tensile serrated flow in the temperature range of 200–600 °C. The alloy has been shown to have a very good tensile flow behavior. The presence of the Portevin-Le Chatelier effect (PLC) due to dynamic strain failure was observed at temperatures lower than 600 °C, respectively, with an average activation energy value of 45 kJ/mol calculated using the quasi-static aging (McCormick) model, and an average activation energy value calculated using the solute resistance (Cottrell) model of 41.8 kJ/mol, which is significantly lower than the 80–130 kJ/mol of conventionally fabricated HX. The effects of temperature and strain rate on fracture morphology and microstructure were analyzed by SEM, and the dynamic recrystallization behavior and nucleation mechanism were characterized by electron backscatter diffraction (EBSD). The changes in the content of recrystallized texture Cube and deformed texture Goss at different deformation temperatures are explained, and the dynamic recrystallization mode changes, from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX) as the deformation temperature increase. Verification of the different DRX mechanisms contributes to a comprehensive understanding of the microstructural evolution of the hot deformation of HX fabricated by LPBF.

Optimization and prediction of thermodynamic parameters in co-pyrolysis of banana peel and waste plastics using AIC model and ANN modeling

The optimization and prediction of thermodynamic parameters including synergistic effects, and kinetic analysis in co-pyrolysis of banana peel (BP) and waste polystyrene (PS) plastic at different heating rates using ANN and AIC models has been performed. Thermogravimetric analysis was performed to determine the initial, maximum, and final degradation temperatures. The synergistic effect was studied using additive formula to determine the theoretical thermal behavior and compared with experimental TGA data. Kinetic parameters were determined by using the advanced isoconversional (AIC) model for estimation of activation energy (Eα), Criado master plot for reaction mechanism (f(α)), and compensation method for frequency factor (Aα). The analysis showed that the average activation energy values were 182.5, 140.6, and 161.8 kJ mol−1 for PS, BP, and PS+BP, respectively. It also clearly shows positive synergy in co-pyrolysis of PS and BP by reducing 11.3 % activation energy compared to that of PS alone. The frequency factor was found to be 1.0 × 1014, 1.0 × 1015, and 1.0 × 1023 s−1 for PS, BP, and PS+BP, respectively. The reaction mechanism was identified as R3, D4, and D4+R3 for PS, BP, and PS+BP, respectively. Further, the obtained kinetic parameters were used to determine the thermodynamic parameters such as enthalpy (ΔH), Gibbs energy (ΔG), and Entropy (ΔS). Finally, ANN was designed to address the co-pyrolysis behavior subjected to various heating rates. Subsequently, the trained ANN model (5 × 4×4 × 4) was employed to forecast thermal degradation behavior. Impressively, the model yielded highly accurate results with a correlation coefficient R2 > 0.998 in each case. The optimized model was further used to predict TGA data and activation energy for unknown mixtures of PS and BP. The suggested ANN model showed a great advantage in optimizing to avoid extensive experiments at various heating rates to achieve the goal.

Non-isothermal kinetics of the organocatalytic ring-opening polymerization of ε-caprolactone with metal-free α‑hydroxy acids: Eco-friendly and facile synthesis process

Metal-free and green α‑hydroxy acids (AHA) such as l-malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The performance of AHAs in the polymerization of ε-CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε-CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε-CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (Ea) values for the ROP of ε-CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (lnA0) for the ROP of ε-CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (Mn) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε-CL with MA and MDA initiators, and the Mn of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε-CL with all AHAs was proposed through the activated monomer mechanism.

Mesoporous Ag@WO3 core–shell, an investigation at different concentrated environment employing laser ablation in liquid

In this study, silver-tungsten oxide core–shell nanoparticles (Ag–WO3 NPs) were synthesized by pulsed laser ablation in liquid employing a (1.06 µm) Q-switched Nd:YAG laser, at different Ag colloidal concentration environment (different core concentration). The produced Ag–WO3 core–shell NPs were subjected to characterization using UV–visible spectrophotometry, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive spectroscopy, electrical analysis, and photoluminescence PL. The UV–visible spectra exhibited distinct absorption peaks at around 200 and 405 nm, which attributed to the occurrence of surface Plasmon resonance of Ag NPs and WO3 NPs, respectively. The absorbance values of the Ag–WO3 core–shell NPs increased as the core concentrations rose, while the band gap decreased by 2.73–2.5 eV, The (PL) results exhibited prominent peaks with a central wavelength of 456, 458, 458, 464, and 466 nm. Additionally, the PL intensity of the Ag–WO3-NP samples increased proportionally with the concentration of the core. Furthermore, the redshift seen at the peak of the PL emission band may be attributed to the quantum confinement effect. EDX analysis can verify the creation process of the Ag–WO3 core–shell nanostructure. XRD analysis confirms the presence of Ag and WO3 (NPs). The TEM images provided a good visualization of the core-spherical shell structure of the Ag–WO3 core–shell NPs. The average size of the particles ranged from 30.5 to 89 (nm). The electrical characteristics showed an increase in electrical conductivity from (5.89 × 10−4) (Ω cm)−1 to (9.91 × 10−4) (Ω cm)−1, with a drop in average activation energy values of (0.155 eV) and (0.084 eV) at a concentration of 1.6 μg/mL of silver.

Kinetics Study of PVA Polymer by Model-Free and Model-Fitting Methods Using TGA.

Thermogravimetric Analysis (TGA) serves a pivotal technique for evaluating the thermal behavior of Polyvinyl alcohol (PVA), a polymer extensively utilized in the production of fibers, films, and membranes. This paper targets the kinetics of PVA thermal degradation using high three heating rate range 20, 30, and 40 K min-1. The kinetic study was performed using six model-free methods: Freidman (FR), Flynn-Wall-Qzawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK), Kissinger (K), and Vyazovkin (VY) for the determination of the activation energy (Ea). TGA showed two reaction stages: the main one at 550-750 K and the second with 700-810 K. But only the first step has been considered in calculating Ea. The average activation energy values for the conversion range (0.1-0.7) are between minimum 104 kJ mol-1 by VY to maximum 199 kJ mol-1 by FR. Model-fitting has been applied by combing Coats-Redfern (CR) with the master plot (Criado's) to identify the most convenient reaction mechanism. Ea values gained by the above six models were very similar with the average value of (126 kJ mol-1) by CR. The reaction order models-Second order (F2) was recommended as the best mechanism reaction for PVA pyrolysis. Mechanisms were confirmed by the compensation effect. Finally, (∆H, ∆G, and ∆S) parameters were presented and proved that the reaction is endothermic.

AC conductivity and dielectric relaxation behavior of lamellar benzyltrimethylammonium/V2O5 nanocomposite

Lamellar benzyltrimethylammonium/V2O5 nanocomposite has been prepared hydrothermally. Electrical and dielectric properties as a function of temperature and frequency of the nanocomposite were reported. The decrease in Z′ with increasing temperatures indicates the existence of a negative temperature resistance coefficient (NTCR) characteristic of the semiconductor material. For T > 432 K, the values of the exponents decrease with increasing temperature indicating that the CBH model is the likely mechanism. When T < 432 K, the NSPT model is an adequate mechanism to characterize electrical conduction. Variation of log(σdc) versus 103/T reveals a rupture around 432 K and the average activation energy values are of the order of 0.240 and 0.085 eV. It has been found that the dielectric constant and the dielectric loss decrease when frequency increases which is explained by the hopping of electrons between V4+/V5+. Moreover, the presence of non-Debye type of relaxation was detected by the complex modulus analysis.

Study on non-isothermal pyrolysis of Azadirachta Indica for kinetic triplets and thermodynamics evaluation

Exploring kinetics and thermodynamics of biomass pyrolysis process is imperative for optimizing the process. This study employs various model-free iso‐conversional methods and a model-fitting method to investigate the kinetics and thermodynamics of non-isothermal pyrolysis of Azadirachta indica biomass under four distinct heating rates of 10, 20, 30 and 40 °C/min. Average values of activation energy and pre-exponential factor ranged from 187.613 to 196.635 kJ/mol and 5.068×1014 − 1.178×1022 min−1, respectively, indicating an endothermic and complex nature of reaction. Integral master plots proved superior in revealing the reaction mechanism, although Criado's master plot unveiled a combination of reaction models, aligning with the intricate degradation mechanisms of biopolymers. The average enthalpy change, Gibbs free energy change and entropy change values spanned from 182.425 to 191.638 kJ/mol, from 167.288 to 173.742 kJ/mol and from 0.014 to 0.039 kJ/mol·K, respectively.

Hot processing map and high temperature deformation behaviour of TB17 Ti alloy

The thermal compression experiments of TB17 titanium alloy under different thermal deformation process parameters were carried out using a thermal simulation compressor. The high-temperature plastic flow behaviour of the alloy was studied. It was found that with the decrease of the deforming temperature and the increase of the strain rate, the flow stress increased, and the discontinuous yield phenomenon occurred in hot deformation. The larger the strain rate, the more obvious the discontinuous yield phenomenon. The thermal activation energy Q decreased with the increase of strain, and the average value of activation energy Q is 209.54 KJ / mol. The constitutive equation of high-temperature plastic flow of TB17 titanium alloy was established. The predicted values of this equation are in good agreement with the experimental values. The average error is 3.987 %, and the correlation coefficient is 0.9972, which has high accuracy. Based on the Prasad criterion, the hot processing map of TB17 titanium alloy was constructed. It was found that the flow instability zone was mainly concentrated in the high strain rate region. The flow instability zone was determined to be 795 °C ~ 895 °C, 0.046s-1 ~ 1s-1, and the stable deformation zone was mainly located in the region with high temperature and low strain rate. The optimum processing parameter range is 860 °C ~ 895 °C, 0.001 s-1 ~ 0.025 s-1.

Effects of green and innovative pretreatment techniques on kinetic parameters of sunflower seed husk

The effects of green pretreatment processes, such as ultrasonic process (US) and deep eutectic solvent (DES), applied to the biomass on kinetic parameters are as important as their effects on characteristic properties. Process conditions and course of reaction progression depend on the knowledge about kinetic parameters, activation energy and reaction model of thermal degradation in scale-up studies. Therefore, in this study, the change in the kinetic parameters with US applied with both distilled water and DES (glycerol:sodium acetate) at 100 W power and 20 kHz frequency for 10 minutes to sunflower seed husk (SSH) was revelaed. Isoconversional methods Kissinger-Akahira-Sunose (KAS) and Flynn- Wall-Ozawa (FWO) were preferred for the evaluation of activation energy of SSH and pretreated SSH at 15°C/min, 20°C/min and 25°C/min heating rates. US pretreatment with DES instead of water resulted in increment of average activation energy values (Ea) from 113.13 to 143.65 kJ/mol in the KAS method. Ea values for all SSH samples changed in the range of 87.72-143.65 kJ/mol and higher Ea values was obtained with KAS method for pretreated SSH samples. Consequently, the use of DES in US pretreatment was more effective to change kinetic parameters of SSH compared to water.

Reutilization of Reclaimed Asphalt Binder via Co-Pyrolysis with Rice Husk: Thermal Degradation Behaviors and Kinetic Analysis.

Realizing the utilization of reclaimed asphalt binder (RAB) and rice husk (RH) to reduce environmental pollution and expand the reutilization technique of reclaimed asphalt pavement (RAP), co-pyrolysis of RAB with RH has great potential. In this study, the co-pyrolysis behaviors, gaseous products, and kinetics were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy (TG-FTIR). The results showed that incorporating RH into RAB improved its pyrolysis characteristics. The interactions between RAB and RH showed initial inhibition followed by subsequent promotion. The primary gaseous products formed during co-pyrolysis were aliphatic hydrocarbons, water, and carbon dioxide, along with smaller amounts of aldehydes and alcohols originating from RH pyrolysis. All average activation energy values for the blends, determined through iso-conversional methods, decreased with RH addition. The combined kinetic analysis revealed two distinct mechanisms: (1) at the lower conversion range, the pyrolysis of the blend followed a random nucleation and three-dimensional growth mechanism, while (2) at the higher conversion range, the control mechanism transitioned into three-dimensional diffusion.

A comprehensive pyrolysis study of sorghum and reed stalk: TG/IR/MS analysis and machine learning-assisted kinetic prediction

This work focused on investigating the pyrolysis characteristics of sorghum stalk (SS) and reed stalk (RS), whose potentiality as value-added feedstocks for thermochemical conversion is largely unexplored. The experimental method, thermogravimetric-infrared-mass spectrometry, was applied to reveal the thermal decomposition process, evaluate the kinetic and thermodynamic parameters, and identify the gaseous products, which could provide fundamental data and valuable information for bioenergy utilization and optimization of reactors. The average activation energy values of SS and RS by isoconversional methods are estimated to be 185.0–210.4 kJ/mol and 192.6–197.0 kJ/mol. Though kinetic parameters, especially activation energy values, play a crucial role in understanding reaction mechanism and guiding further applications, conventional methods are time-consuming and labor-intensive. In the current work, a gradient boosting regression tree model was successfully constructed to achieve fast prediction of activation energy values with a competitive accuracy of R2 > 0.85 without repetitive experiments. In addition, the established model has showed good generalization ability in new datasets, which reveals the great potential of the machine learning approach in the pyrolysis kinetic field.

Simulation of XRD data of Ba(NdxTi(1-2x)Nbx)O3 ceramics with cubic crystal structure and (Na0.5Bi0.5)(NdyTi(1-2y)Nby)O3 ceramics with rhombohedral crystal structure by modified Arrhenius and Lorentz equations

Ba(NdxTi(1-2x)Nbx)O3 (x = 0.025, 0.05, 0.1 & 0.2) and (Na0.5Bi0.5)(NdyTi(1-2y)Nby)O3 (y = 0.0125, 0.025 & 0.05) ceramics were prepared through solid state sintering route. In the present paper X-ray diffraction (XRD) data was obtained using (Philips X-pert Pro Pan Analytical: Model PW3040/60). The XRD data was simulated using modified Arrhenius and Lorentz equation using ORIGIN 6.1 software which was proposed by us earlier. In the case of Ba(NdxTi(1-2x)Nbx)O3 ceramics the values of lattice parameter obtained using modified Arrhenius and Lorentz equations are 3.9597 Ao, 4.2534 Ao, 5.2364 Ao & 5.2690 Ao for x = 0.025, 0.05, 0.1 & 0.2 respectively. The average values of activation energy for x-ray scattering are 74.47 meV, 85.21 meV, 90.20 meV & 95.79 meV for x = 0.025, 0.05, 0.1 & 0.2 respectively. Similar simulation studies were also carried on (Na0.5Bi0.5)(NdyTi(1-2y)Nby)O3 ceramics and the results are presented in this paper.

Thermal Degradation Kinetics of Vacuum Residues in the Presence of Chrysotile Supported Ni-Ti Catalyst

For the first time, thermal decomposition of vacuum residue and a mixture of vacuum residue with binary nanocatalysts based on leached and non-leached chrysotile with applied active metals was studied using the thermogravimetry method. It is shown that the thermokinetic parameters of decomposition of vacuum residue and its mixture with binary nanocatalyst are different. The phase composition of the binary nanocatalyst was established through X-ray phase analysis (XRD): (Mg3Si2O5 (OH), NiO and Ti (SO4)2). The quantitative content of elements on the chrysotile surface was determined using X-ray fluorescence analysis: (Ni (4.88%), Ti (7.29%), Si (24.93%), Mg (7.83%), Fe (0.69%) and S (3.89%)). Using atomic emission spectral analysis, the gross quantitative content of supported metals on chrysotile was determined: Ni (4.85%) and Ti (4.86%). A transmission electron microscope showed the presence of finely dispersed particles adsorbed on the surface of and possibly inside chrysotile nanotubes with sizes ranging from 5 to 70 nm. The acidity of the nanocatalyst obtained from the leached active-metal-supported chrysotile was 267 μmol/g and the specific surface area of the nanocatalyst was 54 m2/g. The Ozawa–Flynn–Wall (OFW) method was used to calculate the kinetic parameters of the thermal degradation of vacuum residue and the mixture of vacuum residue with nanocatalysts. Using the isoconversion method, the average values of activation energies and the pre-exponential factor were calculated: 147.55 kJ/mol and 3.37·1016 min−1 for the initial vacuum residue; 118.69 kJ/mol and 1.54·1018 min−1 for the mixture of vacuum residue with nanocatalyst obtained from non-leached chrysotile with applied metals; 82.83 kJ/mol and 2.15·1019 min−1 for the mixture of vacuum residue with nanocatalyst obtained from leached chrysotile with applied metals. The kinetic parameters obtained can be used in modeling and designing the processes of thermal degradation and hydroforming of heavy hydrocarbon raw materials.

Kinetics, thermodynamics, and thermal decomposition behavior of palm oil empty fruit bunch, coconut shell, bamboo, and cardboard pyrolysis: an integrated approach using Coats-Redfern method.

This study presents the kinetics and thermodynamics of biomass pyrolysis. The kinetics of the pyrolysis process was estimated using ten kinetic models from three different mechanisms, namely chemical reaction, diffusion, and nucleation and growth. Results showed that each pyrolysis subdivision was described by a different reaction model, signifying the complex nature of the pyrolysis process. The average values of activation energy determined from the kinetic models for empty fruit bunch, coconut shell, bamboo, and cardboard are 10.2-64.6 kJ/mol, 18.7-186.2 kJ/mol, 8.0-70.8 kJ/mol, and 13.1-277.3 kJ/mol, respectively. The biomass pyrolysis is endothermic and non-spontaneous and would require external energy to initiate the degradation process. The findings are helpful in characterizing the thermal degradation of biomass in exploring its potential as a source of alternative solid fuel.

A Comprehensive Review on the Thermal Stability Assessment of Polymers and Composites for Aeronautics and Space Applications.

This review article provides an exhaustive survey on experimental investigations regarding the thermal stability assessment of polymers and polymer-based composites intended for applications in the aeronautical and space fields. This review aims to: (1) come up with a systematic and critical overview of the state-of-the-art knowledge and research on the thermal stability of various polymers and composites, such as polyimides, epoxy composites, and carbon-filled composites; (2) identify the key factors, mechanisms, methods, and challenges that affect the thermal stability of polymers and composites, such as the temperature, radiation, oxygen, and degradation; (3) highlight the current and potential applications, benefits, limitations, and opportunities of polymers and composites with high thermal stability, such as thermal control, structural reinforcement, protection, and energy conversion; (4) give a glimpse of future research directions by providing indications for improving the thermal stability of polymers and composites, such as novel materials, hybrid composites, smart materials, and advanced processing methods. In this context, thermal analysis plays a crucial role in the development of polyimide-based materials for the radiation shielding of space solar cells or spacecraft components. The main strategies that have been explored to improve the processability, optical transparency, and radiation resistance of polyimide-based materials without compromising their thermal stability are highlighted. The combination of different types of polyimides, such as linear and hyperbranched, as well as the incorporation of bulky pendant groups, are reported as routes for improving the mechanical behavior and optical transparency while retaining the thermal stability and radiation shielding properties. Furthermore, the thermal stability of polymer/carbon nanocomposites is discussed with particular reference to the role of the filler in radiation monitoring systems and electromagnetic interference shielding in the space environment. Finally, the thermal stability of epoxy-based composites and how it is influenced by the type and content of epoxy resin, curing agent, degree of cross-linking, and the addition of fillers or modifiers are critically reviewed. Some studies have reported that incorporating mesoporous silica micro-filler or microencapsulated phase change materials (MPCM) into epoxy resin can enhance its thermal stability and mechanical properties. The mesoporous silica composite exhibited the highest glass transition temperature and activation energy for thermal degradation among all the epoxy-silica nano/micro-composites. Indeed, an average activation energy value of 148.86 kJ/mol was recorded for the thermal degradation of unfilled epoxy resin. The maximum activation energy range was instead recorded for composites loaded with mesoporous microsilica. The EMC-5p50 sample showed the highest mean value of 217.6 kJ/mol. This remarkable enhancement was ascribed to the polymer invading the silica pores and forging formidable interfacial bonds.

Non-isothermal pyrolysis of Polyalthia longifolia using thermogravimetric analyzer: Kinetics and thermodynamics

Non-isothermal thermogravimetric experiments were carried out at four different heating rates to investigate thermal decomposition of Polyalthia longifolia leaves, with primary goals of determining kinetic triplets (activation energy, frequency factor, and reaction mechanism) and thermodynamic parameters. Kinetics investigation was conducted by utilizing five iso-conversional approaches, viz., Starink (STK), Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), differential Friedman method (DFM), and distributed activation energy model (DAEM). Results indicated that average activation energy (Eα) ranged between 211.57 and 231 kJ/mol. Average values of activation energy obtained by KAS (211.57 kJ/mol) were found to be in the neighborhood of that obtained by other three integral methods, i.e., OFW (210.80 kJ/mol), STK (211.80 kJ/mol), and DAEM (211.57 kJ/mol). Criado's master plots approach revealed that experimental data matches with none of the reaction model until conversion of 0.4 and thereafter follows D3 for conversion of 0.5–0.7, whereas master plots based on the integral form of data disclosed that this method is not appropriate for pyrolysis of the present biomass sample. Finally, pyrolysis of P. longifolia biomass to produce bioenergy is found to be feasible (Eα − ΔH = ∼5–6 kJ/mol).

Characterization of Divalent Metal Soaps of Cannabis Sativa Seed Oil

In this study, the structural characteristics and thermal degradation behaviour of barium, calcium and zinc soaps of hemp seed oil prepared using the metathesis method are reported. Scanning electron micrographs of the metal soaps showed similar plate-like microstructures and are indicative of an orderly packed particulate structure. The bands at 1509, 1539 and 1543 cm-1 in the FTIR spectra showed the association of the carboxylate ion with Ba, Ca and Zn ions respectively The thermal decomposition consisted of one single step on the weight loss – temperature curves located around 250 – 450 oC for all the divalent metal soaps at the various heating rates and the observed loss in weight which occurred before 200 oC was minimal (&amp;lt; 10%). The average values of the apparent activation energy for the thermal process were 18.73, 13.77 and 8.48 kJ/mol for Zn-HSO, Ca-HSO and Ba-HSO respectively. 

Pyrolysis kinetics and thermal degradation characteristics of coffee, date seed, and prickly pear wastes and their blends

This study's objective was to emphasize the renewable lignocellulosic biomasses' energy potential by thermally describing them. The TG/DTG/DTA procedures were used to examine the thermal pyrolysis behavior of coffee wastes (CW), date seeds (DSM), prickly pears (PP), and two blends (50%CW/50%DSM and 33.3%CW/33.3%DSM/33.3%PP by weight), and their physico-chemical compositions were identified and assessed. The activation energy (E) of all tested samples was predicted using iso-conversional models like Friedman (FR), Starink (ST), Kissinger-Akahira-Sunose (KAS), and Ozawa-Flynn-Wall (OFW), and the frequency factor (A) was calculated based on the acquired (E) values utilizing the chemical reaction mechanisms (C1–C8). SEM, EDX, and FTIR techniques were used to examine the microstructure, mineralogy, and functional group present in the studied samples. Every DTG profile displayed a rightward shift when the heating rate (β) rose to higher temperatures. The difference in the average activation energy (Eav) values between the ST, OFW, and KAS models, except for the blend (1), does not surpass 5 kJ/mole. Increases in the (β) value, particularly for blends, were significantly correlated with increases in the maximum pyrolysis rate (−RP), pyrolysis index (CPI), pyrolysis stability index (RW), and volatile release index (Ddev). The ΔGav discrepancies between the results from all kinetic models for all samples varied from 1 to 7 kJ/mole. A little potential energy barrier was noticed when comparing the (Eav) to the average enthalpy (ΔHav).

Kinetics and thermodynamics of non‐isothermal pyrolysis of Terminalia chebula branches at different heating rates

AbstractNon‐isothermal thermogravimetric tests of Terminalia chebula (Helikha) were conducted under inert N2 gas environment for temperatures (25–900°C) at heating rates of 10, 20, 35, and 55°C min−1. Kinetic triplet approximated employing five iso‐conversional methods namely, differential Friedman method (DFM), distributed activation method (DAEM), Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Starink (STK). Average values of activation energy (kJ mol−1) and frequency factor (min−1) calculated by the five models were 227.11, 2.98 × 1021 for DFM; 229.21, 4.63 × 1021 for KAS; 227.11, 3.81 × 1020 for OFW; 225.54, 1.15 × 1018 for STK; and 227.33, 3.02 × 1020 for DAEM respectively over the conversion range up to 0.8. In the kinetics study, correlation coefficient (R2) of greater than 0.97 is noticed in the conversion range of α = 0.1–0.8 for all models. From thermodynamic analysis, average values of ΔH (kJ mol−1), ΔG (kJ mol−1), and ΔS (kJ mol−1 K−1) for DAEM: 221.8, 179.69, and 0.065; for DFM: 236.40, 179.37, and 0.089; for KAS: 221.8, 179.69, and 0.065; for OFW: 220.22, 179.72, and 0.063; and for STK: 222.02, 179.68, and 0.066 were estimated to assess viability and reactivity of the process. Criado's master plots revealed that the data obtained from pyrolysis of selected biomass was followed a multistep reaction pathway.

Research on crack mechanism and kinetic model of alumina ceramic in the degreasing stage based on stereolithography

AbstractGiven that the kinetics of the thermal degreasing process of alumina ceramics based on stereolithography apparatus (SLA) has not been investigated, the mechanism of crack generation is still not fully revealed. This paper aims to elucidate the mechanism of crack generation in the degreasing process of alumina ceramics and to establish a kinetic model for alumina ceramics. Two sintering atmospheres, air, and argon, were selected for the degreasing tests at 100°C–700°C. The reaction products and mass changes of alumina ceramics were analyzed by TG‐FTIR and TG‐DSC (heating rates of 5, 10, and 15°C/min, respectively). Meanwhile, Boswell, Friedman, Ozawa, and DAEM model was used to describe the nonisothermal kinetics of the SLA alumina ceramic degreasing process. The results showed that setting the holding time to 400°C–425°C could promote the slow release of heat from the alumina ceramics. The thermal degreasing stage of the ceramic generated fewer cracks in the argon atmosphere than in the air atmosphere. The corresponding average activation energy values were 105.40 kJ/mol (Boswell model), 112.48 kJ/mol (Friedman model), 108.14 kJ/mol (Ozawa model), and 101.36 kJ/mol (DAEM model). The results of the study could provide an invaluable reference for the fabrication of defect‐free SLA alumina ceramics.