Non-isothermal Analysis Method Research Articles

A Novel Low-Temperature Fluorination Roasting Mechanism Investigation of Regenerated Spent Anode Graphite via TG-IR Analysis and Kinetic Modeling.

Spent anode graphite, a hazardous solid waste discarded from the recovery of spent lithium-ion batteries (LIBs), had created social and environmental issues but has been scarcely investigated. Thus, a feasible, environmentally friendly, and economical process of low-temperature fluorination roasting and water leaching technology was proposed to regenerate spent graphite anodes. The results showed that the physical and chemical properties of regenerated graphite with a purity of 99.98% reached the graphite anode standard of LIBs and exhibited a stable specific capacity (340.9 mAh/g), capacity retention (68.92% after 470th cycles), and high initial Coulombic efficiency (92.13%), much better than that of waste carbon residue and similar to that of commercial graphite. Then the reaction mechanism and kinetic modeling of fluorination roasting of spent anode material was mainly explored by differential thermogravimetry and nonisothermal analysis methods. The results showed that the complexation and phase-transformation process of non-carbon valuable components in spent anode graphite occurred through three consecutive reactions in the 80–211 °C temperature intervals. The reaction mechanism of the whole process can be kinetically characterized by three successive reactions: third-order chemical reaction, Z-L-T eq, and second-order chemical reaction. Moreover, the thermodynamic functions of the fluorination roasting were calculated by the activated complex theory (transition state), which indicated the process was nonspontaneous. The mechanistic information was in good agreement with thermogravimetric-infrared spectroscopy (TG-IR), electron probe microanalysis, scanning electron microscopy, energy-dispersive spectrometry, and simulation experiments results.

Kinetics of oxidation roasting of molybdenite with different particle sizes

The kinetics of oxidation roasting of molybdenum concentrate was studied by differential thermal− gravimetric experiments and non-isothermal analysis methods. The results show that high temperature is beneficial for oxidation of molybdenum concentrate. The initial oxidation temperature of the molybdenum concentrate is 450 °C, and the rapid oxidation occurs above 500 °C. The oxidation process conforms to the unreacted shrinking nucleus model. The early stage of the oxidation is controlled by chemical reaction with the apparent activation energy of 123.180 kJ/mol, while the later stage is controlled by internal diffusion with the apparent activation energy of 80.175 kJ/mol. Moreover, the oxidation rate is closely related to particle size of the concentrate. The smaller the particle size is, the larger the oxidation rate is.

Crystallization Behavior and Optical Properties of Glass-Ceramics Containing Nano-Diopside Crystals

Diopside is a ceramic material with excellent properties including a low dielectric constant, high thermal conductivity, low sintering temperature below 1000 °C, and high mechanical strength. It has been applied to wireless and optical communications, substrates for touch panels, lenses for UV-LED, building materials, and so on. In this study, glass-ceramics containing nano-sized diopside crystals were fabricated, and their transmittance at visible light and photoluminescence were evaluated. In particular, TiO2 was added as a nucleating agent to suppress the surface crystallization phenomenon and Mn was used as a dopant to emit red light. The glass-ceramics were prepared by heat treatment at a temperature lower than the maximum crystal growth temperature (TP) calculated from the non-isothermal analysis method using differential thermal analysis (DTA) for the formation of nano-sized crystals. For glass containing 20 wt% of TiO2, the Avrami constant was calculated to be 2.23 and the activation energy required for crystal growth to be 549 kJ/mol, reflecting typical bulk crystallization behavior. Glass-ceramics with high light transmittance up to 70% were obtained by inducing the bulk crystallization behavior, and the diopside crystal size was less than 10 nm, which was equal to or higher than that of commercialized transparent glass-ceramic products. Glass-ceramic specimens doped with Mn showed luminescence of 736∼766 nm wavelength at excitation light of 365 nm wavelength. The emission peak intensity increased with the amount of dopant added, but gradually decreased with increasing crystallinity of the diopside phase.

Nanometer Scale Microstructure and Optical Properties of BaO-TiO₂-SiO₂ System-Based Glass-Ceramics.

The fresnoite phase, one of the crystals obtainable in the BaO-TiO₂-SiO₂ (BTS) system, is a material with excellent nonlinear optical properties. In this study, glass-ceramic containing nanometer scale fresnoite crystal was prepared by controlling the heat-treatment process from a BTS system, and its properties were analyzed. BTS glasses were prepared by conventional melting and quenching method. The heat treatment conditions were investigated by the non-isothermal analysis method using DTA. The formation of fresnoite crystals and the change of crystallinity according to heat treatment temperature were investigated by a XRD analysis. The glass-ceramics prepared in this study had fine crystal grains less than 100 nm in size and showed surface crystallization behavior growing from the surface to the inside. The transmittance of the prepared specimen in the range of visible light was measured up to 77%. The photoluminescence (PL) intensity of specimen was remarkably high at 470 nm and the emitted light has a blue and white light characteristic as displayed in the CIE coordinates.

The study of forms of bonding marshmallow moisture with different composition by method of thermal analysis

Marshmallow is a sugar confectionary product with increased sugar content and energy value because of the significant content of carbohydrates, in particular sugar-sand. The main drawback of marshmallow is the rapid process of its drying during storage due to the crystallization of sucrose and the gradual removal of moisture from the product. A method for obtaining marshmallow without sugar on the basis of high-conversion glucose syrup. In the work, experimental studies were carried out to determine the content and ratio of free and bound forms of moisture in marshmallow on the basis of sugars and on the basis of high-conversion glucose syrup by Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG). To study the patterns of thermal effects on the properties of marshmallow samples, the non-isothermal analysis method and the synchronous thermal analysis instrument (TG-DTA / DSC) of the STA 449 F3 Jupiter were used. In the process of thermal exposure, the samples decompose sugars and other organic compounds, as a result of which the sample weight decreases due to evaporation of moisture. The process of dehydration in a control sample of marshmallow using sugar occurs in a less wide temperature range than in a sample of marshmallow on the basis of high-conversion glucose syrup, which indicates a greater degree of moisture bonding in the developed sample. A quantitative evaluation of the forms of moisture bonding in the samples was carried out using the experimental curves obtained by the TG method. From the temperature curves, the endothermic effects were determined, which correspond to the release of moisture with different forms and energies. Substitution of sugar for treacle in the formula of marshmallow reduces the share of free moisture and increases the safety of the product without signs of staling.

Evaluation and modeling of thermal kinetic degradation for PVA doped PbS quantum dot

The kinetic analysis of the thermogravimetric curves for the thermal decomposition processes of PVA/PbS was performed. The samples were heated in nitrogen, with three different heating rates: 10, 20 and 30 °C min −1. Various forms of non-isothermal methods of analysis for determining the kinetic parameters were used. The differential and integral models were used to calculate the activation energies. Comparing with pure PVA, the results showed that the maximum activation energy of thermal degradation is achieved for PVA/PbS nanocomposite. Isoconversion model is used for predicting the thermal degradation acceleration. The results showed that the acceleration of thermal degradation for pure PVA was faster than PVA/PbS nanocomposite.

On the crystallization behavior of amorphous Fe–Cr–Mo–B–P–Si–C powder prepared by mechanical alloying

The crystallization behavior and thermal stability of Fe–Cr–Mo–B–P–Si–C amorphous alloy, prepared by mechanical alloying (MA), were investigated by using differential scanning calorimetry (DSC). One exothermic peak was observed on DSC traces, implying that the crystallization process undergoes only one stage. The crystallization kinetic parameters, including activation energy ( E a ), Avrami exponent ( n) were determined with non-isothermal analysis method based on the DSC data. The results suggest that the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth. In addition a relatively high value of activation energy of crystallization (386.04 ± 10 kJ/mol) was found, indicating that this amorphous alloy has high thermal stability.

Nanocrystallization of Cobalt Based Metallic Glass

Effect of copper addition in a Metallic glass 2714A on the nanocrystallization characteristics have been examined in this study. Amorphous ribbon of the alloy composition Co64.5 Fe3.5 Si16.5 B13.5 Ni1Cu1 were prepared by melt spinning technique. Nanocrystallization kinetics was studied using differential scanning calorimeter technique. The kinetic parameters such as activation energy and Avrami exponent were determined using two different non-isothermal analysis methods. The kinetic behavior of individual crystallization event has been rationalized on the basis of these results. The role of addition of copper on the crystallization behavior has been understood by comparing with Metallic glass 2714A. The isothermally annealed nanocrystallized microstructures were characterized by X-ray diffraction.

Crystallization Kinetics of Zr<sub>65</sub>Ni<sub>25</sub>Ti<sub>10</sub> Metallic Glass Alloy

The crystallization reaction of Zr65Ni25Ti10 (at. %) metallic glass was studied by using differential scanning calorimetry (DSC) at constant heating rate. Two distinct exothermic peaks were observed from the continuous heating DSC curves, implying the crystallization process undergoes two different stages. The crystallization kinetic parameters, including activation energy (E), Avrami exponent (n) and frequency factor (K0), were determined with non-isothermal analysis method based on the DSC data. The values of E are 267.353 KJ/mol and 224.293 KJ/mol, n 4.0±0.1 and 6.8±0.1, K0 4.4±0.05E+20 and 2.0±0.08E+15, for the first and second crystallization stage, respectively. The results suggest that the crystallization mechanism is governed dominantly by interface controlled growth with constant nucleation rate for the first crystallization stage and with increasing nucleation rate for the second stage.

Nonisothermal reaction kinetics and preparation of ferroelectric strontium bismuth niobate with a layered perovskite structure

Ferroelectric layered perovskite SrBi2Nb2O9 has been successfully prepared through a new process using BiNbO4 as a precursor. The SrBi2Nb2O9 formation mechanism was investigated using a nonisothermal analysis method at constant heating rates. The weight loss recorded in thermal analysis under different heating rates was analogized to the reaction conversion. A combination of the differential and integral methods was introduced to solve the reaction mechanisms. Analysis using the differential method revealed that two kinds of diffusion-controlled models have higher linear correlation coefficients than other models. Based on the integral method principle, a new integral equation combining the Arrhenius equation and the Lobatto approximation was derived in this study. The established equation significantly simplified the conventional calculation process and improved the accuracy for predicting the reaction models. Analysis using the integral method corroborated that the SrBi2Nb2O9 formation mechanism is governed by Jander's diffusion controlled model, and the activation energy was calculated to be 192.1 kJ/mol. The proposed methods and the derived equations can be further applied to other solid-state-reaction systems to elucidate their reaction kinetics and estimate the related kinetic parameters.

Kinetic of thermal decomposition of residues from different kinds of composting

Non-isothermal kinetic parameters regarding to the thermal decomposition of the ligninocellulosic fraction present in compost from urban solid residues (USR) obtained through stack covered (SC) with composted material, comes from the usine in composing of Araraquara city, Săo Paulo state, Brazil, and from stack containing academic restaurant organic solid residues (SAR). The samples were periodically revolved round 132 days of composting. Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the lignocellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated during that process. The lignocellulosic fraction decomposition, between 200 and 400°C, were kinetically evaluated through non-isothermal methods of analysis. By using the Flynn-Wall and Ozawa isoconversional method, the medium activation energy, Ea, and pre-exponential factor, lgA, were 283.0±14.6, 257.6±1.3 kJ mol-1 and 25.4±0.8, 23.2±0.2 min-1, to the SC and SAR, respectively, at 95% confidence level. From Ea and lgA values and DSC curves, Malek procedure could be applied, suggesting that the SB (Sestak-Berggren) kinetic model is suitable for the first thermal decomposition step.

COMPOSTING OF URBAN SOLID RESIDUES (USR) BY DIFFERENT DISPOSITIONS Kinetics of thermal decomposition

The thermal behavior and non-isothermal kinetics of thermal decomposition of three different kinds of composting of the USR like: stack with drilled PVC tubes (ST), revolved stack (SR) and stack with material of structure (SM), from the usine of composing of Araraquara city, Săo Paulo state, Brazil, within a period of 132 days of composting were studied. Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the cellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated from that process. Due to that behavior, the cellulosic fraction decomposition could be kinetically evaluated through non-isothermal methods of analysis. The values obtained were: average activation energy, Ea=248, 257 and 259 kJ mol-1 and pre- exponential factor, logA=21.4, 22.5, 22.7 min-1, to the ST, SR and SM, respectively. From Ea and logA values and DSC curves, Malek procedure could be applied, suggesting that the SB (Sestak-Berggren) kinetic model is the appropriated one to the first thermal decomposition step.

A study on the kinetics of thermal decomposition of polyaniline

The kinetic analysis of the thermogravimetric curves for the thermal decomposition processes of polyaniline in undoped and doped state (udpan and dpan) was performed. Various forms of non-isothermal methods of analysis for determining the kinetic parameters were used. The results show that the apparent activation energies for both udpan and dpan in static air are 126.5 and 78.5 kJ mol −1, and those in N 2 are 45.2 and 36.6 kJ mol −1, respectively. The mean reaction orders obtained from integral method for udpan and dpan in static air are 2.1 and 2.0, and those in N 2 are 1.9 and 2.1, respectively. Therefore the reaction function f( α) = (1 − α) 2 for the thermal decomposition of both udpan and dpan is reasonable. The thermal decomposition processes for udpan and dpan in N 2 may be a random degradation of polymer chain, whereas in air it should be an oxidation degradation involving the participation of oxygen. Thus the maximum of reaction rate in nitrogen is only 20–26% of those in air and the apparent activation energies for them are only 1/2–1/3 of those in air. But the temperatures corresponding to the maximum reaction rate are higher by about 230–320 K than those in air.

Thermal and structural studies of amide complexes of transition metal(II) chlorides. II: Kinetics

The possibility of correlating the kinetic parameters for the thermal decompositions of a series of NiLCl 2 complexes, where L= N-methylformamide ( nmf), N-methylacetamide ( nma) or acetamide ( aa), with the nature (steric and electronic effects) of the coordinated ligands and the strengths of the metal–ligand bonds has been explored. The rates of removal of L in single endothermic processes were measured using isothermal TG in nitrogen. Plots of α against time are deceleratory and are best described by either the R2 or R3 expressions. An empirical (B2) expression: v r=1−( kt) b , was introduced to give the best description of the results for the Ni( nma)Cl 2 complex. Comparable E a values were obtained using various isothermal and non-isothermal methods of analysis. E a values for the NiLCl 2 system (calculated using the R3 model) generally increased with an increase in basicity of the amide ligand: N- methylformamide∼acetamide<N- methylacetamide E a values were found to be lower than the corresponding decomposition enthalpies (Δ H L), indicating that cleavage of the nickel–amide bond could be the rate-controlling event. The order of E a values was found not to coincide with that of the Δ H L values. Extrapolated onset temperatures ( T e) and temperatures at maximum decomposition rate ( T max) were determined from TG and DSC curves. No simple correlation was found between E a, Δ H L, T e or T max and the spectral properties of the complexes.

The oxidation kinetics of FeV 2O 4 in the range 200–500°C

The oxidation kinetics of FeV 2O 4 were studied using isothermal and non-isothermal methods of analysis. The isothermal experimental data are described in terms of the Jander equation with E a = 141 kJ mol −1. The non-isothermal analysis showed that the kinetics can be described in terms of three different overlapping processes. The first process, oxidation of the spinel to give a solid solution, is described in terms of a first-order nucleation mechanism, E a = 61 kJ mol −1, and take place in the temperature range 180–380°C. The second process, the oxidation of the solid solution, takes place from ≈ 360°C and is described by a diffusion mechanism with E a = 249 kJ mol −1. The third process, oxidation of the remaining spinel, is described by a first-order nucleation model with E a = 345 kJ mol −1 and overlap with the second process. The reaction is completed at ≈ 580°C.

The application of non-isothermal methods of kinetic analysis to the decomposition of calcium hydroxide

In this paper, the kinetic analysis of the thermogravimetric curves for the decomposition process of calcium hydroxide (under dry nitrogen atmosphere) is performed. Various forms of non-isothermal methods of analysis for determining the kinetic parameters are used. The calcium hydroxide samples were a commercial sample and samples prepared by reacting calcium nitrate with sodium hydroxide solutions at concentrations of 1 and 0.1 M. All the methods show that in the heating rate ranges 5–40°Cmin −1, the most probable reaction mechanism for commercial calcium hydroxide is the Avrami-Erofeev equation (A) with n = 1.5 (i.e. A1.5), for calcium hydroxide prepared from 1 M solutions is A2 and for calcium hydroxide prepared from 0.1 M solutions is A1.5. The data also show that the distribution of particles and the change of the particle size are factors which affect the reaction mechanism.

Thermal analysis of non-isothermal crystallization kinetics in glass forming liquids

A brief review is given of previously suggested methods for analysis of experimental data of non-isothermal crystallization kinetics based on the Johnson-Mehl-Avrami transformation rate equation. Conditions for applicability are outlined and an estimate of error is made. A method of non-isothermal analysis is presented which facilitates rapid data evaluation over large temperature ranges and which justifies the previous applications in the literature of Kissinger's method to the analysis of crystallizations kinetics. An extension of these methods is made to the case of growth rates which obey a Vogel-Further temperature relation.