Thermal behaviour studies of procaine and benzocaine

The analysed substances, procaine and benzocaine, are two anaesthetic agents currently being administered in tablet form, also in the topical (cream, gel, balm) and injectable dosage forms. The TG/DTG/DTA curves were obtained in air at different heating rates. For determination of the heat effects, the DTA curves (in μV) were changed with the heat flow curves (in mW), so that the peak area corresponds to an energy in J g^?1 or kJ mol^?1. The non-isothermal experiments are preformed to investigate the thermal degradation process of these active substances, both as a solid and are performed in a dynamic atmosphere of air at different heating rates, by heating from room temperature to 500 °C. The kinetic analysis was performed using the TG data in air for the first step of substance’s decomposition at four heating rates: 7, 10, 12 and 15 °C min^?1. The data were processed according to an appropriate strategy to the following kinetic methods: Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman and NPK, to obtain realistic kinetic parameters, even if the decomposition process is a complex one. Thermal analysis was supplemented using Fourier Transform infrared spectroscopy coupled with the TG device to identify the anaesthetics with any products which may have formed (EGA—the evolved gas analysis).     

Characteristics of the thermal decomposition of antituberculous drugs

The thermal decomposition of antituberculous drugs-ethambutol (base and dihydrochloride), isoniazid, ethionamid and pyrazinamid has been studied by DTA, TG and DTG techniques. General remarks have been made on their thermal destruction. The effect of sample size over the range 20–200 mg and heating rate over the range 3–15 deg·min^?1 on the thermal degradation has also been investigated. Moreover, based on the Kissinger’s equation, the values of the kinetic parameters were determined.     

Thermal behaviour and kinetic study of some triazoles as potential anti-inflammatory agents

Thermogravimetric (TG), differential thermogravimetric analysis and differential scanning calorimetry had been used to characterize the thermal stability of four new heterocyclic compounds with triazolic structure. The four analysed compounds have similar thermal behaviours, namely the thermal mal curves of these new compounds show three thermal events. These compounds were thermally stable up to 110 °C. Above this temperature, the evolution of hydrochloric acid took place as observed by EGA. Identification and the monitoring of gaseous species released during thermal decomposition of pure triazoles in air atmosphere have been carried out by coupled TG–FTIR. Between 110 and 220 °C the main gaseous product is HCl which was identified on the basis of these FTIR spectra. Arguments for a rapid thermooxidation of the four molecules were brought by EGA by identifying the substances which arise from both the destruction of side chains and of triazolic ring. The kinetic analysis of the destruction process of triazolic structure was investigated using the TG data in air for the substance’s decomposition in non-isothermal conditions. The isoconversional methods, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman, were applied to determine the activation energy from the analysis of four curves measured at different heating rates. In order to obtain realistic kinetic parameters, even if the decomposition process is a complex one, the non-parametric kinetics method was also used. A good agreement between the data obtained from the four applied methods was found.     

Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min^?1 in 40 mL min^?1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.     

Thermal behavior and decomposition kinetics of composite solid propellants in the presence of amide burning rate suppressants

The employment of burning rate suppressants in the solid rocket propellant formulation is long known. Different research activities have been conducted to well understand the mechanism of suppression, but literature about the action of oxamide (OXA) and azodicarbonamide (ADA) on the thermal decomposition of composite propellant is still scarce. The focus of this study is on investigating the effect of burning rate suppressants on the thermal behavior and decomposition kinetics of composite solid propellants. Thermogravimetric analysis (TG) and differential thermal analysis have been used to identify the changes in the thermal and kinetic behaviors of coolant-based propellants. Two main decomposition stages were observed. It was found that OXA played an inhibition effect on both stages, whereas the ADA acts as a catalyst in the first stage and as coolant in the second one. The activation energy dependent on the conversion rate was estimated by two model-free integral methods: Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) based on the TG data obtained at different heating rates. The mechanism of action of coolants on the decomposition of solid propellants was confirmed by the kinetic investigation as well.     

Thermal degradation kinetics of semi-aromatic polyamide containing benzoxazole unit

The kinetics of the thermal degradation of a new semi-aromatic polyamide containing benzoxazole unit (BO6) have been investigated by thermogravimetric analysis (TG). Thermal degradation of BO6 could be accomplished by one step. The corresponding kinetic parameters of the degradation process are determined by using Kissinger and Flynn–Wall–Ozawa methods, respectively. Coats–Redfern method is also used to discuss the probable degradation mechanism of the BO6. The results show that the activation energy obtained from Kissinger method is in good agreement with the value obtained by using Flynn–Wall–Ozawa method. The solid-state degradation mechanism of the BO6 is a decelerated R ₁ type (phase boundary controlled reaction one-dimensional movement).     

Thermal analysis and kinetics of the copper-lead matte roasting process

In this paper, the results of copper-lead matte investigations are presented. Investigated copper-lead matte is intermediate product of the lead production in TREPCA-Zvečan. In the first part of the paper characterization of starting material is presented, consisting of: chemical composition analysis (XRQ), scanning electron microscopy (SEM) and diffractometry (XRD). Thermal properties of investigated matte were determined using differential thermal analysis (DTA) at characteristic temperatures. Using results of induced analysis, mechanism of matte oxidation process was determined. In the second part of the paper kinetic parameters describing oxidative roasting of copper-lead matte are presented. For activation energy calculations, non-isothermal methods defined by Kissinger and Ozawa were used [1, 2]. Kinetic equation describing oxidation process was determined using Sharps method of reduced half time of reaction [3].     

Thermal, phase transition, and thermal kinetics studies of carbamazepine

The thermal, phase transition of carbamazepine dihydrate and the solid-state transformation of carbamazepine from form III to form I were performed by Differential scanning calorimetry (DSC), Thermo gravimetry (TG–DTA), and X-ray powder diffraction.The non-thermal kinetic analysis of carbamazepine dihydrate and form III was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The model-free model, the Kissinger method, was used to give the Arrhenius parameters. Arrhenius plots from the kinetic model yielded activation energies corresponding to dehydration of dihydrate and melting of anhydrate CBZ form I were 95.28, 966.06 kJ mol^?1, the pre-exponential factors were 8.34E+11 and 1.41E+149, respectively. For the transformation of carbamazepine from form III to form I, activation energies corresponding to the melting of CBZ form III, recrystallization of form I, and melting of form I were 1160.81, 710.89, 1265.89 kJ mol^?1, the pre-exponential factors were 2.29E+144, 4.43E+91, and 1.61E+151, respectively. As a comparison, Ozawa method was used to verify the activation energy values obtained by Kissinger method. The result shows a close activation energy values between two methods.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Simulation of the thermal degradation and curing kinetics of fly ash reinforced diglycidyl ether bisphenol A composite

Thermogravimetric Analysis (TGA) is concluding expanding applicability in determination of the thermal stability and degradation nature of materials. The present study investigates the thermal degradation behavior and the kinetics of degradation of epoxy mixed with varying percentages of 0, 2.5, 5, and 7.5 ​wt% fly ash. Thermal stability and degradation behavior of fly ash modified epoxy cast were determined by thermogravimetric analysis. The kinetic parameters of the EF composites were calculated by using Coats–Redfern, Broido and Horowitz–Metzger models under best-fit analysis and further proved by linear regression analysis. The kinetics of thermal degradation was calculated from data scanned at a heating rate of 10 ​°C/min. The obtained results reveal that kinetic parameters and thermal behavior of EF composites were improved with the reinforcement of fly ash. The cure kinetics of the varying content of fly ash reinforced epoxy cast were also studied by using a nonisothermal differential scanning calorimetric (DSC) technique at four different heating rates 5 ​°C/min, 10 ​°C/min, 15 ​°C/min and 20 ​°C/min. The curing kinetics of the EF composite was derived from the nonisothermal differential scanning calorimetry (DSC) data with the three Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively.     

溴化轻稀土丙氨酸配合物的热分解动力学

溴化轻稀土丙氨酸配合物的热分解动力学;溴化轻稀土丙氨酸配合物;差示扫描量热法;热分解动力学;分解机理     

Kinetic study of the dehydration of modified Y zeolites

The dehydration of ferric exchanged Y zeolites is studied by thermal analysis. Their DTA shows three endotherms in the temperature range 80–450°C. The order of reaction and apparent energies of activation are calculated using various equations. The order of dehydration is nearly one and the apparent energy of activation is 4–8 kcal mole^?1. The effect of heating rate is studied. The energy of activation as determined by the Kissinger and Ozawa method is about 12 kcal mole^?1, which is comparable with the heat of adsorption of water determined by the gravimetric method, and is more acceptable.     

Thermal degradation of B-group vitamins: B1, B2 and B6

The thermal behaviour of vitamins B₁, B₂ and B₆ under non-isothermal conditions and dynamic air atmosphere was studied. According to our study, it was determined that the most stable compound is vitamin B₂. A kinetic analysis of the thermodegradation process using four different data processing methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and modified NPK) was performed. The NPK was the only method that made it possible to evaluate the contribution to the reaction rate of the temperature and conversion, respectively. The results obtained from kinetic analysis were corroborated with the molecular architecture of the studied compounds.     

Thermal behaviour of erythromycin-active substance and tablets

The application of thermal methods is of great importance in the solution of pharmaceutical problems, such as the control of raw materials, the determination of purity, the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility, the determination of kinetic parameters etc. The evaluation of thermal stability in the solid state is mostly made by analyzing their decomposition under isothermal and non-isothermal conditions. This study reports the study on the thermal behaviour of erythromycin-active substance and tablets, respectively, the determination of the kinetic parameters for the decomposition process under non-isothermal conditions. For the determination of kinetic parameters from the TG/DTG curves, were utilized the following methods: Friedman isoconversional, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Li–Tang, and Kissinger, respectively, a dynamic nitrogen atmosphere and different heating rates: 2.5, 5, 7.5, 10, and 15 °C min^?1. Thermoanalytical curves showed that the active substance is thermally more stable than the tablets and the values of activation energy indicate a considerable thermal stability of active substance. The decrease in stability was attributed to the presence of excipients.     

The Non‐Isothermal Decomposition Kinetics of NaNTO·H2O and the Relationship between its Structure and Properties

NaNTO·H₂O was prepared by mixing 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) aqueous solution and sodium hydroxide aqueous solution. Its thermal decomposition and kinetics were studied under non‐isothermal conditions by DSC and TG/DTG methods. The kinetic parameters were obtained from analysis of the DSC and TG/DTG curves by the Kissinger method, the Ozawa method, the differential method and the integral method. The most probable mechanism function for the thermal decomposition of the first stage was suggested by comparing the kinetic parameters. The critical temperature of thermal explosion (T_b) was 240.93 °C. The theoretical investigation on the structure unit of the title compound was carried out by DFT‐B3LYP/CEP‐31G methods; atomic net charges and the population analysis were discussed.     

Analysis on oxidation process of sulfurized rust in oil tank

The paper focuses on the oxidation process of sulfurized rust in crude oil tank. Firstly, one sort of rust was put into the sulfurization and oxidation experimental apparatus. The chemical compositions and phase of sulfurized rust were analyzed by energy-dispersive X-ray spectrometer–scanning electron microscope technique. The result shows that the main contents are S, Fe and O and give a short length of side and diamond appearance, and a large pore size in structure. The oxidation of sulfurized rust at ambient temperature was investigated, which transferred from electrochemical reactions to chemical reactions. The result of thermal decomposition experiment indicates that the product of electrochemical reactions is ferrous sulfate. Hereafter, the thermo-gravimetric/differential scanning calorimetric (TG/DSC) technique was used to evaluate the self-heating hazards of pre-oxygenized sulfurized rust. The given TG/DSC curves at different heating rates are similar. Every curve consisted of three weightlessness stages and two weight gain stages. The corresponding apparent activation energy values, most probable kinetic model functions and pre-exponential factor values were calculated by the Flynn–Wall–Ozawa method, the Achar–Brindley–Sharp–Wendworth method and the Kissinger method. The final results described the complexity of oxidation process of pre-oxygenized sulfurized rust.     

Thermal decomposition of barium(II) tetraphenylborate

Barium(II) tetraphenylborate, Ba(Bph₄))₂·4H₂O was prepared, and its decomposition mechanism was studied by means of TG and DTA. The products of thermal decomposition were examined by means of gas chromatography and chemical methods. A kinetic analysis of the first stage of thermal decomposition was made on the basis of TG and DTG curves and kinetic parameters were obtained from an analysis of the TG and DTG curves using integral and differential methods. The most probable kinetic function was suggested by comparison of kinetic parameters. A mathematical expression was derived for the kinetic compensation effect.     

Thermal stability of pentoxifylline: active substance and tablets

Thermal analysis is a routine method in the solution of pharmaceuticals problems such as the control of raw materials, to the determination of purity, to the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility, the determination of kinetic parameters, etc. The evaluation of thermal stability in the solid state is mostly made by analyzing their decomposition under isothermal and non-isothermal conditions. The present work reports the study on the thermal behavior of pentoxifylline—active substance and tablets, respectively, the determination of the kinetic parameters for the decomposition process under non-isothermal conditions and in a nitrogen atmosphere at five heating rates: 2.5, 5, 7.5, 10 and 15 °C min^?1. For the determination of kinetic parameters from the TG/DTG curves, the following differential methods were utilized: Friedman isoconversional and Chang, respectively, integral methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Li–Tang, and Starink. Thermoanalytical curves showed that the active substance is thermally more stable than the tablets. The decrease in stability was attributed to the presence of excipients.     

Synthesis of Vegetable Oil‐Based Polyurethane: A Study on Curing Kinetics Behavior

In the present study, biobased polyurethane (BPU) samples were synthesized from three different polyols along with polymeric hexamethylene diisocyanate. The three different polyols were synthesized by reacting castor oil with ethylene glycol, triethylene glycol, and triethanolamine. The synthesized polyols were confirmed using proton nuclear magnetic resonance (¹H NMR) spectra analysis. BPU samples were confirmed by the disappearance of isocyanate peak in the FTIR spectra. The cross‐linking densities of all BPU samples were determined using swelling studies. Curing kinetics behavior of all BPU samples were analyzed using differential scanning calorimetry at three different heating rates (5, 7.5, and 10°C/min). The curing kinetic parameters were studied using three nonisothermal methods such as Kissinger, Flynn–Wall–Ozawa, and Ozawa, respectively. The activation energies were found to increase with increasing degree of cure (α). Surface properties of all the synthesized BPU samples were evaluated by dynamic mechanical analysis and scanning electron microscopy.     

Preparation and characterization of microcapsulated red phosphorus and kinetic analysis of its thermal oxidation

Microcapsulated red phosphorus (MRP) with aluminum hydroxide/phenolic resin coating layer was prepared by a two-step coating process. The results of Fourier-transform infrared spectroscopy and scanning electron microscopy show that red phosphorus (RP) is coated by aluminum hydroxide and phenolic resin. MRP absorbs less water and is more thermally stable than RP. The thermal oxidation kinetics of MRP was investigated by TG/DTG/DTA under air atmosphere using non-isothermal experiments with the heating rates ranging from 10 to 25°C/min. The values of the apparent activation energy E _a were 168 ± 9 kJ/mol as determined by the isoconversional Ozawa–Flynn–Wall method and 164 ± 12 kJ/mol according to the Kissinger?Akahira?Sunose method. Based on Málek’s procedure the kinetic reaction follows the ?esták–Berggren model with f(α) = α0.34(1 ? α)^0.94 (α is RP conversion) and pre-exponential factor A = 3.11 × 10¹² s^–1. The simulated curves were fitted with experimental curves constructed by plotting dα/dt vs temperature at different heating rates.