Thermal behaviour of cephalexin in different mixtures

The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min⁻¹. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min⁻¹. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min⁻¹. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).     

Thermogravimetric Analysis of Cobalt(II)-dothiepin Complexes

The complexes of cobalt(II) with dothiepin (DOT) hydrochloride have been studied for kinetics of thermal degradation by thermogravimetric analysis (TG) and derivative thermogravimetric studies (DTG) in a static nitrogen atmosphere at a heating rate of 10° C min⁻¹. A general mechanism of thermal decomposition is advanced involving dehydration and decomposition process for both organic and inorganic ligands. The thermal degradation reactions were found to proceed in three steps having an activation energy in the range 6.75–170 kJ mol⁻¹. Thermal decomposition kinetics parameters were computed on the basis of thermal decomposition data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-isothermal kinetic analysis and feasibilty study of medium grade crude oil field

In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a limestone matrix. Experiments were performed at a heating rate of 10°C min⁻¹, whereas the air flow rate was kept constant at 50 mL min⁻¹ in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol⁻¹ in LTO region and 189–229 kJ mol⁻¹ in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.     

Study of Thermal Decomposition Kinetics of Low-temperature Reaction of Ammonium Perchlorate by Isothermal TG

The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method. From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic phase, the mean value of the activation energy of 146.3 kJ mol^–1, and the pre-exponential factor of 3.43⋅10¹⁴ min^–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation energy of153.3 kJ mol^–1, and the pre-exponential factor of 4.11⋅10¹⁴ min^–1 are obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic study of wood chips decomposition by TGA

Pyrolysis of a wood chips mixture and main wood compounds such as hemicellulose, cellulose and lignin was investigated by thermogravimetry. The investigation was carried out in inert nitrogen atmosphere with temperatures ranging from 20°C to 900°C for four heating rates: 2 K min⁻¹, 5 K min⁻¹, 10 K min⁻¹, and 15 K min⁻¹. Hemicellulose, cellulose, and lignin were used as the main compounds of biomass. TGA and DTG temperature dependencies were evaluated. Decomposition processes proceed in three main stages: water evaporation, and active and passive pyrolysis. The decomposition of hemicellulose and cellulose takes place in the temperature range of 200–380°C and 250–380°C, while lignin decomposition seems to be ranging from 180°C up to 900°C. The isoconversional method was used to determine kinetic parameters such as activation energy and pre-exponential factor mainly in the stage of active pyrolysis and partially in the passive stage. It was found that, at the end of the decomposition process, the value of activation energy decreases. Reaction order does not have a significant influence on the process because of the high value of the pre-exponential factor. Obtained kinetic parameters were used to calculate simulated decompositions at different heating rates. Experimental data compared with the simulation ones were in good accordance at all heating rates. From the pyrolysis of hemicellulose, cellulose, and lignin it is clear that the decomposition process of wood is dependent on the composition and concentration of the main compounds.     

Investigation of thermal behavior of nicotinic acid

The thermal behavior of nicotinic acid under inert conditions was investigated by TG, FTIR and TG/DSC-FTIR. The results of TG/DSC-FTIR and FTIR indicated that the thermal behavior of nicotinic acid can be divided into four stages: a solid-solid phase transition (176–198°C), the process of sublimation (198–232°C), melting (232–263°C) and evaporation (263–325°C) when experiment was performed at the heating rate of 20 K min⁻¹. The thermal analysis kinetic calculation of the second stage (sublimation) and the fourth stage (evaporation) were carried out respectively. Heating rates of 1, 1.5, 2 and 3 K min⁻¹ were used to determine the sublimation kinetics. The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using the master plots method. The results indicated that sublimation process can be described by one-dimensional phase boundary reaction, g(α)=α. And the ‘kinetic triplet’ of evaporation process was also given at higher heating rates of 15, 20, 25, 30 and 35 K min⁻¹. Evaporation process can be described by model of nucleation and nucleus growing, .     

Degradation behavior and kinetic study of ABS polymer

The degradation kinetics of the ABS terpolymer (acrylonitrile-butadiene-styrene) was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere applying three different heating rates: 5, 10 and 20°C min⁻¹. The Vyazovkin model-free kinetic method was used to calculate the activation energy (E) of the degradation process as a function of conversion and temperature. Between 20 and 80% of conversion, E was calculated and the figures were: for ABS GP, E is 204.5±11.5 kJ mol⁻¹ (medium value); for ABS HI, E is 239.0±9.8 kJ mol⁻¹; for ABS HH, E is 242.4±5.4 kJ mol⁻¹.     

Non-isothermal thermogravimetric pyrolysis kinetics of waste petroleum refinery sludge by isoconversional approach

Pyrolysis of petroleum refinery sludge has received global acclamation as a clean conversion technique for providing solution of sludge disposal as well as efficient resource utilization. This communication reports the kinetics study of pyrolysis of petroleum refinery sludge. Experiments were carried out by means of thermogravimetric analysis at different heating rates of 5, 10 and 20°C min⁻¹. The pyrolytic reaction is significant in the temperature range of 200–350°C and analysis and evaluation of kinetic parameters is done in the 100–500°C region of non-isothermal TG curves obtained in nitrogen atmosphere. The activation energy is calculated by iso-conversional method, then other kinetic parameters are determined by considering single reaction and two reaction global kinetic model. Two-reaction model is found to fit satisfactorily the experimental results.     

Evolved gas analysis at thermal treatment of some solid fossil fuels

Coupled TG-FTIR technique was used for identification of gaseous compounds evolved at thermal treatment of six coal samples from different deposits (Bulgaria, Russia, Ukraine). The experiments were carried out under dynamic heating conditions up to 900°C at heating rates of 5, 10 or 50 K min^–1 in a stream of dry air. The emission of CO₂, H₂O, CO, SO₂, COS, methane, methanol, formic acid, formaldehyde, acetaldehyde, chlorobenzene was clearly identified in FTIR spectra of the samples studied. The formation of ethanol, ethane, ethylene and p-xylene, at least on the level of traces, was also identified. At the heating rate of 5°C min^–1 the temperature of maximum intensities of the characteristic peaks of COS was 270°C, of formaldehyde, formic acid, ethane and methanol 330°C, of SO₂, CO, acetic acid, ethylene and p-xylene 400°C and of chlorobenzene 500°C. At 10°C min^–1 and 50°C min^–1 these temperatures were shifted, respectively, by 70–300°C and 150–450°C towards higher temperatures and the respective absorption bands in FTIR spectra were, as a rule, more intensive.     

Kinetic study of the polymeric binder burnout in green low temperature co-fired ceramic tapes

The binder decomposition and burnout process of a commercial low temperature co-fired ceramic (LTCC) tape and an alumina tape which is used as a sacrificial tape for the constrained sintering process of the LTCC-tape was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 550 °C at different heating rates (from 1.5 to 10 K min⁻¹) in air. TG revealed a multistage degradation behaviour of the binder system for both tapes, but the temperature range of the different degradation stages varied. The activation energy of decomposition was determined by the Flynn–Wall isoconversional method and the Coats–Redfern method.     

Investigation of the thermal properties of [Cd(hydet-en)2Pd(CN)4] AND [Zn(hydet-en)2Pd(CN)4] single crystals

Thermal properties of the single crystals have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. The thermodynamic parameters such as activation energy and enthalpy and thermal stability temperature of the samples were calculated from the differential thermal analysis (DTA) and TG data. The activation energies for first peak of DTA curves were found as 496.65 (for Cd–Pd) and 419.37 kJ mol^–1 (for Zn–Pd). For second peak, activation energies were calculated 116.56 (for Cd–Pd) and 173.96 kJ mol^–1 (for Zn–Pd). The thermal stability temperature values of the Cd–Pd and Zn–Pd compounds at 10°C min^–1 heating rate are determined as approximately 220.7 and 203°C, respectively. The TG results suggest that thermal stability of the Cd–Pd complex is higher than that of the Zn–Pd complex.     

Non-isothermal DSC and TG/DTG analysis of the combustion of Si̇lopi̇ asphaltites

In this research, non-isothermal combustion and kinetics of Silopi (Turkey) asphaltite samples were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). A sample size of 10 mg, heating rates of 5, 10, 15 and 20°C min⁻¹ were used in the temperature range of 20–600°C, under air atmosphere. Two reaction regions were observed in DSC curves. The first region is due to the evaporation of moisture in asphaltite sample whereas, release of volatile matter and burning of carbon is called the second region. A general computer program was developed and the results of four different kinetic models (Arrhenius, Coats-Redfern, Ingraham-Marrier and Horowitz-Metzger) are compared and discussed with regards to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. In general similar activation energy values were obtained when the kinetic models are compared with each other. It was also observed that there was no general trend in the activation energy values from the point of heating rates.     

Thermal behavior of drugs

Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300 and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the heating rate (5, 10, 15, and 20 °C min⁻¹) on the DSC behavior of the both drug samples was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by various methods, the following order for the thermal stability was noticed: naproxen > celecoxib. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Synthesis And Kinetic Analysis of Poly(2,2'-dymethoxy-4,4'-biphenylenevinylene. A novel conducting polymer

The title polymer was obtained electrochemically by the reduction of 4,4'-bis(dibromomethyl)-2,2'-dimethoxybiphenyl under very smooth conditions. The DSC and TG/DTG curves registered at four different heating rates showed that the polymer is stable in air up to 150°C, where smooth degradation starts. Above 300°C, decomposition is fast and exothermic (ΔH= –323 J g^–1) . The activation energy (116±4 kJ mol^–1 ) was determined by Ozawa's method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic study of degradation of heavy oil over MCM-41

Thermogravimetry was applied in order to investigate the catalytic degradation of heavy oil (15.4^oAPI) over silica-based MCM-41 mesoporous molecular sieve. This material was synthesised by the hydrothermal method, using cetyltrimethylammonium bromide as organic template. The physicochemical characterization by nitrogen adsorption, X-ray diffraction, and thermogravimetry, showed that the obtained material presents well-defined structure, with a uniform hexagonal arrangement. The thermal and catalytic degradation of heavy oil was performed by thermogravimetric measurements, in the temperature range from 30 to 900 °C, at heating rates of 5, 10, and 20 °C min⁻¹. By using the model-free kinetics, proposed by Vyazovkin, it was determined that the activation energy to degrade the heavy oil was ca. 128 kJ mol⁻¹, and for degradation of oil in presence of MCM-41, this value decreased to 69 kJ mol⁻¹, indicating the performance of the mesoporores catalyst for the degradation process.     

Cross-linking epoxide resins with hydrolysates of chrome-tanned leather waste

Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C, at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction enthalpy, 519.19 J g⁻¹ (= 101.24 kJ mol⁻¹ of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min⁻¹) and activation energy E _a (kJ mol⁻¹)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics is determined by diffusion.     

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.     

Kinetics study of thermal oxidative degradation of ABS containing flame retardant components

The thermal oxidative degradation kinetics of pure acrylonitrile–butadiene–styrene (ABS) and the flame-retarded ABS materials with intumescent flame retardant (IFR) were investigated using Kissinger, Flynn–Wall–Ozawa, and Horowitz–Metzger methods. The results showed that the degradation of all samples included two stages, the activation energy at the first stage decreased by the incorporation of these flame retardant components, while increased at the second stage. The activation energy order of the flame-retarded ABS samples at stage 2 illustrates the relationship between the composition of IFRs and their flame retardancy, FR materials with appropriate acid agent/char former ratio has higher activation energy and better flame retardancy.     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

Non-isothermal kinetic study of the thermal decomposition of diaminoglyoxime and diaminofurazan

Data on the thermal stability of organic materials such as diaminofurazan (DAF) and diaminoglyoxime (DAG) was required in order to obtain safety information for handling, storage and use. These compounds have been shown to be a useful intermediate for the preparation of energetic compounds. In the present study, the thermal stability of the DAF and DAG was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery-differential thermal analysis (TG-DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the DAF and DAG occurs in the temperature ranges of 230–275°C and 180–230°C, respectively. On the other hand, the TG-DTA analysis of compounds indicates that DAF melts (at about 182°C) before it decomposes. However, the thermal decomposition of the DAG started simultaneously with its melting. The influence of the heating rate (5, 10, 15 and 20°C min⁻¹) on the DSC behaviour of the compounds was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E698 and Ozawa. Based on the values of activation energy obtained by ASTM and Ozawa methods, the following order in the thermal stability was noticed: DAF>DAG.