Isothermal Thermogravimetry Research Articles

Enthalpies and entropies of sublimation and vaporization of aza crown ethers and cryptands measured by TGA

AbstractIn this work, the solid–gas and liquid–gas change of phase enthalpies of three aza crown ethers and two cryptands are derived from thermogravimetric data. For each of the compounds under study, the mass loss rate, dm/dt, was measured by isothermal thermogravimetry, then Pieterse and Focke equation combined with that of Clausius–Clapeyron was applied to correlate mass loss rate with temperature and to derive the respective vaporization or sublimation enthalpies at the experimental temperature and at 298.15 K. Such enthalpies are reported with the derived entropies and Gibbs energies of change of phase for the analyzed compounds. The results show a general trend of increasing value of the thermodynamic property as the number of the nitrogen atoms increases in the molecular structure of the macrocycle.

Influence of polypropylene and high-density polyethylene on isothermal pyrolytic degradation of discarded bakelite: Kinetic analysis and batch pyrolysis studies

The recycling of thermosetting plastics such as discarded bakelite poses greater challenges than thermoplastic polymers like polypropylene (PP) and high-density polyethylene (HDPE), particularly through pyrolysis requiring specialized reactors. This study examines the isothermal thermal degradation kinetics and batch pyrolysis behaviors of bakelite, along with its blends with PP and HDPE, emphasizing the characterization of pyrolytic oils for designing optimized reactors. For the study on isothermal thermal degradation kinetics, isothermal thermogravimetric analysis was performed at specified temperatures (300, 350, 400, 450, and 500°C), chosen based on the predominant non-isothermal degradation behavior of bakelite. The batch pyrolysis of discarded bakelite and blended bakelite with PP/HDPE is carried out at 450°C. The chemical composition analysis of pyrolytic oils is performed using Fourier transform infrared (FTIR) spectroscopy, with comprehensive compound analysis conducted using Gas Chromatography-Mass Spectrometry (GCMS). Isothermal thermogravimetry at temperatures ranging from 300°C to 500°C reveals increased thermal degradation with rising pyrolytic temperatures, reaching maximum weight losses of 55 % for bakelite, 82.74 % for PP-bakelite blends, and 90.8 % for HDPE-bakelite blends at 500°C. The isothermal kinetics study reveals that bakelite degrades via D1-diffusion, polypropylene-blended bakelite via A2-Avrami-Erofeyev, and high-density polyethylene-blended bakelite via A3-Avrami-Erofeyev, with activation energies of 17.178, 7.193, and 3.550 kJ/mol, and Arrhenius constants of 0.095, 0.042, and 0.017 min.−1, respectively. The highest condensable yield of 58.76 % during PP-blended bakelite co-pyrolysis underscores its potential for resource recovery. FTIR and GC-MS confirm the presence of alkanes, cycloalkanes, alkenes, cycloalkenes, aromatic hydrocarbons, and oxygenated compounds in the pyrolytic oils, providing detailed insights into their chemical composition. These findings offer critical insights into the thermal degradation behavior and kinetics of bakelite and polypropylene/high-density polyethylene-blended bakelite, highlighting opportunities for efficient waste plastic utilization through pyrolysis for resource recovery and energy generation, and providing essential knowledge for designing isothermal pyrolysis reactors.

Phase transition study of bathophenanthroline and bathocuproine: A multitechnique approach

The thermal behaviour of bathophenanthroline and bathocuproine has been studied using several techniques, namely, differential scanning calorimetry and thermogravimetry. To determine their respective enthalpies of sublimation, vapor pressure measurements were carried out using different methods, such as Knudsen effusion mass loss/mass spectrometry, isothermal thermogravimetry, and a quartz crystal microbalance technique. Furthermore, the enthalpies of sublimation were determined by measuring the heat change of the sublimation process using high-temperature Calvet microcalorimetry.The results obtained in this work allowed the determination of the standard molar enthalpies of sublimation at 298.15 K, for bathophenanthroline and bathocuproine. The values obtained were (183.8 ± 2.2) kJ⋅mol−1 and (206.2 ± 2.8) kJ⋅mol−1, respectively. Additionally, the standard molar enthalpies of fusion were determined to be (30.4 ± 0.4) kJ⋅mol−1 and (26.5 ± 1.6) kJ⋅mol−1 for bathophenanthroline and bathocuproine, respectively. The analysis of the results allows a deeper understanding of the phase transition behavior for these compounds from the condensed to the gaseous phases, elucidating molecular decomposition and the inherent intermolecular forces governing the species.

Sublimation enthalpies of organic compounds by isothermal thermogravimetry

AbstractAn improved method has been developed to determine the sublimation enthalpies of solid organic compounds using thermogravimetric analysis and applying an isothermal methodology with a TA Instruments® SDTQ600 equipment. This was achieved by measuring the rate of mass loss as a function of the temperature from isothermal experiments in an interval of temperature of 10 to 20 K below the melting temperature of the sample. The resulting rates of mass loss were used by applying the Pieterse and Focke equation, then combined with the integrated Clausius–Clapeyron equation to calculate the heat of sublimation at the experimental temperature and it was corrected to T = 298.15 K. In order to demonstrate the reliability of this methodology, the results for benzoic acid, pyrene and phenanthrene are presented, which are respectively primary, secondary, and tertiary reference compounds in the measurement of enthalpies of sublimation, along with the sublimation enthalpies of picolinic acid, nicotinic acid and isonicotinic acid which are three pyridinecarboxylic acids isomers with the carboxyl group in the ortho, meta and para position, respectively, to the nitrogen of the pyridine.

Experimental thermochemical study of aryl nitriles: A structural energetic approach

The present work comprised a study of the thermochemical properties of three aryl nitriles: Methyl p-cyanobenzoate, p-Acetylbenzonitrile, and p-Methoxybenzonitrile. This study was carried out using calorimetric and thermal analysis techniques. Through differential scanning calorimetry, we obtained the temperatures and enthalpies of fusion, as well as the heat capacities in the crystal phase. Specific combustion energies were determined through static bomb combustion calorimetry, from which, the enthalpies of formation in the condensed phase were derived. Additionally, isothermal thermogravimetry was used to measure the mass loss rate as a function of temperature. Using the Langmuir equation in conjunction with benzoic acid as a calibration material, vapor pressures were determined as a function of temperature. With the obtained vapor pressures and the Clausius-Clapeyron equation, enthalpies of sublimation were calculated. Moreover, entropies and Gibbs sublimation energies were determined at T = 298.15 K. Finally, using these properties, enthalpies of formation in the gaseous phase at T = 298.15 K were calculated for the three mentioned compounds. With these data, an analysis of the energetic effect of different substituents in benzonitrile is presented.

3-formylchromones: Vapor pressures and standard molar enthalpies, entropies and Gibbs energy of sublimation

In present work, the estimation of vapor pressures of 3-formylchromone and 3-formyl-6-methylchromone by the isothermal thermogravimetry method is presented. Briefly, this method consists of measuring the rate of mass loss as a function of temperature in a cylindrical cell and with a flow of nitrogen. To derive the vapor pressure, the Langmuir equation was used, from which the vaporization constant was calculated using anthracene as a calibrating compound. Subsequently, the vapor pressures 3-fromylchromone and 3-formyl-6-methylchromone were estimated. From the vapor pressure, the enthalpy of sublimation was calculated using the Clausius-Clapeyron equation for each compound at its mean sublimation temperature. Finally, the enthalpy of sublimation was calculated at T = 298.15 K. The entropy and Gibbs energy of sublimation at the same temperature were determined. In order to test the validity of the method, the vapor pressures of phenanthrene and pyrene were calculated. The values obtained by isothermal thermogravimetry agree with those reported by other techniques.

A versatile method to fingerprint and compare the oxidative behaviour of lipids beyond their oxidative stability

In this work we propose the use of isothermal thermogravimetry to evaluate the oxidative stability of a lipid and to evaluate how the glyceride composition affects the entire oxidative process, to quantify the oxidation undertaken by the lipid, and numerically compare the oxidative behaviour of different lipids. The innovative aspect of the present method lies in the acquisition of a prolonged “oxygen uptake” curve (4000–10,000 min) of a lipid under oxygen and in the development of a semi-empirical fitting equation for the experimental data. This provides the induction period (oxidative stability), and allows to evaluate the rate of oxidation, the rate and the magnitude of oxidative degradation, the overall mass loss and the mass of oxygen taken by the lipid upon time. The proposed approach is used to characterize the oxidation of different edible oils with different degrees of unsaturation (linseed oil, sunflower oil, and olive oil) as well as chemically simpler compounds used in the literature to model the autoxidation of vegetable oils and lipids in general: triglycerides (glyceryl trilinolenate, glyceryl trilinoleate and glyceryl trioleate) and methyl esters (methyl linoleate and methyl linolenate). The approach proves very robust and very sensitive to changes in the sample composition.

The effect of porosity and particle size on the kinetics of porous carbon xerogels surface oxidation

Carbon surface oxidation was investigated to assess the effects of porosity and particle size on its course. Carbon xerogels that differed in porosity (micro-, micro-meso-, and micro-meso-macroporous materials) and particle size (from fine powders to monolithic cubes) were prepared. The prepared materials were characterized in detail with nitrogen sorption, SEM, and HRTEM. The oxidation of carbon xerogels was studied by isothermal thermogravimetry (TG) in an oxidizing atmosphere (50% O2 and 50% Ar). Isothermal TG experiments showed that the effects of particle size and porosity are interrelated and should be evaluated together as both significantly influence diffusion and heat transfer during carbon oxidation. On the basis of isothermal TG data, apparent kinetic parameters were determined assuming that carbon burn-off, the creation of oxygen surface groups, and the decomposition of created oxygen surface groups are reactions controlling the carbon surface oxidation. Detailed analysis of the obtained parameters proved that porosity and particle size do not affect the basic chemical reactions that occur on the carbon surface during oxidation.

PREDICTION OF ANTI-DIABETIC ALOGLIPTIN STABILITY BY ISOTHERMAL STUDIES

Alogliptin (ALG) benzoate is an oral hypoglycemic drug that works as a DPP-4 inhibitor to prevent incretin degradation. Forced stability studies use high temperatures to decompose drugs and estimate their behavior at low temperatures. We aimed to evaluate the thermal stability of ALG using two techniques: isothermal thermogravimetry (TGA) and degradation in an oven followed by liquid chromatography (LC-PDA) analysis. ALG was subjected to 150, 155, 160, 165, and 170 °C up to 10% of mass loss in isothermal TGA. In the oven, the drug was submitted to 130, 140, 150, 155, 160, and 170 °C. Kinetic parameters were calculated with the Arrhenius model. ALG followed zero-order kinetics, in which the degradation rate did not depend on reagent concentration. Activation energy ranged from 31.0 to 35.9 kcal mol-1. The degraded drug was less toxic in a cytotoxicity assay in CRIB cells than the undegraded drug. The TGA method is faster and more practical than the oven followed by LC-PDA, and the data present a correlation. Here we described the kinetic parameters of ALG degradation, improving the knowledge about the drug and assisting in developing new formulations from the drug.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion.

Four ionic liquids (ILs) based on the bis(trifluoromethanesulfonyl)imide (NTf2) anion were synthesized and characterized concerning their thermal stability, the occurrence of low temperature phase transitions and their volatility. All these physical quantities are highly important for possible applications. Both monocationic and dicationic ILs were considered. All ILs exhibit thermal stability exceeding 350 °C, an extremely high value, due to the presence of the NTf2 anion. Monocationic ILs can undergo crystallization, and they melt at 1 and 38 °C. On the contrary, dicationic ILs containing large positively charged ions display only a glass transition around −40 °C, without any crystallization or melting process; this fact is particularly important in view of the possibly low temperature applications of the dication ILs. The vapor pressure, pv, of the four ILs was measured by isothermal thermogravimetry in the temperature range between 250 and 325 °C; the lowest values of pv were obtained for the two dicationic liquids, suggesting that they are particularly well suited for high temperature applications. The vaporization enthalpy was calculated through the Clausius–Clapeyron equation and was found in the range between ~140 and ~180 kJ/mol depending on the specific IL.

IR-Supported Thermogravimetric Analysis of Water in Hydrogels

Isothermal thermogravimetry in a kinetic mode and time-resolved infrared spectroscopy was used to characterize water and its binding in hydrogels formed by interactions between hyaluronan and micelles of Septonex, an oppositely charged surfactant. Thermogravimetry provided detailed insight into the dehydration kinetics of the gel and thus brought indirect information on the strength of water binding in the hydrogel network. Infrared (IR) spectroscopy complemented the study with a direct analysis of structural changes occurring in the gel during its dehydration. IR spectroscopy thus contributed to understanding the processes which were observed in thermogravimetry, qualitatively, on the molecular level. This study can contribute to a broader application of the combined thermogravimetry–IR approach in the study of hydrogel materials and the development of their applications, especially in bio-related areas where water is among the key players.

Recycling of brass melting slag through the high-temperature oxidation-leaching process

Brass melting slag is a valuable secondary resource for the recovery of copper and zinc. The hydrometallurgical recovery process of this material is a challenge, because of its limited dissolution in sulfuric acid. The present study aimed at studying a combined pyro-hydrometallurgical treatment processes involving high temperature oxidation and sulfuric acid leaching to industrial brass melting slag to recover copper and zinc. The effect of temperature on the performance and efficiency of the high temperature oxidation process was investigated by isothermal thermogravimetry. The results revealed that by increasing the oxidation temperature, leachability improves due to the oxidation of metallic brass particles. The results obtained showed that 3 h oxidation of as-received slag at 900 °C, increased its percent leaching amount in 2 M sulfuric acid from 34 to 81%. The pregnant leach solution containing copper sulfate and zinc sulfate was subjected to the electrowining process to recover the copper as copper cathode. The zinc was also recovered as zinc sulfate via evaporation and crystallization process. Kinetic investigations showed that the 3D diffusion model has a good agreement with the isothermal oxidation results. In this model, the oxidation reaction is controlled by the outward diffusion of zinc from the brass particle. The activation energy of isothermal oxidation was obtained as 311 kJ mol− 1.

On the replacement of traditional stabilizers by guaiacol in environmentally safe nitrocellulose-based propellants

In this work we investigated the possibility of substituting diphenylamine (DPA) by the natural product 2-methoxy phenol, known as guaiacol (CAS 90-05-1), as a stabilizer for nitrocellulose (NC)-based propellants. Stability evaluation, using heat flow calorimetry, revealed lower heat flows associated with our guaiacol-stabilized propellant samples when compared to those of propellants stabilized with the traditional stabilizers. Also, pressure vacuum stability tests showed that our propellant exhibited lower evolved gas volumes. Traditional tests, such as the German Test, and the Bergmann-Junk Test, scored a NO volume, after titration, of 0.87 ml (below the limit-value for acceptance, which is 2.0 ml), and the Storage Test, showed that our samples are stable and do not degrade until 3 days when submitted to a constant temperature of 100 °C. The homogeneity, stability and compatibility of our samples were evaluated through scanning electron microscopy, differential scanning calorimetry, and isothermal thermogravimetry. Ballistic parameters were estimated using a closed vessel along with computational codes developed by our research group, for comparison purposes. Finally, the high-performance liquid chromatography method allowed inferring the stabilizer consumption after artificial ageing of samples. This method also showed that the material met the corresponding stability criteria of AOP-48. Concluding, our results clearly indicate that guaiacol is an effective and efficient substitute for DPA as a propellant stabilizer for single-base NC-based propellants, making them more environmentally friendly.Graphical abstract

Guidelines for a correct evaluation of Deep Eutectic Solvents thermal stability

Deep eutectic solvents (DESs) are a class of versatile and green emerging materials. Despite the huge amounts of applications proposed in the last years, studies on their thermal stability are often missing. In this short review, we propose a guide for a correct evaluation of DES thermal stability, conducted mainly by dynamical thermogravimetry (TGA). We collected all the data reported in the literature on choline chloride (ChCl)-based DESs, as proof of concept to show the potentialities of the technique, highlighting all the parameters that need to be considered for a correct analysis, with particular attention to the possible sources of misleading interpretations (e.g. the adsorbed water, or the formation of undesired products during DES preparation). In many cases, the additional use of isothermal TGA, or TGA coupled with online techniques such as Fourier Infra-Red Spectroscopy or Mass Spectrometry, may help for the data interpretation. Besides, we summarize in a graph the degradation temperatures of many DESs and their precursors, intended as an operative guide to choosing the correct DES for different applications. The findings reported to date, highlight the potentialities of thermal analysis on DESs, as a powerful tool to obtain essential information on their applicability, and to implement the knowledge of their nanostructure from a molecular point of view.

High temperature corrosion evaluation and lifetime prediction of porous Fe22Cr stainless steel in air in temperature range 700–900 °C

This work describes a high temperature corrosion kinetics study of ∼30 % porous Fe22Cr alloys. The surface area of the alloy (∼0.02 m2 g−1) has been determined by tomographic microscopy. The weight gain of the alloys was studied by isothermal thermogravimetry in the air for 100 h at 700–900 °C. Breakaway oxidation was observed after oxidation at 850 °C (∼100 h) and 900 °C (∼30 h). The lifetime prediction shows the investigated porous alloy can be used for >3000 h at temperatures <700 °C. At temperatures ≥700 °C, the lifetime of the porous alloy is limited by the available chromium reservoir.

Reaction mechanism of copper azide nanowires array

In-situ growth of copper azide has endowed this highly sensitive primary explosive new life, but its mechanism study is not enough to support its in-depth study. Hence, azidation reaction was conducted on highly ordered copper nanowires array, which could provide effective channels for gas phase reactant (hydrazoic acid, HN3) to penetrate the solid, further study the mechanism of azidation reaction on copper azide nanowires array, and clarify the relationship between the microstructure and its azidation degree. Gas–solid in-situ azidation technique was used for this in-depth study. The effects of reaction temperature on formation of gaseous HN3 were studied by isothermal thermogravimetry. The azidation results were analyzed by SEM and XRD, the effects of the reaction time, diameter of copper nanowires array precursor and oxidation degree on the azidation degree were studied in detail. This work not only provided deep investigation on the azidation process, but also offered effective guidance for the synthesis of copper azide nanowires array.

Vacuum versus ambient pressure inert gas thermogravimetry: a study of silver carboxylates

A comparative study of vacuum versus ambient pressure inert gas thermogravimetry was performed on silver carboxylates compounds. Some of the complexes from this group have been previously successfully applied as precursors for both chemical vapour deposition and electron beam-induced deposition. Considerable differences were found between the thermogravimetry methods, which we associate with changes in evaporation dynamics. Vacuum thermogravimetry sublimation onsets consistently occurred at lower temperatures than ambient pressure N2-flow thermogravimetry, where the differences reached up to 120 °C. Furthermore, compound sublimation during N2-TGA was suppressed to such an extent that significant thermal decomposition of the compounds into metal and volatile organic fragments was observed while at vacuum the same complexes sublimed as intact molecules. Moreover, thermal stability of silver complexes was investigated using isothermal thermogravimetry. These findings are interesting for the field of thin film synthesis and nanomanufacturing via chemical vapour deposition, atomic layer deposition and focused electron beam induced deposition. In all three methods, delivery of functional precursor over the substrate is crucial. The presented results prove that vacuum thermogravimetry can be used as fast method of pre-screening for novel, especially low-volatility precursors.Graphic abstract

Can green nitrocellulose-based propellants be made through the replacement of diphenylamine by the natural product curcumin?

ABSTRACT This research evaluates the feasibility of replacing diphenylamine (DPA) with the natural product curcumin as a stabilizer in samples of nitrocellulose-based (NC-based) propellants. The stability analysis was performed using heat flow calorimetry, as described in STANAG-4582, as well as the most traditional stability testing protocols: the German test, Bergmann–Junk test, and the Storage test. Ballistic parameters were evaluated using a closed vessel ballistic test and samples underwent Scanning Electron Microscopy (SEM). Also, the Pressure Vacuum Stability Test (PVST), Differential Scanning Calorimetry (DSC), and Isothermal Thermogravimetry (TG) to evaluate the homogeneity, stability, and compatibility with NC were performed. The ballistic parameters were evaluated using a closed vessel ballistic test. All samples of propellants stabilized with curcumin passed the stability test criteria performed in this research, with better scores than the propellant sample stabilized with DPA, which was used as a reference. However, the estimation of ballistic parameters indicated that the deflagration of the propellant stabilized with curcumin exhibits some delay when compared to the reference sample, which can be easily overcome by adjusting the propellant grain dimensions, especially the thickness. Finally, an HPLC analysis method was developed to identify and characterize this new Single-Based (SB) propellant stabilizer. This method was shown to be effective, fast, accurate, and adequate to comply with the stability criteria proposed by the AOP-48 standard, especially because of the depletion of the stabilizer concentration after artificial aging. We believe that our results are promising and support the proposal that curcumin can replace DPA as a stabilizer for SB propellants.

Thermodynamics and kinetics analyses of high CO2 absorption properties of Li3NaSiO4 under various CO2 partial pressures.

The properties of Li3NaSiO4 as a CO2 absorbent were evaluated by thermogravimetry (TG) and X-ray diffraction, which revealed that the CO2 absorption and desorption reaction, Li3NaSiO4 + CO2 ↔ LiNaCO3 + Li2SiO3, is reversible. In scanning-type TG under various CO2 partial pressures (P(CO2)), mass gain ascribed to CO2 absorption started from approximately 400 °C, irrespective of P(CO2). CO2 desorption was observed at a higher temperature, which was considered the approximate equilibrium temperature of the above-mentioned reaction. A pseudo-Ellingham diagram of the reaction between Li3NaSiO4 and CO2, constructed using the obtained approximate equilibrium temperature under each P(CO2), showed similar behavior to that between Li4SiO4 and CO2, especially between 10-2 and 10-1 bar of P(CO2). Kinetics analysis by isothermal TG using the Jander model revealed that the reaction rate of CO2 absorption of Li3NaSiO4 was higher than that of Li4SiO4. The rate-determining step of CO2 absorption by Li3NaSiO4 was the diffusion process at the examined temperatures and P(CO2), which was different from the rate-determining step of the reaction between Li4SiO4 and CO2 under low P(CO2).

Kinetics of thermal oxidative degradation of poly (vinyl chloride) containing Ca and Sn at low temperature

Calcium metal soap and polyol (dipentaerythritol) additives are replacing or partially replacing organotin in poly(vinyl chloride) (PVC) heat stabilizers due to their low cost, nontoxicity and safety. Therefore, investigating the low-temperature thermal oxidative degradation of stabilized plasticized PVC from the source is essential for recycling. This work uses isothermal thermogravimetry to investigate the thermal degradation process and isothermal discoloration of PVC/calcium metal soap/dipentaerythritol/organotin soft products with excellent heat resistance at 453–503 K and under air atmosphere. The chemical kinetics method is used to fit a single equation model of mass loss and time during the thermal oxidation degradation of PVC, and the kinetic equation obtained is: −ln(1 − α) = 3.83 × 103exp (−6834.4/T)t. When the temperature is 453–503 K, the calculation results are basically consistent with the experimental data and are independent of the heating rate and temperature changes. In addition, the isothermal discoloration of different PVC materials was tested under air atmosphere at 468 K. The results show that when the test material is PVC/calcium metal soap/dipentaerythritol/organotin, the heat aging time to become completely blackened is longer than that of the blank sample, which indicates a strong interaction occurs between Sn, Ca and dipentaerythritol complexes and PVC molecules, inhibiting the release of hydrogen chloride. At the same time, in order to recover PVC and prevent it from carbonization, if the temperature is set to 486 K, the thermal oxidation degradation time of PVC should be less than 130 min.