Thermogravimetry Methods Research Articles

Thermal kinetic studies on the decompositions of cefuroxime lysine in different atmospheres and heating rates

The thermal decomposition of a new antibiotic agent, cefuroxime lysine, was investigated by thermogravimetry analysis/derivative thermogravimetry and differential scanning calorimetry (DSC) methods in anoxic and oxidative environments. The influence of heating rates (including 5, 10, 15, and 20 °C/min) on the thermal behavior of cefuroxime lysine was revealed. By the methods of Kissinger and Flynn–Wall–Ozawa, the thermal kinetic parameters of activation energy and pre-exponential factor for the exothermic processes under non-isothermal conditions were calculated using the analysis of corresponding DSC curves.

Investigation on Pulverized Coal Combustion Behavior by Non-Isothermic Integral Thermogravimetry Method

The combustion process of pulverized coal was investigated by non-isothermic integral thermogravimetry. The thermogravimetry curves were fitted by the Coats-Redferm approximation function, and kinetic parameters and characteristic temperatures were obtained. The optimal mixing ratio and particle size can be ascertained. The characteristic temperature of pulverized coal can be obtained from the thermogravimetry curve, and the combustion of coal can be divided into homogeneous and heterogeneous combustion according to the differential thermal analysis curve. The activation energy of a single type of coal ranking from low to high is as follows: bituminous coal, meager-lean coal, and anthracite. In the first mixing method, with more low-price meager-lean coal B replacing high-price anthracite A, the activation energy slightly decreases; with more bituminous coal replacing meager-lean coal, total tendency makes a declining of activation. In the later mixing method, with an increase in particle size, a declining activation energy can be seen in total tendency.

Influence of solid-phase ferritization method on phase composition of lithium-zinc ferrites with various concentration of zinc

Methods of X-ray phase analysis (XRPA) and differential thermogravimetry in a magnetic field (DTG(M)) are used to investigate the phase composition of Li0.5(1−x)Fe2.5−0.5xZnxO4 (xZn = 0.2, 0.4, and 0.6) ferrite spinels synthesized at a temperature of 700 °C during 120 min by thermal annealing of a reagent mixture in a furnace and heating of the mixture using high-power beam of accelerated electrons with energy of 2.4 MeV. Thermal ferritization of all compositions leads to the formation of phases whose composition is close to simple monoferrites. Lithium–zinc ferrite phases are formed during annealing under electron irradiation. It is concluded that the rate of controllable diffusion interaction of monoferrite phases significantly increases under conditions of high-power electron irradiation.

Thermal characterization of HCN polymers by TG–MS, TG, DTA and DSC methods

This paper presents a thermogravimetry (TG) study of hydrogen cyanide polymers, synthesized from the reaction of equimolar aqueous solutions of sodium cyanide and ammonium chloride. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were also used to evaluate the thermal behaviour of these black polymers, which play an important role in prebiotic chemistry. A coupled TG–mass spectrometer (MS) system allowed us to analyze the principal volatile thermal decomposition and fragmentation products of the isolated HCN polymers under dynamic conditions and an inert atmosphere. After dehydration, a multi-step decomposition occurred in this particular polymeric system, due to the release of ammonia, hydrogen cyanide (depolymerization reaction), isocyanic acid (or cyanic acid) and formamide; these two latter species allow us identify bond connectivities. Finally, data collected from TG experiments in an oxidative atmosphere showed significant differences at higher temperatures, above 400 °C. According to these results, the different techniques of thermal analysis here applied have demonstrated to be an adequate methodology for the study and characterization of this complex macromolecular system, whose structure remains controversial even today.

Particulate matter oxidation on Ruddlesden-Popper-type, La1.8Sr1.2Mn2O7

La1.8Sr1.2Mn2O7, La0.5Sr1.5MnO4 and La0.8Sr0.2MnO3 were prepared and their particulate matter oxidation was investigated by thermogravimetry method. Of the three perovskite oxides, La1.8Sr1.2Mn2O7 gave a higher oxidation activity than the other two oxides at a practical level of temperature. The properties of these oxides were also investigated by X-ray photoelectron spectroscopy. The Mn 2p core-level spectra of the La1.8Sr1.2Mn2O7 only shifted towards low energies. These suggested that an electron transfer from Mn–O planes to adsorbed oxygen in the La1.8Sr1.2Mn2O7 was effective for improving the particulate matter oxidation activity.

Comparative Kinetics Study of the Thermal and Thermo-Oxidative Degradation of a Polystyrene-Clay Nanocompozite by TGA and DSC

The methods of thermogravimetry (TGA) and differential scanning calorimetry (DSC) have been used to study the thermal and thermo-oxidative degradation of polystyrene (PS) and a PS-clay nanocomposite. An advanced isoconversional method has been applied for kinertic analysis. Introduction of the clay phase increasers the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.

Modeling of water vapor adsorption isotherms onto polyacrylic polymer

The adsorbed amounts of water vapor onto polyacrylic polymer (polymer ×10) were measured using a thermogravimetry method as a function of pressure at 298 and 313 K. The adsorption isotherms are categorized to type II isotherms by IUPAC classification leading to a hysteresis loop between adsorption and desorption branches. The current study was completed by the measurement of the adsorption heats at 298 K using a differential scanning calorimetry. The calorimetric curves showed two adsorption heats domains. These domains have been attributed to the adsorption of “equivalent monolayer” and the condensation of water between polymeric chains. The correlation of experimental data to some chosen theoretical models shows that the GAB model is the most adequate to describe water vapor sorption isotherms.

Determination of thermal stability and activation energy of polyvinyl alcohol– cassava starch blends

The thermal degradation and activation energy of polyvinyl alcohol (PVOH) blends with cassava starch (CSV) were investigated by thermogravimetry method. Neat PVOH, CSV and PVOH–CSV specimens were prepared by solution casting method. Thermogravimetry is able to provide a clear description about the thermal resistance of PVOH–starch by comparing the onset degradation temperatures and activation energies of neat PVOH, CSV and PVOH–CSV blends (20–50 wt.% of PVOH). The results showed that neat CSV has better thermal resistance than neat PVOH. This is probably due to the presence of cyclic hemiacetal structure in starch is sustainable to thermal attacks. PVOH–CSV blend exhibits enhancement in thermal stability at 40–50 wt.% of PVOH. The activation energies of 40 and 50 wt.% of PVOH loading in CSV are 149.64 and 175.49 kJ/mol, which are 5.47% and 23.69% higher than CSV, respectively. In short, blending of cassava starch with PVOH significantly improved the thermal stability of PVOH.

Composites based on fluorinated carbon fiber and polytetrafluoroethylene: Adsorption properties and heat stability

In this work, the methods of gas chromatography, IR spectroscopy, and thermogravimetry are used to study the adsorption properties, the chemistry of the surface, and the heat stability of composites based on fluorinated carbon fiber (FCF) and polytetrafluoroethylene (PTFE) as a binding agent. It is found that the increase in the PTFE content in the composite from 10–15 wt % has a slight effect on values of the thermodynamic characteristics of adsorption and the form of IR spectra. The increase in the Henry constants and the heats of absorption upon the introduction of binding agent into FCF results from additional lateral interactions with the polymer, which fills a small part of the adsorbing surface of FCF. In addition, the general nature of the intermolecular interactions with the prevalence of the dispersion component under adsorption on FCF and composites on its basis is observed. The adsorbents are found to be heat stable when heated to 400°C in airflow.

Structural Characterization and Thermal Properties of 1-Amino-1-ethylamino-2,2-dinitroethylene

1-amino-1-ethylamino-2,2-dinitroethylene (AEFOX-7) was synthesized by the reaction of 1,1-diamino-2,2-dinitroethylene (FOX-7) and ethylamine aqueous solution at 92 °C. The theoretical investigation on AEFOX-7 was carried out by B3LYP/6–311++G** method. The IR frequencies and NMR chemical shifts were performed and compared with the experimental results. The thermal behavior of AEFOX-7 was studied with differential scanning calorimetry and thermal gravity-derivative thermogravimetry methods, and can be divided into a melting process and an exothermic decomposition process. The enthalpy, apparent activation energy and pre-exponential factor of the exothermic decomposition reaction were obtained as 374.88 kJ/mol, 169.7 kJ/mol, and 1019.24 s−1, respectively. The critical temperature of thermal explosion of AEFOX-7 is 145.2 °C. The specific heat capacity of AEFOX-7 was determined with micro-DSC method and theoretical calculation method, and the molar heat capacity is 214.50 J/(mol K) at 298.15 K. The adiabatic time-to-explosion of AEFOX-7 was calculated to be a certain value between 1.38–1.40 s. The thermal stability of AEFOX-7 is much lower than that of FOX-7.

Principal component analysis of thermal decomposition of magnesium salts used as drugs

Thermal decomposition of magnesium salts of organic acids used in medicine (Mg acetate, Mg valproate, Mg lactate, Mg citrate, Mg hydrogen aspartate, Zn hydrogen aspartate) was analyzed by thermoanalytical, calorimetrical, and computational methods. Thermoanalytical studies were performed with aid of a derivatograph. 50-, 100-, and 200-mg samples were heated in a static air atmosphere at a heating rate of 3, 5, 10, and 15 °C min−1 up to the final temperature of 700–900 °C. By differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG) methods, it has been established that thermal decomposition of the salts under study occurs via two stages. The first stage (dehydratation) was distinctly marked on the thermoanalytical curves. Calorimetrical studies were carried out by using of a heat-flux Mettler Toledo differential scanning calorimetry (DSC) system. Ten milligram samples of compounds under study were heated in the temperature range from 20 to 400 °C at a heating rate of 10 and 20 °C min−1 under an air stream. The studies showed that the values of transitions heats and enthalpies of dehydration for investigated salts varied with the increasing of heating rate. For chemometric evaluation of thermoanalytical results, the principal component analysis (PCA) was applied. This method revealed that points on PC1 versus PC2 diagrams corresponding to the compounds of similar chemical constitution are localized in the similar ranges of the first two PC’s values. This proves that thermal decomposition reflects similarity in the structure of magnesium salts of organic acids.

Clarification of the oxygen adsorption properties of YBaCo 4O 7 at high temperature by thermogravimetry

The oxygen adsorption/desorption properties of YBaCo 4O 7 at high temperature were investigated by thermogravimetry (TG) method, in which two types of oxygen adsorption were combined. The first type adsorbed oxygen at about 700 °C and released the adsorbed oxygen at 880 °C. After the first type oxygen desorption, even the temperature and oxygen flow were kept the same, a second type oxygen adsorption at about 880 °C occurred and the adsorbed oxygen were released at above 980 °C. The combination of these two types of oxygen adsorption/desorption was responsible for the difference in TG curves obtained by different heating programs.

Structural special features in nanodispersed Ni-SiO2 composite materials produced by method of chemical dispersion

The method of chemical dispersion with the use of inexpensive and available initial components is applied to obtain nanodispersed composite powders based on nickel and silicon oxide of various compositions. The methods of X-ray diffraction, electron microscopy, thermogravimetry, and low-temperature adsorption are used to determine the optimum modes of obtaining nanopowders as well as the dependence of their structure and dispersion ability on composition and conditions of metallization. It is shown that the increase in silicon oxide content in samples up to 30 wt % leads to almost complete suppression of the process of sintering and recrystallization of nickel particles at temperatures of 500–600°C. The microscopic studies make it possible to establish that temperature stability of the material is provided by the presence of a gaspermeable envelope of silicon oxide nanoparticles on the surface of nickel particles. The results show that these materials are promising for use as catalysts in various fields, including the processes of synthesis of carbon nanomaterials by the method of catalytic pyrolysis of methane.

Modeling process kinetics in Cu/C nanocomposite synthesis

We have studied the kinetics of chemical transformations in polyacrylonitrile (PAN) and composite Cu/PAN (CCu = 10% (mass)) at P = 10−5 Pa in the range of temperatures of 20–700°C during heating according to the linear law with a velocity of 10°C/min with the method of thermogravimetry. From the conducted kinetic studies of pyrolysis, it can be inferred that kinetic data of the destruction reaction of PAN and a composite of Cu/PAN are described with differential dependences on the basis of heterogeneous chemical reaction equations. Experimental data prove the heterogeneous reactions of the first order. The limiting stages of the process depend on the kinetic processes of chemical bonds opening in the polymer and composite. For the reaction of composite Cu/PAN in a vacuum, the determinant is the decomposition of copper salt and a PAN complex with the formation of copper nanoparticles at 470–570 K.

Novel N-Containing Precursors of Nickel(II) for Film Deposition by MOCVD

The synthesis of volatile nickel(II) complexes with N-containing ligands like CH3C(O,NCH3)CH2C(NR)CH3 (R - H, CH3) was performed. The substances were identified by various physico-chemical methods. The thermal behavior of the compounds in the solid state was investigated by the method of thermogravimetry and difference-scanning calorimetry in vacuum and helium. Using the Knudsen method and static method the temperature dependences of saturated vapor pressure were studied, the standard thermodynamic parameters of sublimation and evaporation process were calculated. By means of high temperature mass spectrometry the thermolysis of complex vapor was studied in vacuum and gas by-products were determined. One of the complexes has been used as precursor for the film deposition. The films obtained were investigated by using XRD analysis.

Phase equilibrium system of RbCl-PrCl3-HCl(12.86 mass %)-H2O at 298.15 K and standard molar enthalpy of formation of new solid-phase compound

The equilibrium solubility of the quaternary system RbCl-PrCl3-HCl-H2O was determined at 298.15 K and the corresponding equilibrium diagram was constructed in this paper. The quaternary system is complicated with three equilibrium solid phases, RbCl, RbPrCl4 · 4H2O (1:1 type) and PrCl3 · 6H2O, of which the new compound RbPrCl4 · 4H2O was found to be congruently soluble in the system. The new compound obtained was identified and characterized by the methods of X-ray diffraction, thermogravimetry, and differential thermogravimetry. The compound loses its crystal water by one step at 343 K to 453 K. The standard molar enthalpy of solution of RbPrCl4 · 4H2O in deionized water was measured to be −24.53 ± 0.22 kJ mol−1 by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be −2743.20 ± 1.09 kJ mol−1.

The characteristics of electrical trees in the inner and outer layers of different voltage rating XLPE cable insulation

The statistical initiation and propagation characteristics of electrical trees in cross-linked polyethylene (XLPE) cables with different voltage ratings from 66 to 500 kV were investigated under a constant test voltage of 50 Hz/7 kV (the 66 kV rating cable is from UK, the others from China). It was found that the characteristics of electrical trees in the inner region of 66 kV cable insulation differed considerably from those in the outer region under the same test conditions; however, no significant differences appeared in the 110 kV rating cable and above. The initiation time of electrical trees in both the inner and the outer regions of the 66 kV cable is much shorter than that in higher voltage rating cables; in addition the growth rate of electrical trees in the 66 kV cable is much larger than that in the higher voltage rating cables. By using x-ray diffraction, differential scanning calorimetry and thermogravimetry methods, it was revealed that besides the extrusion process, the molecular weight of base polymer material and its distribution are the prime factors deciding the crystallization state. The crystallization state and the impurity content are responsible for the resistance to electrical trees. Furthermore, it was proposed that big spherulites will cooperate with high impurity content in enhancing the initiation and growth processes of electrical trees via the ‘synergetic effect’. Finally, dense and small spherulites, high crystallinity, high purity level of base polymer material and super-clean production processes are desirable for higher voltage rating cables.

Study of thermal stability of tetraarenoporphyrazine metal complexes

Thermal stability in air of metal complexes of certain tetraarenoporphyrazines: tetrapyrazineporphyrazine, tetra-2,3-quinoxalinoporphyrazine, and tetra-2,3-naphtholocyanine, and also of copper complexes of tetra(tert-butyl)phthalocyanine, tetrapyrazineporphyrazine, and tetra-2,3-quinoxalinoporphyrazine substituted at the periphery was studied for the first time by the methods of thermogravimetry and differential thermal analysis. The effective thermal oxidation of these compounds occurs in the interval 620–820 K, and the tolerance for it is determined by both the metal nature and the structure of the macrocyclic ligand periphery.

Phase Equilibrium System of RbCl−SmCl3−HCl(12.84, 22.66 % by Mass)−H2O at 298.15 K and Standard Molar Enthalpy of Formation of RbSmCl4·4H2O

Solubility of the quaternary system RbCl−SmCl3−HCl(12.84, 22.66 % by mass)−H2O was determined at 298.15 K, and corresponding equilibrium diagrams were constructed. The quaternary system is complicated with three equilibrium solid phases RbCl, RbSmCl4·4H2O (1:1 type), and SmCl3·6H2O. The solubilities of RbCl, RbSmCl4·4H2O, and SmCl3·6H2O decreased with an increase of the concentration of HCl. The crystallization field decreased for RbCl and SmCl3·6H2O and increased for RbSmCl4·4H2O with an increase in the HCl concentration. The new solid-phase compound RbSmCl4·4H2O was found to be uncongruently soluble in the system. The compound RbSmCl4·4H2O was characterized by the methods of X-ray diffraction, thermogravimetry, and differential thermogravimetry. The compound loses its crystal water by one step at (359 to 457) K. The standard molar enthalpy of solution of RbSmCl4·4H2O in deionized water was measured to be −(29.40 ± 0.26) kJ·mol−1 by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be −(2725.3 ± 1.0) kJ·mol−1.

Effect of metal substitution for cobalt on the oxygen adsorption properties of YBaCo4O7

YBaCo4O7 compound is capable to intake and release a large amount of oxygen in the temperature range of 200–400°C. In the present study, the effect of Zn, Ga and Fe substitution for Co on the oxygen adsorption/desorption properties of YBaCo4O7 were investigated by thermogravimetry (TG) method. Due to fixed oxidation state of Zn2+ ions, the substitution of Zn2+ for Co2+ suppresses the oxygen adsorption of YBaCo4−xZnxO7. The substitution of Ga3+ for Co3+ also decreases the oxygen absorption capacity of YBaCo4−xGaxO7. This can be explained by the strong affinity of Ga3+ ions towards the GaO4 tetrahedron. Compared with Zn- and Ga-substituted samples, the drop of oxygen adsorption capacity is smallest for Fe-substituted samples because of the similar changeability of oxidation states of Co and Fe ions.