Isothermal TG Research Articles

The role of thermal analysis in optimization of the electrochromic effect of nickel oxide thin films, prepared by the sol–gel method. Part I

Nickel oxide thin films have been widely studied as an optical active layer in electrochromic devices. It is well known for these films that thermal treatment is the key factor which determines the electrochromic effect during potential cycling. Therefore, it is extremely important to perform thermal analysis on the thin films rather than on the corresponding xerogels. In this article, the thermal behaviour of sol–gel derived nickel oxide thin films, prepared from NiSO 4 precursor, is compared to that of the corresponding xerogel using dynamic and isothermal TG and dynamic DSC measurements. By regulating the duration of the heat treatment at 270 °C, one can control the thermal conversion of the amorphous thin film into nickel oxide. For the xerogel, this process occurs at 300 °C. Using the EXAFS method, it was confirmed that the amorphous xerogel is analogous to the thin film sample. Thermal decomposition of the amorphous xerogel was studied in detail by IR and MS techniques. From the weight loss curve of the thin film, the substrate to film mass ratio was determined for different substrates. The effect of heat treatment on these films was determined by measuring their electrochromic properties.

Studies on energetic compounds part 28: thermolysis of HMX and its plastic bonded explosives containing Estane

The thermolysis of HMX, Estane and two of their plastic bonded explosives (PBXs) namely HXE 9505 and HXE 9010 were investigated using non-isothermal TG–DTG and DSC under an inert gas (N 2) atmosphere. Non-isothermal TG, isothermal TG and DTA were also undertaken in air atmosphere on the above-said samples. Lowering of decomposition temperature of HMX has been observed when Estane was coated over it, to make their PBXs. The extent of lowering was increased as the amount of Estane increased in the PBX. Kinetic analyses of isothermal TG data has been made by using model fitting methods as well as by using a model free isoconversional method. The merits and demerits of both modes of kinetic analysis have been critically evaluated by making use of the kinetic parameters obtained there from to explain the thermal characteristics of the samples studied. Explosion delay measurements have been made on HMX and its PBXs and the kinetic parameters were also evaluated from this data.

Compatibility between active components of a commercial drug

A thermal and a kinetic analysis on the decomposition processes of a commercial drug named diamplicil (AD), obtained by an antibiotic combination of ampicillin (A) and dicloxacillin (D), have been carried out to find their thermal stability. The DSC/TG curves of this commercial drug were compared with those of its active components and an excipient, the magnesium stearate (M). Kinetic study was carried out using both isothermal and dynamic TG curves. Decomposition mechanisms for both active components and commercial drug tested were not found. The kinetic data obtained by the non-isothermal isoconversional method showed that D component causes a decrease of the kinetic stability of the active A component. Additive magnesium stearate does not decrease the stability of the two components. Moreover, storage time values at room temperature were calculated.

Formation of copper oxide through NaNO 3–KNO 3 eutectic melt and its catalytic activity in the decomposition of ammonium perchlorate

The decomposition of basic copper carbonate in the presence and absence of NaNO 3–KNO 3 eutectic melt has been studied by employing isothermal TG and dynamic TG/DSC techniques. The rate constants for the decomposition in the presence of eutectic melt were found to be higher than when carbonate was heated alone. In both the cases copper oxide was found to be the end product. Catalytic activity of copper oxide obtained by the two methods were tested for the decomposition of ammonium perchlorate.

Some Aspects About Kinetics of Isothermal Degradation of Layered Hydrous Titanate Intercalated with n-Alkyldiamines

Thermogravimetric data were used to calculate the kinetics of isothermal degradation of layered tetratitanate intercalated with n-alkyldiamines H2N(CH2)nNH2 (n=2, 3, 4, 6 or 8). The hydrous matrix showed two mass loss steps from the thermogravimetric curve, corresponding to the release of physisorbed and lattice water molecules. For the intercalated matrices a third mass loss was observed due to the release of organic moiety. From these values, the amine intercalated matrices can be ordered in the following sequence of thermal stability; C4>C2>C3≅C6>C8. Kinetic studies were carried out to the release of lattice water molecules. The kinetic model that best adjusted the experimental isothermal TG data was the diffusion mechanism controlling process.

Sulfonation of arylamines: Part 12. Kinetics of thermal decomposition of dimethylanilinium sulfates

Three dimethylanilinium sulfates (DMAS) have been prepared and characterised by elemental and spectral studies. Thermal decomposition of these salts has been studied by TG and simultaneous TG-DTG technique and kinetic parameters were evaluated from both dynamic and isothermal TG data using mechanism based kinetic equations. The thermal decomposition pathways have also been suggested and it has been found that DMAS salts give dimethyl aminobenzenesulfonic acids (DMABSA) via solid state reaction. The primary step in the thermal decomposition involves proton transfer followed by sulfonation.

Preparation of NiO through NaNO 3–KNO 3 eutectic melt and its catalytic activity during the decomposition of polystyrene

The decomposition of basic nickel carbonate in the presence and absence of NaNO 3 (sodium nitrate)–KNO 3 (potassium nitrate) eutectic melt has been studied by employing isothermal TG and dynamic TG–DSC techniques. The rate constants for the decomposition in the presence of eutectic melt were found to be higher than when carbonate alone was heated. In both cases, nickel oxide was found to be the end product. Catalytic activities of nickel oxide obtained by the two methods were tested for their efficiency in decomposition of polystyrene (PS). It was found that at higher temperature (330 and 360°C), the nickel oxide obtained from eutectic melt was more active than that obtained by direct decomposition.

Dehydration of NiCl 2·6H 2O

Powdered samples of nickel chloride hexahydrate prepared by grinding small crystallites grown by slow evaporation of an aqueous solution have been studied by dynamic and isothermal TG measurements. It is observed from dynamic TG that hexahydrated nickel chloride dehydrates in two steps releasing 5 moles H 2O and 1 mole H 2O at mean temperatures of 224 and 291°C, respectively. Isothermal TG measurements, dependent upon temperature show different dehydration pattern with respect to time. In the temperature range 240–300°C dehydration pattern similar to dynamic TG has been observed. From dynamic and isothermal measurements the kinetic parameters E and Z are calculated. It is observed that the general mechanism of dehydration in these samples for both steps is random nucleation and subsequent growth. The same mechanism is described by different functions in isothermal and dynamic studies.

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.

Kinetics of the thermal decomposition of oil shale from Puertollano (Spain)

The kinetics of the thermal decomposition of Spanish oil shale was studied using isothermal and non-isothermal thermogravimetric analyses (TGA). The isothermal TG data were studied at different particle sizes (0.250×10 −3, 0.505×10 −3 and 0.925×10 −3 m) and three temperature plateaux (703, 688 and 673 K). For the kinetic analysis, the Integral Method was used. The non-isothermal weight-loss data was analysed at different heating rates (5, 10, 15, 20 and 50 K/min) up to 1173 K and for a particle size of 0.250×10 −3 m. Three methods were applied for the determination of the kinetic parameters: the Direct Arrhenius Plot Method, the Integral Method and the Differential Method. From an engineering point of view, the rate of the thermal decomposition of Spanish oil shale can be suitably described by overall first-order kinetics. We also found that transport effect problems affected the observed rate when the heating rates were higher than 10 K/min; additionally, no mass and heat transfer resistance was observed for the different particle sizes studied. The results obtained from the isothermal method give an apparent activation energy of 150 kJ/mol and a frequency factor of 2.11×10 8 s −1, while for the non-isothermal method these results were: E=167 kJ/mol and A=2.16×10 9 s −1. The pyrolysis rates of Spanish shale are compared with those of Anvil Points, Clear Creek and Moroccan shale.

Thermal analysis of ammonium dinitramide (ADN)

Kinetic constants of decomposition were determined for ADN and prilled ADN by DSC and TG. Pressure DSC at 550 psi air or helium had similar kinetic constants for prilled ADN, namely 29 kcal/mol activation energy and a log frequency factor of ∼14.0 min −1. These values were similar to those found in sealed sample pans in which the decomposition gases were confined. DSC and TG runs in open sample pans in nitrogen or helium had higher activation energies and frequency factors, namely 40–43 kcal/mol and 18–20 min −1, respectively. Thus, it appears that confinement of the ADN decomposition gases either under pressurization or a sealed environment accelerates the decomposition of prilled ADN. Kinetics of decomposition of unprilled ADN at atmospheric pressure in nitrogen or helium by DSC and TG were E a=37 kcal/mol and log A=17 min −1. Unprilled ADN had lower activation energies and frequency factor for decomposition than prilled ADN which contained stabilizers. The effect of sample containment (i.e. aluminum, coated aluminum, gold, and glass ampoules) on the shape of the DSC curve of ADN was investigated. Isothermal TG in vacuum of ADN in the 45–75°C region and the DSC analysis of the TG residues showed unusual results in the 60°C region. The rate and enthalpy of decomposition of four dinitramide salts and their dielectric relaxation were related to the basicity of the cation.

Effect of lactic/glycolic acid side chains on the thermal degradation kinetics of chitosan derivatives

The thermal degradation properties of chitosan and lactic and/or glycolic acid grafted chitosan have been studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TG) in the range of 25–500°C. Both DSC and dynamic TG results show that the samples are thermal degraded easily after grafting the lactic and/or glycolic acid. From the isothermal TG experiments, the initial activation energy and the activation energy at different stages is obtained. The initial activation energy of all grafted samples is much lower than that of chitosan, especially for the sample GA/CS=2 and it varies with degree of conversion. The FT–IR spectra of thermally degraded residues give an indication of the chitosan polyscaccharide ring degradation after 30min in 280°C, while sample GA/CS=2 will degrade only after 15min.

Controlled Rate Thermogravimetry: New usefulness of controlled rate thermogravimetry revealed by decomposition of polyimide

Curves obtained by controlled rate TG of polyimide film in air are quite different from those obtained by conventional constant rate heating TG. A two step mass loss was observed during the constant rate heating TG, while mass loss proceeded as a single step process in the controlled rate TG. To elucidate the cause for this difference, kinetic analysis was made, and it was found that the reaction mechanism in a lower temperature range is different from those in a higher temperature range. The lower temperature decomposition is a single step process, and the higher temperature decomposition is a two-step process. The reason for the difference is that only the low temperature single step process is observed in the controlled rate TG, while both reactions are observed in the constant heating rate TG along with the temperature increase. This speculation was confirmed by isothermal TG. These facts show us another usefulness of controlled rate TG. To analyze the three types of TG data together, the Friedman—Ozawa method was used, and it is demonstrated to be the most appropriate and reliable.

Study of the Crystallization of an Aromatic Poly-ether-ketone (PK99) by Calorimetric and X-ray Analysis

An analysis of the crystallization behaviour of a new poly(aryl-ether-ether-ketone-ketone), PK99, by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) is presented. Isothermal crystallization TG were obtained in the whole range between the glass transition temperature (Tg) and the melting temperature (Tm) as a consequence of the slow crystallization kinetics stemming from the closeness of these transitions. The calorimetric results, compared with WAXD data, were applied to determine the theoretical melting temperature and crystallization enthalpy. The DSC and WAXD data were combined in order to calculate the total amount of the crystallizable fraction of the polymer, and a model was proposed to explain the difference between the fractions of crystallinity observed with these techniques. The thermal and X-ray data were also correlated with different lamellar morphologies arising from the crystallization conditions. Finally, DSC experiments on the crystallized sample were used to detect the presence of a rigid amorphous phase which does not relax at Tg.

Studies on Energetic (Non) Compounds. Part 21: Preparation and thermal decomposition of ring substituted dimethyl anilinium bromides

Six isomeric dimethyl anilinium bromides (DMABr) have been prepared and characterized by elemental and spectroscopic studies. Thermal decomposition of these salts has been studied by TG and simultaneous TG-DTA techniques. Kinetic parameters have been evaluated from isothermal TG data using contracting area and contracting cube equations. The decomposition pathways have also been suggested which involves simultaneous sublimation (at lower temperature) and dissociative vaporization/decomposition (at higher temperature).

Kinetic Analysis of the Decomposition of Chelates of Di-alkyldithiocarbamate of Cd(II)

The thermal decomposition kinetics of the solid complexes Cd(S2 CNR2 )2 , where R =C2 H5 , n -C3 H7 , n -C4 H9 or iso -C4 H9 , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R1 . The thermal analysis data suggested the thermal stability sequence Cd(S2 CNBun2 )2 >Cd(S2 CNPrn2 )2 >Cd(S2 CNBui2 )2 >Cd(S2 CNEt2 )2 , which accords with the sequence of stability of the apparent activation energies.

Studies on (non) energetic compounds. Part-14: Thermal decomposition of dimethylanilinium chlorides

Six dimethylanilinium chlorides (DMACl) have been prepared and characterised. Thermal decomposition of these salts have been studied by TG and DSC techniques. Kinetic parameters have been evaluated from the isothermal and non-isothermal TG data, Contracting area, Contracting cube and Coats–Redfern equations have been found to give the best fits. The decomposition pathways have also been suggested. It has been observed that simultaneous sublimation/decomposition processes are involved during the thermal decomposition of DMACl.

Kinetic study of the thermal decomposition on bis(dialkyldithiocarbamate) Cd(II) complexes by isothermal and non-isothermal thermogravimetry

The thermal decomposition kinetics of solid Cd(S 2CNR 2) 2 complexes, where R=C 2H 5, n-C 3H 7, n-C 4H 9 and iso-C 4H 9, has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions occur in the liquid phase. The kinetic model that best adjusted the experimental isothermal TG data was the one-dimensional phase-boundary reaction controlling process R 1. The thermal analysis data suggest the thermal stability sequence Cd(S 2CNBu n 2) 2>Cd(S 2CNPr n 2) 2>Cd(S 2CNBu i 2) 2>Cd(S 2CNEt 2) 2, according to the order of stability of apparent activation energy.

Thermal Decomposition Behavior of Polyester Fabrics Treated with a Bromine-Containing Compound

The thermal decomposition behavior of poly ( ethylene terephthalate) (PET) fabrics containing meso-1,2,3,4-tetrabromobutane (TBB) is investigated using thermogra vimetry (TG), differential thermal analysis (DTA), and pyrolysis gas chromatography- mass spectrometry (Py-GC-MS). Isothermal TG analysis proves that the presence of TBB has little effect on the thermal decomposition of PET. However, isothermal DTA data reveal that the absorbed TBB participates in some reactions in the condensed phase of PET. On the other hand, Py-GC-MS analysis reveals that bromine atoms exist in the thermal decomposition products of PET. Thus, vinyl groups are generated from PET by β-CH hydrogen transfer, and they then react with hydrogen bromide, which is produced by TBB, to form bromine-containing thermal decomposition products. These facts show why TBB molecules, which have strong affinities for PET segments, are effective for Hame retardation.

Study of the Kinetics of the Combustion Reaction on Shuangya Mountain Coal Dust by TG

The combustion behavior of Shuangya Mountain (SYM) coal dust has been investigated by means of TG in this paper. The reaction fraction α can be obtained from isothermal TG data. The regressions of g(α), an integral function of α vs. t for different reaction mechanisms were performed. The mechanism of nucleation and nuclei growth is determined as the controlling step of the coal dust combustion reaction by the correlation coefficient of the regression, and the kinetic equation of the SYM coal dust combustion reaction has been established.