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The kinetics of isothermal dehydration of two crystal hydrates with equivalent water molecule sublattices (LiCOOH.H2O and LiSO4.H2O) was investigated in vacuum with a quartz crystal microbalance, and the dynamics of structural reorganization of the substances was studied by the synchrotron radiation method. Differences were found both in the nucleation stage and in the stage of reaction interface advance. The results indicate that the kinetic behaviour of isothermal decomposition of solids is determined by the structural reorganization of a metastable intermediate.
The reduction kinetics of a pure and a Ca-added hematite, as well as of two iron oxide-containing metallurgical wastes, were studied by means of isothermal TG measurements, using H2 or CO as reducing agents.
The kinetics of thermal dehydration of [Ni2Al(OH)6]2SO4.nH2O has been studied through the analysis of isothermal weight loss data. The results obtained seem to indicate that the process is governed by a diffusion mechanism up to anα value which is dependent on the temperature. An explanation is provided for this behaviour on the basis of the structural properties of the compound and the nature of the water loss.
Abstract
The nitrate complexes of copper, nickel and zinc with diethylenetriamine (dien) i.e. [Cu(dien)2](NO3)2, [Ni(dien)2](NO3)22H2O and [Zn(dien)2](NO3)2 have been prepared and characterised. Thermal studies were undertaken using TG-DTG, DSC, ignition delay (t id) and ignition temperature (IT) measurements. Impact sensitivity was measured using drop mass technique. The kinetic parameters for both non-isothermal and isothermal decomposition of the complexes were evaluated by employing Coats-Redfern (C-R) method and Avrami-Erofeev (A-E) equations (n=2 and 3), respectively. The kinetic analysis, using isothermal TG data, was also made on the basis of model free isoconversional method and plausible mechanistic pathways for their decomposition are proposed. Rapid process was assessed by ignition delay measurements. All these complexes were found to be insensitive towards impact of 2 kg mass hammer up to the height limit (110 cm) of the instrument used. The heat of reaction (?H) for each stage of decomposition was determined using DSC.
Abstract
CL-20 is an attractive HEM having density (>2 g cm-3) and velocity of detonation (9400 m s-1) superior to HMX (1.9 g cm-3 and 9100 m s-1). During this study, CL-20 was synthesized to establish viability of efficient synthesis method. The compound synthesized at HEMRL was characterized by FTIR, 1H NMR and elemental analysis. Thermal studies (dynamic DSC and isothermal TG) were undertaken to determine kinetic parameters and understand the decomposition patterns. An attempt is made to explain the mechanism of decomposition of CL-20 on the basis of the data obtained by the authors and findings of other researchers. The activation energy values obtained during this work by adopting various approaches are close to the values reported for N-NO2 bond cleavage suggesting that it is global rate determining process rather than the collapse of cage structure. Mass spectra also provides evidences in this regard. Monitoring of decomposition products at high temperature supports these findings and brings out that NO2 initiates secondary decomposition processes because of entrapment in cage structure.
Abstract
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.
The kinetics of the thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in condensed state has been investigated by high temperature infrared spectroscopy (IR) and thermogravimetry (TG) in conjunction with pyrolysis gas analysis, differential thermal analysis (DTA) and hot stage microscopy. The decomposition proceeds in two main stages under isothermal conditions and the initial stage involving about 24% loss in weight obeys Avrami-Erofe'ev equation (n= 1), and is governed by an activation energy (E) of 150.58 kJ·mol−1 and log(A in s−1) 12.06. The second stage corresponding to 24 to 90% loss in weight gave best fit for Avrami-Erofe'ev equation,n=2, withE=239.56 kJ·mol−1 and log(A in s−1) 19.88 by isothermal TG. The effect of additives, on the initial thermolysis of TATB has also been studied. Evolved gas analysis by IR showed that NH3, CO2, NO2, HCN and H2O are produced in the initial stage of decomposition. The decomposition in KBr matrix in the temperature range 272 to 311.5°C shows relative preferential loss in the -NH2 to -NO2 band intensity which indicates that the rupture of C-NH2 bond, weakened also by the interaction of the NH2 with the neighbouring NO2 group, appears to be the primary step in the thermolysis of TATB.
Abstract
The thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) (parylene AF-4) films with thicknesses of ca. 7.5 and 10 μm has been studied by both dynamic (10°C min−1) and isothermal TG in either nitrogen or oxygen atmospheres. In dynamic studies with nitrogen, gross decomposition occurs between 546.7±1.4 and 589.0±2.6°C, with 26.8±4.4% of the initial mass remaining at 700°C. With oxygen as the purge gas, the onset of decomposition shifts slightly to 530.8±4.2°C. The end of the transition at 587.4±2.6°C is within experimental error of the nitrogen value, but no polymer remains above 600°C. Isothermal data were obtained at 10°C intervals from 420 to 490°C in nitrogen, and from 390 to 450°C in oxygen. Plots of log(Δ%wt/Δt)vs. T−1 are linear throughout the specified range for oxygen and from 420 to 470°C for nitrogen. The calculated activation energies of (147±16) kJ mol−1 and (150±12) kJ mol−1 in N2 and O2, respectively, are equal within experimental error.
Abstract
This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO3)24H2O, Cu(NO3)24H2O and their mixtures of known compositions in the temperature range 30–1200C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0–60C. The mixture with composition 0.85Zn(NO3)26H2O+0.15Cu(NO3)26H2O showed single melting peak at 29C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu2O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl22H2O into the mixture 0.85Zn(NO3)26H2O+0.15Cu(NO3)26H2O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO3)26H2O+0.15Cu(NO3)26H2O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.
In this work the thermal characteristics of cellulose samples with different structure were investigated. The samples were prepared by reacting the cellulose with ethanolic hydroxide solution. Depending on the time of alkaline treatment, the intensity of cellulose transformation differed. Starting from cellulose I structure, with the highest degree of crystallinity, the other samples consisted of mixed structures of cellulose I and II, or were completely transformed to cellulose II structure with the lowest degree of crystallinity. The thermal behaviour of the samples was studied by using a Perkin Elmer TGS-2 and DSC-2 instruments. The kinetic parameters of dehydration and degradation were determined from non-isothermal TG-data (Nitrogen-inert atmosphere and a heating rate of 20 deg/min). The thermal effects of water evolution (heating rate of 80 deg/min) of the cellulose samples were found to depend on the structural characteristics and the crystallinity of the samples. The activation energy and frequency factor were in correlation with the structural changes.
