Search Results
Abstract
A simplified approach was developed to estimate the vapor pressure of pure compounds from experimental data obtained by isothermal thermogravimetric (TG) analysis. A numerical procedure was developed to estimate the Antoine parameters of the substance by the analysis of isothermal TG data. The results of the experimental validations carried out evidenced that at least a preliminary estimation of vapour pressures of pure substances by the analysis of TG data is possible. The limited time and the reduced amounts of sample required for the experimental runs make the technique attractive with respect to the conventional and more accurate techniques for vapor pressure assessment.
Transformations de la phase supraconductrice a haute T c (Bi,Pb)2Sr2CaCu2O8+x
Etude des variations de stoechiométrie d'oxygène par optimisation de l'analyse thermogravimétrique
Abstract
DTA-DTG systematic study of highT c superconducting phase (Bi,Pb)2Sr2CaCu2O8+x, with and without lead, shows a quantitatively opposite variation of oxygen stoechiometry on heating and cooling. Multiplate sample container, designed for the study, allowed to dissociated PbO loss from oxygen variations. Phases transformations have been studied under severalP O2 by scanning DTA and DTG. Oxygen variations evolution has been evaluated by isothermal TG. The results proved that phase diagram representation must take into consideration theP O2 coordinate.
Simulating minerals pyroprocessing by thermal analysis
Clinkerisation of cement raw mixes
Abstract
TG and DTA studies on laboratory cement raw mixes and raw dolomite have been extensively reported in the literature. This paper discusses four aspects. (1) Calcination kinetics of raw mix by isothermal TG and calculation of rate constants to derive activation energy by Arrhenius plots. (2) Quantification by TG of minerals in Indian laterites. The amount of goethite appears to influence burnability of raw mix. (3) Determination of practical heat of clinker formation from DTA studies and establishment of enthalpy temperature relationship of raw mix for heat transfer studies in rotary kilns. (4) Prediction of material temperature profile in a dolomite kiln from DTA studies of raw dolomite.
The non-oxidative thermal degradation kinetics of poly(di-n-alkyl itaconates), ranging from the methyl to then-octyl derivatives, were studied by non-isothermal and isothermal TG. The thermal degradation activation energy and characteristic mass loss temperatures were found to decrease with increasing substituent size. The shapes of the DTG curves were dependent on the size of the alkyl substituent. The different DTG maxima were ascribed to various modes of initiation of depolymerisation. The thermal stability of poly(di-n-hexyl itaconate) was found to be independent of the initial molar mass of the sample in the range ofM w from 104 to 107 g/mol.
Abstract
The kinetics and mechanism of the initial stage of thermal decomposition of 2,4,6-trinitro toluene (TNT), a widely used high explosive, have been studied, together with its morphology and evolved gaseous products using thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy (IR) and hot-stage microscopy. The kinetics of the thermolysis has been followed by IR after suppressing volatilisation by matrixing and by isothermal TG without suppressing volatilisation to simulate actual user conditions. The best linearity was obtained for Avrami-Erofeev equation for n=1 in isothermal IR and also in isothermal TG. The activation energy was found to be 135 kJ mol−1, with logA (in s−1) 12.5 by IR. The effect of additives on the initial thermolysis of TNT has also been studied. Evolved gas analysis by IR showed that CO2, NO2, NO and H2O are more dominant than N2O, HCN and CO. The decomposition involves the initial rupture of the C-NO2 bond, weakened by hydrogen bonding with the labile hydrogen atom of the adjacent CH3 group, followed by the abstraction of the hydrogen atom of the methyl group by NO2, generated in the initial step.
Abstract
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.
Abstract
Normal pressure thermogravimetry (TG) measurements were used to study the sublimation behavior of several volatile metal compounds, used as metal precursors in thin film fabrication by chemical vapor phase methods, like atomic layer deposition (ALD) and chemical vapor deposition (CVD). The results indicated that dynamic TG measurements may be used to find correct source temperatures to be used in an ALD reactor: a good correlation between the source temperatures used in ALD and temperatures corresponding to mass losses of 10 and 50% in TG was verified. It was also found that isothermal TG measurements offer a simple way for the vapor pressure measurements which otherwise are not trivial for solids with only moderate volatility.
Abstract
The lanthanidic complexes of general formula Ln(C11H19O2)3 were synthesized and characterized by elementary analysis, infrared absorption espectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction of thermal decomposition of complexes has been studied by non-isothermal and isothermal TG. The thermal decomposition reaction of complexes began in the solid phase for Tb(thd)3, Tm(thd)3 and Yb(thd)3 and in the liquid phase for Er(thd)3 and Lu(thd)3, as it was observed by TG/DTG/DSC superimposed curves. The kinetic model that best adjusted the experimental isothermal thermogravimetric data was the R1 model. Through the Ozawa method it was possible to find coherent results in the kinetic parameters and according to the activation energy the following stability order was obtained: Tb(thd)3>Lu(thd)3>Yb(thd)3>Tm(thd)3>Er(thd)3
Abstract
The crystal C81H78N12O6Cd3 was synthesized and its structure was determined by single crystal X-ray diffraction method. The complex crystallizes in the monoclinic system space group P21/n with cell parameters, a=15.959(4) , b=26.222(3) , c=25.907(6) , β=101.60(2). The non-isothermal kinetics of the crystal was studied by use of non-isothermal TG and DTG curves. The kinetic parameters were analyzed by means of integral and differential methods, and mechanism functions of the thermal decomposition reaction for its second step were proposed. The kinetic equation of thermal decomposition is expressed as: dα/dt=Aexp(-E/RT)1.5(1-α)4/3[1/(1-α)1/3-1]−1. The average values of E(kJ mol−1) and lnA/s−1 are 339.25, 43.95, respectively.
Abstract
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 CNBun 2 )2 >Cd(S2 CNPrn 2 )2 >Cd(S2 CNBui 2 )2 >Cd(S2 CNEt2 )2 , which accords with the sequence of stability of the apparent activation energies.
