Showing papers in "Journal of Thermal Analysis and Calorimetry in 1992"
TL;DR: In this paper, the applicability of both conventional Thermal Analysis (TA) and controlled rate thermal analysis (CRTA) for kinetic analysis is discussed, and it is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation.
Abstract: The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved. A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite.
87 citations
TL;DR: The Hi-ResTM TGA TGA 2950 as discussed by the authors is a new thermogravimetric instrument that gives a significant improvement to TG results, and the instrument control parameters are varied as a function of the sample's rate of weight change.
Abstract: A new thermogravimetric instrument is introduced, Hi-ResTM TGA 2950. The Hi-ResTM TQA gives a significant improvement to TG results. The instrument control parameters are varied as a function of the sample's rate of weight change. This novel feature improves resolution and reduces analysis time. The maximum heating rate and resolution index are user selectable.
72 citations
TL;DR: In this paper, a new software package (THESEUS) is assembled for the analysis of the DSC data, Concerning the thermal denaturation of biological macromolecules, which is useful to obtain accurate physico-chemical information, bypassing the casual and systematic errors, very common in these experiments.
Abstract: A new software package (THESEUS) has been assembled for the analysis of the DSC data, Concerning the thermal denaturation of biological macromolecules. The system is useful to obtain accurate physico-chemical information, bypassing the casual and systematic errors, very common in these experiments. It can also be used for handling data from other instruments and methodologies giving thermodynamic, spectroscopic or other kind of data as a function of temperature. Because many of the researches in this field are of exploratory nature and continuously new unfolding mechanisms are described or hypothesized in the current literature, we have written and assembled this powerful and flexible program of general applicability, in order to put the operator in a position to control each step of the calculation procedure and use his own experience for choosing the better way to solve unexpected problems.
68 citations
TL;DR: In this article, a software is described enabling kinetic analysis under non-isothermal or isothermal conditions from DSC, or from TG data, with thirteen methods of kinetic analysis, three for isothermal analysis and two for TG, with eight different functions for the choice of the proper mechanism for each of them.
Abstract: A software is described enabling kinetic analysis under non-isothermal or isothermal conditions from DSC, or from TG data. The program offers thirteen methods of kinetic analysis for DSC, three for isothermal analysis and two for TG, with eight different functions for the choice of the proper mechanism for each of them.
60 citations
TL;DR: ZnO added to the system Portland cement changed the kinetics of the hydration process substantially as mentioned in this paper and inhibited the reaction of tricalcium silicate with water, resulting in an induction period prolongation.
Abstract: ZnO added to the system Portland cement — water changes the kinetics of the hydration process substantially. Amorphous zinc hydroxide is formed and inhibits the reaction of tricalcium silicate with water, resulting in an induction period prolongation. This effect depends on the amount of ZnO added to the hydrated paste. The transformation of zinc hydroxide into calcium hydrozincate provokes the further hydration.
53 citations
TL;DR: In this paper, the influence of various experimental conditions such as sample weight, atmosphere and heating rate on the decomposition of NH4VO3, CaCO3 and V2O5 has been investigated.
Abstract: The influence of various experimental conditions such as sample weight, atmosphere and heating rate on the decomposition of NH4VO3, CaCO3 and V2O5 has been investigated. Results obtained clearly indicate that the course of the reactions and — in turn — the kinetic parameters, are not intrinsic to the particular compound and that they characterize rather the combination of experimental conditions and investigated compound. Such a situation makes it almost impossible to choose ‘standard conditions’ for the calculation of kinetic parameters, because under different circumstances quite different reaction-pathways can occur.
47 citations
TL;DR: In this article, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method in the range from −50° to +130°C.
Abstract: In the range from −50° to +130°C, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied cases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperatureTg on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.
46 citations
TL;DR: In this article, the heat of adsorption of CO2 on zeolites with variable content of mono-and divalent cations was investigated and it was shown that high initial heat is associated with a slow and activated rate of adaption for high contents of Na+, Li+ or Ca2+.
Abstract: Calorimetric measurements of the heat of adsorption of CO2 on zeolites with variable content of mono- and divalent cations lead to common conclusions. High initial heats (up to 120 kJ·mol−1 for NaA), generally associated with a slow and activated rate of adsorption, are found for high contents of Na+, Li+ or Ca2+. They are attributed to a limited number of chemisorption sites (0.3 per α cage in NaA).
39 citations
TL;DR: The stepwise isothermal analysis (SIA) technique was introduced by the author in the late seventies and has proved to be very useful both in thermogravimetric and dilatometric studies as discussed by the authors.
Abstract: The Stepwise Isothermal Analysis (SIA) technique, which was introduced by the author in the late seventies has proved to be very useful both in thermogravimetric and dilatometric studies. By this technique the heating and cooling programme is controlled by the rate of the reactions taking place in the sample, for instance thermal decompositions (TG) or sintering (dilatometry). By an advanced computer programme this control is achieved in the following way: The sample is heated at a constant heating rate until the reaction rate. i. e. the slope of the weight/length versus time curve, exceeds a preset limit at which point the heating is stopped. The reaction thereafter proceeds isothermally until the rate again becomes smaller than the limit where the heating is resumed. By this techniques the reactions thus characteristically take place in isothermal steps.
34 citations
TL;DR: In this article, a simple esterification reaction is used to demonstrate standard procedures for determining the thermokinetic parameters of an exothermic reaction from adiabatic calorimetric data.
Abstract: A simple esterification reaction is used to demonstrate standard procedures for determining the thermokinetic parameters of an exothermic reaction from adiabatic calorimetric data. The influence of variations in the heat capacity of the sample due to changes in temperature and concentration is explored. Shortcomings in the simple interpretation of adiabatic data are identified and isothermal heatflow calorimetry is used to reveal autocatalytic effects which were not apparent from the adiabatic experiments. A more rigourous interpretation of the adiabatic and isothermal data is outlined and used to predict the conditions which can lead to exothermic runaway in a batch reactor. Mathematical simulation of the conditions in a jacketed reactor is used to demonstrate the importance of developing reliable kinetic expressions before assessing the safety of a batch process.
33 citations
TL;DR: In this paper, the dehydration and decomposition characteristics of an undried and a partly dried sample of NiCl2·xH2O have been investigated by isothermal and non-isothermal (TG and DTA) methods in static air as well as flowing nitrogen environment.
Abstract: The dehydration and decomposition characteristics of an undried and a partly dried sample of NiCl2·xH2O have been investigated by isothermal and non-isothermal (TG and DTA) methods in static air as well as flowing nitrogen environment. While the isothermal weight loss method fails to distinguish between different steps of reaction, TG curves upto 800°C reveal as many as five steps in static air and four steps in nitrogen atmosphere. However, both methods indicate that NiCl2 is stable upto 400°C above which dehydrochlorination takes place in presence of water vapour. The intermediate products of dehydration and decomposition at different temperatures have been characterized by chemical analysis, X-ray diffraction, infrared and diffuse reflectance spectroscopy. All these methods reveal the presence of water in samples calcined at even 400°–600°C. Thermodynamic functions for different steps of dehydration have been calculated and discussed in the light of the possible structural changes occurring in the partially dehydrated products.
TL;DR: Several organic compounds like phenanthrene, benzanilide, anisic acid, triphenylene, 2-chloroanthraquinone, hexachlorobenzene, carbazole and 4-iodobenzoic acid were studied in the range 300-600 K.
Abstract: Several organic compounds like phenanthrene, benzanilide, anisic acid, triphenylene, 2-chloroanthraquinone, hexachlorobenzene, carbazole, 4-iodobenzoic acid, perylene, anthraquinone, as new reference materials for temperature and energy calibration of DTA and DSC apparatuses were studied in the range 300—600 K.
TL;DR: In this paper, the kinetic parameters of dehydrochlorination (DHCL) process of PVC and PVC mixed with different amount of ZnCl2 have been determined by using thermogravimetric analysis.
Abstract: The kinetic parameters of dehydrochlorination (DHCL) process of PVC and PVC mixed with different amount of ZnCl2 have been determined by using thermogravimetric analysis. These values have been compared with those obtained by using UV-visible spectroscopic analysis of PVC film containing ZnCh degraded at different temperatures. The values of apparent activation energy (Ea) decreases with the increase of the amount of ZnCl2 and the values obtained in the present work are in reasonable comparison with previous works. The catalytic effect of ZnCl2 on PVC DHCL process is explained here.
TL;DR: In this article, the thermal stability of monolithic TiB2 and of Al2O3-30 vol% and Si3N4-20 vol% composites was investigated.
Abstract: In view of the susceptibility of TiB2 to oxidation, the thermal stability of monolithic TiB2 and of Al2O3-30 vol% TiB2 and Si3N4-20 vol% TiB2 composites was investigated. The temperature at which TiB2 ceramic starts to oxidize is about 400°C, oxidation kinetics being controlled by diffusion up toT≈900°C and in the first stage of the oxidation at 1000°C and 1100°C (up to 800 min and 500 min respectively), and by a linear law at higher temperatures and for longer periods.
TL;DR: In this paper, the authors defined overlapping reactions between CaSO3, CaS, CaSO4 and CaSO2 in air and nitrogen atmosphere, and showed that after disproportionation reaction they are formed via the system: 3CaSO4 + CaS→ → 4CaO + 4SO2.
Abstract: Simultaneous thermogravimetry and differential thermal analysis up to ca. 1400‡C of the thermal stability of CaSO3, CaS, CaSO4 and physical mixture of CaS and CaSO4 (molar ratio = 1∶3) both in air and nitrogen atmosphere has allowed overlapping reactions to be defined. The thermal decomposition of CaSO3 in air does not result in CaO and SO2 either, but after disproportionation reaction they are formed via the system: 3CaSO4 + CaS→ →4CaO + 4SO2. The oxidation reactions of CaSO3 and CaS should also be taken into account. The data from the X-ray diffraction analysis of the stable solid intermediates and from the polythermal X-ray diffraction studies provide supporting evidence for the proposed reaction mechanisms.
TL;DR: In this article, the heat of adsorption and isotherm of water vapor on NiO samples were measured simultaneously at 301 K to examine the energetic properties of the surface.
Abstract: Heat of adsorption and isotherm of water vapor on NiO samples were measured simultaneously at 301 K to examine the energetic properties of the surface. They revealed that NiO has a relatively uniform surface. The heat of adsorption ranging 80–90 kJ·mol−1 indicates the production of surface hydroxyl groups on the (100) plane of NiO. It is relatively small compared with that of other metal oxides, which suggests a weak nature of the Ni2+ ion sites for chemisorption of water. It is suspected that half of the surface Ni2+ ions are covered with hydroxyl groups and the remainings act as relatively strong physisorption sites for water molecules.
Abstract: Thermal analysis is a convenient means of characterizing the soot used as a source of the carbon clusters, the extracted mixture of fullerenes, and the individual clusters themselves. TG in an inert atmosphere will rapidly assay the volatile fractions, presumably the lower molecular weight clusters. TG in oxygen indicates — a slight weight gain for the soots and clusters prior to their combustion. DSC in oxygen is used to determine the heat of combustion for the separated C60 and C70 materials. The combustion occurs around 300°C for the clusters. There is a small exothermic peak before this which is attributed to the oxidation associated with the slight weight gain. The heats of combustion measured are −18.7 and −21.0 kJ·mol−1 for the C60 and C70 respectively. MS-EGA indicates the loss of small amounts of water and argon at temperatures around 250°C in vacuum and of solvent at about 350°C prior to sublimation.
TL;DR: In this article, the authors discuss recent research concerned with characterizing mechanisms within a group of solid state processes that has been the subject of extensive kinetic investigations (including thermal analyses): the dehydrations of crystalline hydrates.
Abstract: Thermal Analysis, the central topic of this conference, is a technique that is widely used for the measurement of reaction rates and from which deductions can be made concerning the identity of the bond redistribution steps contributing to the chemical change being investigated. The mechanistic insights obtained from such studies enable us to identify the factors that determine reactivity and to understand theoretically the controls operating in chemical reactions. The present article points out, however, that kinetic data alone do not usually provide sufficient information to enable detailed identification of the sequence of steps through which reactants are converted into products. This review discusses recent research concerned with characterizing mechanisms within a group of solid state processes that has been the subject of extensive kinetic investigations (including thermal analyses): the dehydrations of crystalline hydrates. Conclusions from previous studies of reactions of this type have contributed extensively to the more general understanding of solid-state reactions. Here we discuss some mechanistic conclusions from a number of recent studies in the field and emphasize the value of complementing rate measurements with other relevant observations, including microscopic examinations of the textural modifications that accompany chemical changes.
TL;DR: In this paper, the thermal analysis of some pesticides using simultaneous TG-DSC measurements and kinetic calculations by the dynamic TG technique have been carried out, and the results showed that the thermal properties of the pesticides were not significantly different from those reported in the literature.
Abstract: The thermal analysis of some pesticides using simultaneous TG-DSC measurements and kinetic calculations by the dynamic TG technique have been carried out.
TL;DR: In this article, the synthesis of malachite was studied through titrations of copper(II) salt solutions with a solution of sodium carbonate at different temperatures and the precipitates were characterized by TG, IR and chemical analysis.
Abstract: The synthesis of malachite CuCO3·Cu(OH)2 or Cu2CO3(OH)2 was studied through titrations of copper(II) salt solutions with a solution of sodium carbonate at different temperatures. The precipitates were characterized by TG, IR and chemical analysis. The composition varies depending on thepH of the solution and the temperature. Purer malachite was synthesized by simple mixing of a solution of copper(II) nitrate or sulfate with a solution of sodium carbonate at 50°C.
TL;DR: The polymorphic transformation of cubic into graphite-like boron nitride was studied by using DTA, high-temperature calorimetry and dilatometry over the temperature range 1000-2500 K as discussed by the authors.
Abstract: The polymorphic transformation of cubic into graphite-like boron nitride was studied by using DTA, high-temperature calorimetry and dilatometry over the temperature range 1000–2500 K. The transformation enthalpy was determined to be +22−11+5 kJ/mol.
TL;DR: In this paper, the authors deal with some of the assumtions and limitations of classical models used in thermal analysis kinetic studies of solid-state rections, and propose a new model based on non-classical models.
Abstract: The paper deals with some of the assumtions and limitations of ‘classical’ models used in thermal analysis kinetic studies of solid-state rections.
TL;DR: In this article, high-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged mesolite, and a high pressure phase resembling talc/mica with excess water.
Abstract: High-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged montmorillonite, kerolite, and a high-pressure phase resembling talc/mica with excess water. Because sealed capsules may be used to contain fluids, it is possible to evaluate the role of H2O in these reactions. A separate paper (Part II) addresses the use of HP-DTA to understand dehydroxylation reactions in these materials.
TL;DR: In this paper, a combination system of thermogravimetric/differential thermal analysis (TG-DTA) and Fourier transform infrared absorption spectroscopy (FT-IR) was described.
Abstract: A combination system of thermogravimetric/differential thermal analysis (TG-DTA) and Fourier-transform infrared absorption spectroscopy (FT-IR) was described. This simultaneous TG-DTA/FT-IR technique gave spectroscopic and weight loss information about the thermal degradation process of engineering polyesters; poly(ethylene terephthalate)(PET) and poly(butylene terephthalate)(PBT). The evolved gases from PET were benzoic acid, carbon dioxide and carbon monoxide, while those from PBT were terephthalic acid esters and benzoic acid esters.
TL;DR: In this paper, the thermal behavior of chemically deintercalated samples obtained by HCl treatment of non-stoichiometric Li/Ni mixed oxides is studied and a multi-step reduction of Ni with O2 evolution is observed between room temperature and 800
Abstract: The thermal behaviour of chemically deintercalated samples obtained by HCl treatment of non-stoichiometric Li/Ni mixed oxides is studied. A multi-step reduction of Ni with O2 evolution is observed between room temperature and 800‡C. Two cation redistribution processes are shown by the exothermal occurrence of a spinel phase at 300‡C and the endothermal reduction to a rock-salt phase with random distribution of Li and Ni cations in octahedral sites at 800‡C.
TL;DR: In this paper, high-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged mesoprocessed montmorillite, kerolite, and a high pressure phase resembling talc/mica with excess water.
Abstract: High-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged montmorillonite, kerolite, and a high-pressure phase resembling talc/mica with excess water. Because sealed capsules may be used to contain fluids, it is possible to evaluate the role of H 2 O in these reactions. A separate paper (Part II) addresses the use of HP-DTA to understand dehydroxylation reactions in these materials
TL;DR: In this paper, the stereochemistry of new cobalt, nickel and copper complexes of 5-(2-thiazolylazo)-barbituric acids was studied on the basis of thermal mea-surements.
Abstract: The stereochemistry of new cobalt(II), nickel(II) and copper(II) complexes of 5-(2-thiazolylazo)-barbituric and thiobarbituric acids was studied on the basis of thermal mea-surements. The orders of reactions and the energies of activation were evaluated. The data were explained from different aspects, mainly with regard to the electronic character of the substituent.
TL;DR: In this article, a continuous fluidized bed reactor (bench scale unit) has been assembled to perform biomass pyrolysis at temperatures ranging from 730° to 930°C at constant feed rate (44 g/h).
Abstract: In order to perform biomass pyrolysis a continuous fluidized bed reactor (bench scale unit) has been assembled. The influence of experimental conditions such as heating-up time and optimum particle diameter is presented. By feeding the biomass (almond shells) directly into the bubbling bed, pyrolysis has been performed at temperatures ranging from 730° to 930°C at constant feed rate (44 g/h). Remarkable increase of H2 in the product gas is observed when steam rather than an inert carrier such as nitrogen is used thus confirming the potential of this approach.
TL;DR: In this paper, a quasi-static thermal analysis is used for the characterization of the thermal behavior of inorganic fluorides, showing the strong dependence of thermal decomposition of hydroxonium fluorometallates, monofluorophosphates, and ammonium fluorometric compounds on the partial pressure.
Abstract: Quasi-static thermal analysis is very useful for the characterization of the thermal behaviour of inorganic fluorides. The strong dependence of the thermal decomposition of hydroxonium fluorometallates, monofluorophosphates, and ammonium fluorometallates on the partial pressure is demonstrated. Non-reciprocal quasi-isobaric investigations are specially suitable to disclose this behaviour. The possibilities of characterization of the reaction mechanism using quasi-static thermal analytical methods as well as the use of these methods as synthetic variants for phase-pure fluorides are demonstrated by further examples. In this context the repression of the amount of hydrolysis products is discussed.
TL;DR: In this article, the processes of thermal destruction of copper(II) bis(dipivaloylmethanate) (Cu(dpm)2) in the temperature range 150°-550°C were studied by using a two-temperature variant of a double chamber Knudsen cell, with mass spectrometric recording of the gas-phase composition.
Abstract: The processes of thermal destruction of copper(II) bis(dipivaloylmethanate) (Cu(dpm)2) in the temperature range 150°–550°C were studied by using a two-temperature variant of a double chamber Knudsen cell, with mass spectrometric recording of the gas-phase composition. The temperature range of stability of the vapour of the complex in vacuum was determined, as were those of its mixtures with oxygen in different proportions. The temperature dependence of the rate constant of the thermolysis of (Cu(dpm)2) vapour was obtained. The thermal stability of Hdpm vapour and the influence of oxygen on the thermolysis of the ligand were studied.