Showing papers in "Thermochimica Acta in 1977"

A new method for the simultaneous determination of the size and shape of pores: the thermoporometry

Abstract: A thermodynamic study of the liquid—solid phase transformations in porous materials provides the relationships between the size of the pores in which solidification takes place and the temperature of the triple point of the divided liquid, on the one hand, and between this temperature and the apparent solidification energy on the other hand. The experimental study of the phase transformations, carried out by means of a microcalorimeter, gives the values of the parameters necessary to calculate the free solid = liquid interphase extension energy γls at different temperatures. A formula γls  f(T) is given for water and benzene. Once this factor is known, it is possible to study the numerical relationship between pore-radius and freezing energy at the equilibrium temperature. By using these relations together with the solidification thermogram (the recording of the power evolved by the solidification of a capillary condensate during a linear decrease of temperature) the authors have been able to determine pore distribution curves. An emphasis is put on the comparison between this method, thermoporometry, and the B.J.H. method. Last of all the comparison of the experimental data for solidification and melting provide information concerning pore shape by means of the evaluation of a thermodynamic shape factor or by a method of simulation of porous material.

The estimation of the thermodynamic properties of ternary alloys from binary data using the shortest distance composition path

Abstract: A new composition path, Xi-Xj=constant, is suggested for the semi-empirical calculation of the thermodynamic properties of ternary ‘substitutional’ solutions from binary data, when the binary systems show deviations from the regular solution model. A comparison is made between the results obtained for integral and partial properties using this composition path and those calculated employing other composition paths suggested in literature. It appears that the best estimate of the ternary properties is obtained when binary data at compositions closest to the ternary composition are used.

Thermal decomposition reactions of solids controlled by diffusion and phase-boundary processes: possible misinterpretation of the mechanism from thermogravimetric data

Abstract: A comparative study of phase -boundary and diffusion-controlled reactions has been carried out using thermogravimetric data. The results reported support the hypothesis that a single TG diagram does not allow the determination of whether a solid decomposition reaction is controlled by a diffusion mechanism or governed by the movement of an interface coming from a nucleation process. However, the analysis of both a single TG diagram and an isothermal curve might be a quick and valid way for discerning between these mechanisms. These statements are confirmed by studying the thermal decomposition kinetics of Ba(OH) 2 and CaCO 3 .

Thermodynamique de composes azotes III. Etude Thermochimique de la glycine et de la l-α-alanine

Abstract: The enthalpies of formation of glycine and L-α-alanine are determined by two complementary techniques: combustion calorimetry and change of state (sublimation) calorimetry. The values of the experimental and theoretical energy of conjugation of these two molecules (partially conjugated) and the energetical value of the CN bond in Laidler's scheme, derived from the experimental enthalpy of atomization, are also given.

Evaluation of kinetic parameters from thermogravimetri traces: Part II. Thermal dehydroxylation of Mg(OH)2

Abstract: A combined numerical method was employed to treat the themogravimetric data for the dehydroxylation of magnesium hydroxide obtained in our own laboratory. Satisfactory results were obtained. The data were also treated with Freeman and Carroll's, Coats and Redfern's and Satava's methode. The agreement between the results obtained by the method and those of Coats and Redfern's and Satava's method were also satisfactory.

Effect of thermal transport mechanisms on the thermal decomposition of CaCO3

Abstract: Isothermal and dynamic techniques were employed to examine the rate of weight loss of CaCO3. Thermogravimetric studies were conducted in atmospheres of He, N2, Ar, and various percentage of CO2 in Ar. Three methods for deriving kinetic parameters from thermogravimetric data were used and these results were then compared with data obtained from isothermal investigations done on identical samples. It was found that the higher the thermal conductivity of the atmosphere, the more repidly the reaction proceeded. Also, as the percentage of CO2 in Ar increased, the temperature range of the decomposition became higher and narrower, resulting in a higher activation energy.

DTA—TG—MS in the investigation of clays: Quantitative determination of H2O, CO and CO2 by evolved gas analysis with a mass spectrometer

Abstract: A thermoanalyzer (Mettler) combined with a quadrupole mass spectrometer (Balzers) by a capillary inlet system allows simultaneous DTA, TG and evolved gas analysis in different atmospheres. Decomposition of CaC2O4·H2O in air and argon, respectively, demonstrates the usefulness of the mass spectrometer for the quantitative determination of H2O, CO2 and CO. Decomposition of NaHCO3 at a heating rate of 10°C min−1 reveals that H2O and CO2 evolved simultaneously at a relatively low temperature (159°C) can also be determined quantitatively and nearly without retardation compared with the weight loss step. In the investigation of clays an example will be given of the usefulness of the described DTA—TG—MS in the quantitative interpretation of overlapping reactions.

Methodological Principles in studying chemical reaction kinetics under conditions of programmed heating

Abstract: The paper describes the methodology of the study of chemical kinetics under non-isothermal conditions realized at programmed heating. A short critical review is given of the available approaches to determine kinetic parameters from thermal analysis data. In order to find thermophysical conditions for a quantitative experiment, the results of a theoretical solution of the problem on the course of a chemical reaction at linear heating are given. An appropriate equipment and methodical ways which provide these conditions are described. For obvious single-stage reactions, the scheme without a priori recalculation of non-isothermal data for isothermal conditions is considered comprehensively, which makes it possible to obtain a kinetic law in a graphic (or parametric) form analogous to that obtained in the isothermal experiment. The aspects of the use of non-isothermal methods for studying the kinetics of complex (multistage) chemical reactions is discussed.

Studies on the thermal decomposition of ferric acetate.

Abstract: The thermal decomposition of ferric acetate,Fe(CH 3 COO) 3 , has been investigated using thermogravimetry (TG), differential thermal analysis (DTA), the conventional method involving the measurement of the volume of gaseous products evolved during decomposition and the X-ray diffraction technique. Analysis of the kinetic data obtained both by the conventional method and the polythermal decomposition using thermogravimetry gave nearly the same activation energy for the decomposition of ferric acetate. The endothermic peaks at 278 and 328°C appear to be due to the decomposition accompanied by the desorption of acetone and carbon dioxide, respectively.

Effect of metal oxide additives on the thermal decomposition of perchlorates, oxalates and hydroxides

Abstract: The effects of α-Fe2O3 and α-Al2O3 additives on the thermal decomposition of perchlorates, oxalates and hydroxides were investigated by means of DTA, TG and X-ray techniques. It was found that the oxide additives catalytically promoted the decomposition of perchlorates (NaClO4, KClO4 and Mg(ClO4)2) and resulted in a lowering of the initial decomposition temperature (Ti). On the other hand, the oxides showed no significant effect on the decomposition of oxalates (FeC2O4 and CuC2O4) and hydroxides (Mg(OH)2 and Al(OH)3). The thermal decomposition of KClO4 was chosen to compare the catalytic effect of twelve metal oxides. The results indicated that the transition metal oxides such as Cr2O3, α-Fe2O3 and CuO markedly accelerated the decomposition; these oxides resulted in a solid-phase decomposition before fusion of KClO4, and the initial decomposition temperature (Ti) of KClO4 with oxides was about 100–200°C lower than that without catalyst. The oxides such as α-Al2O3 and MgO resulted in a slight lowering of the temperature of the fusion and promoted the molten-phase decomposition of KClO4, but their effects were not so remarkable as those of the transition metal oxides. The modified catalytic mechanisms of transition metal oxides were proposed by considering the electron transfer and the oxygen-abstraction models.

Vapor pressure and dissociation energy of (In2O)

Abstract: The vapor pressure of pure liquid indium, and the sum of pressures of (In) and (In2O) species over the condensed phase mixture {In} + , contained in a silica vessel, have been measured by Knudsen effusion and Langmuir free vaporization methods in the temperatue range 600 to 950°C. Mass spectrometric studies reported in the literature show that (In) and (In2O) are the important species in the vapor phase over the {In} + ; mixture. The vapor pressure of (In2O) corresponding to the reaction, deduced from the present measurements is given by the equation, The “apparent evaporation coefficient” for the condensed phase mixture is approximately 0.8. The energy for the dissociation (In2O) molecule into atoms calculated from the above equation is D°0 = 180.0 (± 1.0) kcal mol−1.

Thermoanalytische methoden in der chemischen verfahrensentwicklung

Abstract: Thermal analysis methods are used in process development for the investigation of chemical kinetics, for the evaluation of thermal hazards and for the determination of caloric design data. For these applications heat-flow methods are preferably used. This paper gives a survey of methods and instruments, and then presents a new “bench scale heat-flow calorimeter”. The use of this new instruments is illustrated by investigations on the formation of a Grignard compound and on the isomerisation of trimethyl-phosphite.

Investigation of phase diagrams by DTA and X-ray methods: The systems AX/CoX2 (A = Na-Cs, TI;X = Cl, Br, I)

Abstract: A combination of differential thermal analysis and X-ray structure analysis is advantageously used to investigate the formation of double halides in complicated systems betweeen alkali halides, AX, and divalent halides, MX 2 . Among the systems of CoX 2 (X = Cl, Br.I) this is particularly valid for the systems TICI/CoCl 2 and TlBr/CoBr 2 .

Surface area measurements of clay minerals by glycerol sorption on a thermobalance

Abstract: Glycerol-treated montmorillonite gradually loses one layer of the two-layer glycerol complex upon heating to 150–200°C, forming a monolayer complex with a sharp X-ray reflection at about 14 A. This complex is quite stable on further heating to about 230–250°C. Above 250°C the monolayer complex breaks down rapidly. A gravimetric method has been used to determine the weight of the glycerol monolayer. The procedure involves addition of a 10% glycerol solution to a dried and weighed sample of clay in a platinum crucible followed by a heating and weighing procedure in a thermoanalyzer (Mettler). The method was used to calculate the internal and external surface area of different clays.

Liquid phase PVT data for binary mixtures of toluene with nitroethane and acetone, and benzene with acetonitrile, nitromethane, and ethanol

Abstract: Liquid phase PVT data were obtained at 0°C, 45°C, and 90°C for pressures up to 217.7 atm for various binary mixtures of toulene—nitroethane, toluene—acetone, acetonitrile—benzene, nitromethane—benzane, and ethanol—benzene. Such data are required for purposes of converting excess thermodynamic property data from a constant pressure basis to a constant volume basis. Data are presebt for each pure component and for three separate mole fractions for each binary pair. Because benzene solidifies at 5.5°C, data for pure benzene are reported at 12°C rather than 0°C.

2,4,6-Trinitrotoluene thermal decomposition: kinetic parameters determined by the isothermal differential scanning calorimetry technique

Abstract: The isothermal differential scanning calorimetry technique is used to determine kinetic parameters for the thermal decomposition of 2,4,6-trinitrotoluene (TNT). Values for the activation energy and pre-exponential factor are presented. An analysis of the thermochemical induction period data is presented which allows calculation of the activation energy of the induction reaction.

Thermogravimetry combined with chemical ionization mass spectrometry a new technique in thermal analysis

Abstract: Detailed accounts are given on the simultaneous application of a thermobalance and a quadrupole mass spectrometer with chemical ionization (CI), investigating thermal decomposition reaction under normal pressure most efficiently. In the combined dynamic system the purge gas of the thermoanalyzer is simultaneously used as reaction gas in the chemical ionization source. The use of CI, a type of high pressure mass spectrometry, has the advantage of avoiding all interface problems and of restricting the fragmentation of released volatile compounds. Therefore, this technique allows the identification of volatiles and the determination of their sequence of release even in complex decomposition reactions. The capability of the tandem system is demonstrated by the termal decomposition of some selected compounds.

A calculation of gibbs free energies for ferrous ions and the solubility of magnetite in H2O and D2O to 300°C

Abstract: Gibbs energy and entropy data for aqueous Fe 2+ , FeOH + , HFeO − 2 and FeO 2− 2 are critically reviewed. The most reliable values are used in a Criss—Cobble extrapolation to calculate Gibbs energies to 300°C and, hence, the solubility of Fe 3 O 4 in H 2 O and D 2 O as a function of the pH or pD at 25°C. A set if Gibbs energies is presented which satisfies the Criss—Cobole entropy correspondence principle and which is consistent with both the reliable low-temperature thermodynamic data and all published high-temperature solubilities.

Thermochemistry of decomposition of manganese(II) oxalate dihydrate

Abstract: Differential scanning calorimetry (DSC) has been used to determine the enthalpy of dehydration of manganese(II) oxalate dihydrate and the enthalpies of decomposition in nitrogen and in oxygen of the anhydrous oxalate. The thermodynamic data have been related to the activation energies reported in kinetic studies and to the mechanisms proposed for the thermal decomposition and oxidation processes.

Beitragzur kinetik von festkörperreaktionen unter nicht- isothermen bedingungen

Abstract: On the basis of the method developed by Coats and Redfern for determining kinetic parameters from non-isothermal measurements, a computing programme is described which enables us to find the most probable reaction mechanism from 11 kinetics equations by using a statistic test method. This mechanism can be due to diffusion, nucleation, chemical reactions and phase boundary reactions. First, theoretical studies were carried out to prove the validity of the model equations for the whole TG-curve. The kinetic parameters were calculated with the help of linear regression. The dispersion of them TG-values caused by automatic data acquisition is compensated by weighting each value. The residual dispersion was used as a distinguishing feature for the different kinetic models. The dehydration of kaolin shows the efficiency of the programme and illustrates the selection of the most probable kinetic model. The representation of more results obtained by the described programme makes it possible to compare them with known values from other publications.

Modern methods for coupling quadrupole mass spectrometers with thermoanalyzers for temperatures up to 1500°C☆

Abstract: By coupling a quadrupole mass spectrometer (QMS) with a thermoanalyzer (TA), it is possible to obtain information on the gases evolving during the heating process and this combination has proved to be helpful for the interpretation of thermal processes 1–5 . Necessary conditions for getting full and genuine mass spectrometric information are appropriate devices for sampling and sample tranfer, matched to the respective temperature program, atmosphere and condensation temperature and kind of evolving gases.

A thermogravimetry/differential thermal analysis, evolved gas analysis and pyrolysis/gas chromatography—mass spectrometry study of tetrakis (diethyldithiocarbamato)tin(IV)

Abstract: The thermal decomposition of tetrakis(diethyldithiocarbamato)tin(IV) has been studied by TG/DTA, EGA and P/GC-MS techniques. From the P/GC-MS analysis, it is apparent that the denticity of the dithiocarbamate ligand influences the mechanism of decomposition. Initially, the monodentate ligands decompose by a radical mechanism to form tetraethylthiuramdisulphide which decomposes further into carbon disulphide and diethylamine. The intermediate formed, bis(diethydithiocarbamato)tin(II), decomposes in two different ways. The bidentate ligands decompose with the liberation of carbon disulphide and tetraethylthiourea, whereas the monodentate ligands, formed as a result of the high temperatures, decompose to produce S-ethyl N,N-diethyldithiocarbamate and ethylisothiocyanate. The overall thermal decomposition mechenism of tetrakis(diethyldithiocarbamato)tin(IV) is complex and the primary decomposition involved both ionic and radical recombination reactions.

Thermal techniques in biomembrane and lipoprotein research

Abstract: In structural determinations of inanimate materials, thermal analysis has long proven to be a powerful technique, particularly when coupled with X-ray diffraction or spectroscopic methods. In molecular biology, thermal analysis, frequently combined with other techniques, similarly shows itself to be a powerful tool. Its importance is not limited solely to understanding biological structures but extends to understanding physiological processes as well. This paper describes the application to molecular biology of differential scanning calorimetry (DSC) and the complementary technique of differential scanning dilatometry (DSD). The modification and operation of two commercial differential scanning calorimeters for use in molecular biology is discussed, as well as the design and operation of a novel differential scanning dilatometer together with its auxiliary techniques. Some examples are given of the uses of these methods in understanding the structure, thermodynamic state, and physiological functions of biological membranes. A further illustration of the type of approach taken in applying thermal analysis to molecular biology is provided by a description of an ongoing study. This study uses DSC and DSD in correlation with the temperature dependence of ultraviolet circular dichroism (CD) to elucidate the structures of human high density (HDL) and low density (LDL) serum lipoproteins.

Properties of molten carboxylates part 5. A quantitative differential thermal analysis study of mesophase formation in the sytems lead(II)dodecanoate/lead(II) oxide and lead(II)dodecanoate/hendecane

Abstract: Measurements have been made of the temperatures and enthalpy changes of phase transitions in the systems lead dodecanoate/lead oxide and lead dodecanoate/hendecane. The data have been discussed in terms of the R theory of amphiphylic mesophases. The concepts of the R theory are shown to be useful in the interpretation of phase transitions in molten carboxylate systems.

A thermogravimetry/differential thermal analysis, evolved gas analysis and pyrolysis/ gas chromatography—mass spectrometry study of dihalotin(IV)bisdiethydithiocarbamates

Abstract: Three dihalotin(IV) bisdiethyldithiocarbamates have been subjected to controlled pyrolysis/GC—MS analysis and the major products of the first stage of decomposition identified. These data, in addition to those obtained from TG/DTA analysis are used to determine the decomposition mechanism of the complexes. In an inert atmosphere dihalotin(IV)bisdiethyldithiocarbamate pyrolyses to yield carbon disulphide and tetraethylthiourea as the major volatile products and dihalotinsulphide as the major solid phase intermediate, which subsequently decomposes to yield tin sulphide. It has been conclusively shown that the nature of the halogen ligands has no influence on the mode of thermal decomposition of these complexes. The proposed thermal decomposition mechanism correlates well with the known structure of the complexes.

Relations structure-réactivité grandeurs thermodynamiques de protonation d'h'et'erocycles saturés et non saturés

Abstract: Proton ionisation thermodynamical quantities ot two series of heterocyclic compounds were determined at 25°C, in an aqueous medium of constant ionic strength 0.5M KNO3. The first series consists of some saturated molecules, e.g., imides (pyrrolidine, thiazolidine, 2,4-thiazolidinedione, hydantoin, thiohydantoin, succinimide, parabanic acid, barbituric acid), the second one of azoles (imidazole, benzimidazole, pyrazole, thiazole, 1,2,4-triazole, benzotriazole). The influence of the structure of these molecules on their reactivity towards the hydrogen ion was discussed, on the basis of the related ΔH° and ΔS° functions.

Effect of different carbons on ignition temperature and activation energy of black powder

Abstract: By means of TG, DTG, and DTA, it was shown that the source of carbon can affect the decomposition and reaction characteristics of black powder compositions. Carbons with high volatile content lower the activation energy and reduce the ignition temperature of black powder. The removal of these volatiles causes an increase in ignition temperature and activation energy. It also showed that although sulfur has no effect on the ignition temperature, it does affect the preignition reaction. Sulfurless black powder also has larger activation energies than regular black powder. Compositions of black powder containing channel black have lower activation energies than those with charcoal.

Développement du domaine d'application de la calorimétrie à conduction et de l'analyse calorimétrique différentielle en thermodynamique et en cinétique

Abstract: In a previous paper3 we reported first results concerning the simultaneous determination of equilibrium constants and enthalpies of reaction by titration conduction microcalorimetry The high sensitivity of the calorimeters (Calvet type), its excellent long time stability, allow, under certain conditions an accurate analysis of equilibria If the calorimeter is corrected for inertia, the application field of the titration method is enlarged In this paper, the description of an electronic on-line corrector is given The application field of such an apparatus is interesting for example in titration microcalorimetry, differential calorimetric analysis and for the calorimetric measurement of kinetic parameters

Thermal analysis, calorimetry and chemical thermodynamics —a review

Abstract: An attempt is made to review the level of development of the subjects covered by the Swiss Society for Thermal Analysis and Calorimetry, namely thermal analysis, calorimetry and chemical thermodynamics. A comprehensive presentation and elucidation of the stage of development of these subjects seems to be impossible because of the broadness of each of these subjects with respect to theoretical, methodological and instrumental aspects, and also because of the diversity of applied and basic research in this area. The discussion is therefore restricted to such aspects as definitions and the boundaries of these subjects. Furthermore, the importance of chemical thermodynamics in the application to thermoanalytical methods and to applied research is pointed out.

Evaluation of kinetic parameters from thermogravimetric curves: Part I. Combined numerical method

Abstract: A new method is proposed to evaluate kinetic parameters from thermogravimetric traces. The method consists of two steps, α, T and dα/dT values are first employed to estimate kinetic parameters by linear least squares fitting, using the five types of mechanism for solid phase reactions suggested by Sestak. From the different sets of parameters thus obtained, the most probable mechanism type is decided. The resultant parameters for the chosen type of mechanism may further be improved by differential correction method, if necessary, using the more accurate data of α and T. The proposed method was tested with artificial data and the data for the thermal dehydration of gypsum by Sestak et al. The results were very satisfactory.