Showing papers in "Journal of Thermal Analysis and Calorimetry in 1991"
TL;DR: In the last few years, technological progress has been made in the development of new materials such as "geopolymers" and new techniques, such as ''sol-gel'' as mentioned in this paper, opening up new applications and procedures and transforming ideas that have been taken for granted in inorganic chemistry.
Abstract: Spectacular technological progress has been made in the last few years through thedevelopment of new materials such as «geopolymers», and new techniques, such as «sol-gel». New state-of-the-art materials designed with the help of geopolymerization reactions are opening up new applications and procedures and transforming ideas that have been taken for granted in inorganic chemistry. High temperature techniques arc no longer necessary to obtain materials which are ceramic-like in their structures and properties
3,178 citations
TL;DR: In this paper, the thermal decomposition of hexabromoplatinie acid was studied by derivatograph and differential scanning calorimetry, and the natures of pyrolysis processes were discussed and compared with those obtained for the analogous ehlorocomplexes.
Abstract: The potassium, ammonium and thirteen amine salts of hexabromoplatinie acid were obtained and characterized by chemical analysis. The thermal decompositions of these complex salts were studied by derivatograph and differential scanning calorimetry. The natures of the pyrolysis processes are discussed and compared with those obtained for the analogous ehlorocomplexes. From the TG curves, kinetic parameters were derived for different stages of the thermal decomposition.
216 citations
TL;DR: In this article, a general differential method is developed and described which determines the Arrhenius parameters, energy of activation and the preexponential factor, as functions of degree of conversion from sets of two or more experiments with differing thermal programs.
Abstract: A general differential method is developed and described which determines the Arrhenius parameters, energy of activation and the preexponential factor, as functions of degree of conversion from sets of two or more experiments with differing thermal programs. (These experiments may be performed at any combination of isothermal, constant heating rate or other temperature programs.) The method tests to see whether or not the kinetics follow the equation,f(α)=(1−α)n, and calculates the correct reaction order, n, when such an equation is applicable. The correct energy of activation,E, is determined as a function of both temperature and conversion. The correct preexponential term,A, is calculated for all cases described by equation, d(α)/dt=f (α) A exp(−E/RT), except for the ‘autocatalytic’ case in whichf(α)=0)=0. Calculation of parameters for equations involving other functions forf(α) will be described in a subsequent paper.
89 citations
TL;DR: In this paper, the pyrolysis of brown coal samples and bituminous coal maceral concentrates was investigated by non-isothermal thermogravimetry, and the TG data for these coals reveal a two-stage pyroolysis process.
Abstract: The pyrolysis of a suite of brown coal samples and bituminous coal maceral concentrates is investigated by non-isothermal thermogravimetry. The TG data for these coals reveal a two-stage pyrolysis process. The activation energy for the primary pyrolysis stage is considerably higher than that for the secondary pyrolysis stage. It is evident that a particular coal may be characterised by the weighted mean apparent pyrolysis activation energy which correlates with the corresponding specific energy of the coal.
81 citations
TL;DR: In this paper, the activation energies of a set of reactions were determined by the Coats and Redfern method and the Horowitz-Hugh method, which yielded similar results.
Abstract: The acetates of magnesium, nickel, copper, manganese, sodium and barium were subjected to thermal decomposition by means of thermogravimetric techniques (TG) under a constant flow of nitrogen. The decompositions occurred in steps and the kinetics of every set of reactions was determined by the Coats and Redfern method. These results were analysed to establish the decomposition kinetics and hence to calculate activation energies. The activation energies were also determined by applying the Horowitz-Hugh method, which yielded similar results.
77 citations
TL;DR: In this article, two causes for the kinetic compensation effect (KCE) were recognized for a given solidstate reaction at various heating rates, one due to any change in the range of reaction and the other due to misestimation of the appropriate rate law.
Abstract: Two causes for the kinetic compensation effect (KCE) were recognized for a given solidstate reaction at various heating rates. One is due to any change in the range of reaction. This KCE is quantitative and meaningful, provided thatF(α) remains constant under the given conditions. The other is due to misestimation of the appropriate rate law, which in turn leads to a superficial KCE. It was also shown that the existence of an isokinetic point does not necessarily imply the occurrence of a meaningful KCE.
76 citations
TL;DR: In this article, the shape of the interpolated baseline under a peak is determined by a change in the heat capacity of the sample and the heat transfer characteristics between sample and temperature sensor.
Abstract: In DSC's the shape of the interpolated baseline under a peak is determined by a change in the heat capacity of the sample and the heat transfer characteristics between sample and temperature sensor. The interpolated baseline is constructed according to formal criteria, experimentally or analytically on the basis of physico-chemical assumptions on the change of the heat capacity during transition. By the example of the melting of ice this paper shows analytically on the basis of a simple calorimeter model and a synthetic measuring curve, and experimentally, that the uncertainty of the enthalpy determination depends in general on the type of baseline and is in the order of magnitude of the repeatability of the DSC's (±0.5%).
70 citations
TL;DR: In this paper, the existence of an isokinetic point does not always indicate the kinetic compensation effect as a result of physicochemical reasons, and the correlation of the Arrhenius parameters is given for both the inappropriate kinetic model function and the working temperature interval.
Abstract: Mathematical considerations are used to show that the existence of an isokinetic point does not always indicate the kinetic compensation effect as a result of physicochemical reasons. The correlation of the Arrhenius parameters is given for both the inappropriate kinetic model function and the working temperature interval.
66 citations
TL;DR: In this article, the authors examined sources of error in determining activation energies and went on to consider the form of the alpha function and the value of A. They concluded that allowing significant pressures of product gas to appear in the reaction environment will lead to very high values for apparent activation energies.
Abstract: Following previous work on the measurement of meaningful activation energies and the application of Constant Rate Thermal Analysis (CRTA) to the determination of kinetic parameters [1, 2], here we further examine sources of error in determining activation energies and go on to consider the form of the alpha function and the value ofA. Using theoretical arguments based on transition state theory, we conclude that allowing significant pressures of product gas to appear in the reaction environment will lead to very high values for apparent activation energies. We note that, although this is observed in practice for calcium carbonate, it in no way invalidates the application of the Arrhenius equation to solid state decomposition reactions, provided care is taken to avoid this type of distortion of experimental results. We attempt to determine the alpha function for the decomposition of calcium carbonate using data gathered from a variety of different types of temperature programme and reaction conditions. We find that the apparent alpha function depends on the method adopted and the experimental conditions used. We propose an explanation of why this occurs and tentatively introduce a new way of looking at the development of a reaction interface for this type of reaction. We review the literature and conclude that, while significant variations for the activation energy for the decomposition of calcium carbonate exist, a critical appraisal leads to good agreement amongst values that follow good experimental practice and reliable methods of data reduction. The apparent divergence of results can be explained in the light of the theoretical arguments advanced and the easily understood sources of experimental error.
61 citations
TL;DR: In this article, a series of samples of the system Ni0.65Zn0.35CuxFe2−xO4 (x=0, 0.1, 0 2, 0 3, 0 4, 0 5 and 0.6) are prepared by the usual ceramic technique.
Abstract: A series of samples of the system Ni0.65Zn0.35CuxFe2−xO4 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) are prepared by the usual ceramic technique. X-ray analysis shows that they are cubic spinel (single phase). The lattice parameter, theoretical density (Dx), bulk density (D) and the porosity (P) are measured for the samples. The vacancy concentration of oxygen is an important parameter in the sintering process of spinel ferrites. The decrease in the population of Fe3+ ion in the octahedral sites with the introduction of Cu2+ results in the decrease of lattice parameter. The DTA tracing shows a strong exothermic peak at 90°C.
49 citations
TL;DR: In this article, the role of DSC in the investigation of the component processes which together form the basis of effective freeze-drying: a maximisation of yield, an optimum shelf life and a cost-effective process.
Abstract: The stabilities of protein based products in the freeze-dried state depend critically on the formulation and process variables temperature, pressure, time and moisture content. The principal determinants of biological stability are the glass/rubber transitions of the freeze concentrate and of the dried product and its residual moisture content. This paper describes the role of DSC in the investigation of the component processes which together form the basis of effective freeze-drying: a maximisation of yield, an optimum shelf life and a cost-effective process.
TL;DR: In this article, the kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using integral methods and the effect of procedural factors such as heating rate, sample mass and method of computation on them were also studied.
Abstract: Thermogravimetric studies on two varieties of calcium carbonate viz., analytical reagentgrade and insitu generated from calcium oxalate monohydrate, were carried out. The kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using integral methods and the effect of procedural factors such as heating rate, sample mass and method of computation on them were also studied. The procedural variables in the range studied had no marked influence on the results; however the kinetic parameters were marginally higher for the insitu generated calcium carbonate. This trend is explained by the presence of more micropores in the insitu generated calcium carbonate as well as the mechanism of its decomposition following phase boundary reaction with cylindrical symmetry.
TL;DR: In this article, a stable hydrate between cholesterol and β cyclodextrin (βCD) was characterized using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and nuclear magnetic resonance spectroscopy (13C NMR).
Abstract: Study and characterization of molecular complexes between cholesterol and beta cyclodextrin has been done using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (13C NMR). Whatever the value of the molar ratio cholesterol/βCD used during the preparation, the same compound is always obtained. Corresponding to a molar ratio 1/3 (cholesterol/βCD), this compound is a stable hydrate which, contrary toβCD, contains at room temperature a large amount of molecules of water. It can be dehydrated under low pressure but the thermal degradation occurs at 200°C (250°C forβCD). This implies that cholesterol is strongly bounded toβCD.
TL;DR: In this article, the authors investigated the rehydroxylation of clay minerals and hydration in Bronze and Iron Age pottery from the ‘Land of Geshur’ (east of the Sea of Galilee), by IR thermospectrometry.
Abstract: Rehydroxylation of clay minerals and hydration in Bronze and Iron Age pottery from the ‘Land of Geshur’ (east of the Sea of Galilee), were investigated by IR thermospectrometry. A weak OH band, which resembles those in smectite or illite, exists in most samples, but it is masked by the water bands at lower temperature. Two types of transformation of clay minerals occur during firing of raw materials, reversible and nonreversible dehydroxylation, taking place at a relatively low and high firing temperatures, respectively. Clay minerals rehydroxylate and reconstruct after relatively higher firing temperatures in noncalcareous raw materials than in calcareous ones. These processes take place after higher temperatures in cooking pots made from the former type of raw material as compared with storage and table-ware vessels made from the latter. The absorbed water in the pottery is mainly connected with the dominant X-ray amorphous matter formed by the firing process.
TL;DR: In this article, the acidity and basicity of twenty simple oxides mainly used in catalysis and ceramic materials were investigated by adsorption microcalorimetry of basic and acidic gas probe molecules such as ammonia and carbon dioxide.
Abstract: The acidity and basicity of about twenty simple oxides mainly used in catalysis and ceramic materials were investigated by adsorption microcalorimetry of basic and acidic gas probe molecules such as ammonia and carbon dioxide. The determination of the number, strength and site energy distribution of both acidic and basic sites in all the samples led to an improved description of the surfaces. The results allowed us to classify our samples in three main groups in relation to their acidic, basic or amphoteric character. Their acid-base behaviour was tentatively correlated to more general electronic and redox data given in the literature such as the electronegativity.
TL;DR: In this article, a differential scanning calorimetry was used to study the reaction [Mn(NH3)2]Cl2+ 4NH3 ⇄ [Mm(NH 3)6]Cl 2, which is of potential use in chemical heat pumps.
Abstract: The reaction [Mn(NH3)2]Cl2+ 4NH3 ⇄ [Mn(NH3)6]Cl2, which is of potential use in chemical heat pumps, was studied by means of differential scanning calorimetry. The thermodynamic conditions, the enthalpy of the reaction, and the heat capacity values for MnCl2, [Mn(NH3)2Ch and [Mn(NH3)6Cl2 were measured. The influence of the reaction kinetics of the experimental procedure and some parameters such as sample temperature, ammonia pressure and scanning rate was examined.
TL;DR: In this paper, the electrical conductivity properties of some substituted arylazo-barbiturate complexes at different temperatures were studied. And the σo, ΔE and Eg values were determined.
Abstract: Electrical conductivity properties of someo-substituted arylazo-barbiturate complexes at different temperatures are studied. The σo, ΔE andEg values are determined. The copper complexes derived from −H, −CH3 and −OCH3 substituted organic compounds are with semiconducting properties at low temperatures and insulator at high temperatures. All the carboxy and the cobalt and the the nitro complexes, and nickel-methyl complexes are of semiconducting behaviour. The data are explained in the light of extrensic and lattice vibrations and the width of the forbidden energy gap properties.
TL;DR: The effect of procedural variables, including sample mass, heating rate, particle size and partial pressure of carbon dioxide, on TG, DTG and DTA curves for the decomposition of A R calcium carbonate and limestone has been studied as discussed by the authors.
Abstract: The effect of procedural variables, including sample mass, heating rate, particle size and partial pressure of carbon dioxide, on TG, DTG and DTA curves for the decomposition of A R calcium carbonate and limestone has been studied Such variables have a marked effect, similar in magnitude for both DTG and DTA The effect of sample mass, or depth of undiluted sample, is shown to be due to an increase in the partial pressure of carbon dioxide within the reacting powder and has been called the bed-depth effect This effect is most pronounced in nitrogen but is much reduced in carbon dioxide Inert diluents have little effect on the TG curves but changing the composition of the inert carrier gas causes variations which are correlated with the thermal conductivity of the gas Water vapour causes a lowering of the DTG and DTA peak temperatures
TL;DR: The differences of the thermal curves (DTA-TG) of pyrophyllite measured before and after grinding have been studied to obtain quantitative information about the alteration of the structure of this layer silicate as discussed by the authors.
Abstract: The differences of the thermal curves (DTA-TG) of pyrophyllite measured before and after grinding have been studied to obtain quantitative information about the alteration of the structure of this layer silicate.
TL;DR: In this article, the catalytic effects of doped or mixed CuO-Cr2O3 oxides on the thermal decomposition of ammonium perchlorate (AP) were investigated by using DTA, electrical conductivity and X-ray diffraction techniques.
Abstract: The catalytic effects of doped or mixed CuO-Cr2O3 oxides on the thermal decomposition of ammonium perchlorate (AP) were investigated by using DTA, electrical conductivity and X-ray diffraction techniques. The results obtained revealed that the decrease in the defect electron of CuO catalyst doped with 1 at.% Cr3+ inhibited its activity, while the opposite effect was observed when Cr2O3 was doped with 1 at.% Cu2+. On increase of the concentrations of both oxides, the catalyst containing 70 at.% Cr3+ was found to be the most active during the decomposition of AP. The existence of CuCr2O4 at this ratio was demonstrated by X-ray diffraction. The activity of this spinel was explained on the basis of a hopping mechanism between Cr3+/Cr4+ active sites. Finally, the activation energies of different decomposition stages of AP alone and mixed with catalysts were calculated.
TL;DR: In this paper, the adaption of the metachromic cationic dyes crystal violet (CV) and ethyl violet (EV) by Na-kaolinite and Na-montmorillonite has been studied by visible spectroscopy and titration calorimetry.
Abstract: Adsorption of the metachromic (colour depends on concentration) cationic dyes crystal violet (CV) and ethyl violet (EV) by Na-kaolinite and Na-montmorillonite has been studied by visible spectroscopy and titration calorimetry. In the kaolinite system, metachromasy stems from association of the dye cations on the external surface of the clay. Enthalpies of adsorption at small dye/clay ratios are −3.5 and −3.8 kJ/mol for CV and EV, respectively. In the montmorillonite system, which has been studied more thoroughly, metachromasy stems from theπ electron interactions between the dyes and the oxygen plane of the alumino-silicate. Enthalpies of adsorption (more exothermic than for kaolinite) depend on the dye/clay ratio in ways that are consistent with the spectra and the derived picture of dye/clay interactions.
TL;DR: In this paper, the glass transformation temperature and onset temperature of mass loss were determined by differential scanning calorimetry and thermogravimetry, respectively, in the series [Ge0.3S0.7]100-xIx where 0≤x≤30 have been prepared and have potential applications as short length infrared optical fibres.
Abstract: Chaicogenide-halide glasses in the series [Ge0.3S0.7]100-xIx where 0≤x≤30 have been prepared and have potential applications as short length infrared optical fibres. Asx is increased the expansion coefficient increases, in addition the glass transformation temperature and onset temperature of mass loss both decrease as determined by differential scanning calorimetry and thermogravimetry, respectively. Melt viscosities in the range 107–1010.7 Pa s have been determined via penetration viscometry and isoviscous points are at lower temperatures asx increases. These results have been discussed in relation to known structural information and the fragility of the melts has been compared. Predicted fibre drawing temperatures tend to lie close to the onset of mass loss.
TL;DR: The thermal decomposition of the complexes: [Fe(C17H24O4)1.5·2H2O]n and [UO2(C 17H 24O4 ·2H 2 O]n, and evaluation of kinetic parameters (E, Z and ΔS) by making use of Piloyan-Novikova, Coats-Redfern and Horowitz-Metzger equations are reported in this article.
Abstract: The thermal decomposition of the complexes: [Fe(C17H24O4)1.5·2H2O]n and [UO2(C17H24O4·2H2O]n, and evaluation of kinetic parameters (E, Z andΔS) by making use of Piloyan-Novikova, Coats-Redfern and Horowitz-Metzger equations are reported. The complexes are found to decompose in three well defined steps involving random nucleation mechanism. The intermediates formed during decomposition usually undergo further decomposition without remaining stable over a considerable range of temperature.
TL;DR: In this article, the results obtained by thermogravimetry and DSC calorimetry of ancient, fresh and waterlogged wood samples are discussed and the criteria by which the percent content of lignin, cellulose, water and ashes (residue after heating at 700
Abstract: TG, DTG and DSC curves are presented and analytical results, obtained by thermogravimetry and DSC calorimetry, of ancient, fresh and waterlogged wood samples, are discussed. The criteria by which the percent content of lignin, cellulose, water and ashes (residue after heating at 700‡) were obtained by thermogravimetry, are outlined. Finally DSC curves are reported and the degradation which happen in some wood samples evidenced, especially in the case of waterlogged wood.
TL;DR: In this article, the spectrum of available techniques, from the conventional photoacoustic detection to novel photothermal laser probing and frequency multiplexing is discussed, and their utilization for the measurement of thermophysical thermal transport-related parameters of solids is presented.
Abstract: Major application of optically-induced thermal waves to the thermal and thermodynamic analysis of solids are reviewed. The spectrum of available techniques,from the conventional photoacoustic detection to novel photothermal laser probing and frequency multiplexing is discussed, and their utilization for the measurement of thermophysical thermal transport-related parameters of solids is presented. These include the thermal diffusivity, effusivity, conductivity and specific heat. The ability of photothermal methods to perform thermal analysis on large classes of solids, including conducting and insulating bulk materials, crystals, layered porous and coated structures, thin films and inhomogeneous thermal profiles is highlighted. Finally, special capabilities of photothermal analysis, such as the monitoring of surface thermodynamic phenomena and phase transition studies, including high-Tc superconductors, are described in order to give a complete overview of the rich potential of photothermal-based methodologies.
TL;DR: In this article, a mechanism for the decomposition of nickel(II) nitrate hexahydrate is proposed. But the mechanism is limited to the case of NiO, NiO and hydrated nitrate.
Abstract: Fine, hollow, spherical particles with an average size of one micronmeter were formed through pyrolysis of aerosol of nickel nitrate solution. The aerosol product obtained by fast heating to 450°C consisted of tiny crystallites of NiO, hydrated nitrate, and other non-crystalline phase(s). By heating above 480°C, it consisted only of crystalline NiO. To understand the reactions occurring during the aerosolization process, thermal analysis was conducted on nickel nitrate hexahydrate in stagnant and flowing air using different heating rates. The mechanism for the decomposition of nickel(II) nitrate hexahydrate is proposed.
Abstract: The development of methods for temperature and heat calibration of DSC and DTA supported by the German Society of Thermal Analysis (GEFTA) are presented. Reasons are given for the recommendation of the temperature calibration method, which refers to the valid international temperature scale (ITS 90) and takes into account the fact that the fixpoints of this scale are defined in two phase equilibrium.
TL;DR: Amorphous solid of tri-O-methyl-β-cyclodextrin was formed by grinding the crystalline sample with a vibrating mill at room temperature as discussed by the authors.
Abstract: Amorphous solid of tri-O-methyl-β-cyclodextrin was formed by grinding the crystalline sample with a vibrating mill at room temperature. The amorphising process was examined by X-ray powder diffraction technique and differential scanning calorimetry (DSC). The Bragg peaks disappeared and the enthalpy of crystallization became constant for the sample ground for 25 min, indicating the apparent completion of the amorphization. A glass transition of the ground amorphous solid was found by DSC. The glass transition temperature Tg moved from 58°C to 79°C with grinding. The saturated Tg of the ground sample was the same as that of the liquid-quenched glass. No significant difference between the ground and liquid-quenched amorphous solids was found in the X-ray diffraction patterns. Infrared spectra of both amorphous solids, however, showed a definite difference for the band at 1194 cm−1 assigned to the rocking of the CH3 groups which are located at the molecular periphery.
TL;DR: In this article, the thermal properties of the Si/Sb2O3, Si/KNO3 and Si/Fe2O2 pyrotechnic systems were examined in relation to the behaviour of individual constituents.
Abstract: Thermogravimetry (TG) and differential scanning calorimetry (DSC) have been used to examine the thermal behaviour, in N2 and in air, of the Si/Sb2O3, Si/KNO3, Si/Fe2O3 and Si/SnO2 pyrotechnic systems, in relation to the behaviour of the individual constituents.
TL;DR: The second stage of the decomposition of dolomite is strongly dependent on these procedural variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesia as discussed by the authors.
Abstract: TG, DTG and DTA curves of magnesite are dependent on procedural variables, especially sample mass, heating rate and partial pressure of carbon dioxide, in a similar manner to those of calcite [1], although the magnitude of the effect is less for magnesite. The first stage of the decomposition of dolomite varies with increasing partial pressure of carbon dioxide in an anomalous manner and hence the effects of these procedural variables (except heating rate) are not similar to those observed for magnesite and calcite. The second stage of the decomposition of dolomite is, however, strongly dependent on these procedural variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesia. A 1∶1 molar mixture of magnesite and calcite also behaves as would be predicted from the behaviour of the single carbonates but differently from that of dolomite.