scispace - formally typeset
Search or ask a question

Showing papers in "Journal of Thermal Analysis and Calorimetry in 1995"


Journal ArticleDOI
TL;DR: In this paper, the changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor with an increasing of aging time.
Abstract: Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time. The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.

187 citations


Journal ArticleDOI
TL;DR: In this paper, a small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60-350 K using the Nernst method has been constructed, and the performance of this apparatus was evaluated by heat capacity measurements on α-alumina.
Abstract: A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm3 in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N2 (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.

151 citations


Journal ArticleDOI
TL;DR: In this article, the thermal decomposition of nitrocellulose (NC) has been studied with regard to kinetics, mechanism, morphology and the gaseous products thereof, using thermogravimetry, differential thermal analysis (DTA), IR spectroscopy, differential scanning calorimetry (DSC), and hot stage microscopy.
Abstract: The thermal decomposition of nitrocellulose (NC) 12.1% N, has been studied with regard to kinetics, mechanism, morphology and the gaseous products thereof, using thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy, differential scanning calorimetry (DSC) and hot stage microscopy. The kinetics of the initial stage of thermolysis ofNC in condensed state has been investigated by isothermal high temperature infrared spectroscopy (IR). The decomposition ofNC in KBr matrix in the temperature range of 142–151°C shows rapid decrease in O−NO2 band intensity, suggesting that the decomposition of NC occurs by the rupture of O−NO2 bond. The energy of activation for this process has been determined with the help of Avrami-Erofe'ev equation (n=1) and is ≈188.35 kJ·mol−1. Further, the IR spectra of the decomposition products in the initial stage of thermal decomposition ofNC, indicates the presence of mainly NO2 gas and aldehyde.

48 citations


Journal ArticleDOI
TL;DR: In this article, the preparation, identification and especially the thermal properties of four hitherto noncharacterized compounds of this group of general formula (CH3CH2COO)2Zn·2L·H2O are described.
Abstract: Zinc carboxylates complexed with N-donor ligands have potential antifungal effects. The preparation, identification and especially the thermal properties of four hitherto non-characterized compounds of this group of general formula (CH3CH2COO)2Zn·2L·H2O are described in this paper. The experimental results are confronted with present knowledge on analogous compounds.

48 citations


Journal ArticleDOI
TL;DR: The DSC purity analysis as mentioned in this paper is based on thermodynamic phase diagrams for substances (purity ≥ 98%) which undergo a melting point, and the impurities which have eutectic behaviour with the analyte are determined together.
Abstract: DSC purity analysis is based on thermodynamic phase diagrams for substances (purity ≥98%) which undergo a melting point. Impurities which have eutectic behaviour with the analyte are determined together.

46 citations


Journal ArticleDOI
TL;DR: The thermal decomposition of borax has been investigated by thermal, XRD and FTIR methods as well as SEM microscopy in this article, and it has been revealed that it proceeds according to the mechanism of internal reactions in the structure of the precursor as a medium.
Abstract: Thermal decomposition of borax has been researched by thermal, XRD and FTIR methods as well as SEM microscopy. Study have revealed that it proceeds according to the mechanism of internal reactions in the structure of the precursor as a medium. The following stages of the process have been distinguished: (1) dehydration, (2) internal structure reconstitution—formation of tincalconite, (3) amorphization of crystal structure, (4) gradual dehydroxylation and crystallization of Na2O2B2O3 inside the amorphous matrix.

44 citations


Journal ArticleDOI
TL;DR: The model of regular solutions, that may be applied to binary alloys (e.g. Au−Pt, Si−Ge) has been compared to binary societies: blacks −nonblacks in the US, catholics −non-catholics, foreigners −German citizen.
Abstract: The model of regular solutions, that may be applied to binary alloys (e.g. Au−Pt, Si−Ge) has been compared to binary societies: blacks—non-blacks in the US, catholics—non-catholics, foreigners—German citizen. The excellent agreement of phase diagrams and intermarriage data encourages a calculation of the multicultural society by functions of thermodynamics: Solubility corresponds to integration, miscibility gap to segregation, free enthalpy to happiness and temperature to tolerance of a society. Only a high level of tolerance will integrate ghettos and lead to a peaceful multicultural society.

42 citations


Journal ArticleDOI
TL;DR: In this article, the authors make use of Arrhenius kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures.
Abstract: Attempts are made to use kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures. However, besides the obvious measurement and extrapolation errors (which can be considerable), there are two fundamental reasons why quantitative long range extrapolations can not be made for complex condensed phase systems. They are: 1) Arrhenius kinetics parameters can not be extrapolated through phase transitions or softening temperatures; 2) Arrhenius kinetics parameters can not be extrapolated through the ceiling temperature region. Satisfactory lifetime prediction methods can be developed only after a thorough analysis of the causes of service failure. A real method has been taken from literature to illustrate the correct procedures.

41 citations


Journal ArticleDOI
TL;DR: In this paper, a procedure for calibrating the temperature scale of a DSC is described and a different calibration trend was obtained using the transition points of organic compounds compared to that found using the melting points of highly pure metals.
Abstract: A procedure for calibrating the temperature scale of a DSC is described. A different calibration trend was obtained using the transition points of organic compounds compared to that found using the melting points of highly pure metals. The crystal-crystal transitions of three ammonium salts were studied by this method; ammonium dihydrogen phosphate and ammonium sulphate were found to be suitable reference materials in the region −150 to 0°C, but ammonium nitrate was found to be unsuitable due to poorly defined transition points and inconsistent thermal behaviour.

41 citations


Journal ArticleDOI
TL;DR: In this article, a new analytical method based on thermogravimetry and applied to chemically functionalized surfaces is proposed, where mass losses of surfaces modified with alkoxysilane reagents, Sup-CH2CH2 CH2−R (Sup=support andR=Cl, SH, NH2, NHCONH2,NHNHCOCH3 or (CH2)4NH), are interpreted by considering the physically adsorbed water, the silanol groups and the organic moiety.
Abstract: A new analytical method based on thermogravimetry and applied to chemically functionalized surfaces is proposed. The mass losses of surfaces modified with alkoxysilane reagents, Sup-CH2CH2CH2−R (Sup=support andR=Cl, SH, NH2, NHCONH2, NHNHCOCH3 or (CH2)4NH), are interpreted by considering the physically adsorbed water, the silanol groups and the organic moiety. The elemental analyses calculated from these data are in agreement with those obtained by classical elemental analysis. The method is quick and reproducible, and requires the use of only a few milligrams of material.

39 citations


Journal ArticleDOI
TL;DR: In this paper, desorption energy distributions for temperature-programmed TPD of ammonia from isolated bridging SiOHAl groups of H zeolites of different type significantly differ from each other in shape.
Abstract: Desorption energy distributions were calculated for temperature-programmed desorption (TPD) of ammonia from H zeolites of different type by means of regularization. This method does not require any limiting assumptions about the distribution function. It could be shown that the desorption energy distributions obtained are nearly independent of the experimental conditions and therefore they should represent a suitable measure for the distribution of the strength of acidic sites. The calculated desorption energy distributions for the ammonia desorption from the isolated bridging SiOHAl groups of H zeolites of different type significantly differ from each other in shape. The increase of the desorption energy of the main range of the distribution functions correlates well with the increase of the average acid strength of the SiOHAl groups with decreasing Al content of the zeolites.

Journal ArticleDOI
TL;DR: In this article, the dehydrated lactose forms αH and αS were investigated by time and temperature-resolved X-ray powder diffractometry and differential scanning calorimetry.
Abstract: The dehydrated lactose forms αH and αS were investigated by time- and temperature-resolved X-ray powder diffractometry and differential scanning calorimetry. We found different X-ray structures for these two forms, which is probably related to the different dehydration processes. The rapidly dehydrated form αH obviously has the same X-ray structure as the starting material α-lactose monohydrate, although the crystallinity is reduced. A thermally induced transition of the αH-form into the αS-form was observed. This transition should allow one to “switch” between the physicochemical properties of the excipient, which may be important for applications in pharmaceutical and food industries.

Journal ArticleDOI
TL;DR: In this article, a preliminary DSC study on bovine (BSA) and human (HSA) serum albumins is reported, which shows that at accurate HPLC analysis the commercial proteins show three peaks: Fraction V-I, probably globulins, fraction V-II (about 15-18% of the product) and fraction V -III that represents pure BSA or HSA.
Abstract: In a previous paper, we report a preliminary DSC study on bovine (BSA) and human (HSA) serum albumins. However, at accurate HPLC analysis the commercial proteins show three peaks: Fraction V-I, probably globulins (as declared by the producers), Fraction V-II (about 15–18% of the product) and Fraction V-III that represents pure BSA or HSA. A hypothesis is that the Fraction II is a covalent dimer, or trimer or a mixture of both, generated during the scalf-life of the commercial product. Denaturation enthalpies of the purified Fraction V-III and Fraction V-II of BSA, have been determined calorimetrically, at changing thepH, and the results of both compared with those obtained on the untreated protein. Few calorimetric experiments have been also carried on a BSA monomer derivative with sulphidril group protected. Computer program have been developed for the deconvolution of exo- and endothermic effects and for the analysis of thermal denaturation profiles.

Journal ArticleDOI
S.A.A. Mansour1
TL;DR: The thermal decomposition of copper acetate monohydrate (CuAc) was examined on heating up to 600°C at various rates, by TG, DTA and DSC as discussed by the authors.
Abstract: The thermal decomposition course of copper acetate monohydrate (CuAc) was examined on heating up to 600°C at various rates, by TG, DTA and DSC. Non-isothermal kinetic and thermodynamic parameters were determined in air or nitrogen. SEM was used to describe the decomposition course and the solid products were identified by IR and XRD analysis. The results indicated that CuAc was dehydrated at 190°C and then partially decomposed at 220°C, giving rise to CuO in addition to a minor portion of Cu2O and Cu4O3. The last two oxides seemed to facilitate the decomposition of the rest of the anhydrous acetate. Cu2O and Cu4O3 were oxidized in air at >400°C, in a process that did not occur in nitrogen.

Journal ArticleDOI
TL;DR: In this paper, a short description of the thermal analysis methods used for the investigation of polymer degradation processes is given, and the fields of application of TG, DTA and DSC for polymers are presented.
Abstract: A short description of the thermal analysis methods used for the investigation of polymer degradation processes is given. The fields of application of TG, DTA and DSC for polymers are presented. A kinetic approach to the thermal degradation processes is also given.

Journal ArticleDOI
TL;DR: In this paper, the kinetics of thermooxidation of edible oils: soybean oil, rapeseed oil, corn and peanut oil were investigated in two ways: the DSC and its pressure version (PDSC) were used for measurements under the isothermal and non-isothermal conditions in atmosphere of oxygen.
Abstract: The kinetics of thermooxidation of edible oils: soybean oil, rapeseed oil, corn and peanut oil was investigated in two ways. The DSC and its pressure version (PDSC) were used for measurements under the isothermal and non-isothermal conditions in atmosphere of oxygen. Comparing these two methods for each oil the differences between the values of activation energies were observed. However, mechanism of oxidation in both method was different.

Journal ArticleDOI
TL;DR: In this paper, the specific heat capacity of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter, and the experimental specific heat capacities are within ± 1% precision with a 95% confidence level.
Abstract: The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min−1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level.

Journal ArticleDOI
TL;DR: The accuracy and scope of application of previously reported approximations of the temperature integral were evaluated in this article, where the exact solution was obtained independently by solving the Simpson's rule, the trapezoidal rule and the Gaussian rule.
Abstract: The accuracy and scope of application of previously reported approximations of the temperature integral were evaluated. The exact solution was obtained independently by solving the temperature integral numerically be Simpson's rule, the trapezoidal rule and the Gaussian rule. Two new approximations have been proposed: \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\begin{gathered} P(X) = e^{ - x} (1/X^2 )(1 - 2/X)/(1 - 5.2/X^2 ) \hfill \\ P(X) = e^{ - x} (1/X^2 )(1 - 2/X)/(1 - 4.6/X^2 ) \hfill \\ \end{gathered}$$ \end{document} whereX=E/RT. The first equation gives higher accuracy, with a deviation of less than 1% and 0.1% from the exact solution forX≥7 andX≥10, respectively. The second equation has a wider scope...

Journal ArticleDOI
TL;DR: In this article, phase diagrams of four binary systems (C10H21NH3) and their binary mixtures were investigated by means of DSC, and it was shown that they can retain energies between 74 and 115 J/g during solid-state transformations at temperatures between 70 and 105°C.
Abstract: The phase diagrams of four binary systems (C10H21NH3)2CoCl4−(C16H33NH3)2CoCl4, (C12H25NH3)2CoCl4−(C16H33NH3)2CoCl4, (C10H21NH3)2ZnCl4−(C16H33NH3)2ZnCl4 and (C12H25NH3)2ZnCl4−(C16H33NH3)2ZnCl4 were investigated by means of DSC. These six compounds and their binary mixtures can retain energies between 74 and 115 J/g during solid-state transformations at temperatures between 70 and 105°C, and they are therefore being considered for potential use in solar energy systems.

Journal ArticleDOI
TL;DR: The molar excess enthalpies for the water + N-methyl-2-pyrrolidinone binary mixtures have been measured as functions of mole fraction at 298.15, 308.15 and 318.15 K, using isoperibol rotating calorimeter.
Abstract: The molar excess enthalpiesH E for the water +N-methyl-2-pyrrolidinone binary mixtures have been measured as functions of mole fraction at 298.15, 308.15 and 318.15 K, using isoperibol rotating calorimeter. A hydrogen bonding pairs model proposed by Luzar was fitted to the experimental dataH E,G E for the binary mixtures of water with hexamethylphosphoric triamide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidinone.

Journal ArticleDOI
TL;DR: In this paper, the influence of different thermal loads on the 2D temperature distribution in AlGaAs/GaAs gain-guided laser arrays is investigated, and the results of steady-state two-dimensional finite element computations of temperature distributions of high power semiconductor laser arrays are presented.
Abstract: New results of steady-state two-dimensional finite-element computations of temperature distributions of high power semiconductor laser arrays are presented. The influence of different thermal loads on the 2D temperature distribution in AlGaAs/GaAs gain-guided laser arrays is investigated. TheFEM model is tested by comparing it with analytical solutions. For numerical convenience, the latter is rewritten in a novel form, which is free of overflow problems. The maximum temperatures calculated by both methods agree within 1%. Several factors determining the thermal resistance of the device are quantitatively examined: the ratio of light emitting to non-emitting areas along the active zone, the amount of Joule losses, the current spreading, the solder thickness, and voids in the solder. This yields design rules for optimum thermal performance.

Journal ArticleDOI
TL;DR: In this article, the effects of electron correlation were taken into account at the second order Moller-Plesset level of theory, and the correlation for the basis set superposition error was also included for CaC2O4·H2O, the enthalphies and free enthalpies of consecutive dehydration of CaC 2 O 4·H 2 O, decarbonylation of Ca C 2O4 and decomposition of Ca CO 3 towards Ca O and CO 2 were determined on the basis of avialable data from the literature or those predicted th
Abstract: Geometries and energies of isolated CaC2O4·H2O, CaC2O4, CaCO3, CaO, H2O, CO and CO2 were determined at the ab initio level using effective core potential valence basis sets of doublezeta quality, supplemented with polarization functions. The effects of electron correlation were taken into account at the second order Moller-Plesset level of theory. For CaC2O4·H2O, the correlation for the basis set superposition error was also included. Common routines were employed to evaluate entropies, heat capacities, as well as enthalpies and free enthalpies of formation of all entities. The enthalphies and free enthalpies of consecutive dehydration of CaC2O4·H2O, decarbonylation of CaC2O4 and decomposition of CaCO3 towards CaO and CO2 were determined on the basis of avialable data from the literature or those predicted thoretically. Assuming that upon all the above mentioned processes the system maintains equilibrium, the fractions reacted, enthalpy changes and differential dependencies of thesevs. temperature were derived and compared with experimental thermoanalytical data.

Journal ArticleDOI
TL;DR: A stimulated influence of irradiation at comparable temperature conditions may be a subject of technological interest taking into account that increase of reaction rate can reach significant values in high temperature chemistry of solid state as discussed by the authors.
Abstract: Use of electron beams allows to obtain new effects in high temperature chemistry of solid state. A stimulated influence of irradiation at comparable temperature conditions may be a subject of technological interest taking into account that increase of reaction rate can reach significant values.

Journal ArticleDOI
TL;DR: The behavior of the molten system acetamide-electrolyte, including the peculiarity of the structure and the consequent relevant properties, such as the megavalue of the dielectric constant, was reported earlier as discussed by the authors.
Abstract: The behavior of the molten system acetamide-electrolyte, including the peculiarity of the structure and the consequent relevant properties, such as the megavalue of the dielectric constant, was reported earlier. The probable structure is a micellar system composed of salt micelles dispersed in an amorphous solvent. The present paper reports measurements in a related system: fluoroacetamide-sodium trifluoroacetate. The phase diagram, the ultrasonic absorption of both longitudinal and shear waves, and the longitudinal relaxation time of the nuclear magnetic momentum were measured at different temperatures. The most importnat result was thatT 1 (NMR relaxation time) on the19F nucleus shows that the amide and salt participate in different environments. The amide environment is less rigid; this proves that the system must be considered microheterogeneous. Moreover, the present system exhibited: 1) a less extended concentration area where supercooling phenomena occur; 2) a much broader curve of the re...

Journal ArticleDOI
TL;DR: In this paper, the influence of microporous carbon surface oxidation on the energetics of methane adsorption at 308 K was discussed, and it was shown that carbon micropores oxidized with carbon dioxide can change the methane adorption process.
Abstract: The influence of microporous carbon surface oxidation on energetics of methane adsorption at 308 K is discussed. Obtained adsorption heats and integral molar entropies of the adsorbate show that microporous carbon surface oxidation changes the methane adsorption process. This is probably resulted by the existence of an endothermic effect during adsorption in oxidized carbon micropores.

Journal ArticleDOI
TL;DR: The role of calorimetry in adsorption is discussed in this article, where the differences between calorimietric adsoreption heats and those calculated from Clausius-Clapeyron equation for the systems ethanol-activated carbons are presented.
Abstract: The role of calorimetry in adsorption is shortly reviewed. The differences between calorimetric adsorption heats and those calculated from Clausius-Clapeyron equation for the systems ethanol-activated carbons are presented. Obtained results, together with the results presented previously for other adsorbates, confirm that calorimetry is indispensable for a real thermodynamical description of the adsorption process in this type of system.

Journal ArticleDOI
TL;DR: In this paper, the specific heat capacity of triglyeerides was obtained by using heat-flux DSC under improved operating conditions, such as the scanning rate, the sample mass and the atmosphere within the DSC chamber.
Abstract: Reproducible specific heat capacities (Cp) of triglyeerides can be obtained by using heat-flux DSC under improved operating conditions. The improved operating parameters, such as the scanning rate, the sample mass and the atmosphere within the DSC chamber, were established via statistical analysis of the experimental data with trilaurin as a sample. The specific heat capacity results on trilaurin were compared with the values calculated by using estimation methods. The precision of the specific heat capacity measured for trilaurin under these conditions was within +1%.

Journal ArticleDOI
TL;DR: In this article, the authors applied the stationary point method to the data obtained from thermogravimetric curves, apparent activation energy, preexponential factor and compensation parameter for each blend were calculated.
Abstract: The PVC/ABS blends were degradated by means of isothermal thermogravimetry at temperatures at 210...240°C in nitrogen. Applying the stationary point method to the data obtained from thermogravimetric curves, apparent activation energy, preexponential factor and compensation parameter for each blend were calculated. The constancy of compensation parameters points to an unchanged mechanism of poly (vinyl-chloride) (PVC) thermal degradation in the presence of acrylonitrile butadiene-styrene (ABS). Upon increasing the fraction of ABS in the blend up to 50% only the kinetics of the process is changed.

Journal ArticleDOI
TL;DR: In this paper, the effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se7Te3) have been studied by DTA measurements at different heating rates.
Abstract: The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se7Te3) have been studied by DTA measurements at different heating rates (α=5 deg·min−1, 10 deg·min−1, 15 deg·min−1 and 20 deg·min−1). From the heating rate dependence of the values ofT g,T c andT p, the glass transition activation energy (E t) and the crystallization activation energy (E c) have been obtained for different compositions of (Se7Te3)100−xInx (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT g and crystallization kinetics are discussed in terms of the modif...

Journal ArticleDOI
TL;DR: A few possible methods for estimating the kinetic parameters of the coal pyrolysis process, on the basis of thermogravimetric analysis in non-isothermal conditions, have been presented in this article.
Abstract: The main problems of the kinetic description of the coal pyrolysis process have been discussed. A few possible methods for estimating the kinetic parameters of the process, on the basis of thermogravimetrical analysis in non-isothermal conditions have been presented.