Showing papers in "Thermochimica Acta in 1975"
TL;DR: In this article, the performance of an LKB flow microcalorimeter has been improved through changes in the auxiliary equipment and operating technique, and measurements of excess enthalpies, precise to 0.5% or better, are reported for several test systems.
Abstract: The performance of an LKB flow microcalorimeter has been improved through changes in the auxiliary equipment and operating technique. Measurements of excess enthalpies, precise to 0.5% or better, are reported for several test systems.
159 citations
TL;DR: In this article, the heat of immersion of natural magnetite in aqueous solutions has been determined by the isothermal differential microcalorimeter (ΔHi = −646±25 erg cm−2).
Abstract: The heat of immersion of natural magnetite in aqueous solutions has been determined by the isothermal differential microcalorimeter (ΔHi = −646±25 erg cm−2). The zero point of charge of natural magnetite was also determined (pHzpc=6.5). The value obtained for the heat of immersion is a linear function of the zero point of charge of the natural magnetite examined.
135 citations
TL;DR: In this article, a method for the experimental determination of critical temperatures on a routine basis is presented for most common explosives, and it is shown that agreement between calculated and experimental values is excellent.
Abstract: The kinetics constants for the decomposition reaction of an explosive can be used to calculate the lowest temperature (critical temperature, Tm) at which any specific size and shape of explosive can self heat to explosion; however, the accuracy of the calculation is in doubt without an independent experimental determination of a critical temperature for a known size and shape of the explosive. A method is presented for the experimental determination of critical temperatures on a routine basis, and it is shown that agreement between calculated and experimental values is excellent for most common explosives.
134 citations
TL;DR: In this paper, the oxidation behavior of palladium, ruthenium and iridium powders of different grain sizes was investigated by TG, DTA and X-ray methods.
Abstract: The oxidation behavior of palladium, ruthenium and iridium powders of different grain sizes was investigated by TG, DTA and X-ray methods. The solid oxides formed during heating up (PdO, RuO 2 , IrO 2 ) show different stability and decomposition temperatures depending on the oxygen pressure. The kinetics of the reaction MeO x → Me+ x /2 O 2 is discussed. High temperature X-ray studies confirmed the strong anisotropy of thermal expansion in the case of RuO 2 and IrO 2 . The thermal expansion behavior of these oxides is compared to that of other rutile-type oxides.
110 citations
TL;DR: In this article, the partial molal volumes of both components of the mixed system have been calculated and deviations from ideal volumes of mixing have been evaluated; structural correlations have been made with previous results on acid-base properties; they allow to distinguish several interaction regions between components of binary systems.
Abstract: Densities of water+acetonitrile mixture have been measured from 308.15 to 278.15 K over the entire composition range. Partial molal volumes of both components of the mixed system have been calculated and deviations from ideal volumes of mixing have been evaluated. Literature data on viscosity have also been treated by a least square method and activation thermodynamic functions of viscous flow computed. Structural correlations have been made with previous results on acid-base properties; they allow to distinguish several interaction regions between components of binary systems.
108 citations
83 citations
TL;DR: In this paper, the mechanism of decomposition of metal sulphates is discussed, making use of additional information obtained from isothermal studies and X-ray diffraction measurements, and the activation energies of these reactions were calculated and found to increase, with almost the same increments, in the order Zn
Abstract: The thermal decomposition temperatures of some metal sulphates (iron, copper, cobalt, nickel, zinc and lead sulphates) have been investigated by TG and DTA. The mechanism of decomposition of these sulphates is discussed, making use of additional information obtained from isothermal studies and X-ray diffraction measurements. The activation energies of these reactions were calculated and found to increase, with almost the same increments, in the order Zn
62 citations
TL;DR: In this paper, the authors show that compounds of the type (n-C n H 2n+1 NH 3 ) 2 MCl 4 with n = 12 or n = 16 and with M = Mn, Cu, Co, Fe, Hg, Zn show order-disorder solid-solid phase transitions in the temperature range 300-380 K.
Abstract: Compounds of the type (n-C n H 2n+1 NH 3 ) 2 MCl 4 with n = 12 or n = 16 and with M = Mn, Cu, Co, Fe, Hg, Zn show order-disorder solid-solid phase transitions in the temperature range 300–380 K. Three general types of thermal behaviour can be observed for compounds with different metals, but with the same n . The different thermal behaviour appears to be related to different coordination geometries at the metal atoms.
53 citations
TL;DR: In this paper, the authors show that random nucleation occurs, producing perfectly oriented but disordered γ-Fe 2 O 3 crystals of about 70 A size, which can be accomodated with an atomistic model of lattice collapse.
Abstract: The dehydration of γ-FeOOH to γ-Fe 2 O 3 in vacuo has been investigated by thermoanalysis. Results have been checked by electron microscopy and diffraction and by x-ray diffraction. Authors find that formal kinetics are not conclusive. Electron micrographs, however, show directly that random nucleation occurs, producing perfectly oriented but disordered γ-Fe 2 O 3 crystals of about 70 A size. The results can be accomodated with an atomistic model of lattice collapse.
52 citations
TL;DR: In this paper, a computer programm is given, which permits the determination of the more probable reaction mechanism by use of 17 different kinetic equations, including chemical reaction, nucleation, phase boundary reaction and diffusion.
Abstract: By using the kinetic parameters calculated from non-isothermal measurements according to Freeman and Carroll a computer programm is given, which permits the determination of the more probable reaction mechanism by use of 17 different kinetic equations. The computer programm includes the kinetic equation for chemical reaction, nucleation, phase boundary reaction and diffusion and can easily be extended to other equations. The evaluation of the experimental values by a distinct kinetic equation is quantitatively characterized by means of the correlation coefficient.
The kinetic parameters are calculated on the basis of a regression analysis. By dividing the thermogravimetric curve in different reaction intervals a differential calculation is possible.
Decomposition of CaCO3, MgCO3 and CaSO4·2H2O is discussed from the results of the computer calculation. It is seen that the kinetic parameters and the reaction mechanism are not constant during the reaction. Further experiments for a physical interpretation are being carried out.
51 citations
TL;DR: In this paper, seven copper(II) dithiocarbamate complexes [Cu(R 2 Dtc) 2 : R 2 = Me 2, Et 2, nPr 2, nBu 2, cycHex 2, Et Ph, pyrrol and pip] have been prepared and examined by thermogravimetric analysis (TG).
Abstract: Seven copper(II) dithiocarbamate complexes [Cu(R 2 Dtc) 2 : R 2 = Me 2 , Et 2 , nPr 2 , nBu 2 , cycHex 2 , Et Ph, pyrrol and pip] have been prepared and examined by thermogravimetric analysis (TG). All the complexes show similar TG profiles whether heated in an atmosphere of air or nitrogen. Complete TG, DTA data are reported for copper diethyldithiocarbamate (air, nitrogen and vacuum atmospheres). Copper diethyldithiocarbamate is completely volatile (190–260°C) under vacuum (0.8τ), but in air and nitrogen only partial volatility is exhibited; thermal decomposition begins at 220°C and a residue of cuprous sulphide results at 350°C.
TL;DR: In this article, a recently described method is used to characterise thermal gradients in a DSC-2 and the results are compared with a conventional temperature calibration, under certain circumstances the latter may be in error by several degrees with consequent adverse effects on calculated heat capacities.
Abstract: A recently described method is used to characterise thermal gradients in a DSC-2 and the results are compared with a conventional temperature calibration. Under certain circumstances the latter may be in error by several degrees with consequent adverse effects on calculated heat capacities. The errors are removed when allowance is made for variations in thermal lag from sample to sample.
TL;DR: In this article, the accuracy of a simple, well-known approximation to the solution of the adiabatic explosion problem is examined, and it is shown that, with a minor modification, the approximation can be converted to a form accurate to 1% or better for a wide range of the input parameters.
Abstract: The accuracy of a simple, well-known approximation to the solution of the adiabatic explosion problem is examined, and it is shown that, with a minor modification, the approximation can be converted to a form accurate to 1% or better for a wide range of the input parameters. The final result lies well within the capabilities of even the simpler scientific calculators. The effects of depletion of the reactant and a temperature-dependent heat capacity, not included in the development, are briefly evaluated.
TL;DR: In this paper, the breakdown of the supercooling of drops of liquids dispersed in an emulsifying medium has been measured by differential scanning calorimetry (DSC), and the limits of the validity of the methods exposed have also been indicated.
Abstract: To study the breakdown of the supercooling of drops of liquids dispersed in an emulsifying medium, the heat involved at the time of the change in state has been measured by differential scanning calorimetry (DSC). In order to determine the number of drops crystallizing either as a function of temperature and of time during a continuous cooling or as a function of time at a fixed temperature, the heat generated by the thermal phenomenon itself has been determined by an analysis of the principle of DSC and the basic equations of the apparatus which has been used. The limits of the validity of the methods exposed have also been indicated. Provided that the signals obtained during either cooling or heating are correctly (and differently) delimited, it has been proved possible to measure directly the total heat of crystallization.
TL;DR: In this paper, the authors investigated the thermal decomposition of strontium titanyl oxalate tetrahydrate (SITO) and calcium titanyl Oxalate hexahydrate using TG, DTA, gas and chemical analysis.
Abstract: Thermal decomposition of strontium titanyl oxalate tetrahydrate and calcium titanyl oxalate hexahydrate have been studied employing TG, DTA, gas and chemical analysis. The decompositions proceed through three major steps: dehydration, decomposition of the oxalate to a carbonate and the decomposition of the carbonate to yield the final products, the metatitanates. The intermediates of the oxalate decomposition are found to be Sr 2 Ti 2 O 4+x (CO 3 ) 2 -x(CO 2 ) x and Ca 2 Ti 2 O 4 (CO 3 ) 2 , respectively. The entrapment of carbon dioxide in the former and the presence of non-equivalent carbonate groups in the latter are substantiated by their i.r. spectra. The penultimate solid residues are poorly crystalline Sr 2 Ti 2 O 5 CO 3 and amorphous Ca 2 Ti 2 O 5 CO 3 . Decompositions of these carbonates are accompanied by growth in particle size of the products, SrTiO 3 and CaTiO 3 , respectively.
TL;DR: In this article, the solid-state thermal dissociation reactions of the complexes of all the lanthanide(III) nitrates and thiocyanates (except Pm) with the cyclic polyether dibenzo-18-crown-6 were investigated.
Abstract: The solid-state thermal dissociation reactions of the complexes of all the lanthanide(III) nitrates and thiocyanates (except Pm) with the cyclic polyether dibenzo-18-crown-6 were investigated. Thermal analysis was carried out in a dynamic atmosphere of dry nitrogen and under reduced pressure (5·10 −2 mm Hg). In both the conditions examined, the two series of complexes exhibit different thermal behaviours. The values of enthalpy change and “activation energy” for the dissociation reactions of the complexes with lanthanide thiocyanates show a periodic trend along the lanthanide series.
TL;DR: In this article, the enthalpies of formation of solid Fe-Ga and Co-Ga solutions were determined using solution calorimetric methods involving a BrBrH mixture as the solvent.
Abstract: Solution calorimetric methods involving a BrBrH mixture as the solvent have been used to determine the enthalpies of formation of solid FeGa and CoGa solutions. The enthalpies of formation exhibit large negative values. The maximum values are −8.5 kcal g-at.−1 for the FeGa system and −10.7 kcal g-at.−1 for the CoGa system. An evaluation of the melt equilibria in the FeGa system indicates that the entropies of formation also exhibit large negative values. The discussion of the results pertaining to these systems shows that structural differences between the components and homopolar and heteropolar contributions to the binding exert considerable influence on the thermodynamic properties of the solid alloys.
TL;DR: The thermal decomposition of pure ammonium perchlorate (AP) was investigated in various gaseous atmospheres at pressures up to 51 atm, using a technique of thermal analysis as mentioned in this paper.
Abstract: The thermal decomposition of pure ammonium perchlorate (AP)was investigated in various gaseous atmospheres at pressures up to 51 atm, using a technique of thermal analysis. It is concluded that the first and second stage decompositions of AP in an atmosphere of oxygen or nitrogen are appreciably accelerated as the pressure is increased. Platinum has a catalytic effect in the high-temperature decomposition and suppresses the sublimation of AP at high temperature ranges in helium atmosphere even at 1 atm. The reaction heat for the high-temperature decomposition of AP in the platinum cell was calculated from the peak temperatures of DTA curves at various pressures to be 77.9 kcal mol −1 . The activation energies of the sublimation in helium at 1 atm and of the high-temperature decomposition in the platinum cell at various pressures of helium have also been obtained, giving similar values of 23–25 kcal mol −1 .
TL;DR: In this article, the enthalpies of formation of solid nickel-gallium alloys were determined by solution calorimetry using liquid tin as the solvent and the free energies of formation have been determined from EMF-measurements using galvanic cells containing solid electrolytes which were oxygen-ion conducting.
Abstract: The thermodynamic properties of solid nickel-gallium alloys have been measured. The enthalpies of formation have been determined by solution calorimetry using liquid tin as the solvent and the free energies of formation have been determined from EMF-measurements using galvanic cells containing solid electrolytes which were oxygen-ion conducting. The system exhibits a strong tendency toward compound formation. The enthalpies of formation are negative and amount to up to − 11.5 kcal g-at. −1 . The entropies of formation determined from the enthalpies and free energies of formation also show large negative values. The enthalpy of fusion determined for an alloy with 36 at.% Ga shows moreover that the unusually strong tendency toward compound formation is also present in the liquid NiGa alloys to the same extent. A comparison with the enthalpies of formation of solid NiAl-alloys made it possible to estimate the enthalpy of transformation occurring when gallium transforms from its orthorhombic structure into a hypothetical face-centered cubic structure. This enthalpy is Δ H u Ga = 6.5 ± 3 kcal g-at. −1
TL;DR: In this article, the thermal properties of the complexes of cinchomeronic and dinicotinic acid with several divalent metal ions were determined by thermogravimetry (TG) and differential thermal analysis (DTA).
Abstract: The thermal properties of the complexes of cinchomeronic and dinicotinic acid with several divalent metal ions were determined by thermogravimetry (TG) and differential thermal analysis (DTA). For the thermal stability of the anhydrous compounds a sequence may be observed for the metal ions with cinchomeronic (3,4-H 2 PC) and dinicotinic acid (3,5-H 2 PC): The thermal stability of the pyridine carboxylic acid for each metal of the series is: dinicotinic > cinchomeronic The activation energy values for each thermal reaction were also calculated, using the Coats and Redfern algorism, by the Univac 1108 computer, by a program properly implemented for the statistical analysis of the data to obtain the reaction order and the activation parameters with the relative confidence limits.
TL;DR: The thermal behavior of compounds of the type (n-C n H 2n+1 NH 3 ) 2 CoCl 4 with n = 9, 10 ⋯ 17 is investigated by means of differential scanning calorimetry in the temperature range 280-470 K as discussed by the authors.
Abstract: The thermal behavior of compounds of the type (n-C n H 2n+1 NH 3 ) 2 CoCl 4 with n = 9, 10 ⋯ 17 is investigated by means of differential scanning calorimetry in the temperature range 280–470 K. All compounds show solid—solid phase transitions at temperatures lower than 380 K and melt around 440 K. Total molar transition and melting entropies are discussed in terms of conformational disorder of the alkyl chains in the high temperature stable modifications.
TL;DR: In this paper, various analytical methods of non-isothermal kinetics have been applied to DSC curves to determine the kinetic parameters ruling the lattice reorganization (primary recrystallization) of prestrained pure copper.
Abstract: Various analytical methods of non-isothermal kinetics have been applied to DSC curves to determine the kinetic parameters ruling the lattice reorganization (primary recrystallization) of prestrained pure copper. The techniques by Borchardt and Daniels, and Rogers and Smith have been modified to make them suitable for complex phenomena other than nth-order reactions. The results supplied by the new formulas are consistent with the data previously obtained under isothermal conditions. The same applies to the other methods tested, provided an accurate temperature calibration be made to correct the thermal lag of the calorimetric sensors. Such a calibration is of prime importance when DSC peak shifts are analyzed as a function of heating rate.
TL;DR: In this article, a fresh outcrop of silicified limestones at the Burgenstock (Switzerland) contained palygorskite, which showed an alteration in the unit cell dimensions.
Abstract: Slickensides and fissures in a fresh outcrop of silicified limestones at the Burgenstock (Switzerland) contained palygorskite. According to TG, DTA and heating X-ray experiments, dehydration of the palygorskite took place in four steps. Each step clearly showed an alteration in the unit cell dimensions. Exothermic reactions which occur at higher temperatures resulted in the formation of a Mg-Al- silicate high phase together with some clinoenstatite and the formation of β- cristobalite with some cordierite, respectively.
TL;DR: In this paper, the heats of formation were measured using a direct isoperibol calorimeter and the composition and equilibrium state of the samples have been checked by chemical, metallographic and X-ray analyses.
Abstract: In the PrBi system the heats of formation were measured using a direct isoperibol calorimeter. The composition and equilibrium state of the samples have been checked by chemical, metallographic and X-ray analyses. The following values were found for the two known compounds (reaction in the solid state, 300 K): The results obtained, compared with those already achieved in other REBi systems, are briefly discussed.
TL;DR: The first-order kinetics of the dehydroxylation of talc have been measured in the temperature interval 1100-1160 K by means of isothermal weight-change determinations as mentioned in this paper.
Abstract: The kinetics of the dehydroxylation of talc have been measured in the temperature interval 1100–1160 K by means of isothermal weight-change determinations. The reaction follows first-order kinetics. Over the indicated temperature range the enthalpy of activation was found to be 101±4 kcal mol−1, and the entropy of activation was found to be 16±4 cal mol−1 K−1. The error estimates correspond to one standard deviation. The enthalpy necessary to break the MgOH bond was estimated from the heat of reaction for MgOH(g) → Mg(g)+OH(g). This turns out to be 97 kcal mol−1 in reasonable agreement with the measured enthalpy of activation. These activation parameters are consistent with the mechanism proposed for dehydroxylation of talc consisting of MgOH bond scission and subsequent migration of magnesium. These results contradict a previous report on the kinetics of talc dehydroxylation in which a diffusion-controlled expression was claimed to represent the rate of talc weight loss. It is suggested that the presence of adsorbed water on the talc used in the previous investigation is responsible for the discrepancy.
TL;DR: In this article, thermal dissociation reactions of lanthanide(III) nitrates and thiocyanates solid complexes of the cyclic polyether benzo-15crown-5 were studied in dynamic atmosphere of dry nitrogen and under reduced pressure.
Abstract: Thermal dissociation reactions of lanthanide(III) nitrates and thiocyanates solid complexes of the cyclic polyether benzo-15-crown-5 were studied in dynamic atmosphere of dry nitrogen and under reduced pressure (5·10 −2 mm Hg). The complexes of lanthanide nitrates undergo dissociation with ligand decomposition while from those of lanthanide thiocyanates the ligand is released undecomposed. Values of enthalpy change and “activation energy” for the dissociation reactions of the complexes with lanthanide thiocyanate were obtained and briefly discussed.
TL;DR: In this paper, a study of the thermal decomposition of intimate mixtures of different molar ratios of KClO4 and chromium(III) oxide was conducted employing thermogravimetry, differential thermal analysis, chemical analysis, infrared spectroscopy and X-ray diffraction analysis.
Abstract: A study of the thermal decomposition of intimate mixtures of different molar ratios of potassium perchlorate and chromium(III) oxide, and potassium perchlorate and nickel(II) chromite(III) was conducted employing thermogravimetry, differential thermal analysis, chemical analysis, infrared spectroscopy and X-ray diffraction analysis. Upon heating to 400°C Cr(III), in 2:1 molar ratios, is oxidized to potassium dichromate. Only a stoichiometric amount of Cr(III) was oxidized from molar ratios less than 2:1, leaving behind excess Cr2O3 and NiCr2O4 whereas from molar ratios greater than 2:1, Cr(III) was completely oxidized and the excess KClO4 started decomposing around 410°C which is much below the decomposition temperature of pure KClO4.
TL;DR: In this paper, the decomposition of hydrated selenates of manganese, cobalt, nickel, copper(II), zinc and cadmium has been studied using different methods.
Abstract: Thermogravimetry, differential thermal analysis and differential thermogravimetry have been used to study the decomposition of hydrated selenates of manganese(II), cobalt, nickel, copper(II), zinc and cadmium. Based on the results obtained, mechanisms of decomposition have been proposed. The decomposition temperatures of non-hydrates show a gradual increase from manganese(II) selenate to zinc selenate and then a sudden drop for cadmium selenate.
TL;DR: Using differential scanning calorimetry (DSC) in combination with effluent analysis, differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray analysis, the dehydration of ZnSO 4 ·7H 2 O and NiSO 4 −6H 2O was investigated and a few transition enthalpies were measured as discussed by the authors.
Abstract: Using differential scanning calorimetry (DSC) in combination with effluent analysis, differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray analysis, the dehydration of ZnSO 4 ·7H 2 O and NiSO 4 ·6H 2 O was investigated and a few transition enthalpies were measured. The dehydration of both compounds showed a great analogy. For NiSO 4 ·6H 2 O the α—β phase transition was studied. The dehydration scheme of both hydrates can be given as follows: