Showing papers in "Journal of Thermal Analysis and Calorimetry in 1986"

Applicability of friedman plot

Abstract: By expanding the initial equation, it is shown that the Friedman method for estimating the activation energy of chemical reactions by using both the conversion and the rate in the thermoanalytical data has wide applicability to crystal growth from pre-existing nuclei, diffusion and other processes in which a single unit process is involved.

Melting memory effect of the β-modification of polypropylene

Abstract: The pureβ-modification of polypropylene has been prepared. It has been found that the nature of the melting of theβ-modification strongly depends on the thermal history of the sample (melting memory effect). The melting of samples cooled to room temperature after crystallization is a complex process consisting of three partially overlapping processes (β-melting→ recrystallization in theα-modification (βα-recrystallization)→ α-melting). If heating starts at the temperature of crystallization, theβ-modification melts separately, withoutβα-recrystallization. Under melting conditions free from the interference caused byβα-recrystallization, theβ-modification exhibits the melting characteristics of thermodynamically stable modifications. The thermodynamic equilibrium melting point of theβ-modification has been determined to beT m 0 (β)=456 K.

On the compensation effect

Abstract: Arrhenius equation is popularly used to relate the change in the rate constant with temperature. The linearized form of Arrhenius equation has often been used to establish a relation between InA andE for a series of related reactions. Occurrence of such a compensating behavior between InA andE has been widely reported in the literature. The validity of the compensation effect has been heatedly debated. Compensation effect can arise from computational artifact or can arise from various chemical factors. This depends entirely on the data set used to establish the compensation behavior. This article stresses the importance of statistical analysis and the use of simple Arrhenius plots to draw conclusions regarding the occurrence of compensation effect. With the help of a few examples, some checkpoints to draw conclusions regarding the occurrence of true or false compensation effect are suggested.

The thermal decomposition of palladium acetate

Abstract: The nature, products, and enthalpy of the thermal decomposition of [Pd(CH3CO2)2]3 were determined in air, nitrogen and vacuum. Thermogravimetry, differential thermal analysis, evolved gas analysis, differential scanning calorimetry, and infrared spectroscopy were used to characterize the process and products. In vacuum the trimer volatilizes completely below 200 °C. The IR spectrum of the gas phase species is reported. At atmospheric pressure the material decomposed to Pd between 200 and 300 °C depending upon the rate of heating. The apparent activation energy for this process is about 115 ± 5 kJ mol−1 and the enthalpy is 440 ± 20 kJ mol−1. In the presence of oxygen, however, oxidation of the ligands leads to an overall exothermic process. The resulting the Pd then slowly oxidizes to PdO2 up to the decomposition temperature of the oxide near 800 °C. There is the slight loss of a Pd containing species, presumably due to sublimation or gas entrainment, during the decomposition below 300 °C. The extent of this loss increases with increasing heating rate, approaching 10% of the total Pd at heating rates of 64 °C min−1.

Thermochemical studies on the systems ACl/CeCl3 (A=Na-Cs)

Abstract: The pseudobinary systems ACl/CeCl3 (A=Na-Cs) were reinvestigated by means of DTA. The following compounds were found and identified through their X-ray patterns (primarily detected compounds in italics):NaCe1.67Cl6; K3CeCl6, K2CeCl5,KCe1.67Cl6;Rb3CeCl6, Rb2CeCl5,RbCe2Cl7; Cs3CeCl6, Cs2CeCl5,CsCe2Cl7. The compounds A2CeCl5 crystallize with the K2PrCl5 structure. The high-temperature modifications of the compounds A3CeCl6 have the cubic elpasolite structure. The hexagonal unit cell of KCe1.67Cl6 is related to the CeCl3 structure: 0.33 Ce3+ are substituted by one Ks+. The structure of CsCe2Cl7 can be described with a hexagonal subcellZ=4,a=9.72 andc=14.94 A; however, small superstructure reflexions reduce the symmetry.

Thermal decomposition and creation of reactive solid surfaces

Abstract: Three chromia precursors, namely CrO3, (NH4)2Cr2O7 and chromia gel, were subjected to thorough thermal analysis by means of TG and DTA. The thermal decomposition products obtained by calcination of these precursors at various temperatures (150–500°) for 5 h were investigated by infrared and X-ray techniques. The results obtained allowed a thorough physicochemical characterization of the intermediate steps and products throughout the thermal decomposition.

A systematic solution to the problem of sample background correction in DSC curves

Abstract: The problem of sample background correction in differential scanning calorimetric curves is addressed in this paper. An equation is derived for the heat capacity of the system, which corresponds to the sample background. Thereby, it is assumed that during the thermal event the system is a two-component mixture of the initial substance and the final product. According to this model, the variation in heat capacity of the system is due both to the increase in the partial concentration of the product at the expense of the initial substance and to the physical change in the specific heats of the two components, resulting from the temperature increase. The final result of the derivation is an integral equation which can be solved by means of a numerical technique. The algorithm used is presented in detail. The model is general, and can be applied to diverse exothermic or endothermic processes. The melting of a semi-crystalline polymer and the cure process of a thermoset are given as demonstrative examples. The method improves the reliability and the reproducibility of the data.

An addition scheme of heat capacities of linear macromolecules. Carbon backbone polymers

Abstract: It is shown that heat capacities of linear macromolecules consisting of all-carbon single-bonded backbones can be calculated from the appropriate contributions of substituted carbon atoms to a precision of about − 0.2±2.5% (155 data points), which is similar to the experimental precision. Heat capacity contributions of 42 groups are given over the full range of measurement and reasonable extrapolation. The quality of the addition scheme is tested on 16 series of measurements on homopolymers, copolymers and blends. The addition scheme works for all these different states of aggregation of the constituent groups. The basis of the addition scheme is discussed.

The FeVO4-MoO3 system

Abstract: A phase diagram of the FeVO4-MoO3 system has been constructed from the results of DTA and X-ray analysis. The components of the system form a compound FeVMoO7. This compound melts incongruently at 680±5 °C, with separation of the solid Fe4V2Mo3O20.

The kinetics of the thermal degradation of calcium carbonate

Abstract: The decomposition of calcium carbonate fine powder in a flowing nitrogen atmosphere has been investigated by non-isothermal thermogravimetry at heating rates in the range, 10–50 deg min−1. The analog percentage weight change record was digitized at 1 deg intervals. The resulting data, transformed into dimensionless extents of reaction and calculated rates of reaction, was then subjected to the Arrhenius, Friedman and Generalized Kissinger analyses, using a recently developed FORTRAN program system. The value ofn namely 0.39 ±0.04, resulting when the data is analyzed assuming an nth order reaction, strongly indicates that the most probable rate controlling step is a three-dimensional diffusion process (D4 mechanism), withE=172.4 kJ·mol−1 andA=1.97·104 K−1·min−1. Reasons for the wide disparity in previously reported kinetic data are discussed.

Thermal analysis of secondary crystallization in polymers

Abstract: With a particular experimental technique of differential scanning calorimetry, the melting of the secondary crystals in polymers is observed separately from the melting of the primary crystals, and methods for the detection and quantitative analysis of the secondary crystals have been developed. By this means, a number of particular features of secondary crystals could be found which are not mentioned in the literature. Two types of crystal formation are found for linear polymers, with no regard as to kinetics, growth and other characteristics of crystallization. Secondary crystallization is interpreted as the formation of crystals of “fringed micelle” type. The equation describing secondary crystallization is deduced. It is shown that some specific features of the DTA and DSC curves of polymers are caused by the behaviour of secondary crystals in the polythermal regime.

Control of purity and crystallinity of MVO4 compounds (M=Al, Cr, Fe, In, Y, Nd) by DTA

Abstract: Two aqueous methods were followed for the synthesis of MVO4 (M=trivalent element). The first, with vanadium pentoxide and M nitrate yielded crystalline InVO4 III and amorphous FeVO4. The second method, using ammonium metavanadate and M nitrate, led to amorphous compounds with M=In, Fe, Cr or Al, and semi-amorphous compounds with M=Nd or Y. The crystallinity and purity of these products were examined by DTA. Starting with amorphous compounds, two irreversible effects appeared; the first, at about 100°, was endothermic and corresponded to a considerable loss of water; the second was exothermic and corresponded to the crystallization of the compounds in the temperature range from 250 to 550°. Only InVO4 presented two more irreversible exothermic peaks, corresponding to allotropic transformations, as proved by the X-ray diagrams. A reversible effect then appeared, showing an invariant equilibrium corresponding to a peritectic process for InVO4 III, FeVO4, CrVO4 and AlVO4 at 1134, 870 and 765°, respectively; these temperatures agreed with the known M2O3-V2O5 phase diagrams. The DTA curves of the semi-amorphous Nd and Y compounds showed only a loss of water at about 100°; crystallization then occurred gradually during heating; X-ray analysis confirmed these results.

An addition scheme of heat capacities of linear macromolecules: Part II: Backbone-chains that contain other than C-bonds

Abstract: The prior developed addition scheme of heat capacities is expanded to macromolecules that contain non-C-bonds in the backbone. Tables for 31 groups are given. 713 data points which have been averaged for group contributions for which more than one measurement was available showed a deviation of 0.1±1.5% (internal consistency). Calculated heat capacities of homopolymers and copolymers for which independent measurements have been made showed average errors of 0.60% and a standard deviation of ±2.35% (177 data points).ZusammenfassungDas früher entwickelte Additionsschema für Wärmekapazitäten wird auf Makromoleküle erweitert, die Nicht-C-Bindungen im Stützgerüst enthalten. Tabellen für 31 Gruppen sind angegeben. Von 713 Meßdaten wurden für Gruppenbeiträge, für die mehr als ein Meßwert zur Verfügung stand, Mittelwerte berechnet, wobei sich eine Abweichung von 0.1±1.5% (interne Konsistenz) ergab. Berechnete Wärmekapazitäten von Homopolymeren und Kopolymeren, für die unabhängige Messungen ausgeführt wurden, weisen einen mittleren Fehler von 0.60% bei einer Standardabweichung von 2.35% auf (177 Meßwerte).РезюмеРазвитая ранее аддит ивная схема расчета теплоемкостей приме нена к макромолекула м, не содержащим углеро дных связей в остове м олекулы. Приведены таблицы дл я 31 группы. 713 точечных данных, изме ренных более чем один раз и усредненных для груп повых вкладов, показали отклонение 0.1±1.58% (внутренняя совмес тимость). Теплоемкости для гом ополимеров и сополимеров, вычисл енные на основе незав исимых измерений, показали с редние ошибки 0,60% и стандартно е отклонение ±2,35% (177 точеч ных данных).

Limiting temperatures of the thermal decomposition of polymers and their determination by rapid thermal analysis

Abstract: Experimental and theoretical foundations are established for the limiting temperatures of thermal decomposition of thermoplastic polymers. The correlation between the limiting temperatures and the intermolecular interactions of the polymers investigated is reported.

Phase Transformations in Cu-Al and Cu-Zn-Al alloys

Abstract: Phase transformations in Cu-12.4% Al and Cu-14.4% Zn-8.4% Al alloys were examined by DTA. The influence of the rate of temperature change on the sequence of phase transformations was studied. It was found that the rates of heating and cooling were the major factors determining the transformations which take place in these alloys.

Thermal analysis of amide derivatives of N,N-dialkylaminoazobenzene

Abstract: Thermal analysis was performed on amide derivatives ofN,N-dialkylaminoazobenzene. A correlation was found between the stability of the investigated dyes and the nature of the amide residue. The intermolecular interaction and the mechanism of thermal decomposition are discussed.

Some aspects of mathematical statistics as applied to nonisothermal kinetics

Abstract: As a numerical characteristic of the sensitivity of the kinetic parameter calculation method to the form of the kinetic function in non-isothermal kinetics, the value of the curvature of the line plotting residual dispersionvs. formal reaction order at the minimum point is suggested. The efficiency of this characteristic is exemplified.

Dielectric-differential thermal analysis part I: Method

Abstract: A thermal analyzer design is described The instrument is capable of performing simultaneously differential thermal analysis and dielectric thermal analysis under the same experimental conditions The theoretical basis of dielectric thermal analysis is superficially analyzed, and results obtained on different kinds of substances are presented

Kinetic analysis of complex reactions

Abstract: TG and DSC techniques have been extensively used to study complex solid state reactions. For complex reactions (constituting of all exothermic or all endothermic one step first order individual reactions), it has been shown that the results of TG and DSC instruments may not be identical. This is because the TG instrument is incapable of correctly recording the true effective reaction rate of complex reactions (if the reaction rate is not proportional to the total amount of reactants). This may happen when the reaction rates of the individual reactions in the composite reaction mixture are significantly different. In this communication it has also been suggested that the Friedman analysis of obtaining activation energy (E) may be inapplicable for complex or composite reaction due to the fact that, there may be no unique effective constant conversion at various heating rates.

Thermal decompositions of some transition metal polyacrylates

Abstract: Polyacrylales of Fe, Cr, Ni, Co and Mn were synthesized by the reaction of poly(sodium)acrylatc with metal halides. The salts obtained were investigated by thermal analysis. During heating in argon or air, all the salts behaved in a similar way. The initial decomposition temperature of the investigated salts increased in the following sequence: Fe

Parent and mixed ligand complexes in the copper(II)-ethylene glycol-sulphate system

Abstract: Eleven copper(II)-ethylene glycol-sulphate complexes of different compositions were prepared, one of them-CuGl2(H2O)2SO4-in single-crystal form. A thermoanalytical study of these complexes revealed three types of thermal decomposition pattern. The X-ray structure of the single-crystal demonstrated the presence of ethylene glycol bridges resulting in endless chains in the crystal.

Characterization of [Ni(Py)4]Br2 and its thermal decomposition

Abstract: The stepwise thermal decomposition of [Ni(py)4]Cl2 was studied by means of a derivatograph. The stepwise mode of thermal decomposition allowed the preparation of new complexes. X-ray powder diffraction and IR methods were used to study the structures of the decomposition intermediates. [Ni(py)4]Cl2 was applied as a model substance. The decompositions of a great number of complex compounds of similar type have been reported, but only a few of them have been investigated structurally by single-crystal X-ray diffraction techniques due to the difficulty of obtaining large single-crystals.

Thermo-dielectric analysis

Abstract: By means of thermo-dielectric analysis, some natural and synthetic zeolites were studied (clinoptilolite, mordenite,X, Y andA). The results indicate the existence of two effects, one related to water evolution, reflected in a decrease of dielectric constant; the second peak is related to ionic conduction at high temperature. Both peaks characterize zeolites, in thermo-dielectric analysis.

Thermal analysis of the interaction between stearic acid and pyrophillite or talc. IR and DTA studies

Abstract: Pyrophyllite and talc sorb stearic acid on edge surfaces. The grinding of clay-stearic acid associations in the presence of alkali halides converts some of the acid into the ionic form, this occurring more readily with talc than with pyrophyllite. Heating in a closed or semi-closed system causes dissociation of stearic acid adsorbed on talc, but not on pyrophyllite. The infrared absorption frequencies of the adsorbed ionic form vary with the clay mineral and the amount of water present. The thermal stabilities of the clay-stearic acid associations depend on the rate of escape of the acid, which is determined by the strength of bonding to the clay and the nature of the system, and on the degree of dissociation of the acid on the clay surfaces.

RepresentationT-V-x des systemes binaires a tension de vapeur non negligeable

Abstract: The effect of the variableV/m on the appearance of DTA endotherms has been used to obtain quantitative data on theT-V-x representation of the NdAs-As system.

Thermische Zersetzung von CuInSe2, LiInSe2 und LiInTe2

Abstract: Die thermische Zersetzung von CuInSe2, LiInSe2 und LiInTe2 wurde mit TG/DTG - MS - - Kopplung bei hohen Temperaturen im Vakuum untersucht. Fur CuInSe2 wurden zwei deutlich getrennte Stufen registriert. Bis 1000° verdampft Se und In2Se, spater Cu2Se. Die Li-Verbindungen zeigen ahnliches Verhalten, jedoch wurde Li+ auch wahrend der ersten Stufe nachgewiesen. Offenbar dissoziiert Li2Se eher als Cu2Se. Bis zur vollstandigen Verdampfung von CuInSe2 erscheinen keine Cu+-Spezies in der Gasphase.

Gas diffusion during the thermal analysis of pyrite

Abstract: Maximum rates of weight loss were measured during thermal analysis experiments involving the oxidation of thin layers of pyrite particles (<37 to 212–300 μm screen size fractions) in oxygen-containing atmospheres (10–100%). The experimentally determined rates were compared with those calculated for several diffusion-based models. Good agreement was obtained with the model involving gas diffusion in the crucible.

Etude du systeme binaire selenium-tellure

Abstract: Integral heats of mixing have been measured at 738 K by drop calorimetry. Liquidus and solidus temperaturesT9 and recrystallisation temperatures have been measured by thermal analysis.

Determination of liquid vapour adsorption and desorption on and from solids by means of the derivatograph II: Determination of kinetics and isotherms of adsorption and desorption of water vapour on silica gel

Abstract: Studies of water adsorption and desorption on silica gel with a modified derivatograph are described. The dynamic gas chromatography step profile method was used to determine isotherms of adsorption and desorption from the TG curve. The obtained isotherms agree with those from other methods. The properties of surface liquid layers can be investigated by this method.ZusammenfassungDie Untersuchung der Adsorption und Desorption von Wasser an Silikagel mittels eines modifizierten Derivatographen wird beschrieben. Die dynamische gaschromatographische Stufenprofilmethode wurde zur Bestimmung der Ad- und Desorptionsisothermen aus den TG-Kurven herangezogen. Die erhaltenen Isothermen stimmen gut mit denen nach anderen Methoden bestimmten überein. Die Eigenschaften flüssiger Oberflächenschichten können mit dieser Methode untersucht werden.РезюмеС помощью модифициро ванного дериватогра фа изучена адсорбция и д есорбция воды на еиликагеле. Ме тод ступенчатой дина мической газовой хроматограф ии был использован для определения изот ерм адсорбции и десор бции на основе кривой ТГ. Полу ченные изотермы согласуются с таковы ми, найденными на осно ве других методов. Описанным ме тодом можно исследовать свойств а поверхностных жидк их слоев.

Study of the solid solution of MoO3 in Fe2V4O13

Abstract: Differential thermal and phase X-ray analyses have shown that MoO3 and Fe2V4O13 form a solid substitution solution, in which Mo6+ ions are incorporate into the crystal lattice of Fe2V4O13 in place of V5+ ions. The solubility limit of MoO3 in Fe2V4O13 at ambient temperature is 18 mole % of MoO3. The phase equilibria in the system Fe2V4O13-FeVMoO7, were also studied. Results are presented in the form of a phase diagram.