Interference by second order reactions in activation analysis

Equations to calculate the second order reaction interferences in activation analysis have been derived. A simple approximation as well as the exact solution have been investigated. A new algorithm is proposed for fast and accurate calculations, without the need of a computer with high precision arithmetic. The method can be used for all higher order reaction chains. Aspirant NFWO     

Fossil age determination by thermal analysis

Subsequent to a comparative examination of recent bone material the author has recently completed the paleobiogeochemical evaluation of classical Quaternary and Pliocene terrestrial fossils of vertebrata from Hungary. A derivatograph (MOM) has been used to determine two thermoanalytical parameters which are closely associated with the passage of geological time: the total bound organic-matter content of the fossil and the fossilization cofficient.Derivatographic measurement of the organic matter in the bones is supplemented by fine-structure analysis of bone-tissue slides.Sample material of unknown age from several provenances was evaluated with the new dating method. The importance of the procedure is even greater in cases when only indefinite sporadic finds can be obtained from the sediments.

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Zusammenfassung Nach einer vergleichenden Untersuchung an neuzeitlichem Knochenmaterial hat der Autor kürzlich die paleobiogeochemische Auswertung der klassischen Quaternären und Pliocenen terrestren Fossilien von Vertebraten aus Ungarn ergänzt.Ein Derivatograph (MOM) wurde zur Bestimmung zweier thermoanalytischer Parameter eingesetzt, die eng mit dem Fortschreiten der geologischen Zeit verbunden waren: dem Gesamtgehalt an gebundenem organischem Material und dem Fossilisationskoeffizienten.Die derivatographische Messung der organischen Substanz in den Knochen wurde durch die Feinstrukturanalyse von Knochengewebeschnitten ergänzt.Probenmaterial unbekannten Alters verschiedener Herkunft wurde mit der neuen Methode ausgewertet. Die Bedeutung des Verfahrens ist in den Fällen noch grösser, wenn aus den Sedimenten nur unbestimmte sporadische Funde erhalten werden können.

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The author wishes to thank the staff of the Department of Experimental Physics of L. Kossuth University for the neutron activation measurements and the Computer Center of the University for the calculation work.     

Thermal reactions by automated mass spectrometric thermal analysis

Combination of differential thermal analysis (DTA) with time-of-flight mass spectrometry and data storage on magnetic tape is used to study thermal decompositions.A modified Du Pont 900 DTA cell is used for reactions at atmospheric pressure with evolved gas sampling into a small time-of-flight spectrometer.For fast reactions a specially developed DTA cell is operated within the mass spectrometer and operates at high vacuum.A combination of both operational modes yields pressure dependencies of chemical decomposition.Examples studied include inorganic compounds and complexes, organometallics and organic chemicals such as fire retardants.The data are presented as intensity/temperature curves for each observed fragment, which not only yields decomposition temperatures but also—by the curve shapes—information on the mode of decomposition.     

Kinetic analysis of thermal decomposition reactions

The effect of⁶⁰C0-gamma radiation on the kinetic parameters of the thermal decomposition of potassium bromate crystals has been investigated. Radiation did not modify the mechanism of thermal decomposition reaction, but resulted in a decrease in activation energy and frequency factor with a rate which is large at small doses and decreases at higher doses. The results showed that the increase in the concentration of decomposition nuclei tends to be more important than the increase in the porous character of the solid.     

Dynamic thermal analysis of solid-state reactions

There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no best method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations [1]. Here we propose a method for extractingE from non-isothermal data, that promises general validity.     

Investigations of thermal elimination reactions of polymers by thermal volatilization analysis and ultraviolet spectroscopy

Using thermal volatilization analysis with differential condensation of volatile products, with film samples on flat-bottomed silica glass reaction tubes to permit measurements of UV spectra of partly degraded polymer, the thermal stability, the types of volatile products and the development of conjugation in the involatile residue have been compared for poly(vinyl chloride), polychloroprene, poly(vinyl acetate) and vinyl acetate/ethylene copolymers, poly(vinyl formate) and poly(vinyl alcohol). All undergo a side-group elimination reaction at lower temperatures, and polyene breakdown occurs in all the samples between 400 and 500°. The longest polyene sequences are formed by PVC. All the polymers except PVC show some complexity of products in the elimination reaction.

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Zusammenfassung Die Anwendung der thermischen Verdampfungsanalyse durch Differentialkondensation der flüchtigen Produkte an Filmproben in flachen Quarzglasreaktionsrohren gestattet die Ermittlung der UV-Spektren von teilweise degradierten Polymeren sowie Aussagen über die thermische Stabilität und Types des flüchtigen Produktes. Die Bindungen in dem nichtflüchtigen Rest wurden untersucht und im Falle der Copolymere Poly(vinylchlorid), Polychloropren, Poly(vinylacetat) und Vinylacetat/Äthylen, weiterhin Poly/vinylformat und Poly/vinylalkohol verglichen. Alle erleiden eine Eliminierungsreaktion an der Seitengruppe bei niedrigeren Temperaturen und Polyenabspaltung zwischen 400 und 500°. Die längsten Polyensequenzen werden durch PVC gebildet. Abgesehen vom PVC zeigten alle übrigen Polymere eine gewisse Komplexität in der Eliminierungsreaktion.

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Résumé L'emploi de la méthode d'analyse par volatilisation thermique avec condensation différentielle des produits volatils, sur des échantillons en film sur tubes de réaction en verresilice à fond plat permet l'examen des spectres ultraviolets des polymères partiellement dégradés et l'étude de la stabilité thermique, outre l'identification des constituants volatils. On a comparé le développement de la conjugaison dans le résidu non-volatil pour les polychlorure de vinyle, polychloroprène, polyacétate de vinyle et les copolymères acétate de vinyle/éthylène, polyformiate de vinyle et polyalcool vinylique. Dans chaque cas, on a observé une réaction d'élimination du groupe latéral à basse température et rupture du polyène entre 400 et 500°. Les plus longues séquences ont été formées dans le cas du PCV. Tous les polymères, excepté le PCV, montrent une certaine complexité de produits dans la réaction d'élimination.

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Some parts presented at the International Symposium on Macromolecular Chemistry, Budapest, 1969.

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One of the authors (D.L.G.) thanks the Science Research Council for the award of a studentship. Some of the experiments with PVF were carried out by Mr. A. Jamieson. Differential condensation TVA curves were obtained by Mr. R. G. Perrett.     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

Thermophysical property determination of high temperature alloys by thermal analysis

Differential scanning calorimetric measurements to determine solidus and liquidus temperatures and latent heat of fusion of two high temperature materials, PWA1484 and an experimental gamma titanium aluminide alloy, are presented. The solidus and liquidus temperatures of PWA1484 are 1340 and 1404°C. The solidus and liquidus temperatures of the titanium aluminide alloy are 1453 and 1522°C. Solidus and liquidus temperatures determined from actual heating and cooling curves, which were measured using imbedded thermocouples and analyzed by a pseudo-differential thermal analysis technique are found to be in good agreement with the differential scanning calorimetric measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Continuous determination of carbon monoxide evolved during thermal decomposition reactions

A device suitable for the continuous detection of carbon monoxide evolved during themal decomposition processes is described. The detector can be connected directly to thermoanalytical equipment of controlled gas atmosphere. Carbon monoxide collected by the carrier gas is passed through the device containing hopcalite catalyst. In the presence of oxygen carbon monoxide is converted to carbon dioxide in the cell and the temperature change caused by the heat of reaction is measured. According to experience, the change of temperature is linearly proportional to the amount of carbon monoxide released.The signal curve of the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which carbon monoxide was released.The detector is not completely selective to carbon monoxide, but in most cases the interferring gases can be removed from the carrier gas by various packings placed between the detector and the thermoanalytical equipment.

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Zusammenfassung Es wird ein geeignetes GerÄt zur kontinuierlichen Detektierung von in thermischen Zersetzungsprozessen freigesetztem Kohlenmonoxid beschrieben. Der Detektor kann direkt an eine thermoanalytische Apparatur mit überwachter GasatmosphÄre angeschlossen werden. Das vom Carriergas aufgenommene Kohlenmonoxid wird durch das GerÄt geleitet, das einen Hopcalit-Katalysator enthÄlt. In Gegenwart von Sauerstoff wird das Kohlenmonoxid in Kohlendioxid überführt und die durch die ReaktionswÄrme verursachte TemperaturÄnderung gemessen. ErfahrungsgemÄ\ ist die TemperaturÄnderung proportional der entwickelten Menge Kohlenmonoxid.Das Detektorsignal kann mit den gleichzeitig aufgezeichneten thermoanalytischen Kurven verglichen und zur Bestimmung dessen benutzt werden, in welchem Teilschritt Kohlenmonoxid freigesetzt wird.Der Detektor zeigt keine vollstÄndige SelektivitÄt, jedoch können Störgase durch verschiedene Füllungen zwischen Thermoanalysator und Detektor vom Carriergas getrennt werden.

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The authors thank Dr. A. Felinger for his kind help in the computer processing of the recordings.     

Continuous determination of carbon dioxide evolved during thermal decomposition reactions

A simple device suitable for continuous monitoring of carbon dioxide evolved during thermal decomposition reactions is described. Carbon dioxide is transported by a carrier gas through the device connected to thermoanalytical equipment and absorbed by soda lime reagent. The reaction heat released is linearly proportional to the amount of carbon dioxide absorbed.     

Kinetic analysis of second order reactions using UV-VIS spectroscopy

A new method was recently developed for the spectroscopic kinetic analysis of reactions with two linearly independent concentration variables. Firstly, the results of this theory applied to experimental data are represented. For this investigation, reactions of the mechanism type A + Bk (1)--> C + D and A + E uc-->|k(2)|F + G were chosen since both reaction steps can be studied separately. The evaluation of the reaction system consisting of both reaction steps gives satisfactory results when the methods of "formal integration" and "singular value decomposition" (SVD) are used. Absorption coefficients of absorbing species are not needed for the evaluation. Only time dependent spectroscopic measuring values and initial concentrations are used in the presented practical example.     

Investigation of gas-solid reactions by means of thermal analysis/mass spectrometry

During the production of powder-metallurgical and ceramic materials the evolution of gaseous reaction products can result in large structural imperfections. Reaction sintering of titanium aluminides from mixtures of elemental powders can be accompanied by swelling effects combined with considerable volume swelling of the sintered parts [1]. The firing of thick-film pastes containing ruthenium oxide on substrates of AlN ceramics entails the formation of bubbles impairing the function of thick film resistors [2]. These investigations contribute to the clarification of the causes of both phenomena.     

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

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.

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Zusammenfassung Experimentelle und theoretische Grundlagen der Grenztemperaturen der thermischen Zersetzung von thermoplastischen Polymeren werden behandelt. Es besteht eine Korrelation zwischen den Grenztemperaturen und den intermolekularen Wechselwirkungen der untersuchten Polymere.

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Simultaneous determination of nitrogen and lithium by thermal neutron activation analysis

The determination of lithium and nitrogen in a variety of materials by thermal neutron activation is described. The nuclear reactions used are ¹⁴N(n,p)¹⁴C and ⁶ Li(n,α)³H. Radionuclides. ¹⁴C and ³H for counting are isolated by fusion of the irradiated sample in a vacuum system. Data are presented on lithium and nitrogen concentrations in several terrestrial standards. The new method allows reliable measurements on 10–50-mg samples.     

Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

On the non-isothermal determination of activation energy for thermal decomposition reactions

Attention is called to the frequently encountered linear sector in the isothermal course of the topochemical processes which is used in the kinetic treatment of the differential curves of thermal CoOOH decomposition. The effect of sample weight and heating rate on the values of the activation energy of this process under polythermal conditions has been investigated. Most of the values obtained are in good agreement among themselves as well as with those found isothermally. Existing differences have been explained satisfactorily.     

Zone melting as an aid to impurity determination by thermal analysis

The determination of the impurity content of a sample by means of the meltingcurve method (calorimetric analysis) is often seriously hampered when solid soluble contaminants are present. Solid solutions often occur in substances purified by crystallization or extraction. A simple test on mixed crystals is described. When three or more impurities are present the relations obtainable from a melting curve are insufficiently accurate for computing the unknown concentrations and distribution coefficients to an acceptable extent. Only melting curves obtained from samples containing one or two impurities permit an exact, simple interpretation. A complex of impurities may be analysed when the sample is subjected to zone melting and a set of melting curves is obtained for parts of the ingot.     

The determination of tin in explosive materials by thermal neutron activation analysis

A method, based on the measurement of the -photopeak at 332 keV arising from a¹²⁴Sn(n, )^125mSn reaction, has been developed for the rapid measurement of Sn at concentrations of 20 g g^–1, present as the cross-linking agent, in explosive charges. The method is comparative, and has a limit of detection of 0.6 g g^–1 and a precision of 5% RSD. The method requires no sample preparation and is economical in effort.     

New method for determination of heats of thermal gas-phase reactions yielding intermediates

A new procedure for the determination of the heats of thermal gas-phase reversible reactions leading to intermediates in the framework of the adiabatic compression method is proposed. A model problem is solved, and the error of the method is evaluated (-1 %). The validity of the method was confirmed using the reversible formation of the I,2-biradical from tetrafluoroethylene as an example. Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 64–67, January, 1996.