Investigating safety aspects by Thermal Analysis

Recent accidents in chemical plants involving compounds previously thought to have been Harmless, demonstrate the importance of complete safety screening. Modern DSC instruments using rugged sensors and CRT graphics allow fast investigations of substances and mixtures in question.In addition to potential hazard due to exothermic reaction, DSC supplies information concerning drying, melting, purity, polymorphic transitions, sublimation and vaporization. Our paper deals with measurements of selected inorganic and organic samples that undergo decomposition in the applied temperature range of room temperature up to 700°C. The measurements are performed by the Mettler TA 3000 Thermal Analysis System with the new computer graphics and evaluation software GraphWare TA72.

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Zusammenfassung Die vorgekommenen Chemiewerksunfälle, in denen Verbindungen eine Rolle spielten, die zuvor als ungefährlich angesehen wurden, unterstreichen die Bedeutsamkeit komplexer Sicherheitsuntersuchungen. Moderne DSC Geräte mit robusten Sensoren und CRT Graphik erlauben eine schnelle Untersuchung der fraglichen Substanzen und Gemische.Zuzüglich zu potentieller Gefährlichkeit durch exotherme Reaktionen liefern DSC Angaben über Trocknen, Schmelzen, Reinheit, polymorphe Umwandlungen, Sublimation und Verdampfen. Diese Arbeit beschäftigt sich mit Untersuchungen an anorganischen und organischen Proben, die sich im untersuchten Temperaturbereich Raumtemperatur — 700°C zersetzen. Dazu wurde ein METTLER TA3000 Thermoanalysensystem mit der neuen Computergraphik- und Auswertesoftware GraphWare TA72 verwendet.

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TG and DSC kinetics of thermal decomposition and crystallization processes

The simplen ^th order model equation combined with the Arrhenius approach of the temperature dependency of the reaction rate constant is widely used in thermal analysis. The new Mettler software package for thermal analysis, GraphWare TA72 allows to access a full model comprising the power law and the crystallization kinetics (AvramiErofe'ev). The kinetics of the following reactions are studied to illustrate some applications:

thermal decomposition of dissolved dibenzoylperoxide, (dynamic and isothermal DSC measurement)

crystallization of polyethylene terephthalate (PET) (isothermal DSC measurements).

The kinetic model applied and the accuracy of the kinetic data obtained are discussed by means of a comparison of a predicted behaviour with the kinetic data measured isothermally.     

Electrochemical and mechanochemical formation of solid solutions of potassium copper(II)/zinc(II) hexacyanocobaltate(III)/hexacyanoferrate(III) KCu x Zn1-x [hcc] x [hcf]1-x

Electrochemical reduction/oxidation cycles of immobilised powder mixtures of KCu[hcc] and KZn[hcf] as well as their mechanical milling lead to the formation of a quaternary solid solution (mixed crystals) with Cu²⁺ and Zn²⁺ on the nitrogen coordinated sites and Fe³⁺ and Co³⁺ on the carbon coordinated sites. The reaction products were studied by the X-ray diffractometry and voltammetric techniques. The formation of solid solutions of the general formula KCu_xZn_1-x[hcc]_x[hcf]_1-x is the first example of an electrochemical and mechanochemical reaction leading to mixed hexacyanometalates.Dedicated to Professor Dr. G. Horányi on the occasion of his 70th birthday.     

Kinetic measurements on polymers — Applications and limits

A modern kinetic evaluation method for nonisothermal reactions measured with TG or DSC is presented. The obtained kinetic data are the basis for computation of a reaction process under any condition, e.g. isothermal or adiabatic. The measurements were performed on a Mettler TA3OOO system with built-in evaluation software. Mainly the following reactions are discussed: polyaddition of an epoxy premix and pyrolysis of polystyrene. To judge the reliability of the results, 4 check procedures are recommended.

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Zusammenfassung Es wird eine moderne kinetische Auswertungsmethode für durch TG oder DSC verfolgte nichtisotherme Reaktionen vorgestellt. Die erhaltenen kinetischen Daten stellen die Basis der Berechnung der Reaktionsprozesse unter jeder, z.B. isothermer oder isobarer Bedienung dar. Die Messungen wurden mit dem Mettler-System TA3000 mit Auswertungs-software ausgeführt. In erster Linie werden die folgenden Reaktionen diskutiert: Polyaddition eines Epoxy-Vorgemisches, Pyrolyse von Polystyrol. Zur Beurteilung der Zuverlässigkeit der Ergebnisse werden 4 Testverfahren empfohlen.

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Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

Ternary potassium-iron sulfide, KFeS₂, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, etc. While some of the measurements can be satisfactorily described, the deficiency of the entropy changes upon the magnetic transition and the spin state of the iron ion remains a challenge for the further understanding of magnetism. In this work, high-quality single-crystalline samples of KFeS₂ were grown by the Bridgman method, and their stoichiometry, crystal structure, and absence of alien magnetic phases were checked, utilizing wave-length dispersive X-ray electron-probe microanalysis, powder X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy, respectively. An ab initio approach was developed to calculate the thermodynamic properties of KFeS₂. The element-specific phonon modes and their density of states (PDOS) were calculated applying the density functional theory in the DFT + U version, which explicitly takes into account the on-site Coulomb repulsion U of electrons and their exchange interaction J. The necessary calibration of the frequency scale was carried out by comparison with the experimental iron PDOS derived from the inelastic nuclear scattering experiment. The infrared absorption measurements confirmed the presence of two high-frequency peaks consistent with the calculated PDOS. The calibrated PDOS allowed the calculation of the lattice contribution to the specific heat of KFeS₂ by direct summation over the phonon modes without approximations and adjustable parameters. The temperature-dependent magnetic specific heat evaluated by subtraction of the calculated phonon contribution from the experimental specific heat provides a lower boundary for estimating the reduced spin state of the iron ion.     

Temperature Modulated DSC (TMDSC) Applications and Limits of Phase Information, cp Determination and Effect Separation

The ADSC (Alternating DSC [1]) technique superimposes upon the conventional constant heating rate a periodically varying modulation [2–8]. The modulation creates high instantaneous heating rates which increases sensitivity. The low underlying constant heating rate is used to get better resolution. With ADSC it is possible to separate overlapping thermal effects without loss of sensitivity and to determine heat capacities under quasi-isothermal conditions. It has been reported that there are also some limitations for the use of the modulation techniques, i.e. that the accuracy of c_p determination is reduced at higher modulation frequencies due also to thermal diffusivity within the sample itself [9, 10]. In this contribution, the limitations given by the measuring system itself will be discussed. A key value is the limit frequency of the sensor arrangement. In the Mettler Toledo DSC821^c this frequency is approximately 1/3 Hz. From these findings the following recommendations amongst others can be given: for light mass crucibles, 30 s periods are reasonable with amplitudes not exceeding the heating/cooling rates possible. A blank and a calibration measurement will eliminate cell asymmetry and will enhance the accuracy of c_p measurements even at higher modulation frequencies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Perspectives for low energy antiproton physics at FAIR

The CRYRING accelerator, previously located at the Manne Siegbahn Laboratory of Stockholm University, has been chosen by the FLAIR collaboration as the central accelerator for the planned facility. It has been modified to allow for high-energy injection and extraction and is capable of providing fast and slow extracted beams of antiprotons and highly charged ions. It is currently being installed at the ESR of GSI Darmstadt where it can be used with highly charged ions. The future possibilities for its use with slow antiprotons will be discussed.     

Magnetic properties of substitutional solid solutions of nickel and iron hexacyanoferrate–hexacyanochromate

In order to evaluate the influence of substitution at the central metal ion position in transition hexacyanometallates in some detail, the magnetic studies were carried out on a series of solid solutions of metal hexacyanometallates of the composition M[Fe^II(CN)₆]_{1? x} [Cr^III(CN)₆] _x , where M?=?Ni^II and Fe^III. The temperature and field dependences of magnetization were studied using a superconducting quantum interference device magnetometer. The field dependence of the samples at 5?K shows a hysteresis behaviour. For M?=?Ni^II, the transition temperature increases with increase in the substitution of low-spin Fe(III) by Cr(III) in the hexacyanometallate unit. The saturation magnetization was found to decrease with increase in the iron concentration. The observed variation in the magnetic properties, such as the value of T _C and the nature of magnetic ordering, is attributed to the variation in the composition of the transition-metal ion in the coordination sphere of carbon. On the other hand, for M?=?Fe^III, the transition temperature and saturation magnetization remained almost unchanged, indicating that substitution at the carbon coordination site did not produce any change in the magnetic interaction among the transition-metal ions through the cyanide ions.     

Atomic Spectroscopy and Collisions Using Slow Antiprotons – the ASACUSA Experiment at CERN-AD

Hyperfine Interactions - The scope of the ASACUSA experiment is the study of atomic physics with low-energy antiprotons, namely high-precision spectroscopy of antiprotonic atoms, the study of...