Formalkinetische Behandlung des Masseverlustes bei thermischen Abbauprozessen von Polymeren unter nichtisothermen Bedingungen

Zusammenfassung Eine formalkinetische Auswertung nichtisothermer TG-Kurven des Polyphenylens ist mit Hilfe der Methode von Flynn und Wall und der von Zsakó durchgeführt worden. Die Auswertung nach diesen Methoden führt zunächst zu unrealen Ergebnissen, da festgestellt werden konnte, daß der thermooxidative Abbau des Polyphenylens durch das System zweier sich überlagernder, unabhängig verlaufender Reaktionen bestimmt wird. Durch die Anwendung einer speziellen Beziehung zwischen dem Umsatzgrad der Bruttoreaktion und dem der beiden Komponenten gelingt es, die formalkinetischen Parameter beider Teilreaktionen mit Hilfe der Methode von Zsakó zu bestimmen.

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Kinetic values from non-isothermal thermogravimetric curves of polyphenylene have been calculated using the method of Flynn and Wall and that of Zsakó. These methods at first give unreal kinetic parameters, for it has been established that the degradation of polyphenylene is a system of two mutually independent reactions occurring simultaneously. With the use of a special relation between the degree of conversion of the unit reaction and that of the components, the kinetic parameters of the two reactions could be investigated by the method of Zsakó.

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Résumé On a calculé les paramètres cinétiques du polyphénylène à partir des courbes thermogravimétriques non-isothermes en se servant de méthodes de Flynn et Wall et de celle de Zsakó. Ces méthodes ont d'abord donné des paramètres cinétiques non-réels, du fait qu'il a été établi que la dégradation du polyphénylène pouvait être définie par un systè me à deux réactions mutuellement indépendantes qui ont lieu simultanément. En utilisant une relation spéciale entre le degré de conversion de la réaction de base et celui des composants, il devient possible d'étudier les paramètres cinétiques des deux réactions par la méthode de Zsakó.

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On multi-pion multi-nucleon states

Commets are presented concerning hadronically stable clusters of negatively charged pions and neutrons (pineuts) with reference to recent theoretical and experimental studies on the subject.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Darstellung und Kristallstruktur von Rb2Sn3S7 · 2H2O und Rb4Sn2Se6

Preparation and Crystal Structure of Rb₂Sn₃S₇ · 2 H₂O and Rb₄Sn₂Se₆ Rb₂Sn₃S₇ · 2 H₂O has been prepared by hydrothermal reaction of SnS₂ and Rb₂CO₃ in an with H₂S saturated aqueous solution at 190°C. The crystal lattice contains chain anions [Sn₃S₇^2?] which display both SnS₄ tetrahedra and SnS₆ octahedra. Methanolothermal reaction of SnCl₂ with Se and Rb₂CO₃ at 145°C leads to the formation of Rb₄Sn₂Se₆ which contains edge-bridged bitetrahedral [Sn₂Se₆]^4? anions.     

Characterization of laser-nitrided iron and sputtered iron nitride films

Laser-nitriding may be a promising technique for substituting conventional nitriding processes. We have irradiated pure iron with pulses of an excimer laser and achieved high nitrogen contents in a thin surface layer. We found that the nitrogen is dissolved into -Fe, leading to a large amount of retained austenite. This was also verified by X-ray diffraction (XRD) measurements. Three subspectra can be resolved in the Mössbauer spectra (CEMS) for this nitrogen austenite. The nitrogen concentration can be calculated in terms of site occupation, indicating a content as high as 16(1) at%, which is consistent with the results of Rutherford backscattering spectroscopy (RBS), resonant nuclear reaction analysis (RNRA) and Auger electron spectroscopy (AES) measurements. This is more than the solubility limit for -Fe(N). By reactive magnetron-sputtering it is possible to produce thin iron nitride films of various stoichiometries. We report on the production of-Fe _x N and FeN _y films. These films were again characterized by CEMS, RBS, RNRA (¹⁵N(p, )) and XRD. For-Fe _x N, produced in the range 2x3 with medium nitrogen flows during reactive sputtering, the Mössbauer spectra can be well resolved in terms of different iron sites, enabling an accurate calculation of the nitrogen content. For high nitrogen flows during sputtering a phase FeN _y withy>0.5 is produced. This phase is not reported in the Fe-N phase diagram.     

Analysis of laser-nitrided stainless steel via nuclear methods

Laser nitriding of iron and other metals is governed by the complicated interplay of the laser-plasma-liquid surface interactions which lead to a superposition of several mechanisms. This article reports on the influence of the nitrogen gas pressure on the nitriding process for stainless steel. The effects of the nitrogen gas pressure on the nitrogen depth profiles and the phase formation are revealed by resonant nuclear reaction analysis, Mössbauer spectroscopy, and X-ray diffraction. We found that the surface nitrogen concentration reaches 10 at. % with a mean value of about 7.5 at. % in the first 150 nm. There seems to be a pressure window between 0.1 and 0.7 MPa for the most efficient treatment. In the surface layer, an additional %-Fe(N) phase can be distinguished from the original %-phase of the stainless steel.     

Mössbauer measurements backscattering technique (CXMS) of laser irradiated cold forming tool steel (X210CR12)

Conversion x-ray Mössbauer measurements (CXMS) in backscattering technique are performed on a commercial cold forming tool steel (X210Cr12), subjected to single-pass laser irradiation. The structure of the affected layer is examined for laser powers ranging from 2700 W to 3050 W at different depths. The results of the spectra analysis are discussed in connection with Vickers hardness and metallographic data. If a complete molten layer is quenched, a high carbon content austenite is retained down to room temperature. This phase is mixed with some low carbon martensite and (Cr 0.5 Fe 0.5)> C₃ carbide. The effects of carbon diffusion from the coating medium into the bulk are discussed. It is demonstrated that Mössbauer spectroscopy is a sensitive tool for phase analysis, including information about phase formation, and for delimiting the range of the quenched molten layer after laser treatment. It is thus a promising technique in this special kind of steel engineering.     

Magnetic texturing of xenon-ion irradiated nickel films

Thin polycrystalline Ni films of typically 75 nm thickness evaporated on Si or SiO₂ substrates were irradiated with 30-900 keV Xe-ions to fluences of 2.5 x 10¹³ - 4 x 10¹⁴/cm². The magnetization of the Ni films was measured using the longitudinal Magneto-Optical Kerr Effect and Vibrating Sample Magnetometry. The Ni-film thickness and Xe-concentration profiles were determined with Rutherford backscattering spectroscopy and the lattice dilation with X-ray diffraction. The Xe-irradiations were found to induce an in-plane uniaxial magnetic anisotropy within the Ni-films. This magnetic texture was investigated in relationship to the microstructure as function of the ion energy and fluence, the sample temperature, the presence of an external magnetic field during the irradiation and the stress field produced before, during and after the implantations.Received: 30 September 2004, Published online: 14 December 2004PACS: 61.82.Bg Metals and alloys - 68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc. - 75.30.Gw Magnetic anisotropy - 75.70.-i Magnetic properties of thin films, surfaces, and interfaces     

Formalkinetische Behandlung des Masseverlustes bei thermischen Abbauprozessen von Polymeren unter nichtisothermen Bedingungen

On the basis of the formal basic relation $$\frac{{d\alpha }}{{dt}} = A \cdot e^ - \frac{E}{{RT}}(1 - \alpha )^n $$ methods of calculating kinetic values from non-isothermal thermogravimetric curves have been critically evaluated. It has been established that in general integral methods are preferable to differential methods. Methods basing on a series expansion of the exponential integral $$\int\limits_0^T {e^ - \frac{{ET}}{{RT}}} dT$$ are applicable without limitations to any cases. It has been concluded that the integral method suggested by Zsakó is the most reliable.