Simultaneous TG-DTA mass-spectrometry to 1550‡

Newly developed coupling systems are introduced and discussed for the combination of a simultaneous TG-DTA apparatus with a quadrupole mass-spectrometer. In the study of decomposition processes under atmospheric pressure, two-stage pressure reduction systems allow an exact gas analysis by the simultaneous operation of a mass-spectrometer up to 1550. For measurements under high vacuum, the pressure reduction systems are removed, and by direct viewing between test body and ion source a high sensitivity is achieved. The function of these combined units is demonstrated by means of applications in inorganic and organic chemistry.

---

Zusammenfassung Für die Kombination einer simultanen TG-DTA-Anlage mit einem Quadrupol-Massenspektrometer werden neuentwickelte Kopplungssysteme vorgestellt. Beim Studium von ZersetzungsvorgÄngen unter AtmosphÄren druck erlauben die zweistufigen Druckreduziersysteme eine exakte Gasanalyse durch die gleichzeitige Betriebsmöglichkeit eines Massenspektrometers bis 1550. Für Messungen im Hochvakuum werden die Druckreduziersysteme entfernt und durch die direkte Sichtverbindung zwischen Probe und Ionenquelle wird eine hohe Nachweisempfindlichkeit erzielt. Die Funktion der GerÄtekombination wird mit Anwendungsbeispielen aus der anorganischen und organischen Chemie demonstriert.

---

Résumé On présente des systèmes de couplage récemment développés pour relier un appareil simultané de TG -ATD à un spectromètre de masse quadrupole. En étudiant la décomposition sous pression atmosphérique, les systèmes réducteurs de pression à deux étages permettent une analyse des gaz exacte, en opérant simultanément avec un spectromètre de masse jusqu'à 1550. Afin d'effectuer des mesures sous haut vide, on met hors circuit les systèmes réducteurs de pression et parvient à une haute sensibilité par examen direct entre le corps à examiner et la source d'ions. On montre le fonctionnement de ces unités combinées par des examples d'application en chimie inorganique et organique.

---

, — - . , - 1550. , . .

     

Small-angle neutron scattering study of poly(methyl methacrylate-block-sodium acrylate-block-methyl methacrylate) and poly(sodium acrylate-block-methyl methacrylate-block-sodium acrylate) triblock copolymers in aqueous solutions

 Small-angle neutron scattering experiments were made on poly(methyl methacrylate-block-sodium acrylate-block-methyl methacrylate) [p(MMA-b-NaA-b-MMA)] and p(NaA-b-MMA-b-NaA) solutions by varying the composition and the concentration of the polymer with and without 1 M NaCl added. Scattering curves could be evaluated by assuming that the polymers aggregate into polydisperse micelles. The experiments support the expectation that in the case of the p(MMA-b-NaA-b-MMA) block sequence the hydrophilic blocks form closed loops connected by both ends to the micellar cores; in the case of the p(NaA-b-MMA-b-NaA) block sequence they float freely in the solvent. The micellar cores exert considerable stability against dilution and added electrolyte. The interaction of charged micelles could be formally described in terms of volume exclusion and the Derjaguin–Landau–Verwey–Overbeek potential. Received: 20 December 2000 Accepted: 18 August 2001     

A method for the temperature calibration of pushrod dilatometers

A method for the temperature calibration of pushrod dilatometers and thermomechanical analysis systems using the melting points of metal standards has been established. With this technique, the measured melting temperatures of high-purity metal standards are determined from the sharp change in the length curve which accompanies melting. This procedure was used for the absolute temperature calibration of a pushrod dilatometer capable of operation up to 2000 °C. The results of this calibration show that the technique can be used with a high degree of accuracy and confidence.

---

Zusammenfassung Mit Hilfe von Schmelzpunkten metallischer Standards wurde eine Methode zur Temperatureichung von Schubstangendilatometern und TMA-Systemen entwickelt. Die verwendete Technik basiert darauf, daß beim Erreichen der Schmelztemperatur des hochreinen, scheibenförmigen Metallstandards, der zusammen mit einem neutralen Probekörper verwendet wird, eine deutliche, spontan einsetzende Längenänderung in der Dilatometerkurve erkennbar wird. Dieses Verfahren wurde zur absoluten Temperatureichung eines Schubstangen-Dilatometers, das bis 2000 °C arbeitet, angewandt. Die Ergebnisse dieser Kalibrierung zeigen, daß diese Technik mit einem hohen Grad an Genauigkeit und Zuverlässigkeit eingesetzt werden kann.

---

, -. - . , 2000 °. , .

---

---

On sabbatical leave from the University of Rhode Island, Kingston, RI 02881, U.S.A.

---

The authors wish to express their thanks to Mr. E. Braun, Netzsch Gerätebau, for his work with the dilatometer and the preparation of the test samples.     

Homogenization and two-scale models for liquid phase epitaxy

We consider models for liquid phase epitaxy without and with elasticity. The models are based on continuum models for fluid flow and transport of adatoms in the liquid solution and a BCF–model for the growth of the solid phase. Using homogenization by formal asymptotic expansion, we obtain two–scale models that are appropriate to describe the evolution of microstructures in the solid phase for processes of technically relevant macroscopic length scales. The two–scale models consist of macroscopic equations for fluid flow and solute transport in the liquid and microscopic cell problems for the growth and elastic deformation of the solid. For the case without elasticity and a phase field approximation of the BCF–model, an estimate of the model error is presented.     

A morphological study of vicinal surface growth based on a hybrid algorithm

A hybrid algorithm that combines a phase-field model and a lattice gas model evolving according to a kinetic Monte-Carlo (KMC) simulation scheme is used to investigate the dynamics of vicinal surface growth during vapor phase epitaxy. The algorithm is computationally far more efficient than pure KMC schemes, and this gain in efficiency does not correspond to a loss in information on the kinetics of individual atoms. We present numerical studies on the temperature dependence of macroscopic properties of the growing surface, evaluating the relevant stochastic processes (attachment, detachment, diffusion and island dynamics) as a function of their rates. We show that the temperature at which step flow is replaced by island nucleation depends on incoming flux, diffusion parameters and interstep distance. Moreover, we validate these finding by comparison to experiments and by analytical investigations.     

High-temperature XRD study of thermally induced structural and chemical changes in iron oxide nanoparticles embedded in porous carbons

Magnetic carbon-based nanomaterials have promising applications in many fields owing to their biocompatibility and thermal/mechanical stability. This study describes a high-temperature X-ray diffraction (XRD) study of the chemical and structural transformations suffered by superparamagnetic iron oxide nanoparticles embedded in porous carbons. The nanoparticles were prepared from the decomposition of iron pentacarbonyl over porous carbons, resulting in nanometer-sized iron oxides homogeneously dispersed into the carbon matrix. The thermally induced changes in these materials were followed by in situ high-temperature XRD, using synchrotron radiation. The growing of the nanoparticles and of the carbon crystallites were first observed, followed by the reduction of the iron oxides to form α-Fe (at temperatures as low as 400 °C in some cases) and γ-Fe(C). The temperatures at which these chemical reactions occurred were dependent on the total time spent on heating and on the nature of the iron oxides formed in the as prepared materials. A noticeably large thermal expansion coefficient was also observed for the iron oxide nanocrystals. The formation of austenitic iron, stabilized by the presence of carbon, was found to be only partially reversible upon cooling.     

An Epoxy Resin Tells its Life Story: Thermal analysis as a constant companion from development to disposal

With the aid of thermal analysis, epoxy (EP) resins have been characterized from the curing of the components all the way to disposal. The methods employed for the investigations were DSC, TMA, DMA, TG and TG-QMS. The experimental results obtained will be used here to demonstrate the typical possibilities offered by these methods for characterization of an epoxy resin from cradle to grave.This revised version was published online in November 2005 with corrections to the Cover Date.     

A phase-field model for incoherent martensitic transformations including plastic accommodation processes in the austenite

If alloys undergo an incoherent martensitic transformation, then plastic accommodation and relaxation accompany the transformation. To capture these mechanisms we develop an improved 3D microelastic–plastic phase-field model. It is based on the classical concepts of phase-field modeling of microelastic problems (Chen, L.Q., Wang Y., Khachaturyan, A.G., 1992. Philos. Mag. Lett. 65, 15–23). In addition to these it takes into account the incoherent formation of accommodation dislocations in the austenitic matrix, as well as their inheritance into the martensitic plates based on the crystallography of the martensitic transformation. We apply this new phase-field approach to the butterfly-type martensitic transformation in a Fe–30 wt%Ni alloy in direct comparison to recent experimental data (Sato, H., Zaefferer, S., 2009. Acta Mater. 57, 1931–1937). It is shown that the therein proposed mechanisms of plastic accommodation during the transformation can indeed explain the experimentally observed morphology of the martensitic plates as well as the orientation between martensitic plates and the austenitic matrix. The developed phase-field model constitutes a general simulations approach for different kinds of phase transformation phenomena that inherently include dislocation based accommodation processes. The approach does not only predict the final equilibrium topology, misfit, size, crystallography, and aspect ratio of martensite–austenite ensembles resulting from a transformation, but it also resolves the associated dislocation dynamics and the distribution, and the size of the crystals itself.     

Computer simulation of heterogeneous nucleation on curved surfaces using a simplified string method combined with phase-field simulations

We show how the combination of string method with the phase-field approach can be extended from simulations of homogeneous nucleation to heterogeneous nucleation. From these simulations, it is possible to directly obtain nucleation barriers for heterogeneous nucleation on arbitrary surfaces as well as information about the size and shape of the critical nucleus. We test the method by comparing the dependence of the nucleation barrier for heterogeneous nucleation on concave and convex surfaces on the surface curvature obtained from three-dimensional phase-field simulations with predictions from classical nucleation theory and find good agreement between them.