Stabilized Barium Titanate Ceramics for Capacitor Dielectrics

The effects of additions of La₂O₃ and La₂O₃-3TiO₂ on the electronic properties of barium titanate have been investigated. It has been found that small additions of these components markedly increase the lifetime of this material subjected to dc fields of 50 v per mil at 200°C.     

Pore segmentation of cement-based materials from backscattered electron images

A technique to segment pores from a normal backscattered electron (BSE) image of cement-based materials is presented. The upper threshold grey level for porosity is determined from the inflection point of the cumulative brightness histogram of the BSE image. This represents a critical point where a small incremental grey value will cause a sudden increase in thresholded area, a condition termed as overflow. The proposed technique was found to be more consistent and reliable than existing methods. Significantly fewer images are required to achieve a satisfactory level of statistical confidence for quantifying porosity.     

Der Einfluß von Düsenaustrittswinkeln und Druckkräften auf die Kontur drallbehafteter Gashohlstrahlen

Zusammenfassung Untersucht wird die Strahlform von rotationssymmetrischen, drallbehafteten Gashohlstrahlen. Die Berechnungsmethode, die ohne Berücksichtigung von Reibungskräften durchgeführt wurde, ermöglicht die Angabe von geschlossenen Lösungen für die Darstellung des Verlaufs der Strahlkontur in Abhängigkeit der Umgebungsdruck-und der Zentrifugalkräfte sowie eines durch die Düsenkonstruktion vorgegebenen Austrittswinkels. Die vergleichenden Experimente zeigen eine befriedigende Übereinstimmung mit der analytischen Behandlung und lassen den Gültigkeitsbereich und die Brauchbarkeit des Rechenmodells erkennen.

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The influence of the flow angle at the nozzle exit and of the pressure forces on the contour of rotating hallow gas-jets

Summary The form of rotating hollow gas-jets was the object of this investigation. The calculation method based on a model not considering friction forces, enables to give a complete analytical solution which allows to determine the jet contour as function of the external pressure- and centrifugal forces as well as of the flow angle fixed by the nozzle design. The comparing experiments show satisfying agreement with the analytical treatment and give a general view of the usefullness and correctness of the calculation method.

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Bezeichnungen und Indizes b Breite des Hohlstrahls - c Geschwindigkeit - p Druck - r mittlerer Radius des Hohlstrahls - t Zeit - Eu Eulerzahl - Winkel - Dichte - a außen - i innen - r radial - x axial - u azimutal - 0 kennzeichnet die Verhältnisse an der Düsenmündung - Differenz Mit 9 Abbildungen     

Void formation in an Al-Mg-Si alloy under different precipitation conditions after irradiation with 100 keV Al ions

The influence of different precipitation treatments upon the radiation-induced void formation was studied on an Al-Mg-Si alloy and the results were compared with those obtained on high-purity Al. The changes in the microstructure and the void formation were investigated by TEM methods for the dose range 0.8 to 80 dpa and the temperature range 55 to 250° C. The irradiations were carried out using 100 keV Al ions. Highpurity Al showed void formation over the whole temperature range investigated with a maximum volume increase V/V of 3.4% at 150° C. The behaviour of the Al-Mg-Si alloys depends strongly upon the thermal pretreatments. The alloy in its homogenized state shows no voids between 55 and 140° C. Trapping of vacancies on solute Si atoms could be the explanation. An ageing treatment leading to coherent precipitates results in the complete suppression of void formation for the temperature region of highest swelling (0.35 T _sT0.44 T _s). On the other hand, treatments which cause incoherent or partially coherent precipitates result in swelling. The amount of swelling, however, is lower compared to pure Al and the temperature of the swell maximum is shifted to lower temperatures. These results could be explained by the mechanism of trapping vacancies by solute atoms, on the one hand, and the coherent precipitates acting as recombination centres, on the other.