Surface tension induced convection in encapsulated liquid metals in microgravity: Apollo-Soyuz test project experiment no. MA-041

This experiment was designed to determine the extent of surface tension induced convection caused by a steplike compositional variation in a liquid metal. Preliminary results are presented

Calculations of shape and stability of menisci in Czochralski growth with tables to determine meniscus heights, maximum heights and capillary constants

The shape and stability of menisci occurring during Czochralski growth have been studied by means of numerical methods for the case of the free surface. The existence of minimal joining angles is shown, beyond which the growing crystal will separate from the melt. The dependence of the interface height on the joiningangle for different crystal diameters was calculated. The maximum stable heights and the corresponding joining angles were determined as a function of crystal diameter. A method for measuring the capillary constant of the melt during Czochralski growth is proposed. Our results are compared with known analyticalapproximations. Limitations of the applications caused by a finite crucible radius or low g values are pointed out. For practical use the following functions have been tabulated: a) meniscus height in dependence on joining angle and crystal radius, b) the radius-height-ratio in dependence on radius and angle for the calculation of the capillary constant, c) the maximum stable height and the corresponding growth angle as a function of crystal radius

Herstellung und Charakterisierung von Einkristallen der kubischen Laves-Phasen Se-Al2_{2}

Im Kristall-Labor des Instituts für Festkörperforschung wurden folgende Legierungseinkristalle für die verschiedensten Experimente gewünscht.La Al$_{2}$ (La Ce) Al$_{2}$ (La Er) Al$_{2}$ Y Al$_{2}$ (Y Ce) Al$_{2}$ Ce Al$_{2}$ Auftraggeber waren: 1. Das Institut für Festkörperforschung Jülich 2. Der Sonderforschungsbereich Köln - Aachen - Jülich / Im folgenden Bericht sollen die Herstellungs- und Charakterisierungsverfahren erläutert werden. 1. Probenpräparation 2. Art und Wahl der Kristallzüchtung 3. Probencharakterisierung 4. Messungen und Ergebnisse der Experimente Aus der Literatur war bis dahin nur ein Hersteller solcher Einkristalle bekannt. Aus den Veröffentlichungen konnten nur wenige Daten und Einzelheiten entnommen werden /1/2/3/4. Es war deshalb notwendig, vorher einige grundlegende Dinge zu erlernen, z. B. Probenpräparation, Wahl des Tiegelmaterials, Impflingherstellung. Die Problemstellung war, Einkristalle in verschiedenen Größen und Orientierungen herzustellen, von 2 $\varnothing$ mm 50 mm lang, bis 10 $\varnothing$ mm 80 mm lang, deren Stabachsen oder sein sollten

EVALUATION OF MICROPOROSITY BY MHz-ATTENUATION MEASUREMENTS

Attenuation due to the scattering of ultrasound by micropores has been measured in Mn, S and Be doped copper single crystals grown by the Czochralski- and Bridgeman-techniques. After suppression of dislocation damping by γ-irradiation the attenuation αp due to pore scattering has been determined quantitatively in the frequency range 10 to 300 MHz. By fitting the theoretical αp(f)-dependence for spherical holes to the measured αp(f)-data we obtain the porosity P and the mean pore-diameter dp

X-ray standing wave analysis of highly perfect Cu crystals and electrodeposited submonolayers of Cd and Tl on Cu surfaces

Experimental requirements for measuring the structure and coverage of adsorbates in the monolayer regime on single crystals with x-ray standing wavefields are discussed in detail along with a thorough description of the theory. The near-surface region of Cu crystals was probed depth selectively by detecting K as well as L fluorescence as a function of fluorescence escape angle. The effects of crystalline imperfections and of dispersive crystal arrangements on the spatial resolution of standing wave measurements are described. Copper crystals with (111) and (100) surface orientation were used as substrates for electrodeposition of Cd and Tl from an aqueous electrolyte using cyclic voltammetry. Submonolayer amounts of Cd and Tl deposited in the underpotential range were investigated on the emerged electrodes with x-ray standing waves keeping the samples under atmospheric pressure, in air, or in inert atmosphere

Kristallzucht im Weltraum

Anlaß zu dieser Studie war die Frage, ob unter Schwerelosigkeit /63/ Kristalle größerer Perfektion als unter Erdschwere gezüchtet werden können. Dieses Problem wurde im ad-hoc Ausschuß des Bundesministeriums für Forschung und Technologie "Möglichkeiten der industriellen Forschung, Entwicklung und Produktion im Weltraum" und von der Gesellschaft für Weltraumforschung aufgeworfen im Hinblick auf eine sinnvolle Nutzung des zukünftigen Weltraumlabors "Space Lab" /64/ auf dem Gebiet der Materialwissenschaften. Im Institut für Festkörperforschung der Kernforschungsanlage Jülich wird experimentell und theoretisch auf dem Gebiet desKristallwachstums und der Kristallzucht gearbeitet /65, 66/. Aufgrund dieser Erfahrungen wurde versucht, in der relativ kurzen Zeit von November 1974 bis Januar 1975 möglichst originelle und kritische Meinungen zu einigen Aspekten der Kristallzucht unter Schwerelosigkeit zu entwickeln. Dabei galt es, zahlreiche theoretische und experimentelle Arbeiten auf diesem Gebiet, die vor allem in den USA publiziert wurden /67, 68, 69, 70, 71, 72,149, 73/, zu analysieren und zu berücksichtigen

Numerical simulation of convective flow of the melt in the classical Czochralski method and in CACRT. 2 : simulation of combined free and forced convection

In part 2 of this report, we describe the extension of our procedure presented in part 1 for the numerical solution of the time-dependent Navier-Stokes equations with Boussinesq approximation and the convective he at conduction equation in the Czochralski crystal-growth arrangement. By means of several digital simulations with a low kinematic viscosity, typical for liquid metals, and characteristic rotational angular velocities of crystal and crucible, the influence of free buoyancy driven convection on the familiar forced convective flow patterns of part 1 is studied with special emphasis on the occurrence of flow and temperature oscillations. Additionally, we show the combined free and forced convective flow patterns in the isorotational and the counterrotational Czochralski Accelerated Crucible (and Crystal) Rotation Technique arrangement (CACRT) for a fluid of the viscosity of liquid silicon

A model for macroscopic Czochralski growth : |btheoretical and experimental investigations

A very important process to grow single crystals is the method developed by Czochralski /1/. It is used in industry to grow single crystals of silicon, germanium, gallium phosphide, and arsenide and several other substances. It is also used in research to produce more or less perfect metal single crystals for neutron and electron scattering, superconductivity, NMR, residual resistance, optical, and Fermi surface experiments. In some cases, e.g. if the crucible attacts the melt or if the melting temperature is so high that there exists no suitable crucible material, the floating zone method is used (e.g. for growth of tungsten, niobium, and oxygen free silicon single crystals) /2/. To get an impression of the importance of crystal growth, the industrial production of single crystals in 1977 is given in table 1 /3/. However, the Czochralski and the floating zone process are very complicated, because the shape of the crystal and also, but in an even more complicated way, the perfection, are determined by the g r o w t h p a r a m e t e r s. For example a sudden change in the melt temperature of 1 °C means for a copper crystal with a diameter of 1 cm a decrease or an increase of the crystal diameter of about 5 % /4/. It is therefore necessary to control the temperature very weIl, but in order to grow a crystal with a constant diameter, the melt temperature additionally [Tabelle 1 ...] has to be increased or decreased continuously during the growth process in dependence on the crystal diameter (see paragraph 4.1). So for a particular crystal shape, a certain melt temperature program is necessary. To reproduce this shape this m e l t t e m p e r a t u r e p r o g r a m has to be controlled automatically. For that reason, and additionally for direct control of the crystal diameter (in order to apply the optimizing theory), the knowledge of the influence of the different growth parameters on the macroscopic shape is very important. The purpose of this investigation has been the study of this influence on the macroscopic shape for the Czochralski method applied on non-faceting metals. In consequence of these considerations, a growth model was developed to calculate the temperature distribution in the solid and the melt temperature program. This model is described in the second chapter. In thethird chapter the different methods for c o n t a c t l e s s t e m p e r a t u r e a n d g r o w t h p a r a m e t e r m e a s u r e m e n t s are described. In the fourth chapter the experimental da ta are compared with the theoretical results