Pál Bárczy

Melt motions during unidirectional solidification of AlAl3Ni eutectics

Abstract AlNi eutectics and near-eutectics were unidirectionally solidified under normal and microgravity conditions. The effects of gravity-driven melt convection on growth rate, eutectic cell morphology and eutectic spacing were investigated experimentally. In an experiment performed under microgravity a decrease in growth rate and a decrease of the eutectic spacing was found. In interpreting the results an interaction is assumed between solidification rate and melt flow in order to minimize the energy consumption.

Foam Evolution and Stability at Elevated Gravity Levels

Foaming experiments in order to understand the evolution of the foam structure blown in different directions and levels of gravity have been carried out. The key elements of the experiment are the foam generator body (henceforth FG) and the controlled blowing apparatus. The FG was a polymer foam infiltrated with a suspension (distilled water, pure tenside (SDS, 0.05m%) and SiO2 nanoparticles (2m%)) Foams were blown out at 1.5, 2, 4, 6, 10 and at 15g levels in three different directions (0, 90 and 180o, measured to the direction of the gravity vector). The elevated gravity condition was implemented in a hyper-g centrifuge (ZARM Bremen). Results show that foams can be created even at high gravity levels though the foamability and foam structure alters a lot by varying gravity level and foaming direction. At higher g-levels, under fixed gas flow rate and blowing time less foam could be produced. The average cell size varied with the blowing directions but proved constant on any gravity levels. On base of the gravity direction dependent pressure curves the foaming process was interpreted in detail. It was found that the sedimentation ruled capillary clogging is the main process by causing the gravity direction dependent foaming phenomena. The unexpected observation is that the foam stability does not depend on the gravity level.

Production of Single Crystal Thermoelectric Bismuth Telluride Alloys

Thermoelectric (TE) semiconductor materials are widely used for miniaturized versatile cooling devices in a wide spectrum of equipments and energy generation in space vehicles. The bismuth telluride pseudobinary alloy family presents the best characteristics for room temperature TE cooling applications. Using appropriately oriented single crystals instead of the well known polycrystalline materials made by powder metallurgy methods, the efficiency of the TE device (Thermoelectric Cooler – TEC or Thermoelectric Generator – TEG) could be almost doubled. For having good quality TE material it is required to produce equally doped single crystals by the controlled crystallization process, namely with the Bridgman-Stockbarber method. Our experiments were made in the Universal Multizone Crystallizator Type UMC, developed by the ADMATIS Ltd., Miskolc, using a quartz tube under high vacuum conditions and automatically controlled thermal field parameters. The crystallographic analysis of the obtained samples was made by Scanning Electron Microscopy – (SEM), X Ray Diffraction – (XRD), and neutron diffraction (TOF spectrometry).

Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)

In this study, crystals of CdTe were grown from melts, which have undergone different thermal history, by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWBXT), atomic force microscopy (AFM), electrical conductivity and Hall measurements.

Universal Multi-Zone Crystallizator, the ISS Oriented Hungarian Apparatus

This is a description of a high tech space device for single crystal growth in microgravity. The particular specialty of the apparatus is a well-controlled temperature field with arbitrary gradients travelling operation mode under high stability without any mechanical motion The technical specification and references are included Bridgmann-Stockberger, travelling heater, physical vapout transport and single crystal casting experimental serials in order to grow semiconductor single crystals are demonstrated.

Investigating the Foamability Decrease of Water-SiO2 Suspension

Shelf-lives of surfactant containing water SiO2 suspensions were investigated by observing the loss of foamability with time and by making various measurements on the compounds used. Main purposes were to discover the reason of the strong foamability decrease with time and to separate the gravity driven effects. These questions arose in the frame of FOCUS - Foam Casting and Utilisation in Space microgravity experiment preparations (ID: SURE AO-019/PECS 98045, EC contract no: RITA-CT-2006-026069). Foams were prepared using special foaming cartridges, by gas introduction after loading the suspension into the porous structure of the foam generator (FG). Freshly infiltrated FG-s showed superior foamabilities, but this feature was lost after a few days of storage. Several possible chemical or physical reasons were investigated experimentally, including the direction of storage position, composition change, storage temperature, etc. Investigation of gravity-driven sedimentation and creaming tendencies were also examined using dynamic light scattering (DLS) method. These effects found to have significant impact on foamability.

In Vivo Failure Phenomena of Ultra-High Molecular Weight Polyethylene Acetabular Cups

During this study the distortion phenomenon was investigated on selected UHMWPE cups removed from patients, using 3dimensional measurement method. The cups investigated were machined by Metrimed Ltd. from ram extruded Chirulen 1020 type UHMWPE rods. The samples were measured with a 3D touch coordinate measurement device with an accuracy of 3 microns.

Single Crystal Growth – New Techniques on Old Base

The progress in advanced single crystal growth demands versatile, advanced equipment. Multizone furnaces are able to fulfill unusual technological requirements providing versatile and reliable all-in-one tools for laboratories on the ground or in space. The concept of the Universal Multizone Crystallizator (UMC), its hardware and software components along with several application examples are demonstrated.

Materials Science or Materials Design

Interactions and contradictions between academic investigations and indust rial material development are demonstrated. The structure of AlMgSi with optima l properties was understood recently after its 50 years industry scale production. The applicable SiC t ool production is underway despite of the lack of the phenomena controlling its skeleton structur e and binding mechanism. Biaxial polyethylene (PE) foils are far widely used but its difficult partly crystalline oriented lamellar structure could be just nowadays descripted. These exam ples seem to demonstrate the priority of the purpose and profit oriented material design.

The Effect of Gravitation Forced Convection on Structure of Al-Ni Eutectic

The effect of different kinds of experimental parameters such as gravitational acceleration (microgravity, highgravity), temperature gradient, solidification rate, primary phase, (aluminium dendrite, Al 3 Ni compound), mechanical instability of the liquid (micro gravity, high gravity, vertically stabilized and unstabilized, horizontal arrangement) on the melt motion and on the Al-Al 3 Ni rodlike eutectic structure was investigated.