Papers by Author: János Szőke

Abstract: 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.

Abstract: 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.

Abstract: The aim of our research work is to study the microstructure formation during casting of technical alloys under diffusive and magnetically controlled convective conditions on earth and in space. Unidirectional solidification experiments under steady-state conditions were performed with Al-Si binary alloys containing three different amounts of Si, using electromagnetic stirring of the melt. The influence of the rotating magnetic field on the microstructure evolution (particularly on the secondary dendrite arm spacing) as compared to experiments without stirring was studied.

Abstract: 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.

Abstract: The paper focuses on the microstructural investigation of Al-Si binary alloys solidified under steady- and non-steady state conditions using a unidirectional heat removal. A brief description of the developed solidification simulation software and its validation by computer aided image analysis are also given.