A laboratory based high resolution x-ray radiograph was developed for the investigation of solidification dynamics in alloys. It is based on a low-power microfocus x-ray tube and is potentially appropriate for x-ray diagnostics in space. The x-ray microscope offers a high spatial resolution down to approximately 5 μm. Dynamic processes can be resolved with a frequency of up to 6 Hz. In reference experiments, the setup was optimized to yield a high contrast for AlCu-alloys. With samples of about 150 μm thickness, high quality image sequences of the solidification process were obtained with high resolution in time and space.

We have designed and built a compact x-ray microtomography system to perform element mapping and absorption imaging by exploiting scanning fluorescence tomography and full-field transmission microtomography, respectively. It is based on a low power microfocus tube and is potentially appropriate for x-ray diagnostics in space. Full-field transmission tomography yields the three-dimensional inner structure of an object. Fluorescence microtomography provides the element distribution on a virtual section through the sample. Both techniques can be combined for appropriate samples. Microradiography as well as fluorescence mapping are also possible. For fluorescence microtomography a small and intensive microbeam is required. It is generated using a polycapillary optic. Operating the microfocus tube with a molybdenum target at 12 W, a microbeam with a full width at half maximum lateral extension of 16 microm and a flux of about 10(8) photonss is generated. As an example of application, this beam is used to determine the element distribution inside dried plant samples. For full-field scanning tomography, the x-ray optic is removed and the sample is imaged in magnifying projection onto a two-dimensional position sensitive detector. Depending on the sample size, a spatial resolution down to about 10 microm is possible in this mode. The method is demonstrated by three-dimensional imaging of a rat humerus.

The influence of a transverse rotating magnetic field on the fluid motion in semiconductor melts has been investigated, both experimentally and by means of numerical simulations. Hereto a magnet array based on two pairs of electromagnet s for generating a rotating magnetic field has been developed and accommodated into a spacecompatible multizone heater. A maximum induction of 11 mT could be achieved with a primary power of 100 W. The frequency for the field rotation ranges from 5 to 400 Hz. In a gallium melt as reference configuration a transition from a 3D time-dependent to a 2D axi-symmetric flow regime could be observed for an induction of less than 1 mT. Crystal growth experiments on germanium yielded a reduction of dopant striations and an indication for an enhanced mass transport. The numerical simulations showed a good agreement with the experimental results. It can be concluded that the forced convection is a powerful tool to create well-defined stationary flow fields for semiconductor crystal growth. A similar magnet system as presented is planned for the Low Gradient Furnace of the Materials Science Laboratory to be flown on the International Space Station. Furthermore, an implementatio n of such a magnet system in the Commercial Float Zone Furnace (CFZF) to be flown again on a S/H mission is envisaged.

For damping residual, unsteady flows in semiconductor melts a space-compatible multizone furnace including a magnetic damping array consisting of two radially magnetized permanent magnet rings has been developed. The performance of the whole system has been verified by measuring the temperature fluctuations caused by the time-dependent thermal convection in a Ga melt at 850 °C. By applying a static magnetic induction of 186 mT the fluctuations could be reduced from about 1.5 °C to less than 0.02 °C. For these high precision measurements optical fiber sensors have been used to measure the temperature in the Ga melt and to control the multizone furnace as well. A temperature constancy of ΔT≤0.03 °C in the melt could be established over a period of 16 h.

The development and the test results of an electron-beam furnace for the later utilization in a microgravitational environment are reported. By just varying the deflection pattern by means of the electron-optical components two reference profiles, a gradient profile with a maximum slope of 220 K/cm, and a hot zone profile with a zone temperature of 1520 K could be established and maintained. A beam power of 550 W had to be applied to a sample made of massive Ta for the gradient profile, for creating a hot zone profile an input power of only 250 W onto a sample with a ceramic core was sufficient. A continuous pyrometric measurement system with a high local and time resolution has been realized. By temperature sensing of the sample with this system an intrinsic feature of electron-beam heating could be directly observed, the sharply localized energy deposition at the sample surface.