Electronic structure of REREAuMg and REREAgMg (RERE = Eu, Gd, Yb)

We have investigated the electronic structure of the equiatomic EuAuMg, GdAuMg, YbAuMg and GdAgMg intermetallics using x-ray photoelectron spectroscopy. The spectra revealed that the Yb and Eu are divalent while the Gd is trivalent. The spectral weight in the vicinity of the Fermi level is dominated by the mix of Mg $s$, Au/Ag $sp$ and $RE$ $spd$ bands, and not by the $RE$ $4f$. We also found that the Au and Ag $d$ bands are extraordinarily narrow, as if the noble metal atoms were impurities submerged in a low density $sp$ metal host. The experimental results were compared with band structure calculations, and we found good agreement provided that the spin-orbit interaction in the Au an Ag $d$ bands is included and correlation effects in an open $4f$ shell are accounted for using the local density approximation + Hubbard $U$ scheme. Nevertheless, limitations of such a mean-field scheme to explain excitation spectra are also evident.Comment: 4 pages, 3 figures, Brief Repor

Dendritic growth kinetic of Al68.5Ni31.5 under reduced gravity conditions

Containerless processing of a metallic specimen offers the potential to directly observe solidification undisturbed by any interaction of the liquid melt with container walls. Since heterogeneous nucleation from containerwalls is completely circumvented it is furthermore realizable to undercool the liquid below its equilibrium melting temperature. On Earth, levitation requires strong electromagnetically fields which however induce strong fluid flow effects (forced convection). This fluid flow affects heat and mass transport and consequently governs the solidification dynamics. Weightlessness on the other hand essentially reduces fluid flow effects so that crystal growth is controlled by intrinsic material-specific transport. In the present experiment Electro-Magnetic Levitation aboard the TEXUS 49 sounding rocket is utilized to measure the dendrite growth velocity of Al68.5Ni31.5

Electromagnetic Levitation onboard the International Space Station

The Electromagnetic Levitator onboard the International Space Station (ISS) in the Columbus module is an ESA facility for material research under microgravity. It allows to position and inductively heat metallic or semiconducting samples without contact to container walls under vacuum or noble gas atmosphere for the measurement of thermophysical properties in a wide temperature range and observation of non-equilibrium solidification from the undercooled melt. EML is operated by the Microgravity User Support Center (MUSC) at DLR cologne and serves as a research facility for an international science community. Since its installation in the Columbus Lab in 2014, EML has been in continuous use in orbit. Currently, the third batch of 18 samples is under investigation, whereby each sample is processed multiple times with different scientific objectives. The preparation of the experiment program in EML is performed at the Institute of Material Physics & MUSC in close coordination with the individual scientific teams. The scientific support at DLR starts with the so called ground support program, which comprises the definition of experiment procedures and parameters and validation runs on the EML ground model. Followed then by the on-orbit performance of the experiment in the MUSC control room in cologne and finally data archiving and distribution by a dedicated archiving system accessible via internet after the experiments. The present paper shall give an overview on the research facility and also on the science and maintenance operations on EML. A focus will be laid on the replacement of the Gas Circulation Pump of EML performed by Matthias Maurer during his Cosmic Kiss Mission in 2022. Moreover, an outlook to the planned operations for the upcoming years will be provided

Material Science Lab operations onboard the International Space Station

The Materials Science Laboratory (MSL) onboard the International Space Station is designed for the research on solidification processes under microgravity conditions. It is equipped with two exchangeable furnace inserts of Bridgman-type allowing temperatures of up to 1400 ◦C. MSL is operated under ESA contract by the Microgravity User Support Center (MUSC) at DLR in Cologne in collaboration with Marshal Space Flight Center at Huntsville which is responsible for the Materials Science Research Rack (MSRR) which hosts MSL and provides services. MSL was launched in 2009 and installed in the US Destiny laboratory module. Since then a number of experiments by different project teams have been performed and research is still ongoing. Since 2018, a new type of cartridges developed by NASA allows investigation of sintering processes within MSL. The paper will give a survey on MSL operations over the last decade and provide an outlook for future MSL planning

Material Science Lab Operations onboard the International Space Station

The Materials Science Laboratory (MSL) onboard the International Space Station (ISS) is designed for the research of various solidification processes under microgravity conditions – ranging from directional solidification over sintering processes to growth of semiconductor crystals from vapor deposition. It is equipped with two exchangeable furnace inserts of Bridgman-type allowing processing temperatures of up to 1400 °C with various temperature gradients. MSL is operated under ESA contract by the Microgravity User Support Center (MUSC) at DLR in Cologne in collaboration with Marshall Space Flight Center (MSFC) at Huntsville, Alabama USA, which is responsible for the Materials Science Research Rack (MSRR-1) that hosts MSL. MSL, launched in 2009 and installed in the US Destiny laboratory module, performed in the course of 13 years in operation more than 48 experiments by different international project teams, with research still ongoing. With the deployment of NASA’s unique multi-purpose cartridge - first utilized for investigations of sintering processes within MSL between 2019/2020, ESA and NASA, will utilize MSL for future investigations. This paper will give an overview on the new challenges MSL science operations will face in these future activities, ranging from directional solidification to semiconductor growth from vapor deposition, with different requirements

Structural aspects of glass-formation in Nb-Ni melts

We report on investigations of the static structure factors of glass-forming Ni59.5Nb40.5 alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni59.5Nb40.5 is characterized by a large nearest neighbor coordination number of Z(NN) = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation. (C) 2014 AIP Publishing LLC.Postprint (published version

Structural aspects of glass-formation in Ni-Nb melts

We report on investigations of the static structure factors of glass-forming Ni59.5Nb40.5 alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni59.5Nb40.5 is characterized by a large nearest neighbor coordination number of Z(NN) = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation. (C) 2014 AIP Publishing LLC