Single crystals of congruently and incongruently melting oxides have been grown by the optical floating zone (OFZ) and traveling solvent floating zone techniques. Both relatively low-cost methods work especially well for oxides melting above the maximum operating temperature of conventional crucibles or that were previously impossible to grow due to crucible oxidation or reaction of the melt with the crucible material. For incongruently melting oxides, solvents with experimentally determined composition allow for creation of practical steady state conditions. This extends the range of materials that now can be crystallized in oxidizing, reducing, and neutral atmospheres and elevated pressure. Distribution of dopants is relatively uniform. The important problems of zone stabilization and its dependence on the conditions applied are discussed from the experimental point of view. Basic characterization of the grown crystals and most characteristic defects is presented. An extensive list of oxide crystals grown by the OFZ method is included. Floating zone crystal growth with radio frequency (RF) heating is an important technique for the preparation of single bulk crystals. The absence of any crucible is advantageous for the growth of single crystals of reactive materials with high melting points. The melt convection driven by the induction heating and the heat radiation from the surface leads usually to a solid–liquid interface being concave toward the solid phase outer rim. These concave parts inhibit the growth of single crystals over the whole cross-section. The concave solid–liquid interface can be prevented by a two-phase inductor that melts the material but also stirs it in a certain way. The basic design of this two-phase inductor is given, and its application for the growth of industrially relevant single crystals of RuAl and TiAl intermetallic compounds as well as interesting compounds for research such as antiferromagnetic Heusler MnSi compounds or biocompatible TiNb alloys is described.

We present a comprehensive transport investigation of the itinerant antiferromagnet Mn3Si which undergoes a spin density wave (SDW) order below T_N~21.3K. The electrical resistivity, the Hall-, Seebeck and Nernst effects exhibit pronounced anomalies at the SDW transition, while the heat conductivity is phonon dominated and therefore is insensitive to the intrinsic electronic ordering in this compound. At temperatures higher than T_N our data provide strong evidence for a large fluctuation regime which extends up to ~200K in the resistivity, the Seebeck effect and the Nernst effect. From the comparison of our results with other prototype SDW materials, viz. LaFeAsO and Chromium, we conclude that many of the observed features are of generic character.

Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.

The floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to unfavorable solid–liquid interface geometry and insufficient mixing of the melt which depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system with radio frequency (RF) heating has been developed which enables the control of the melt flow by a significant change of the flow field. The magnetic system was used for the crystal growth of the Heusler compound Mn3Si due to their interesting properties such an itinerant antiferromagnetic and incommensurate spin-density wave state. The grown crystals were oriented and cut to samples with the crystallographic orientations (100) and (110) normal to a plane. Measurements of the temperature dependence of magnetization and specific heat are discussed in terms of contributions of other thermodynamic phases and phase transitions.

We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two-phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0° to 90°. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically, and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.

beta-Ti70Nb30 (at.%) singles crystals were grown by a magnetic field controlled floating-zone technique with two-phase radiofrequency electromagnetic heating. The Young's moduli of the crystals show pronounced anisotropy. The lowest value is E-100 = 39.5 GPa. Comparison of the present results with recently published data and extrapolation to low Nb content of about 20 at.% shows that the preparation of beta-Ti1-xNbx-based alloys with E-100 approximate to 20-30 GPa should be possible, which would match the modulus of bone. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

TiAl intermetallic alloys are being developed as potential materials for applications in aerospace and automotive industries, and also for chemical and biomedical applications, because of their excellent chemical and physical properties such as low density, high modulus and corrosion resistance at high temperatures. The thermophysical properties (electrical conductivity, thermoelectric power and thermal conductivity) of the solid and liquid intermetallic alloy Ti40Al60 have been measured during melting and solidification processes in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

The aim of this work is growth and characterisation of Ti55Nb45 (wt%) single crystals by floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced by additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid–liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. For this, a tailored magnetic two-phase stirrer system has been developed, which enables a controlled influence on the melt ranging from intensive inwards to outwards flows. Since Ti is favourably light, strong and biocompatible, it is one of the few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations [100] and [101] normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly determine crystal orientation and to localize grain boundaries. The formation of oxidic nanotubes on Ti surfaces in dependence of the grain orientation was investigated, performed electrochemically by anodic oxidation from fluoride containing electrolyte.

Microstructure evolution and metastable phase formation in undercooled melts of Fe-Ni based soft magnetic alloys were studied by the electromagnetic levitation technique in ground-based experiments and under microgravity during parabolic flight campaigns. Discontinuous changes in the microstructure were observed in samples of a commercial soft magnetic alloy quenched at distinct melt undercooling Delta T. The results were successfully interpreted within the framework of the dendrite breakup model. No metastable phase formation was detected in commercial soft magnetic alloys which possess higher Ni contents. Under microgravity conditions the lifetime of the metastable bcc phase formed for Fe90Ni10 beyond a critical melt undercooling increases. The surface tension of the levitating droplets under microgravity was determined from high speed video recordings of the oscillations of the droplets. The value obtained, sigma = 1.90 +/- 0.01 Nm(-1), agrees well with values from the literature.

Die thrombotisch-thrombozytopenische Purpura (TTP) ist ein schweres Krankheitsbild mit Mikrothromben in verschiedenen Organen. Die idiopathische Form der TTP ist durch eine verminderte Aktivität der Proteinase ADAMTS13 und durch das Vorhandensein von Autoantikörpern gegen ADAMTS13 gekennzeichnet. Über die Induktion dieser Autoantikörper ist bisher wenig bekannt. Bestimmte Medikamente können über einen Haptenmechanismus die Bildung von Anti-ADAMTS13-Antikörpern initiieren.

BACKGROUND:A normal computed tomography (CT) scan of the pulmonary arteries in the presence of parenchymal and pleural abnormalities may indicate a false-negative diagnosis of pulmonary embolism (PE). Multi-channel detector CT (MDCT) with thinner collimation may improve the detection of small peripheral PEs causing such abnormalities.PURPOSE:To investigate parenchymal and pleural findings visualized by contrast-enhanced MDCT in patients with and without PE, and to identify possible predictors of PE.MATERIAL AND METHODS:129 patients with clinical signs of PE were included. In all patients an iopromide-enhanced 64-MDCT (64x0.625 mm collimation, pitch 1.375, overlapping reconstruction with a slice thickness of 0.625 mm, increment of overlapping slice reconstruction 0.43) was performed within 24 h after the onset of the symptoms.RESULTS:MDCT detected PE in 45 of the 129 patients (35%). PE and parenchymal/pleural findings were localized predominantly within the lower lobes. Wedge-shaped opacities were significantly associated with PE (OR =3.00; 95% confidence interval 1.13-7.91). Vascular signs were only visualized in patients with PE. Nodules, consolidations, atelectasis, or effusions were not predictive of PE.CONCLUSION:The present MDCT study verified that parenchymal and pleural findings can be found in patients with or without PE. Wedge-shaped opacities and vascular signs were significantly associated with PE and therefore can be potential predictors of PE.

The radio frequency floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid–liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure is created at a preferable phase shift of 90°. This change in the flow field has a significant influence on the shape of the solid–liquid interface. Due to their attractive properties for high temperature applications such as high melting temperature, low density, high modulus and good oxidation resistance, the magnetic system was applied to the crystal growth of TiAl alloys.

The oxygen content of binary Ti45Al55 and ternary Ti44Al52Nb4 single crystals and polycrystalline alloys was quantified with secondary ion mass spectrometry (SIMS) using Cs+ primary ions. The SIMS measurements were calibrated with respect to concentration and depth scale using oxygen implanted samples. The measurements revealed considerably lower oxygen content in the ternary alloy indicating a protecting impact of the Nb addition in grain boundaries against oxygen contamination. The relative strong surface oxide layer thickness of the investigated samples was determined to about 1μm.

Dendrites are one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and volume fraction of properitectic α-Fe was investigated during solidification of stoichiometric Nd–Fe–B alloys using the forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analyzing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values, averaged from about 80 to 120 dendrites in different zones. The α-Fe volume fraction, measured by vibrating sample magnetometer (VSM), reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient.

Nd-Fe-B alloys are widely used in many technical applications due to their excellent permanent magnetic properties. YNi2B2C intermetallic compounds receive much attention because of the coexistence of superconductivity and magnetic ordering phenomena. Er2PdSi3 alloys with hexagonal A1B2-type crystallographic structure are of special interest because of their complex magnetic ordering, Kondo and heavy fermion behavior. The thermophysical properties (electrical conductivity, thermoelectric power, thermal conductivity and viscosity) of these liquid multicomponent intermetallic alloys have been measured in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

Single crystal and polycrystalline near-stoichiometric RuAl alloys were grown with the magnetic field controlled RF-floating zone technique. The resistivity measured from the room temperature to 4.2K decreases linearly up to 70K. The reciprocal residual resistance ratio is very sensitive to changes in composition and shows a maximum value of 6.7 close to the stoichiometric composition. However, the Vickers hardness decreases to a minimum where the reciprocal residual resistance ratio is maximum.

The influence of melt convection on the microstructure during solidification of peritectic Nd-Fe-B and Ti-Al alloys was investigated. Since the magnetic and mechanical properties of these technologically relevant materials depend strongly on the microstructure and especially on the volume fraction of the properitectic phase, there is a growing scientific interest for such an investigation. On the basis of numerical simulation of melt convection modes in an inductively heated metallic melt, novel techniques for the modification of the melt convection were developed. This is the forced rotation technique and a modified floating zone facility equipped with a specially designed double coil system, which enabled the application of additional magnetic fields. The forced rotation technique, in which the crucible rotates with well-defined frequencies, leads in accordance with numerical simulation to a strong reduction of the melt convection depending on the frequency. The volume fraction of the soft magnetic α-Fe phase could be drastically reduced in comparison with the common induction melting accompanied by a simultaneous reduction of the secondary dendritic arm spacing. The floating zone facility with the patented double coil system allows the tailoring of the melt convection over a wide range from nil motion to strong stirring. The microstructure of the investigated Ti-Al alloy changed from dendritic to globulitic morphology under strong stirring, whereas the volume fraction of the properitectic phase increased with increasing stirring. The mechanical properties show a significant increased plastic deformation of the samples solidified under strong stirring. The possible reason for the change in morphology is explained as a result of spherical growth under forced convection. The study of the influence of melt convection on the microstructure formation of peritectic alloys showed the feasibility of tailoring the microstructure and the properties of the resulting alloy by customized melt convection using magnetic fields.

Studies of phase selection and microstructure evolution in high-performance magnetic materials are an urgent need for optimization of production routes. Containerless solidification experiments by electromagnetic levitation and drop tube solidification were conducted in undercooled melts of Fe-Co, Fe-Ni soft magnetic, and Nd-Fe-B hard magnetic alloys. Melt undercooling under microgravity was achieved in the TEMPUS facility during parabolic flight campaigns. For Fe-Co and Fe-Ni alloys significant effects of microgravity on metastable phase formation were discovered. Microstructure modifications as well as metastable phase formation as function of undercooling and melt flow were elucidated in Nd-Fe-B. Modeling of solidification processes, fluid flow and heat transfer provide predictive tools for microstructure engineering from the melt. They were developed as a link between undercooling experiments under terrestrial and microgravity conditions and the production routes of magnetic materials.