Stephen D. Durbin

Microstructures in oxide eutectic fibers grown by a modified micro-pulling-down method

The micro-pulling-down method has been adapted to grow fibers with diameters as small as 150 μm. We describe the use of this method to grow fibers of the oxide eutectic materials Al2O3/Y3Al5O12 and Al2O3/GdAlO3, which have exceptional mechanical properties at high temperature. The “Chinese script” microstructure of Al2O3/Y3Al5O12 is stable and uniform, and varies with the pulling rate in the same way as the conventional lamellar eutectics. The microstructure of Al2O3/GdAlO3 is finer, but less stable and homogeneous, particularly at high pulling rate. Fibers produced at low growth rate exhibited self-cladding by the sapphire phase.

Effects of a magnetic field on the growth rate of tetragonal lysozyme crystals

The growth process of tetragonal lysozyme crystals under static and homogeneous magnetic field of 11 T was observed in situ by using an optical microscope which was specially designed and prepared. This optical system, having a spatial resolution of 0.5 μm, was used to measure the growth rate of the lysozyme crystals under 0 and 11 T. The effect of the magnetic field of 11 T was to decrease the growth rate of the crystals. The effect of a magnetic field on the dissolution process of the crystal was also investigated.

Phase identification of Al2O3/RE3Al5O12 and Al2O3/REAlO3 (RE = Sm-Lu, Y) eutectics

Abstract Growth of various kinds of eutectic fibers based on Al 2 O 3 and oxides of Y and rare earths from Sm to Lu using micro-pulling-down (μ-PD) method was investigated. The effect of rare-earth element substitution on growth, microstructure and mechanical properties are discussed. Eutectic materials were classified into Al 2 O 3 /garnet system and Al 2 O 3 /perovskite system types at the boundary between Gd and Tb. Al 2 O 3 /garnet eutectic fibers showed superior high-temperature strength properties. This is the first systematic study of the characteristics of these eutectic materials.

Effect of a magnetic field on the orientation of hen egg-white lysozyme crystals

Recent experiments have shown that lysozyme crystallization in a magnetic field of the order of 1 T can result in a significant degree of orientation of the crystals. We present more extensive experimental results and propose a model to account for this phenomenon. Because of the small susceptibility anisotropy of most protein molecules, the orienting effect is unimportant for smaller aggregates, even those much larger than a critical nucleus. However, during sedimentation crystals grow larger and are more likely to become aligned. The degree of orientation thus depends on crystal growth rate and container geometry, in addition to magnetic field strength, as we have confirmed experimentally.

Incorporation of impurity to a tetragonal lysozyme crystal

Abstract Concentration of a phosphor-labeled impurity (ovalbumin) incorporated into protein (hen egg white lysozyme) crystals during growth was measured by fluorescence.This technique enabled us to measure the local impurity concentration in a crystal quantitatively. Impurity concentration increased with growth rate, which could not be explained by two conventional models (equilibrium adsorption model and Burton–Prim–Slichter model); a modified model is proposed. Impurity concentration also increased with the pH of the solution. This result is discussed considering the electrostatic interaction between the impurity and the crystallizing species.

Magnetic Damping of the Temperature-Driven Convection in NaCl Aqueous Solution Using a Static and Homogeneous Field of 10 T

Temperature-driven convection in 25 wt% NaCl aqueous solution was observed in situ under a static and homogeneous magnetic field of 10 T. The convection in the solution was visualized using polystyrene latex particles of 5 µm diameter. A magnetic field of 10 T reduced the velocity of convection by a factor of two. Magnetic damping of convection in an electrolyte solution could be a useful technique to control the growth of crystals such as proteins.

Model for the microstructure of oxide eutectics and comparison with experimental observations

Abstract The properties of eutectic materials depend strongly on their microstructure. In the case of oxide systems, which exhibit complex microstructures due to the tendencies of the two phases to grow in a faceted manner, conventional eutectic growth theory has been unable to give a detailed account of the process of microstructure formation. We describe here a cellular automata-based model that is able to reproduce key features and general trends observed experimentally in our investigations of oxide eutectic fibers of Al2O3/R3Al5O12, Al2O3/RAlO3, and related systems, where R is one of a series of rare earth elements. The most important parameters controlling the type of microstructure that develops are the volume fractions and faceting tendencies of the two components. The model provides guidelines for the design of materials with optimized microstructures for particular applications.

New growth method of oxide crystals by PO2 change applied to SmBa2Cu3Ox single crystals

Abstract Reliable liquidus lines of SmBa 2 Cu 3 O x in the SmBa 2 Cu 3 O x –Ba 7 Cu 18 O 25 system under various oxygen partial pressures were determined precisely by in situ observation. The dependence of the liquidus line on oxygen partial pressure was revealed: as the oxygen partial pressure increased, the liquidus shifted to higher temperature. Using this data, SmBa 2 Cu 3 O x crystals were grown. This process was successfully observed in situ by high-temperature optical microscopy.

Effects of a Magnetic Field on the Crystallization of Protein

Many studies in applying a magnetic field to control crystal growth processes have been carried out since the 1960s; in particular, magnetic fields have been widely applied for damping convection in semiconductor melts [1, 2, 3]. However, except for this magnetic damping effect on conducting liquids, no significant phenomenon that could be attributed to a magnetic field effect was found in the field of crystal growth until the late 1990s. In recent years, rapid developments in superconducting magnets of liquid helium-free type [4] have facilitated studies of the influence of a magnetic field on crystallization. In particular, considerable attention has been paid to the application of a magnetic field to the crystallization of proteins, complex biological macromolecules for which a general method of preparing large, high quality single crystals is strongly desired. In the crystallization of protein, magnetic field effects on the orientation [5, 6, 7,9, 10, 11, 12], crystal habit [6], number [6,8] and growth rate [13] of crystals, convection in aqueous solution [14,15], and crystal perfection [16, 17, 18] have been reported previously. In the case of organic compounds with low molecular weight, similar studies on the magnetic orientation of crystals were reported [19, 20, 21].