We have investigated the technique of evaporation and condensation of material in an inert gas (ECIIG) for the purpose of preparing ultrafine particles (of order 10 nm in diameter) with a narrow distribution of sizes. Gravity driven convection increases the rate of coalescence of the particles leading to larger sizes and a broader distribution. Here we report on analysis and experiments to investigate coalescence of particles. The possibility of reducing coalescence in micro-gravity is discussed. An experimental test in reduced gravity to be performed in a KC135 aircraft is described briefly.

Gravity induced stresses in terrestrial laboratory specimens comprising of relatively weak and soft granular materials, are often of the same magnitude as the external tractions that are applied during investigations of constitutive behavior especially at low intergranular stress levels. The presence of heterogeneous strain and stress fields within such a specimen makes it difficult if not impossible to obtain objective and unambiguous constitutive properties and to devise relevant constitutive equations. To fill this technological gap, microgravity experiments are now planned which will be performed during future flights of the Space Shuttle, in conjunction with ground-based tests. This paper deals with analytical and experimental issues related to constitutive modeling of granular materials.

Twenty monodisperse polystyrene latexes were made by seeded emulsion polymerization in the MLR-SEP flight hardware on theSTS-3 and STS-4 flights of the Columbia and the STS-6, STS-7, and STS-11 flights of the Challenger. Two polymerizations were small-particle-size controls; the other eighteen were of large particle size. Of these, six failed: four on STS-4 owing to malfunction of the flight hardware; one on STS-6 owing to a broken wire; one on STS-11 owing to a broken stirrer shearpin. Nine monodisperse latexes of 4–30 μm size had narrower particle size distributions than the ground-based controls. The 10 μm STS-6 latex and the 30 μm STS-11 latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in space for sale on earth. The polymerization rates in space were the same as on earth within experimental error. The flight polymerizations produced only negligible amounts of coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, so that these controls were discontinued after the STS-7 experiments. These results confirmed the original rationale of the experiments that polymerization in space would give more uniform large-particlesize monodisperse latexes with less coagulum by: 1. the better uniformity of all 5 μm or larger flight latexes; 2. the more perfect sphericity of the 10 and 30 μm particles; 3. the smaller number of offsize larger particles; 3. the negligible amounts of coagulum; 4. the broadening of the particle size distribution and the formation of more larger offsize particles during the completion on earth of the polymerization of the partially converted STS-4 flight latexes.

A containerless method that produces highly uniform microspheres (> 50 microns in diameter) from many materials has been developed for biomedical applications. A piezoelectrically vibrated drop generator forms uniform (monodisperse) monomer droplets that are either electrostatically levitated and polymerized using UV irradiation, or free radical polymerized. Spheres of 2-hydroxyethyl methacrylate (HEMA) polymer have been produced with diameters of 155 microns ±1.57%.

We present an engineering analysis of the rate of evaporation of solvent in the hanging drop method of protein crystal growth. Our results are applied to 18 different drop and well arrangements commonly encountered in the laboratory. We take into account the chemical nature of the salt, the drop size and shape, the drop concentration, the well size, the well concentration, and the temperature. We find that the rate of evaporation increases with temperature, drop size, and with the salt concentration difference between the drop and the well. The evaporation possesses no unique half-life. Once the salt in the drop achieves about 80% of its final concentration, further evaporation suffers from the law of diminishing returns.

Containerless glass forming experiments conducted aboard the space shuttle STS-61A in October 1985, which used a single axis acoustic levitator/furnace (SAAL) are described. A total of eight spherical samples =6±1 mm diameter were used. Each sample had one or more of the following objectives; (1) obtain quantitative evidence for the suppression of heterogeneous nucleation/crystallization in containerless melts in micro-g, (2) study melt homogenization in the absence of gravity driven convection, (3) develop procedures for preparing precursor samples suitable for space experiments, (4) perform comparative property analysis of glasses melted on earth and in micro-g, (5) determine the feasibility of preparing glass shells in micro-g for use as laser fusion targets, and (6) assess the operational performance of the SAAL for processing multicomponent, glass forming melts in micro-g. Depending upon their composition, the samples were melted between 900 and 1500°C for about 5 to 12 minutes.

Motion pictures of solid and liquid samples showed that the levitator/furnace operated as planned. A ternary calcia-gallia-silica glass prepared in micro-g was reasonably homogeneous and provided evidence for 2 to 3 fold increase in the tendency for glass formation in space. Melt homogenization in space was reasonably fast for this calcia-gallia-silica melt and hot-pressing appeared to be a feasible way of preparing precursor samples for use in micro-g flight experiments. Valuable information for the technology of materials processing in space was obtained.

Seventy wt% PbO · 30 wt% B2O3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.

The radius-time history of a gas bubble located concentrically within a spherical liquid drop in a space laboratory is analyzed within the framework of the quasistationary approximation. Illustrative results are calculated from the theory which demonstrate interesting qualitative features. For instance, when a pure gas bubble dissolves within a liquid drop in an environment containing the same gas and some inert species, the dissolution can be more or less rapid than that in an unbounded liquid depending on the initial relative size of the drop. Further, given a similar growth situation, indefinite growth is not possible, and the bubble will initially grow, but always dissolve in the end.

The fundamental processes of melting, the well known Stefan and Neumann problems, have been of great interest from a theoretical point of view as well as for their wide applications. The yet unmolten part of the material undergoing phase change within spherical containments is generally presumed to remain stationary, an unlikely occurrence in practice. The differing densities of the liquid and the solid may readily cause a force imbalance on the solid in gravitational and perhaps microgravitational environments, thereby moving the solid away from the center. In the present work, an approach related to the theories of lubrication and film condensation was employed and an approximate closed-form solution of melting within spheres was obtained. It was shown that a group of dimensionless parameters containing, Prandtl, Archimedes and Stefan numbers describes the melting process. Fundamental heat transfer experiments were also performed on the melting of a phase-change medium in a spherical shell. Free expansion of the medium into a void space within the sphere was permitted. A step function temperature jump on the outer shell wall was imposed and the timewise evolution of the melting process and the position of the solid-liquid interface was photographically recorded. Numerical integration of the interface position data yielded information about the melted mass and the energy of melting that support the theory.

The kinetics of phase separation in the succinonitrile-water system are being investigated. Experiments involve initial physical mixing of the two immiscible liquids at a temperature above the consolute, decreasing the temperature into the miscibility gap, followed by imaging of the resultant microstructure as it evolves with time. Refractive index differences allow documentation of the changing microstructures by noninvasive optical techniques without the need to quench the liquid structures for analysis.

A laser pyrometer has been developed for acquiring the true temperature of a levitated sample. The laser beam is first expanded to cover the entire cross-sectional surface of the target. For calibration of such a system, the reflectivity signal of an ideal 0.95cm diameter gold-coated sphere (reflectivity = .99) is used as the reference for any other real targets. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of a blackbody furnace (emissivity = 1.0) at a known, arbitrary temperature. Since the photo sensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. Preliminary results indicate that true temperatures thus obtained are in excellent correlation with thermocouple measured temperatures.

Multiple-color pyrometric measurement of particles reacting in an electrodynamic thermogravimetric analyzer is discussed. Attempts to measure the emissivity of heated tungsten particles are presented. The data are too scattered to provide reliable results.

Experimental evidence for the sensitivity to noise and the speed of response of pyrometers is presented, and a brief theoretical discussion of the causes is presented.

A simple and inexpensive space shuttle experimental apparatus to conduct microgravity melting and solidification is presented. A Get-Away-Special (GAS) space furnace was initially developed as a student design project at the United States Air Force Academy and further refined at the NASA Lewis Research Center. The experiment package consists of a melting chamber, battery power system, temperature data recording systems, and electronic controller. The melting chamber is a thin-walled tube wrapped by heating resistance wire. Thermocouples are used to record the specimen thermal history. Power is supplied by two volt batteries wired to produce 360 watts. The millivolt output of the thermocouples is amplified, cold-junction compensated, and converted to a frequency which is then recorded on an off-the-shelf cassette stereo tape recorder. A back up data recording system which digitizes the amplified signal and records the data on EEPROMs (electrically erasable programmable read-only memory) has also been included. This experimental device demonstrates that basic science research can be kept simple and inexpensive.

During the Dl-Spacelab mission, several samples of semiconductor and aluminium alloy have been processed in a single ellipsoid mirror furnace (ELLI) and a gradient furnace (GFQ), respectively. Both furnaces operate under inert gas atmosphere at reduced pressure (100 to 200 mbar). In weightlessness, the heat transfer characteristic changed due to absence of convection. For the ELLI, power consumption in space decreased by 15 to 21 %, while the thermal inertia of the system increased by a factor of 2. In contrast to that, the gradient furnace required higher heater temperatures in space, while the influence on the sample thermal profile was rather low.

A new hypothesis is presented which proposes that major microstructural features of many meteorites are products of non-equilibrium solidification under microgravity conditions. These materials exhibit microstructural features both similar to and different from materials produced on Earth. Evidence is given to show that the differences can be attributed to microgravity solidification while the similarities can be attributed to nonequilibrium solidification. This hypothesis leads to a new interpretation of the formation mechanism for the Widmanstatten structure commonly observed in meteoritic nickel-iron alloys. Several meteorite synthesis experiments are suggested to test the hypothesis. The hypothesis implies that the study of meteoritic materials can lead to a deeper understanding of microgravity solidification; conversely, the principles of microgravity solidification can lead to insights into meteorite formation.

In this paper, we describe the design and the performance of an electrostatic-acoustic hybrid system and its application to a charge drop rotation experiment. This system can levitate a charged drop electrostatically and induce drop rotation or oscillation by imposing an acoustic torque or an oscillating acoustic pressure. Using this system, the equilibrium shapes and stability of a rotating charged drop were experimentally investigated. A 3 mm size water drop was rotated as a rigid body and its gyrostatic equilibrium shapes were observed. Families of axisymmetric shapes, two-lobed shapes, and eventual fissioning have been observed. With the assumption of “effective surface tension” in which the surface charge simply modified the surface tension of neutral liquid, the results agree exceptionally well with the Brown and Scriven's prediction for uncharged drops.

Laser induced fluorescence (LIF) detection of atomic vapors was used to study evaporation from electromagnetically levitated and CW CO2 laser heated molydenum spheres and resistively heated tungsten filaments. Electromagnetic (EM) levitation in combination with laser heating of tungsten, zirconium, and aluminum specimens was also investigated. LIF intensity vs temperature data were obtained for molybdenum ( 7S3 ) atoms and six electronic states of atomic tungsten, at temperatures up to the melting point of each metal. The detected fraction of the emitted radiation was reduced by self-absorption effects at the higher experimental temperatures.Vaporization enthalpies derived from data for which less than half the LIF intensity was self-absorbed were ΔHo0 = -636 ± 24 kJ/g-mol for Mo and 831 ± 32 kJ/g-mol for W. Space-based applications of EM levitation in combination with radiative heating are discussed.

Off-eutectic compositions of Bi-Mn were directionally solidified in applied transverse magnetic fields up to 3 kG to determine the effects odn thermal and solutal convection. For Bi-rich compositions, the magnetic field appeared to increase mixing as determined from thermal, morphological, chemical and magnetic analyses. For Mn-rich compositions morphological and chemical analyses suggest some reduction in mixing due to application of the magnetic field. Conductivity gradients in the melt are suggested as a possible mechanism for the observed results.