bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of a Ag Monolayer on Pt by Surface Enhanced Raman Scattering
Authors: Miragliotta Joseph , Furtak T. E.
Published: March 2011

We report the results of a surface enhanced Raman scattering investigation of a Ag monolayer (ML) electrochemically deposited on a Pt substrate. The poor electromagnetic enhancing properties of this surface insure that the observed Raman scattering intensity is short–range in origin, arising from an electronic resonant process between the surface adatom and the probe molecule. Raman spectra showed the probe molecule, pyridine, to be bound to an electron-deficient Ag site. This supports earlier vacuum studies of the Ag/Pt surface which reported an electron transfer from the Ag ML into the Pt substrate leaving a partial positive charge in the ML. The transfer is due to the work function difference between Ag and Pt.
Surface Science Investigations of Thin Metal Films on Metal and Metal Oxide Supports
Authors: White J. M.
Published: March 2011

Chemisorption and catalysis on overlayer metals and metal oxides is rich and complex. Thin film model systems, suitable for UHV surface science, are attractive candidates for studying the fundamental interactions involved. In this paper, we discuss three examples: (1) O2 and N2O dissociative adsorption on Cu-covered Ru(0001), (2) molecular CO chemisorption on K-covered Ag(111), and (3) CO, H2 and NO chemisorption on clean and TiOx covered Pt and Rh. In each of these cases, evidence is presented for significant chemical interactions between the two substrate materials.
Surface Chemistry of Thin Palladium Films
Authors: Neiman David L. , Koel Bruce E.
Published: March 2011

The properties of Pd monolayers on several transition metal substrates are dramatically different from the surface properties of bulk Pd single crystals. The changes include a large rehybridization of the Pd atoms to a noble metal electronic configuration and a concomitant reduction in CO and H2 chemisorption bond strengths. We present here temperature programmed desorption (TPD) studies of CO, NO, H2, and C2H4 chemisorption on thin epitaxial Pd films on Nb(110). Our resuAs confirm for all of these gases a large reduction in the chemisorption bond energy for adsorption on Pd thin (<2 ML) films. Our TPD results for CO, which give a CO binding energy of about 10 kcal/mole, confirm previous UPS studies which show that a Pd monolayer forms only a weak chemisorption bond to CO. Thicker Pd films ( > 5 ML ) have CO TPD spectra that agree qualitatively with previous studies on Pd(111) single crystals, where the CO binding energy is about 30 kcal/mole. These results for Pd/Nb(110) will be discussed with respect to recent work on related systems involving thin Pd films on other transition metal substrates.
Adsorption and Reaction on Thin Metal Overlayers
Authors: Berlowitz Paul J. , Peden Charles H. F. , Goodman D. Wayne
Published: March 2011

These studies have addressed the adsorption of CO on very thin (submonolayer to multilayer) deposits of Cu, Ni, Pd, and Fe on single crystals of Ru and W. The kinetics of the methanation, ethane hydrogenolysis, and cyclohexane dehydrogenation reactions have also been measured over these model bimetallic catalysts. Temperature programmed desorption (TPD) spectra of CO at submonolayer coverages reveal new desorption features which have significantly perturbed peak maxima from those observed on the bulk metals, indicating the unique character of these monolayer metallic films. This behavior has been correlated with LEED, ARUPS, work function, and kinetic measurements.
Structural Energetics of Thin Coherently Strained Metallic Overlayers
Authors: Dodson Brian W. , Taylor Paul A.
Published: March 2011

Understanding of the growth, stability, and structural properties of coherently strained metal overlayers has achieved considerable importance because of the recent discovery of unique interfacial electronic states and catalytic properties of such systems. The structural stability of coherently strained metal films grown on a substrate composed of a different and lattice-mismatched metal is determined via atomistic calculations. An equilibrium energy balance criterion is used, which is evaluated with a Monte Carlo annealing optimization procedure in which the structural energy of the bimetallic system is obtained using the embedded atom method. The stability of coherently strained (100) bimetallic structures chosen from combinations of the fcc metals Ag, Au, Cu, Ni, Pd, and Pt has been studied. The predicted critical thicknesses agree remarkably well with experimental results, but disagree quantitatively with the continuum models.
A Study of Epitaxial Films of Bcc Nickel on FE{001} with leed Intensity analysis and Total Energy Band Calculations
Authors: Marcus P. M. , Moruzzi V. L. , Wang Z. Q. , Li Y. S. , Jona F.
Published: March 2011

Analysis of LEED intensities of thin films of Ni grown epitaxially on bcc Fe{001} establishes that the structure is bcc up to six layers, but with a contraction of 5% of the first layer spacing and expansion of 5% of the second layer spacing. At thicknesses above six layers there is a gradual change to a new surface and bulk structure with increasing disorder. Spin-polarized total-energy band calculations show that the bcc Ni film is stretched 1.4% from its equilibrium value and thereby changed from nonmagnetic to ferromagnetic. The calculated results on stable and metastable phases of Fe, Co, Ni and Cu show that the equilibrium lattice parameters and differences in binding energies favor mutual epitaxy for any bcc or fcc pair. There are six pairs in which a possible metastable phase is grown epitaxially on a stable substrate.
Oxidation of the (111) Surface of an Al-Be Alloy: Effect of a BeO Layer
Authors: Ahmad M. , Blakely J. M.
Published: March 2011

Growth of a thin BeO layer on the (111) surface of a dilute Al-Be alloy has been studied under oxidizing condition. At 500°C, in the presence of oxygen, Be atoms diffuse to the surface to form BeO. This oxide grows epitaxially with its (0001) basal plane orientation parallel to Al (111). During room temperature oxygen exposure of the AI(111) surface precovered with a BeO layer, it was found that oxygen diffused through the BeO overlayer and formed amorphous Al2O3 at the AI-BeO interface. The thin BeO film remained well ordered even when separated from the substrate by the amorphous layer. The effect of various coverages of BeO on the kinetics of oxidation of Al (111) at room temperature was studied; the influence of the BeO was found to be small in comparison with the case of a polycrystalline sample with predominantly (001) textures.
The Influence of Predeposition of Nonolayer Thin Titanium Filns Upon the Crystallography of Subsequently Formed Pd2Si Layers on (100) Silicon
Authors: McGinn J. T. , Hoffman D. M. , Thomas, III J. H. , Tams III F. J.
Published: March 2011

This paper reports upon a new technique for the formation of epitaxial Pd2Si on (100) silicon using thin predeposited titanium layers. Improvements in the quality of epitaxy in Pd2Si on {111} silicon by this technique will also be shown. A preliminary model for the formation of epitaxy will be given. Discrepancies between this model and results in the literature will be discussed and experiments suggested to resolve the uncertainties.
Optical Second Harmonic Generation from Surface Segregants and Adsorbed Oxygen on an Fe-18Cr-3Mo (110) Surface
Authors: Hamilton J. C. , Anderson R. J. , Foltz G. W.
Published: March 2011

Optical second harmonic generation is a new surface diagnostic applicable both in ultra-high vacuum and ambient environments and capable of examining gas-solid, liquid-solid and solid-solid interfaces. Studies of surface segregation of chromium and nitrogen on Fe-18Cr-3Mo(II0) single crystal surfaces in ultra-high vacuum are described. Major increases in second harmonic intensity generated by 700 nm excitation at the surface are seen upon heating to temperatures at which chromium and nitrogen cosegregate. Adsorption of oxygen has also been studied on this surface. Second harmonic generation shows promise in providing structural and electronic information for surfaces and interfaces in a wide variety of environments.
Modification of the Properties of Metal Overlayers oN Nb(110) and Ta(1l0)
Authors: Ruckman M. W. , Strongin Myron , Pan Xiaohe
Published: March 2011

Modification of the physical and chemical properties of noble and near-noble metal monolayer films supported on Nb(110) or Ta(l10) is demonstrated using photoemission and LEED. Strong adlayer-substrate bonding leads to the formation of commensurate Pd or Pt overlayers at low coverage (8 < 0.7 ML). Ni and Cu form incommensurate structures because the additional interfacial misfit cannot be overcome by substrate-overlayer bonding. Ag and Au form commensurate overlayers at coverages le ss than 3 ML because the lattice misfit is small. The strong overlayer-substrate bonding produces large changes in the chemical activity of near-noble metal overlayers. Photoemission measurements on Pt monolayers show that the hybridized metal d-states are shifted further below the Fermi level “EF” and show a reduction in the surface density of states at EF. This absence of bonding d-states near EF effects CO chemisorption. However, as additional layers of Pd and Pt are deposited, the d-occupancy at EF grows, with “constant” atomic structure and the amount of CO increases. Hence, in these systems chemisorption changes can be studied as a function of changing electronic structure while holding the surface structure fixed.
Microstructure of Cement Paste and Mass Transfer of Gas through Concrete
Authors: Mills R. H.
Published: March 2011

Gas flow through concrete may be modelled by a relationship:

where D* is the specific permeability, N* is the number of unit pores per m2, and α, β and γ are experimental constants.

A unit pore is defined by the hydraulic mean radius a* equal to the total porosity divided by the BET surface area. The value of a* is estimated from porosity and hydration parameters to lie between 1.6 and 2.8 nm for water-cement ratios from 0.42 to 0.77 and initial porosities from 0.292 to 0.150. Estimation of pore radius a from gas flow yielded values of a/a* varying from 72 to 6. There appears to be fair correlation between N* and D*, but it appears that flow passes through microcracks rather than the natural pore system.
Relationships Between Microstructure and Engineering Properties
Authors: Pratt P. L.
Published: March 2011

The calculation of such macroscopic engineering properties as elastic modulus and compressive strength for cement pastes and concrete depends upon the establishment of a realistic model of the microstructure. Increasingly complex models are considered, which appear capable of predicting the elastic modulus in terms of a modified Rule of Mixtures. The same models are able to account for the broad features of the compressive strength, because strength is always scaled by the elastic modulus of the material. The actual value of the compressive or the bend strength is determined by the mechanics of crack initiation and crack propagation in the particular test used. Crack initiation is controlled by the defects present in the material and crack propagation by the fracture toughness of the different phases and the porosity in the microstructure. Thus the strength depends upon microstructure in a number of different but interrelated ways, determined by the fracture toughness of the material.
Microstructural Aspects of Stress Corrosion of Cementitious Materials
Authors: Schneider U. , Nagele E. , Dujardin N.
Published: March 2011

Stress corrosion phenomena, i.e. significant effects of mechanical stresses on the corrosion resistance of materials, have been reported for a large variety of materials, including metals, oxides and halides. Recently it has been shown [1,2] that cementitious materials are also sensitive to stress corrosion. The time dependent decrease in the flexural strength of chemically stressed concrete and mortar depends significantly on the mechanical stress acting simultaneously with the chemical attack.

For cementitious materials a comprehensive study of the stress corrosion phenomena has been started. In this paper the latest results from the current research program are presented and the interrelations between the microstructure of hardened cement mortar and the strength reduction caused by stress corrosion, are briefly discussed.
Pore Structure Development in Portland/Fly Ash Blends
Authors: Cook David J. , Cao Huu T. , Coan Everett P.
Published: March 2011

Pore structure development in portland/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally <0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.
Cement Paste Microstructure in Concrete
Authors: Diamond Sidney
Published: March 2011

An understanding of the microstructure of cement paste in actual field concrete is considered to be the primary objective of cement microstructural studies. Cement paste in concrete is shown to consist of narrow ribbons of the order of 80 to 150 μm separating sand and coarse aggregate grains, and interrupted by frequent air voids. Individual cement grains form shells around themselves early in the hydration process. In subsequent hydration they either deposit dense layers of internal hydration product or empty out in a hollow-shell mode and precipitate hydration products in the empty spaces between nearby shells. Analogous shells are similarly formed around fly ash particles, which then react by progressive etching from within the shells. Interfacial zones around aggregates are pictured as having a complex characteristic structure including at least four different forms of calcium hydroxide particles with various preferred orientations. It is suggested that the conventional picture of the “aureole de transition” derived from successive x-ray diffraction measurements may have been misinterpreted.
TEM Studies of Cement Hydration
Authors: Groves G. W.
Published: March 2011

The application of transmission electron microscopy to the study of the early stages of hydration C3S and the microstructure of very mature C3 S paste is reported. In the former case the effect of water-cement ratio appears to be very important. In the latter, a detailed evaluation of the microstructures of inner C-S-H, outer C-S-H and CH is possible and the relationship of these to models of cement hydration is discussed.
Analysis of Phases in Cement Paste using Backscattered Electron Images, Methanol Adsorption and Thermogravimetric Analysis
Authors: Scrivener Karen L. , Patel H. H. , Pratt P. L. , Parrott L. J.
Published: March 2011

In backscattered electron (bse) images of polished cement sections, anhydrous material, calcium hydroxide, other hydration products (mainly C-S-H) and porosity can be distinguished on the basis of their grey level in the image. Using an image analyzer connected directly to the SEM, it is possible to resolve these four components and so measure their relative proportions and distributions. The effects of magnification and the number of fields measured on the accuracy of bse image analysis are examined. The volume fractions of anhydrous material, porosity and calcium hydroxide derived from bse image analysis are compared with those obtained by other techniques and good correlation was found for the measurement of anhydrous material and porosity.
Measurement and Modeling of Porosity in Drying Cement Paste
Authors: Parrott Leslie
Published: March 2011

Preliminary models for predicting the performance of exposed concrete show that the porosity sub-model plays a pivotal role in linking properties with the developing gradients of cement paste microstructure that arise from drying and carbonation. The difficulties of porosity characterization are reviewed and some alternatives to traditional methods are considered. Property/porosity relationships are considered with particular reference to the volume, size-distribution and continuity of the larger pores. The factors influencing porosity under normal exposure conditions, such as cement hydration, drying and carbonation, are reviewed and the possibilities of modeling their effects are considered. Some comparisons between predicted and measured values of porosity are given. It is concluded that progress in modeling the performance of exposed concrete is likely to be linked with improvements in methods of pore structure characterization.
Leachate Composition at an Experimental Test Cell of Coal Combustion Fly Ash
Authors: Labuz L. L. , Viliaume J. F. , Bell J. W.
Published: March 2011

In an effort to characterize the waste streams at a typical utility fly ash landfill, a large outdoor test cell of compacted fly ash was constructed in 1984 at the Pennsylvania Power & Light Company's Montour Steam Electric Station. The test cell is a scaled-down version of the active dry fly ash disposal facility at the plant and includes a liner, a leachate collection system, and surface water runoff perimeter drains. It is 100 feet by 100 feet at the base and 10 feet high with 2:1 vertical:horizontal side slopes, giving a top area of 60 feet by 60 feet. The test cell is instrumented to measure precipitation, infiltration, surface runoff, unsaturated flow, evapotranspiration and leachate drainage. This paper presents a preliminary evaluation of the chemical composition of leachate generated from the test cell during the first year of leachate production. Leachate samples are periodically collected from a concrete sump to which the leachate collection system drains. Leachate first appeared in the sump in October 1985, approximately one year after the test cell was constructed. Samples are analyzed for pH, specific conductance, 22 metals, and 10 ions. The concentrations of parameters present in the test cell leachate are compared to drinking water standards and to standard laboratory extraction results. Parameters not detected in the leachate are also identified. The preliminary findings of the leachate monitoring effort are providing valuable information on the initial quality of leachate generated under field conditions. This data will be useful in the design of leachate control systems, wastewater treatment facilities and ground water monitoring programs for future ash disposal operations.
Aluminum Sulfate Hydration Retarders for High-Calcium Fly Ash Used in Highway Construction
Authors: Tohidian M. , Laguros Joakim G.
Published: March 2011

The rapid hydration and setting associated with the use of high-calcium fly ash as an additive in soil and aggregate base stabilization in highway construction imposes certain limitations in regards to operational time and volume of work executed. Aluminum sulfate and its ammonium salt were evaluated as hydration reaction retarders. Mixtures of Ottawa sand and Class C high lime fly ash in a 1:1 weight ratio were used for the evaluations. These additives minimized the adverse effects of delayed compaction by recovering some of the compressive strength lost to the rapid hydration, although in all cases the density of the mixes decreased. The recovery of strength was related to the heat of hydration, wherein the peak temperature was reduced from 90°F to the range of 86–78°F at 2 hours; further temperature decreases were observed as reaction time increased. The availability of the sulfate ions, as manifested by the presence of ettringite, helps the hydration process continue, minimizes the adverse effects of delayed compaction and assists positively in the reduction of the void area of mixes and in stratlingite formation, which contributes to a strong crystalline framework.
Recent Developments in the Utilization of Western U.S. Coal Conversion Ash
Authors: Manz O. E. , Laudal Dennis L.
Published: March 2011

The utilization of ashes from combustion or gasification of western U.S. coals offers many possibilities for useful products. Of the possible uses, the following have been identified in an earlier study [1] as having sufficient potential for laboratory development and testing: mineral wool, sulfur concrete, high flexural-strength ceramics, replacement of cement in concrete, and road stabilization. Three lignite-derived ash products from the Beulah, ND, site were used in the present study: fixed-bed gasification ash; a dry scrubber ash; a combination bottom ash/economizer ash from an electrical power plant, Where possible, ASTM fabrication and testing procedures were used. Mineral wool of similar physical character to commercial wool and at lower potential cost was produced using 100 percent of various western ashes. Sulfur concrete utilizing 80% ash and 20% modified sulfur developed flexural and compressive strengths in excess of 2,250 and 5,000 psi, respectively. An economically competitive vitrified ceramic product with flexural strength above 7,800 psi was produced from a mixture of 50% ash, 45% sand, and 5% clay. By using a total ash mixture of 26% gasifier ash and 74% combustion ash, a very satisfactory, economical and durable roadbed material was developed. The replacement of up to 50% of the cement in concrete with western fly ash produces economical, high strength concrete.
Enhanced Resource Recovery by Beneficiation and Direct Acid Leaching of Fly Ash
Authors: Berry E. E. , Hemmings R. T. , Golden D. M.
Published: March 2011

An investigation was conducted into the use of beneficiated ash fractions as feed materials for direct acid leaching to recover Al and other metals. A low-Ca (1.4% CaO) ash was selected from which four fractions (classifier fines, classifier rejects, magnetic concentrate, and non-magnetics) were produced by mineral beneficiation methods. The raw ash and the four ash fractions were leached with 6 M HCl under reflux. Mass balance data were obtained to determine extraction efficiency for Si, Al, Fe, Ca, Mg, Na, K and Ti. It was found that size separation of the ash had a marked influence in enhancing extraction efficiency from the fine fraction for all of the elements studied except Fe. Extraction of Fe from the magnetic fraction was less efficient than from the non-magnetic fraction. Examination of the solid residue after leaching showed that, although most of the acid-soluble components were removed from the glassy phases of the ash, a significant part of the ash comprised non-reactive glass of high-Si content. A relationship between extractable Al in ash and leachable alkali and alkaline earth metals was identified and discussed in terms of glass modification theory.
Properties and Environmental Considerations Related to AFBC Solid Residues
Authors: Berry E. E. , Anthony E. J.
Published: March 2011

Atmospheric-pressure fluidized bed combustion (AFBC) produces solid residues that are different from the familiar pulverized coal ashes. When limestone beds are used to adsorb SOx, high-Ca residues, comprised largely of CaO and SO4, are produced. Leachates from high-Ca AFBC residues are strongly alkaline (pH >11) and contain high levels of dissolved solids (TDS >3000 mg/L). If water is added during handling, hydration of CaO may cause a temperature rise and hydration of CaSO4 may result in premature hardening of the residues. Trace elements and organic components may leach from disposal sites. This paper presents an overview of the nature of AFBC residues and the factors influencing their disposal.
Charged Drop Levitators and their Applications
Authors: Rhim W. K. , Chung S. K. , Hyson M. T. , Elleman D. D.
Published: March 2011

Charged drop levitation is described for two different kinds of levitators. It is demonstrated that the feedback-controlled electrostatic levitator is capable of levitating a several milimeter size large drop in 1 g, and it can be used in various experiments such as crystal growth, supercooling and solidification, and drop dynamics. Charged droplet levitation in a vertical, linear quadrupole levitator is described, and its advantages are demonstrated taking the charged drop instability experiment as an example. The cause of the observed premature burstings are speculated to be not by the Rayleigh limit but, rather, by an electron avalanch in the surrounding gaseous medium. No evidence was found that the burtings accompaied by mass loss, in direct contrast to the most of the previous reports by Doyle et.al.and Abbas and Latham.
Spatial Profile of Thermoelectric Effects During Peltier Pulsing in Bi and Bi/MnBi Eutectic
Authors: Silberstein R. P. , Larson D. J.
Published: March 2011

We have studied the spatial profile of the thermal transients that occur during and following the current pulsing associated with Peltier Interface Demarcation during directional solidification. Results for pure Bi are presented in detail and compared with corresponding results for the Bi/MnBi eutectic. Significant thermal transients occur throughout the sample that can be accounted for by the Peltier effect, the Thomson effect, and Joule heating. We have separated these effects and studied their behavior as a function of time, current density, and position with respect to the solid/liquid interface.
Analysis of the Free-Fall Behavior of Liquid-Metal Drops in a Gaseous Atmosphere
Authors: McCoy J. Kevin , Markworth Alan J. , Brodkey Robert S. , Collings E. W.
Published: March 2011

The free fall of a liquid-metal drop and heat transfer from the drop to its environment are described for both a gaseous atmosphere and vacuum. A simple model, in which the drop is assumed to fall rectilinearly with behavior like that of a rigid particle, is developed first, then possible causes of deviation from this behavior are discussed. The model is applied to describe solidification of drops in a drop tube. Possible future develop-ments of the model are suggested.
Containerless Processing of Undercooled Melts
Authors: Shong D. S. , Graves J. A. , Ujiie Y. , Perepezko J. H.
Published: March 2011

Containerless drop tube processing allows for significant levels of liquid undercooling through control of parameters such as sample size, surface coating and cooling rate. A laboratory scale (3m) drop tube has been developed which allows the under-cooling and solidification behavior of powder samples to be eval-uated under low gravity free fall conditions. The level of undercooling obtained in an InSb-Sb eutectic alloy has been eval-uated by comparing the eutectic spacing in drop tube samples with a spacing/undercooling relationship established using thermal analysis techniques. Undercoolings of 0.17 and 0.23 Te were produced by processing under vacuum and He gas conditions respec-tively. Alternatively, the formation of an amorphous phase in a Ni-Nb eutectic alloy indicates that undercooling levels of approximately 500°C were obtained by drop tube processing. The influence of droplet size and gas environment on undercooling behavior in the Ni-Nb eutectic was evaluated through their effect on the amorphous/crystalline phase ratio. To supplement the structural analysis, heat flow modeling has been developed to describe the undercooling history during drop tube processing and the model has been tested experimentally.
Ultrafine Particle and Fiber Production in Micro-Gravity
Authors: Webb George W.
Published: March 2011

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.
Glass Formation in Microgravity
Authors: Ray C. S. , Day D. E.
Published: March 2011

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.
The Dissolution or Growth of a Gas Bubble Inside a Drop in Zero Gravity
Authors: Kondos Pericles A. , Shankar R. , Weinberg Michael C.
Published: March 2011

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.
Space Processing Viewed by a Scientist-Astronaut
Authors: Wang Taylor G.
Published: March 2011

Space Processing is a fledgling and somewhat controversial subject. The scientific community as well as NASA have not yet quite made up their minds as to what to do with Space Processing. The scientific society views Space Processing with some suspicion, and rightfully so. They're not sure whether this is something real or just a Class “A” con job. NASA has made a lot of promises to this program and has delivered very little. Space Processing has a good chance of becoming a self-fulfilled prophecy. Therefore, responsibility is laid on the shoulders of those of us who believe in this program to convince the scientific community that there is something real there and lobby NASA that they should either “put up or shut up.” This is one of the reasons why I took up the challenge to fly in the Space Shuttle and to live and train with these “Space jocks” for a total of about three years.
Low Cost Get-Away-Special (GAS) Furnace
Authors: Turner Glon D. , degroli Henry C. , Antoon Fred A.
Published: March 2011

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.
Isothermal Dendritic Growth - A Low Gravity Experiment
Authors: Glicksman M. E. , Winsa E. , Hahn R. C. , Lograsso T. A. , Rubinstein E. R. , Selleck M. E.
Published: March 2011

The growth of dendrites in pure melts and alloys is controlled by diffusion-limited transport of heat and/or solute. The presence of temperature or concentration gradients within a molten phase subject to gravitational forces generally promotes convection, which in turn, modifies the diffusion processes. The vigor of melt convection is controlled by several parameters often expressed as a lumped dimensionless group, the Grashof number Gr = gβΔTℓ3/ν2, where g is the acceleration due to gravity; is the volumetric expansion coefficient; ΔT is the undercooling; ν is the kinematic viscosity; and ℓ is the relevant length scale, e.g., the characteristic diffusion distance. Dendritic growth, by its nature, does not permit independent manipulation of the controlling length scale, ℓ, which is determined by materials properties (e.g. diffusion coefficient or thermal diffusivity) and the undercooling or supersaturation. The reduction of g through orbital free fall is often the only practical way to lower Gr sufficiently to permit careful observation of the morphological and kinetic characteristics of isothermal dendritic growth. Previously conducted ground-based studies and the current approach to performing these studies in low earth orbit will be described.
Solidification of Undercooled Ni-Sn Eutectic Alloy Under Microgravity Conditions in the Space
Authors: Piccone Shuttle T. J. , Harf F. H. , Wu Y. , Shiohara Y. , Flemings M. C. , Winsa E. A.
Published: March 2011

The Space Shuttle Columbia carried an Alloy Undercooling Experiment on its STS 61-C mission in January, 1986. The experiment was performed in the electromagnetic levitator (EML) designed and produced by the General Electric Company. A sample of Ni-32.5wt% Sn eutectic was melted and solidified under microgravity conditions in the Space Shuttle. The specimen achieved only a fairly small undercooling, probably less than 30 K.

The specimen was examined by optical and scanning electron microscopy. The surface and cross-sectional microstructures were primarily composed of normal lamellar eutectic, but showed several interesting features, including an apparent surface nucleation site, curved dendrites with non-orthogonal secondary arms, dendrite fragments with extremely fine arm spacing, submicron precipitates, and faceted crystals. The results of the space experiment are presented and compared with ground-based results obtained with the same alloy.
Vibrational Spectra of Oxide Doped Fluorozirconate Glasses
Authors: Kosinski S. G. , Bruce A. J.
Published: March 2011

Raman, IR transmission, and reflectance spectra have been measured for a series of zirconium fluoride glasses deliberately doped with 0.4, 0.8 and 1.2 mole % lanthanum oxide. The effect of such impurities on the attenuation near the loss minimum in these glasses is discussed. In addition the utilization of Raman and IR spectroscopy to quantify the oxide contamination levels and optical absorption respectively, in heavy metal fluoride glasses is demonstrated.
Structure, Vibrational Spectra and Related Physical Properties of Various Glasses in the PbO-Bi2O3-GeO2 System
Authors: Canale J. E. , Condrate R. A. , Nassau K. , Cornilsen B. C.
Published: March 2011

Vibrational spectroscopy and various physical property measurements (density, molar volume and glass transformation temperature) were used to investigate the structural changes that occurred with changes in composition for glasses prepared by standard melting and quenching techniques in the PbO-Bi2O3-GeO2 system. Regions of constant glass transformation temperature (Tg) were noted for these glasses at high GeO2 compositions, as determined from DSC measurements. These results clearly indicated the presence of amorphous phase separation. A model was proposed that could qualitatively interpret both the infrared and Raman spectra, and the molar volume data. At low lead oxide and bismuth oxide concentrations, lead acted primarily as a network modifier while bismuth acted as a mixed network former and modifier. At high concentrations, both lead and bismuth acted as network formers in linking discrete GeO4-units and possibly forming a lead oxide/bismuth oxide portion of the network. The observed results were also interpreted on the basis of Ge-O bonds involving bridged and non-bridged oxygen atoms, and on the basis of a possible change in coordination for germanium from four to six with metal oxide additions.
Effects of Defect Modification and Reduction Techniques on the Radiation Sensitivity of Optical Fibers
Authors: Wei T. , Singh M. P. , Miniscalco W. J. , Wall J. A.
Published: March 2011

We have investigated the relationship of precursor defects in as-drawn optical fiber to glass composition and processing conditions in order to understand the radiation sensitivity of doped-core optical fiber. Techniques are reported for improving the radiation hardness of graded-index multimode fibers through reducing the concentration of doping- and processing-induced defects as well as modifying the residual defects in as-drawn fiber. Significant decreases in radiation-induced loss have been observed for fibers pretreated with hydrogen. An investigation of the role of drawing-induced defects indicates that a lower draw temperature produces slightly harder fiber. A study of core/clad interfacial stress revealed that such stress does not play a major role in radiation sensitivity.

Measurement techniques included in situ loss measurements at 850 nm and spectral loss measurements before and after -γ irradiation. In addition, photoluminescence proved to be an effective tool for characterizing specific defect centers. It was found for Ge/P-codoped fibers that the luminescence band at 650 nm attributed to drawing/radiation induced centers has an inverse correlation with induced loss. Previously unreported emission bands have been observed, including one at 720 nm which may be related to fluorine doping.
Non-Destructive Characterization of Porous Soot Boules
Authors: Glantschnig Werner J. , Holliday Albert , Pohl Knut D.
Published: March 2011

Owing to their opacity to visible light porous soot boules cannot be analyzed by standard optical methods. Yet it would be of considerable help to the preform maker to be able to measure the density and dopant concentration profiles of an unsintered soot boule. This realization prompted the development of a non-destructive soot boule characterization method.

This method amounts to a three step measurement process based on Xray tomography. First the attenuation of a well collimated X-ray beam is measured as it is scanned across the boule perpendicular to the boule axis. Next the linear attenuation coefficient profiles of the boule are reconstructed for a certain number of distinct X-ray energies. Finally, the mass density and dopant concentration profiles of the soot boule are obtained from the attenuation coefficient profiles. Hence, the method reported here allows a fairly complete analysis of the macroscopic structure of a soot boule before sintering.
The Effect of Laser Heating on Optical Properties of Germania Doped Silica Optical Waveguides
Authors: Starr E. M. , Nourshargh N. , McCormack J. S.
Published: March 2011

We report the use of CO2 laser heating for inducing an increase in the refractive index of germania doped silica films. UV absorption spectroscopy and XPS analysis have confirmed that the index change is a result of GeO2 being reduced to GeO. The technique has been successfully used for the direct writing of integrated optical strip waveguides.
Sol-Gel Processing of Optical Fiber
Authors: Elias M. E. , Elias A. M.
Published: March 2011

A new method for optical fiber production is shown. Hydrolytic polycondensation of tetramethoxysilane using a low concentration of α-picoline, 1.56×10−3% in water, gives SiO2 gel which was dried at 22 °C to a transparent amorphous material.

The densification process shows an exponential time dependence with a final value of 2.253 g/cm3 after 30 days. The specific surface area of the porous gel varies from 500 to 600 m2/g but pores are eliminated by the sintering process. Before sintering the gel, it is treated under an oxidizing atmosphere above 700 °C. At 1200 °C the pores are eliminated and a solid glass rod obtained.

After the sintering process a fiber is obtained from the rod which shows a transmission loss as low as 5.5 dB/km at 840nm.
What Limits Magnetic Polaron Energies in DMS?
Authors: Wolff P. A. , Ram-Mohan L. R.
Published: March 2011

Magnetic polarons are ferromagnetic spin clusters created by the exchange interaction of a carrier spin (electron or hole) with localized spins imbedded in a semiconductor lattice. They were first studied in magnetic semiconductors [1]; more recently, there have been extensive investigations [2] of polaron behavior in diluted magnetic semiconductors (DMS), such as Cd1−xMnxTe. DMS are favorable media for magnetic polaron studies because they have simple s-p bands and excellent optical properties. Two types of magnetic polarons have been identified in DMS - the bound magnetic polaron (BMP), whose carrier is localized by an impurity [3], and the free polaron (FP) consisting of a carrier trapped by its own, self-consistently-maintained, exchange potential [4].
Saturation Behaviour of Superhyperfine Structure of Mn2+ in PbTe
Authors: Reddoch A. H. , Bartkowski M. , Northcott D. J.
Published: March 2011

X-band EPR measurements have been made on single crystals and powders of PbTe doped with Mn below 100 ppm. A seven-fold splitting of each Mn hyperfine structure line is shown to arise from tellurium superhyperfine structure. Microwave saturation results are presented which indicate that the spin-lattice relaxation time is different for different superhyperfine lines. This asymmetry is not readily explained by conventional models.
Ground and Excited Electronic Energy Surfaces of the MnS4 Cluster in ZnS:Mn2+
Authors: Richardson J. W. , Janssen G. J. H.
Published: March 2011

Gaussian-based Self Consistent Field (SCF) MOs are obtained at various nuclear geometries for the MnS4 cluster in the external potential of cubic ZnS. Electronic relaxation and d-shell electron correlation effects are then included. For Td symmetry, quartet d-d excitation energies calculated as functions of R(Mn-S) qualitatively resemble the simple CF diagram. While separations between successive quartet levels agree closely with experiment, the threshold is about 0.5 eV high; much of this discrepancy is removed by including additional correlation effects from charge-transfer states. Large Jahn-Teller (JT) splittings of 4T1 and 4T2 levels are found with D2d distortion. Difficulty in accurately evaluating force constants interferes with predicting the corresponding deformations and stabilization energies. Estimates, encorporating the observed Stokes'; shift and JT stabilization energy, are that R(Mn-S) decreases by ∼0.1 Å and the S-Mn-S dihedral angle increases by 7sim;8°, in the lowest quartet level.
DC- and FIR-Magneto-Transport in Zn(1−x)Mn(x)Se
Authors: Erhardt W. , von Ortenberg M. , Twardowski A. , Demianiuk M.
Published: March 2011

DC- and FIR-magneto-transport measurements on Zn(1−x)Mn(x)Se for x<0.05 are interpreted in terms of nonresonant spin-flip hopping and resonant spin-flip conductivity. In combination with magnetization data the exchange-matrix element of the conduction band is determined to α = 0.32 eV.
Synthesis of the Dilute Magnetic Semiconductor CdMnTe by Ion Implantation of Mn into CdTe
Authors: Braunstein G. H. , Heiman D. , Withrow S. P. , Dresselhaus G.
Published: March 2011

The dilute magnetic semiconductor CdMnTe has been synthesized by ion implantation of Mn into CdTe. Samples of CdTe have been implanted with Mn ions of 60 keV energy to fluences in the range 1 × 1013 cm−2 to 2×1016 cm−2 and subsequently annealed, using rapid thermal annealing, for 10–15 sec at temperatures 300 ≤ TA ≤ 730°C. The successful formation of a near surface layer of CdMnTe is demonstrated by studies of the structural, electronic and magnetic properties of the ion implanted and annealed sampies; Rutherford backscattering-channeling analysis of the radiation-induced damage indicates complete recovery of lattice order after annealing at 700°C. Photoluminescence measurements, performed at 2K, reveal an increase in the energy band gap of the ion implanted alloy with respect to CdTe. Application of magnetic fields, up to 8T, produce both the characteristic energy shift of the excitonic recombination peak and polarization of the emitted radiation (in the Faraday configuration) previously observed in bulk–grown CdMnTe material.
Submicron Heterostructures of Diluted Magnetic Semiconductors
Authors: Gunshor R. L. , Kolodziejski L. A. , Otsuka N. , Datta S. , Nurmikko A. V.
Published: March 2011

The successful thin film growth of diluted magnetic semiconductors (DMS) by molecular beam epitaxy has “nucleated” a new field of research in which the DMS material is incorporated in a variety of novel superlattice and quantum well structures. The observation of reflection high energy electron diffraction intensity oscillations in ZnSe and MnSe has enabled the fabrication of ultrathin layered structures involving the “hypothetical” zincblende magnetic semiconductor MnSe. The expected antiferromagnetic ordering of MnSe is increasingly inhibited as the MnSe layer thickness is reduced from ten monolayers to the quasi-2D limit of one monolayer. Further developments include new observations of the epitaxial growth and nucleation of ZnSe, utilizing GaAs epilayers as the substrate material.
Far Infrared Magnetoabsorption in Hg1-xMnxTe/HgTe Superlattice
Authors: Yang Z. , Dobrowolska M. , Luo H. , Furdyna J. K. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: March 2011

Hg-based superlattices (SL)-e.g., the HgTe/CdTe SL–exhibit interesting and important physical properties. Among these are the tunability of the band gap, achieved by varying the thicknesses of the two constituent materials; and the existence of the vajeqnce band offset, on which the details of the valence bands of the SL largely depen. Recently a new type of Hg-based SL, the Hg1-xMnxTe/HgTe SL, has been successfully prepared. In addition to the ability of varying its band gap by controlling the Mn content, this SL has the advantage that some of its important parameters, including the band offset, can be tuned by an external magnetic field because of the spin-spin exchange interaction in the Hg1-xMnxTe layers. So far, the electronic and optical properties of this type of SL have not been explored.