bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic Structure of Binary Alloy Surfaces
Authors: Davis H. L. , Noonan J. R. 
Published: March 2011

ABSTRACTAfter discussions of multilayer relaxation for monatomic metallic surfaces and low-energy electron diffraction (LEED) procedures, some available results concerning the atomic structure of alloy surfaces are reviewed briefly. Results are discussed only for surfaces of ordered binary alloys and crystalline, substitutionally random binary alloys. Surfaces for which detailed results are available are highlighted as examples which illustrate some general crystallographic effects that occur at alloy surfaces. Specific effects included in the examples are the rippling of atomic constituents in the surface layers of ordered alloys, the preferential termination of alloys by a specific type of layer where more than one type of layer exists in the bulk, a mixture of two possible terminations, and the alternating enrichment and depletion of an atomic constituent in the surface layers of alloys which are disordered in the bulk.
Multilayer Relaxations of the Clean Nickel Aluminum (110) Surface
Authors: Yalisove S. M. , Graham W. R. 
Published: March 2011

ABSTRACTThe multilayer relaxations of the clean NiAl(II0) surface have been measured using Medium Energy Ion Scattering in a Channeling and Blocking (MEIS/CB) experiment. A high sensitivity to the first layer ripple (10% ripple with the Al on top) is reported and a multilayer model is proposed. The present results are in excellent agreement with a recent single layer LEED intensity analysis.
A Comparison of the Surface Composition of Solid and Liquid Alloys
Authors: Barnard J. A. , Wynblatt P. , Johnson William C. , Mullins W.W. 
Published: March 2011

ABSTRACTThe surface compositions of three In-Pb alloys (1.42a/o Pb, 3.07a/o Pb, and 5.86a/o Pb) have been obtained as a function of temperature in both solid and liquid states using a scanning Auger microprobe. All data were obtained at temperature, from equilibrated samples in a region of about fifty degrees on either side of the liquidus temperature. Lead was found to be the segregating component in all cases. From these measurements, the heat of segregation has been calculated for all alloys in both states. In each alloy the magnitude of the heat of segregation declines significantly on melting although the absolute surface compositions are found to be continuous across the two phase solid-liquid field. These results are interpreted in the light of current segregation theories. Particular attention is paid to the role of elastic effects on solute segregation to free surfaces.
Pore Structure of Hydrated Portland Cement Measured by Nitrogen Sorption and Mercury Intrusion Porosimetry
Authors: Hansen Will , Almudaiheem Jamal 
Published: March 2011

ABSTRACTThe pore structure (i.e. surface area, pore size distribution and pore volume) of well-hydrated portland cement pastes of water-cement ratios 0.4, 0.6, and 0.75 were investigated by the nitrogen sorption and mercury intrusion porosimetry (MIP) techniques. The effect of solvent replacement by methanol on the pore structure was studied as well. It was concluded that the solvent replacement drying procedure preserves the original pore structure of hydrated cement because the calculated and measured bulk densities of the different water-cement ratio systems investigated were in excellent agreement. Capillary condensation analysis was used to estimate the volume of capillary pores smaller than 4 nm in pore diameter for the 0.6 and 0.75 water-cement ratio pastes. The 0.4 water-cement ratio paste has pores smaller than can be determined from capillary condensation analysis. The volume of pores smaller than 4 nm was estimated from volume-thickness (V-t) analysis. For the three systems investigated, the volume of pores greater than 4 nm was obtained by MIP. For solvent-replaced pastes that showed capillary condensation according to V-t analysis, excellent agreement was obtained between the nitrogen sorption and MIP techniques in the pore diameter range of 4 nm to 30 nm.
A Study of Tricalcium Silicate Hydration from Very Early to Very Late Stages
Authors: Rodger S. A. , Groves G. W. , Clayden N. J. , Dobson C. M. 
Published: March 2011

ABSTRACTThe hydration of a tricalcium silicate paste has been examined from very early stages, i.e. during the induction period, up to two and half years using both scanning and transmission electron microscopy as well as solid state nuclear magnetic resonance. This latter technique can be used to reveal the degree of hydration of the sample and the nature of the silicate units which make up the C-S-H gel. Solid state NMR shows that during the induction period a small amount of material containing hydrated monomeric silicate units is formed, although this is difficult to identify using SEM. However during the acceleratory period SEM shows the development of the typical fibrillar C-S-H material. Backscattered electron imaging shows the cores of anhydrous material surrounded by the denser inner product.Thermogravimetric analysis has been used to find the C/S ratio of this material, which is approximately 1.8, whilst solid state NMR shows that the hydrated silicate units are largely dimeric at this stage. As hydration proceeds, the fracture surfaces become increasingly dominated by large calcium hydroxide crystals, although some fibrillar material can be identified even after over two years. The C-S-H contains progressively more middle units in silicate chains at the expense of the end units. A sample of tricalcium silicate hydrated for 26 years has also been examined.
Effect of Hydration Temperature on Cement Paste Structure
Authors: Odler I. , Abdul-Maula S. , Zhongya Lu 
Published: March 2011

ABSTRACTThe effect of temperature on the progress of hydration and cement paste structure and properties was studied using four laboratory-synthesized portland cements, hydrated at temperatures between 5 and 95°C for up to 90 days. In addition to an accelerated progress of hydration, elevated temperatures altered the phase composition and pore structure of the resulting hydrated material. Below 75°C the effect of temperature on the intrinsic bond properties of the hydrates formed remained negligible.
Hydration Reactions in Cement Pastes Incorporating Fly Ash and Other Pozzolanic Materials
Authors: Glasser F. P. , Diamond S. , Roy D. M. 
Published: March 2011

ABSTRACTA model for reactions that occur in hydrating portland cement is now generally well developed. Incorporation of various by-products to form blended cements modifies both the hydration reactions and the physical properties of the resulting pastes. A review of recent progress in understanding the effects of blending agents on these reactions is presented. The blending agents considered are low-calcium (Class F) fly ash, high calcium (Class C) fly ash, blast furnace slag, silica fume, biosilica and natural pozzolans. Effects of the blending agents on physical properties such as rheology are also considered. Particular attention is given to the essential role of alkalies in pore solutions and the beneficial reactions that occur with high silica content blending agents.
A Review of the use of Proton Magnetic Resonance to Study Superplasticizers
Authors: Regourd M. 
Published: March 2011

ABSTRACTProton pulse nuclear magnetic resonance can be used to follow the hydration of C3S and C3A, individually and mixed, with and without gypsum and superplasticizers. The variation of the spin-lattice relaxation time from early ages up to the times of setting and hardening is related first to the mobility of water molecules in rapid exchange, then to the progress of solid-water interfaces.Plasticizers act as retarders to lengthen the induction period. They behave differently with pure phases taken separately than with mixtures, in which a mutual interaction of C3S, C3A, gypsum and admixture has been characterized. Among the three superplasticizers studied, the sulfonated melanine formaldehyde was the strongest retarder, while the sodium sulfonated naphthalene was the weakest.
Volume Relationships for C-S-H Formation Based on Hydration Stoichiometries
Authors: Young J. Francis , Hansen Will 
Published: March 2011

ABSTRACTVolume changes can be calculated from the hydration stoichiometry of C3S if the composition of C-S-H is taken as C1.7SH4.0 with a density of 1.85 g/cm3. The results are in general agreement with the volume changes determined by Powers. However, the calculated evaporable water content is higher and the space-limiting water-cement ratio is calculated to be 0.42. The calculations can be applied also to the pozzolanic reaction and predict a marked increase in solid volume. In that case the composition of C-S-H is modified to C1.5SH3.8.
Bound Water in Cement Pastes and its Significance for Pore Solution Compositions
Authors: Taylor H. F. W. 
Published: March 2011

ABSTRACTThe problem of defining bound water in a cement paste is discussed; a reasonable definition is one that includes interlayer water in C-S-H and AFm phases, structural water in ettringite, and adsorbed water, but not water in micropores or in larger pores. On this basis, structural considerations indicate a value of around 32% on the ignited weight for a fully hydrated paste. ‘Non-evaporable’ water, typically around 22% on the ignited weight at full hydration, cannot be identified with bound water, because dehydration to the state in which only non-evaporable water remains causes major loss of interlayer water and destruction of ettringite. In the interpretation of pore solution data, the definition of bound water, and the value assumed for this quantity, are important, because the ionic concentrations in the pore solution are greatly affected by the volume of free water available to dissolve them. If cement is partially replaced by low calcium fly ash, the quantity of bound water at any given age is substantially reduced. This effect contributes to the relatively low concentrations of alkali metal and hydroxyl ions that are observed in the pore solutions of many portland-fly ash cement pastes.
Thermal Characterization of Coal Ash Powders: Heat Capacities and Minimum Sintering Temperatures
Authors: Ledesma R. , Compo P. , Isaacs L. L. 
Published: March 2011

ABSTRACTAshed mineral matter from ground coals were prepared by combustion at 973 K. Five coal samples ranging in rank from lignitic to high-volatile bituminous coals were used as starting materials. The heat capacities of the coal ash materials were measured between 140 K and 900 K by differential scanning calorimetry. The minimum sintering temperatures of each of the ash powders were determined using a high temperature dilatometer.
Laboratory Modeling and XRD Characterization of the Hydration Reactions of Lignite Gasification and Combustion Ash Codisposal Waste Forms
Authors: Kumarathasan P. , McCarthy Gregory J. 
Published: March 2011

ABSTRACTCementitious reactions in gasification and combustion ash derived from North Dakota lignite permit the fabrication of monolithic wastes forms from nonhazardous ash by-products and hazardous liquid wastes from a coal gasification plant. To better understand such cementitious reactions, x-ray diffraction has been used to characterize the hydration reaction products of crystalline phases in the gasification and combustion ashes from the Beulah, ND, complex and the crystalline reaction products formed. A cementitious lignite fly ash was also studied. pH of solutions at a liquid to solid ratio of 2.4 and times up to 14 days was measured, and compared to pH calculated from leachate chemical analyses. Reactions were monitored for up to one year. Among the principal crystalline phases in gasification ash, carnegieite (Na1.5Al1.5Si0.5O4) was the most reactive. Solution pH's for two samples of gasification ash were in excess of 13; carnegieite reaction may be responsible in part for these very high pH's. Hydration products included gaylussite, (Na2 Ca(CO3)2·5H20), a carbonate-sulfate ettringite structure phase, calcite and three or more zeolites (NaA, laumontite, faujasite and/or NaX). Ettringite and calcite were the principal hydration reaction products of scrubber ash, fly ash and the composite codisposal waste form. The formation of ettringite may be one of the principal reactions responsible for consolidation of the waste forms (along with noncrystalline calcium silicate hydrate formation which could not be observed by XRD). Ettringite was observed to decrease in abundance at long reaction times. Calcium aluminate monosulfate hydrate formed in the later stages of the fly ash reaction.
Microstructure of Cement Blends Including Fly Ash, Silica Fume, Slag and Fillers
Authors: Regourd Micheline 
Published: March 2011

ABSTRACTThe hydration of a blended cement through hydraulic or pozzolanic reactions results in heterogeneous polyphase materials. Because portland cement clinker is the major component in most cement blends, the microstructural development of portland cement hydrates, including C-S-H and pore structures, is first discussed. Slag, fly ash, silica fume and limestone filler cements are then compared to portland cement with regards to C-S-H morphology and composition, aluminate crystallization, cement paste interfaces and pore size distribution.
Leaching Behavior of Fossil Fuel Wastes: Mineralogy and Geochemistry of Calcium
Authors: Rai Dhanpat , Eary L. E. , Mattigod S. V. , Ainsworth C. C. , Zachara J. M. 
Published: March 2011

ABSTRACTA literature review [1] of the leaching behavior of inorganic constituents contained in fossil fuel wastes indicated that most of the available information deals primarily with (1) determination of the elemental composition of different wastes, (2) examination of the physical characteristics of waste solids, and (3) empirical leaching studies involving different solutions and procedures (e.g., water, acids, extraction procedure, toxicity characteristic leaching procedure). A comprehensive mechanistic approach and data are needed to predict accurately the composition of pore waters from fossil fuel wastes. An approach that relates the aqueous concentrations in leachates to solubility-controlling or adsorption-controlling solid phases- in the wastes is described. The behavior of calcium is used as an example to show the relevance of existing data to predicting leachate composition and to identify the type of data needed. The application of this approach to pore waters from flue gas desulfurization sludge shows that Ca concentrations can be accurately predicted from the nature of the Ca solids present and the thermo-chemical data descriptive of precipitation/dissolution and complexation reactions.
Consistency of Performance of Concretes With and Without Fly Ash
Authors: Hester Weston T. 
Published: March 2011

ABSTRACTFly ash and other pozzolans are increasingly used in concretes that must consistently achieve high compressive strength and other measures of performance. In contemporary design and construction practice, however, there is some concern as to whether or not use of commercial fly ash materials contribute to or reduce variations observed in field compressive strengths and properties of the fresh concrete. Regardless of its potential for improving the performance of the concrete, if the daily ongoing use of commercial fly ash will decrease the consistency of the concrete produced, the use of fly ash will be curtailed. In this paper, the experiences of geographically diverse, specific concrete suppliers using their respective sources of fly ash are summarized in detail. The nominal compressive strength of concretes, made with and without fly ash, are analyzed statistically. Special attention is given to moderate- and high-strength concretes. In conclusion, it is shown that concretes made with fly ash may not be more consistent than concretes with only portland cement.
Some Properties of Contrasting End-Member High Calcium Fly Ashes
Authors: Diamond Sidney , Olek Jan 
Published: March 2011

ABSTRACTHigh-calcium fly ashes with CaO contents >20% do not necessarily contain the glass type found to be characteristic of such ashes in previous results. Instead of this glass (asymmetrical x-ray maximum at 32 deg. CuK-alpha radiation), the fly ash may contain a lower calcium content glass (symmetrical x-ray maximum near 27 deg.) and a substantial content of crystalline CaO. The properties of a representative fly ash of each type are briefly illustrated, and the characteristics of fly ash pastes and of cement-fly ash pastes produced from the two fly ashes are examined.
An ESCA and SEM Study of Changes in the Surface Composition and Morphology of Low-Calcium Coal Fly Ash as a Function of Aqueous Leaching
Authors: Soroczak Myra M. , Eaton H. C. , Tittlebaum M. E. 
Published: March 2011

ABSTRACTThe reactivity of coal fly ash is dependent on the chemical composition of the surface. As reactions occur the ash particle size decreases and new material is available for reaction. This means that the near-surface chemistry can also be important. In the present study the surface chemistries of three ashes are determined by x-ray photoelectron spectroscopy both before and after exposure to a hydrating/leaching environment. Scanning electron microscopy is used to reveal ash morphology. The concentration of sulfur, found at the ash surfaces as a sulfate, and sodium decreased after leaching while the amount of iron and aluminum increased. Other elements, including calcium, increased and decreased with leaching depending on which ash was analyzed. Changes which occurred in the ash morphology after the removal of leachable elements are discussed.
Electrochemical Stability of Embedded Steel and Toxic Elements in Fly Ash/Cement Beds
Authors: Malek R. I. A. , Roy D. M. 
Published: March 2011

ABSTRACTThe electrochemical stability in fly ash/cement beds is of major concern to the durability of construction metals (iron or steel) embedded in the matrix as well as the stabilization (fixation) of toxic elements. The electrochemical stabilities were evaluated by measuring the redox potential as a function of both time and leach solution. For simulating the field conditions, the measurements were made on leachates of a prepared solution simulating rain composition in the area of application and results were contrasted to those obtained on leachates of standard deionized water. Two leaching techniques were used: the standard EPA-EP test; a test developed at MRL/PSU for simulating field conditions in which leaching fluids are pumped up a fly ash/cement column. The redox potentials (based on hydrogen scale), Eh's, were plotted vs. pH of the leachates and the regions of stability of various construction materials and toxic elements were predicted. Tafel plots were also constructed for iron in contact with different leachates, and its corrosion rate was estimated.
Projects of the Consortium for Materials Development in Space
Authors: Lundquist Charles A. 
Published: March 2011

AbstractThe Consortium for Materials Development in Space amalgamates private industries, the federal government, and universities for a common goal, commercial developments in space. The Consortium embraces research and development projects that benefit from unique attributes of space and that also rely on innovative applications of physical chemistry, material transport and their interactions. Three projects employ vapor transport of material from a solid source at one end of a sealed container to a growing crystal at the other end. The fourth and fifth projects have desired surface properties of materials as their objectives. In one of these, surfaces are electrodeposited, often with inert solid particles codeposited in the surface layer. The other project investigating surface properties makes use of the atomic oxygen environment outside a spacecraft. A surface exposed toward the direction of orbital motion is impacted by a beam predominantly of 5 electron volt oxygen atoms. This can produce unusual chemical reactions and surface morphology. The sixth project uses demixing of immiscible polymers in low-g to better understand the role of phase segregation in the properties of polymer blends and to accomplish the purification of materials by partitioning between two liquid phases.
The Use of Molten Salts as Physical Models for the Study of Solidification in Metals and Semiconductors
Authors: Koziol Jurek K. , Sadoway Donald R. 
Published: March 2011

AbstractProduct morphology in metal casting and semiconductor crystal growth is strongly influenced by the nature of the solid-liquid interface during solidification. Since in situ observation of solification in these technologically important systems is not possible, investigators have resorted to the use of physical models, such as water and organic liquids, which while they are transparent to visible light, suffer from the fact that their Prandtl numbers are too high. Molten alkali halides are better physical models in this respect, and are transparent to visible light. The purpose of the present study is to examine solidification in the LiCl-KCl system to determine if phenomena such as solute rejection can be observed by laser schlieren imaging.
Gravity and Conduction Driven Melting in a Sphere
Authors: Bahrami P A. , Wang T. G. 
Published: March 2011

AbstractThe 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.
Charged Drop Dynamics Experiment Using an Electrostatic-Acoustic Hybrid System
Authors: Rhim W. K. , Chung S. K. , Trinh E. H. , Elleman D. D. 
Published: March 2011

AbstractIn 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.