bluuebunny/crossref_metadata_2025 huggingface dataset:
The Strength and Ductility of Intermetallic Compounds: Grain Size Effects
Authors: Schulson E.M. , Baker I. , Frost H.J.
Published: March 2011

Since writing on this subject two years ago [1], a number of developments have occurred, particularly in relation to the mechanical properties of the L12 nickel aluminide Ni3Al. Some elucidate the nature of the yield strength and the extraordinarily beneficial effect of boron on low-temperature ductility. Some others expose, at least in part, the nature of the marked reduction in ductility at elevated temperatures. Another considers the mechanisms dominating creep deformation. Also during this period, contradictions have appeared: the relationship between the yield strength and the grain size, d, at room temperature has been contested, and opposing views of grain refinement on ductility have been reported.

This paper reviews these developments. Although broadly directed at intermetallic compounds, the discussion is specific to Ni3Al. The hope is that the knowledge and understanding gained about this compound will benefit the class as a whole.
Deformation of Single Crystalline Mn3Sn
Authors: Lee J. Y. , Pope D. P. , Vitek V.
Published: March 2011

Single crystalline Mn3Sn was chosen as a model material for a study of the deformation machanism of DO19 ordered alloys. Single crystals were grown by the Bridgman method in an argon atmosphere. Compression test specimens of six different orientations were cut from the bulk single crystals by electric discharge machining and polished for slip trace analysis. Compression tests were carried out in an Instron testing machine at a strain rate of 1.2 X 10−3 s−1 at temperatures ranging from 77 OK to 1180 oK. Tests at temperatures above 400 oK were performed in an argon atmosphere while those of lower temperatures were performed in air.

Preliminary results were obtained and analyzed in order to determine the temperature and orientation dependence of the operating slip systems and the yield stress. Basal slip was observed to be the dominant slip mechanism. Slip lines were observed on specimen surfaces compressed at low temperatures but such observations were difficult on specimens deformed at temperatures above 1000 OK due to surface contamination.

An anomalous positive temperature dependence of the critical resolved shear stress for basal slip was found, similar to that reported for octahedral slip in many intermetallic compounds with the Ll2 structure.
Fatigue of Intermetallic Compounds
Authors: Stoloff N.S. , Fuchs G.E. , Kuruvilla A.K. , Choe S.J.
Published: March 2011

The fatigue behavior of intermetallic compounds is reviewed. The effects of long range order, stoichiometry, test temperature and test environment on crack initiations high cycle fatigue lives and crack growth rates are emphasized. In the case of Ni3Al+B stoichiometry affects high cycle lives largely through the influence of aluminum on ductility and notch sensitivity. High cycle fatigue behavior of Fe3Al is dependent upon stoichiometry and temperature in a complex way which is connected with the formation of superlattice dislocations and with phase changes during high temperature exposure. Oxygen and hydrogen are shown to be detrimental to high cycle fatigue and crack growth in several compounds.
Deformation of the Intermetallic Compound Al3Ti and Some Alloys with An Al3Ti Base
Authors: Yamaguchi M. , Umakoshi Y. , Yamane T.
Published: March 2011

In this paper, firstly, the results of deformation experiments which have been made on Al3Ti and Al3Ti-base alloys are reviewed. Secondly, the possibility of the improvement of ductility of Al3Ti by alloying processes is discussed, and then possible alloying elements for this purpose are suggested. Thirdly, the oxidation resistance of Al3Ti is described and then possible future technological applications of Al3Ti are briefly discussed.
High-Temperature Fatigue Crack Propagation in P/M Ni3Al-B Alloys
Authors: Chang K.-M. , Huang S.C. , Taub A.I.
Published: March 2011

Ductile Ni3Al-B type intermetallic alloys show a unique fatigue crack growth behavior at elevated temperatures. A crack propagation mechanism has been investigated in an experimental P/M alloy by testing the alloys with different fatigue frequencies at 400°C. The Ni3Al-B intermetallic alloy shows a substantial time-dependence of fatigue cracl growth rate when tested in air. Under a given cyclic stress intensity, an order of magnitude difference of crack growth rate was observed by decreasing the fatigue frequency. However, such a time-dependence did not occur when the alloy was tested in vacuum. It is concluded that “dynamic” embrittlement in an oxidation environment is the major factor controlling the fatigue crack growth in ordered Ni3Al-B alloys at elevated temperatures.
Structure and Properties of Powder Metallurgy Ni3Al Alloys
Authors: Krueger D.D. , Marquardt B.J. , Field R.D.
Published: March 2011

A Ni3AI + B base composition and derivatives containing Hf, Zr, Nb, or Nb + Hf substitutions for Al were processed by powder metallurgy, consolidated by compaction + extrusion, and evaluated for mechanical properties. The mechanical property evaluation consisted of tensile tests performed in air and vacuum, and fatigue crack growth tests performed in air. Microstructures, test specimen fracture morphologies, and tensile and fatigue deformation features were also studied. Some of the substitutions improved certain properties, but none improved ductility. The discussion considers property-fracture morphology-deformation structure relationships.
Effect of Aluminum Addition on Ductility and Yield Strength of Fe3Al Alloys with 0.5 wt % TiB2
Authors: McKamey C. G. , Horton J. A. , Liu C. T.
Published: March 2011

Studies have been conducted of the mechanical properties of Fe3Al alloys containing 24 to 30 at.% Al, to which 0.5 wt% TiB2 was added for grain refinement. In tensile tests conducted at room temperature, it has been found that, as the aluminum content is increased, the yield strength decreases sharply from 760 to 310 MPa. The decrease in yield strength is accompanied by a four-fold increase in room-temperature ductility. Ordered iron aluminides (containing no disordered α phase) showed a clear increase in yield strength with temperature above 300°C. Their strength reached a maximum around 600°C, above which it decreased sharply. All these results will be discussed and correlated with stability of superlattice dislocations as a function of aluminum content.
Dispersoids in Intermetallic Alloys: a Review
Authors: Koch Carl C.
Published: March 2011

The existing work on structure and mechanical behavior of intermetallic alloys containing dispersed second phases — dispersoids — is reviewed. The dispersoids considered in the review are those given the conventional definition as inert, stable, insoluble phases in the matrix, such as oxides. The only detailed mechanistic studies of dispersoids in intermetallics have been carried out on the model material Cu3Au, and these did not include elevated temperature, eg. creep, mechanical behavior. A number of investigations on dispersoids in the potentially important elevated temperature materials — the aluminides — are reviewed. The materials discussed include FeAI, Fe3AI, NiAI, Ni3AI, and Ti3Al. Many of these studies are preliminary in nature and much more research anddevelopment is needed to allow for the design of intermetallic-dispersoid materials with improved fabricability and elevated temperature performance.
B2 Alulinides for High Temperature Applications
Authors: Vedula K. , Stephes J.R.
Published: March 2011

The B2 aluminides are currently being investigated for potential high temperature structural applications. Although they are not being as actively pursued as the titanium aluminides or the L12nickel aluminide, the B2 aluminides are very attractive from density gonsiderations. Several recent reviews of the potential for aluminides are available in literature [e.g Ref. 1,2]. Table I is a comparison of the titanium, nickel and iron aluminides of interest and shows that B2 NiAl and FeAl have the major advantage of lower densities than Ni3Al and Fe3Al. In addition, the melting point of NiAl is over 200K higher than convetitional nickel based superalloys. Hence, although low density is the prime driving force, at least in NiAl a temperature advantage is also possible. Both of these aluminides have the advantage of containing very inexpensive elements. In fact, the thrust towards the B2 aluminides evolved from a program aimed at conserving strategic aerospace materials at NASA Lewis Research Center. A recent thrust at NASA Lewis Research Center has been to consider these aluminides as matrix materials for fiber reinforced composite systems.
Selection of Intermetallic Compounds for High-Temperature Mechanical Use
Authors: Fleischer Robert L.
Published: March 2011

In the widespread search for structural materials for high temperatures, it is useful to first apply basic physical considerations to eliminate the least promising candidates. Certain basic quantities are indicators of some of the several properties that are demanded of hightemperature materials. Those properties are high strength and specific strength, high stiffness and specific stiffness, and low creep and thermal expansion coefficient. The basic quantities (structure-insensitive in that they vary little with processing history and consequent microstructural changes) which are chosen to measure these properties are melting temperature Tm, specific gravity ρ, and elastic moduli Cij. Fortunately the most readily available of these structure-insensitive properties, Tm and ρ, are the most useful. As Tm increases, the general trend is for stiffness and strength to increase and thermal expansion and creep to decrease. For space and aircraft applications, knowledge of ρ allows relative values of specific stiffness and specific strength to be estimated from the ratio Tm/ρ. Data for more than 280 intermetallic compounds have been collected and subdivided by crystal class so as to allow the most promising compounds and groups of compounds to be selected. The Ll2 structures tend to lie in the least desirable regions of Tm and ρ and therefore are not the first m candidates for maximizing high-strength at elevated temperatures. At present we have no simple structure-independent indicators of ductility and oxidation resistance--two other properties that are needed in hightemperature structural materials.
Grain Boundary and Surface Segregation in Boron Doped Ni3Al
Authors: White Calvin L. , Choudhury Ashok
Published: March 2011

Grain boundary segregation, and its effects on strength and ductility, play an especially important role in the performance of intermetallic alloys based on Ni3Al. The effect of a given segregant on grain boundary strength appears to be determined to some extent by its tendency to segregate to free surfaces. In this paper, we briefly review the available information on grain boundary and surface segregation in boron doped Ni3Al.
Processing Technology for Nickel Aluminides
Authors: Sikka Vinod K.
Published: March 2011

Ductile ordered intermetallic alloys of nickel aluminum or nickel aluminum chromium have been developed at the Oak Ridge National Laboratory (ORNL) by optimized additions of boron. These alloys show excellent elevated temperature mechanical properties and corrosion properties. However, in order for the alloys to find use in various applications, they should be fabricable by either the well established or innovative processing technologies. The present paper will discuss the details of fabrication technology being pursued at ORNL. The processes being investigated include powder consolidation by extrusion, powder consolidation by capping, isothermal forging of powder compacted material, twin-roller casting to thin sheet followed by cold-rolling, direct casting rod from liquid, extrusion of billets made by argon-induction melting and electroslag remelting processes, injection molding of powders, and hot isostatic pressing of powders. Relative merits of each process will be discussed. Mechanical properties data on products made by various processes will also be presented and compared.
Room Temperature Tensile Ductility in Powder Processed B2 FeAi Alloys
Authors: Crimp M. A. , Vedula K. M. , Gaydosh D. J.
Published: March 2011

It has been shown that it is possible to obtain significant room temperature tensile ductility in FeAl alloys using iron-rich deviations from stoichiometry. A comparison of the room temperature tensile and compressive behaviors of Fe−50at% Al and Fe−40at% Al shows that FeAl is brittle at higher Al contents because it fractures along grain boundaries before general yielding. Lower aluminium contents reduce the yield stress substantially and hence some ductility is observed before fracture.

Addition of boron results in measurable improvements in ductility of Fe−40at% Al and is accompanied by an increase in transgranular tearing on the fracture surface, suggesting a grain boundary strengthening mechanism.

Increasing the cooling rate following annealing at 1273 K results in a large increase in the yield strength and a corresponding decrease in ductility.
High Temperature Mechanical Behavior of Some Advanced Ni3Al
Authors: Hsu S. E. , Hsu N. N. , Tong C. H. , Ma C. Y. , Lee S. Y.
Published: March 2011

High temperature mechanical properties of various Zr and Cr strengthened single phase Ni3Al are investigated, with emphasis on the ability of each element to elevate Tp, the temperature corresponding to the peak yield strength. It is observed that Zr is a very effective strengthener, more so below Tp than above it, while a combination of Cr and Zr is capable of shifting Tp to a higher temperature. The combination results in an effective improvement of the rupture strength of Ni3Al. The strengthening mechanisms of each element will be discussed in this paper.
Modeling of Antiphase Boundaries in L12Structures
Authors: Sanchez J.M. , Eng S. , Wu Y.P. , Tien J.K.
Published: March 2011

The thermodynamic properties of conservative (111) antiphase boundaries in L12ordered structures are modeled using the tetrahedron approximation of the cluster variation method. The concentration and long-range order parameter profiles are determined as a function of temperature and composition of the bulk alloy. Characteristic wetting transitions, with a macroscopic disordered layer growing from the antiphase boundary as the transition temperature is approached, are found for all cases investigated. The effectof antiphase boundaries on the disordering of ordered alloys and on the gliding of superdislocations are discussed.
Fim/atom Probe Studies of B—doped and Alloyed Ni3Ai
Authors: Sieloff D.D. , Brenner S.S. , Burke M.G.
Published: March 2011

Field—ion microscopy and atom probe microanalysis have been used to determine thestructure and chemistry of grain boundaries in ductile, recrystallized Ni3Al containing 0.23 at % B (500 wt.ppm). The results indicate that the boron concentration fluctuates along the boundary plane and that the boron enriched zone is wider than expected from equilibrium—type adsorption. It was also found that boron lowers the aluminum concentration of some of the boundary regions.
Improving Signal-to-Noise Limits in High Resolution Transmission Electron Microscopy
Authors: Gibson J.M. , McDonald M.L.
Published: March 2011

Signal-to-noise ratios for Si <110> lattice images are measured for a variety of different specimen preparation techniques, including ion-milling, chemical polishing, cleavage and in-situ surface cleaning by heating. The noise levels are significantly lower in the latter, possibly permitting new classes of experiments in image quantitation and impurity imaging.
Annealing Effects in Ion Bombarded GaAs: Raman Measurements
Authors: Burns Gerald , Dacol F. H. , Baglin J. E. E. , Wie C. R. , Burstein E. , Cardona M.
Published: March 2011

The surface layer of single crystal GaAs that has been bombarded with high energy (2-15 MeV) ions is strained and contains many defects, but it remains crystalline. We have studied the isochronal annealing behavior of this layer using phonon shifts and widths, which were detected by Raman measurements. We do not find any sharp annealing stages to 500 C, at which temperature the phonons have returned to their positions in the unbombarded crystals. These results are consistent with the idea that the phonon shifts are primarily due to antisites and their complexes with other primary defects. However, other extended defects may still be present, and the Raman data show some evidence for this.
The Temperature Dependence of Ion Beam Mixing of Zr on A12O3
Authors: Farlow G. C. , Withrow S. P. , Easton D. S.
Published: March 2011

Three hundred angstrom Zr films were deposited on A12O3 substrates and irradiated with 300 keV Xe ions to a dose of 1 × 1016 /cm2. The irradiation was carried out at 77 K, 300 K (ambient temperature), and 800 K. Changes in the deposited film and the Zr-A12O3 interface were examined by comparing Rutherford backscattering spectra from irradiated and unirradiated regions of the samples. Ion beam induced reactions were observed at all three temperatures. The systematics of the temperature dependence of ion beam mixing are discussed.
Atomic Displacements Around Nitrogen Interstitial Impurities in Ta and Nb
Authors: Rao S. , Savino E. J. , Houska C. R.
Published: March 2011

The core as well as the long range elastic displacements around N octahedral interstitial atoms in Ta and Nb are modelled using the Green Function – Kanzaki force method. The theoretical calculations are compared with experimental attenuation factor and diffuse scattering data, reported in the literature, for both N in Nb and N in Ta [1,2,3]. It is shown that a third neighbor radial Kanzaki force model is needed to explain the experimental findings, and the long range elastic displacement field is non-spherical.
X-Ray Topographic Methods for Stress-Strain Tensor Analyses of Crystals
Authors: Weissmann S. , Mayo W.E. , Kalman Z.H.
Published: March 2011

Two methods for the strain tensor analysis of crystals will be presented. One of them is based on a modified x-ray back-reflection divergent (BDB) method. By the interposition of a wire grid between crystal and film, a computer-aided ray tracing technique was developed resulting in simultaneous precision measurements of d-spacings of several (hkl) planes. The strain input data for the tensor analysis are = (dn-dn°)/dn°, where dn° is the d value of the corresponding unstrained (hkl) planes, the precision of the strain measurements being ± 0.02%. The strain tensor εij obtained from the strain components, referred to the cubic coordinate system, is calculated by a least square method and the principal strains and their directions are determined. From the principal strains and known elastic constants the complete stress-strain configuration as well as the stored elastic energy are determined. An example of application to the elucidation of strains in premartensitic Al Ni crystals will be given. The other x-ray method presented is based on a computer-aided rocking curve analysis (CARCA) method, which is particularly well suited for the tensor analysis of non-uniform strain distribution in epitaxially grown microelectronic materials. This method determines not only the full elastic strain tensor, but also its distribution about a strain center with a resolution of approximately 60 Pm. As an example the strain distribution in an InGaAsP epitaxial film on an InP substrate is presented.
The Structural and Electrical Characterization of Copper Decorated Boundaries in Silicon Bicrystals
Authors: Miller F.S. , Betrabet H.S. , Clark W.A.T.
Published: March 2011

Silicon bicrystals have been fabricated by sintering together single crystal {001} and {111} wafers with low angle misorientations In the range of 0.5 to 3.0 degrees. The interfaces in these bicrystals contain regular arrays of screw dislocations with observed spacings of 10 to 40 nm. The dislocations were decorated with copper which was first sputter-deposited on an external surface, then diffused into the interface by annealing the bicrystal at 400°C for 15 minutes. Analytical electron microscopy was used to characterize the spacing, orientation, and copper concentration of these dislocation arrays. The electrical properties of both decorated and undecorated bicrystals were determined using a two-probe step I-V method, and the behavior of both types of bicrystals compared.
Multimodal Time Delays in the Photoplasticity of Mercury Cadmium Telluride
Authors: Pellegrino Joseph , Partridge Julian P. , Son Yo Ho
Published: March 2011

The plastic response of deforming crystals of mercury cadmium telluride to light occurs with a time delay that depends on wavelength, temperature, and bias voltage. The time delay exhibits a temperature dependence which increases as the temperature is lowered, andis approximately 60 seconds at 20°C. A detailed examination of a number of measurements of the time delay at constant temperature reveals that the time delay falls into one of four separate peaks. These peaks shift with temperature with an overall activation energy of approximately 0.2 eV. Furthermore, the photoplastic responses of a given crystal indicate that softening is observed roughly 40% of the time and hardening the remaining 60%. It has also been observed that the relative positions of the time delay peaks can be markedly affected by a static bias voltage.

A model which explains these observations involves the coulombic interaction of charged point defects with jogs on dislocations. The model predicts four separate time delay peaks as well as the correct ratio of hardening to softening.
Structure Determination of Tilt Boundaries in Gold by High Resolution Electron Microscopy
Authors: Krakow William , Smith David A.
Published: March 2011

A number of tilt grain boundaries prepared from evaporated gold thin films have been investigated by high resolution transmission microscopy. When the grain boundary is parallel to the electron beam and the beam is parallel to a low index rotation axis such as [110] or [001]it is possible to identify atomic positions at the cores of these boundaries as demonstrated here by a Σ = 3 70.5°/[110], (112) growth twin. In many cases it is not possible to make a full atomistic structure determination because the specimen does not have translational periodicity in the beam direction. This may be because the boundary plane is not parallel to the beam or the specimen contains dislocations which have a component of Burgers vector parallel to the beam. Examples are given of various low angle boundary structures in goldwhere there are complications because of the three dimensional nature of their structure.
Interaction between Domain Walls and Point Defects in Tetragonal BaTiO3
Authors: Boser O. , Beshers D. N.
Published: March 2011

Dopants in ferroelectric materials affect the dielectric constant and the shape of the hysteresis loop. To understand and quantify these effects it is necessary to calculate the interaction between dopant and domain wall. In the following the dopant ion is modelled as an elastic dipole. The stresses surrounding a 180° domain wall are calculated in analogy to calculations in the magnetic case for Bloch walls. It is assumed that electrostrictive effects control the strains and that the spontaneous polarization does not rotate but decreases to zero at the center of the domain wall and increases in the opposite direction on the other side of the domain wall. The calculations are made assumingisotropic elastic constants. It is found that only elastic dipoles oriented in the planeof the domain wall interact with it. The interaction forces as a function of perpendicular distance between wall and dipole show an antisymmetric characteristic.
Surface Dynamics of Small Particles
Authors: Ajayan P.M , Marks L.D , Dundurs J.
Published: March 2011

We investigate the energetics of structure changes in small particles, a phenomena recently observed by high resolution electron microscopy. The energy variations during transformations from a single crystal to symmetric and asymmetric decahedral multiply twinned particle (MTP) structures are evaluated. We examine briefly a few possible energy gain mechanisms during the particle-beam interaction which enable the particles to cross the activation energy barriers and fluctuate between various local energy minima of the morphological potential energy surface.
Surface Faceting of (110) GaAs: Analysis and Elimination
Authors: Parechanian-Allen L. , Weber E.R. , Washburn J. , Pao Y.C.
Published: March 2011

A systematic study has been made on (110) GaAs grown by molecular beam epitaxy. This work represents the first systematic investigation of commonly observed faceting on the (110) GaAs surface which has led to the consistent elimination of the defects. This study involved the analysis of facet geometry, a kinetic model of initial facet formation, and the electrical and optical analysis of facet free (110) GaAs. The latter was obtained with proper growth conditions and a Ga rich surface exposure from a GaAs substrate angled 6° toward (111)Ga.
Nuclear Reaction Spectroscopy of Vibrational Modes of Solids
Authors: Zinke-Allmang M. , Kalbitzer S. , Weiser M.
Published: March 2011

The effects of target-atom vibrations on nuclear reaction kinetics have been examined. In particular, Doppler broadening of resonance-type and elastic- scattering reactions has been considered in detail. Depending on the specific process parameters, the resulting energy widths can be many orders of magnitude larger than the energies of the vibrational states of the target solid. Comparison of experimental results on a hydrogen-bearing thin target with the theoretical predictions shows excellent agreement. We will show the importance of this effect in hydrogen profiling measurements and point out the feasibility of vibrational spectroscopy on hydrogen in solids.
Investigation of the Resonant Vibration Modes of Self Interstitial Atoms in Al by Diffuse Inelastic Neutron Scattering
Authors: Urban R. , Ehrhart P. , Chilling W. , Schober H.R. , Lauter H.
Published: March 2011

Single crystals of Al were irradiated up to 480 ppm of Frenkel defects using a specially developed irradiation facility for high dose electron irradiation of large samples below 20 K. Diffuse inelastic neutron scattering measurements have been performed at these samples to study the dynamics of single self interstitial atoms. The measurements were made at 6 K on the sample before annealing and after annealing at 46 K (above stage I) and at 300 K (after complete recovery). The irradiated samples showed a significant increase of the inelastic scattering intensity at transferred energies between 0.7 and 2 THz. By comparison with the results of computer calculations the different frequencies of the energy loss spectrum could be attributed to the different vibration modes of interstitial atoms. The frequencies of the most significant modes of the self interstitial atom are determined to be υ = 0.75 THz and υ = 1.35 THz for the translation-(A2u) and libration-(Eg) mode, respectively.
Analysis of Oxide Surfaces by High Resolution Transmission Electron Microscopy
Authors: Krakow W. , Castano V.
Published: March 2011

We have investigated the surface structure of oxides with low atomic number metallic components (Cu and Al) using two different high resolution electron microscopy techniques. First, using flat-on microscopy normal to the surface, we have studied the epitaxy of vapor deposited Cu on single crystal (110) and (111) surfaces of Au and the subsequent oxidation of the Cu under ambient conditions. Three structural variants of (110) oriented Cu2O were found relative to the underlying ( 11I) Au film and the oxide surface has a shifted, 1/2[110], (1 × 1) surface reconstruction. A (211) Cu2O structure was found for the (110) Au film orientation. This case has two structural variants at 90° to each other where one of these variants exhibits surface roughness of ∼5Å. The second structure has atomic step heights of ∼6Å, and a rectangular surface supercell structure of ∼3.0Å × 7.39Å due to (211) bulk lattice layers.
Atomic Structure of Binary Alloy Surfaces
Authors: Davis H. L. , Noonan J. R.
Published: March 2011

After 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

The 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

The 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

The 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

The 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

The 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

A 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

Proton 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

Volume 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

The 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.
Correlations of Chemistry and Mineralogy of Western U.S. Fly Ash
Authors: McCarthy G. J. , Manz O. E. , Johansen D. M. , Steinwand S. J. , Stevenson R. J.
Published: March 2011

Fly ashes derived from low-rank coals mined principally in Montana, Wyoming and North Dakota are being studied by the Western Fly Ash Research, Development and Data Center [1]. Previous studies of the mineralogy of western U.S. fly ash by McCarthy et al. [1–3] using x-ray diffraction (XRD) form the framework of the present study. A database of chemical, mineralogical and physical properties, along with precursor coal characteristics, is being assembled. Based on studies to date of several hundred fly ash samples derived from lignite and subbituminous coals, as well as from several bituminous ashes, correlations of chemistry and mineralogy have been hypothesized and are being tested. These correlations are discussed below.
Thermal Characterization of Coal Ash Powders: Heat Capacities and Minimum Sintering Temperatures
Authors: Ledesma R. , Compo P. , Isaacs L. L.
Published: March 2011

Ashed 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

Cementitious 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

The 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

A 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

Fly 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

High-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

The 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

The 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.