bluuebunny/crossref_metadata_2025 huggingface dataset:
Displacive Phase Transformations in Zirconia-Based Ceramics
Authors: Muddle B. C.
Published: March 2011

A review is presented of experimental observations of the mechanism and crystallography of the martensitic tetragonal to monoclinic transformation occurring both in dispersed tetragonal ZrO2 particles in partially stabilized zirconia and in polycrystalline tetragonal zirconia. Preliinary results of determination of the orientation relationship and habit plane for the stress-activated transformation in a CeO2 –stabilized TZP ceramic are reported and compared with predictions of the crystallographic theory for the transformation. This orientation relationship is such that (100)m//(100)t and [001]m//[001]m, and for this variant of the orientation relationship the habit plane is approximately ( 301 )t. These results are in good agreement with theoretical predictions. Progress in the application of the formal theory of martensitic transformations to the transformations in both types of system is examined critically and implications for theories of transformation toughening are discussed.

Attention is also given to tetragonal orthorhombic and orthorhombic monoclinic transformations occurring in Zro2 particles in thin foil specimens of partially stabilized zirconia. Formation of a metastable orthorhombic phase appears a possible, but not essential, intermediate stage in the tetragonal to monoclinic transition. However, present evidence strongly suggests that the orthorhombic structure only occurs in those particles experiencing the relaxed matrix constraints typical of thin foil specimens.
The Stress Induced Transformation by Fracture in Y2 O3 Containing Tetragonal Zirconia Polycrystals
Authors: Katagiri G. , Ishida H. , Ishitani A. , Masaki T.
Published: March 2011

The stress induced transformation in Y2 O3 containing tetra gonal zirconia polycrystals (Y-TZP) by a three-point bending test was studied by Raman microprobe. Transformation zone extends to as large as 100μm in the starting side of the fracture and the transformation zone size becomes smaller in the direction from the starting to the ending side of the fracture. The transformation zone size has no correlation with fracture toughness and Y2O3 content. It is suggested that the transformation plastici y may operate in the initial stage of the fracture. The obtained results have remarkable contrast with the case of the fracture of a pre-indented specimen. The transformation behavior of defect-dominating fracture is also discussed.
Change of D/Tc, Ratio During Heat Treatment of Fe90-xSixB10 Amorphous Alloy
Authors: Minor Wladyslaw
Published: March 2011

The ferromagnetic transition temperature Tc for Fe-Si-B amorphous alloys with iron concentration exceeding 75 atomic percent changes monotonically with the annealing time. This change of Tc is accompanied by a drastic change of the magnetic excitation spectrum measured by means of low angle neutron inelastic scattering. It was observed that a small amount of α-Fe(Si) precipitated in an amorphous matrix during the heat treatment even at relatively low temperatures, leading to a decrease of the spin-wave stiffness constant D. Because at the same time T, increases, the D/Tc ratio (which is about 0.3 for “as quenched” Fe-Si-B system) decreases abruptly.
The Effect of Surface on the Kinetics of Crystallization of Pd-Si Glassy Metals
Authors: Calka A. , Radliński A. P.
Published: March 2011

Introduction

The isothermal devitrification by nucleation and growth of metallic glasses is usually analysed using the Johnson-Mehl-Avrami (JMA) equation: where x is the volume fraction crystallized after time t, K is a thermally activated rate constant, τ is the nucleation lag time, and n is the so-called Avrami exponent. If the nucleation conditions and growth morphology remain unchanged during the crystallization then n is a constant. There is ample experimental evidence that for the Pd-Si system the growth process is either eutectic or interface-controlled. Therefore, one expects n=3 for crystallization on pre-existing nuclei (zero nucleation rate) and n=4 for crystallization at constant nucleation rate, both for three-dimensional growth. When the growth dimensionality is decreased by one these values decrease stepwise by one as well.
Electronic Properties of Icosahedral Mg-Ai-Zn Alloys
Authors: Baxter David V. , Ström-Olsen J. O.
Published: March 2011

The resistivity and magnetic susceptibility of icosahedral Mg32(Al1-xZnx)49 have been measured for compositions between x=0.5 and x=0.69. Both quantities exhibit a stronger compositional dependence than do the same properties of the similar metallic glass Mg1-xZnx. The resistivity at low temperatures displays the classic behaviour as a function of temperature and magnetic field associated with the phenomenon of weak localization, and we are able to use this fact to measure the absolute resistivity in a way which is independent of sample geometry.
On the Glass Formation in Systems Forming Icosahedral Quasicrystals
Authors: Bendersky Leonid A. , Ridder Stephen D.
Published: March 2011

Rapidly solidified micron and submicron size droplets of Al-14 a/o Mn have been used to study the possibility of glass formation and nucleation behavior of icosahedral phase. Homogeneous nucleation of icosahedral phase is assumed, based on the high grain density (>1015 mm−3). Extremely low nucleation resistance of icosahedral phase can be understood when possible topological similarities between liquid and icosahedral quasicrystal structures are considered. Configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that Al-Mn “glass” probably has a microquasicrystalline structure.
Surface Crystallization of Metal-Metalloid-Glasses
Authors: Küster Uwe , Punge-Witteler Barbara
Published: March 2011

Preferential crystal nucleation and growth may occur at surfaces because of a decrease in surface energy, a greater ease of diffusion and stress relaxation or a change in surface composition. Segregation as well as selective oxidation are assumed to possess the strongest influence on surface crystallization.

Crystal nucleation and growth at both surfaces of melt-spun ribbons has been studied systematically in a number of Ni-B and Co-B glasses by means of quantitative light and electron microscopy. Crystal diameter distributions indicate a transient type heterogeneous nucleatior mode for surface crystallization. The results will be compared wi th crystallization in the bulk.
Icosahedral Symmetry and Magnetism
Authors: McHenry M. E. , O– R. C.
Published: March 2011

We examine the implications of icosahedral symmetry on electronic structure and especially magnetic properties in alloys. From simple geometric and synmetry arguments to detailed electronic structure calculations it is clear that icosahedral symmetry carries important consequences for magnetism in a wide range of alloys. Enhanced local magnetic moments, reduced anisotropies and new magnetic domain structures are predicted. We also propose a course of further study focussed on producing a strongly magnetic quasicrystalline phase and we describe interesting new metastable Co-Er phases produced in the preliminary phase of this investigation.
On Dominant Factors for C-Axis Orientation of Co-Cr Films in Sputter-Deposition
Authors: Nakagawa S. , Niimura Y. , Naoe M.
Published: March 2011

Co-Cr thin film with the excellent c-axis orientation is required as the media for ultra high density perpendicular recording. There are two dominant factors that affect the c-axis orientation. One is the process condition such as argon gas pressure and targets-substrate distance L which change the kinetic energies of arriving atoms on substrate. The concept of mean collision number was introduced to get better understanding the relation between c-axis orientation and kinetic energy of particles. In this study, Facing Targets Sputtering (FTS) system was used because of its superiority as the plasma free sputtering. And the other is the interfacial effect between the substrate and the deposited film. In order to investigate the Interfacial effect, it has been performed to prepare the CoCr(500Å)/CoCr(500Å) double layer. By controlling the argon gas pressure, thin layers with different c-axis orientation can be easily obtained. When the c-axis well oriented 1st layer was used as the under layer, good c-axis orientation of 2nd layer was obtained even at the high argon gas pressure at which c-axis orientation in the single layer is poor. However, this improvement of c-axis orientation did not continue with the increase of the thickness of 2nd layer. It was clarified that there was the critical thickness in the 2nd layer affected by the c-axis orientation of under layer. As a result, it was concluded that the process condition was the superior dominant factor for c-axis orientation.
Effects of Elastic Anisotropy on the Anomalous Yield Behavior of Cubic Ordered Alloys
Authors: Yoo M. H.
Published: March 2011

The positive temperature dependence of yield stress in certain L12 and B2 alloys, e.g. Ni3Al and β′-CuZn, is analyzed on the basis of the nature of dislocation dissociations predicted by anisotropic elasticity theory. In the case of Ni3Al, the torque due to the tangential component of the elastic interaction between two superpartials is a major driving force for either the cross-slip pinning model or the force couplet model. The corresponding torque term is relatively unimportant in the B2 structure. The core transformation of individual superpartials may be important for the anomalous increase of yield stress in β′-CuZn.
The Segregation of Boron and Its Effect on the Fracture of An Ni3Si Based Alloy
Authors: Oliver W. C. , White C. L.
Published: March 2011

It is now well established that microalloying additions of B to Ni3Al drastically reduce low temperature grain boundary fracture and consequently increase the ductility of this intermetallic compound. One possible explanation for such effects involves the relationship between boron segregation to grain boundaries and free surfaces, and the resulting effect of such segregation on the cohesive energy of the grain boundaries. This study involves the extension of these concepts to an alloy based on Ni3Si. Auger spectroscopy has been carried out on fractured grain boundaries, grain interiors, and free surfaces to determine how B segregates in Ni3(Si,Ti). The consequences of the segregation of B on the cohesive energy of grain boundaries in Ni3Si based alloys are discussed.
High Temperature Ordered Intermetallic Alloys
Authors: Pope D. P.
Published: March 2011

This paper is intended to be a general introduction to this conference and is therefore not a review of the state of our current knowledge. Instead, it will address questions like the following: Why are intermetallic compounds interesting? What alloys are being studied, and which are being ignored? Since most research work is now being performed on L12 alloys, with by far the greatest emphasis on Ni3Al, the balanceof the paper will concentrate on strengthening mechanisms and mechanisms of ductility control in Ni3Al, pointing out the interesting questions and controversies which arose during this conference.

The conclusions to be drawn from this paper are that ordered intermetallic alloys are very valuable materials for high temperature use, but engineers probably must become more sophisticated in the use of materials with limited ductilities at low temperatures before intermetallics will gain widespread usage. Furthermore, additional research needs to be performed on more complex intermetallic compounds than L12 since L12 compounds, as a group, do not have particularly high melting temperatures. However,since alloys with complex structures, e.g. Laves phases, are well known for their brittleness at low temperatures, it is all the more important that the properties of such alloys be studied and methods found to improve their ductilities.
SiC Reinforced Aluminide Composites
Authors: Brindley Pamela K.
Published: March 2011

The tensile properties of SiC fiber, Ti Al+Nb and SiC/Ti3Al+Nb composite have been determined from 300 to 1365K. The Composite results compared favorably to rule-of-mixtures (ROM) predictions in the intermediate temperature regime of 475 to 700K. Deviations from ROM are discussed. Composite tensile results were compared on a strength/density basis to wrought superalloys and found to be superior. Fiber-matrix compatibility was characterized for the composite at 1250 and 1365K for 1 to 100 hours.
High Temperature Oxidation and Corrosion of Metal-Silicides
Authors: Meier G.H.
Published: March 2011

The high temperature oxidation of metal silicides is briefly reviewed followed by a description of recent experiments on the oxidation and mixed oxidant corrosion of Ni- and Fe-silicides. The oxidation kinetics are related to the structure and composition of the oxide films formed under various exposure conditions. Finally, the effects of pre-formed SiO2 films on minimizing the corrosion of Ni- and Fe-base alloys in sulfur-bearing gases are presented.
Calculation of the Defect and Interface Properties of Ni3Al
Authors: Foiles Stephen M.
Published: March 2011

The structure and energetics of point defects, surfaces and grain boundaries in Ni3A1 are investigated using the Embedded Atom Method. The approach is shown to reproduce the experimental phase diagram of the Ni-Al system and the elastic properties of Ni3AL. The vacancy and anti-site defect energies are calculated and used to predict the vacancy concentration as a function of bulk composition. The preferred geometries and energies of the low index surfaces are also computed. The equilibrium structure of certain ideal grain boundaries are computed by Monte Carlo computer simulations as a function of bulk composition. It is found that the boundaries act as a sink for anti-sitedefects and the degree of ordering at the boundaries is strongly affected by the bulk composition. The cohesive energy of grain boundaries in Ni3A1 is computed and is found to be comparable to that for pure Ni.
Antiphase Domain Boundary Tubes in Ordered Alloys
Authors: Hazzledine P.M. , Hirsch Peter
Published: March 2011

APB tubes have been observed in both a B2 and an L12 ordered alloy by means of weak beamtransmission electron microscopy. The tubes are attached to near—edge dislocations, either to single superdislocations or to superdipoles. The majority appearto have been formed by cross slip of screw dislocations. A computer model of the cross slip process in B2 alloys is described. The tubes formed by cross slip drag on edge dislocations and are capable in principle of explaining the extra work hardening shown by ordered over disordered crystals. The temperature and orientation dependence of the work hardening are similar to those of the proof stress which is also thought to be controlled by cross slip. This new mechanism of work hardening is shown to give order of magnitudeagreement with experiment.
Impurities in SiO2: Atomic States of Phosphorus and Arsenic
Authors: Rhodes H. E. , Apai G.
Published: March 2011

We have studied the atomic states of arsenic (As) and phosphorus (P) in SiO2 using X-ray photoelectron spectroscopy (XPS). Silicon dioxide implanted with As or P shows multiple XPS core level peaks corresponding to the impurity atoms located in two distinct atomic sites. The binding energies of the two arsenic 3d core levels occur at 45.8 and 42.3 eV and the two phosphorus 2p core levels occur at 134.7 and 130.3 eV. When the implanted oxides are annealed in an oxygen ambient between 900°C and 950°C, only the highbinding- energy peaks of P and As are observed. This identifies the highbinding- energy core level peaks as being associated with the impurity (P or As) on silicon sites. Annealing in nitrogen at 950° C results in an increase in the low-binding-energy signal. The low-binding-energy peaks are associated with the impurity (P or As) bonded to silicon neighbors. The relative amounts of dopants in silicon and oxygen sites depend on ambient purity and processing details. Reference to previous work shows that the presence of As or P on silicon sites in SiO2 corresponds to a fast diffusing state whereas As or P on oxygen sites corresponds to a slow diffusing state [1].
Grain Boundary Dislocations in GaAs
Authors: Smith D.A. , Krakow W.
Published: March 2011

A preliminary survey of the dislocation structures of grain boundaries in Bridgman grownpolycrystalline GaAs suggests that many of the phenomena observed in grain boundaries inface centered cubic metals, silicon and germanium also occur in boundaries of a polar semiconductor. Our experiments show that low angle grain boundaries are comprised of crystal lattice dislocations and deviations from coincidence orientations are accommodated bysecondary dislocations; specifically, in twins, the a-fringe technique reveals that there are multiple structures where the different domains are separated by partial grain boundary dislocations.
Grazing Incidence X-Ray Scattering Study of Surface Defects
Authors: Liang K. S. , Eisenberger P.
Published: March 2011

Grazing incidence x-ray scattering is emerging to become an important structural probe for surface and interface studies, especially in conjunction with the development of high brilliant synchrotron sources. In this paper, we give a brief review of the experimental principle and examples of how the technique can be applied to study surface defects.
Detection of Near-Surface 52Cr Segregation in Irradiated 51V(Cr) By Rbs
Authors: Rehn L. E. , Baldo P. M.
Published: March 2011

Irradiation at elevated temperatures of V(Cr) alloys is known to create a near-surface layer of nonequilibrium Cr enrichment. Highly reproducible RBS spectra were accumulated from a V-15%Cr alloy irradiated at 750°C, and from unirradiated portions of the same specimen. Differences between these spectra are used to demonstrate the high sensitivity of conventional RBS techniques for determining near-surface segregation behavior. Sensitivities obtained utilizing differences in the acquired spectra are much higher than those typically assumed for RBS measurements. Using 1.8 MeV 4He, and conventional RBS equipment and scattering geometries, segregation of < two atomic layers of 52Cr in 51V- 15at.%Cr over a depth of ∼5 nm has been observed.
A Comparison of Small Angle Neutron Scattering and X-Ray Diffraction Studies of Cobalt Precipitates in A Cu-0.95 at. % Co Alloy
Authors: Spooner S. , Iida S. , Larson B. C.
Published: March 2011

A detailed comparison of small-angle scattering (SANS) and large angle x-ray diffraction methods of characterization of precipitates was undertaken. Cobalt-rich precipitates on the order of 50 Å developed after a 17 hour anneal at 570°C were studied in a single crystal sample with SANS and with diffuse x-ray scattering near the (400)Bragg peak. Each scattering data set was analyzed independently in terms of a distribution of precipitate sizes; a detailed comparison is made of the size distribution obtained. A small interparticle interference effect is seen.
Arups Studies of the Interaction of Co with the Interface States for Strained-Layer Cu on Ru 0001)
Authors: Houston J. E. , Peden C. H. F. , Feibelman P. J. , Hamann D. R.
Published: March 2011

During the growth of the first monolayer, Cu has been shown to form in 2d islands pseudomorphic to the Ru 0001) surface under a tensile strain of -6%. The chemical behavior of such films has been found to be unlike that of either of the pure elements both from the standpoint of catalytic activity and molecular adsorption properties. In addition, these strainedlayer films have unique electronic properties. Specifically, we have identified a set of interface and surface states near the K point in the surface Brillioun zone. Here are shown new results concerning the behavior of the interface states with respect to CO adsorption. Specifically, CO is found to attenuate all Cu/Ru ARUPS structures except those due to the antibonding components of the interface states and these components move to higher binding energy with CO coverage. An analysis of these results, based on the properties of the interface states, indicates that there is negligible direct interaction between the CO orbitals and the metal d states. The increased bonding that is seen for CO on Cu/Ru compared to CO on Cu is suggested to result from an enchanced polarizability of the Cu 4s states due to the proximity of the Ru substate.
The Characterization of Thin Platinum Films on Alumina
Authors: Altman E. I. , Gorte R. J.
Published: March 2011

Industrial metal catalysts are usually in the form of small metal particles supported on a porous oxide. The typical size of these metal particles ranges between 1.0 and 10.0 nm and it is well known that the particle size and the oxide substrate can affect the catalytic properties of the metal for some important reactions[1]. Previous work with adsorption on small particles has indicated that desorption temperatures[2–4] and the ability to dissociate CO[5,6] can also be affected by the particle size. To further investigate these size and substrate effects, we have examined the adsorption properties of several simple gases on small Pt particles supported on alumina using temperature programmed desorption (TPD). We will show that the desorption curves for CO, H2, and NO on these particles are very similar to curves measured on single crystals.
Potassium Adsorption on Pt(111) and its Effect on Co Chemisorption
Authors: Greenlief C. Michael , Radloff Patricia L. , Akhter Sohail , White J. M.
Published: March 2011

Temperature programmed desorption (TPD) and secondary ion mass spectrometry (SIMS) have been used to study the chemisorption properties of carbon monoxide on potassium predosed Pt. SIMS cluster ions (such as K+, K2+, KO+ and KCO+) were monitored to probe, K-CO interactions. Large changes in the SIMS yields are observed as the potassium coverage is varied. The SIMS results are correlated with previous work function change and TPD studies. Temperature programmed secondary ion mass spectrometry of potassium-containing ions indicates a local interaction between potassium and CO molecules.

As typically observed on transition metal surfaces, two different CO TPD states are observed. The lower temperature state shifts to higher temperatures with increasing potassium coverage and to lower temperatures with increasing CO exposure. The high temperature CO state builds in with increasing potassium coverage and is accompanied by simultaneous potassium desorption. Evidence for the occurrence of both long-range (indirect) and short-range (direct) potassium effects on adsorbed CO is presented.
Oxygen Adsorption on and Oxidation of NiAl Surfaces
Authors: Zehner D. M. , Gruzalskia G. R.
Published: March 2011

Oxygen adsorption on and the eventual oxidation of the (100), (110), and (111) surfaces of NiAl was studied extensively using a variety of surface sensitive techniques. While the initial rate of uptake at 22°C varied significantly with orientation and surface composition, in all cases it was possible to form an overlayer region containing the equivalent of several monolayers of oxygen. No ordered overlayers were observed. Information about the chemical bonding was obtained from changes in core-level binding energies. Examination of the Al 2p region showed evidence for two different oxide environments, depending on surface treatment. Comparison of these results with those for both Ni and Al clearly shows effects due to alloying.
Second Harmonic Generation from Alkali Thin Films on AG(110)
Authors: Song K. J. , Heskett D. , Urbach L. , Dai H. L. , Plummer E. W.
Published: March 2011

The sensitivity of second harmonic generation at interfaces has been utilized to probe the spatial and frequency dependence of the local field generated near the surface of a nearly free electron metal by an externally imposed electromagnetic field. The longitudinal screening field was found to oscillate with a wavelength on the order of 10Å and to propagate into the bulk several layers deep.
Electronic and Vibrational Properties of Single Crystal Surfaces of NiAl
Authors: Lui S.-C. , Mundenar J. M. , Plummer E. W. , Mostoller M. E. , Nicklow R. M. , Zehner D. M. , Ford W. K. , Erskine J.
Published: March 2011

Surface and bulk electronic structure of the ordered NiAl alloy were measured using angle resolved photoelectron spectroscopy. The measured bulk d-bands (Ni like) were observed to be narrower than theoretically calculated d band widths which are 20 to 40% wider (depending upon what is used as a measure of the width). At least two surface states were observed on both the (110) and (111) surfaces. The nature of these surface states and their relationship to the bulk band structure is discussed. Dispersion of bulk phonons was measured by neutron scattering and fitted with a fourth nearest neighbor Born-von Karman model. Dipole active surface phonons on the (110) and (111) surfaces were observed by inelastic electron scattering and the frequencies also calculated assuming a truncated bulk surface. The calculated surface modes present a qualitative picture of the atomic displacement at each surface and also show that the surface phonon energy and intensity depends upon the structure of the surface.
Carbon Monoxide Adsorption on (111) and (110) Single-Crystal Nickel-Aluminum Alloy Surfaces
Authors: Mundenar J. M. , Gaylord R. H. , Lui S. C. , Plummer E. W. , Zehner D. M. , Ford W. K. , Sneddon L. G.
Published: March 2011

Carbon monoxide chemisorption on the (111) and (110) surfaces of a single-crystal NiAI alloy has been studied using several surface sensitive techniques, including work function change measurements, ultra-violet photoelectron, thermal desorption and electron energy loss spectroscopy. Results from these experiments indicate that the reactivity of these NiAI surfaces toward CO is distinctly different and that although the CO/NiAI (111) surface behaves more like CO adsorbed on pure nickel surfaces, the CO/NiAI (110) surface is neither like CO adsorbed on pure nickel nor aluminum surfaces. The local CO bonding sites, as probed with photoemission and electron energy loss spectroscopy, are similar on both NiAI surfaces.
New Preparation Method For Liquid Alloy Surfaces and Their Characterization by Electron Spectroscopy
Authors: Indlekofer G. , Oelhafen P. , Güntherodt H.- J.
Published: March 2011

Surface investigations of liquid metals in ultra-high vacuum are scarce as compared with solid state studies, mainly because of experimental difficulties of preparing atomically clean liquid surfaces. A new technique has been developed in order to prepare clean liquid metal surfaces. According to the characterization with electron spectroscopy it proved to be an effective way to obtain high purity liquid surfaces and hence offers the possibility to study a variety of metals and alloys in the liquid state.

Information about the surface composition, segregation properties and its purity in the liquid state and the valence electron structure has been obtained by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS, respectively). Exciting new insights in the electronic structure of various liquid alloys such as Au-Si, Cu-Sn, Ga-Sn and TI-Bi have been obtained from these measurements.
Ag Layers on Cu(110): Bonding, Structure, and Stability
Authors: Taylor T. N. , Hoffbauer M. A. , Borodovsky L. , Beery J. G. , Maggiore C. J.
Published: March 2011

The atomic-level properties ( bonding, structure, composition ) and thermal stability of Ag overlayers on Cu(110) have been investigated using combined surface and high energy ion beam techniques. Analysis of the first Ag adatom layer with LEED shows that the Ag is initially confined to the [110] troughs and that further deposition results in a Ag(111) layer exhibiting c(2×4) symmetry. Rutherford backscattering analysis gives absolute coverages that are consistent with the surface science coverage determination. Thermal desorption of CO from the trough composite reveals a lower ( more Ag-like ) binding energy than that for clean Cu(110). Continuous films grown cold at thicknesses <115 Å are found to agglomerate above 500 K exposing a tenacious Ag-Cu interface like that formed by one monolayer deposition. Ion beam analysis has been employed to characterize the agglomerate coverage and depth distribution for these degraded films. Thin films grown 900Å thick exhibit much higher thermal stability, giving detectable interfacial degradation only after heating above 725 K.
Microstructure of Cement Blends Containing 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.
The Role of Sodium Hydroxide in the System C3A-CaSO4-H2O at 30°C
Authors: Ghorab Hanaa Youssef , Fetouh Safaa Hussein Abou El
Published: March 2011

The hydration reaction of C3A with gypsum (molar ratio = 1:1.5) has been studied in water and in sodium hydroxide solutions at 30°C. The hydration product were analyzed microscopically and by means of X-ray diffraction. The concentration of sulfate and aluminum in solution was determined spectrophotometrically. In the absence of alkali, the amount of ettringite formed passes through a maximum and is accompanied by almost complete consumption of sulphate ion in solution. Alkali depresses the formation of ettringite and accelerates that of calcium hydroxide. The monosulfate hydrate appears immediately in alkaline solutions and water then reappears after a day as a solid solution with the tetracalcium aluminate hydrate. The formation of the monophase solid solution is accompanied by the consumption of C3A, ettringite, and calcium hydroxide and by an increase in the amount of the dissolved aluminum. The presence of alkali markedly increases the initial sulfate ion concentration from solution.
Homogeneity of Particle Dispersion in Slag/Cement Blends and its Effect on Hydration Rate
Authors: Lee S. , Roy D. M. , Malek R. I. A.
Published: March 2011

Effective particle dispersion is believed to play a significant role in hydration reactivity of slag/cement blends and consequently on the development of physical and mechanical properties of the hardened pastes. The effects of various factors (superplasticizer and mixing time) on the particle dispersion were evaluated using a computer controlled scanning electron microscope. Backscattered electron signals and elemental maps were resolved for polished mounts of slag and cement particle mixtures. The adequacy of dispersion of slag and cement particles was determined by analyzing about 1000 particles per analysis with appropriate calculations and statistical treatment. These results were related to the hydration behavior of the slag/cement blends. The results obtained can be used to evaluate some of the physical phenomena and the kinetics of slag-cement hydration.
Relationships Among Retardation, Expansion, Microstructure, and Phase Composition for a Salt-Saturated Expansive Grout
Authors: Wakeley Lillian D.
Published: March 2011

A salt-saturated and sulfate-expansive grout was formulated with four levels of sodium citrate to determine effects on workability and setting time. Linear expansion of restrained grout prisms increased with amount of citrate used, apparently a function of extent of retardation of the grouts. This relationship was observed both for grouts cured for at least 53 days, and for a concrete formulated from the same cementitious materials cured for at least 180 days age.

The microstructures of the grouts at 28 days age showed notable increases in extent of reaction of the sulfate phases and in formation of ettringite with increasing citrate content, and thus with increasing retardation of set. XRD also revealed an increase in well-crystallized ettringite and decrease in gypsum with greater retardation. These observations provide a microstructural and compositional link between retardation and expansion of cementitious materials formulated to be expansive.
Towards Computer-Based Microstructure Models for Cement-Based Systems
Authors: Jennings Hamlin M.
Published: March 2011

Computer-based models represent an important development that should provide a scientific basis for in-depth predictions of the behavior of materials. Aspects of microstructure models for cement-based systems are described. A computer model is described that can incorporate many assumptions in the form of sub-models. Specific algorithms are selected to solve specific parts of the problem. The algorithm chosen depends on specific problem requirements at each stage of calculation, and these problem requirements may not be anticipated in advance. An important part of these computer models is that they incorporate a file of numbers, representing the microstructure, which can be operated on to effect an incremental change in the system.
Effect of Particle Size Distribution on Hydration Kinetics
Authors: Pommersheim James M.
Published: March 2011

A general method has been developed for determining the effects of particle size distribution (PSD) on the kinetics of hydration. Given the PSD and the kinetic rate for particles having a single size, expressions can be derived for the variation of the total degree of hydration with time. The method was applied to PSD and kinetic functions typical of cement systems that account for reaction, diffusion and expansion of spherical hydrate layers. The PSD was found to critically affect the kinetics. A key feature of the theory follows with time those particles that have become totally hydrated, so-called “dead” particles. This produces a dead-particle hydration curve having approximately the same shape and location as the overall hydration curve. It can be represented analytically in all cases and gives a measure of the disguise provided by the distribution.
The Reactivity of C109 Sand: A Closer Look
Authors: Grutzeck Michael W.
Published: March 2011

It was observed that standard ASTM C 109 sand (St. Peter Sandstone) from working quarries in the Ottawa area (northeastern Illinois) is nearly always sub-angular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications the frosted surface of the quartz sand was found to consist of a thin layer of micron-sized, coprecipitated quartz crystals and occasional kaolinite flakes. Upon reaction of the sand with either a saturated Ca(OH)2 solution or as part of a sand-cement paste, some of these features were preserved, whereas others were lost. Micrographs of sand cured in cement paste at 90°C are presented showing that the kaolinite flakes react and become “puffy” and rounded in appearance. Also, the smooth surfaces of the large, terminated quartz overgrowths are severely etched as a result of dissolution. Sand reacted at 38°C in saturated Ca(OH)2 solution demonstrated more subtle effects, perhaps obscured by precipitated CaCO3 and C-S-H on the surfaces of the quartz overgrowths. These results suggest that ASTM C 109 sand is not entirely inert, but exhibits a limited amount of temperature-dependent pozzolanic activity.
Pore Structure Development in Portland Cement/Fly Ash Blends
Authors: Cook David J. , Cao Huu T. , Coan Everett P.
Published: March 2011

Pore structure development in portland cement/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.
Comparison of the Behavior of Trace Elements During Acid Leaching of Ashes from Several Coals
Authors: Watson J. S.
Published: March 2011

The leaching of fly ash from eastern U.S. coals with strong mineral acid is the initial step in a series of potential processes for producing useful and marketable materials from the ash. This initial leaching step removes most, or all, of the more soluble (generally amorphous) materials from the ash and leaves an inert residue, believed to be mostly mullite and silica. Chemical analyses of the leachate and the residual inert materials indicate the original distribution of the trace elements in the phases. Significant differences in crystallography, composition and leaching behavior have been noted in ash samples from coals from various regions, of various types, and sometimes even in ash samples from the same or similar coals. Trace element analyses of fly ash leachates provide a useful means of studying coal characteristics and of determining how the trace elements are incorporated in various types of fly ashes.
Status of ASTM and Other National Standards for the Use of Fly Ash Pozzolans in Concrete
Authors: Majko Richard M.
Published: March 2011

The Subcommittee of ASTM that is responsible for pozzolan specifications, (C09.03.10) is currently revising C 618, the standard specification, and C 311, the standard test methods. It is no small task. It is generally considered that dividing fly ashes into two classifications (Class F and Class C) is no longer acceptable. The Subcommittee has reached the tentative conclusion that one class of fly ash pozzolan is more appropriate and less ambiguous, provided it is accompanied by an optional table outlining the appropriate limits for sulfate resistance, heat of hydration, hydraulic properties, etc. That is, the engineer need specify only a fly ash pozzolan. If the engineer needs more than a “general purpose” fly ash he calls for special characteristics from the optional requirement table. Any major revision in the C 618 specification challenges the Subcommittee to look for better and more useful test methods in C 311. The committee is looking at C 1012 for a sulfate resistance procedure, conduction calorimetry as a heat of hydration method, and better methods to evaluate pozzolanic activity. The committee is aware of the limited usefulness of hydrated lime or sodium hydroxide in evaluating pozzolanic activity. Perhaps a more suitable term, i.e. the activity index with cement, is more appropriate. Fly ash properties that need to be evaluated include water reduction, activation by lime and alkalies, hydraulic or self-cementing properties and pozzolanic activity. Any test that tends to compensate for a fly ash's lower reactivity (i.e., accelerated thermal curing at 35°C or 65°C) probably leads to misleading results. A critical look at the national standards of other countries might allow the committee to take a visionary yet practical approach toward a new fly ash specification.
Studies of Zinc, Cadmium and Mercury Stabilization in OPC/PFA Mixtures
Authors: Poon C. S. , Perry R.
Published: March 2011

The utilization of pulverized fuel ash (PFA) (fly ash) for the stabilization of heavy metal waste is described. Solutions of the group IIB elements (zinc, cadmium and mercury) are used as model materials because of their significance as industrial wastes. The study included aqueous chemistry determinations, a leaching test, the use of SEM to examine microstructure, and compressive strength measurements. The use of PFA in a cementitious matrix lowers the alkalinity of the overall system and thus improves the immobilization of the amphoteric metal such as zinc. The interaction between mercuric solution and PFA plays an important role in improving the retention of the blended system for mercury. SEM results show that the microstructure of the ordinary Portland cement (OPC)/PFA blended system is significantly modified by the incorporation of the waste material. The advantages of using the blended system over a pure OPC system are described in physical and chemical terms.
Stabilization of Drilling Fluid Waste with Fly Ash
Authors: Deeley George M. , Canter Larry W. , Laguros Joakim G.
Published: March 2011

Water based drilling muds typically contain clays, barite, lime, caustic soda and other chemicals, such as polymers. Land disposal of these wastes raises the possibility of groundwater pollution which can be abated if the waste is stabilized either by chemical reaction or by solidification through some form of cementation. Many ASTM high-calcium (Class C) fly ashes are cementitious and thus may be useful in stabilization of drilling mud. The basic idea is to stabilize the clay-containing muds using the model of soil and roadbed stabilization with high-calcium fly ash [1]. Fly ash that is not utilized is considered to be a solid waste, so this application would would actually constitute codisposal of two wastes.
SEM Study of Chemical Variations in Western U.S. Fly Ash
Authors: Tevenson Robert J. , Huber Timothy P.
Published: March 2011

Scanning electron microscope/electron microprobe chemical analyses of individual grains of several western fly ashes have shown an inter-grain variation in composition for ashes derived from both lignite and subbituminous western coals. SRM 2689 (a Class F fly ash from a bituminous coal) and SRM 2691 (a Class C fly ash from a subbituminous coal) have been included in the study and also show inter-grain chemical variation. A classification scheme of fly ash grain compositions has been developed and has proven to be useful in illustrating the differences and similarities of the ashes. There is a positive correlation, for example, between grains rich in SiO2 and Al2O3 and the Na2O content of the grains in lignite and subbituminous coal derived fly ashes. There is also a positive correlation between grains rich in CaO and the MgO content of the grains in both classes of fly ashes.
Microgravity Materials Processing for Commercial Applications
Authors: Kohli R. , Brusky P. L. , Diamond S. , Markworth A. J. , McGinniss V. D. , Melling P. J. , Spinosa E. D. , Collings E. W.
Published: March 2011

Materials processing in a microgravity environment is aimed at developing commercial materials as well as investigating basic phenomena to improve earth-based processing. Materials research in space has dealt with glasses and ceramics, crystal growth, electronic materials, metals and alloys, polymers, composites, and biological materials. Battelle has been conducting research in this area since the early-1970s. Several important results have been obtained in: immiscible alloys, containerless under-cooling of clustering alloys, sol-gel glasses, and collagen fibers.

More recently, Battelle's Advanced Materials Center for the Commercial Development of Space (CCDS) has been established to utilize the microgravity environment in the commercial development of composite and mixed-phase materials with substantially improved properties. Currently, the Center is conducting research in catalysts (variant-phase chlorides, zeolites, and mixed oxides), polymer systems, electronic materials (float-zone crystal growth on Type II-VI semiconductor crystals, particularly CdTe), and con-trolled- porosity glass. The present program focuses on a proof of principle for each research thrust, utilizing ground-based and suborbital facilities, together with modeling to demonstrate the potential for producing commercially important materials.

Each of these research programs is outlined. In addition, the more important developments in each of the major categories of microgravity materials research is reviewed.
Containerless Polymeric Microsphere Production for Biomedical Applications
Authors: Rhim W. K. , Hyson M. T. , Chung S. K. , Colvin M. , Chang M.
Published: March 2011

A containerless method that produces highly uniform microspheres (> 50 microns in diameter) from many materials has been developed for biomedical applications. A piezoelectrically vibrated drop generator forms uniform (monodisperse) monomer droplets that are either electrostatically levitated and polymerized using UV irradiation, or free radical polymerized. Spheres of 2-hydroxyethyl methacrylate (HEMA) polymer have been produced with diameters of 155 microns ±1.57%.
PbO Reduction and Crucible Reactions of 70 wt% PbO · 30 wt% B2O3 Glass
Authors: Schilling Christopher H. , Lee Mark C.
Published: March 2011

Seventy wt% PbO · 30 wt% B2O3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.
Experimental Studies in Fluid Mechanics and Materials Science Using Acoustic Levitation
Authors: Trinh E. H. , Robey J. , Arce A. , Gaspar M.
Published: March 2011

Ground-based and short-duration low gravity experiments have been carried out with the use of ultrasonic levitators to study the dynamics of freely suspended liquid drops under the influence of predominantly capillary and acoustic radiation forces. Some of the effects of the levitating field on the shape as well as the fluid flow fields within the drop have been determined. The development and refinement of measurement techniques using levitated drops with size on the order of 2mm in diameter have yielded methods having direct application to experiments in microgravity. In addition, containerless melting, undercooling, and freezing of organic materials as well as low melting metals have provided experimental data and observation on the application of acoustic positioning techniques to materials studies.