bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of Damage Structures in Proton-Implanted Gallium Arsenide by Cross-Sectional Tem
Authors: Loretto D , Brown G. T. , Jones I. P.
Published: March 2011

Semi-insulating and SI-doped <100> GaAs have been irradiated to a dose of 1016 protons cm−2. Samples have been annealed for 20 minutes at 400,500 and 600°C. Cross-sectional TEN has shown the as-implanted and 400°C annealed GaAs to contain no visible damage. After 500 and 600°C anneals a heterogeneous distribution of planar raft-like defects apears on {(11} and {110}. The density of these defects is much lower in the Si-doped material.
A Model for the Application of Dlts on Normally-on Hemt Structures
Authors: Huang Y. J. , Ioannou D. E.
Published: March 2011

This paper presents an analytical model for the application of capacitance DLTS on the normally-on HEMT structure. Based on the charge conservation law, the DLTS signal is derived by taking into account both the Schottky gate and the heterojunction depletion layer capacitances. It is shown that the anomalous features observed by using the conventional DLTS technique on a HEMT structure can be reasonably explained with this model. Some results obtained by simulation of typical measurements are presented, which confirm our conclusions.
Nondestructive Evaluation of Tubing Closure Welds
Authors: Rehbein D. K. , Hsu D. K. , Thompson R. B. , Jones T. A.
Published: March 2011

Resistance tube closure welds, referred to as pinch welds, are used to reliably seal small stainless steel tubing [1]. The quality of the bond is dependent upon, among other factors, the cleanliness of the tube bore. Post weld inspections are therefore desired as process control procedures. In previous studies, ultrasonics was shown to have considerable promise in this application. Thomas et al. [1] demonstrated that pattern recognition algorithms could be applied to the ultrasonic signals transmitted through the tubes to produce a correct classification of good and bad welds in several different sets of samples. The algorithms were somewhat dependent on the material from which the samples were fabricated, but all showed a good deal of commonality. In a parallel study, Rehbein et al. [2] examined, from a more mechanistic point of view, sets of tubes fabricated at the same time. They observed that gross disbonds could be easily detected from changes in signals either reflected from or transmitted through the bond line. When such disbonds were not present, they observed that signals doubly transmitted through the interface (i.e., the back surface echo) showed a trend to lower values as the bond quality decreased. This paper describes the sequel to that study, having the objective of developing a quantitative understanding of the interaction of the ultrasound with the pinch welds.
Combined Atom-Probe and Electron Microscopy Characterization of Fine Scale Structures in Aged Primary Coolant Pipe Stainless Steel
Authors: Bentley J. , Miller M. K.
Published: March 2011

The capabilities and complementary nature of atom probe field-ion microscopy (APFIM) and analytical electron microscopy (AEM) for the characterization of finescale microstructures are illustrated by examination of the changes that occur after long term thermal aging of cast CF 8 and CF 8M duplex stainless steels. In material aged at 300 or 400°C for up to 70,000 h, the ferrite had spinodally decomposed into a modulated fine-scaled interconnected network consisting of an iron-rich α′ phase and a chromium-enriched α phase with periodicities of between 2 and 9 nm. G-phase precipitates 2 to 10 nm in diameter were also observed in the ferrite at concentrations of more than 1021 m−3. The reported degradation in mechanical properties is most likely a consequence of the spinodal decomposition in the ferrite.
The Contrast of Dislocations in X-Ray Topographs of Homogeneously Bent Silicon Crystals
Authors: Loxley Neil , Tanner Brian K.
Published: March 2011

The contrast of dislocations in X-ray transmission topographs has been studied as a function of specimen curvature. It has been shown that in the symmetric Laue geometry, contrast differences between Lang and Hirst Curved Crystal topographs are attributable to inhomogeneous bending of the specimen wafers.
Digital X-Ray Rocking Curve Topography
Authors: Ananthanarayanan T. S. , Rosemeier R. G. , Mayo W. E. , Dinan J. H.
Published: March 2011

There is a considerable body of work available illustrating the significance of X-ray rocking curve measurements in micro-electronic applications. For the first time a high resolution (100-150µm) 2-dimensional technique called DARC (Digital Autcmated Rocking Curve) topography has been implemented. This method is an enhancement of the conventional double crystal diffractometer using a real time 2-dimensional X-ray detector.

Several materials have been successfully examined using DARC topography. Same of these include: Si, GaAs, AlGaAs, InGaAs, HgMnTe, Al, Inconel, steels, etc. By choosing the appropriate Bragg reflection multi-layered micro-electronic structures have been analyzed nondestructively. Several epitaxial films, including HgCdTe and ZnCdTe, grown by molecular beam epitaxy, have also been characterized using iARC topography. The rocking curve half width maps can be translated to dislocation density maps with relative ease. This technique also allows the deconvolution of the micro-plastic lattice strain ccaponent from the total strain tensor.
Infrared Cathodoluminescence Studies from Dislocations in Silicon in tem, a Fourier Transform Spectrometer for Cl in Tem and Els/cl Coincidence Measurements of Lifetimes in Semiconductors
Authors: Graham R. J. , Spence J.C.H. , Alexander H.
Published: March 2011

In this paper we report the first observations by cathodoluminescence in TEM of radiative infrared emission from dislocations in silicon. These results were obtained at 23-25K in a Philips EM400 electron microscope. Our results are interpreted in the light of earlier photoluminescence work, and the prospects for obtaining spectra from a small number of well characterized dislocations with high spatial resolution are reviewed. Preliminary results are also reported showing the infrared band-gap emission spectrum of GaInAs at 90K recorded using a small Fourier Transform Spectrometer fitted to the same electron microscope. Finally, we describe timing coincidence experiments from samples in which only those visible CL photons are counted which arrive at the detector at the same time as the corresponding transmitted electron energy loss event. We describe the use of this technique for life-time mapping in semiconductors.
Partial Dislocation Mobility in GaAS
Authors: Cooman B. C. De , Carter C.B.
Published: March 2011

The dislocation loop shape in high stress deformed GaAs can be used to obtain information on the relative velocity of individual dislocation segments. It is shown that 30/90 β-dislocations and 90/30 β-dislocations have different velocities. A variety of loop shapes observed can be modelled by focussing on differences in mobility of individual kinks. It is shown that the observation of faulted dipoles is only possible in high stress p-type GaAs in which the screw dislocation segments have appreciable velocity at the low temperatures used during the deformation.
Dislocation-Solute Interactions at Twin Boundaries in Dendritic Web Silicon
Authors: Jayaram R. , Spitznagel J. A. , Meier D. L. , Greggi J. , Burke M.
Published: March 2011

DLTS, TEM and APFIM techniques have been used to study impurity-defect interactions responsible for reducing minority carrier diffusion lengths in solar cells of dendritic web silicon. Fine scale precipitates of SiOx, which decorate dislocations piled up at the twin planes in low eff clency cells, appear to be the dominant recombination centers.
Nondestructive Evaluation of Dislocation Subgrain Structures in Silicon Using Thermal Wave Imaging Techniques
Authors: Regnault William F.
Published: March 2011

Chemical sensors are being developed for in-dwelling biomedical applications. As sensor technologies progress, there is a tendency to fabricate more complex devices in a smaller area, thus enabling multiple sensors to be placed within a single in-dwelling catheter. As the active area of the detector is decreased, the defect structure of both the substrate and the various layers that make up the device plays an increasingly significant role in determining the ultimate sensitivity and reliability. A simple screening test to evaluate the viability of the substrate and the interfaces would aid in the initial evaluation of the fabricated device. To this end, thermal-wave imaging techniques have been applied to the study of a dislocation subgrain structure in a polycrystalline silicon wafer. Comparisons have been made between the results obtained using thermal-wave imaging, defect etching studies, and EBIC measurements.
Photoluminescence Investigation of Dislocation-Related Defects in High Purity Silicon
Authors: Hunter A. T. , Schumacher Kimberly L.
Published: March 2011

We conducted a luminescence investigation of the D1-D4 luminescence lines (0.8 to 1.0 eV) in three samples of high-purity, float-zone silicon. We conclude that the D3 line is a transverse-optical-phonon replica of the D4 line. In the samples studied, all of the defects were formed in the bulk of the crystals by high temperature thermal stress. The free-exciton lifetimes are short, varying between ∼20 nsec at a dislocation density of 1 × 106 cm−2 to ∼200 nsec at a density of 7 × 104 cm−2. The D4 decay shows a small temperature dependence, and varies between samples.
Dislocation Dynamics Investigated by Means of Nuclear Magnetic Resonance a Complementarynew Technique
Authors: De Hosson J. Th. M. , Kanert O.
Published: March 2011

Pulsed nuclear magnetic resonance proved to be a new complementary technique for the study of moving dislocations in Al—base alloys. Spin—lattice relaxation measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in Al—base alloys are different compared to those in ultra—pure Al. From the motion induced part of the spin—lattice relaxation rate the mean jump distance of mobile dislocations has been determined as a function of strain. Measurements have been performed on Al—Cu, Al—Li and Al—Zn binary alloys. Asa typical illustration of the strength of this technique, this paper reports the resultsobtained of Al—(1—2 at%) Zn solid solution.
Dislocation—like Defects in an Amorphous Lennard—jones Solid
Authors: Shi L. T. , Chaudhari P.
Published: March 2011

It has been found, using computer simulation techniques, that both edge and screw dislocations can be stably introduced into an amorphous Lennard-Jones solid, and can be moved through the model under an applied shear stress.
Cathodoluminescence of Ingaas-GaAs Single Heterostructures
Authors: Fitzgerald E.A. , Kavanagh K.L. , Ast D.G , Kirchner P.D. , Pettit G.D. , Woodall J.M.
Published: March 2011

Mismatched InGaAs-GaAs epitaxial layers were grown by molecular beam epitaxy (MBE) on substrates containing 9800 or <100 dislocations/cm2. Cathodoluminescence (CL), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray analysis (EDX) were used to analyze the effect of mismatch and substrate dislocation density on interface morphology. Surface ridges in scanning electron microscopy (SEM) images were found to correlate with areas of high recombination in CL. The spacing of dark recombination lines seen in CL was found to be an order of magnitude larger than the spacing of misfit dislocations seen in TEM. CL/IEM correlation reveals that some areas of the misfit array act more strongly as recombination centers than others. CL of step etched samples show that interface defects propagate into the GaAs buffer layer to depths of 4000 Å below the interface. The substrate dislocation density does not have a major effect on the number or spacing of the dark recombination lines.
Interfacial Particles in Mbe Sillicon Homoepitaxy Growth
Authors: Chrenko R.M. , Hall E.L. , Lewis N. , Smith G.A.
Published: March 2011

Particles are observed at the epitaxial layer-substrate Interface of silicon MBE layers when Improper pre—deposition cleaning methods are used. HRTEM shows that the particles In our material are 5 nm to 10 nm In size, and Molre fringe patterns suggest the material Is crystal line. Using a combination of SIMS, HRTEM, and x-ray microanalysis methods, It Is concluded that the Interfacial particles In our material contain carbon and not oxygen, and are beta-SiC growing epitaxially with the silicon.
Tm Analysis of Interfaces Beiween Nb and Al2O3 Precipitates
Authors: Mader W.
Published: March 2011

A Nb—Al alloy has been internally oxidized to produce A12O3precipitates. The interface between plate—like AI2O3 precipitates and the Nb matrix has been investigated by diffraction, CTEM, and HREM techniques. Periodic arrays of misfit dislocations were observed which acted as diffraction gratings for the electrons. The location of misfit dislocation cores could be determined from HREM images within an accuracy of a few lattice spacings. It can be concluded that the misfit dislocations lead to a good matching of atomic rows across the interface. The dislocation arrangement at this partially coherent interface is in accordance with theoretical expectations from dislocation theory.
Solute-Atom Segregation and Two-Dimensional Phases at Internal Interfaces: Atomic Resolution Observations
Authors: Herschitz Roman , Seidman David N. , Brokman Avner
Published: March 2011

Solute-atom segregation effects to individual stacking faults (SFs) in Co-0.96 at.% Nb and Co-0.98 at.% Fe alloys were studied employing the atom-probe field-ion microscope (FIM) and transmission electron diffraction techniques. The mean composition of individual SFs was measured for bulk specimens which had been equilibrated in the range 450-575°C. In addition, the composition was measured with a spatial resolution, within the plane of the SFs, of ~1 Å and with a spatial resolution of <4 Å perpendicular to the SFs. These measurements demonstrated the following: (a) The meancompostion of the SFs increased with decreasing temperature according to an Arrhenius-like expression; (b) The Nb or Fe concentrations fall off very quickly with distance--within <4 Å from the plane of the SF the bulk concentation is achieved; (c) The SFs equilibrated above 4500 C contained solute-atom fluctuations (≈5 to 20 \ diameter) which correspond to compositions with stoichiometries of ≈Co2Nb or ≈Co3Fe. In the case of the Co(Nb) alloy, a transmission electron diffraction pattern was obtained ofa SF--with the electron beam normal to the SF--which exhibited superlattice reflections with six-fold symmetry around the hcp matrix reflections. This latter result is consistent with a two-dimensional phase in the SF plane with the composition Co2 Nb. Both the atom-probe FIM and the electron diffraction studies are consistent with two dimensional (2D) ordered phases in the SFs.
Structure Imaging and Defects in Crystallized Oxynitride Glasses
Authors: Rai R.S. , O'Keefe M.A. , Thomas G.
Published: March 2011

High resolution electron microscopy has been employed to elucidate fault defects and structural details of the δ1 and δ2-Y2Si2O7 crystalline phases. From this study δ1 and δ2-Y2Si2O7 have been found to be orthorhombic having the same cell parameters but different atomic arrangements due to a change in their space groups. Computer simulations were necessary for interpreting details from the high resolution electron micrographs.
Interlayer Spacing of Sputter Deposited Vanadium Pentoxide
Authors: Aita Carolyn Rubin , Kwok Chee-Kin , Kao Mei Lee
Published: March 2011

Vanadium pentoxide films were grown by sputtering a V target in O2-bearing atmospheres containing 0 to 98% Ar. The interlayer spacing was siudied as a function of sputtering gas 02content. The results are discussed in terms of defects in thevanadyl 0 layir and correlated with target surface oxidation.
Characterization of Surface Roughness in Thin Films and Small Particles
Authors: Silva R. , Perez-Ramirez J.G. , Romeu D. , Herrera R. , Perez R. , Yacaman M. Jose
Published: March 2011

The surface roughness of small metallic particles and thin films is determined using TEM weak beam dark field images (WBDF) combined with image processing techniques. It is shown that the well known sensitivity of WBDF images to monoatomic steps on the sample surface can be largely improved by the use of image processing. The optimum conditions for step imaging and for the processing for small particles of Au, Pt and Pd and thin films of Au and Ag are discussed. It is found that under most conditions the surface of the particles and the films is very rough at the atomic level in agreement with the current theories of crystal growth.
Surface Disorder and Exfoliation in Lithographically Textured Molybdenum Disulfide
Authors: Roxlo C. B. , Deckman H. W. , Dunsmuir J. H. , Ruppert A. F. , Chianelli R. R.
Published: March 2011

Lithographic techniques have been used to prepare transmission electron microscopy samples of MoS2, allowing examination of the edge surface with single-layer resolution. We observe that these surfaces are easily disordered by chemical treatments common in the catalysis industry. In some cases treatment in H2/H2S leads to an exfoliation of the layered structure, a process which can be observed as it occurs in the microscope.
Atomistic Simulations of Surface Relaxations in Ni, Al, and Their Ordered Alloys
Authors: Chen S. P. , Voter A. F. , Srolovitz D. J.
Published: March 2011

We have performed a series of simulations to examine the atomistic nature of surface relaxations in pure metals and ordered alloys. The surface relaxations (∆dn, n+1) are shown to be oscillatory and to decay rapidly into the bulk. The period and form of the oscillation may be determined by simple geometrical arguments. The oscillation wavelength is always of the order of an atomic diameter. In pure metals, the surface layer of atoms always displaces inward. However, in the ordered alloys the larger atom may displace outward. On planes composed of more than one atom types, rippling occurs.
The Agglomeration of Point Defects in Transition Metal Monoxides
Authors: Gartstein E. , Radler M. , Mason T. O. , Cohen J. B.
Published: March 2011

Recent results on the diffuse scattering from single crystals of Fe1−xO at high temperatures reveal that the defect structure is in striking agreement with embedded cluster calculations by Ellis et al. The dominant defect is an imperfect 7:2 cluster. Mixtures of this and a larger complex (13:4) can explain the electrical properties. XANES studies of this oxide are in agreement with Ellis' theoretical work. However, in both FOx and MnxO it is not possible to use the shift of the cation K absorption edge to characterize valence. In fact in the latter case the shift passes through a minimum, perhaps indicating the onset of clustering.
Diffuse Neutron Scattering and Short-Range Order in Alloys – Contrast Variation and Contrast Enhancement by Isotopic Replacement
Authors: Mueller P.P. , Reinhard L. , Schoenfeld B. , Kostorz G. , Buehrer W. , Schaerpf O.
Published: March 2011

In Al-Cu alloys containing Guinier-Preston zones, the scattering contributions due to short-range order and atomic displacements vary differently when the scattering contrast between Al and Cu is changed. The diffuse neutron scattering of Al-Cu single crystals containing 63Cu or 65Cu is compared and evaluated to test the current methods of separating the two scattering contributions. - The nature of a sugggtted ordered state in α-brass is also studied by neutron scattering, using Cu to enhance the scattering contrast in a Cu-30 at.% Zn alloy. A broad diffuse peak is found in powdered, appropriately aged samples, confirming that the first Warren-Cowley short-range order parameter is negative.
Infrared Absorption Spectra of CO Adsorbed on Cu-Ru(001)
Authors: Hoffmann F. M. , Paul J.
Published: March 2011

The electronic properties and dispersion of copper layers on Ru(001) are investigated utilizing high resolution vibrational spectroscopy (FTIR) and carbon monoxide as a molecular probe. Adsorption of CO on an annealed, epitaxial copper monolayer reveals that copper is modified by the underlying substrate. Both the C-O stretching frequency at low CO coverage and its shift upon increase in coverage indicate stronger backdonation than for thick copper films which exhibit Cu(lll) behavior. At submonolayer coverages (0.25 < θCu < 1.0), copper forms islands on Ru(001) which behave similar to the copper monolayer. Rough copper films evaporated at 85K exhibit a drastically different behavior upon CO adsorption. Vibrational spectra allow us to distinguish 2-dimensional and 3-dimensional copper aggregates of random orientation as well as clusters of small size (1–3 atoms). Annealing of a θCu = 1.0 layer leads to 2- and 3-dimensional ordering at 250K and to complete surface wetting of the copper monolayer at 350K to 540K.
Calculation of the Surface Segregation of Pd-Cu, Pd-Ag, and Pd-Au Alloys
Authors: Foiles Stephen M.
Published: March 2011

The surface composition of the (111) surfaces of the binary alloys Pd-Cu, Pd-Ag, and Pd-Au have been computed by Monte Carlo computer simulation with the energetics determined by the Embedded Atom Method. Ag and Au are found to segregate to the first atomic layer of their alloys with Pd while for Pd-Cu alloys the degree of segregation is small but occurs mainly on the second atomic plane. The short-range order of the surfaces is addressed by studying the relative abundance of different compositions of nearest neighbor triangles on the (11) surfaces. The presence of triangles containing only atoms of one element is found to be suppressed by the short-range order. This result is shown to follow from the enhancement for these alloys of nearest neighbor pairs of atoms of different types.
Structural Characterization of Thin Metal Overlayers by X-ray Photoelectron and Auger-Electron Forward Scattering
Authors: Egelhoff W. F.
Published: March 2011

Forward scattering of XPS and Auger electrons by atoms in a crystalline lattice produce beams of enhanced intensity radiating out from the surface at angles corresponding to the internuclear axes present in the top few atomic layers. This effect has been applied to analyze the mechanism of surface segregation in ultrathin metal films, to analyze the interdiffusion at the interfaces of ultrathin films, and to assess the effects of substrate contamination on the growth of epitaxial films. The systems studied in this work are Cu, Ni, and Co on Ni(100), however the purpose of this work is not to investigate these particular systems but to use them to illustrate the capabilities of forward scattering.
High-Resolution Core Level Study of the Co/Si(111) Interface
Authors: Boscherini F. , Joyce J. J. , Ruckman M. W. , Weaver J. H.
Published: March 2011

There has recently been considerable interest in the reaction between Co and a clean Si surface. This interest stems from the epitaxy of CoSi2 and NiSi2 on Si and its potential for the construction of reliable and stable metal-semiconductor structures. In fact, the fabrication of a Si/CoSi2/Si transistor has been recently reported.[l] On a more fundamental side, it has been possible to address the problem of the relation between Schottky barrier height and structure at the NiSi2/Ni interface, which exhibits both a rotated (B-type) and unrotated (A-type) geometry.[2] For CoSi2/Si only the 180° rotated, B-type disilicide is formed. By studying the room temperature interface, we have attempted to describe the nature and physical extent of reaction products; such knowledge is important to understand the formation of interface silicides which ultimately control the nature of the high temperature epitaxial interface.
Influence of Type of Cement and Curing on Carbonation Progress and Pore Structure of Hydrated Cement Pastes
Authors: Bier Th.A.
Published: March 2011

Different series of cement paste specimens were prepared with ordinary portland cement, with portland, blast furnace slag cements having slag contents of 30, 50 and 75% by mass, with commercial fly ash cement and with portland cement containing fly ash additions of 10, 20, 30 and 50% by mass. Moist curing of the specimens varied between 3 and 28 days before the pore size distribution and characteristics of the phase composition were analyzed. Subsequent to curing, the specimens were subjected to drying in air of 65% RH with a controlled CO2 content of 0, 0.03 and 2% CO2 by volume. Depth of carbonation, pore size distribution of the carbonated paste, and the phase composition were investigated after 28 days and 6 months of drying, respectively. The results show that carbonation alters the prevailing pore structure of the hydrated paste. Important parameters are the type of cement used and the duration of curing.
Microstructure and Microchemistry of Slag Cement Pastes
Authors: Harrisson A. M. , Winter N. B. , Taylor H. F. W.
Published: March 2011

Pastes of a portland cement (60%) blended with a granulated blastfurnace slag (40%) were examined, principally by SEM with EDX analysis. Reaction rims around slag particles and relicts of fully reacted slag particles had compositions compatible with mixtures, in varying proportions, of C-S-H having Si/Ca -0.62 and a phase of the hydrotalcite family having Al/Mg -0.38. Calculations taking into account relevant densities and water contents indicated that replacement of the slag by its in situ hydration products entails little or no change in the numbers of Mg and 0 atoms per unit volume, but that substantial proportions of the Ca, Si and Al are released and an equivalent amount of H gained. In other respects, the microstructures qualitatively resembled those of pure portland cement pastes of similar ages, but less CH was formed and the C-S-H not formed in situ from the slag had a Si/Ca ratio of 0.56, higher than that of 0.50 to 0.53 found in the absence of slag. None of the individual phases in the slag cement pastes showed significant compositional variation with time in the 28 day to 14 month period studied. The relative amounts of Ca, Si and Al expelled from the slag are such that, in order to form C-S-H and AFm phase, more Ca is required. It is obtained partly at the expense of CH formation, and partly through increase in the Si/Ca ratio of the C-S-H formed from the clinker phases. Mass balance, volume composition and bound water content were calculated for the 14 month old paste and compared with corresponding results for the pure portland cement.
Microstructural Study of Different Types of Very High Strength Concretes
Authors: Aitcin Pierre-Claude , Sarkar Shondeep L. , Diatta Yaya
Published: March 2011

Very high strength concretes with water-cement ratios ranging from 0.21 to 0.27, having compressive strengths varying between 73 and 118 MPa, were prepared. One series was made with only high early strength cement (Type III), and the other series contained 6% to 11% silica fume.

In general, the microstructure of very high strength concrete is very dense and is composed mainly of C-S-H in the gel and crystalline phases. Mg, Al, S, Cl, K and Fe were detected in a number of C-S-H locales. The Ca/Si ratio was variable. In concretes without silica fume, the CH content is much lower than in normal concrete, and in the silica fume concretes it is still lower and not well crystallized. A few large, partly reacted and unreacted silica fume particles with surface cracks were present.

Strong cement-aggregate bonding is seen in concretes with silica fume containing limestone aggregates, whereas the gravel concretes show microcracks and a weaker bonding.
Microstructural Development During Suspension Hydration of Tricalcium Silicate Under “Floating” and Fixed pH Conditions
Authors: Ramachandran A. R. , Grutzeck Michael W.
Published: March 2011

The suspension hydration of tricalcium silicate (water-solid 500) has been studied under both floating and fixed pH (8 to 12) conditions. In addition to solution analysis, the microstructure and chemical composition of the hydrate products was also studied. The results are interpreted as suggesting the existence of two C-S-H phases in the system CaO-SiO2-H2O, the stabilization of each being dependent on the pH of the solution phase.
The Microstructure of Anhydrous Cement and its Effect on Hydration
Authors: Scrivener Karen L.
Published: March 2011

The hydration and microstructural development of cement are affected by the arrangement of anhydrous phases within the cement grains. Backscattered electron images and X-ray microanalysis can be used to characterize the microstructure of anhydrous cement. An image analyzer has been used to measure the overall proportions of silicate and interstitial phases in several cements and to measure the proportions of these phases that are exposed on the surface. These results are compared with the rates of heat evolution during the hydration of the cements.
A Comparison of the Pore Structure of Cement and Fly Ash/Cement Mortars Made with Sea Water and Fresh Water
Authors: Marsh B. K. , Joshi R. C. , Balasundaram A.
Published: March 2011

Pore structures of portland and blended cement mortars prepared with sea water were assessed by mercury intrusion porosimetry. Comparison is made with similar mortars made with fresh water. Mortars were made using cement containing 0%, 25% or 50% (by volume) of one of two Alberta fly ashes. They were tested after 90 days of continuous immersion in sea water at 5°C or 20° C. Results show that the mortars made with sea water generally contained a much higher volume of fine pores although the porosity was, in some cases, greater than that of mortars made with fresh water. Nevertheless, the volume of larger pores was lower in the mortars made with sea water. The pore structure of the various mortars is discussed in relation to potential durability.
Microstructure of Concretes Cast in the Canadian Arctic: Role of CaCl2 Used as an Anti-Freezing Agent
Authors: Regourd M. , Hornain H. , Aitcin P.-C.
Published: March 2011

Two concretes were made in the Canadian Arctic at sub-freezing temperature using an unusually high amount of calcium chloride, about 9% of the cement mass. Calcium chloride in such a high dosage was mainly used as an antifreezing admixture, because it was impossible to heat the cement and the aggregates prior to the batching and cure the concrete properly after its pouring.

One of these two concretes was cast inside a mine, where the temperature is about −10°C all year round. After one year of service, the strength of this concrete was determined to be 39 MPa at room temperature. The second one was cast outside the mine at −30°C during winter and was exposed to temperatures above 0°C the following summer. After one winter of service the strength of this was 5 MPa.

These two concretes were examined under the SEM and show quite a dense microstructures containing chloroaluminates.
Some Physical, Chemical and Mineralogical Properties of Some Canadian Fly Ashes
Authors: Joshi R. C. , Marsh B. K.
Published: March 2011

This paper gives physical and chemical properties of some Canadian fly ashes. Specific surface area, magnetic fraction, water soluble fraction and fraction finer than 45 μm were determined as part of the physical tests. Thermo-gravimetric analyses (TGA) in oxygen and nitrogen were conducted on raw ash samples. The change of pH with time in suspensions of the different ashes in water was also determined. Pozzolanic activity of the ashes with lime for all the ashes was evaluated to measure ash reactivity.

The ash activity seems to be related to fineness of the ash measured by the Blaine air permeability method, but not to the fineness measured by nitrogen sorption. Generally the greater the specific surface area, the higher the reactivity of the ash. The correlation was, however, not strong and no other physical or chemical parameter measured in this investigation seems to be related to pozzolanic activity.

The results of pH and TGA tests indicated that the ashes differ in many respects from each other. The TGA data suggest that loss on-ignition in many of the ashes is not entirely due to the presence of unburned carbon. Specific surface area determined by various methods seems to provide different values. No characterization parameter was found that was uniquely related to coal type.
Microstructure and Microchemistry of Slag Cement Pastes
Authors: Harrisson A. M. , Winter N. B. , Taylor H. F. W.
Published: March 2011

Pastes of a portland cement (60%) blended with a granulated blastfurnace slag (40%) were examined, principally by SEM with EDX analysis. Reaction rims around slag particles and relicts of fully reacted slag particles had compositions compatible with mixtures, in varying proportions, of C-S-H having Si/Ca -0.62 and a phase of the hydrotalcite family having Al/Mg -0.38. Calculations taking into account relevant densities and water contents. indicated that replacement of the slag by its in situ hydration products entails little or no change in the numbers of Mg and O atoms per unit volume, but that substantial proportions of the Ca, Si and Al are released and an equivalent amount of H gained. In other respects, the microstructures qualitatively resembled those of pure portland cement pastes of similar ages, but less CH was formed and the C-S-H not formed in situ from the slag had a Si/Ca ratio of 0.56, higher than that of 0.50 to 0.53 found in the absence of slag. None of the individual phases in the slag cement pastes showed significant compositional variation with time in the 28 day to 14 month period studied. The relative amounts of Ca, Si and Al expelled from the slag are such that, in order to form C-S-H and AFm phase, more Ca is required. It is obtained partly at the expense of CH formation, and partly through increase in the Si/Ca ratio of the C-S-H formed from the clinker phases. Mass balance, volume composition and bound water content were calculated for the 14 month old paste and compared with corresponding results for the pure portland cement.
The Diffusion of Chloride Ions in Fly Ash/Cement Pastes and Mortars
Authors: Malek R. I. A. , Roy D. M. , Licastro P. H.
Published: March 2011

Fly ashes having three distinctly different levels of calcium, designated low-calcium (Class F), intermediate-calcium (Class F/C), and high-calcium (Class C) comprised the basic material for the present study. Pastes and mortars were made out of the three types of fly ashes and one type of cement (Type I) at various levels of replacement as well as different water/solid ratios (w/c). Chloride ion diffusion was measured by applying an electrical potential across cured cylindrical samples and measuring the amount of current passed in a certain period of time (proportional to amount of Cl− passed in this time). Other supportive measurements were made, e.g., porosity and pore size distribution, water permeability and surface area. The Cl− ion diffusivities were correlated with the chemical composition of fly ash (FA), mix proportioning, and water permeabilities of the tested hardened pastes or mortars.
Modeling the Effects of Fly Ash Characteristics and Mixture Proportions on Strength and Durability of Concretes
Authors: White Elizabeth L. , Roy Della M. , Cady Philip D.
Published: March 2011

Factor analyses and cluster analyses were the modeling tools used to relate the chemical and physical characteristics of fly ash and cement to the strength, sulfate resistance, and freeze-thaw durability of fly ash-modified concrete. A Type I Portland cement was mixed with base load and upset load condition fly ashes from three different power plants in each of five regions in the United States. Based on the interactions between the reactive constittuents of the cement and fly ash, common factor loadings were identified. Cement loaded onto the early strength factor; fly ash loaded onto the later strength factor. In some subgroups the quantity of mixing liquid loaded separately as representative of the high water/cement ratio, which masked the reactive interactions between the fly ash and cement. In other subgroups the inter-relationships between sulfate resistance and strength with fly ash/cemment fineness, CaO content, and alkali content were represented in the factor analysis as well as in the numerical analysis models.
The Effect of Simulated Large Pour Curing Conditions on the Temperature Rise and Strength Growth of PFA Containing Concrete
Authors: Coole M. J. , Harrisson A. M.
Published: March 2011

When concrete is poured in large volumes, it is necessary to be able to predict the temperature rise which may occur inside the mass because of the effect this may have on the ultimate properties of the hardened concrete. It is known that the elevated temperatures generated may have a detrimental effect on final strengths and that if the difference in temperature between the centre and the surroundings exceeds 20–25°C, cracking may occur. In order to study these effects, a calorimetric controlled apparatus has been designed that is able to simulate the temperature rise profile occurring within any size of concrete pour. The apparatus is also used to control a curing bath thus enabling the compressive strength of match cured concrete to be determined. Results have been obtained for both temperature rise and strength growth at the centre of simulated 0.8, 1.5 and 3 m deep pours, using plain Portland and Portland PFA cement concrete. These show that in the larger sized pours the strength of concrete from a Portland PFA cement blend grows, after 2–3 days, at a greater rate than that of pure Portland cement, while giving lower temperature rises. Comparative strengths at 28 days are 48 Nmm−2 for the PFA cement concrete and 38 Nmm−2 for the pure Portland cement concrete. The influence of temperature on the reactivity of the PFA under these conditions has been studied using a dilute acid dissolution method. The hydrates formed and the progress of the pozzolanic reaction within the actual concretes has been monitored using scanning electron microscopy.
Monitoring of Fluctuations in the Physical Properties of a Class C Fly Ash
Authors: Schlorholtz Scott , Bergeson Ken , Demirel Turgut
Published: March 2011

The “quality” of fly ash produced during 1985 at Ottumwa Generation Station, was evaluated by two different experimental programs. The first consisted of the physical tests specified in ASTM C 311; these results are applicable to the use of fly ash as an admixture to portland cement concrete. The second consisted of monitoring the changes in the physical properties of fly ash pastes; these results would be applicable to the use of fly ash as a grout or a soil base stabilization agent. The physical properties monitored during the testing program were compressive strength, volume stability and setting time. In general, the results obtained from the two testing programs were quite different. When using testing procedures defined by ASTM C 311 the fly ash appeared quite uniform, but results obtained from the fly ash pastes were quite erratic. It was found that compressive strengths of the pastes can vary by a factor of five in rather short periods of time.
Evaluation of Potential Uses of AFBC Solid Wastes
Authors: Berry E. E. , Anthony E. J.
Published: March 2011

This paper presents a brief review of the literature dealing with utilization of atmospheric-pressure fluidized bed combustion (AFBC) solid wastes. The uses that have been proposed for AFBC residues include the following: agricultural lime, waste neutralization and stabilization, low-strength backfill, soil cementing and asphaltic concrete aggregate. An evaluation of a high-Ca waste from a Canadian AFBC installation is discussed. The waste was found to be unsuitable for applications in Port-land cement concrete because of poor strength development and expansion in mortars. The waste was compatible with Portland cement for soil cementing purposes but the resulting mixes were not resistant to freezing and thawing. Applications in asphaltic concrete were found to be successful in the laboratory and a small field trial is in progress.
Carbochlorination of Fly Ash in a Fused Salt Slurry Reactor
Authors: Dobbins M. S. , Burnet G.
Published: March 2011

Carbochlorination of the metal oxides in fly ash by suspending the solid reactants in a NaCl-AlCl3 melt at 530–850°C and then sparging chlorine into the melt has been investigated. A mechanically agitated, semi-batch reactor was used to test the effects of temperature, oxide and carbon loading, salt composition and gas flow on the reaction rate. The process was modeled using the carbochlorination of pure alumina, the rate of which was found to be chemical reaction controlled at temperatures below about 650°C and gas-liquid mass transfer controlled at higher temperature. The carbochlorination rate of the mixed oxides in coal fly ash was also mass transfer controlled at higher temperatures when aluminum recoveries were less than about 50%. At higher aluminum recoveries, the overall rate was limited by the rate of ash dissolution into the melt.
Speciation in Size and Density Fractionated Fly Ash II. Characterization of a Low-Calcium, High-Iron Fly Ash
Authors: Hemmings R. T. , Berry E. E. , Cornelius B. J. , Scheetz B. E.
Published: March 2011

Morphological, chemical and mineralogical speciation of a low-Ca, high-Fe fly ash from a bituminous coal has been investigated by examination of size, density and magnetic fractions. Fractionation by size revealed little information as to speciation among particle types. However, separation of the ash into eight density fractions and into magnetic and non-magnetic components showed major differences in particle properties. It was found that glasscontaining particles can be divided into three general types: Type 1, being low-Fe content, low-density hollow spheres comprising aluminosilicate/mullite glass ceramics; Type 2, of intermediate density, being ferroaluminosilicate/ mullite glass ceramics; and Type 3, high density composite particles of spinel/hematite crystals embedded in an iron-substituted glass. It is proposed that Type 1 and Type 2 particles are derived from thermal decomposition of clay minerals with a range of Fe contents. Type 3 particles are considered to arise from thermal decomposition of pyrite in the presence of small quantities of aluminosilicate minerals. Two general types of glass were distinguished: Glass I(f), being largely a low-iron aluminosilicate; and Glass II(f), being a ferroaluminosilicate of high Fe-content. XRD and vibrational spectroscopic evidence suggest that, in both glass types, Fe is substituted for Al in an aluminosilicate-type structure.
Characteristics of Fluid Flow in the Combustion Synthesis of TiC From the Elements
Authors: Valone S. M. , Behrens R. G.
Published: March 2011

Finite reservoir effects on capillary spreading at small reservoir dimensions are explored numerically and related to wave propagation in combustion synthesis of TiC from elemental Ti and C. In addition a convective instability which may be activated by gravitational, surface tension or contact forces may cause void regions to coalesce, thereby altering the void distribution in combustion synthesis products.
Undercooling of Bulk High Temperature Metals in the 100 Meter Drop Tube
Authors: Hofmeister William , Robinson M. B. , Bayuzick R. J.
Published: March 2011

The 100 meter Drop Tube at NASA Marshall Space Flight Center provides an excellent opportunity to study the effects of containerless, microgravity processing in metals and alloys. In a series of experiments high melting temperature pure metals were melted in an electron beam furnace and dropped in vacuum. Sample sizes ranged from 0.175-1.2 grams. Large undercoolings on the order of 18% of the melting temperature were observed in Ti, Zr, Nb, Mo, Rh, Ta, and Pt. Undercoolings of 5-18% Tm were observed in Ru and Ir. These undercooling results are consistent, repeatable, and occur in a high percentage of experiments. The experimental technique will be presented as well as the resultant microstructures of undercooled drops. The data will be discussed with respect to nucleation theory.
Microgravity Experiments on Granular Materials
Authors: Costes Nicholas C. , Jano V. C. , Sture S.
Published: March 2011

Gravity induced stresses in terrestrial laboratory specimens comprising of relatively weak and soft granular materials, are often of the same magnitude as the external tractions that are applied during investigations of constitutive behavior especially at low intergranular stress levels. The presence of heterogeneous strain and stress fields within such a specimen makes it difficult if not impossible to obtain objective and unambiguous constitutive properties and to devise relevant constitutive equations. To fill this technological gap, microgravity experiments are now planned which will be performed during future flights of the Space Shuttle, in conjunction with ground-based tests. This paper deals with analytical and experimental issues related to constitutive modeling of granular materials.
Evaporation Kinetics in the Hanging Drop Method of Protein Crystal Growth
Authors: Baird James K. , Frieden Richard W. , Meehan E. J. , Twigg Pamela J. , Howard Sandra B. , Fowlis William A.
Published: March 2011

We present an engineering analysis of the rate of evaporation of solvent in the hanging drop method of protein crystal growth. Our results are applied to 18 different drop and well arrangements commonly encountered in the laboratory. We take into account the chemical nature of the salt, the drop size and shape, the drop concentration, the well size, the well concentration, and the temperature. We find that the rate of evaporation increases with temperature, drop size, and with the salt concentration difference between the drop and the well. The evaporation possesses no unique half-life. Once the salt in the drop achieves about 80% of its final concentration, further evaporation suffers from the law of diminishing returns.
Phase Separation Kinetics in Immiscible Liquids
Authors: Ng Lee H. , Sadoway Donald R.
Published: March 2011

The kinetics of phase separation in the succinonitrile-water system are being investigated. Experiments involve initial physical mixing of the two immiscible liquids at a temperature above the consolute, decreasing the temperature into the miscibility gap, followed by imaging of the resultant microstructure as it evolves with time. Refractive index differences allow documentation of the changing microstructures by noninvasive optical techniques without the need to quench the liquid structures for analysis.
Noncontact True temperature measurement
Authors: Lee Mark C. , Allen James L.
Published: March 2011

A laser pyrometer has been developed for acquiring the true temperature of a levitated sample. The laser beam is first expanded to cover the entire cross-sectional surface of the target. For calibration of such a system, the reflectivity signal of an ideal 0.95cm diameter gold-coated sphere (reflectivity = .99) is used as the reference for any other real targets. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of a blackbody furnace (emissivity = 1.0) at a known, arbitrary temperature. Since the photo sensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. Preliminary results indicate that true temperatures thus obtained are in excellent correlation with thermocouple measured temperatures.
Three Channel Optical Temperature Measurement of Laser-Heated Reacting Particles.
Authors: Erik R. , Bolsaitis Pedro P.
Published: March 2011

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

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