bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTLithographic 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

ABSTRACTWe 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

ABSTRACTRecent 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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTForward 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.
Influence of Type of Cement and Curing on Carbonation Progress and Pore Structure of Hydrated Cement Pastes
Authors: Bier Th.A. 
Published: March 2011

ABSTRACTDifferent 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

ABSTRACTPastes 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

ABSTRACTVery 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTPore 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

ABSTRACTTwo 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

ABSTRACTThis 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

ABSTRACTPastes 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

ABSTRACTFly 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

ABSTRACTFactor 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

ABSTRACTWhen 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

ABSTRACTThe “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

ABSTRACTThis 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.