bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pore Size Distributions in Hardened Cement Paste by Sem Image Analysis
Authors: Diamond Sidney , Leeman Mark E. 
Published: April 2011

AbstractTechnical requirements for determining the size distribution of capillary pores in hardened cement paste by SEM image analysis are discussed. Results of such measurements are reported for a set of hardened cement pastes of w:c ratio 0.40 and 0.25, and of ages ranging from 1 to 28 days. Pore size distributions based on conventional mercury intrusion porisimetry are presented for the same pastes. Estimates of pore diameters by mercury intrusion are two orders of magnitude smaller than the sizes revealed by the image analysis. Diameters of air voids are even more drastically underestimated by mercury intrusion. Typical micrographs are provided to illustrate the physical reality of the image analysis results, and the technical reasons underlying the conventional misinterpretation of MIP results for hydrated cements are reviewed.
Durability And Microstructure of Pore Reduced Cements(PRC)
Authors: Geslin N.M. , Israel D. , Lachowski E.E. , Macphee D.E. 
Published: April 2011

AbstractThe pore structure characteristics of cementitious materials play an important role in defining their mechanical and durability performance. The mechanical properties of pore reduced cements (PRC) have already been reported [5] as a function of the product density. This paper reports recent data on the durability of PRC and attempts to relate the pore properties of the material to its resistance against deterioration in aggressive environments.
Compressive Yield Stress of Cement Paste
Authors: Miller Kelly T. , Shi Wei , Struble Leslie J. , Zukoski Charles F. 
Published: April 2011

AbstractCompressive yield stresses have been measured for pastes (0.35 ≤ w/c ≤ 0.50) of portland cement, calcium aluminate cement, and weakly and strongly flocculated alumina (Φ0 = 0.20) using the centrifuge sediment height technique. Equilibrium sediment heights are reached quickly, allowing all measurements to be taken during the cement's induction period. The compressive behavior showed little dependence on the compressive history. Compressive yield stress was, however, dependent upon initial volume fraction, decreasing as the initial volume fraction increases. This behavior was observed in both the cements and alumina suspensions, implying that strong dependencies on initial structure may be a general property of the compressive behavior of flocculated suspensions.
Optical Microscopy and Digital Image Analysis of Bond-Cracks in Cement Based Materials
Authors: Vervuurt Adri , Van Mier Jan G.M. 
Published: April 2011

AbstractA new testing method is presented in which the properties of the bond zone between aggregate and matrix in concrete are investigated. The reason for starting the investigation is the improvement of the lattice model, which is developed at the Stevin Laboratory. In the lattice model the material is schematized as a lattice of beam elements. The fracture properties of the individual beam elements are purely brittle, and the use of fracture energy parameters as a material property can be avoided for simulating the non-linear fracture process. In spite of the fact that a locally brittle law is used, the global behaviourshows softening of the material. An improved optical microscopy technique in combination with image processing is adopted for investigating the fracture process during loading.
Changes Induced by PVA in the Cement Microstructure Surrounding Aggregate
Authors: Chu Un-Jen , Kim Jae-Ho , Park Cheol , Robertson Richard E. 
Published: April 2011

AbstractThe presence of poly(vinyl alcohol) (PVA) in portland cement during its hydration was found to induce changes in the microstructure and behavior of the paste that forms around aggregate. The microstructure was studied with scanning electron microscopy in secondary electron, backscattered electron, and EDX mapping modes and with Fourier-transform infraredspectroscopy. The adhesion between cement paste and aggregate was examined with planar aggregate surfaces. With concentrations of the order of 1% by weight of PVA based onthe weight of the cement, the deposition of calcium hydroxide on the aggregate surface was found to be diminished and the porous layer that usually surrounds the aggregate to be reduced in thickness. Also, the bond between the aggregate and cement paste was increasedenough for the bond to approach the strength of the cement.
Further Studies on Fracture Properties of Paste/Rock Interfaces
Authors: Alexander Mark G. , Stamatiou Andreas 
Published: April 2011

AbstractThe results of fracture tests on rocks, pastes, and paste/rock interfaces are presented. Variables included rock type (andesite, dolomite, and granite), w/c ratio (0.3 - 0.55) and age of test (3 - 91 d). The results illustrate the variability inherent in toughness measurements on naturally fractured rough rock interfaces, but also indicate that interface toughness is not necessarily intrinsically lower than that of pure paste.
Microcrack Study of Cement-Based Materials by Means of Image Analysis
Authors: Alhassani Yahia , Bascoul Alain , Ringot Erick 
Published: April 2011

AbstractThe relationship between microscopical damaging of concrete and its mechanical parameters such as Young's modulus and degree of reversibility is a basic issue. In the same time, transport properties and of course the durability of civil engineering and hydraulic structures are linked to the state of microcracking.The replica technique has been developed in our laboratory in order to study microcracks with a scanning electron microscope. This non-destructive method allows observation of the imprint of the concrete surface and to follow the evolution of the alterations with time. An objective quantitative analysis requires numerous replicas and many microscopic fields within each replica.After a brief state of the art of the automatic method of extraction of lines by image processing, we propose a specific algorithm of image analysis which allows the cleaning of the pictures and the extraction of the microcrack skeleton. Today, this procedure has been validated on cement paste samples. It has to be improved to be applied on concrete.The measured parameters are the microcrack specific lengths and their orientation. The objective values measured by means of this procedure compare favorably to results obtained by hand drawing.
Heat Curing and Delayed Ettringite Formation
Authors: Lewis M.C. , Scrivener Karen L. , Kelham S. 
Published: April 2011

AbstractThis paper reports some preliminary results from a study of the effect of elevated temperature curing on mortars and the phenomenon of delayed ettringite formation (DEF). Mortars made from cements with sulphate levels of 3%, 4%, and 5% and with 5% sulphate and added alkali were cured at 20 and 90° C and subsequently stored in water. Expansion measurements showed a pessimum effect with increasing S03 content. Mortars which expanded showed a corresponding decrease in strength. X-ray diffraction (XRD) studies indicated that no ettringite is present after heat treatment but re-forms over time within the material. However, the ultimate levels of ettringite reached do not correspond to the magnitude of expansion observed. X-ray microanalysis shows that immediately after the heat treatment the aluminate species and most of the sulphate species are incorporated within the C-S-H gel. The concentrations of these species decrease during expansion, such that at the end of expansion the amounts remaining correspond to the presence of AFm phase mixed with C-S-H.
Hydrothermal Synthesis of Alumina Pillared Layered α- Zirconium Phosphate
Authors: Mérida-Robles Josefa , Olivera-Pastor Pascual , Jiménezlópez Antonio , Rodriguez-Castellón Enrique 
Published: April 2011

AbstractA new strategy to prepare alumina pillared α-zirconium phosphate with enhanced surface area and narrow pore size distribution is reported. The required precursor, a highly expanded single phase intercalate, is obtained in two steps. In the first one, the oligomeric solution of aluminium, prepared by dissolving aluminium in a solution of A1C13at 95°C, is contacted with colloidal α-zirconium phosphate under reflux, in the presence of fluoride. Subsequently, the resulting intercalation compound is treated again with a diluted solution of fluoride under hydrothermal conditions at 200°C. It is thought that fluoride ions complex aluminium monomers present in the pillaring solutions, and remove aluminium from the external surface of the phosphate. The pillared materials obtained by calcination in the range 400-600°C present BET surface areas between 184-140 m2g−1and basal spacings between 17.3-15.4 Å. These results contrast with those reported using classical methods, which systematically lead to materials with BET surface areas <80m2g−1.
Porous Solids of Boron Phosphate, Aluminum Phosphate, and Silicon Phosphate
Authors: Babb K. B. , Lindquist D. A. , Rooke S. S. , Young W. E. , Kleve M. G. 
Published: April 2011

AbstractAnhydrous sol-gel condensation of triethyl phosphate [(CH3CH2O)3PO] with boron trichioride (BCl3), triethyl aluminum [(CH3CH2)3Al] or silicon tetrachloride [SiCI4] in organic solvents led to rigid gels. The pore fluid of the gels was removed under supercritical conditions in a pressurized vessel to form porous solids. The condensation chemistry prior to the gel point was monitored by solution 1H, 13C, 31P, and 11B NMR. The materials were then calcined at progressively higher temperatures to produce high surface area phosphates. Nitrogen gasphysisorption was used to determine the surface areas, total pore volume, and average pore radius of the products. FT-IR was used to determine functional groups in the materials. The microstructure was also examined by scanning electron microscopy.
Nitrogen and Water Sorption Properties of Ethyl-Substituted Silica Aerogels and Xerogels
Authors: Liu Chunling , Komarneni Sridhar 
Published: April 2011

AbstractHigh surface area ethyltrimethoxysilane (ETMS) modified silica aerogels and xerogels were synthesized by cohydrolyzing the mixtures of ETMS and tetramethylorthosilicate (TMOS). The effects of ETMS content, pH value and solvent addition were investigated. The surface area, pore structure and hydrophobicity were studied using nitrogen and water sorption measurements. By ETMS modification of TMOS gels, high surface area, density and hydrophobicity were achieved. The 25 mole% ETMS-75 mole% TMOS was found to be the best composition for both aerogel and xerogel, which are hydrophobic and have surface areas of 1221 and 832 m2/g, respectively.
Synthesis of Porous Transition Metal Oxides by the Salt-Gel Method
Authors: Stein Andreas , Fendorf Mark , Jarvie Thomas P. , Mueller Karl T. , Garcia Maurie E. , Mallouk Thomas E. 
Published: April 2011

AbstractComposites of surfactants with certain transition metal oxides can be arranged into periodic arrays with giant tunnel structures. Transmission electron micrographs of these structures resemble images of mesoporous silicate molecular sieves synthesized in the presence of surfactants. However, data in this study lead to the conclusion that Keggin-ions of the type (H2W12O40)6-are formed during the hydrothermal synthesis of a cetyltrimethylammonium/tungstate composite. These cluster anions are not connected to each other. Removal of the organic template therefore results in the collapse of the tunnel structures.A strategy has been developed which uses pre-arranged surfactant-salt structures as precursors for microporous and mesoporous framework materials. Transition metal silicates with long-range structural order have been synthesized by reacting surfactant salts of niobotungstate clusters with tetraethylorthosilicate to form a salt-gel. Infrared and solid-state NMR double resonance spectra indicate that, in addition to linkages between silicate tetrahedra, niobium-oxygen-silicon linkages have been formed in this reaction. Removal of the cationic surfactants by acid-extraction has resulted in porous structures with surface areas up to 265 m2/g.
Synthesis, Characterization and Modification of Mcm-41 Molecular Sieves
Authors: Sayari A. , Karra V.R. , Reddy J.S. , Moudrakovski I.L. 
Published: April 2011

AbstractA series of crystalline mesoporous molecular sieves were prepared using alkyl hexadecyl dimethyl ammonium bromide salts (C16H33)(CnH2n + 1)(CH3)2NBr, in which the number of carbon atoms (n) in one alkyl group was varied from 1 to 12. The influence of (n) value on the nature of the final phase obtained and on its pore size was investigated. A hexagonal phase was obtained for n = 1, 3, 5 and 7, while a lamellar phase was obtained for all other templates. Vanadium and titanium modified MCM-41 molecular sieves were also prepared in the presence of C12H25(CH3)3N+ and C16H33(CH3)3N+ ions, respectively. These materials were characterized by XRD, nitrogen physisorption, FTIR, solid state NMR, XPS, UV-Vis and catalytic testing in the oxidation of 1-naphthol, 2,6-di-tert-butylphenol, norbornylene, n-hexane and propylamine. Ti-MCM-41 exhibited considerable catalytic activity only in the oxidation of aromatics, olefins and alcohols. V-MCM-41 was found to be a good catalyst in the oxidation of aromatics and alkanes.
Preparation of Hollow Shell ICF Targets Using A Depolymerizing Mandrel
Authors: Letts Stephan A. , Fearon E. M. , Buckley S. R. , Saculla M. D. , Allison L. M. , Cook R. C. 
Published: April 2011

AbstractA new technique for producing hollow shell laser fusion fuel capsules was developed that starts with a depolymerizable mandrel. In this technique we use poly(alpha-methylstyrene) (PAMS) beads or shells as mandrels which are overcoated with plasma polymer. The PAMS mandrel is thermally depolymerized to gas phase monomer, which diffuses through the permeable and thermally more stable plasma polymer coating, leaving a hollow shell. We have developed methods for controlling the size of the PAMS mandrel by either grinding to make smaller sizes or melt sintering to form larger mandrels. Sphericity and surface finish are improved by heating the PAMS mandrels in hot water using a surfactant to prevent aggregation. Using this technique we have made shells from 200 μm to 4 mm diameter with 15 to 100 μm wall thickness having sphericity better than 2 μm and local surface finish better than 10 nm RMS.
Low Dielectric Constant Laminates Containing Microspheres
Authors: Japp Robert M. , Papathomas Kostas I. 
Published: April 2011

AbstractAs electronic devices become faster, the effective dielectric constant of the circuit packaging connecting them becomes more important. The dielectric constant of standard epoxy/glass laminates can be significantly reduced by the addition of hollow glass microspheres. However the addition of such microspheres usually results in the degradation of other physical, electrical and mechanical properties which are prerequisites for materials to be used in commercial circuit packaging. By carefully optimizing the formulation many of these undesirable effects can be avoided. These topics and others pertaining to the development and testing of a microsphere laminate are discussed.
Synthesis of Indium Oxide Microspheres for Antistatic Spacecraft Coatings
Authors: Speckman Donna M. , Jackson C. A. 
Published: April 2011

AbstractIndium oxide microspheres were synthesized for potential use in novel, polymer-based antistatic coatings for exposed spacecraft surfaces. Non-agglomerating indium oxide microspheres with diameters ranging from 0.5–2.0 μm were produced using an aerosol spray pyrolysis technique. The precursor solution used to generate the aerosol droplets for pyrolysis consisted of indium acetate dissolved in water; however, the actual indium species present in solution was identified as the hydrolysis product, dihydroxy(acetato)indium. Thermogravimetric analyses of commercial indium acetate and of pure crystals of the dihydroxy(acetato)indium compound both demonstrated clean solid-state pyrolyses to generate pure indium oxide, as confirmed by x-ray diffraction and infrared spectroscopic analysis. Air was used as the carrier gas for the aerosol droplets for the spray pyrolysis experiments, and pyrolysis took place within a 2′′ tube furnace. The microspheres were characterized by x-ray diffraction and scanning electron microscopy. The non-agglomerating characteristics of the microspheres, combined with their small size, indicates that these particles are highly promising for dispersion within a polymer matrixes required for novel polymer-based antistatic films.
Porous Spherical Shells and Microspheres by Electrodispersion Precipitation
Authors: Harris Michael T. , Sisson Warren G. , Hayes Susan M. , Bobrowski Sophie J. , Basaran Osman A. 
Published: April 2011

AbstractPulsed electric fields have been used to enhance the dispersion of aqueous metal (Zr and Al) salt solutions from a nozzle and into a nonconducting liquid continuous phase that is immiscible with the aqueous phase. The diameter of the resulting microdroplets ranged in size from approximately 0.1 to 10 μm. Precipitation of hydrous metal oxides occurred as ammonia, which was dissolved in varying amounts in the continuous phase, diffused into the aqueous microdroplets. Spherical shells were formed at higher ammonia concentrations and microspheres were produced at lower ammonia concentrations. Upon drying, dimples appeared in the particles that were synthesized at higher ammonia concentrations. The latter result accords with the well known fact that under certain conditions spherical shells collapse when a fluid is extracted from the core of the particle. No dimples were observed in the microspheres that were produced at lower ammonia concentrations. Analog X-ray dot maps for aluminum and zirconium were done to determine the spatial distribution of each metal in the particles.
Formation of Solid and Hollow Spherical Particles by Spray Pyrolysis
Authors: Zhang Shi C. , Messing Gary L. , Lee Seong Young , Santoro Robert J. 
Published: April 2011

AbstractSpray pyrolysis offers a number of opportunities for the synthesis of either solid or hollow spherical particles. As predicted by the evaporation model, particles with different shell thicknesses can be obtained depending on the concentration gradient at the onset of precipitation. If the precipitate shell has a sufficiently high permeability for removal of the remaining solvent, then the shell can be preserved and a hollow particle obtained. By drying at a lower temperature solid particles are readily formed from precursor salts but hollow particle formation by SP at these low temperatures imposes demanding heating rate requirements.
X-Ray Absorption Spectroscopy from H-Passivated Porous Si and Oxidized Si Nanocrystals
Authors: Schuppler S. , Friedman S. L. , Marcus M. A. , Adler D. L. , Xie Y.-H. , Ross F. M. , Harris T. D. , Brown W. L. , Chabal Y. J. , Szajowski P. J. , Chaban E. E. , Brus L. E. , Citrin P. H. 
Published: April 2011

AbstractQuantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The H/Si ratios, as large as 1.2, were independently confirmed by ir-absorption and α-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 Å. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.
Analysis of the Dimerized Sb/Si(001)-(2×l) Surface by X Ray Standing Waves
Authors: Lyman P. F. , Qian Y. , Bedzyk M. J. 
Published: April 2011

AbstractX ray standing wave measurements were undertaken to study the bonding position of Sb adatoms on the Sb-saturated Si(001)−(2×1) surface. Using the (004) and (022) Bragg reflections, we find that the Sb atoms form dimers, and that the center of the Sb ad-dimers lies 1.64 Å above the bulk-like Si(004) surface atomic plane. This work describes the extraction of structural parameters for a dimerized surface from in-plane measurements. Our results are compared to two structural models consisting of dimers whose bonds are parallel to the surface plane and whose centers are either shifted or unshifted (parallel to the dimer bond direction) relative to the underlying substrate planes. We thus find two special cases consistent with our data: one with symmetric (unshifted) dimers having a dimer bond length of 2.81 Å, and the other with midpointshifted dimers, having a bond length of 2.88 Å and a lateral shift of 0.21 Å.
The Structure and Phases of a Relaxed Langmuir Monolayer of Methyl Eicosanoate as Determined by Grazing Incidence Xray Diffraction and Brewster Angle Microscopy
Authors: Foster W. J. , Shih M. C. , Pershan P. S. 
Published: April 2011

AbstractThe molecular structure and phase diagram of relaxed monolayer films of methyl eicosanoate at the air/water interface were studied using x-ray diffraction and Brewster Angle Microscopy. Six phases have been identified in relaxed films in a temperature range of 5 to 28 degrees Celsius.
High-Resolution X-Ray Diffraction Measurements of SiGe/Si Structures
Authors: Jordan-Sweet J. L. , Mooney P. M. , Stephenson G. B. 
Published: April 2011

AbstractHigh-resolution x-ray diffraction is an excellent probe of strain relaxation in complex SiGe structures. The high flux provided by synchrotron sources enables us to make extensive reciprocal space map measurements and evaluate many samples. The diffraction peak positions of each layer in a step-graded structure, measured for two different reflections, yield quantitative values for the relaxation and alloy composition in the layer. Grazing-incidence diffraction allows us to determine the in-plane structure of very thin layers, which have thickness-broadened peaks at conventional diffraction geometries. We demonstrate the power of these techniques with two examples.
Exafs Study of Co/Cu Multilayers: Mbe Versus Sputtered
Authors: Foiles C. L. , Franklin M. R. , Loloee R. , Clarke Roy , Morrison T. I. 
Published: April 2011

AbstractEXAFS data are used to probe the local structure of Co/Cu multilayers having comparable dimensions but prepared by two different techniques, MBE and sputtering. Significant differences are found. The nearest neighbor distance in all Co layers increases about the same amount relative to the bulk value and MBE Co layers are less disordered than sputtered Co layers. Nearest neighbor distances in thinner Cu layers are less than bulk values but approach bulk value for thicker Cu layers. Nearest neighbor distances in thin MBE Cu layers are more contracted and have a more rapid thickness dependence than in sputtered Cu layers.