bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydration Characteristics and Morphological Features of Concretes from Structures in Australia, England and the United States
Authors: Baweja Daksh , Roper Harold , Cabrera Jose G. , Cook David J. 
Published: March 2011

ABSTRACTScanning electron microscope studies were carried out on concretes obtained from structures in Australia, England and the United States as part of an assessment of their durability performances. The ages of the structures ranged from nine to thirty years. All structures contained fly ash concretes in some sections, and, in a few cases, direct comparison between these concretes and ordinary portland cement (OPC) concretes was possible. Water: cement ratios of the concretes varied from 0.44 to 0.90. The sources of fly ash were identified in each case. The structures chosen had a range of use classifications encompassing building, hydraulic structures, bridge structures, towers and foundations. Deterioration effects of concretes in some structures were more common than in others. Based on observations, conclusions were drawn on the morphological features and hydration characteristics of the concretes.
The Permeability of Chloride Ions in Fly Ash-Cement Pastes, Mortars and Concrete
Authors: Malek R. I. A. , Roy D. M. 
Published: March 2011

ABSTRACTFly ash-cement pastes are known to develop fine pore structures that may retard the transport of ionic species. The rapid chloride permeability technique for studying the Cl- ion diffusion in hydrated fly ash/cement pastes, mortars and concrete was used. The technique applies an electrical potential across a cylindrical sample and measures the charge passed in a certain period of time. The results obtained on pastes and mortars cured for 28 days were reported previously and contrasted with those of neat cement pastes and mortars. The present paper reports more extensive studies made to examine the chloride permeabilities of pastes and mortars cured for up to 90 days. In addition, the effect of variable fly ash contents was examined. Concrete samples were included in the test scheme and the data were compared with pastes and mortars. Two important factors controlling the test results are discussed: first the mix design and curing conditions; second the experimental conditions during Cl- permeability measurements. In the second factor, the amount and rate of heat build up and the chloride ion concentrations are compared with the current passed. In addition, measuring current versus resistivity are critically discussed in terms of the voltage-current varistic characteristics of cement matrices.
On the Glass in Coal Fly Ashes: Recent Advances
Authors: Hemmings R. T. , Berry E. E. 
Published: March 2011

ABSTRACTRecent advances in the characterization of the glassy aluminosilicate phases in coal fly ashes are reviewed and discussed in terms of the development of new models describing their mechanism of formation, composition, structural relationships and chemical reactivity. Characterization techniques such as electron microscopy, x-ray diffraction, infrared and Raman spectroscopy, nuclear magnetic resonance and Mössbauer spectroscopies, thermal analysis, acid dissolution, silanation, and density fractionation have been used as experimental probes, and reveal a range of information relating to the glass phases from the macro, through the micro, to the nano-structural levels. Complex inter- and intra-particle heterogeneity in ash is observable not only in bulk chemical and mineralogical analyses but also at the molecular level in the constituent glasses. Remarkable relationships between ash particle size, density and glass composition have been observed and lead to a new proposed mechanism for ash morphogenesis based on temperature-viscosity effects in the mineral precursor melts in the boiler flame. A glass-ceramic model for fly ash particle structure is proposed and discussed in terms of phase relations in the CaO–SiO2–Al2O3 and FeO–Fe2O3–A12O3–SiO2 systems, modification of the aluminosilicate glasses by alkali and alkaline earth metal cations, and microheterogeneity involving glass devitrification and phase separation.
The effect of Bond Characteristics Between Steel Slag fine Aggregate and Cement Paste on Mechanical Properties of Concrete and Mortar
Authors: Yuji Wang 
Published: March 2011

ABSTRACTThe ordinary fine aggregate in concrete has been replaced by ground and sieved steel slag fine aggregate, treated and exposed to air for three months. Compared with concrete made from natural sand, properties such as compressive strength, flexural strength, elastic modulus, permeability and abrasion resistance are considerably improved. The improvement increases with a decrease in w/c ratio, an increase in curing time and an increase in the replacement weight of sand. These results are due to the fact that the steel slag contains some active minerals such as C3S, C2S, C4AF, etc., and shows favorable surface physical characteristics that improve the bond between steel slag particles and cement paste. The results of XRD, SEM and EPM microhardness showed that there are heavier concentration of ions, with finer crystals and a lower degree of CH orientation at the interfacial zone between steel slag particles and cement paste. The study also found small cementitious and fibrous C-S-H crystals growing from the fine aggregate, which are linked with hydrated products from cement paste making the bond and structural characteristic more favorable with cement. The steel slag fine aggregate is an active mineral similar to cement. The bond between the aggregate and cement paste is strengthened both physically and chemically.
Submicroscopic Structure and Characteristics of Intermediate-Calcium Fly Ashes
Authors: Dudas M. J. , Warren C. J. 
Published: March 2011

ABSTRACTThe surface and near surface characteristics of alkaline fly ash particles were studied to evaluate the heterogeneous chemistry and structure of ash in order to provide data and understanding of the dissolution behavior of elemental constituents. Fly ash was subjected to a range of chemical weathering intensities in laboratory column experiments. Weathered ash from columns were then analyzed for surface morphology and chemical compositional change. Determinations included chemical characterization by instrumental neutron activation analyses, surface analysis by SEM-EDXA of whole and fractured particles, surface glass analysis by selective dissolution, and mineralogy by powder x-ray diffraction. These data were used to develop a physical model of fly ash particles that describes the heterogeneous distribution of elements on or in a reactive glass hull and in matrix glass and mullite. The model is discussed in terms of elemental partitioning and its application to the mechanistic approach advocated for prediction of leachate composition.
Fixation of Leachable Elements in Composite Waste Forms from North Dakota Lignite Coal Conversion Ash
Authors: Hasseti D. J. , Hassett D. F. 
Published: March 2011

ABSTRACTComposite waste forms prepared using solid and liquid waste streams from an integrated coal gasification facility at Beulah, North Dakota, were evaluated for the potential leachability of select trace elements using batch tests. Cylinders were fabricated from seven blends of the solid components using liquid waste incinerator blowdown, multi-effect evaporator concentrate, or tap water. Individual waste forms and composites were leached using the same protocols. Both long term and short term leaching tests were used to evaluate these composite waste forms.Comparisons of measured concentrations of elements with values calculated from data on individual components were used to determine any change in leachability that may have occurred. These changes were expressed as a fixation factor, which is a term derived by dividing the calculated leachability by the measured concentrations from the actual leaching tests. Results from these experiments indicated that leachability of some elements could be lowered by the mixing of various solid and liquid waste streams. Ettringite formation is one possible mechanism responsible for fixation of several of the elements.
Bulk Composition of the Glassy Phase in Some Commercial PFA's
Authors: Qian J. C. , Glasser F. P. 
Published: March 2011

ABSTRACTThe bulk chemistries of five Class F and one Class C pulverized fuel ash (PFA) are compared with the chemical compositions of the glass phase therein, the latter having been determined by analytical electron microscopy. Relative to the bulk, the glasses of Class F ashes concentrate Al2O3 and alkalis but reject Fe2O3. The glass phase is notably inhomogeneous on a micrometer scale; for example, large local variations occur in its Al2O3/SiO2 ratios. The Class C ash contained amorphous material with lower average Al2O3 contents than in Class F, but the extent of compositional homogeneities were greater.
Microstructure and Chemical Variation in Class F Fly Ash Glass
Authors: Qian J. C. , Lachowski E. E. , Glasser F. P. 
Published: March 2011

ABSTRACTFly ash consists of mixtures of crystalline substances in a glassy matrix. This matrix is itself inhomogeneous. The combustion process gives rise to compositional fluctuations typically on a micrometer scale; these fluctuations are preserved in the glass and are gradational. However, high-resolution transmission electron microscopy of Class F ash also reveals the existence of interfaces on a nanometer scale. These arise as a consequence of phase separation. Textures and interfaces typical of spinodal decomposition and possibility also suggestive of classical immiscibility have been observed. It is believed that the occurrence of phase separation resulting in nanometer-scale inhomogeneities will be a feature common to most Class F glasses. The consequences of this complex microstructure to reactivity are not as yet known, but some speculations are presented.
Speciation in Size and Density Fractionated Fly Ash III. The influence of HCL Leaching on the Glassy Constituents of a High-Ca Fly Ash
Authors: Berry E. E. , Hemmings R. T. , Cornelius B. J. 
Published: March 2011

ABSTRACTAsh density fractions, separated from a high-Ca fly ash, were leached with 6M HCl at 105°C. The density fractions (<0.79 and >2.85 g.cm−3) selected for leaching have been shown in previous work to consist largely of two different glass types, designated Glass I and Glass II. It was shown that both Glass I and Glass II are leachable to yield solutions containing Al and modifier cations. Acid attack on Glass I appears to involve hydrolysis of Si–O–Al (silalane) bridges along with ion exchange at available non-bridging oxygen sites. Attack on Glass II is more extensive, with both silalane and siloxane bridges being hydrolysed, and ion-exchange occurring at non-bridging oxygens. The products of leaching are aluminosilicates. In the case of Glass I, these remain as pseudomorphic, hollow spheres; whereas, for Glass II, substantial reprecipitation of silica (alumina) gel was found.
The Internal Structure of a Low-Calcium Fly Ash
Authors: Kilgour Carol I. , Diamond Sidney 
Published: March 2011

ABSTRACTA low calcium fly ash, rich in iron oxide, was subjected to shaking in 1% HF for up to 20 hours, and measurements were made at intervals of the following parameters: total weight loss, composition of the dissolved material, x-ray peak intensities of crystalline components and residual glass, and internal structures present within the fly ash spheres as revealed by the progressive dissolution treatments. The same fly ash was subjected to similar but longer-term treatment with simulated cement pore solution (potassium and sodium hydroxide). The compositions of the magnetically separated fraction and the non-magnetic residue were also separately determined. As a result of these studies, it was suggested that: (a) the time at which all of the potassium is dissolved might be used as an indicator of the completion of glass dissolution; (b) the position of the x-ray band for residual (more resistant ) glass shifts to higher 2Θ angle before the glass is completely dissolved; (c) in this fly ash, as determined by chemical analysis, all of the iron is in the magnetically-separable fraction, a feature that permitted estimation of the overall glass composition; and (d) this fly ash contains certain poorly understood components including silica-rich spheres, small spheres yielding EDXA signals only for iron, and “patches” of silica and alumina bearing material not of mullite composition, but all of which are highly resistant to HF dissolution.
Characterization of North American Lignite Fly Ashes I. Chemical Variation
Authors: Stevenson Robert J. , Collier James C. , Crashell John J. , Quandt Larry R. 
Published: March 2011

ABSTRACTThe chemical variation of central North American lignite fly ash can be compared using the major and minor oxide analyses and the distribution pattern of the inter-grain chemistries of the individual fly ash particles. AAS and electron microprobe chemical analysis of nineteen fly ashes have been used to illustrate the variations in bulk sample and individual grain chemistry. This information documents the chemical variability of the lignite fly ashes by geographic region. There is a direct relationship between grains rich in SiO2 and Al2O3 and in the Na2O content of the grains in lignite derived fly ashes. There is also a direct relationship between grains rich in CaP and the MgO and SO3 content of the grains in lignite derived fly ashes.
Cross-Sectioning Magnetic Thin Films for Tem
Authors: Ho H.-M. , Thomas G. , Schooley C. N. , Gau J.-S. 
Published: March 2011

ABSTRACTOblique incidence magnetic thin films are considered to be the most appropriate recording media for the next generation of video tape applications. In order to study the microstructure of such thin films, a specimen preparation technique employing ultramicrotomy has been developed. Because oblique incidence thin films have a porous structure and poor adhesion to the substrate, the problem of splitting of the thin films from the substrate is severe. This problem is reduced considerably by the following exercises: 1. using an acrylic embedding resin e.g. LR White (London Resin Co.), 2. thorough degreasing with solvents, 3. using a 55° diamond knife, and 4. trimming the block with a microtome before actual sectioning. The details of this preparation technique and some results obtained with this technique are presented.
Dimpling of Cadmium Telluride Samples for Transmission Electron Microscopy
Authors: Lee Michael E. , Neijs E. O. de , Letsoalo A. M. 
Published: March 2011

ABSTRACTA technique for preparing thin sections in CdTe samples for transmission electron microscopy by a method of mechanical dimpling combined with chemical etching has been investigated. The dimpling rates and surface morphologies of dimpled (100) CdTe samples as a function of pressure, abrasive size and viscosity are presented. This technique produces dimpled samples of well controlled geometries and surface morphologies and offers the advantage of a high dimpling rate and the precise determination of the dimple position. The disadvantage of this technique is that a final application of chemical etching or atom milling is still required to produce electron thin sections.
Preparation of Thin-Foil TEM Specimens from Sub-Millimeter Particulate
Authors: Kelly Thomas F. , Libera Matthew R. , Sande John B. Vander 
Published: March 2011

ABSTRACTThe particulate produced by many of the methods of rapid solidification, such as atomized powder, is of order 50 microns in diameter and is thus much too small to form the 3mm diameter disc conventionally used for thin-foil microscopy. 50 microns is, however, much too thick for direct TEM study on a support film and grid. A technique is described in detail that produces a composite wafer where atomized metal powder is sandwiched between two layers of electroplated nickel. This wafer is about 25 mm in diameter and about 250 microns thick. 3mm diameter TEM discs can be punched from the wafer and thinned by combinations of grinding, dimpling, jet-polishing, and ion milling. Depending on the composition and structure of the powder under study, the composite nature of the wafer can sometimes promote undesirable galvanic effects during jet polishing and differential thinning rates during ionmilling. Typical results are presented and discussion of the benefits and shortcomings of this technique is made. The method should be applicable to a variety of materials and geometries.
Specimen Cage Modification for Tem in-Situ Shearing
Authors: Meike Annemarie 
Published: March 2011

ABSTRACTIn-situ strain experiments with the electron microscope have contributed substantially to our understanding of deformation in metals and ceramics. However, physical characteristics of rock-forming minerals limit the direct application of experimental procedures developed for metals. The minerals muscovite (KAl2(Si3Al)O10(OH,F)2) and biotite (K(Mg0.6–1.8 Fe2.4–1.2) (Si3Al)O10 (OH,F)2) are chosen to develop techniques for preliminary deformation experiments. The present communication describes modifications of sample preparation techniques for micas. The standard tensile straining configuration is altered to a simple shear geometry by means of an intermediary specimen cage to allow the use of a more favorable sample orientation. The extension of the shearing geometry to the in-situ deformation of other rock-forming minerals is discussed.
Preparation of in Situ Cu-Nb Composite Sheet and Wire for Tem Analysis
Authors: Trybus C. L. , Laabs F. C. , Pelton A. R. , Spitzig V. A. 
Published: March 2011

ABSTRACTCu-Nb in situ composites attain anomolous increases in strength upon mechanical deformation. The unique filamentary microstructures that evolve during processing (cold rolling and/or wire drawing) are the source of the strengthening. Results from transmission electron microscopy characterization studies have played a key role in the understanding of the relationships between structure and properties. However, the fabrication of reliable TEM samples has been extremely challenging for the following reasons: (1) traditional electrochemical techniques are not suitable for the two-phase microstructure, (2) preparation of longitudinal and transverse sections of fine (∼150 μm diameter wires) and thin (∼60 μm thick) sheet is tedious, and (3) it is necessary to avoid excessive heat (< 30°C) during sample preparation to preserve the metastable structural arrangements. This paper will review the procedures used to prepare TEM specimens from bulk wire and sheet samples as well as from extracted Nb filaments. Proper techniques for plating, mounting, sectioning, polishing, and ion-thinning will be discussed.
A Rapid Specimen Preparation Technique For Cross-Section Tem Investigation Of Semiconductors and Metals
Authors: Vanhellemont J. , Bender H. , Rossou L. 
Published: March 2011

ABSTRACTA simple and rapid specimen preparation technique for the cross section TEM investigation of layered structures is discussed. Its wide applicability is illustrated for the investigation of processed silicon, compound semiconductors, silicon on quartz and also for metal/metal oxide interfaces.
Preparation of Liquids and Colloidal Dispersions for Tem: Cryo-Sem Studies of Bare-Film and Freeze-Fracture Specimens
Authors: Bellare J. R. , Sheehan J. G. , Davis H. T. , Scriven L. E. 
Published: March 2011

ABSTRACTLiquid and colloidal microstructures can be imaged at high resolution with cryo-TEM and cryo-SEM by fast-freezing with a Controlled Environment Vitrification System. Frozen bare-films can be directly imaged by TEM, while films sandwiched between metal plates can be frozen, fractured, and directly imaged with cryo-SEM or indirectly imaged by TEM after replication. We describe sample preparation techniques and report cryo-SEM studies of particle distributions and fracture patterns in such specimens.
A Technique for Preparing Transmission Electron Microscope Specimens Using Cleavage
Authors: Boone T. , Nakahara S. 
Published: March 2011

ABSTRACTA technique for observing both plan view and cross sections of a specimen directly in a transmission electron microscope (TEM) without relying on a tedious thinning operation was developed. This technique involves cleaving a specimen perpendicular to the plane, so that the thin (electron transparent) section of the cleaved edge can be directly imaged by TEM. The only limitations of this technique are that a specimen must be readily criacked or cleaved and that, since the transparent region is often bounded by a 90° corner, the extent of electron transparent region is somewhat localized. Nevertheless, the technique has the advantages of the ease of specimen preparation, and the absence of contamination or damage introduced in other conventional thinning methods. The geometry of the cleaved specimen is also suitable for reflection electron microscopy.
Properties of Patterned Gallium Arsenide on Silicon
Authors: Matyi R.J. , Shichijo H. , Kim T.S. , Tsai H.L. 
Published: March 2011

AbstractThe growth of GaAs on Si by MBE through openings in an oxide or nitride represents a convenient means for achieving monolithic GaAs/Si integration. We have examined a number of the materials growth and processing issues that must be resolved in order to achieve this goal. Some of the specific areas that have been investigated are (a) the effect of trench etching on the morphology of the patterned GaAs; (b) the dependence of patterned feature size on Hall mobility in both as-grown and postgrowth annealed samples; (c) the effect of annealing on the defect structure in the transition region from single crystal GaAs to polycrystalline growth; (d) the dependence of GaAs MESFET performance on proximity to the polycrystal transition; and (e) the performance of Si MOS devices following the GaAs MBE growth. Specific growth and processing issues concerning the integration of GaAs and Si device functions have also been examined.
Defect Reduction in Mocvd Grown Si/GaAs
Authors: Al-Jassim M.M. , Nishioka Takashi , Itoh Yoshio , Yamamoto Akio , Yamaguchi Masafumi 
Published: March 2011

AbstractThe effectiveness of thermal annealing and strained layer superlattices (SLS's) in defect reduction in Si/GaAs structures was studied. The GaAs layers were grown on (100) Si substrates by low pressure MOCVD. They were evaluated by TEM, HREM, EBIC and PL. As-grown layers contained dislocation densities in the 108-109 cm−2 range, depending on the layer thickness. Post-growth and in situ annealing were performed on a wide variety of these structures. TEM examination showed that in situ annealing was more effective as it resulted in confining a large portion of the threading dislocations to the interface region. Furthermore, the interaction of threading dislocations to form closed loops was evident. Additionally, the effect of GaAs/GaInAs and GaInAs/GaAsP SLS's on dislocation bending was investigated. The former SLS, although not lattice matched to GaAs, proved more effective.
MBE Growth of GaAs on an Exactly (001)-Oriented Si Substrate and Selective Epitaxial Growth for Fabrication of Modulation-Doped Fet's
Authors: Noge H. , Kano H. , Hashimoto M. , Igarashi I. 
Published: March 2011

AbstractGaAs layers free of antiphase domains (APD's) have been grown by molecular beam epitaxy (MBE) on nominally (001)-oriented Si substrates. This is achieved by preheating the substrates at 950 °C over 60 min or at 1000 °C over 5 min in an ultrahigh vacuum. The maximum Hall mobility at 293 K is 5300 cm2 /Vs for the APD-free GaAs layer doped with Si at a concentration of 2×1016 cm−3 . Selective epitaxial growth of GaAs has been carried out on a Si substrate pattrened with SiO2, which was formed by wet O2 oxidation. By choosing an appropriate thickness of the SiO2 layer, the warpage of wafers can be reduced to zero. While single-crystalline GaAs is grown on Si-exposed areas, highly-resistive (ρ ≧ 105 Ωcm) poly-crystalline GaAs is deposited on SiO2 . This technique has been successfully applied for the device isolation of modulation-doped FET's (MODFET's, HEMT's, etc.) on Si without mesa-etching. The transconductance of the MODFET with a 3 µm-long gate reaches 88 mS/mm at 293 K.