bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Porosity and Pore Structure of Hydrated Cement Pastes as Revealed by Electron Micrsocopy Techniques
Authors: Richardson Ian G. , Groves Geoffrey W. , Rodger Sally A. 
Published: March 2011

AbstractThe application of transmission electron microscope techniques to the study of cement hydration can reveal the nature of the fine pore structure present in dried cement pastes. Studies of OPC cement pastes and OPC/fly ash or blast-furnace slag blends are presented and compared. Preliminary results of a technique which allows effective imaging of the porosity which is important in permeation, and which is involved in mercury porosimetry measurements, are presented.
Corrosion of Hardened Cement Paste by NH4NO3and Acetic and Formic Acids
Authors: Bajza Adolf 
Published: March 2011

AbstractEffects of NH4NO3, CH3COOH and HCOOH solutions on the pore structure and other properties of hardened cement pastes made out of portland, slag, and fly ash cements at different water-to-cement ratios are discussed.Total porosity and the volume of pores detectable by mercury intrusion porosimetry (MIP) increased with increasing water-to-cement ratio, concentration of aggressive solution, and time of immersion. The weight, bulk density, and compressive strenath of the samples decreased at the same time. Use of blended cements did not result in improvement of the long-term durability of the samples. The degradation of the cement pastes increased from NH4NO3to CH3COOH to HCOOH.
Studies Of Cement Grouts And Grouting Techniques For Sealing A Nuclear Fuel Waste Disposal Vault
Authors: Onofreic Maria , Gray Malcolm N. , Keil L. Douglas , Pusch Roland 
Published: March 2011

AbstractA cement-based grout (90% Type 50, 10% silica fume, 0.4 < water-to-cement ratio, w/c < 0.6) has been used in field trials at AECL's Underground Research Laboratory in Canada and at the OECD/NEA Stripa Mine in Sweden, to evaluate suitable grouts and grouting techniques that could be used for sealing a nuclear fuel waste disposal vault mined deep in granite. Laboratory studies have been carried out to determine the following grout properties: hydraulic conductivity (k); resistance to piping and erosion during setting; influence of grout on the pH and chemical composition of water permeating grouted rock; and the ability of the grout to self-seal after fracturing.Laboratory tests have confirmed the low intrinsic k of these cement mixtures (10−14 m/s). Using a specially developed cone-in-cone apparatus, we have studied the effect of fracture dilation and temperature changes on the k of thin films of cement. If fractured, the grout has an ability to self-seal and the rate of self-sealing increases with increasing temperature.The pH and ionic composition of the water permeating grouted fractured granite rock were found to vary with grouted fracture aperture and grout/rock volume ratio. The field tests demonstrated that grout can penetrate and seal very fine fissures (apertures less than 50 μm).
Seawater Leachability Of Cement Solidified Heavy Metal Wastes
Authors: Elkorchi Tahar , Campbell Kristine , Gress David 
Published: March 2011

AbstractThe seawater leachability of portland cement solidified cadmium and lead wastes is investigated. The synthetic seawater leachates were analyzed for metals content using atomic absorption spectrophotometry. The pH and alkalinity of the leachate was also measured. The cumulative cadmium release after 46 days of leaching was approximately 1.0 percent of the initial total amount added to the portland cement mixture. Lead was not detected in the leachate. The pH was initially higher and the alkalinity lower and subsequently approached the pH and alkalinity values for seawater after 30 days of leaching.The microstructure of the solidified waste was investigated using the SEM, XRD, MIP and helium pycnometry. Cadmium was detected as cadmium hydroxide while lead was not detected in crystalline form. The total porosity of cadmium and lead wastes were similar however the cadmium waste had a higher volume of pores larger than 0.2 microns.During the leaching process the surficial microstructure of the solidified waste exhibited a dynamic layer of calcite, aragonite and brucite while the internal structure showed large amounts of ettringite crystals in the cadmium waste only which caused excessive expansion and cracking. A proposed leaching mechanism experienced by the solidified waste is related to the microstructural characteristics of the matrix.
Relationships Between Permeability And Microstructural Characteristics Of Fly Ash Mortars
Authors: Day Robert L. , Konecny Ladislav 
Published: March 2011

AbstractThe paper describes research to evaluate permeability and the microstructure of mortars containing fly ash as a partial replacement for cement. The replacement levels of cement by fly ash were 35 and 50% by volume and 50% by weight; effectiveness of mortars made with four types of fly ash at two water/cement ratios, 0.47 and 0.65, were assessed. Three types of permeability measurements were made: (a) water permeability, (b) oxygen permeability and (c) permeability to chloride ion by the 6-hour rapid permeability test. Measurements were performed at 7, 28 and 160 days age. Strength gain in the mortar mixes was also monitored. In an attempt to explain trends observed in permeability, the pore structures of oven-dried and solventexchanged specimens were examined by mercury porosimetry. Mortars manufactured with fly ash displayed superior engineering properties when compared to the control mortars. Significant correlations were found among measurements of permeability by water, oxygen and chloride ion. Relationships were also observed between permeability and some microstructural indicators, especially the volume of mercury intruded up to a pressure of 41 MPa (6000 psi).
Pore Structure, Permeability, And Chloride Diffusion In Fly Ash-And Slag-Containing Pastes And Mortars
Authors: Malek R. I. A. , Roy D. M. , Fang Y. 
Published: March 2011

AbstractThe transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.
Chloride Permeability Of Concrete Containing A Flyash And A Blastfurnace Slag
Authors: Kawamura Mitsunori , Torii Kazuyuki 
Published: March 2011

AbstractThe effects of curing conditions on the chloride permeability of concrete with various replacements of Portland cement by a flyash and a blastfurnace slag was investigated. In order to relate the porosity and pore size distribution of concretes to their chloride permeability, mercury intrusion porosimetry measurements were also conducted. The results showed that exposure of concretes to a relatively low humidity at early ages increased their chloride permeability. It was also found that the chloride permeability of concrete increased proportionally with increasing volume of pores larger than 0.1 μm in diameter.
Densification And Migration Of Ions In Blast Furnace Slag-Portland Cement Pastes
Authors: Feng Q. L. , Lachowski E. E. , Glasser F. P. 
Published: March 2011

AbstractWell-cured slag cement blends are known to give rise to paste matrices of low permeability. Electron microscopy has been used to follow microstructural development in slag cement pastes. An initially dense layer of hydrated product develops around the slag grains. Its chemistry and microstructure are not constant but evolve with time. These variations have been explored by analytical electron microscopy, X-ray diffraction, etc. Mg is concentrated in this zone and serves as a useful chemical marker. However an outer matrix of mixed hydration products also develops, to which slag and cement both contribute. The additional contribution of Ca, Al and Si derived from slag to this matrix is considered to explain its gradual densification and resultant low permeability.
As Review Of Conventional And Non-Conventional Pore Characterization Techniques
Authors: Gerhardt Rosario 
Published: March 2011

AbstractA series of techniqu1es were employed to characterize the pore microstructure of a group of colloidal silica-alkali silicate gels. Methods used included mercury penetration porosimetry, nitrogen desorption measurements, transmission electron microscopy, single and multiple small angle neutron scattering, nuclear magnetic resonance relaxation measurements, x-ray tomography and dielectric constant measurements. Comparison of results of pore volume, pore size and size distribution as well as homogeneity of the pore structure are presented.
Methodologies Of PSD Measurements In HCP : Postulates, Peculiarities, And Problems
Authors: Diamond Sidney 
Published: March 2011

AbstractA brief discussion is presented of some of the characteristics of hardened cement paste (hcp) and hcp in concrete that bear on the measurement of pore size distribution. The postulates underlying several present and potential measurements are discussed individually, and an attempt is made to assess the applicability of each in light of the peculiar characteristics of hcp. Some of the problems inherent in each procedure are briefly described.
Formation of Interstitial Defects in High Concentration Shallow Phosphorous Diffusions in Si.
Authors: Jaccodine Ralph 
Published: March 2011

ABSTRACTAn experimental study of high concentration (1019 –1021 /cm3 shallow diffusion was undertaken using TEM to investigate the nature of these diffusion-related defects. Phosphorous from a wide variety of sources (PBr3, POCl3, etc.) other than ion implantation was used in temperature range from 950°– 1100°C and for times of 15 minutes to 1 hour. Care was taken in surface preparation and material selection to avoid extraneous defects from sources other than the diffusions.A high concentration of small dislocation loops (1012/ cm2) was present in the top few microns of the wafers. Diffraction contrast on the loops revealed that they are of edge character with Burger's vector b = ½<110>. Identification of the nature of these loops by tilting method [(g·b)·s] and anomalous dark-faced black-white lobes show they are of the interstitial type, i.e. the observed defects place the surrounding matrix in a compressive state.
Infrared-Absorption of Thermal Donors in Silicon
Authors: Oeder Robert , Wagner Peter 
Published: March 2011

ABSTRACTThermal donors generated in CZ-silicon by annealing at 450° C are investigated by infrared absorption spectroscopy.Up to nine double-donors can be distinguished due to their line spectra characteristic for effective-mass-like donors.Their number and their concentrations depend on the duration of the thermal treatment. The formation of the different donors is ruled by complicated kinetics.
Correlation of Oxygen and Recombination Centers on a Microscale in Asgrown Czochralski Silicon Crystals
Authors: Nauka K. , Gatos H. C. , Lagowski J. 
Published: March 2011

ABSTRACTQuantitative microprofiles of the interstitial oxygen concentration and of the excess carrier lifetime, with a spacial resolution of about 20 μm, were obtained in as-grown dislocationfree CZ-Si crystals employing a double laser absorption technique. It was found that maxima (minima) in oxygen concentration along the crystal growth direction coincide with minima (maxima) of the lifetime. It was further found that the relation between changes in oxygen concentration and in lifetime varies in the radial direction indicating that “as-grown” oxygen precipitates are involved in lifetime limiting processes.
Oxygen Precipitation in Silicon - Its Effects on Minority Carrier Recombination and Generation Lifetime
Authors: Varker C. J. , Whitfield J. D. , Fejes P. L. 
Published: March 2011

ABSTRACTThe effects of oxygen precipitation on the minority carrier recombination lifetime (TR) and the carrier generation lifetime (TG) have been characterized for a ‘typical’ silicon crystal grown with the Czochralski method. Infrared (IR) absorption measurements were obtained on polished wafers, before and after 2 step thermal anneals at 800°C and 1050°C to characterize the axial distribution of interstitial and precipitated oxygen in the ingot. Computerized measurements on NMOS diode and capacitor arrays were used to characterize the axial and radial distributions of carrier lifetime. The results indicate that oxygen precipitation is the dominant mechanism contributing to the degradation of both minority carrier recombination andgeneration lifetime.
Crystalline Particles in Thermally Grown Silicon Dioxide
Authors: Ponce F. A. , Yamashita T. 
Published: March 2011

ABSTRACTSmall crystalline particles in the vicinity of the Si/SiO2 interface have been directly observed by high resolution transmission electron microscopy. These crystallites have typical diameters between 20 and 120 Å. Based on the observed interplanar spacings and angles in lattice images, the structure of these particles has been found to match those of cristobalite. Some orientation relationships also appear to exist between these particles and the silicon layer.
Deep Radiative Transitions in InP
Authors: Temkin H. , Dutt B. V. 
Published: March 2011

ABSTRACTResults of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by bulk and epitaxial techniques with a variety of dopants are reported. In order. to understand the origin of the photoluminescence spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the LPE wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cddiffused bulk samples.Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donor-like level related to the P-vacancy-impurity complex. Bands at 1.21 eV and 1.15 eV appear to be due to emission to native acceptor levels associated with the In-vacancy. The 1.08 eV band is attributed to emission to a level involving the complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these bands and residual impurities is discussed. A comparison with the work of other investigators tends to support these assignments.
Analysis of Defects in Heavily-Doped MBE-GaAs
Authors: Carter C.B. , Desimone D.M. , Griem H.T. , Wood C.E.C. 
Published: March 2011

ABSTRACTGaAs Has Been Grown By Molecular-Beam Epitaxy (MBE) With Large Concentrations (∼1018CM−2) Of Sn, Si, Ge, And Mn As Dopants. The Heavily-Doped N-Type Material Has Been Found To Contain Regions Of A Very High Dislocation Density. An Analysis Of The Less Complex Defect Areas Shows That The Dislocations Originate In The MBE-Grown Layer. These Observations And Others On More Complex Defect Clusters Are Compared With Recent Studies Of Defects In Material Grown By Liquid Phase Epitaxy (LPE). The More Heavily Doped P-Type Material Contains Discs Of Mn-Rich Material At The Surface Of The MBEgrown Epilayer. Both The Structure And Composition Of These Regions Have Been Examined.
Process-Induced Defects in High-Purity GaAs
Authors: Campbell P. H. , Aina O. , Baliga B. J. , Ehle R. 
Published: March 2011

ABSTRACTHigh temperature annealing of Si 3 N4 and SiO2 capped high purity LPE GaAs is shown to result in a reduction in the surface carrier concentration by about an order of magnitude. Au Schottky contacts made on the annealed samples were found to have severely degraded breakdown characteristics. Using deep level transient spectroscopy, deep levels at EC–.58eV, EC–.785eV were detected in the SiO2, capped samples and EC–.62eV, EC–.728eV in the Si3N4 capped Samples while none was detected in the unannealed samples.The electrical degradations are explained in terms of compensation mechanisns and depletion layer recombination-generation currents due to the deep levels.
Interaction of Dislocations with Impurities and its Influence on the Mechanical Properties of Silicon Crystals
Authors: Sumino Koji 
Published: March 2011

ABSTRACTA review is presented of the work on the influence of impurities on the dynamic behavior of dislocations in silicon crystals and also on the resulting effects in the mechanical strength performed by the author's group. Special emphasis is laid on the effects of light element impurities such as oxygen, nitrogen and carbon. Although all of these impurities do not affect the velocities of dislocations moving under relatively high stresses, oxygen and nitrogen atoms are found to lock slowly moving dislocations and dislocations at rest very effectively. Such locking of dislocations results in the decreases in the activities of generation and multiplication centers for dislocations, leading to the strengthening of the crystals. The high strength of silicon crystals brought about by the impurities is lost when the crystals are subjected to the heat treatments which allow the precipitation of the impurities on a macroscopic scale. This softening is shown to be caused by dislocations punched out from precipitates and by the exhaustion of the impurities dissolved in the matrix crystal.
Shear Force Effects on Sidewall Penetration of Extended Dislocations in Phosphorus Implanted Emitters
Authors: Tseng W. F. , Davis G. E. 
Published: March 2011

ABSTRACTPhosphorus implanted emitters are known to have a dislocation network formed to relieve the strain caused by the lattice contraction of solute phosphorus ir, silicon. The extension of the dislocation network into the emitter-base regior, has also been related to the degradation of leakage current and the generatiol, of excess noise in an NPN bipolar transistor. The penetration of the extendeot dislocation network is shown in this paper to be related to a shear force. The shear force is the resultant of the compressive force generated from the solute phosphorus and an induced surface force generated from the thick oxide layer over the emitter formed during high temperature heat treatments. This shear force can pull the dislocation network through the junction sidewall.
Photoplastic Effects in II-VI Crystals
Authors: Takeuchi Shin , Maeda Koji , Nakagawa Kiyokazu 
Published: March 2011

ABSTRACTA reversible change in the flow stress with the illumination of a band gap light (photoplastic effect: PPE) is observed commonly in II-VI semiconducting compounds both with the zincblende and the wurtzite structures. After reviewing the experimental results accumulated so far concerning the usually observed PPE, detailed microscopic experiments on CdTe (partly on CdS) single crystals are described. In-situ TEM straining experiments with a laser illumination system clarified that the dislocation mobility, evidently controlled by the Peierls mechanism, is not affected by light illumination.The investigation of the dislocation glide behavior over a longer range using the etch pit method and the cathodoluminescence microscopy with a SEM revealed that the dislocations are apt to become immobilized after traveling a certain distance from the sources with a high velocity.The dislocation loops and cusps observed by TEM suggest that the immobilization is caused by jog formation along screw segments. Those results suggest that the positive PPE is caused by the decrease in the mean free path of multiplied dislocations due to the enhanced jog formation by illumination. This viewpoint is supported by the high density of dislocation debris left in specimens deformed under illumination, the enhanced work hardening rate under illumination and the reduction of the PPE when the dislocation mean free path becomes determined by other photoinsensitive factors such as forest dislocation cutting and specimen size. The microscopic mechanism of the enhanced jog formation is discussed in terms of electrostatic interaction between charged point defects and dislocation charge which is increased with the illumination.
Quenched-in Defects in CW Laser Irradiated Virgin Silicon.
Authors: Chantre A. , Kechouane M. , Bois D. 
Published: March 2011

ABSTRACTQuenched-in defects in cw laser irradiated silicon have been identified using deep level transient spectroscopy. Four among the five dominant defect states arise from transition metal impurities (iron, chromium) present in precipitates in the as-grown material and dispersed into the crystal upon heat treatment. Native defects are involved in the form of phosphorous-vacancy complexes, which account for the remaining level.
Combined Oxygen - Nitrogen Ion Implants into Ti6Al4V
Authors: Greenwald Anton , Daly James , Meroth John , Oliver Richard , Sioshansi Piran , Clayton Clive 
Published: March 2011

AbstractThe alloy preferred for medical protheses, Ti6Al4V, was ion implanted with oxygen and nitrogen alone and in combination at varying energies, 25 to 120 keV, and varying dose levels, 1017 to 1018 ions/cm2. Measurements were made of microhardness, corrosion resistance, chemical bonding of implanted species, and (with UHMpWol yethylene) pin-on-disk wear and friction. The addition of oxygen to nitrogen implants now used in production was found to have little effect on wear or any other parameter.
A Review of European Trends in Space Tribology and its Application to Spacecraft Mechanism Design
Authors: Rowntree Robert A. , Todd Michael J. 
Published: March 2011

AbstractThe development of space tribology and its application in the design of spacecraft moving mechanical assemblies (MMA's) in Europe has followed a different course from that in the USA. This is probably because of the distinct preponderance of 3-axis stabilised space vehicles - used for communications and for earth observation over Europe - together with the preference for solid lubricants in such devices as solar array drives and some types of scanner and de-spin mechanism. The paper reviews the current status and discernible future trends in European space tribology. Examples of current MMA types are given where evolved lubricants and lubrication techniques have been applied.
MoS2 Interactions with 1.5 eV Atomic Oxygen
Authors: Martin J.A. , Cross J.B. , Pope L.E. 
Published: March 2011

AbstractExposures of MoS2 to 1.5 eV atomic oxygen in an anhydrous environment reveal that the degree of oxidation is essentially independent of crystallite orientation and thesurface adsorbed reaction products are MoO3 and MoO2. A mixture ofoxides and sulfide exist over a depth of about 90 Å and this layer has a low diffusion rate for oxygen. It is concluded that a protective oxide layer will form on MoS2 upon exposure to the atomic-oxygen-rich environment of low earth orbit.