bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuum Damage Mechanics Studies on the Dynamic Fracture of Concrete
Authors: Chen E. P. 
Published: March 2011

ABSTRACTThe dynamic fracture of concrete in tension is studied by applying a continuum damage model developed by the author and his coworkers [1–3]. In this model, the degree of damage in concrete corresponds to the fraction of concrete volume that has been tension relieved, and tensile microcracking has been taken as the damage mechanism. In compression, the concrete is assumed to respond in an elastic/perfectly plastic manner. Strain-rate effects have been explicitly included in the model. Accumulation of damage in the material is reflected by the progressive weakening of the material stiffness. Examples involving center- and edge-cracked plate specimens subjected to the action of step and ramp loads are used to demonstrate the material responses predicted by the model. The bulk pressure versus strain relationships at locations close to the crack tip clearly show strainsoftening behavior. The damage tends to localize around the crack and its extent in the specimen is dependent upon both the crack geometry and the loading type. These results are presented and their implications are discussed.
Elliptical Surface Representation of Continuum Vectorial Damage
Authors: Galloway Rodney G. 
Published: March 2011

ABSTRACTThis paper focuses on the establishment of a simple damage surface that allows the use of a vector representation of damage to be applied in a two or three dimensional framework. Specifically for contrast to some types of tensor representations [1], the surface is developed in such a manner to allow maximum damage to occur in planes adjacent to the plane of maximum tensile strain. The limitations of this surface then are pointed out. Comparison of this postulate with recent data from Jan van Mier [2] is also presented.
Tensile Strength of Concrete at Different Strain Rates
Authors: Soroushian Parviz , Choi Ki-Bong , Fu Gung 
Published: March 2011

ABSTRACTResults of dynamic tensile strength tests of concrete, produced by the authors and other investigators, were used to study the effects of strain rate on the tensile strength of concrete. The influence of moisture content and compressive strength of concrete, and type of test (splitting tension, flexure, or direct tension) on the strain rate-sensitivity of the tensile strength were evaluated. An empirically developed expression is presented for the dynamic-to-static ratio of concrete tensile strength in terms of the rate of straining.
A Procedure for the Interpretation of Fly Ash Particle Size Data
Authors: Diamond Sidney , Kilgour Carol L. 
Published: March 2011

ABSTRACTA procedure has been developed for organizing and displaying the results of particle size distribution determinations on fly ash so as to promote simple and useful comparisons. The procedure involves comparative plots of histograms displayed on a logarithmic size basis, and is illustrated by selected data drawn from a larger suite of analyses of Indiana fly ashes.
Fly Ash Beneficiation and Utilization in Theory and in Practice
Authors: Butler W. Barry , Mearing Marc A. 
Published: March 2011

ABSTRACTOver the years there have been hundreds of papers written on benefication of fly ash to extract alumina, magnetite, activated carbon, cenospheres, etc., and to enhance the properties of the fly ash itself for concrete making purposes. Several of the processes have been patented. Few of them have been exploited commercially. We examine some of the more popular processes, the history of their success or failure, and current achievements with fly ash beneficated for use in Portland cement concrete.
Identification of Chemical Compounds in Fly Ash by X-Ray Absorption Spectroscopy and Proton-Induced X-Ray and Gamma-Ray Emission Analyses
Authors: Lytle N. W. , Eatough D. J. , Hansen L. D. , Hill M. W. , Mangelson N. F. , Lytle F. W. , Greegor R. B. 
Published: March 2011

ABSTRACTProton-induced X-ray emmision and proton-induced gamma-ray emission analyses have been used to determine the elemental content of four oil fly ash samples collected from the flue line of an oil-fired power plant. X-ray absorption spectroscopy was used to characterize the vanadium and nickel compounds present in the fly ash. Vanadium was present primarily as VOSO4·3H2O and nickel was present as a mixture of NiSO4 and NiO.
Surface Characterization of the Mechanism for Decreased Boiler Slagging via Fly Ash Surface Modification
Authors: Macey Christopher J. 
Published: March 2011

ABSTRACTSlagging difficulties encountered in large, pulverized coal-fired utility boilers can be alleviated by using recently developed chemical conditioners designed to inhibit the agglomeration of molten fly ash particles. Slagging results from the impaction and accretion on the boiler interior surfaces of molten ash particles in the flue gas resulting from the combustion of coal. Electron Spectroscopy for chemical Analysis (ESCA) and ion sputtering depth profiling were utilized to examine the mechanism whereby a fuel conditioner containing copper oxychloride effectively reduced slag deposition rates during a pilot-scale, pulverized coal combustion experiment.
Carbonation Effects in Hardened Fly Ash Cements
Authors: Meland Inger 
Published: March 2011

ABSTRACTCarbonation in hardened pastes of fly ash cements, stored in a CO2 atmosphere and exposed to different relative humidities, has been investigated in order to study its effects upon different properties of cement pastes. Thermogravimetry (TG), x-ray diffractometry, SEM, and mercury porosimetry (MIP) have been used to characterize the carbonation phenomenon. The results indicate that different relative humidities in the storage chambers lead to carbonation of different solid phases in the hydrated pastes. This effect is discussed in terms of TG- and x-ray analysis. Changes in pore size distribution due to carbonation have been analyzed by MIP and SEM.
Diffusion and Pore Structure in Portland Cement Pastes Blended with Low Calcium Fly Ash
Authors: Kumar Amitabha , Roy Della M. 
Published: March 2011

ABSTRACTEffective coefficients for the diffusion of Cs+ and Cl− ions accross hardened plates of Portland cement and Portland cement-fly ash blend pastes were measured at 27°, 38° and 60° for samples cured up to 28 d. The porosity and pore size distributions of the same hardened plates were also determined. The fly ash blends show lower anion and cation diffusion rates at higher temperatures, although the porosity is not significantly different from the neat paste. The finer pore size is considered responsible for the slower diffusion in the blends. The electronegative nature of the pore surfaces also contributes to the slower cation diffusion.
A Strength Model for Concretes Containing Fly Ash, Blast-Furnace Slag and Silica Fume
Authors: Dunstan Edwin R. 
Published: March 2011

ABSTRACTThis paper describes preliminary a model for the strength of concretes containing industrial by-products such as fly ash, blast-furnace slag, and silica fume. A formula that describes the various strength production mechanisms of these by-products is developed. These materials produce strength by pozzolanic reaction, by latently hydraulic reactions and by self-cementing reactions similar to Portland cement. A method of separating the effect of each mechanism is proposed. A parameter for each of these strength producing mechanisms can be determined from concrete strength data.
Leaching Behavior of Fixed-Bed Gasification Ash Derived from North Dakota Lignite
Authors: Hassett D. J. , Henke K. R. , McCarthy G. J. 
Published: March 2011

ABSTRACTthree different fixed-bed gasifiers have been leached using: (1) the EPA-EP leaching test; (2) a similar test that starts with a synthetic North Dakota groundwater; (3) the ASTM D3987–81 method; (4) a long-term (120 day) leaching experiment. The gasification ashes were highly alkaline and produced pH's in the range 10–13 during tests 2 through 4. Compositions of major, minor and trace elements were determined by AAS and ICAP analyses of leachates. None of the EPA-EP test leachates from any of the ashes exceeded the EP Trigger values that define a hazardous waste according to the RCRA criteria. The long-term leaching experiments provided insights into the rates of extraction of elements from ash and could be useful in modeling selected failure scenarios in an ash disposal pit. At various times during the long-term leaching experiments, substantial fractions of the Na, K, Al, S, As, Mo, Se and V in the ash were extracted. Liquid to solid (l:s) ratios were important in determining the quantities of elements extracted and in controlling solution pH; during most of the 120 day experiments, pH's were near 13 in a 2:1 ratio experiment and just below 10 in a 20:1 ratio experiment. X-ray diffraction analysis of the leaching residue indicated that only a portion of the ash reacted with the leaching solutions. The reaction products were largely noncrystalline, but minor amounts of zeolites, calcite and gibbsite were identified. The formation of such secondary solid phases appears to be important in controlling leachant concentrations.
Thermal Properties of Fly Ash-Slag Cement Waste forms for Disposal of Savannah River Plant Salt Waste
Authors: Kaushal S. , Roy D. M. , Licastro P. H. , Langton C. A. 
Published: March 2011

ABSTRACTWaste processing at the Savannah River Plant will involve reconstitution of the salts (NaNO3, NaNO2, Na2 SO4 and NaOH) into a concentrated solution followed by solidification in a cement-based waste form. Phase stability and mechanical durability of this material will depend to a considerable extent on the thermal properties of the waste form. Fly ash has been used to moderate the hydration and setting processes so as to avoid high temperatures which could cause thermal stresses. Both high-calcium (Class C) and low-calcium (Class F) fly ashes were studied. Other constituents of the mixes include granulated blast furnace slag and finely crushed lime-stone. The adiabatic temperature increases and thermal conductivities were measured and related to matrix mineralogy and microstructure as determined by x-ray diffraction and scanning electron microscopy, respectively.
A Survey of Ash Sources for Mineral Recovery
Authors: Watson J. S. 
Published: March 2011

ABSTRACTTwenty-two ash samples from utility companies across the country were studied to determine their potential use for mineral recovery. Most tests were limited to chemical analyses and determination of leachable metal values in the ashes, but samples from two utilities were examined in more detail. The more detailed analyses included physical as well as chemical properties. This work was part of a broad-based effort supported by the Electric Power Research Institute (EPRI), and the results from this study were used in economic assessments of mineral recovery from fly ash made by Kaiser Engineers in another part of the EPRI program. Although the compositions and properties of the ash samples varied considerably, only two of the 22 ash samples studied appeared to be unsuitable for mineral recovery. These results indicate that large portions of the ash produced in this country are suitable for potential resource recovery, but further work to evaluate potential upgrade of the leached ash residue is recommended.
Monolithic Integration of Si and GaAs Devices
Authors: Choi H. K. , Turner G. W. , Tsaur B-Y. , Windhorn T. H. 
Published: March 2011

ABSTRACTIntegration of Si MOSFETs with GaAs MESFETs and with GaAs/AlGaAs double-heterostructure LEDs on monolithic GaAs/Si substrates is reported. Both Si MOSFETs and GaAs MESFETs show characteristics comparable to those for devices fabricated on separate Si and GaAs substrates. In LED/MOSFET integration, the cathode of each LED is connected with the drain of a MOSFET. This is the first time that Si and GaAs devices have been monolithically interconnected. LED modulation rates up to 27 Mbps have been achieved by applying a stream of voltage pulses to the MOSFET gate.
High Volume Production Growth of GaAs on Silicon Substrates
Authors: Ito Chris R. , Feng M. , Eu V. K. , Kim H. B. 
Published: March 2011

ABSTRACTA high-volume epitaxial reactor has been used to investigate the feasibility for the production growth of GaAs on silicon substrates. The reactor is a customized system which has a maximum capacity of 39 three-inch diameter wafers and can accommodate substrates as large as eight inches in diameter. The MOCVD material growth technique was used to grow GaAs directly on p-type, (100) silicon substrates, three and five inches in diameter. The GaAs surfaces were textured with antiphase boundaries. Double-cyrstal rocking curve measurements showed single-cyrstal GaAs with an average FWHMof 520 arc seconds measured at four points over the wafer surface. Within-wafer thickness uniformity was ± 4% with a wafer-to-wafer uniformity of ± 2%. Photoluminescence spectra showed Tour peaks at 1.500, 1.483, 1.464, and 1.440 ev. Schottky diodes were fabricated on the GaAs on silicon material.
Photoluminescence and Photoluminescence Excitation Spectra of GaAs Grown Directly on Si
Authors: Zemon S. , Shastry S. K. , Norris P. , Jagannath C. , Lambert G. 
Published: March 2011

ABSTRACTThe photoluminescence of GaAs/Si grown by OMCVD has been analyzed as a function of temperature and the dominant high temperature line identified as a conduction-band-to-valence-band transition. Photoluminescence excitation spectra indicate that the transition is excitonic at 4.2 K. A second line, also identified as intrinsic, dominates the spectra below 100 K. A biaxial tensile strain is proposed to account for the two intrinsic lines through a splitting of the valence band degeneracy.
MBE Growth of Low Dislocation and High Mobility GaAs-on-Si
Authors: Lee Jhang Woo 
Published: March 2011

ABSTRACTData is presented on the optimization of several molecular beam epitaxial growth processes to provide low dislocation density and high mobility GaAs single crystals on (100) Si wafers. The substrate tilt angle, the growth temperature, and the first buffer layer structure, were investigated Tor this purpose. Using Hall measurements the GaAs layers grown on 2 or 3-degree tilt (100) Si showed consistently high mobilities which are equivalent to the homoepitaxial GaAs mobility. Transmission electron microscopy (TEM) revealed that on tilted (100) Si substrates most of the misfit dislocations were confined within the first 50 Å GaAs layer by forming a type of edge dislocation at the Si surface step edges. Also low temperature grown buffer layers always gave better morphologies and lower etch pit densities while keeping the high mobilities on overgrown GaAs layers.
Microstructure of thin layers of MBE-grown GaAs on Si substrates
Authors: Rosner S. J. , Koch S. M. , Harris J. S. , Laderman S. 
Published: March 2011

ABSTRACTThe ability to grow high quality epitaxial GaAs films directly on Si substrates has recently been demonstrated by Molecular Beam Epitaxy. Many of the most successful growth techniques include initial growth at low temperatures and slow growth rate to nucleate the compound on the elemental semiconductor with subsequent normal growth under conditions used for homoepitaxial GaAs MBE. The mechanisms for the success of this method are still poorly understood. This work focusses on a study of the structural evolution of this low temperature initial layer and conventionally grown overlayer. Thin films in the 5 to 300 nm range were used to evaluate the effect of the temperature and thickness on the growth process. Thicker films, described elsewhere, were used to evaluate the crystalline and optical quality of potential device layers.The structure of the thin buffer layers was studied as a function of both temperature and thickness. The crystalline quality of these layers was found to be quite poor, with substantial disorder at the GaAs/Si interface. The quality improved slowly as a function of thickness. The effect of the conventional overgrowth on this initil layer was also investigated. It was found that the quality of the low tumperature layer improved as normal overgrowth continued, as measured by ion channeling aligned yields. After 200 nm of overgrowth, ion channeling aligned yields from the material at the interface had declined substantially. This indicates that substantial regrowth and annealing of defects occurs as growth continues. These observations are further confirmed by TEM.
Characteristics of Thin Layers of SiO2 Fabricated by Rapid Thermal Oxidation
Authors: Prasad S. , Haase J. , Früchtnicht R. , Ferretti R. , Haack D. 
Published: March 2011

ABSTRACTThin layers of SiO2 (60-300 Å) were fabricated by rapid thermal oxidation (RTO). Growth rate on (100) and (111) Si was determined. Two different high-temperature anneal cycles were used to reduce the interface state density. Work function difference between metal and semiconductor depends upon technology and can be attributed to the changes in Si-SiO2 barrier height.
A Comparison of RTO and Furnace Oxides
Authors: Burnham Marie E. , Legge Ronald N. , Jaim Nulman Jaim Nulman , Fejes Peter L. , Brown James F. 
Published: March 2011

ABSTRACTThe original intent of this study was to compare rapid thermal, thin (80-100Å) gate oxides with standard, furnace-grown, thin gate oxides for endurance. Wafer processing before gate oxide growth was chosen to duplicate processing used ina typical non-volatile memory product. In particular, care was taken to duplipate pre- and post- gate growth processing of field oxide isolated polysilicon capacitors for all wafers in order to eliminate the previous difficulties in comparing oxides when different cleans and processing steps are used.[1] Substrate defects, atypical to this process, were presumably introduced during the initial wafer cleaning and scattered the time-to-breakdown (TTB) values during a constant current stress of these oxides to the point where statistical comparison of TTB averages was dubious. However, for unannealed wafers and for post polysilicon definition heat treatments of 900°C, RTO oxides grown with HCL had the same oxide trapping rate as the furnace oxides grown with TCA and RTO oxides grown in pure O2 had a faster trapping rate. Higher temperature post polysilicon definition heat treatments had different effects. RTO oxides exhibited better yield than the furnace oxides. These results illustrate the differences between RTO and furnace oxidation in the presence of non-ideal wafer substrates.
Rapid Thermal Nitridation of Thin Oxides
Authors: Shih D.K. , Lee S.K. , Ku Y.H. , Kwong D.L. , Lee S. 
Published: March 2011

ABSTRACTIn this paper the kinetics of initial nitridation of thermal oxides is studied by using rapid thermal nitridation of thin oxides. FTIR and AES were used to investigate the chemical properties of nitrided oxide films. The amount of the nitrogenincorporated in and the oxygen escaped from 100Å oxides has been characterized quantitatively as a function of RTN conditions. Results show that RTN at 1100° for 120s incorporates about 85% and 12% of the maximum nitrogen concentration value at oxide surface and bulk, respectively. The nitrogen pile up peak at interface can be seen after RTN at 1100°C with the time as short as 5 s. Study of the effects of the nitridation temperature and the original oxide film thickness indicates that the reaction species has permeated through oxides before effective replacement reaction takes place. The diffusion coefficient of the permeating species is estimated of the value larger than 40−13cm2/s.
Comparison of the Growth Kinetics of Oxides Grown in Tungsten-Halogen and Water Cooled Arc Lamp Systems
Authors: Paz de Araujo C.A. , Gelpey J.C. , Huang Y.P. , Kwor R. 
Published: March 2011

ABSTRACTRapid thermal oxidation of silicon has been performed in a tungsten-halogen system (AG-410) and a water-wall arc lamp system (Eaton ROA-400). Growth kinetics of the oxides are studied with particular attention to ramp-up ambient conditions, dwell time, maximum wafer temperature and difference in activation energies. These parameters are characterized using ellipsometry in order to measure system bias with respect to growth rate and breakdown. Experiments were designed to identify the differences in the initial enhanced growth conditions, and their effect on growth kinetics during the dwell cycle.
In-Situ Processing of Silicon Dielectrics by Rapid Thermal Processing: Cleaning, Growth, and Annealing
Authors: Nulman J. 
Published: March 2011

ABSTRACTThe in-situ processing of silicon dielectrics by rapid thermal processing (RTP) is described. RTP includes here three basic sequentially performed processes: wafer cleaning, oxidation and annealing. The insitu cleaning allows for reduction of chemical and native oxides and silicon surface chemical polish, resulting in interface density of states as low as 5×l09 cm-2eV-1. Kinetics of oxide growth indicates an activation energy of 1.4 eV for the initial linear oxidation rate.
Resistivity Differences in C49 Tisi2 Films Formeid by Rapid Thermal Processing
Authors: Reader A.H. , Van Ommen A.H. , Van Houium H.J.W. 
Published: March 2011

ABSTRACTTiSi2 films produced from co-sputtered Ti/Si mixtures by rapid thermal processing at temperatures around 630°C were found to have a higher resistivity than films formed by the solid state reaction of deposited Ti with (100) silicon during asimilar anneal. Diffraction studies indicated the films comprised of the C49 phase only. It is argued that the resistivity difference arises from the extremely high (3106cm−1) stacking fault density in the annealed co-sputtered layers.
High Purity Titanium Silicide Films Formed by Sputter Deposition and Rapid Thermal Annealing
Authors: Brat T. , Wei J.C.S. , Poole J. , Hodul D. , Parikh N. , Wickersham C. 
Published: March 2011

ABSTRACTWe have investigated the formation of titanium silicide films sputter deposited from a high purity (99.995%) composite TiSi2.2 target. The films, sputtered at a rate of 3.7 nm/sec, were deposited on Si(100), Si02 , and N+ Poly-Si substrates at temperatures ranging from room temperature to 425°C. Room temperature depositions produced amorphous films, while heated substrate depositions formed crystalline films with a metastable C49 TiSi2 structure. Rapid thermal processing of these films at temperatures higher than 700°C resulted in the formation of a stable C54 TiSi2 structure. Stoichiometry of the deposited films over a 10 cm diameter wafer was found to be independent of the substrate temperature. Stress in the films was measured as a function of deposition and annealing parameters. The amorphous films showed a tensile stress of about 0.1 GPa, while films deposited on substrates at 425°C had an order of magnitude higher tensile stress level.The resistivity measured on the 400°C deposited films was about half of that obtained with the films deposited at roomtemperature. A comparison between films deposited on a hot substrate and those which were rapid thermal processed is presented.
omparisons of Silicide Formation by Rapid Thermal Annealing and Conventional Furnace Annealing
Authors: Ma E. , Natan M. , Lim B.S. , Nicolet M-A. 
Published: March 2011

ABSTRACTSilicide formation induced by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) in bilayers of sequentially deposited films of amorphous silicon and polycrystalline Co or Ni is studied with RBS, X-ray diffraction and TEM. Particular attention is paid to the reliability of the RTA temperature measurements in the study of the growth kinetics of the first interfacial compound, Co2Si and Ni2Si, for both RTA and CFA. It is found that the same diffusion-controlled kinetics applies for the silicide formation by RTA in argon and CFA in vacuum with a common activation energy of 2.1+0.2eV for Co2Si and 1.3+0.2eV for Ni Si. Co and Ni atoms are the dominant diffusing species; during silicide formation by both RTA and CFA. The microstructures of the Ni-silicide formed by the two annealing techniques, however, differs considerably from each other, as revealed by cross-sectional TEM studies.