bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Chemistry of Al-Tobermorite and its Coexisting Phases AT 175°C
Authors: Barnes Mary W. , Scheetz Barry E. 
Published: March 2011

AbstractThe substitution of Al into the structure of tobermorite was investigated, along with the resultant phase assemblages that compatibly coexist with the Al-tobermorite. All experiments were conducted under hydrothermal conditions at saturated steam pressure. The temperatures of the experiments varied from 90° to 190°C and times from 1 to 28 days. Ca/Si ratios varied from 0.7 to 1.7, Al/(Al+Si) from 0.12 to 0.30. NaOH varied from none to 5 moles/mole tobermorite constituents. X-ray diffraction was used not only to identify phases but to determine degree of substitution and the rate of approach to steady state.Maximum Al substitution was found to be Al/(Al+Si) = 0.13, and the maximum interlayer spacing was 11.42 ± 0.015 Å. This is in agreement with previously published work which found a trace of hydrogarnet at Al(Al+Si) = 0.15 and a maximum interlayer spacing of 11.45 ± 0.02 A. When Al concentrations in the mix are greater than enough to make maximum Al-tobermorite, “low”-hydrogarnet (“low”-hydrogarnet has ∼0.1 SiO2 per mole). As Al concentration is raised, a variable composition hydrogamet is formed and then a “high”-garnet of constant composition (SiO2 = 0.7 moles/mole hydrogarnet) is formed.NaOH was found to have a major effect on the kinetics and the phase assemblages at a given time. Al-tobermorite, although stable at 90°C, converts to xonotlite at 175°C in the absence of NaOH. In its presence, even at a level too low to make Na-containing phases, Al-tobermorite persists at 21 days at 175°C. In the absence of NaOH, at 175°C, Al-tobermorite forms at up to 7–10 days but is converted to xonotlite at 28 days. Coexisting phases are gyrolite and cowlesite at Ca/Si ≥ 1 and hillebrandite and “low”-garnet at Ca/Si > 1. When there is enough NaOH to form Na-containing phases, Al-tobermorite coexists with reyerite and analcime at Ca/Si > 1. At Ca/Si < 1 and Al less than the composition on the tie line between Al-tobermorite and “low”-garnet, Al-tobermorite coexists with “low”-garnet and portlandite. In the compatibility triangle between Al-tobermorite, “low”-garnet, and “high”-garnet, Al-tobermorite coexists with variable Si-gamet. When Al exceeds its limiting value on the tie line, Al-tobermorite-“high”-gamet, the assemblage is Al-tobermorite-“high”-gamet-cowlesite.
Fracture-Exafs: A New Method for the Study of Interfaces in thin films and Polycrystalline Materials
Authors: Barrera E. V. , Maruyama Benji , Heald S. M. 
Published: March 2011

ABSTRACTFracture-EXAFS is a technique, proposed here for the first time, which combines an appropriate mechanical test with EXAFS analysis to investigate the atomic processes involved in the fracture process. Fracture-EXAFS builds upon the fracture-Auger electron spectroscopy technique, which was used to study the elemental composition of fracture surfaces, and has yielded significant insight into phenomena such as grain boundary embrittlement and composite interface fracture. Extended X-ray Absorption Fine Structure (EXAFS) analysis yields structural, as well as chemical information. The identity, coordination number, position and degree of disorder of atoms in the vicinity of interfaces and surfaces can be determined. Thus, EXAFS comparison of the imminent (latent) fracture surface to the fracture surface can yield structural, as well as chemical information about the fracture process. In this preliminary report, emphasis will be given to the application of Fracture-EXAFS to the study of interfaces in thin films. Discussion will also include the use of Fracture-EXAFS to study grain boundaries in polycrystalline materials.
Metastable Phases in Rapidly Solidified Aluminum-Rich Al-Fe Alloys
Authors: Shechtman D. , Swartzendruber L.J. 
Published: March 2011

ABSTRACTAluminum-rich Al-Fe binary alloys up to and including Al3Fe were prepared by melt spinning in order to study the metastable phase structure and its transformation following heat treatment. Transmission electron microscopy and nuclear gamma-ray resonance were utilized in the study. The rapidly solidified structure was found to contain up to three metastable phases. One of the phases, with a composition and a gamma-ray resonance spectrum appropriate for Al6Fe, has either a globular or a cellular morphology upon quenching.
Ta and Nb Reinforced MoSi2
Authors: Carter David H. , Martin Patrick L. 
Published: March 2011

AbstractMoSi2matrix composites have been recognized lately as potential materials for structural applications at elevated temperatures. Specifically, MoSi2composites may exhibit useful properties at temperatures to 1400°C. Previous work improved the yield strength of MoSi2at 1400°C by a factor of five through SiC whisker reinforcement. Current research is directed towards increasing the fracture toughness of MoSi2through the addition of ductile phase reinforcements such as niobium and tantalum. The reaction between Nb and MoSi2to form (Mo,Nb)5Si3proceeds with faster kinetics at hot isostatic press temperatures as low as 1100°C when compared to the reaction between Ta and MoSi2to form (Mo,Ta)5Si3. This reaction product exhibits very poor properties, as evidenced by crack propagation through this layer during fracture. The feasibility of hot working these composites to produce tailored microstructures is examined.
Mechanical Behavior and Failure Mechanisms of SCS-6/Ti3Al Composites
Authors: Jeng S. M. , Yang C. J. , Yang J.-M. , Rosenthal D. G. , Goebel J. 
Published: March 2011

AbstractThe mechanical properties and failure mechanisms of the SCS-6/Ti3Al composite have been studied. Both tensile and notched bend tests were conducted at room temperature on the monolithic and fiber-reinforced Ti-25Al-10Nb-3V-1Mo. Optical and scanning electron microscopy were used to study the crack initiation and propagation mechanisms. The role of the fiber, matrix and interfacial properties on the composite behavior was also assessed.
Interfacial Shear Behavior of Sapphire-Reinforced NiAi Composites
Authors: Moose C. A. , Koss D. A. , Hellmann J. R. 
Published: March 2011

AbstractThe interfacial shear behavior in near-equiatomic NiA1 reinforced by sapphire filaments has been examined at room temperature using a fiber pushout test technique. The loaddisplacement data indicate a large variability in the initial interface failure stress, although reverse push behavior indicates a comparatively constant interfacial sliding friction stress. The observed behavior suggests that the presence of asperities on the fiber surfaces and nonuniformities in fiber diameter require constrained plastic flow within the NiAl matrix in order for interfacial shear to occur. The location, shape, severity, and distribution of fiber asperities as well as the uniformity of fiber diameter are critical to the interfacial shear process.
Ductile Phase Toughening of Brittle Intermetallics
Authors: Anton D. L. , Shah D. M. 
Published: March 2011

AbstractOne method of imparting damage tolerance into intermetallic compounds is to introduce ductile particles in a fine uniform distribution. Systematic criteria are given as to the necessary requirements for such ductile phase reinforced systems. Two composite systems, Cr2Nb/Nb and Nb3Al/Nb were selected for further evaluation. Both microstructural evaluations as well as thermal stability were demonstrated in both systems. Small cracks introduced via micro-hardness indentations were measured as a function of precipitate size. In Cr2Nb/Nb the crack lengths decreased with increasing particle size which was explained through increasing effectiveness of ductile particles with minimum effective particle radii calculated at 6-10 μm. Larger particles along with poor ductile phase distributions led to lower damage tolerance in aged Nb3Al/Nb. By maintaining uniform ductile particle distributions, intermetallic compounds possessing superior damage tolerance have been demonstrated.
High Strength, Porous, Brittle Materials
Authors: Haggerty J. S. , Lighfoot A. , Ritter J. E. , Nair S. V. 
Published: March 2011

AbstractContrary to existing models, strengths need not be a strong function of porosity for intermediate density, brittle materials. Flaw sizes can remain small (<50μm) if the void space is distributed uniformly in minimum dimension pores. For RBSN, fracture toughness decreases linearly with porosity for 0< porosity <40%. Strains to failure and specific strengths of these materials are higher than fully dense counterparts.
Micro-Reinforced Cementitious Materials
Authors: Banthia Nemkumar , Sheng Jiakang 
Published: March 2011

AbstractReinforcement of cements with very fine fibers of carbon and steel in mono- and hybrid-forms has been investigated. While both carbon and steel fibers led to considerable improvements in strength and toughness, on a comparative basis, carbon fibers bring about a better improvement in the toughness or energy absorption, and the steel fibers impart higher tensile strengths to the base cement matrices. In the hybrid-fiber systems, the improvements lie somewhere in between those of the equivalent mono-fiber systems.
Rapid Thermal Processing of Ferroelectric Thin Films
Authors: Wu Zheng , Pascual Roberto , Vasant Kumar C.V.R. , Amd David , Sayer Michael 
Published: March 2011

AbstractThe preparation of ferroelectric lead zirconate titanate (PZT) thin films by rapid thermal processing (RTP) is reported. The films were deposited by chemical sol gel and physical sputter techniques. The heating rate of RTP was found to have significant influence on the crystallization behavior. Faster heating rates lead to lowering of the crystallization temperature and reduction of grain size. PZT films were obtained with dielectric constants ~ 1000, remanent polarizations between 20 and 30μC/cm2, coercive fields 20 to 60kV/cm, and no significant fatigue for 109 to 1010 stressing cycles.
Diffusion Barriers with Sputtered TaN, Ta-Si-N, and TaSix for Thermal Stable Contact
Authors: Wang W.G. , Chang C.S. , Chen W.S. , Huang F.S. 
Published: March 2011

AbstractTantalum nitride, Ta-Si-N, and tantalum silicide films were investigated for use as a diffusion barrier in Al/Si metallization. The former two films were deposited by reactive sputtering of a Ta or TaSi2 target in Ar/N2 gas mixture. The TaSix films were fabricated by sputtering of TaSi2 target. Then, the Ta-Si-N and TaSix film were annealed at temperature 950°C for 15 seconds by RTA. The resistivities of Ta-Si-N, TaN, and TaSix films are about 180, 250, and 60 µohm-cm, respectively. The X-ray photoelectron spectroscopies were made to study the chemical structure of the films. For both nitrides, TaO comprises the native oxide formed at room temperature. A large amount of silicon nitride was formed on the surface of TaSix film during the RTA. Rutherford backscattering and Auger profile were performed to understand the degradation. It was found that these three films are effective diffusion barriers at temperature 620°C.
Advances in Ultrasonic Disk Cutting and Precision Dimpling
Authors: Fischione Paul E. , Kelly Thomas F. , Dalley Amber M. , Holzman Louis M. , Dawson-Elli David 
Published: March 2011

AbstractMany of today's advanced materials are prepared using a combination of ultrasonic disk cutting, dimpling, and ion milling. In order to optimize the analytical results from a single specimen, several improvements have been made in instrumentation for ultrasonic disk cutting. Also, a system has been developed for detecting either at or near-electron transparency in TEM specimens. Both of these aspects are described. Examples are provided for silicon, metal/ceramic composites and blanket substrate layers for electronic devices.
Phase Stability and Diagrams from First Principles
Authors: Sanchez J.M. , Becker J.D. 
Published: March 2011

ABSTRACTFirst principles theories of alloy phase equilibrium have been successfully used in recent years to compute temperature-composition phase diagrams for solid state phases. One particular approach, originating with the successful phenomenological Ising models to describe the alloy Hamiltonian, uses a cluster expansion of the configurational energy in terms of short-ranged pair and many-body interactions. The approach is deeply rooted in our ability to compute accurate total energies of relatively complex compounds, using density functional theory in the local approximation, from which effective interactions may be obtained. Fundamental aspects of the method which include convergence of the cluster expansion, treatment of the configurational entropy and description of vibrational modes are reviewed. Applications of the theory are given for binary alloys in the Ru-Zr-Nb system using the Linear Muffin Tin Orbital method for the total energy calculations, the Cluster Variation method for the description of the configurational entropy, and the Debye-Gruneisen approximation for the vibrational modes. The results are used to compute the equilibrium phase diagram for the Zr-Nb system and to assess current experimental data on phase stability in the Ru-Nb system. In the latter case, the calculations indicate that the DO19 structure is a likely candidate structure for the experimentally observed hexagonal-based compound Ru3Nb. Investigation of the energies and interactions of tetragonal structures as a function of the c/a ratio suggest the L10 structure as a likely candidate for the observed tetragonal phase near 1:1 stoichiometry.
Effects of Radiation Exposure on Glass Alteration in a Steam Environment
Authors: Wronkiewicz D. J. , Wang L. M. , Bates J. K. , Tani B. S. 
Published: March 2011

ABSTRACTSeveral Savannah River Plant (SRL) glass compositions were reacted in steam at temperatures of 150 to 200°C. Half of the tests utilized actinide-doped monoliths and were exposed to an external ionizing gamma source, while the remainder were doped only with U and reacted without gamma exposure. All glass samples readily reacted to form secondary mineral phases within the first week of testing. An in situ layer of smectite initially developed on nonirradiated SRL 202 glass test samples. After 21 days, a thin layer of illite was precipitated from solution onto the smectite layer. A number of alteration products including zeolite, Casilicate, and alkali or alkaline earth uranyl silicate phases were also distributed over most sample surfaces. In the irradiated SRL 202 glass tests, up to three layers enveloped rounded, and sometimes fractured, glass cores. After 35 to 56 days these remnant cores were replaced by a mottled or banded Fe- and Si-rich material. The formation of some secondary mineral phases also has been accelerated in the irradiated tests, and in some instances, the irradiated environment may have led to the precipitation of a different suite of minerals. The alteration layer(s) developed at rates of 2.3 and 32 μm/day for the nonirradiated and irradiated SRL 202 glasses, respectively, indicating that layer development is accelerated by a factor of ∼10 to 15X due to radiation exposure under the test conditions.
Principles of the Selection of Effective and Economic Corrosion-Resistant Alloys in Contact with Biologically Active Environments
Authors: Dowling Nicholas J.E. , Lundin Carl , Sachs Dan , Bullen Jan A. , White David C. 
Published: March 2011

ABSTRACTCurrent field experience with microbiological influenced corrosion (MIC) has now extended into the medium-grade stainless steels containing 4% molybdenum and in excess of 20% chromium. These may indeed be special cases where a combination of synergistic effects, temperature, and wet-dry cycles have aggravated a situation that is already subject to a mild form of MIC. Data are presented from a fresh water field site, comparing the relative performance of several welded coupons, including AISI 304L, 316L, and higher alloyed grades, 622, C276, C-22, 25-6Mo exposed to principally iron-oxidizing bacteria. Specific data is also presented from a saltwater laboratory study of AISI 316/E308 welds where sulfate-reducing bacteria were included. Normally this weld configuration is considered “mismatched” however has nevertheless been employed at several inland power stations. Data is presented which suggests that under “freshwater” conditions (ie. < 150 ppm Cl−) excluding deposits originating from other sources, for example, calcareous scales, an increase in chromium content may significantly reduce the problem. The laboratory study showed that severe generalized rusting of 316/E308 welds may be expected in the presence of fermentative and sulfate-reducing bacteria in chloride environments. The relationship of these data, and of those available in the literature, to the problem of long-term radioactive waste disposal, is discussed with respect to materials selection.
Diffusion of Corrosion Products of Iron in Compacted Bentonite.
Authors: Idemitsu K. , Furuya H. , Inagaki Y. 
Published: March 2011

ABSTRACTCarbon steel is one of the candidate overpack materials for high-level waste disposal. The corrosion rate of carbon steel is reduced by the presence of buffer materials such as bentonite and seems to be affected by the diffusion of corrosive materials and corrosion products through the buffer material.The apparent diffusivities of corrosion product of iron were measured in some bentonite specimens in contact with carbon steel. The apparent diffusivities of iron were also measured without carbon steel for comparison. The apparent diffusivities of corrosion product were on the order of 10−12 m2/s and showed a tendency to decrease with increasing density of the bentonite specimen. There was no significant effect of silica sand on the apparent diffusivities. The apparent diffusivities of iron in the system without carbon steel were in the range of 10−14 m2/s and showed a tendency to increase with increasing silica sand content. The difference of the diffusivities between corrosion product and iron without carbon steel seems to be due to the difference of diffusing species. The color of the corrosion product was dark-green during contact with bentonite specimens and became red on exposure to air in a few minutes. Gas bubbles were also observed in the corrosion product. This suggests hydrogen generation during corrosion of the carbon steel. Thus the diffusing species seems to be in a reduced state, probably ferrous ion. On the other hand, the diffusing species of iron without carbon steel was probably a ferric hydroxide complex that was negatively charged. This suggests that ferrous ion could diffuse in the surface water adsorbed on bentonite, while ferric complex was excluded.
Accelerated Glass Reaction Under PCT Conditions
Authors: Ebert W. L. , Bates J. K. , Buck E. C. , Bradley C. R. 
Published: March 2011

ABSTRACTStatic leach tests similar to the PCT were performed for times up to two years to assess the long-term reaction behavior of high-level nuclear waste glasses similar to those expected to be produced at the Defense Waste Processing Facility. These tests show the reaction rate to decrease with the reaction time from an initially high rate to a low rate, but then to accelerate to a higher rate after reaction times of about one year, depending on the glass surface area/leachant volume ratio (SAN) used. The solution concentrations of soluble glass components increase as the reaction is accelerated, while the release of other glass components into solution is controlled by secondary phases which form during the reaction. The net result is that the transformation of glass to stable phases is accelerated while the solution becomes enriched in soluble components that are not effectively contained in secondary phases. The rate becomes linear in time after the acceleration and may be similar to the initial forward rate. A current model of glass reaction predicts that the glass reaction will be accelerated upon the formation of secondary phases which lower the silicic acid solution concentration. These tests show the total silicon concentration to increase upon acceleration of the reaction, however, which may be due to the slightly higher pH that is attained with the acceleration. The sudden change in the reaction rate is likely due to secondary phase formation.
Luminescence Processes in Si1-xGex/Si Heterostructures Grown by Chemical Vapor Deposition
Authors: Sturm J.C. , Xiao X. , Mi Q. , Lenchyshyn L.C. , Thewalt M.L.W. 
Published: March 2011

AbstractWell-resolved band-edge exciton photoluminescence (PL) has been observed in strained Si1-xGex. heterostructures grown on Si(100) by rapid thermal chemical vapor deposition. The luminescence is due to shallow-impurity bound excitons at low temperatures (under 20K) and at higher temperatures is due to free excitons or electron-hole plasmas, depending on the pump power. The luminescence can also be electrically pumped, with both the electroluminescence and PL persisting above room temperature in samples with a sufficient bandgap offset. Loss of carrier confinement and subsequent non-radiative recombination outside the Si1-xGex. is found to be the reason for reduced PL and EL at high temperature.
Investigation of Colloidal Si Prepared from Porous Silicon
Authors: Berhane S. , Kauzlarich S. M. , Nishimura K. , Smith R. L. , Davis J. E. , Lee H. W. H. , Olsen M. L. S. , Chase L.L. 
Published: March 2011

AbstractSi nanocrystallites have been prepared by ultrasonicating thin sections of porous silicon. The materials produced from 20 and 49 wt % HF are characterized and compared. Samples were characterized by optical absorption and photoluminescence spectroscopy, and HRTEM.
Stress-Induced Voiding vs Temperature and Passivation Thickness IN Al-0.5%Cu-2%Si, AI-0.5%Cu AND Al-1%Si
Authors: Sullivan T. D. , Miller L. A. 
Published: March 2011

ABSTRACTStress-induced voiding in microelectronics chips has been reported to exhibit a variety of dependencies on temperature and on passivation stress. The dependence of line failure is reported here at four different temperatures (150, 225, 285, and 315 ºC) for AI-0.5%Cu and, AI-0.5%Cu and AI-1%Si lines with passivation thicknesses (silicon oxide or silicon nitride) ranging from 0.1 to 2.5 times the metal thickness. Failure distributions change in a complex manner with changing passivation thickness, and with temperature for a specific passivation thickness, raising questions on the validity of using the conventional median time to failure (t50) and lognormal slope (σ) to project field failure rates from data generated by accelerated life testing.
Edge Delamination Testing: A Method for Measuring the Adhesion of Thin-film Coatings in Microelectronic Applications Part 1: Numerical Analysis and Preliminary Results
Authors: Shaffer Edward O. , Mcgarry Frederick J. , Trusell Fred 
Published: March 2011

ABSTRACTWe propose a new test to measure the adhesion of thin polymeric coatings used in microelectronic applications. Similar to previous tests [1-3], the edge delamination test (EDT) takes advantage of the thermal residual stress present in the coating to induce delamination. However, in the EDT, we take advantage of lithography to fabricate test geometries that probe a complete range of debond energies. As a result, nearly a hundred adhesion tests can be performed on a single wafer. In this report, we apply finite element analysis to assess the debond energy generated at the coating/substrate interface to determine the feasibility of the test. The analysis also quantifies the effect of various geometries and boundary conditions. We apply the EDT to study the adhesion of Cyclotene™ 3022 polymer to silicon coated with evaporated aluminum. The critical mode I strain energy release rate for the Cyclotene/Aluminum interface with no adhesion promoter is 10.5±0.2 J/m2.