bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Thermomechanical Response of Ore Materials During Microwave Processing
Authors: Williamson R. L. , Salsman J. B. , Tolley W. K.
Published: April 2011

A finite element numerical model is used to predict the thermal and mechanical response of mineral-bearing ores irradiated by microwave energy. The model considers a small, spherical, pyrite particle surrounded by a matrix of calcite. Power density data are determined from the dielectric properties of the mineral and host rock materials at typical microwave frequencies and power capabilities. The effects of varying power density and mineral particle diameter are studied. Using power densities within the expected achievable range for pyrite, significant temperature differences are predicted between the mineral particle and host rock. These temperature gradients lead to circumferential tensile stresses in the host rock well in excess of the reported uniaxial tensile strength of common rock materials. It is shown that, for a fixed microwave energy source, both the temperature difference between the mineral and host rock, and the peak tensile stress in the host rock are reduced as the mineral particle size is reduced. Recent experimental efforts to corroborate this numerical study are briefly described.
Nox Reduction on Char using Microwaves Carolynn
Authors: Buenger W. , Peterson Edward R. , Cha Chang-Yul
Published: April 2011

More than 18 million tons of nitrogen oxide (NO and NO2) are emitted into the air over the United States each year. These oxides contribute to the formation of acid rain and street level ozone, and are most concentrated in areas of industrial and commercial activity. The response of the Environmental Protection Agency to the problem has been to legislate anti-pollution laws and regulations which will be enforced in increasingly strict stages beginning in 1997. Existing NOx abatement technologies do not meet the long range NOx abatement needs of the processing industries and utilities.

Char, a heat treated and volatile form of coal, can effectively adsorb NOx from waste gas. Microwave energy, when properly applied, can convert the NOx and carbon via reduction to nitrogen and carbon dioxide. The basic principles of this technology are taught as well as some of the pertinent development aspects currently under investigation.
The use of Magnetite as a Facilitator for the Microwave Heating of Contaminated Soils
Authors: George Clifford E. , Rao Gunda V.N. , Guice Jennifer D.
Published: April 2011

Previous research work in the area of microwave heating for low temperature thermal desorption of contaminates has led to a novel method of delivering heat energy to contaminated materials (soils) that have poor electrical characteristics for the absorption of microwaves. This method involves the use of a heating facilitator. The facilitator, which in this case is a ferromagnetic material (magnetite), is admixed with the soil or sludge to be treated. When exposed to microwave energy, the facilitator preferentially absorbs the energy and transfers heat to the contaminated matrix. Using this method, it has been possible to achieve temperatures in excess of 900 °C (1650 °F) in test soils. At these temperatures, even the highest molecular weight hydrocarbon contaminants are compelled to desorb from the soil.

The advantage of using magnetite is that it can be separated by conventional separation methods for recycle and reuse. The technology has implications of being useful in several chemical processing operations.
Microwave Processing at the University of Florida
Authors: Clark D. E. , Folz D. C. , Schulz R. L. , Fathi Z. , Cozzi A. D. , Boonyapiwat A. , Komarenko P. , DiFiore R. , Jones C. B.
Published: April 2011

Microwave energy for processing materials is emerging as a vital manufacturing technology for the nineties and beyond. Research to date has shown significant advantages in several areas, including drying and sintering, joining, surface modification and waste remediation. Increased processing rates, improved physical and mechanical properties and, in some cases, reduced hazardous emissions have sparked the interest of many manufacturers in the ability to integrate microwave processing techniques into existing and future manufacturing operations. This presentation will provide an overview of the microwave processing research and development work in progress at the University of Florida.
Rapid Selective Annealing of Cu thin films on Si Using Microwaves
Authors: Brain R. A. , Atwater H. A. , Barmatz M.
Published: April 2011

A key requirement for future integrated circuit fabrication is lower processing temperatures at all stages of fabrication. Typical rapid thermal annealing processes, utilizing infrared radiation, heat the film as well as the substrate and create the potential for device reliability problems. Microwave annealing may enable a novel solution to the problem of selective annealing of metallic or other conductive thin films, which is possible in the limit where the metal film thickness is less than the skin depth of the material at microwave frequencies. This technique is advantageous because the relatively low absorption of silicon deters substrate heating and the metallic thin film shields the rest of wafer.

We have investigated the quality factor, Q, and temperature of silicon as a function of its doping concentration and power input into the microwave cavity. As a particular application of microwave selective annealing, we have microwave annealed sub-micron Cu thin films sputtered on patterned SiO2/Si substrates and demonstrated an improvement in trench filling for use in interconnect metallization applications.
Microwave Sintering of Continuous Zirconia Ceramic Fibers
Authors: Vogt Gerald. J. , Unruh Wesley. P. , Plovnick Ross. H.
Published: April 2011

Continuous yttria-stabilized zirconia ceramic fibers approximately 10–15 μm in diameter have been rapidly sintered by pulling them through a tuned, 2.45 GHz single-mode TE103 microwave cavity in ambient air. The resulting fibers were analyzed by X-ray diffraction, scanning electron microscopy, and single-filament tensile tests. They were found to be unsplit, to have a submicron grain structure and a tetragonal crystal structure, and to exhibit considerable strength and flexibility.
Continuous Microwave Sintering of Ceramics
Authors: Cheng Jiping , Fang Yi , Agrawal Dinesh K. , Wan Zhangguo , Chen Lei , Zhang Yunjin , Zhou Jian , Dong Xuebing , Qiu Jinyu
Published: April 2011

The microwave sintering technology is still at the developmental stage due to the limitation of the volume (or size) and batch of the ceramic products that can be fabricated by microwave processing. The present paper introduces a new microwave processing technique, i.e. a continuous microwave sintering, which makes it possible to sinter ceramic products with an infinite length in a microwave field. By this technique, alumina-mullite ceramic rollers of 40 mm in diameter and 2400 mm in length have been successfully microwave sintered. The exploratory results show this new technique could offer some new opportunities to scale up microwave sintering for industrial applications.
Metalorganic and Microwave Processing of Eutectic Al2O3-ZrO2 Ceramics
Authors: Willert-Porada M. , Gerdes T.
Published: April 2011

The spatial distribution and sintering activity of ZrO2 governs the microstructure evolution upon microwave sintering of alumina-zirconia ceramics. Using the same microwave sintering profile thermal runaway occurs, when ZrO2-powders with high specific surface area are employed, yielding ceramics with eutectic Al2O3-ZrO2 inclusions, whereas ZTA-type ceramics are obtained from low specific surface area powders. Microwave sintering yields ceramics with a higher density at a particular sintering temperature as compared to conventional sintering.
A Cascaded Microwave Plasma Source for Synthesis of Ceramic Nanocomposite Powders
Authors: Vollath Dieter
Published: April 2011

Based on the experience of the synthesis of nanophased ceramic powders with particle size in the range of a few nanometers, a new device for the synthesis of ceramic nanocomposite powders was designed. The new equipment is based on a 915 MHz microwave system built of IEC 153 R9 waveguide elements. The microwaves coming from the magnetron are split up in two branches using an E-plane power splitter. The reaction tube, made of quartz, passes consecutively both branches of the wave-guide system. Behind the applicators with the reaction tube, the waveguides are terminated with sliding shorts. These sliding shorts are adjusted in a way to ignite and operate a plasma in both branches of the waveguide system simultaneously. The system allows the production of homogeneous powders for nanocomposites. “Nanocoated particles” can be obtained in some special cases;for example ZrO2 particles synthesized with sizes in the range between 4 and 5 nm can be coated with a 1 to 2 nm layer of Al2O3 or vice versa. Metal chlorides are selected as precursors for the reactions. A mixture of, argon with 20 vol% oxygen is used as a plasma gas.
Microwave Curing of Silicon Carbide Ceramics from a Polycarbosilane Precursor
Authors: Shan Tzyy-Heng Alex , Cozzens Robert
Published: April 2011

Silicon carbide ceramic materials have been successfully formed from commercially available polycarbosilane using microwave radiation as the sole source of heat. Conventional thermal processing of the same polymeric precursor was also studied for comparison with microwave processing. Microwave heating enhances crystallinity at much lower curing temperature and within shorter times. Possible explanations for microwave enhanced processing are proposed.
Luminescence Parameters of PBX2 (X=F, CI, Br, I) Crystals
Authors: Voloshnovskii A. S. , Pidzyrailo M.S. , Mikhallik V.B. , Rodnyi P.A.
Published: April 2011

Spectral and kinetic parameters of PbX2 (X=F, Cl, Br, I) crystals emission are investigated under pulse photo- (∆t=l.0 ns) and X-ray (∆t=l.5 ns) excitation in the temperature region from 77 to 293 K. X-ray luminescence of the PbF2, PbC12 and PbBr2 crystals is considered as radiative decay of the self-trapped excitons at the defects, while subnanosecund and nanosecond emission components are regarded to the result of the thermal quenching. The nature of the fast X-ray luminescence for PbI2 crystals is discussed from the viewpoint of the possibility for observation of radiative core-valence transition.
Dye Mixtures for Ultrafast Wavelength Shifters
Authors: Cangopadhyay S. , Barashkov N. , Liu L. , Palsule C. , Borst W. , Wigmans R.
Published: April 2011

We have produced fast wavelength shifters using mixtures of various Coumarin dyes with DCM in epoxy-polymers (DGEBA+HHPA) and measured the properties of these wavelength shifters. The particular mixtures were chosen because there is a substantial overlap between the emission spectrum of Coumarin and the absorption spectrum of DCM. The continuous wave and time-resolved fluorescence spectra have been studied as a function of component concentration to optimize the decay times, emission peaks and quantum yields. The mean decay times of these mixtures are in the range of 2.5-4.5 ns. The mean decay time increases with an increase in Coumarin concentration at a fixed DCM concentration or with a decrease in DCM concentration at a fixed Coumarin concentration. This indicates that the energy transfer is radiative at lower relative DCM concentrations and becomes non-radiative at higher DCM concentrations.
Heavy Fluoride Glasses as an Alternative to Crystals in High Energy Physics Calorimetry
Authors: Dafinei I. , Auffray E. , Lecoq P. , Schneegans M.
Published: April 2011

In the quest for low cost scintillators to equip the very large electromagnetic calorimeters for future High Energy Physics experiments, scintillating glasses can offer an attractive alternative to crystals. The expected production price is indeed supposed to be reduced as compared to crystals, especially for very large volumes. An intense R&D effort has been made by the Crystal Clear collaboration to develop heavy scintillating fluoride glasses in close collaboration with the industry. Results will be shown on the fluorescence and scintillation properties as well as on the radiation resistance of different types of fluoride glasses. Ideas about possible improvement of present performances will also be given.
Nanosecond Uv-Scintillations in Cesium Iodide
Authors: Gavrilov Vladimir , Chernov Stanislav
Published: April 2011

Fast UV-luminescence of CsI has been studied by time resolved luminescent spectroscopy. Experimental data support the conclusion that the high temperature (150–500 K) fast UV-luminescence arises from the trapping of free excitons in sites perturbed by lattice defects.
Fast Luminescence and Absorption in BGO and SiO2
Authors: Gavrilov Vladimir , Chernov Stanislav
Published: April 2011

The spectra and kinetics of the fast luminescence and optical absorption of Bismuth Germanate (BGO) after excitation by single high-power nanosecond and subnanosecond electron pulses were studied. The short-lived optical absorption of the center responsible for BGO scintillations is assigned. The cause for the low scintillation yield in BGO is discussed in comparison with analogous measurements in crystalline and amorphous silicon dioxide. The ultrafast (decay time < 50 ps) luminescence is observed and it is concluded that it can be connected to intraband transitions.
The Kinetics of Excitonic Luminescence in Mixed Silver Halides
Authors: Kotomin E. , Millers D. , Grigorjeva L. , Eglitis R.
Published: April 2011

Two kinds of luminescence (excitonic luminescence and excitonic molecule luminescence) were investigated for solid solutions AgBr1-xClx after pulsed electron beam and N2 laser irradiation. Careful theoretical treatment of a set of experimental excitonic luminescence kinetics is presented. It is shown that the effective activation energy of Agoi migration is a linear function of the composition x. The narrow peak of the excitonic molecule luminescence shifts from 2.66ev in pure AgBr towards higher energies as x increases.
A Modified Fast Analog Technique for Determining Luminescence Decay Times of Scintillators
Authors: Liu L. , Borst W. , Palsule C. , Gangopadhyay S.
Published: April 2011

We have modified our previous fast analog technique to determine the luminescence decay times of scintillators following an excitation with a Sr90β3-source. In the original technique [1], the sample was excited with a nitrogen-pumped dye laser, and the fluorescence pulses (consisting of typically 50 to 1000 photons) were detected by a multi-channel plate photomultiplier tube (MCP-PMT). The output from the MCP-PMT was directed to a fast waveform digitizer triggered externally by the exciting laser. In the modified technique, the digitizer acquires the fluorescence decay in the internal trigger mode, as no corresponding external trigger pulse is available from the Sr90source. For efficient light collection from scintillators, an ellipsoidal mirror assembly has been tested. The fluorescence decays are acquired as multi-photon pulses and are subsequently corrected for the temporal instrument response by using a deconvolution technique. The overall time resolution of the technique is about 100 ps. The fluorescence decay time obtained using this technique for a commercial scintillator (SCSN-81) agrees well with literature. We also discuss our results on new epoxy-polymer based scintillators prepared in our laboratory. The primary motivation for this work was development of new scintillators with shorter fluorescence decay times for high collision rate experiments.
Electronic Structure and Associated Optical Properties of LAPO4:Ce
Authors: Mishra K. C. , Johnson K. H.
Published: April 2011

Lanthanum phosphate activated by cerium and terbium is a well known lamp phosphor which is used for its green emission. In this paper, we have investigated the electronic structure and associated optical properties of lanthanum phosphate doped with cerium using the self consistent field scattered wave molecular orbital cluster approach. Relativistic corrections are included for the lanthanum and cerium centered clusters. In spite of the small magnitude of crystal field splitting, a significant admixture of the f-like orbitals with the ligand orbitals is observed for cerium. The optical transitions are calculated using the transition state formalism. The absorption peaks due to electronic transition from the f-like states to d-like states of cerium are found to be 271 rim, 259 nm, 245 nm, 208 nm and 194 nm which are in good agreement with the experiment. The nature of the band gap transition in lanthanum phosphate is also discussed.
Methods For A Systematic, Comprehensive Search for Fast, Heavy Scintillator Materials
Authors: Derenzo S. E. , Moses W. W. , Weber M. J. , West A. C.
Published: April 2011

Over the years a number of scintillator materials have been developed for a wide variety of nuclear detection applications in industry, high energy physics, and medical instrumentation. To expand the list of useful scintillators, we are pursuing the following systematic, comprehensive search: (1) select materials with good gamma-ray interaction properties from the 200,000 data set NIST crystal diffraction file, (2) synthesize samples (doped and undoped) in powdered or single crystal form, (3) test the samples using sub-nanosecond pulsed x-rays to measure important scintillation properties such as rise times, decay times, emission wavelengths, and light output, (4) prepare large, high quality crystals of the most promising candidates, and (5) test the crystals as gamma-ray detectors in representative configurations. An important parallel effort is the computation of electronic energy levels of activators and the band structure of intrinsic and host crystals to aid in the materials selection process.
Scintillation Mechanism and Radiation Damage in CexLa1-xF3 Crystals
Authors: Wojtowicz A. J. , Lempicki A. , Wisniewski D. , Brecher C. , Bartram R. H. , Woody C. , Levy P. , Stoll S. , Kierstead J. , Pedrini C. , Bouttet D. , Koepke CZ.
Published: April 2011

Recent spectroscopic and radiation damage experiments on a series of CexLa1-xF3 crystals suggest that the scintillation light output is limited by an unusual quenching mechanism, which also plays a major role in minimizing radiation-induced damage. The intensity of the radiation-induced absorptions is a strong function ofthe Ce content x, reaching a maximum for x = 0.03 and a minimum for x = 1. This peculiar dependence appears to be due to the influence of deep-lying Ce levels onboth scintillation mechanism and radiation damage. We suggest that various charge transfer processes can explain many aspects of the performance of CexLa1-xF3 scintillators.
Light Output and Radiation Damage in A YAIO3:Ce Crystal
Authors: Kierstead J.A. , Stoll S.P. , Woody C.L.
Published: April 2011

The optical absorption, light output and effects of radiation damage have been studied ina 2.1 × 2.1 × 2.1 cm3 crystal of YA103:Ce. The light yield produces approximately 2867 photoelectrons per MeV on a photomultiplier tube with abialkali photocathode. The scintillation and light transmission properties of the crystalwere characterized before and after exposure to 1 Mrad of 60 Co gamma rays. Significant radiation induced optical absorption was observed near the optical band edge ofthe crystal, along with an extremely intense phosphorescence after irradiation. Partial spontaneous recovery from the damage occurred at room temperature, and it was possible to induce additional recovery by optical bleaching.
Electronic Trap Defects in Y2O3:Eu and (Y,Gd)2O3:Eu X-Ray Scintillators
Authors: Duclos Steven J. , Greskovich Charles D. , O'clair Chester R.
Published: April 2011

Detailed properties of the defects and energy transfers responsible for afterglow in transparent sintered ceramic Y2O3:Eu and (Y,Gd)2O3:Eu based scintillators have been determined by transient thermoluminescence ('TL) and spectral measurements of afterglow emission. X-ray excited TTL spectra between 150 K and 350 K reveal 4 defect transitions for 3 mole percent Eu. Adequate modeling of this data requires for each defect transition a trap depth energy, an attempt-to-escape frequency, a broadened density of trap state energies, and a trap filling frequency. These defect parameters have been determined and can be used to predict afterglow dependence on time after excitation shut-off, exposure time, and temperature. The afterglow emission spectra at all temperatures are characteristic of Eu under S6 site-selective UV excitation of these rare-earth C-type structure scintillators. This indicates that states associated with the Eu activator on the S6 site are the terminal states upon thermal release of trapped charge carriers.
A Review of the Status and Developmental Issues for Continuously-Reinforced Ti-Aluminide Composites for Structural Applications
Authors: Miracle D. B. , Smith P. R. , Graves J. A.
Published: April 2011

A significant materials-based activity to develop Ti-aluminide metal matrix composites for high temperature aerospace structural applications is now underway. A review of the approaches, progress, and status of the development of continuously-reinforced Ti-aluminide metal matrix composites with matrices which contain a significant volume fraction of the ordered orthorhombic Ti2AlNb phase will be presented. The principal application considered is a gas turbine compressor rotor ring, and this influences the development approaches and properties goals. Specific development activity that will be presented includes modification and control of the matrix composition and microstructure, fiber coating treatments to control interdiffusion between the fiber and the matrix, and to improve the ability of the interface to support a mechanical load, and efforts to improve the properties of SiC monofilaments used as reinforcements. Critical issues that define the requirements for additional studies will be presented.
Fracture and Fatigue Resistance of Ag/Ta-coated SCS-6/Ti3Al Composites
Authors: Chiu Hsing-Pang , Yang J.-M.
Published: April 2011

The effect of a Ag/Ta coating on the fracture resistance of a notched SCS-6 fiber-reinforced Ti3Al matrix composite under both static and fatigue loading was investigated. The crack propagation patterns and damage mechanisms under various loading conditions were characterized and compared with the uncoated composite counterparts. The results show that the Ag/Ta-coated composites exhibit typical mode-I failure patterns under both static and fatigue loading, while mixed mode-I & H failure patterns were observed in the uncoated SCS-6/Ti-25-10 composite. Localized interfacial debonding, matrix cracking and fiber fracture in the crack wake were the responsible damage mechanisms for the Ag/Ta-coated SCS-6/Ti-25-10 composite. Extensive interfacial debonding, crack splitting and branching, however, were found to be the dominant mechanisms in the uncoated SCS-6/Ti-25-10 composite.
Composites Based on Molybdenum Disilicide: Progress and Prospects
Authors: Hardwick D. A.
Published: April 2011

As the temperature demands increase in advanced aerospace systems, engineering materials that can withstand 1200° to 1600°C exposure in air must be developed. MoSi2 is an intermetallic compound that has many, though not all, of the necessary physical and mechanical properties for use in this temperature regime. At ambient and moderate temperatures MoSi2 is brittle, but once the ductile-to-brittle transition temperature (DBTT) is exceeded, it rapidly loses strength. Recent progress in, and current status of, the research efforts in MoSi2 matrix composites will be reviewed, with an emphasis on the critical issues that currently impede progress to application.
The Influence of Mobile Dislocation Density on the Fracture Toughness of B2-Based Ni-Fe-Al Alloys
Authors: Misra A. , Noebe R. D. , Gibala R.
Published: April 2011

The deformation and fracture behaviors of two directionally solidified multi-phase Ni-Fe-Al ordered alloys were investigated. One alloy consisted of continuous β+γ lamellae with fine γ precipitates within the γ phase. The NiAl-based β phase of this alloy exhibited <100> slip even when deformed parallel to the [001] growth direction. This material exhibited an initiation fracture toughness of ∼ 30 MPa √m and tensile ductility of 10%. The second alloy consisted of aligned but discontinuous γ lamellae within a continuous β phase. Again, the γ phase contained γ precipitates, but unlike the previous alloy, the β phase also contained a fine dispersion of bcc precipitates due to spinodal decomposition. The β phase of this alloy deformed by <111> slip. This four-phase alloy exhibited a fracture toughness of ∼ 21 MPa √m and tensile ductility of 2%. Observations of the plastic zone in both alloys indicated significant plasticity in the β phase due to easy slip transfer from the ductile second phase. The enhanced fracture resistance of these multiphase materials compared to single phase β alloys is attributed in large part to intrinsic toughening of the β phase by an increased mobile dislocation density due to efficient dislocation generation from the β/γ interfaces.
Fracture Toughness of Two Cr2Hf+Cr Intermetallic Composites as a Function Temperature
Authors: Ravichandran K. S. , Miracle D. B. , Mendiratta M. G.
Published: April 2011

Fracture toughness as a function of temperature was evaluated for two Cr2Hf+Cr intermetallic composites, each in two different microstructural conditions. The proeutectic microstructures based on Cr-6.5Hf (at%) showed a significant increase in fracture toughness with an increase from room temperature to 600°C. The coarse microstructure obtained by heat treatment at 1500°C showed evidence of ductile behavior of Cr at a lower test temperature (200°C) relative to that of one heat treated at 1250°C (400'C). In the eutectic microstructures based on Cr-13Hf, only a small increase in fracture toughness at 600°C was seen. The results are analyzed in the light of fracture micromechanisms.
Microstruciture and Properties of Intermetallic Matrix Composites Produced by Reaction Synthesis
Authors: Alman D. E. , Hawk J. A. , Dogan C. P. , Ziomek-Moroz M. , Petty A. V.
Published: April 2011

In this US Bureau of Mines study, a variety of TiAl based composites were produced in situ by reaction synthesis. Mixtures of elemental Ti, Al and B and Ti, Al, and Si powders were reactive hot-pressed to form TiAl reinforced with 10, 20, 25 or 60 vol. pct. TiB2 or Ti5Si3. Microstructural evaluation of the resultant composites confirmed that the reaction products were primarily TiAl and TiB2 or Ti5S3, with a small amount of Ti3Al. The hot-press temperature and pressure had a significant effect on the density of the composites. In general, higher temperatures and initiating the reaction under pressure promoted dense composites. Room temperature biaxial flexure strength tests indicated that the addition of the reinforcing phases can improve the strength of TiAl. Potentiodynamic experiments revealed that TiAl, TiAl+TiB2 and TiAl+Ti5Si3 composites display active-passive corrosion behavior in both acidic and alkaline solutions.
Processing and Mechanical Properties of Laminar Al2O3-Ni3Al Composites
Authors: Schneibel J. H. , Alexander K. B.
Published: April 2011

Several compositions of the intermetallic alloy Ni3Al were examined with respect to (a) their wetting of Al2O3 and (b) their energy absorption capability in Al2O3/Ni3Al laminates. Wetting is enhanced by small additions of carbon (e.g., 0.1 at. %), and bonding by additions of zirconium (e.g., 1 at. %). Chevron-notched laminate specimens were tested in three-point bending to assess the energy absorption due to the presence of a thin layer of Ni3Al. A nickel aluminide with the composition Ni-22Al-lZr-0.1C-0.1B was found to have a reasonable combination of wetting, adhesion and energy absorption. Interfacial bonding was found to be weak in all laminates.
Fibers and Fiber Coatings for IMCs
Authors: Misra Ajay K.
Published: April 2011

This paper presents a review of the current status of fibers and fiber coatings for intermetallic matrix composites (IMCs). The properties of commercial and developmental fibers are reviewed and their potential as reinforcements for various intermetallics discussed. The potential fibers for near-term IMC applications are SiC (both monofilament and tow), single crystal Al2O3 and YAG/Al2O3 eutectic monofilaments, and sol-gel derived Al2O3- mullite nanocomposite tow fiber. The chemical compatibility of these fibers with various intermetallic matrices is reviewed. The issues related to the coefficient of thermal expansion (CTE) mismatch between the fiber and the matrix, attaining optimum interfacial bond strength, and fiber damage during composite processing are addressed. The effectiveness and limitations of fiber coatings in accommodating various fiber-matrix incompabilities, both chemical and mechanical, are discussed.
Microstructure and High Temperature Properties of 85% Al2O3-15% SiO2 Fibers
Authors: Wilson D. M. , Lieder S. L. , Lueneburg D. C.
Published: April 2011

A new sol/gel fiber which exhibits exceptional high temperature properties was recently developed at 3M. This fiber has the composition 85% Al2O3-15% SiO2 (85A-15S). High temperature tensile strength and creep properties were measured in the temperature range 1000°C – 1300°C. The creep rate for the 85A-15S fibers was three orders of magnitude less than single phase polycrystalline alumina fibers such as Nextel 610, and 90% of room tensile strength was retained at 1250°C. These exceptional high temperature properties were attributed to a unique, two-phase microstructure consisting of globular and elongated grains of a-Al2O3 and mullite (3Al2O3-2SiO2). The room temperature single filament strength of the 85% Al2O3-15% SiO2 fibers was 2130 MPa, and the elastic modulus was 260 GPa.
Layered Silicate/ATBN Nanocomposite
Authors: Moet A. , Akelah A. , Salahuddin N. , Hiltner A. , Baer E.
Published: April 2011

Composites of amine terminated butadieneacrylonitrile (ATBN) and montmorillonite (MMT) were prepared by ion exchange between the onium salt of the polymer and the interlamellar cation of the mineral following two different preparation approaches. The first carried out the ion exchange in situ and used dioxane, a better solvent for the polymer, and the second administered the onium salt to MMT using dimethylsulfoxide (DMSO). Elemental analysis and IR spectroscopy indicated that all the ionic sites of the mineral have been occupied by polymer end groups. The d (001) spacing and the span between the internal lamelar surface were only expanded to about 14 Å and 5 Å, respectively, suggesting horizontal packing of the polymer molecules. TEM of microtome sections prepared from compression molded composites revealed that the lamellae, laminated with polymers assembled into multiplets of about 5 nm for both preparations. The multiplets clustered into mineral rich domains whose average size was 250 nm for the DMSO preparation. Finer clusters (70 nm) were obtained by the first method. This three fold decrease in the average domain size was attributed to the strong solvation power of dioxane in the binary solvent and to the locale of ion exchange.
Self-Assembly of Cobalt/Bipyridine Multilayers Modeled After Hofmann Clathrate Compounds
Authors: Ansell Michael A. , Zeppenfeld Astrid C. , Ham William K. , Page Catherine J.
Published: April 2011

Progress has been made towards the development of inorganic-organic multilayered films modeled after Hofmann clathrate compounds. Cobalt-bipyridine multilayers were grown layer by layer on a silicon substrate. The resulting films were characterized using ellipsometry, grazing angle X-ray diffraction, Auger electron spectroscopy and EPMA (Electron Probe Micro- Analysis). Results indicate that moderately well ordered layers have been synthesized, but cross-linking with M(CN)42(M = Ni, Pd, or Pt) to simulate the model structure does not significantly occur.
Processing of Nanostructured Zirconia Ceramics
Authors: Skandan G. , Hahn H. , Kear B. H. , Roddy M. , Cannon W. R.
Published: April 2011

The inert gas condensation (IGC) technique was employed to synthesize non-agglomerated nanoparticles of ZrO2 and Y2O3 with different average particle sizes ranging from 4 to 14 run. The sintering behaviors (in air and vacuum) of single phase n-ZrO2 (monoclinic crystal structure) and Y2O3-ZrO2 mixture (Y-TZP) were studied in terms of densification rate and final sintering temperature. There was a strong correlation between densification characteristics and properties of the starting powder compacts such as average particle size, particle and pore size distributions. n-ZrO2 was sintered to full density in air at temperatures as low as 1125°C (0.47 Tm) and in vacuum at 975 °C (0.42 Tm). Although the grain sizes in the fully sintered samples were well below 100 nm, the grains had grown by a factor of 10 as compared to the initial particle size. Therefore, a pressureassisted sintering technique was employed to further reduce the densification temperature and final grain size. Threshold effects in this process are also discussed.
Biomimetic Processing of Calcium Carbonate-Chitosan Composites
Authors: Zhang Sukun , Gonsalves K. E.
Published: April 2011

Ceramic-polymer composites produced by natural organisms are known to have properties far beyond those that can be achieved in present technological materials [1]. The mollusk shell, for example, starting with relatively weak structural ingredients calcium carbonate and chitin is one such ceramic-polymer composite. In nacre, the overall composite is more than 95 volume percent calcium carbonate, with the remainder an organic matrix of protein and chitin. The inorganic phase consists of highly oriented aragonite platelets forming the bricks and the organic matrix forming the mortar in between [1]. Even though nacre consists of a high amount of the inorganic component, it has excellent fracture toughness and high strength. Studies have been conducted to understand the factors which control the nucleation and orientation of crystallization [2-4]. However, very limited knowledge about the ceramic polymer interfaces, structure, chemistry and whether the interfacial interaction involves ion-binding is known.
Surface Chemistry of Nanocrystalline Cerium Oxide
Authors: Tschöpe Andreas , Ying J.Y. , Amonlirdviman K. , Trudeau M. L.
Published: April 2011

Nanocrystalline cerium oxide was synthesized by magnetron sputtering of a metallic target, followed by controlled post-oxidation. The resulting cerium oxide clusters were <10 nm in size, and highly non-stoichiometric in nature. The oxygen deficiency of such materials was associated with the unusual catalytic activity in oxidation and redox reactions. This paper compares the surface chemistry of nanocrystalline CeO2−x with stoichiometric CeO2. It further explores the promoting effect of Cu-doping on surface reduction and oxidation.

The oxidation states of metal cations were examined with X-ray photoelectron spectroscopy after various oxidizing and reducing heat treatments in a connected reaction chamber. Isothermal pulsed reduction and oxidation of the samples were investigated by thermogravimetric analysis. Reduction properties of the different materials are discussed in terms of their microstructure, oxygen deficiency and chemical composition. These studies will help to understand the importance of bulk defects and synergistic effects in multicomponent and multiphase materials for high surface reactivity.
Organic/Inorganic Superlattices: Structural and Optical Properties
Authors: Tokito Shizuo , Sakata J. , Taga Y.
Published: April 2011

A new class of superlattices consisting of alternating layers of organic and inorganic materials has been prepared from 8-hydroxyquinoline aluminium (Alq), copper phthalocyanine (CuPc), 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) and MgF2 by molecular beam deposition. Small-angle x-ray diffraction data and cross-sectional transmission electron micrograph of the superlattices reveal that the superlattices have layered structure throughout the entire stack. From comparison of the x-ray diffraction patterns, it is found that the interface roughness between organic and MgF2 layers depends on the materials for organic layers. High-angle x-ray diffraction data indicate that there is a structural ordering in the CuPc and PTCDI layers. From the optical absorption and photoluminescence measurements, it is found that the exciton energy of Alq shifts to higher energy with decreasing Alq layer thickness.
Formation and Properties of Silane Monolayers on Iron and Aluminum Surfaces
Authors: Petrunin Maxim A. , Nazarov Andrey P.
Published: April 2011

The adsorption of ethoxysilanes RSi(OEt)3 on the Fe and Al surfaces from the vapor phase, water and toluene solutions was studied by the piezoquartz nanobalance and ellypsometry. The values of the “landing sites” and the energy of the interaction for different silanes were calculated. The self-assembling silane monolayers with good adhesion to the Al surface (due to the covalent bonds Al–O–Si) was shown to format during adsorption from dilute water solution. The influence of silane monolayers on the H2O adsorption and wetting of the surface was studied. The silane layers have considerably hydrophobic effect and prevent the growth of hydroxide film on the Al. The synthesis of charged silane nanophases was carried out by the addition of the acid (sulfo-, imididiaoetate-) and the basic (amino-) groups into the epoxysilane molecule. The effect of the charge density and the surface potential on the ion adsorption at the interface metal/electrolyte was investigated.
Small Angle Neutron Scattering from Nanocrystalline Pd and Cu Compacted at Elevated Temperatures
Authors: Sanders P.G. , Weertman J.R. , Barker J.G. , Siegel R.W.
Published: April 2011

Nanocrystalline (n-) Cu and Pd, prepared by inert gas condensation (IGC) and in situ room temperature (RT) and elevated temperature (warm) compactions, have been studied by small angle neutron scattering (SANS). Previous work [1] on room temperature compacted and subsequently annealed n-Pd seemed to show that all the scattering could be accounted for by a distribution of pores. Analysis of more extensive SANS measurements, together with the results of prompt gamma activation analysis (PGAA), indicates that the SANS can be explained by the presence of pores and hydrogen. Warm compaction reduces the hydrogen impurity level, while increasing the bulk density and decreasing the pore size. This can lead to a dramatic hardness increase in these materials.
Atomistic Simulation of Vapor-Phase Nanoparticle Formation
Authors: Zachariah Michael R. , Carrier Michael J. , Blaisten-Barojas Estela
Published: April 2011

In order to understand from a fundamental view how nanoparticles form and grow, classical molecular dynamics simulations of cluster growth and energy accommodation processes have been conducted for clusters of silicon (< 1000 atoms), over a wide temperature range. Simulations involved solution of the classical equations of motion constrained with the three body Stillinger-Weber potential. The results show the large heat release and resulting cluster heating during a cluster-cluster collision event, and the corresponding time evolution of the internal energy to a more stable state. Dynamic effects associated with the temperature of the cluster and the impact parameter are also clearly evident. In particular, clusters show a large sensitivity to temperature in the rate of coalescence, particularly at low temperature. Calculated diffusion coefficients are significantly larger than surface diffusion constants stated in the literature. Phonon density of states spectra do not seem to show size effects.
A New Process for Preparing Nanosize Ceramic Powders
Authors: Zhen Yong S. , Hrdina Kenneth E. , Remick Robert J.
Published: April 2011

We have developed a new poly-foam process for the cost effective preparation of ceramic nanoparticles. The process utilizes the chemistry of polyurethane reactions and is proven to be effective for forming nanometer size ceramic powders of a great variety of single metal oxides and mixed metal oxides. In general, ceramic powders can be prepared by this process having a range of average particle size between 3 to 50 nm, with very narrow particle size distribution. They are free of hard agglomerates, are chemically pure and uniform, and are essentially spherical in shape.
Physical Properties of Diamond-Like Nanocomposite Films
Authors: Dorfman B. , Abraizov M. , Pypkin B. , Strongin M. , Yangn X.-Q. , Yan D. , Pollak Fred H. , Grow J. , Levy R.
Published: April 2011

Diamond-like nanocomposite (DLN) and metal containing DLN (Me-DLN) films, synthesized in a combined process of deposition of carbon-silicon precursor and magnetron sputtering of a metal target, have been examined by Auger electron spectroscopy, Raman and IR spectroscopy, nanoindentation and internal stress measurements. The stability of the films under ion and electron irradiation and thermal annealing has been tested.
Thermal Conductivity Reductions in Sige via Addition of Nanophase Particles
Authors: Scoville Nancy , Bajger Clara , Rolfe Jon , Vandersande Jan
Published: April 2011

Transport models have predicted that the thermal conductivity of SiGe alloys could be appreciably reduced by incorporating a discrete 40Å particles with the SiGe grains. Such a thermal conductivity reduction would lead to substantial improvements in the figure-of-merit of thermoelectric materials. This paper reports on recent results on adding 40Å particles to SiGe via a spark erosion process. Thermal conductivity reductions consistent with the transport models have been achieved, however, the improvement in figure-of-merit has not been as large as predicted.
Polymerizable Self-Organized Membranes: A Novel Class of Organic Compounds
Authors: Singh Alok , Markowitz Michael , Chow Gan Moog
Published: April 2011

Molecular Self-assembly of amphiphilic phospholipid molecules (containing a hydrophobic acyl chain and a hydrophilic phosphate group attached to glycerol backbone) and other amphiphiles offers a versatile approach to form ordered structures. Stabilization of lipid microstructures by polymerization renders them useful for practical applications in the areas ranging from controlled release technology to template mediated synthesis of metals. Our efforts are focussed on the development and use of polymerizable diacetylenic phospholipids and their microstructures as template for chemical synthesis. The surface of vesicles and lipid microcylinders (0.5 μm dia.) is made reactive by chemically modifying the hydrophilic region of phospholipids. Lipids with chemically reactive sites were incorporated into lipid membranes predominantly formed from charge neutral lipids and used for binding metal ions and growing fine metal particles.
Preparation of Nanocomposites Containing Poly(Ethylene Oxide) and MoS2, TiS2, or MoO3
Authors: Lemmon John P. , Wu Jinghe , Lerner Michael M.
Published: April 2011

Single-phase nanocomposites containing montmorillonite, MoS2, MoO3or TiS2with poly(ethylene oxide) are obtained by the exfoliation of the layered solid, adsorption of polymer, and subsequent precipitation of solid product. Aqueous solutions can be employed for all syntheses except PEO/TiS2, which is prepared from lithiated TiS2in an N-methyl formamide (NMF) solution. X-ray diffraction indicates that the resulting solids increase in basal-plane repeat by approximately 4 or 8 Å, consistent with the incorporation of a single or double layer of polymer between the inorganic layers. Reaction stoichiometries and elemental analyses provide compositions for the single-phase products.
Absorption Study of the Tc(IV) on Rocks and Minerals Under Simulated Geological Conditions
Authors: Amaya Takayuki , Kobayashi Wataru , Suzuki Kazunori
Published: April 2011

The absorption of the technetium on rocks and minerals have been studied by using freshly quarried rocks to provide reducing conditions, without the addition of reductive reagents. The initial99Tc concentration in this study was about 1x10-8mol/1 (0.62 Bq/ml). Technetium was not absorbed on tuff or granite under oxidizing conditions, but higher Kd values of Tc were obtained for granite under reducing conditions. The Tc absorbed on granite was not desorbed under reducing condition. This indicates the absorption reaction is irreversible.
Reversibility of Strontium Sorption on Fracture Fillings
Authors: Cui Daqing , Eriksen Trygve E.
Published: April 2011

We have carried out a comparative study of sorption and desorption of strontium in groundwater on separated size and magnetic fractions of fracture fillings from deep granite. Complete reversibility of the sorption process was demonstrated by identical Freundlich isotherms, isotopic exchangeability and pH dependence of the distribution coefficient Rd.
Studies of the Liquid-Solid Ratio Effect on the Distribution Ratio Rd, in Sorption
Authors: Bors J. , Erten H. N. , Assemi S.
Published: April 2011

The variation of the distribution ratio Rdas a function of aqueous volume to solid mass ratio (V/M) for several sorption systems involving the cations Zn2+, Co2+, Ba2+, the anion I−and different solid matrices has been extensively examined. Empirical relationships for the concentrations of the sorbed species in the aqueous and solid phases as well as for the distribution ratio Rdare proposed. Generally Rdis found to increase with increasing V/M for tracer concentrations. A gradual increase in the initial concentration of the sorbed species eventually leads to a decrease in Rdwith V/M.
The Use of Some Ion-Exchange Sorbing Tracer Cations in Insitu Experiments in High Saline Groundwaters
Authors: Byegård J. , Skarnemark G. , Skålberg M.
Published: April 2011

The possibility to use alkali metals and alkaline earth metals as slightly sorbing tracers in in-situ sorption experiments in high saline groundwaters has been investigated. The cation exchange characteristics of granite and some fracture minerals (chlorite and calcite) have been studied using the proposed cations as tracers. The results show low Kd’s for Na, Ca and Sr (∽0.1 ml/g), while the sorption is higher for the more electropositive cations (Rb, Cs and Ba). A higher contribution of irreversible sorption can also be observed for the latter group of cations. For calcite the sorption of all the tracers, except Ca, is lower compared to the corresponding sorption to granite and chlorite. Differences in selectivity coefficients and cation exchange capacity are obtained when using different size fractions of crushed granite. The difference is even more pronounced when comparing crushed granite to intact granite.
Analysis of Radionuclide Migration Behavior in Loess Medium
Authors: Zhiming Wang , Shushen Li , Zede Guo , Yingjie Zhao , Zhentang Li , Shengfang Li , Yamamoto Tadatoshi , Takebe Shinichi , Ogawa Hiromichi , Tanaka Tadao , Mukai Masayumi
Published: April 2011

A five-year cooperative research program has been carried out by China Institute for Radiation Protection and Japan Atomic Energy Research Institute to develop safety assessment methodology for disposal of low level radioactive waste. Migration behavior of radionuclides 3H and 85Sr through field tests, simulation tests in the laboratory and determination of distribution coefficients is discussed and analyzed in this paper. The results show that the retardation coefficients, Rd, from field tests are about 0.08−3.3 times those from simulation tests and Rd from batch tests are 1.1−44 times those from field tests for 85Sr and loess medium. It was observed from field tests that radionuclides moved mainly downward under artificial sprinkling and a part of them moved up besides downward under natural rain condition. In addition, it was discovered that the retardation coefficient, Rd , increases with velocity of unsaturated water flow, u, in the analysis.