bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect Of O2 Plasma Exposure On The Performance Of Polycrystalline Silicon Thin Film Transistors
Authors: Kim Chul Ha , Lee Il , Sohn Ki Soo , Chun Su Chul , Jang Jin
Published: April 2011

We have studied the effect of O2 plasma exposure on the performance of polycrystalline silicon (poly-Si) thin film transistor (TFTs). The field effect mobility is increased and the drain currents at negative gate voltages are reduced by O2 plasma exposure on the surface of the TFT. These improvements in the performance of the poly-Si TFTs are larger in offset structure compared to overlap one. We obtained the on/off current ratio of ∼ 108 after O2 plasma exposure for the poly-Si TFTs with 3 or 4 μm offset length.
Overview Activities Within the Eug at the University of Cambridge
Authors: Metaxas Andrew C.
Published: April 2011

Electricity today plays a prominent role in many diverse processes in manufacturing and other industries. Understanding the fundamental principles behind a host of electrically driven processes is the remit of electroheat as an academic discipline. Centres of electricity utilisation at Universities, funded by the electricity utilities, should be encouraged and supported at the embryonic stage of development in order to facilitate the transfer of the electroheat technology between industry and academe.
Open-Ended Coaxial Probes for Nondestructive Testing of Substrates and Circuit Boards
Authors: Baker-Jarvis James , Janezic Michael D.
Published: April 2011

The results of the full-wave model theory for the open-ended coaxial probe with lift-off are presented and are applied to measurements of thin materials. The model allows the study of the open-ended coaxial probe as a nondestructive testing tool. The equations presented are valid for both dielectric and magnetic materials. The analysis yields insight into the effects of air gaps on probe measurements. Numerical results indicate that the probe is very sensitive to lift-off at low frequencies. This sensitivity decreases somewhat as frequency increases. In order for the field to penetrate the air gap, larger size coaxial line or higher frequencies need to be used. An application of the theory is performed by numerically solving the inverse problem using measured reflection coefficient.
FDTD Simulation of an Open-Ended Metallized Ceramic Probe for Broadband High-Temperature Dielectric Properties Measurements
Authors: Bringhurst Shane , Iskander Magdy F. , Gartside Paul
Published: April 2011

Open-ended coaxial probes have been used in broadband dielectric properties measurements for several years. To aid in the ongoing numerical simulation and microwave sintering research at the University of Utah, we have found it necessary to make dielectric properties measurements up to temperatures as high as 1400 °C. The available cavity perturbation techniques were unsuitable in this application due to their relatively narrow band, and the available metal probes are also unsuitable due to the differential thermal expansions of the inner and outer conductors, which makes it difficult to carry out accurate and on-line calibration procedures for these probes.

To help us achieve both broadband and high-temperature dielectric properties measurements, we have developed a new metallized ceramic coaxial probe. The detailed design of this probe is described and the metallization procedure is discussed.

Also to optimize the design of the probe and in particular to increase the penetration of fields in samples under test and hence improve the probe sensitivity to variation in properties of a larger class of materials, and to determine the required minimum thickness of various samples to obtain accurate results, we modeled and simulated the probe performance using the Finite-Difference Time-Domain (FDTD) method. Results from the FDTD simulation are presented and some guidelines that may be used to optimize the design of the probe are discussed.
Complex Dielectric Constant as a Function of Frequency for a Liquid Hydrocarbon Fuel in the Microwave Region
Authors: Wiegand Donald A. , Murray Frank
Published: April 2011

The incident, reflected and transmitted powers were measured and the reflection and transmission coefficients calculated for a liquid fuel. Two sizes of double ridge waveguide were used to cover the frequency ranges 2.5 to 7.5 and 7.5 to 18 GHz and corrections were made for waveguide losses. Strong interference effects were observed and the real part of the dielectric constant, ε', was obtained primarily from the separation of interference maxima and minima while the loss tangent, ε“/ε', was obtained by curve fitting to the normalized power loss. The final values of ε′ and ε“/ε′ were determined at each frequency by minimizing the difference between the experimental and theoretical values of the reflection coefficient and the normalized power loss. With increasing frequency ε' decreases and then becomes constant while ε“/ε' decreases throughout the frequency range within experimental accuracy.
Estimation of the Local Electric field inside an Isotropic Mixture.
Authors: Roussy Georges , Thiebaut Jean-Marie , Madi Med
Published: April 2011

As a consequence of the BERGMAN - MILTON theory, which expresses the effective permittivity of a two phase mixture with an integral of a density function, it has been possible to evaluate the local electrical field strength inside a heterogeneous mixture. The developed formula can be used advantageously for modeling the local temperature inside a ceramic material during its microwave sintering.
Assessment of Microwave Permittivity for Detecting Fruit Maturity
Authors: Nelson Stuart O. , Forbus W. Roy , Lawrence Kurt C.
Published: April 2011

Permittivity measurements from 0.2 to 20 GHz were taken on fresh peaches of three varieties at three stages of maturity during the growing season to determine whether dielectric properties might be correlated with maturity. Other physical properties of the peach tissue, such as density, moisture content, firmness, and total soluble solids content, were also determined. Two indices, based on dielectric constant and loss factor values at 0.2 and 10 GHz were found to correlate with stage of maturity, but they were dependent on the variety, and further study is necessary to determine their practical usefulness.
FDTD Modeling of Realistic Microwave Sintering Experiments
Authors: Huang Zhenlong , Iskander Magdy F. , Tucker James , Kimrey Hal D.
Published: April 2011

Computer modeling and numerical simulation provide a valuable tool for providing guidelines towards a successful routine experimentation with microwave sintering of ceramics. It is also expected that continued efforts in numerical simulation will lead to establishing procedures for the scale up and commercial utilization of this new technology.

In this paper, we utilize the FDTD technique to model sintering ceramics in multimode microwave cavities. The role of using process stimulus such as SiC rods on improving the uniformity of the microwave sintering process are also simulated. To help experimentally validate the obtained results, the FDTD electromagnetic power deposition results were combined with a 3D heat transfer program to calculate temperature distribution in samples and surrounding insulation. Results from the FDTD codes and comparisons with experimental measurements of sintering experiments are presented.

To improve the efficiency of the simulation and achieve more accurate results, we developed a variable mesh FDTD code to help focus the numerical results and hence improve the resolution in critical sites inside the sintering oven. Detailed solution procedures are described. We solved some test geometries with the uniform grid and the developed variable mesh codes and compared the obtained results to validate and check the accuracy of the solution procedure. Results from these comparisons are presented.
Microwave Energy for Waste Remediation Applications
Authors: Schulz R. L. , Folz D. C. , Clark D. E. , Wicks G. G.
Published: April 2011

Results of research on the use of microwave energy for several waste remediation applications are discussed. Studies include; processing of simulated nuclear waste glass frits, the destruction/vitrification of electronic circuitry from commercial and defense applications, the decomposition of organic compounds and the possible use of microwave energy in off-gassing operations during the ashing of electronic circuitry. Results of leach tests on simulated nuclear waste glass are presented as well as results from preliminary tests on organic wastes.
Microwave System Design and Dielectric Property Measurements
Authors: Tinga Wayne R.
Published: April 2011

In high temperature microwave systems, property variations of the process material can cover orders of magnitude causing significant changes in microwave coupling efficiency, heating rate, impedance matching, field strength and penetration depth. We created some first-order, temperature dependent models of these system parameters for a number of materials and calculated typical values over the temperature range of 0–1000 C. The results show that the input impedance of a resonator, the relative energy dissipation the power density and the penetration depth in the process material are strongly influenced by the temperature dependent dielectric constant. Process control algorithms require models of the system parameters and hence our models are useful for automated microwave processing systems. Moreover, it is shown that the relative dielectric loss factor of the process material can be monitored via the reflection coefficient of the microwave resonator containing the material.
Calcination of Metal Oxide/Activated Carbon Catalysts Under Electromagnetic Fields
Authors: Kim Hee Y. , Jeon Jong Y.
Published: April 2011

Effects of microwave heating were investigated for calcining metal-oxide precursors that were supported on an activated carbon. To obtain the heterogeneous metal oxide/activated carbon catalysts, calcination of the precursors impregnated onto the activated carbon was executed for 10 minutes at 300°C within a cavity of 2.45 GHz microwave. Such an electromagnetic treatment was compared with the calcination in a conventional muffle furnace. Activities for the oxidation of the benzene or oil adsorbed on the catalysts prepared by the two methods were examined with a micro-pulse reactor as well as with thermogravimetric analysis. Experiments revealed that the time required for the calcination in the electromagnetic field is much shorter than that in the muffle furnace. The catalytic activities in the low-temperature oxidation were also enhanced by the application of microwave in the calcination. In addition, the oxidative reaction of the adsorbates could be obtained without the activated carbon being burned. The microwave effects were outstanding for Co3O4/activated carbon catalysts.
Microwave Sintering of Metal-Ceramic and Ceramic-Ceramic Composites
Authors: Gerdes T. , Whxert-Porada M.
Published: April 2011

Polyphase ceramic and metal ceramic composites with at least one high dielectric loss component are potential candidates for application of microwave sintering, because of the high effectiveness of power dissipation and short sintering times. In order to identify material parameters essential for effective microwave sintering, different mixtures of conductive, semiconductive and insulating phases were investigated. When only a limited amount of a highly dissipative component is present, a modification of the grain size and morphology of the dissipative phase has been identified as major factor leading to optimized microwave heating behavior. Surprisingly, microwave sintering is also possible in the presence of a metallic liquid phase.
Microwave Sintering of Zirconia Toughened Mullite (ZTM)
Authors: Cai J. , Song C. Y. , Li B. S. , Huang X. X. , Guo J. K. , Tian Y. L.
Published: April 2011

Microwave sintering of zirconia toughened mullite (ZTM) has been performed in a single mode applicator. In comparison with conventional sintering, microwave processing of ZTM leads to a higher density and finer grain size. Microstructure of microwave sintered ZTM was characterized by TEM and HRTEM techniques. The pinning of intergranular ZrO2 dispersoids retarded the grain growth of mullite matrix. The observation of a considerable number of trans-granular microcracks indicates that microcracking toughening is the main toughening mechanism for ZTM.
Use of Variable Frequency Microwave Energy as a Flexible Plasma Tool
Authors: Johnson A. C. , Rudder R. A. , Lewis W. A. , Hendry R. C.
Published: April 2011

This paper reports on the use of frequency as a control parameter in the generation of microwave-excited plasmas for applications such as chemical vapor deposition, chemical vapor infiltration, or plasma etching. By changing the excitation frequency of a plasma in a multi-mode chamber, the locations of the maxima and minima of the power density within the chamber are also changed. This allows localization of the plasma discharge in the precise processing area desired in order to increase the process' efficiency. In a similar fashion, sweeping of the processing frequency during the process cycle can theoretically “scan” the plasma across an arbitrarily-shaped target surface. A series of experiments was conducted to evaluate the flexibility of variable frequency microwave energy as a plasma process tool. The results of these tests are presented.
Microwave Induced Plasma (MIP) Nitriding of Titanium Alloy
Authors: Doroudian M. , Samandi M.
Published: April 2011

Titanium alloys possess several attractive properties such as light weight, high strength and excellent corrosion resistance. However, wider application of these alloys, especially for load bearing components operating under sliding conditions, are restricted due to poor tribological (friction and wear) behaviour. It has been shown previously [1] that nitriding of titanium by using DC plasma is an effective means of increasing the hardness and reducing friction and wear. In this work nitriding response of titanium alloy (Ti-6A1–4V) was investigated using a Microwave Induced Plasma (MIP). The plasma was generated in a TM012 stainless steel cylindrical cavity using 1.5 kW power supply operating at 2.45 GHz. The cavity was water cooled and tuned by two sliding shorts. Nitriding experiments in nitrogen-hydrogen mixture at 70 to 100 torr pressure established that MIP provides an excellent mass transfer medium for nitriding titanium alloy. Furthermore, significant advantages over DC plasma have been discerned. For instance, reduced sputtering, uniformity of treatment and temperature stability can be cited. In this work, preliminary results of characterisation of MIP nitrided surfaces by x-ray diffraction and optical microscopy will be presented to demonstrate the effectiveness of MIP for nitriding titanium.
A Non-Thermal Vacancy-Drift Mechanism of Plastic Deformation of Grains in Ceramics During Microwave Sintering
Authors: Rybakov K. I. , Semenov V. E.
Published: April 2011

The plastic deformation of grains is shown to take place due to the vacancy drift perturbations caused by space charge formation in the near-surface layer and by surface permeability asymmetry with respect to the direction of the motion of atoms through it.
Cerium-Doped Orthophosphate Scintillators
Authors: Wojtowicz A. J. , Lempicki A. , Wisniewski D. , Boatner L. A.
Published: April 2011

Cerium-doped lutetium orthophosphate (LuPO4:Ce) is one of the most promising new scintillator materials. In this paper we report on the effects of total or partial replacement of Lu by Yb. When not doped with Ce, crystals of YbxLu1-xPO4 scintillate rather poorly, the emission being due to the Yb charge transfer transition. Activation with Ce reduces the light output from Yb even further, while correspondingly the addition of Yb to LuPO4:Ce also degrades that material's scintillation performance. We suggest that the nonradiative decay of the (Yb2+-Ce4+) charge transfer state is responsible for the mutual quenching of these ions. The differences in performance of LuPO4:Yb and LuPO4:Ce indicate that energy transfer mechanisms ordinarily associated with materials containing molecular anionic groups may not be quite sufficient to explain the results. Suggestions are presented that under γ-excitation the lattice-to-ion energy transfer in orthophosphates is accomplished by sequential capture of charge carriers rather than the more conventional mechanism of exciton hopping between molecular groups.
Fluorescence Properties of CeF3 and of Some Other Cerium Doped Crystals and Glasses Under VUV and X-RAY Synchrotron Excitation
Authors: Pedrini C. , Belsky A.N. , Vasil'ev A.N. , Bouttet D. , Dujardin C. , Moine B. , Martin P. , Weber M.J.
Published: April 2011

Reflectivity and fluorescence excitation spectra and fluorescence decays of CeF3 and LaF3:Ce have been recorded and analyzed in the VUV range up to 120 eV and in the X-ray region using the synchrotron radiation. Dominant mechanisms are identified in various regions of excitation, leading to different shapes of the excitation spectra and typical profiles of the decay curves. Strong difference in the light yield of fluorides and oxides are shown and discussed in terms of relative energies of levels of cerium and of the valence and conduction bands of the solid compounds.
Luminescence Kinetics Of Orthorhombic PbF2
Authors: Alov D.L. , Rybchenko S.I.
Published: April 2011

An extremely dense single crystal of PbF2 with the orthorhombic structure is an attractive material for use as a scintillator. Its luminescence properties are quite different from those of the currently well-known cubic PbF2 crystal. The spectroscopic study of orthorhombic and cubic monocrystals of PbF2 as well as of crystals of mixed structure containing both the orthorhombic and cubic phases is presented in the paper. The orthorhombic PbF2 luminescence contains a visual part with the rapid kinetics (≈100 ns) at temperatures near 100 K.
Subnanosecond Scintillations in Diamond
Authors: Gavrilov Vladimir , Aluker Eduard , Chernov Stanislav
Published: April 2011

Data about fast luminescence of natural and synthetic diamonds are presented. Analysis of the luminescence spectra and the kinetics of both the luminescence and pulse conductivity leads to the conclusion that these processes are determined by the band electron lifetime.
Van De Graaff ion Beams as a Useful Instrument of Scintillation Study of Crystals
Authors: Egorov V.K. , Zuev A.P.
Published: April 2011

The search of new efficient scintillators can be simplified by the application of ion beams. The beam flux density of the order magnitude 1012–1014 ions/cm2sec can be easily achieved. The light yield visualization takes place even for weak scintillators as PbF2 under excitation by such beams. The light response of crystals for ion beams with E0 = 1–2 MeV is not connected with the Cherenkov's radiation. Ion excitation enables one to find the crystals with surface scintillation. Measurement were performed by means of 0.15–2.0 MeV H+, D+ and 4He+ ions with current 0.1–10 nA. Quantitative values of the light yield for the cubic phase of monocrystal PbF2 in random and channeling were obtained. Restrictions of the technique applicability are discussed.
Computer Modeling of the Optical Properties of Transition-Metal Ions in Solids
Authors: Bartram Ralph H.
Published: April 2011

Computational methods for modeling the optical properties of substitutional transition-metal impurities in insulating solids, potentially applicable to some scintillator and phosphor materials, are reviewed. Methods considered include crystal-field and semi-empirical ligand-field models; SCF-Xα-SW, SCF-RHF-LCAO, SCF-UHF-LCAO and CI ab initio methods: and ICECAP and HADESR embedded cluster methods with lattice relaxation. A detailed example of the application of the HADESR method to crystal-field spectra of Cr3+ in halide elpasolites is described. In this method, ab initio molecular-orbital calculations with effective core potentials are performed for selected ionic configurations. Simultaneous relaxation of the cluster and surrounding lattice, with mutual pair. potential interactions, is accomplished by a modified lattice statics program. Calculated properties include pressure-dependent optical transition energies, vibration frequencies and radiationless transition rates.
Calculation of Energy Levels of Cerium in Inorganic Scintillator Crystals
Authors: Andriessen J. , Dorenbos P. , van Eijk C.W.E.
Published: April 2011

Fully relativistic ab initio calculations have been performed on energy levels of cerium in BaF2, LaF3, YAP and YAG. Also nonrelativistic calculations were done on cerium in LSO. The results are in fair agreement with experiment. Both the splitting of the 4f and 5d levels and the 4f–5d energy gap can be explained in the high symmetry crystal BaF2 as well as in the low symmetry crystals LaF3, YAP, YAG and LSO.
Charge-State Stability and Optical Transitions of Oxygen Impurities in Barium Fluoride Crystal
Authors: Wang L. M. , Chen L. Y. , Wu X.
Published: April 2011

The linear combination of atomic orbital-molecular orbital embedded-cluster is used to investigate the electronic structure and binding energies of small oxygen impurity clustersin the local density theory. Binding energies for substitutional oxygen ions in BaF2 crystal are studied for its 2–, 1–, and 0 charge states. These are used to assess charge-state stability. The energy eigenvalue spectra and optical transitions are obtained by transition state calculations for the oxygen impurities. These results of optical transition calculations obtained are very good and provide a useful interpretation of the ultraviolet-absorption experiments.
Charge-Transfer Transitions of RE3+ —O2– Associates in BaF2 Crystal
Authors: Wang L. M. , Chen L. Y. , Wu X.
Published: April 2011

Local-density-functional calculations have been performed to study the electronic structure and charge-transfer transitions of RE3+ —O2–(RE=Eu and Tm) associates in barium fluoride crystal. These systemsare simulated by small clusters which are surrounded by over 2000 point charges. It is found that the presence of oxygen in the lattice strongly influences the optical propertiesof RE3+ ions. The charge transfer transitions of RE3+O2– and RE ions with ligand F— ions derived from the embedded cluster are equal to 5.1 eV and 6.2 eV. The energy gap derived from the HFS model with REOBa2F6 clusters embedded in the crystal is 9.8 eV,which is near the experimental results.
Low Dose Rate Tests of Plastic Scintillator Plates and Wavelength Shifting Fibers
Authors: Zorn C. , Burkert V. , Kross B. , Majewski S. , Weisenberger A. , Wojcik R. , Asryan G. , Amaryan M. , Demirchyan R. , Egiyan K. , Sharabyan Yu. , Stepanyan S.
Published: April 2011

A low dose rate evaluation of several scintillators and wavelength shifters of interest to the CEBAF program was performed with a 60Co line source to a total dose of 160 Gray at a rate of 0.5 Gy/hr in a slowly flowing oxygen atmosphere. The samples included the following: (1) a 2 meter piece of Bicron BC412 scintillator being extensively used in the CEBAF Large Acceptance Spectrometer, (2) a 1 meter long piece of green scintillator doped with a uniquely fast green fluor (G2), (3) wavelength shifting fiber dopedalso with G2, and (4) grooved acrylic-based scintillator that is readout with the WLS fiber. The data indicates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 meters. The fast green scintillator (and fibers) showed no damage. When read out by WLS fibers, the acrylic scintillator displayed a loss in intrinsic light output, but no change in attenuation.
Barium Fluoride Crystals for Future Hadron Colliders
Authors: Zhu Ren-yuan , Ma Da-an , Newman Harvey
Published: April 2011

This report summarizes the radiation resistance of the current production BaF2crystals. An approach to implement optical bleachingin situis also presented. By using optical bleaching current production quality BaF2crystals could serve as an excellent candidate to construct a precision electromagnetic calorimeter at future hadron colliders.
Strength of Single Crystal Al2O3 Fibers in Ni-Based Intermetallic and Superalloy Composites
Authors: Bowman Randy R. , Locci Ivan E. , Draper Susan L. , Misra Ajay K.
Published: April 2011

Strength degradation of single crystal Al2O3 fibers due to the effect of fiber/matrix interaction and processing of NiAl and superalloy matrix composites, was investigated. Strength loss was quantified by tensile testing fibers that were exposed to the matrix alloy using two different methods. In one method, the fibers were incorporated into a composite by either the Powder Cloth (P-C) or binderless powder technique. The fibers were then extracted from the composite by chemical dissolution of the matrix and subsequently tensile tested and examined by scanning electron microscopy. In the other method, fibers were sputter-coated with a similar matrix composition and heat-treated to simulate conditions similar to those experienced during composite powder fabrication methods. In the sputter coating method, the contribution of fiber-matrix reaction on fiber strength loss was isolated from the effects of the various mechanical loads which are present during powder fabrication. For all matrices studied, significant strength loss was observed both in fibers extracted from composites and in fibers sputter-coated and annealed. Although surface ridges and pores were observed on the degraded fibers, it remains uncertain whether these features were responsible for the strength loss.
Powder Metallurgy Processing of Intermetallic Matrix Composites
Authors: German Randall M. , Iacocca Ronald G.
Published: April 2011

Intermetallic compounds are similar to ceramics because they are stoichiometric, with limited compositional ranges and brittle behavior. The limited ductility forces a reliance on powder techniques for shaping and consolidation. The high temperature character of intermetallics is beneficial to high temperature service, but this same attribute contributes to difficulty in processing. This paper reviews the several powder approaches to forming intermetallic structures. Examples are given on powders, consolidation options, and properties. Densification maps are introduced for estimation of consolidation cycles. Unfortunately, many of the composites exhibit little strengthening benefit from incorporation of reinforcing phases.
Pest Resistant and Low CTE MoSi2-Matrix for High Temperature Structural Applications
Authors: Hebsur M. G.
Published: April 2011

The objective of this investigation was to identify a pest resistant MoSi2-base matrix composition having properties suitable for SiC reinforcement. A 30 vol.% addition of fine Si3N4 particulates to MoSi2 significantly improved the low temperature accelerated oxidation resistance and thereby eliminated pest failure. Addition of Si3N4 also improved the high temperature oxidation resistance, strength and more importantly lowered the CTE of MoSi2 such that cracking was eliminated in a hybrid composite consisting of 30 vol.% Si3N4 and 30 vol. % SCS-6 fibers.
Processing Map and Flow Localization of a TiAl/TiB2 XD Composite
Authors: Zhao D. , Chaudhury P. K. , Thirukkonda M. , Valencia J. J.
Published: April 2011

Isothermal compression tests were conducted on a particulate reinforced Ti-44Al–3V+7.5v/o TiB2 composite produced by the XD® process over wide ranges of temperatures and strain rates, 1050 to 1300 C and 0.001 to 1.0 s-1, respectively. Flow localization parameter analysis was performed to analyze the flow behavior of the composite under various processing conditions, and the results were compared to those by dynamic material modeling. Microstructural characterization was also conducted to correlate the flow behavior with post-deformation microstructures. With combined information on flow behavior and microstructures, the processing condition for relatively stable flow and uniform microstructure was determined to be 1300 C and 0.01 to 0.1 s-1.
Synthesis and Processing of Nanograined Fe - (Fe, Mo)6C Composite Powders
Authors: Sadangi R. K. , Kear B. H. , McCandlish L. E.
Published: April 2011

Spray Conversion Processing was used to synthesize high volume fractions (0.52 - 0.74) of nanograined (Fe, Mo)6C carbide dispersions in iron, starting from water soluble precursors. The essential features of the process are, (1) preparation of a chemically homogeneous precursor powder, and (2) thermochemical conversion of the precursor powder to the desired nanostructured composite powder through controlled gas-solid reactions. The thermodynamic and kinetic features of the gas-solid reactions, and the influence of various processing parameters on the structures developed, are discussed. The powders were consolidated to near theoretical density by pressureless sintering and hot pressing. All the consolidated samples had bicontinuous structures. Compared to M2 high speed tool steels, these high volume fraction carbide strengthened iron alloys display superior hardness values up to 500°C.
Preparation of Polypeptide-Dye Multilayers by an Electrostatic Assembly Process
Authors: Cooper Thomas M. , Angela L. Campbell , Noffsinger Carol , Gunther-Greer Janelle , Crane Robert L. , Adams W. Wade
Published: April 2011

To develop novel optical thin films, we have prepared self-assembled polypeptide films by an electrostatic process. The films were placed on a glass slide previously silanized by an amino silane and given a positive charge by immersion in aqueous acid. Subsequent immersion of the slide in aqueous anionic solutions of either poly(L-glutamic acid), congo red, copper phthalocyanine tetrasulfonic acid orp-nitroaniline-modified poly(L-glutamic acid) resulted in deposition of the anions on the surface. Following anionic immersion, the slides were dipped into a cationic poly(L-lysine) solution. Alternate dipping into anionic and cationic solutions yielded multilayers. The thin films were characterized by optical absorption and circular dichroism. The optical density increased with dipping cycles. Circular dichroism measurements of the thin films showed induced dichroism of the congo red and phthalocyanine-containing films, suggesting formation of a locally ordered dye-polypeptide complex. Solution circular dichroism measurements of the polypeptides indicated a coil conformation, while poly(Lglutamic acid)/poly(L-lysine) complexes showed circular dichroism spectrum characteristic of a β-sheet.
Exfoliation of MoS2 Catalysts: Structural and Catalytic Changes
Authors: Valle M. Del , Avalos-Borja M. , Cruz J. , Fuentes S.
Published: April 2011

A study of the microstructural differences between exfoliated and non-exfoliated MoS2-based materials is presented, relating them to differences in their catalytic activity. Both commercial (crystalline) MoS2 and molybdenum sulfide catalysts prepared by thiosalt decomposition are subjected to chemical exfoliation reported to separate MoS2 monolayers from the original structure. Electron microscopy results show that the chemical treatment yields non-typical MoS2 nanostructures. Average surface area is also modified by exfoliation. The thiophene HDS activity of commercial MoS2 increases after exfoliation, while it decreases after exfoliation in the case of MoS2 catalysts.
Structure and Properties of Strained Crystalline Multilayers
Authors: Hoekstra J. , Yan H. , Kalonji G. , Jonsson H.
Published: April 2011

We present a computer simulation study of thin crystalline multilayers constructed from two FCC solids with differing lattice constants and binding energies. Both materials are described by Lennard-Jones interatomic potentials and initially have the same orientation and coherent interfaces. We have studied systems in which interfaces are perpendicular to the common [100] and [111] directions, respectively. A novel technique for analyzing local atomic ordering, Common Neighbor Analysis, is used to identify structural characteristics in these systems. We have found several structural changes in the layers of smaller atoms, including an FCC to HCP transition. In a system with (111) texture, a coherent interface to incoherent interface transformation is observed. Calculations of elastic constants of these multilayer structures show that elastic anomalies are associated with the structural variations.
Chemical Vapor Synthesis of Nanostructured Ceramics
Authors: Chang W. , Skandan G. , Hahn H. , Danforth S. C. , Kear B.
Published: April 2011

A modification of the conventional inert gas condensation apparatus for making nanostructured powders, wherein as evaporative source is replaced by a chemical source, is described. The new chemical synthetic process, called chemical vapor condensation(CVC), combines rapid thermal decomposition and expansion of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1-50 mbar. The process has been used to synthesize loosely agglomerated nanoparticles (6 to 10 nm) of n-SiCxNy, starting from hexamethyldisilazane (HMDS) as precursor compound. The phase, morphology, and composition of n-SiCxNy powders can be modified by heat treatment. β-SiC particles with grain size less than 10 nm form after annealing at 1300°C in flowing Ar. In a 1:1 NH3/H2 mixture n-SiCxNy powders transform into α-Si3N4 whiskers, with [100] growth direction.
FT-IR Characterization and Ab Initio Study of the Surface Species of a Nanosized SiC Powder
Authors: Baraton Marie-Isabelle , Besnaïnou Sylvette , Merhari Lhadi
Published: April 2011

The v(SiH) stretching absorption band is known to be sensitive to the local environment of the silicon atom. The presence of SiH groups on silicon carbide surface can be taken advantage of to evaluate the oxidation degree of this ceramic powder.

The surface analysis of a SiC nanosized powder was performed by FT-IR spectrometry. The evolution of the v(SiH) absorption band, followed in situ under controlled temperatures and oxygen pressures, consists in a frequency shift toward higher wavenumbers when oxidation proceeds. The resolution of the Sill absorption range into four subbands corresponding to the HSiOxC3−x possible surface groups showed the relative evolution of the different species. Ab initio SCF MO calculations on molecular models gave evidence of the charge transfer to the more electronegative oxygen atom, making the silicon atom more positive and seemingly strengthening the SiH bond and thus inducing an upward shift of the v(SiH) frequency.
Self-Assembly of Inorganic/Organic Multilayer Films
Authors: Zeppenfeld Astrid C. , Page Catherine J.
Published: April 2011

In order to investigate the influence of substrate functionalization on the subsequent selfassembly of multilayer films, multilayers composed of alternating hafnium and 1,10-decanediylbis(phosphonic) acid (DBPA) have been grown on three different substrates. Substrates studied include gold wafers functionalized with 4-mercaptobutylphosphonic acid, silicon wafers functionalized using a hafnium oxychloride solution, and silicon wafers coated with an octadecylphosphonate LB-template layer. The nature of these films is probed using ellipsometry and grazing angle x-ray diffraction. These studies indicate that the overall order and the individual layer thickness can vary substantially from sample to sample and depend strongly on the initial surface functionalization prior to multilayer growth.
Layered Silicate/Polystyrene Nanocomposite
Authors: Moet A. , Akelah A. , Hiltner A. , Baer E.
Published: April 2011

Nano-composites have been prepared from Na+ and Ca++ montmorillonite (MMT) in a polystyrene matrix via chemical intercalation. Vinyl monomer-g-MMT was prepared by exchanging the mineral cation by vinylbenzyl trimethylammonium chloride, thus rendering the mineral organophilic and forming polymerizable moieties directly bonded to the lamellar surface of the mineral. Styrene was added and polymerized by free radical in selected solvents. The ratio of mineral to the bound polymer ranged from 0.3 to 1.25 (by weight) depending on the initial mineral concentration in the feed and on the solvent used. The mineral domains in the composite, measured from suspension cast film fall in the range of 150 nm to 400 nm. Measured from compression molded samples, the domains were ca. 50 nm which is much smaller than the mineral aggregate and comparable to that of the primary particle of the mineral. WAXD disclosed that the d (001) spacing of MMT in the composite ranged from 1.7 to 2.5 nm suggesting that the mineral aggregates (ca. 10 μm) were dissociated into individual layers then reassembled into lamellar nanoclusters.
The Effect of Na-Bearing Thermal Solutions on Ca-Mg-Bentonite Sorption of Sr and Cs
Authors: Mukhamet-Galeyev Alexander P. , Kudrin Alexey V. , Nikonov Boris S. , Shikina Nadezhda D.
Published: April 2011

The sorption of Sr and Cs has been investigated on Ca-Mg-bentonite preliminary treated by 0.1–1.0 m NaCl solutions at 25, 170–250°C during 0.5–7 months. The bentonite remained stable in these conditions. Moreover, hydrothermal treatment has raised the sorption activity of the bentonite. The treated bentonite has shown a strong selectivity for Sr and less pronounced one for Cs. The sorption of the elements increased with temperature and decreased with NaCl content more significant for Sr, than for Cs. The distribution ratio Rd was nearly independent on ion loading for Cs and strongly increased up to 104.5 mL/g in 10−2.0−10−0.5 meq/g ion loading interval for Sr, dropping sharply at more concentrations.
Modeling Relations Between the Composition and Properties of French Light Water Reactor Waste Containment Glass
Authors: Ghaleb D. , Dussossoy J. L. , Fillet C. , Pacaud F. , Jacquet-Francillon N.
Published: April 2011

Models have been developed to calculate the density, molten-state viscosity and initial corrosion rate according to the chemical composition of glass formulations used to vitrify high-level fission product solutions from reprocessed light water reactor fuel. Developed from other published work, these models have been adapted to allow for the effects of platinoid (Ru, Pd, Rh) inclusions on the molten glass rheology.
Sorption Aspects for in Situ Matrix Diffusion Modelling at Palmottu Natural Analogue Site, Sw Finland
Authors: Rasilainen Kari , Suksi Juhani , Hakanen Martti , Olin Markus
Published: April 2011

Concentration profiles in rock matrix around water-carrying fissures were measured at Palmottu U deposit. The profiles were interpreted by the classical matrix diffusion concept. Site-specific sorption studies were performed for U using standard batch experiments and surface complexation modelling; the response of sorption isotherms was also tested. Sitespecific matrix properties as well as initial and boundary conditions were used in simulations. Our results indicate that matrix diffusion alone cannot explain the observed enrichment of U and its daughters in the rock matrix.
Principles and Practice of Reactive Transport Modeling
Authors: Lichtner Peter C
Published: April 2011

This paper presents a review of the principles underlying a continuum formulation of reactive transport in a porous medium. Partial differential equations representing conservation of mass are derived for transport by advection, diffusion, and electrochemical migration combined with chemical reaction of aqueous species and solids. Several examples are presented to illustrate the general theory. These include weathering along a narrow crevice, electrochemical migration in a dilute NaCl solution, secondary pyrite formation mediated through intermediate sulfur oxidation states, and a description of a uranium roll-front deposit. Numerical techniques which take advantage of the quasi-stationary state approximation, based on the much longer time scale involved in mineral alteration compared to that characterizing changes in the aqueous phase, permit solving the reactive transport equations over geologic time scales.
Mobility of Uranium, Thorium and Lanthanides Around the Bangombe Natural Reactor (Gabon)
Authors: Bros R. , Gauthier-Lafaye F. , Larque P. , Samuel J. , Stille P.
Published: April 2011

New mineralogical and isotopic studies were carried out on samples from the Bangombé natural nuclear reactor. This reactor is located at shallow depth in the weathering profile and has been subjected to severe supergene alteration. Textural evidence indicates partial dissolution of uraninite in the Bangombé ore related to precipitation of Fe-Ti oxi-hydroxides and clay minerals (kaolinite and metahalloysite). As a consequence of the alteration of the uraninite, uranium and f issiogenic rare earth elements were released in the clayey border of the reactor, whereas radiogenic232Th remained confined in the close vicinity of the core. A retention effect is also evidenced, under reducing conditions, in the black shales located above the reactor.
Modelling Study on Uranium Migration in Rocks Under Weathering Condition
Authors: Ohnuki Toshihiko , Murakami Takashi , Isobe Hiroshi , Sato Tsutomu , Yanase Nobuyuki
Published: April 2011

A modelling study has been completed to understand the effect of rock alteration on uranium migration at the Koongarra ore deposit, Australia. The model considers the weathering process, the mechanism and rate of chlorite alteration, a major mineral of the host rock, and assumes the presence of reversible sorption sites of chlorite and the presence of reversible and irreversible sorption sites of the weathering products. One- and two-dimensional, calculated uranium concentrations were compared with those observed. Good agreement between the calculated and observed uranium concentration profiles was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of Fe-minerals produced during weathering of chlorite. On the other hand, the conventional Kd model failed to estimate an adequate uranium concentration profile. The results suggest that the fixation of uranium to Fe-minerals has dominated the migration of uranium in the vicinity of the Koongarra ore deposit.
Hydrogeochemical Investigation of Groundwater in the Tono Area, Japan
Authors: Iwatsuki T. , Sato K. , Seo T. , Hama K.
Published: April 2011

Measurements of chemical compositions of groundwaters, carbon isotope analysis of dissolved inorganic carbon and batch experiments on water-rock interaction have been carried out in order to evaluate the chemical evolution of groundwater in the sedimentary rocks of the Tono area, Japan. The activities of Na and Ca ions in the groundwater plotted along the boundary between Na- and Ca-montmorillonite stability fields on a diagram of 2pH+log[Ca2+] vs. pH+log[Na+], which indicates that the two mineral phases are in equilibrium. Groundwater samples, rich in Ca ions (14.8 ppm Ca ions and 16.3 ppm Na ions), were collected from the shallow zone of the Tono area, and were reacted with the sedimentary rocks in the batch experiments. The experiments have revealed that ion exchange occurs between Na ions in the rock samples and Ca ions in the groundwater samples, and the final solutions became rich in Na ions (1.2 ppm Ca ions and 35.2 ppm Na ions). The results of the batch experiments are in agreement with the variation of Na and Ca concentrations in the groundwater in the sedimentary rocks. The carbon isotope data showed that the fraction of HCO3 derived from the dissolution of calcite increases from 25% to 75% of the total HCO3 content with increasing depth. The molality of Na ions in the groundwater was measured to be twice that of HCO3 ions derived from calcite, which supports the Na and Ca ion exchange in the groundwater. The results suggest that the chemical evolution of the groundwater is characterized by the variation in Na, Ca and HCO3 concentrations, and that ion exchange and dissolution of calcite are dominant reactions in the evolution of groundwater in the Tono area.
Application of a Selective Phase Extraction Procedure to Samples from the Adamello Contact Aureole (Italy)
Authors: Payne T. E. , Lumpkin G. R. , McGlinn P. J. , Hart K. P.
Published: April 2011

Hydrothermal veins, rich in Ti, Zr, rare earth elements (REE’s), and actinides, occur in the pure dolomitic marbles of the Adamello contact metamorphic aureole. A selective phase extraction using 9M HC1 was applied to samples from within and near these veins to chemically separate acid-soluble phases from residual phases, and to study the associations of U, Th, and REE’s with these phases. The samples were from the phlogopite, titanian clinohumite, and forsterite vein zones, and from the country rock. The effects of the extraction were studied by SEM/EDS and by chemical analysis. Isotopes of U and Th were analysed by alpha-spectrometry.

The chemical data and SEM/EDS results indicated that dolomite, calcite, apatite, and much of the pyrrhotite were dissolved by the 9M HC1, whereas spinel, phlogopite, titanite, chal copy rite, and zirconolite were among the acid-resistant phases. In all vein samples, the REE-patterns of acid-soluble phases were consistent with the dissolution of REE-rich apatite. In samples from the phlogopite zone, the majority of U, Th, and REE’s were in residual phases, and the REE pattern of the residue was similar to that of REE-rich titanite. In the titanian clinohumite zone, a substantial proportion of these elements were in acid-soluble phases, and the REE pattern of the residual phases resembled that of zirconolite. Clinohumite was partially dissolved by the HC1 treatment. The sample from the forsterite zone contained substantial amounts of REE's in acid-soluble phases, whereas Th and U were mostly in residual phases. The dolomite (country rock) samples contained small amounts of an acid-resistant, uranium-rich phase which, while only comprising about 0.2% of the mass, accounted for 40–60% of the uranium present.
Extraction of Lanthanide(III) and Uranyl(VI) from Nitric Acid Solution by Malonamides
Authors: Nakamura Takashi , Matsuda Yuki , Miyake Chie
Published: April 2011

The extractive properties of two malonamide extractants, DMDBO3NPDA and DMDBMA were investigated for the extraction of lanthanide(III) and uranyl(VI) ions in benzene-nitric acid systems. It was found that DMDBO3NPDA has a higher extractive capacity than DMDBMA. The difference in their extracting capacities is discussed, based on the enthalpy changes for the extraction reactions and IR data for complexes of metal nitrates with malonamides. In addition, the applicability of a mixed solvent of n-dodecane and some aliphatic alcohols as a diluent for DMDBO3NPDA was examined. The longer the carbon chain and the higher the concentration of the aliphatic alcohol, the more the phase compatibility improves. The distribution ratios of neodymium(III) ion increase with an increase in the carbon chain length of linear aliphatic alcohol and with a decrease in its concentration.
Diffusion Rate of Na+ and Cs+ in Hydrous Titanium(iv) Oxide
Authors: Kasuga Fuminori , Yamazaki Hiromichi , Inoue Yasushi
Published: April 2011

The diffusion rates of Na+ and Cs+ in two types of hydrous titanium(IV) oxide, precipitated at pH 6 (exchanger A) and pH 13 (exchanger B), were determined radiochemically. The rate of Cs+ in exchanger A is faster than that of Na+; diffusion coefficients are 4.9xl0-11 and 1.9xl0-11 m2 s-1 for Cs+ and Na+, respectively (pH 12, 5.0 °C). The activation energy for Cs+ diffusion is 21 kJ mol-1 and slightly smaller than that for Na+ diffusion, 29 kJ mol-1. The rates of these ions in exchanger B are much slower than those in exchanger A, and can be explained by assuming the existence of two kinds of independently diffusing ions (fast and slow species) in the exchanger. The diffusion coefficients are of the order of 10-12 and 10-13 m2 s-1 for the fast and the slow species, respectively. The activation energies are 48–60 kJ mol-1 for Na+ diffusion and 32–33 kJ mol-1 for Cs+ diffusion (pH 12). The marked difference in kinetics between two exchangers was interpreted in terms of the difference in the acid-base property and in the microstructure of the matrix.