bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microwave Sintering of ZnO Varistor Ceramics
Authors: Levinson Lionel M. , Comanzo Holly A. , Schultz William N. 
Published: March 2011

ABSTRACTZnO varistors are electronic ceramics whose electrical behavior is dominated by grain boundary effects. A careful evaluation of the effect of microwave sintering compared to conventional sintering revealed no significant differences between varistor devices processed by these two methods. A slight apparent enhancement of grain growth was observed for microwave processing, but further evaluation of this effect leads us to believe that it arises from a small systematic shift in temperature derived from the different experimental configurations.
Densification kinetics of Alumina During Microwave Sintering
Authors: Cheng Jiping , Qiu Jinyu , Zhou Jian , Ye Neng 
Published: March 2011

ABSTRACTSome kinetics parameters of alumina during microwave sintering were studied and compared with that during conventional sintering. The results demonstrated that the sintering rates for microwave processing were much greater than that for conventional processing, and the grain growth of alumina was rapid with prolonged time at high temperature in a microwave field. It was indicated that the microwave sintering at higher temperatures for a shorter time was favorable for preparing high density and fine-grained alumina ceramics.
Microwave Joining of Ceramics: A Study on Joining Alumina Both Directly and with Alumina Gel
Authors: Al-Assafi Salwan , Clark David E. 
Published: March 2011

ABSTRACTAlumina ceramics of different purities were joined using alumina gel as an interlayer and microwave energy as the heating source. Direct microwave joining of alumina was also accomplished. A comparison between the two joining methods was made. The effect of the gel on joining time and joining temperature was determined. Knoop microhardness was measured across the joint to show the change in the microhardness at the joint region. Joints of hardness as high as that of the bulk were produced when the joining parameters were properly selected. The dielectric properties of the aluminas used in this study were measured. X-ray maps and SEM micrographs were taken for different joints.
Microwave Curing and Drying of Cellular Concrete
Authors: van Loock Walter M. 
Published: March 2011

ABSTRACTTraditionally the heating and curing of cellular concrete takes place in an autoclave. This building material is a thermal insulator so the curing and drying processes are energy and time consuming. Volumetric heating is an attractive method for improving the throughputs.A feasibility study leads to the conclusion that microwave processing is not likely to be applied in a large scale production process.
Use of the Inverse Temperature Profile in Microwave Processing of Advanced Ceramics
Authors: Binner J.G.P. , Al-Dawery I.A. , Aneziris C. , Cross T.E. 
Published: March 2011

ABSTRACTAttempts are being made to exploit the inverse temperature profile which can be developed with microwave heating with respect to the processing of certain advanced ceramics. This paper discusses the results obtained to date during the microwave sintering of YBCO high-Tc superconductors and the microwave reaction bonding of silicon nitride.
Computer Modeling of Two Dimensional Temperature Distributions in Microwave Heated Ceramics
Authors: Tian Y.L. , Feng J.H. , Sun L.C. , Tu C.J. 
Published: March 2011

ABSTRACTA two dimensional model for computer simulation of microwave heating of ceramics has been developed. The effects of microwave power, properties of ceramics, and thermal insulation on dynamic temperature distributions of ceramics under various processing conditions have been simulated. The practical solutions for eliminating thermal runaway and improving temperature homogeneity under microwave rapid heating can be approached using this computation technique.
Automation of Microwave Processing of Graphite / Epoxy Composite Materials using an Expert Systems Technique
Authors: Adegbite Valerie , Hawley Martin , Decker Dave , Sticklen Jon 
Published: March 2011

ABSTRACTMicrowave curing of composite materials is a novel technology which can be an alternative to conventional thermal curing and has many advantages over thermal curing, i.e, fast and direct heating, selective heating, and controllability. Currently, the existing technology is more empirical and cannot be easily described by traditional process models. One key enabling step for realizing the advantages of the microwave curing technology is a capability for utilizing all the available existing knowledge in a concise manner. The major elements of a control system which utilizes traditional control techniques and (non-traditional) expert systems techniques in a real time microwave cure monitoring and control is discussed.
Modeling and Controlling During Microwave and Thermal Processing of Composites
Authors: Wei Jianghua , Sundaram Ananthapadmanaban , Hawley Martin C. 
Published: March 2011

ABSTRACTA process model was developed and coded in FORTRAN to simulate the temperature and the extent of cure profiles across the thickness of the composite during microwave and thermal processing. A simplified five-parameter microwave power absorption model was developed for microwave processing. The computer code was used to predict the behavior of Hercules AS4/3501-6 prepreg during thermal processing using various laminate thickness and boundary conditions. The simulation results show that 4.0 cm is the thickest composite that can be processed with the manufacture's cure cycle. The advantages of microwave processing over thermal processing are fully demonstrated.
Microwave Imaging Techniques for Non-Destructive Testing of Materials
Authors: Bolomey J.Ch. , Pichot Ch. 
Published: March 2011

ABSTRACTRecent technological advances for microwave multiport sensors lead us to look for efficient wavefront processing techniques in order to improve image quality, in terms of spatial resolution and contrast. This paper reviews some of these techniques which can be used for Non-Destructive Testing purposes. Mutual advantages and limitations are analysed.
Microwave Based and Microwave Aided non Destructive Test Methods
Authors: d'Ambrosio G. , Massa R. , Migliore M.D. , Ciliberto A. , Sabatino C. 
Published: March 2011

ABSTRACTThe reflection coefficient of Fiberglass/Kevlar slabs, including a layer of a different material was calculated as a function of permittivities, thicknesses, defect depth, and microwave frequency. Experimental tests were done with a single-frequency, amplitude and phase sensitive circuit, and with a swept-frequency amplitude only sensitive set-up. In this latter case a suitable processing of data allowed effective and fast defect detection. First experiments on microwave heating for thermographic NDT were also performed.
RF and Microwave Dielectric Measurements to 1400°C and Dielectric Loss Mechanisms
Authors: Hutcheon R.M. , Jong M.S. De , Adams F.P. , Lucuta P.G. , McGregor J.E. , Bahen L. 
Published: March 2011

ABSTRACTA system has been developed, based on the cavity perturbation technique, for measuring the complex scalar permittivity of materials at frequencies between 50 MHz and 3 CHz, and up to a temperature of 1400°C. Measurements have been made on several classes of materials, including metallic oxides, conventional and advanced ceramics, fabrics, earthenwares, geological and biological materials, foods, glasses, organics and ferrites. Some materials remain unchanged by thermal cycling, but many undergo irreversible changes; the latter are of interest in microwave processing. The system measures the complex dielectric constant of materials during conventional heating, curing or sintering. Correlating these microwave measurements with other diagnostic techniques will help in the understanding of these processes in several classes of materials.
High-Temperature Dielectric Properties Measurements of Ceramics
Authors: Bringhurst Shane , Andrade Octavio M. , Iskander Magdy F. 
Published: March 2011

ABSTRACTThis paper dicusses experimental arrangements, describes measurement techniques and presents experimental results for hightemperature broadband dielectric properties measurements of ceramics. The cavity perturbation technique and the open-ended coaxial line method are used in these experimental measurements. The design and construction details of cavities and probes are described and representative results of measurements on zirconia and alumina samples (green and sintered) are presented. Results of measurements made on insulating materials are shown. In general measurements are made in the frequency band 1 to 10 GHz and temperatures up to 1000°C.
Calibration Method for Open-Ended Coaxial Probe/Nector Network Analyzer System
Authors: Blackham David 
Published: March 2011

ABSTRACTThe vector network analyzer readily lends itself to a variety of techniques for measuring material properties. The open-ended coaxial probe is one technique that allows swept frequency measurements of permittivity. The open-ended coaxial probe technique requires little or no sample preparation and can make non-destructive measurements on a variety of materials. It is especially suited for materials in liquid or semi-solid form. An understanding of network analyzer calibration and the coaxial probe model provides insight into calibration techniques that minimize systematic errors. This understanding also.facilitates the extension of measurement conditions beyond normal measurement constraints leading to a simple procedure which provides a first order correction of perturbations to the systematic errors.
Modeling The Microwave Frequency Dielectric Properties of Thermoplastic Composite Materials
Authors: Jackson Mitchell L. , Stern Curtis H. 
Published: March 2011

ABSTRACTMixture models were studied in an effort to predict the microwave frequency permittivities of unidirectional-fiber-reinforced thermoplastic-matrix composite materials as a function of fiber volume fraction, fiber orientation relative to the electric field, and temperature. The permittivities of the constituent fiber and plastic materials were measured using a resonant cavity perturbation technique at 9.4 GHz and at 2.45 GHz. The permittivities of the composite specimens were measured using a reflection cavity technique at 9.4 GHz and at 2.45 GHz. Simple “rule-of-mixtures” models that use the fiber and plastic permittivities have been found to approximate the complex dielectric properties of the composite for varied fiber volume fractions. The permittivities of oriented composites were modeled using a tensor rotation procedure. Composite permittivities were modeled with temperature up to the glass transition temperature of the thermoplastic matrix.
Ceramic Materials for High-Quality Dielectric Resonators of Microwave Range
Authors: Nenasheva Yelizaveta A. 
Published: March 2011

ABSTRACTThe dielectric properties of ceramic materials and dielectric resonators on the basis of oxides of Ba,Ti and alkaline earth elements, and also of the calcium titanate-lanthanum aluminate system, with ε =82 and ε =40…48, frequency temperature coefficient (TCf) from - 10ppm/°C to + 10ppm/°C have been studied. Ceramics with ε =82 ensures the DR Q-factor of 3000 and more at f=3GHz. The Q-factor of DR made of ceramics with ε=42, TCf =0 reaches 8000 at f=7GHz.
Highlights from Panel Discussion on “Key Issues for Future Developments in Microwave Processing”
Authors: Gac Frank D. , Iskander Magdy F. 
Published: March 2011

This proved to be a very insightful discussion, thanks to an enthusiastic audience and the team of panelists listed below:Peter Angelini, Oak Ridge National LaboratoryRaymond F. Decker, Wavemat/Paton Tek Inc.E. Eugene Eves, III, RaytheonFrank D. Gac, Los Alamos National LaboratoryJohn F. Gerling, Gerling LaboratoriesMagdy F. Iskander, University of UtahBernard Krieger, Cober ElectronicsRichard Smith, Electric Power Research InstituteWilliam B. Snyder, Microwave Materials Technology, Inc.Wayne R. Tinga, University of AlbertaAlthough the panelists represented a mix of individuals from government, academia, and industry, only one aspect of industry was represented, namely microwave system manufacturers. For future panel discussions, it is recommended that the materials manufacturing (i.e., microwave user) sector also be represented.
Electromagnetic Field Modeling of a Loaded Microwave Cavity
Authors: Chaussecourte P. , Lamaudiere J.F. , Maestrali B. 
Published: March 2011

ABSTRACTThe unavoidable way of a better conception of cavities for industrial applications is electromagnetic field numerical computation with the aim of placing the fields E and H into the material, and furthermore to obtain some characteristics like the input impedance of the cavity or the dissipated power in the sample. From Maxwell's equations and using a Finite Element Method with 3D edge elements we get a linear system from which, after resolution, we can obtain several kinds of results: research of eigen modes of an empty or partially dielectric loaded cavity, that is, for a bounded domain, all the frequencies that could be excited, using only dimensionnal (L,l,h) and physical (εʹ,εʺ) characteristics, or response of a loaded cavity to an external excitation, that is, setting a TE10 mode in a waveguide feeding a cavity, obtain the distribution of field inside the oven and the dielectric. An original approach allows us, by projection of the excitation on eigen modes, to understand the behavior of the cavity and the interaction wave-product. Our computation is in very good agreement with analytical results we can obtain in some specific configurations (eigenvalues of an empty cavity, or transmission of only the TE10 mode in a correctly shaped waveguide).
Coupling with an Adjustable Compound Iris in a Single Mode Applicator
Authors: Sa'adaldin Hussamaldin S. , Black W. Murray , Ahmad Iftikhar , Silberglitt Richard 
Published: March 2011

ABSTRACTCoupling of the input power to a dielectric in a rectangular microwave cavity by using a compound iris having both inductive and capacitive slits, has been investigated. The compound iris is used in combination with a variable tuning plunger to maintain a resonant frequency of 2.45 GHz and minimize the reflected power. Under certain conditions, the compound iris has been observed to achieve an improved coupling of the input power, resulting in higher temperature of cylindrical 0.95 cm rods of silicon carbide (SiC) and alumina (A12O3). By placing the SiC perpendicular to the applied E field (with SiC enclosed in a porous insulation partially filling the applicator), coupling with the compound iris by adjusting both inductive and capacitive slits was achieved for a wide range of values compared to the use of a single pair of inductive slits. The coupling was more sensitive to a precise positioning of the single inductive slit. Such a difference was not observed for the case where the sample was placed parallel to the E field. In temperatures over 1600°C have been reached with a 600 W of power injected into the cavity. In tests with low loss alumina samples (99.8% pure) placed parallel to the E field, the compound iris permitted a greater coupling and higher temperature. The presence of alumina insulation had a significant effect in achieving higher temperatures, and occassionally preventing the initiation of arcing.
Synthesis of Fullerenes (C60 AND C70) by Combustion of Hydrocarbons in A Flat Flame Burner
Authors: Mitra S. , Pope C. J. , Gleason K. K. , Makarovsky Y. , Lafleur A. L. , Howard J. B. 
Published: March 2011

ABSTRACTFullerene (C60 and C70) synthesis by combustion of ethylene and benzene in a flat flame burner was investigated. This method of fullerene synthesis is particularly attractive because of its potential of scale up. Also the ability to change the flame conditions andcontrol the yield of C60 and C70 makes this method versatile. No fullerenes were found in soot samples collected from the ethylene flame. However, fullerenes were formed in a benzene flame with C/O = 0.88 and operated at 40 torr, with cold gas velocity of 25.3 cm/s (273 K) and containing 10% argon. The concentration of fullerenes in this flame was found to depend strongly on the height above the burner surface. It exhibited a strong maxima at about 1.0 cm above the burner height suggesting the presence of both growth and destruction mechanisms.
Temperature Dependent Structural Studies of K- and RB- Doped C60
Authors: Zhou Otto , Zhu Qing , Vaughan Gavin B.M. , Fischer John E. , Heiney Paul A. , Coustel Nicole , Mccauley John , Smith Amos B , Cox David E. 
Published: March 2011

ABSTRACTThe temperature dependent structural evolutions of RbxC60 (x = 3, 5, 6) and K4C60 were studied using both in-house andsynchrotron x-ray powder diffraction and thermal analysis techniques over a temperature range of 10K - 673K. The superconducting face centered-cubic (fcc) Rb3C60 and the body centered-tetragonal (bct) M4C60(M = K, Rb) phases are found to be line compounds in this temperature range, while the body centered-cubic (bcc) phase forms a solid solution in which the solubility of vacant M sites increases with temperature. The orientation of the C60 molecules in the K4C60 phase was analyzed. A crystalline fcc Rb1C60 phase is stable only above room temperature.
Nucleation, Cluster Growth, and Structure of Crystalline C60 and C70
Authors: Yao Nan , Behal S. K. , Klein C. F. , Disko M. M. , Fung S. C. , Sherwood R. D. , Creegan K. M. , Cox D. M. 
Published: March 2011

ABSTRACTThe nucleation and cluster growth of C60 and C70 crystallites on various substrates at ambient temperature have been investigated using electron microscopy. It was found that the initial nucleation is closely associated with surface defects, and the fullerenes are much more strongly bonded to each other than to the substrate. Sublimed C60 or C70 crystallites nucleate at the step edge in the liquid state and are aligned with the step walls and terraces through the process of coalescence. Reflection Electron Microscopy (REM) studies have shown an abnormal profile of C60 grown crystals as a result of the interaction of C60 molecules with the surface strain field during crystal growth. Transmission electron diffraction patterns reveal a twin structure with (110) habit plane for the low temperature ordered phase.
Calculation of the Stability and the Polarizability of Isolated Fullerene Molecules as a Function of Charge State
Authors: Quong Andrew A. , Pederson Mark R. 
Published: March 2011

ABSTRACTWe present first-principles local density functional calculations of the electronic structure and energetics of neutral and negatively charged fullerene molecules. We find thatthe negatively charged -1 state is stable relative to the neutral molecule and that the -2 state is stable relative to the neutral molecule but not to the -1 state of the molecule. We have also performed calculations of the electronic polarizabilities for different charged states and developed a simple model to estimate the dielectric constant of fullerene based crystals.
Structural Models of Negatively Curved Graphitic Carbon
Authors: Townsend S. J. , Lenosky T. J. , Muller D. A. , Nichols C. S. , Elser V. 
Published: March 2011

ABSTRACTWe have developed an automatic computational method for generating graphitic carbon structures. We propose models for crystalline and amorphous forms of carbon consisting of a single negatively curved graphitic sheet forming an extended structure. Stability and elastic properties are computed using an energy estimate fit to local density approximation(LDA) calculations. These forms of carbon are found to be more stable than C60. The radial distribution function for the random structures closely matches that of films of amorphous carbon grown on NaCI substrates from sublimated graphite.
Preparation and Properties of Low Density Replica Carbon Foams
Authors: Hulsey S. S. , Poco P. K. 
Published: March 2011

ABSTRACTLow density foams are used for a variety of applications, including catalytic supports, battery anodes, microporous membranes, and laser fusion targets. The technique for making replica carbon foams described in this paper has been previously reported[I] and involves a process in which an inorganic substrate (sodium chloride) is infused with a carbonizable polymer. After carbonization, the substrate is removed by a leaching process and the wet foam is dried; the resultant foam is referred to as replica carbon. This paper describes improvements in the processing which result in a smaller pore size and improved foam homogeneity.The original substrate is the single most important factor affecting the resultant structure. Techniques to improve the uniformity of the substrate and the translation of substrate anomalies into the final product are described.
Production and Characterization of Metal-Encapsulated Fullerenes
Authors: Johnson Robert D. , Yannoni Costantino S. , Hoinkis Mark , Vries Mattanjah de , Salem Jesse R. , Crowder Mark S. , Bethune Donald S. 
Published: March 2011

ABSTRACTWe report here the arc-production and spectroscopic characterization of fullerene-encapsulated metal atoms and metal-atom clusters. In particular, both solution and solid-stateelectron paramagnetic resonance (EPR) spectra of LaC82', YC82', SCC82' and Sc3 C82 have been obtained. Additional species containing rareearth atoms and clusters have been produced. The results suggest, for example, that the three scandium atoms in Sc3C82 form a molecule In the shape of an equilateral triangle — as was previously suggested for Sc3 molecules Isolated In a cryogenic rare-gas matrix. The spectraof the MC82 species (M =La, Y, Sc) exhibit small hyperfine couplings and g-values close to 2, suggesting that they can be described as a +3 metal cations within – 3 fullerene radical anion cages. Sc2C2n species — the most abundant metailofuilerenes In the scandlum-fullerene mass spectrum — are EPR-silent, even though Sc2 is EPR-actlve In a rare-gas matrix at 4.2K. A broader Implication of this work Is that production of macroscopic quantities of metal-containing fullerenes may make possible the fabrication of exotic new structures with regular arrays of metal atoms or clusters Isolated in fullerene molecules, resulting in new typesof host/guest nanostructured materials.
Mass Spectrometry of Metallofullerenes
Authors: Ross Mark M. , Nelson H.H. , Callahan J.H. , Mcelvany S.W. 
Published: March 2011

ABSTRACTFullerenes with a metal atom inside of the cage, metallofulierenes, were produced by either laser vaporization or a graphite arc and characterized using a variety of mass spectrometric methods. First, yttrium-fullerene adducts were formed by direct laser vaporization of samples consisting of graphite, yttrium oxide and fullerenes. Fragmentation and oxidation ion/molecule reactions showed that the laser-generated adducts are endohedral complexes (Yx@Cn), in contrast to externally-bound Y(Cn)+ species formed by gas-phase reactions. In addition, evidence was obtained for laserinduced bulk coalescence reactions yielding the metallofullerenes. Second, negative ion/desorption chemical ionization mass spectrometry was used to characterize metallofullerenes in arc-generated soot, pyridine extracts and the extract residue. The pyridine extracts of La2O3/graphite soot contain mostlyLa@C82 and La2@C80', in addition to (empty) fullerenes. However, the raw soot and the extract residue contain a broader range of metallofullerenes with relative abundances different than those observed from the extract (e.g. abundant La@C60', Lax@Cn') and La@C74). The thermal desorption behavior of the doped and undoped fullerenes indicate an interaction between the Cn and Lax@Cn species. Analysis of aqueous solutions of dried pyridine extracts of La2O3/graphite soot show Cn and Lax;@Cn' which is consistent with the possible presence ofmetallofullerene/ fullerene ionic complexes, (Lax@Cn)+C-n.