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Microwave processing of ceramics

Description: Recent work in the areas of microwave processing and joining of ceramics is briefly reviewed. Advantages and disadvantages of microwave processing as well as some of the current issues in the field are discussed. Current state and potential for future commercialization of this technology is also addressed.
Date: April 1, 1993
Creator: Katz, J. D.
Partner: UNT Libraries Government Documents Department

Microwave assisted chemical vapor infiltration

Description: A microwave assisted process for production of continuous fiber reinforced ceramic matrix composites is described. A simple apparatus combining a chemical vapor infiltration reactor with a conventional 700 W multimode oven is described. Microwave induced inverted thermal gradients are exploited with the ultimate goal of reducing processing times on complex shapes. Thermal gradients in stacks of SiC (Nicalon) cloths have been measured using optical thermometry. Initial results on the ``inside out`` deposition of SiC via decomposition of methyltrichlorosilane in hydrogen are presented. Several key processing issues are identified and discussed. 5 refs.
Date: December 31, 1991
Creator: Devlin, D. J.; Currier, R. P.; Barbero, R. S.; Espinoza, B. F. & Elliott, N.
Partner: UNT Libraries Government Documents Department

Experimental observations of thermal spikes in microwave processing of ceramic oxide fibers

Description: Microwave heating of alumina/silica fiber tows in a single-mode microwave cavity at 2.45 GHz have produced a surprising thermal spike behavior on the fiber bundles. During a thermal spike, a ``hot spot`` on the tow brightens rapidly, persists for a few seconds, and rapidly extinguishs. A hot spot can encompass the entire tow in the cavity or just a localized portion of the tow. Some local hot spots propagate along the fiber. Thermal spikes are triggered by relatively small (<15%) increases in power, thus having obvious implications for the development of practical microwave fiber processing systems. A tow can be heated through several successive thermal spikes, after which the tow is left substantially cooler than it was originally, although the applied microwave electric field is much larger. X-ray diffraction studies show that after each temperature spike there is a partial phase transformation of the tow material into mullite. After several excursions the tow has been largely transformed to the new, less lossy phase and is more difficult to heat. Heating experiments with Nextel 550 tows are examined for a pausible explanation of this microwave heating behavior.
Date: April 1, 1994
Creator: Vogt, G. J.; Unruh, W. P. & Thomas, J. R. Jr.
Partner: UNT Libraries Government Documents Department

Temperature distribution in microwave sintering of alumina cylinders

Description: Small cylinders of high-purity alumina were encased in a `casket` of low-density zirconia insulation and heated to sintering temperature in a large multi-mode microwave oven. Optical fiber sensors were used to monitor the temperature at several locations in the system. It was found that the alumina samples heat faster than the zirconia insulation at temperatures above 1000 C, and that the temperature distribution in the sample is essentially uniform during the heating process. A two-dimensional mathematical model of the heat transfer process was developed which reproduces the essential features of the observed phenomena. Literature data for all temperature-dependent properties were incorporated into the model. The model suggests that the alumina samples absorb a significant fraction of the microwave energy.
Date: April 1, 1994
Creator: Thomas, J. R. Jr.; Katz, J. D. & Blake, R. D.
Partner: UNT Libraries Government Documents Department

Y-12 development organization technical progress report period ending February 1, 1994. Part 7, Lithium and uranium chemical processing

Description: Microwave energy was used successfully to consolidate small lots of uranium powder. Factors varied were max power, hold time, heating rate, gas pressure, batch composition, crucible material, insulation configuration. Results indicate that that the microwave consolidation process was rugged against all 7 factors for their respective parameters.
Date: March 8, 1994
Creator: Smith, W. E.
Partner: UNT Libraries Government Documents Department

Thermal Wadis in Support of Lunar Exploration: Concept Development and Utilization

Description: Thermal wadis, engineered sources of heat, can be used to extend the life of lunar rovers by keeping them warm during the extreme cold of the lunar night. Thermal wadis can be manufactured by sintering or melting lunar regolith into a solid mass with more than two orders of magnitude higher thermal diffusivities compared to native regolith dust. Small simulant samples were sintered and melted in the electrical furnaces at different temperatures, different heating and cooling rates, various soaking times, under air, or in an argon atmosphere. The samples were analyzed with scanning electron microscopy and energy dispersive spectroscopy, X-ray diffraction, a laser-flash thermal diffusivity system, and the millimeter-wave system. The melting temperature of JSC-1AF simulant was ~50°C lower in an Ar atmosphere compared to an air atmosphere. The flow of Ar during sintering and melting resulted in a small mass loss of 0.04 to 0.1 wt% because of the volatization of alkali compounds. In contrast, the samples that were heat-treated under an air atmosphere gained from 0.012 to 0.31 wt% of the total weight. A significantly higher number of cavities were formed inside the samples melted under an argon atmosphere, possibly because of the evolution of oxygen bubbles from iron redox reactions. The calculated emissivity of JSCf-1AF simulant did not change much with temperature, varying between 0.8 and 0.95 at temperatures from 100 to 1200°C. The thermal diffusivities of raw regolith that was compressed under a pressure of 9 metric tons ranged from 0.0013 to 00011 in the 27 to 390°C temperature range. The thermal diffusivities of sintered and melted JSC-1AF simulant varied from 0.0028 to 0.0072 cm2/s with the maximum thermal diffusivities observed in the samples that were heated up 5°C/min from RT to 1150°C under Ar or air. These thermal diffusivities are high enough for the rovers ...
Date: October 12, 2009
Creator: Matyas, Josef; Wegeng, Robert S. & Burgess, Jeremy M.
Partner: UNT Libraries Government Documents Department

Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source at LBNL

Description: Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source (AECR) at Lawrence Berkeley National Laboratory (LBNL) has been significantly improved by application of various new techniques. Heating the plasma simultaneously with microwaves of two frequencies (10 and 14 GHz) has increased the production of very high charge state heavy ions. The two-frequency technique provides extra electron cyclotron resonance heating zone as compared to the single-frequency heating and improves the heating of the plasma electrons. Aluminum oxide on the plasma chamber surface improves the production of cold electrons at the chamber surfaces and increases the performance of the AECR. Fully stripped argon ions, {gt} 5 enA, were produced and directly identified by the source charge state analyzing system. High charge state ion beams of bismuth and uranium, such as {sup 209}Bi{sup 51+} and {sup 238}U{sup 53+}, were produced by the source and accelerated by the 88-Inch Cyclotron to energies above 6 MeV/nucleon for the first time. To further increase the production of high charge state ions to support the nuclear science research programs at the 88-Inch Cyclotron, an upgrade is taking place to increase the AECR magnetic field strengths and mirror ratios to improve the plasma confinement. Conceptual design is underway for a 3rd Generation ECR that uses superconducting magnets to reach higher magnetic field strengths and higher mirror ratios, high secondary emission chamber walls to increase the yield of cold electrons at the chamber surfaces and microwaves of multiple frequencies to improve plasma heating.
Date: September 1, 1995
Creator: Xie, Zu Qi & Lyneis, C.M.
Partner: UNT Libraries Government Documents Department

Adsorption and desorption of sulfur dioxide on novel adsorbents for flue gas desulfurization. Final report, September 1, 1994--February 29, 1996

Description: A sol-gel granulation method was developed to prepare spherical {gamma}-alumina granular supports and supported CuO granular sorbents for flue gas desulfurization. The prepared {gamma}-alumina supported CuO sorbents exhibit desirable pore structure and excellent mechanical properties. The sorbents contain higher loading (30-40 wt. %) of CuO dispersed in the monolayer or sub-monolayer form, giving rise to a larger SO{sub 2} sorption capacity ({gt}20 wt.%) and a faster sorption rate as compared to similar sorbents reported in the literature. With these excellent sulfation and mechanical properties, the sol-gel derived {gamma}-alumina supported CuO granular sorbents offer great potential for use in the dry, regenerative flue gas desulfurization process. Research efforts were also made to prepare DAY zeolite supported sorbents with various CuO contents by the microwave and conventional thermal dispersion methods at different conditions. Monolayer or sub-monolayer coating of Cu(NO{sub 3})sub 2 or CuO was achieved on several DAY supported sorbents by the microwave heating method but not by the conventional thermal dispersion method. The DAY zeolite supported CuO sorbents prepared by the microwave heating method can adsorb up to 15 wt.% of SO{sub 2}. The results obtained have demonstrated the feasibility of effective preparation of zeolite supported CuO sorbents by the microwave heating method.
Date: August 5, 1996
Creator: Lin, Y.S. & Deng, S.G.
Partner: UNT Libraries Government Documents Department

[A variable frequency microwave furnace]. CRADA final report for CRADA Number ORNL91-0055

Description: The goals of this CRADA were to: (1) development and demonstrate a highly frequency-agile microwave furnace; (2) explore applications of the furnace for materials processing; and (3) develop control systems and packaging that are robust, user-friendly, and suitable for sale as a turnkey system. Microwave Laboratories, Inc. (MLI) designed, built, and successfully brought to market a benchtop Variable Frequency Microwave Furnace (VFMF). The concept has demonstrated advantages in polymer curing, waste remediation, and diamond (CVD). Through experimentation and modeling, the VFMF approach has gained credibility within the technical community.
Date: December 8, 1994
Creator: Lauf, R. J.
Partner: UNT Libraries Government Documents Department

Non-fusion applications of RF and microwave technology

Description: The processing of materials using rf and/or microwave power is a broad area that has grown significantly in the past few years. The authors have applied rf and microwave technology in the areas of ceramic sintering, plasma processing, and waste processing. The sintering of ceramics in the frequency range of 50 MHz-28 GHz has lead to unique material characteristics compared to materials that have been sintered conventionally. It has been demonstrated that sintering can be achieved in a variety of materials, including alumina, zirconia, silicon carbide, and boron carbide. In the area of plasma processing, progress has been made in the development and understanding of high density plasma sources, including inductively coupled plasma (ICP) sources. The effects of processing conditions on the ion energy distribution at the substrate surface (a critical processing issue) have been determined for a variety of process gases. The relationship between modeling and experiment is being established. Microwave technology has also been applied to the treatment of radioactive and chemical waste. The application of microwaves to the removal of contaminated concrete has been demonstrated. Details of these programs and other potential application areas are discussed.
Date: December 1, 1995
Creator: Caughman, J.B.O.; Baity, F.W.; Bigelow, T.S.; Gardner, W.L.; Hoffman, D.J.; Forrester, S.C. et al.
Partner: UNT Libraries Government Documents Department

Application of microwave solidification technology to radioactive waste

Description: The EPA has declared vitrification to be the Best Available Demonstrated Technology (BDAT) for High Level Radioactive Waste (40 CFR 268.42). Vitrification has been chosen as the method of choice for treating a number of radioactive residues and wastes in the DOE complex. Vitrification offers advantages of waste volume reduction, the ability to handle changing waste forms, and a stable, nonleachable final waste form. Microwave heating is a superior method for vitrification of radioactive wastes. Advantages of microwave heating include: (1) direct waste heating, eliminates need for electrodes, refractories and other consumables; (2) ``in-can`` processing allows for treatment of the material in its final container, (3) a mechanically simple system where the microwaves are generated away from the treatment area and transmitted to the treatment applicator by a wave guide, thus minimizing worker exposure to radiation; (4) easier equipment maintenance; and (5) a high degree of public acceptance.
Date: September 28, 1995
Creator: Harris, M.; Sprenger, G.; Roushey, B.; Fenner, G. & Nieweg, R.
Partner: UNT Libraries Government Documents Department

The use of solid-state NMR techniques for the analysis of water in coal and the effect of different coal drying techniques on the structure and reactivity of coal; Quarterly report, September 1--November 30, 1993

Description: For the research program reported here, different methods of drying are being investigated to determine if drying can be accomplished without destroying coal reactivity toward liquefaction. In an effort to understand the mechanism of water for enhancing coal liquefaction yield, the reactions of D{sub 2}O with the molecular constituents of coal during coal liquefaction are being investigated. This study involves the use of solution-state deuterium NMR, as well as, conventional solution-state {sup 1}H and {sup 13}C NMR analyses of the coal, and the coal liquids and residue from a coal liquefaction process. These D{sub 2}O transfer reactions will be conducted on coals which have been dried by various methods and rehydrated using D{sub 2}O and by successive exchange of H{sub 2}O associated with the coals with D{sub 2}O. The drying methods include thermal, microwave, and chemical dehydration of the coal. The overall objectives of this study are to develop a nuclear magnetic resonance (NMR) method for measuring the water in coal, to measure the changes in coal structure that occur during coal drying, to determine what effect water has on retrograde/condensation reactions, to determine the mechanism by which water may impact coal reactivity toward liquefaction, and to conduct D{sub 2}O exchange studies to ascertain the role of water in coal liquefaction. The objectives for this quarterly report period were (1) to measure the volumetric swelling ratio for thermally- and microwave-dried coals and (2) to conduct preliminary experiments concerning the exchange of water in coal with deuterium oxide (D{sub 2}O).
Date: December 31, 1993
Creator: Netzel, D.A.
Partner: UNT Libraries Government Documents Department

Use of a variable frequency source with a single-mode cavity to process ceramic filaments

Description: Rapid feedback control is needed for practical microwave processing of continuous ceramic oxide filaments to regulate the process temperature where the -dielectric properties of the filaments change rapidly with temperature. These dielectric changes can produce large rapid changes in the resonant frequency, the reflectivity, and the power density of the cavity. A broadband traveling wave tube (TWT) amplifier provides a highly versatile process control platform for filament processing. By comparing a RF signal from the cavity to a reference signal from the TWT, phase information can be used in a negative feedback loop to allow the oscillator to track the cavity frequency as it shifts due to the changing dielectric constant in the filaments being heated. By sampling the electric field level in the cavity with a detector, amplitude control can be done to maintain a constant absorbed power in a fiber tow, which is important for controlling the tow heating and temperature. This paper describes the design and testing of feedback controller with mullite rods in a single-mode TE{sub 10n} resonator driven by a commercial TWT.
Date: September 1, 1995
Creator: Vogt, G.J.; Regan, A.H.; Rohlev, A.S. & Curtin, M.T.
Partner: UNT Libraries Government Documents Department

Sintering of ceramics using low frequency rf power

Description: Sintering with low frequency rf power ({approximately}50 MHz) is a new technique with unique capabilities that has been used to sinter a variety of ceramic materials, including zirconia-toughened alumina, alumina, silicon carbide, and boron carbide. Processing with low frequencies offers many advantages compared to processing with conventional microwave frequencies (915 MHz and 2.45 GHz). Because of the longer wavelength, the rf electric field penetrates materials more than microwaves. This effect allows the processing of a wider variety of materials and allows for an increase in the physical size of the material being processed. In addition, the material is heated in a single mode cavity with a uniform electric field, which reduces the occurrence of hot-spot generation and thermal runaway effects. This technique has been used to sinter large crack-free alumina samples (3 inch square) to > 97% density. The sintering and/or annealing of a number of carbide materials has been demonstrated as well, including silicon carbide, boron carbide, tungsten carbide, and titanium carbide.
Date: July 1, 1995
Creator: Caughman, J.B.O.; Hoffman, D.J.; Baity, F.W.; Akerman, M.A.; Forrester, S.C. & Kass, M.D.
Partner: UNT Libraries Government Documents Department

Novel Direct Steelmaking by Combining Microwave, Electric Arc, and Exothermal Heating Technologies

Description: Steel is a basic material broadly used by perhaps every industry and individual. It is critical to our nation's economy and national security. Unfortunately, the American steel industry is losing competitiveness in the world steel production field. There is an urgent need to develop the next generation of steelmaking technology for the American steel industry. Direct steelmaking through the combination of microwave, electric arc, and exothermal heating is a revolutionary change from current steelmaking technology. This technology can produce molten steel directly from a shippable agglomerate, consisting of iron oxide fines, powdered coal, and ground limestone. This technology is projected to eliminate many current intermediate steelmaking steps including coking, pellet sintering, blast furnace (BF) ironmaking, and basic oxygen furnace (BOF) steelmaking. This technology has the potential to (a) save up to 45% of the energy consumed by conventional steelmaking; (b) dramatically reduce the emission of CO{sub 2}, SO{sub 2}, NO{sub x}, VOCs, fine particulates, and air toxics; (c) substantially reduce waste and emission control costs; (d) greatly lower capital cost; and (e) considerably reduce steel production costs. This technology is based on the unique capability of microwaves to rapidly heat steelmaking raw materials to elevated temperature, then rapidly reduce iron oxides to metal by volumetric heating. Microwave heating, augmented with electric arc and exothermal reactions, is capable of producing molten steel. This technology has the components necessary to establish the ''future'' domestic steel industry as a technology leader with a strong economically competitive position in world markets. The project goals were to assess the utilization of a new steelmaking technology for its potential to achieve better overall energy efficiency, minimize pollutants and wastes, lower capital and operating costs, and increase the competitiveness of the U.S. steel industry. The objectives associated with this goal were to (a) generate a solid base ...
Date: March 28, 2005
Creator: Huang, Dr. Xiaodi & Hwang, Dr. J. Y.
Partner: UNT Libraries Government Documents Department

Microwave heating for production of a glass bonded ceramic high-level waste form.

Description: Argonne National Laboratory has developed a ceramic waste form to immobilize the salt waste from electrometallurgical treatment of spent nuclear fuel. The process is being scaled up to produce bodies of 100 Kg or greater. With conventional heating, heat transfer through the starting powder mixture necessitates long process times. Coupling of 2.45 GHz radiation to the starting powders has been demonstrated. The radiation couples most strongly to the salt occluded zeolite powder. The results of these experiments suggest that this ceramic waste form could be produced using microwave heating alone, or by using microwave heating to augment conventional heating.
Date: July 30, 2002
Creator: O'Holleran, T. P.
Partner: UNT Libraries Government Documents Department

Decontamination of Radionuclides from Concrete During and After Thermal Treatment

Description: The objective was to clarify from the theoretical viewpoint the mechanical, diffusional, thermodynamic and electromagnetic aspects of the decontaminations problem, by means of developing a powerful computational model to evaluate the effect of a very rapid heating regime on the on the contaminated concrete walls or slabs. The practical objective was to assess the feasibility of the microwave heating scheme envisaged and determine its suitable parameters such as power and duration. This objective was complementary to, but separate from, the chemical and nuclear aspects of long-time processes that led to the contamination and various conceivable alternative methods of decontamination which were investigated by Dr. Brian Spalding of Oak Ridge National Laboratory, with whom the start-up phase of this project was coordinated.
Date: September 15, 1998
Creator: Bazant, Z. P.
Partner: UNT Libraries Government Documents Department

Low density inorganic foams fabricated using microwaves

Description: The objective of our work was to determine if high temperature foams could be made using microwave heating; and if so, to investigate some of their properties. Several foams were made and their compressive strengths, tensile strengths and densities were determined. Foams were made of glass, metal-glass, glass-fiber, metal-glass-fiber, and fly ash. The microwave source used was a Litton model 1521 microwave oven which operated at 2.45 GHz and had an output of 700 watts.
Date: January 1, 1985
Creator: Meek, T.T.; Blake, R.D. & Gregory, T.G.
Partner: UNT Libraries Government Documents Department

Microwave sintering of alumina-SiC composites at 2. 45 and 60 GHz

Description: Composites of alumina-10 vol % silicon carbide whiskers were sintered to 70% of theoretical density using both 2.45 and 60 GHz microwave radiation. Further densification was inhibited by formation of a constrained network of whiskers. Alumina-10 vol % silicon carbide platelet composites were sintered to 94% of theoretical density with 2.45 GHz microwaves in less than 20 minutes. 4 refs., 11 figs.
Date: January 1, 1988
Creator: Katz, J.D.; Blake, R.D. & Petrovic, J.J.
Partner: UNT Libraries Government Documents Department

Precision timing and interlocks systems for FEL (free-electron laser) heating experiments on MTX (Microwave Tokamak Experiment)

Description: A new precision timing system has been installed on the Microwave Tokamak Experiment (MTX) at Lawrence Livermore National Laboratory (LLNL). The purpose of the system is to synchronize the tokamak's plasma discharge with a 140-GHz, 2-GW microwave pulse generated by a free-electron laser (FEL). The installation involved modifying the existing sequencer system and adding Digital delay generators, three in-house-designed CAMAC modules and other components. The system controls placement of the 30-ns FEL pulse during the MTX plasma discharge. It also provides precision triggers for the microwave plasma diagnostics. These triggers are distributed over 100-Mbit/s fiber-optic links. The MTX interlock system has been expanded to provide personnel safety during FEL experiments, to protect the FEL and related equipment, and to control the path of the FEL beam starting from the FEL's output, through the beam transport system, and into the tokamak. This paper describes how the existing MTX timing and interlocks systems were upgraded to accommodate these new FEL experiments. 4 refs., 4 figs.
Date: September 20, 1989
Creator: Petersen, D.E. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Microwave heating and current drive in tokamaks

Description: The use of powerful microwave sources provide unique opportunities for novel and efficient heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. Free- electron lasers and relativistic klystrons are new sources that have a number of technical advantages over conventional, lower-intensity sources; their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. This paper reports on modeling of absorption and current drive, in intense-pulse and quasilinear regimes, and on analysis of parametric instabilities and self-focusing. 16 refs., 2 figs.
Date: August 23, 1988
Creator: Cohen, B.I.; Cohen, R.H.; Kerbel, G.D.; Logan, B.G.; Matsuda, Y.; McCoy, M.G. et al.
Partner: UNT Libraries Government Documents Department

Operational characteristic of a compact microwave ion source

Description: A small microwave ion source has been fabricated from a quartz tube with one end enclosed by a two grid accelerator. The source is also enclosed by a cavity operated at a frequency of 2.45 GHz. Microwave power as high as 500 W can be coupled to the source plasma. The source has been operated with different geometries and for various gases in a cw mode. For hydrogen, ion current density of 200 mA/cm/sup 2/ with atomic ion species concentration as high as 80% has been extracted from the source. It has also been demonstrated that low energy oxygen ion beams (5 to 10 eV) can also be extracted from the source.
Date: March 1, 1986
Creator: Walther, S.R. & Leung, K.N.
Partner: UNT Libraries Government Documents Department

Microwave hybrid heating of alumina filaments

Description: Low loss oxide ceramics filaments are not readily heated to sintering temperatures (>900[degrees]C) by direct microwave heating at 2.45 GHz. Use of high power levels typically yields thermal runaway with catastrophic melting. In other studies, hybrid, or indirect, heating has been successfully applied to processing bulk oxide ceramics. In this work, commercial alumina-based filaments have been indirectly heated to 700[degrees]--900[degrees]C through a lossy carbon coating on the filament tow. Specific filaments can reach higher temperatures by direct coupling after preheating with a lossy coating. The results of microwave hybrid heating in a single mode TE[sub 102] cavity will be described for commercial alumina-based filaments.
Date: January 1, 1993
Creator: Vogt, G.J. & Unruh, W.P.
Partner: UNT Libraries Government Documents Department

Microwave processing of ceramics

Description: This paper discusses the following topics on microwave processing of ceramics: Microwave-material interactions; anticipated advantage of microwave sintering; ceramic sintering; and ceramic joining. 24 refs., 4 figs. (LSP)
Date: January 1, 1989
Creator: Katz, J.D.
Partner: UNT Libraries Government Documents Department