131 Matching Results

Search Results

Advanced search parameters have been applied.

Applications of microwave radiation environmental remediation technologies

Description: A growing number of environmental remediation technologies (e.g., drying, melting, or sintering) utilize microwave radiation as an integral part of the process. An increasing number of novel applications, such as sustaining low-temperature plasmas or enhancing chemical reactivity, are also being developed. An overview of such technologies being developed by the Department of Energy is presented. A specific example being developed at Argonne National Laboratory, microwave-induced plasma reactors for the destruction of volatile organic compounds, is discussed in more detail.
Date: May 1, 1993
Creator: Krause, T. R. & Helt, J. E.
Partner: UNT Libraries Government Documents Department

Microwave Sintering of Nanophase Ceramics Without Concomitant Grain Growth

Description: A method of sintering nanocrystalline material is disclosed wherein the nanocrystalline material is microwaved to heat the material to a temperature less than about 70% of the melting point of the nanocrystalline material expressed in degrees K. This method produces sintered nanocrystalline material having a density greater than about 95% of theoretical and an average grain size not more than about 3 times the average grain size of the nanocrystalline material before sintering. Rutile TiO{sub 2} as well as various other ceramics have been prepared. Grain growth of as little as 1.67 times has resulted with densities of about 90% of theoretical.
Date: April 15, 1991
Creator: Eastman, Jeffrey A.; Sickafus, Kurt E. & Katz, Joel D.
Partner: UNT Libraries Government Documents Department

Report on the sintering and properties of MgO and MgO-5% TiC

Description: Sintering of technical grade MgO yields higher fractional densities compared to pure MgO. TiC reacts with MgO under sintering of MgO-TiC composites in air, yielding Mg{sub 2}TiO{sub 4} and CO or CO{sub 2}. This can be suppressed in vacuum by plasma sintering. Plasma sintering of MgO at 1300 C and short times does not produce satisfactory results. 5 vol% TiC increases the sinterability of MgO during conventional air sintering; larger additions (50 vol%) decrease sinterability due to macropores formed by gaseous reaction product. Microwave sintering of MgO is possible. Mechanical properties of MgO are improved by additions of small amounts of TiC to starting powders.
Date: July 1, 1992
Creator: Bengisu, M. & Inal, O. T.
Partner: UNT Libraries Government Documents Department

Evaluations of glass vitrification techniques on iron ratio determinations

Description: High-level liquid waste at the Savannah River Site (SRS) will be processed into borosilicate glass at the Defense Waste Processing Facility (DWPF). Waste glass will be transported to a geologic repository for permanent disposal. Control of the redox properties of the melter feed is necessary for smooth operation of the melter. The Fe(II)/total Fe ratio in glass is a measure of the redox conditions in the melter. To simulate final glass product conditions, melter feed samples will be vitrified at the DWPF laboratory. A colorimetric method was used to determine the Fe(II)/total Fe ratio on vitrified melter feed samples. Because the crucible vitrification technique can have a large effect on the Fe(II)/total Fe ratio, crucible sealing during vitrification of the waste feed sample, and the type of heating applied vitrification, were the variables investigated for Fe(II)/total Fe ratio measurement effects. Various lid sealants were used for determining crucible sealing effects. Microwave and conventional heating were tested for glass vitrifications. Microwave heating and a nepheline gel sealant, to exclude oxygen from the alumina crucibles during vitrification, was adopted for use at the DWPF laboratory. This paper discusses microwave vitrification and crucible sealing techniques.
Date: December 31, 1991
Creator: Spencer, R. B.
Partner: UNT Libraries Government Documents Department

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

Ceramic matrix composites by microwave assisted CVI

Description: Chemical vapor infiltration (CVI) processes for producing continuously reinforced ceramic composites are reviewed. The potential advantages of microwave assisted CVI are noted. Recent numerical studies of microwave assisted CVI are then reviewed. These studies predict inverted thermal gradients in fibrous ceramic preforms subjected to microwave radiation and suggest processing strategies for achieving uniformly dense composites. Comparisons are made to experimental results obtained using silicon based composite systems. The importance of microwave-material interactions is stressed. In particular, emphasis is placed on the role played by the relative ability of fiber and matrix to dissipate microwave energy. Results suggest that microwave induced inverted gradients can in fact be exploited using the CVI technique to promote inside-out densification.
Date: May 1, 1993
Creator: Currier, R. P. & Devlin, D. J.
Partner: UNT Libraries Government Documents Department

Chemical vapor infiltration using microwave energy

Description: This invention is comprised of a method for producing reinforced ceramic composite articles by means of chemical vapor infiltration and deposition in which an inverted temperature gradient is utilized. Microwave energy is the source of heat for the process.
Date: December 31, 1992
Creator: Devlin, D. J.; Currier, R. P.; Laia, J. R. & Barbero, R. S.
Partner: UNT Libraries Government Documents Department

Microwave enhanced pyrochemical reactions of PuO{sub 2}, UO{sub 2}, and U{sub 3}O{sub 8}

Description: Experiments in the high level cells at WSRC have established that PuO{sub 2} has an extremely high absorption factor the microwaves: temperatures in excess of 1000{degrees}C were reached in less than 5 minutes with a multi mode, 2450 MHz, 600 watt, microwave oven. In other microwave heating experiments: stoichiometric compositions of PuO{sub 2}-UO{sub 2} were prepared and U{sub 3}O{sub 8} was reduced to U{sub 4}O{sub g}.
Date: December 31, 1990
Creator: Sturcken, E. F. & McCurry, L. E.
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

Mathematical model of thermal spikes in microwave heating of ceramic oxide fibers

Description: Experiments on microwave sintering of ceramic fibers in a single-mode cavity have revealed the presence of thermal spikes and `hot spots` which sometimes travel along the fiber and eventually disappear. They are triggered by relatively small increases in microwave power, and thus have obvious implications for the development of practical microwave-based fiber processing systems. These hot spots are conjectured to originate at slight irregularities in the tow morphology, and propagate as the result of solid phase transitions which take place at elevated temperatures and reduce the dielectric loss coefficient {epsilon}{double_prime}. An elementary mathematical model of the heat transfer process was developed which reproduces the essential features of the observed phenomena, thus lending support to the conjecture. This model is based on the assumption of one-dimensional heat conduction along the axis of the fiber tow, and radiation losses at the surface.
Date: April 1, 1994
Creator: Thomas, J. R. Jr.; Unruh, W. P. & Vogt, G. J.
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

Prospects for vitrification of mixed wastes at ANL-E

Description: This report summarizes a study evaluating the prospects for vitrification of some of the mixed wastes at ANL-E. This project can be justified on the following basis: Some of ANL-E`s mixed waste streams will be stabilized such that they can be treated as a low-level radioactive waste. The expected volume reduction that results during vitrification will significantly reduce the overall waste volume requiring disposal. Mixed-waste disposal options currently used by ANL-E may not be permissible in the near future without treatment technologies such as vitrification.
Date: December 1, 1993
Creator: Mazer, J. & No, Hyo
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

High-level waste melter alternatives assessment report

Description: This document describes the Tank Waste Remediation System (TWRS) High-Level Waste (HLW) Program`s (hereafter referred to as HLW Program) Melter Candidate Assessment Activity performed in fiscal year (FY) 1994. The mission of the TWRS Program is to store, treat, and immobilize highly radioactive Hanford Site waste (current and future tank waste and encapsulated strontium and cesium isotopic sources) in an environmentally sound, safe, and cost-effective manner. The goal of the HLW Program is to immobilize the HLW fraction of pretreated tank waste into a vitrified product suitable for interim onsite storage and eventual offsite disposal at a geologic repository. Preparation of the encapsulated strontium and cesium isotopic sources for final disposal is also included in the HLW Program. As a result of trade studies performed in 1992 and 1993, processes planned for pretreatment of tank wastes were modified substantially because of increasing estimates of the quantity of high-level and transuranic tank waste remaining after pretreatment. This resulted in substantial increases in needed vitrification plant capacity compared to the capacity of original Hanford Waste Vitrification Plant (HWVP). The required capacity has not been finalized, but is expected to be four to eight times that of the HWVP design. The increased capacity requirements for the HLW vitrification plant`s melter prompted the assessment of candidate high-capacity HLW melter technologies to determine the most viable candidates and the required development and testing (D and T) focus required to select the Hanford Site HLW vitrification plant melter system. An assessment process was developed in early 1994. This document describes the assessment team, roles of team members, the phased assessment process and results, resulting recommendations, and the implementation strategy.
Date: February 1, 1995
Creator: Calmus, R. B.
Partner: UNT Libraries Government Documents Department

Ceramic matrix composites by microwave assisted CVI

Description: Chemical vapor infiltration (CVI) processes for producing continuously reinforced ceramic composites are reviewed. The potential advantages of microwave assisted CVI are noted. Recent numerical studies of microwave assisted CVI are then reviewed. These studies predict inverted thermal gradients in fibrous ceramic preforms subjected to microwave radiation and suggest processing strategies for achieving uniformly dense composites. Comparisons are made to experimental results obtained using silicon based composite systems. The importance of microwave-material interactions is stressed. In particular, emphasis is placed on the role played by the relative ability of fiber and matrix to dissipate microwave energy. Results suggest that microwave induced inverted gradients can in fact be exploited using the CVI technique to promote inside-out densification.
Date: January 1, 1993
Creator: Currier, R.P. & Devlin, D.J.
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 sintering of large alumina bodies

Description: The application of microwaves as an energy source for materials processing of large alumina bodies at elevated temperatures has been limited to date. Most work has concerned itself with small laboratory samples. The nonuniformity of the microwave field within a cavity subjects large alumina bodies to areas of concentrated energy, resulting in uneven heating and subsequent cracking. Smaller bodies are not significantly affected by field nonuniformity due to their smaller mass. This work will demonstrate a method for microwave sintering of large alumina bodies while maintaining their structural integrity. Several alumina configurations were successfully sintered using a method which creates an artificial field or environment within the microwave cavity.
Date: January 1, 1993
Creator: Blake, R.D. & Katz, J.D.
Partner: UNT Libraries Government Documents Department

Microwave sintering of titanium diboride

Description: Titanium diboride was heated to high temperatures using microwaves. The highest temperature obtained was 2245/degree/C. Unfortunately, oxidation was a problem, especially at the higher temperatures, although an argon flush and a carbon getter were used. To completely stop oxidation, the oxygen potential must be below 10/sup /minus/18/ atmospheres. Using an argon flush and a carbon getter, titanium diboride was successfully densified to 82% of theoretical without measurable oxidation by heating with microwaves to 1860/degree/C. Density actually decreased upon reaching temperatures above 1860/degree/C due to void formation adjacent to the surface. Void formation is thought to be due to the formation of B/sub 2/O/sub 3/(g) which evolves rapidly above 1860/degree/C because of the loss of a TiO/sub 2/ protective film which melts at this temperature. 9 refs., 12 figs., 2 tabs.
Date: January 1, 1989
Creator: Katz, J.D.; Blake, R.D. & Scherer, C.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

Microwave processing of radioactive materials-I

Description: This paper is the first of two papers that reviews the major past and present applications of microwave energy for processing radioactive materials, with particular emphasis on processing radioactive wastes. Microwave heating occurs through the internal friction produced inside a dielectric material when its molecules vibrate in response to an oscillating microwave field. For this presentation, we shall focus on the two FCC-approved microwave frequencies for industrial, scientific, and medical use, 915 and 2450 MHz. Also, because of space limitations, we shall postpone addressing plasma processing of hazardous wastes using microwave energy until a later date. 13 refs., 4 figs.
Date: January 1, 1989
Creator: White, T.L. & Berry, J.B.
Partner: UNT Libraries Government Documents Department

Power balance in ELMO Bumpy Torus: bulk electrons and ions in a 37 kW discharge

Description: The power balance of the bulk electrons and ions in discharges with 37 kW of applied microwave power in the ELMO Bumpy Torus (EBT) is examined in a zero-dimensional model using data on the intensity and linewidth of the molecular and atomic hydrogen emission. At least 60% of the applied power is ultimately dissipated by processes involving the neutral particles, including dissociation of molecules, ionization of and radiation from atoms, and heating of cold electrons produced during atomic ionization. The molecular influx rate and the density of atoms are used independently to determine the bulk electron particle confinement time, and an upper bound estimate is made of the diffusional power loss from the bulk plasma electrons. Parameters derived from the basic spectroscopic data presented in this paper include the neutral atom density 2 - 5x10/sup 10/ cm/sup -3/, incident molecular flux 3 - 5x10/sup 15/ cm/sup -2/s/sup -1/, bulk ion temperature approx. =3 eV, and particle confinement time <1.1 ms. The bulk electron energy confinement time is 0.7 ms or less in the standard operating regime. Published data on the nonthermal electron and ion populations in the plasma are used to evaluate approximately the overall energy flow in the discharge. 54 refs.
Date: October 1, 1985
Creator: McNeill, D.H.
Partner: UNT Libraries Government Documents Department

Detoxification of hazardous waste streams using microwave-assisted fluid-bed oxidation

Description: Microwave-assisted oxidation of trichloroethane (TCE) performed at 500-580{degree}C has been found to be significantly more efficient than conventional oxidation methods. Experiments were conducted using a 6 kilowatt, 2.45 gigohertz power supply and a 6 inch bed of silicon carbide granules in a 1 inch diameter quartz reactor tube which in turn was placed in a microwave cavity. After heating the reactor to a given temperature a TCE-air stream was passed through the silicon carbide bed. TCE was almost completely detoxified (98--99%) in a single pass through the silicon carbide bed at 500--580{degree}C. The oxidation products are HCl, CO{sub 2} and CO. By comparison the corresponding single-pass detoxification using conventional thermal methods results in only partial conversion. The principal products being dichloroethylene (C{sub 2}H{sub 2}Cl{sub 2}) and HCl. 5 refs., 1 tab.
Date: January 1, 1990
Creator: Varma, R.; Nandi, S.P. (Argonne National Lab., IL (USA)) & Katz, J.D. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Applications of microwave radiation environmental remediation technologies

Description: A growing number of environmental remediation technologies (e.g., drying, melting, or sintering) utilize microwave radiation as an integral part of the process. An increasing number of novel applications, such as sustaining low-temperature plasmas or enhancing chemical reactivity, are also being developed. An overview of such technologies being developed by the Department of Energy is presented. A specific example being developed at Argonne National Laboratory, microwave-induced plasma reactors for the destruction of volatile organic compounds, is discussed in more detail.
Date: January 1, 1993
Creator: Krause, T.R. & Helt, J.E.
Partner: UNT Libraries Government Documents Department