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Comparison of properties of sintered and sintered reaction-bonded silicon nitride fabricated by microwave and conventional heating

Description: A comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: (1) sintered silicon nitride (SSN) and (2) sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.
Date: October 1, 1994
Creator: Tiegs, T. N.; Kiggans, J. O. Jr.; Lin, H. T. & Willkens, C. A.
Partner: UNT Libraries Government Documents Department

Microwave sintering of ZrO{sub 2}-12 mol% CeO{sub 2}

Description: Sintering of ZrO{sub 2}-12 mol% CeO{sub 2} was accelerated by microwave processing at 2.45 GHz as compared with conventional firing. However, the size of the ``microwave effect`` was significantly smaller than that which was previously observed for microwave sintering of ZrO{sub 2}-8 mol% Y{sub 2}O{sub 3}. The difference in the effect that the microwave field had on the two zirconia systems is interpreted in terms of their ionic conductivities.
Date: December 31, 1993
Creator: Janney, M. A.; Jackson, M. L. & Kimrey, H. D.
Partner: UNT Libraries Government Documents Department

Materials processing using a variable frequency microwave furnace

Description: We describe a materials processing system that uses a high power traveling wave tube (TWT) as the microwave source. The TWT provides approximately one octave bandwidth and variable power levels up to 2 kW into a multimode cavity. By controlling the frequency, efficient coupling to the load can be maintained even as the load`s dielectric properties change. Alternatively, can be used as a means of mode stirring at rates far beyond those attainable through mechanical stirring. The system has been tested for sintering alumina ceramics, annealing a tungsten penetrator alloy, curing epoxy resin, and depositing diamond films from a microwave plasma.
Date: December 31, 1993
Creator: Lauf, R. J.; Bible, D. W.; Maddox, S. R.; Everleigh, C. A.; Espinosa, R. J. & Johnson, A. C.
Partner: UNT Libraries Government Documents Department

Microwave sintering of multiple aritcles

Description: Disclosed are apparatus and method for producing articles of alumina and of alumina and silicon carbide in which the articles are sintered at high temperatures using microwave radiation. The articles are placed in a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.
Date: December 31, 1992
Creator: Blake, R. D. & Katz, J. D.
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: May 1, 1993
Creator: Vogt, G. J. & Unruh, W. P.
Partner: UNT Libraries Government Documents Department

Design of a tunable 4-MW Free Electron Maser for heating fusion plasmas

Description: There is an ongoing program at the FOM institute, The Netherlands, to develop a 1-MW, long-pulse, 200-Ghz Free Electron Maser (FEM) using a DC accelerator system with depressed collector. We present an extrapolation of this design to more than 4MW of output microwave power in order to reduce the cost per kW and increase the power per module in a plasma heating system.
Date: September 1, 1993
Creator: Caplan, M.; Kamin, G.; Shang, C. C. & Lindquist, W.
Partner: UNT Libraries Government Documents Department

Advanced Industrial Materials Program. Annual progress report, FY 1993

Description: Mission of the AIM program is to commercialize new/improved materials and materials processing methods that will improve energy efficiency, productivity, and competitiveness. Program investigators in the DOE national laboratories are working with about 100 companies, including 15 partners in CRDAs. Work is being done on intermetallic alloys, ceramic composites, metal composites, polymers, engineered porous materials, and surface modification. The program supports other efforts in the Office of Industrial Technologies to assist the energy-consuming process industries. The aim of the AIM program is to bring materials from basic research to industrial application to strengthen the competitive position of US industry and save energy.
Date: June 1, 1994
Creator: Stooksbury, F.
Partner: UNT Libraries Government Documents Department

Crystallization of grain boundary phases in silicon nitride with low additive contents by microwave annealing

Description: Microwave annealing of dense Si{sub 3}N{sub 4}-4% Y{sub 2}O{sub 3} materials showed improvements over conventional heating. Increases in fracture toughness were observed for annealing between 1200--1650C. The high temperature strength was related to the residual {alpha}-Si{sub 3}N{sub 4} content which is indicative of a finer average grain size in the specimens. The high temperature dynamic fatigue showed increased stress to failure for specimens microwave annealed between 1400--1550C for periods >5 h. Silicon nitrides with different sintering additives would require different conditions for optimum crystallization. While there were some observed property improvements, they were not so dramatic to justify abandoning conventional over microwave heating. The Si{sub 3}N{sub 4}-4% Y{sub 2}O{sub 3} materials used in the study were developed for elevated temperature use and already posses excellent good high temperature strength, fatigue resistance and creep properties. This is due to the very refractory nature of the grain boundary phases and the small quantity of secondary phase present. However, microwave annealing of these materials may be necessary in applications where the maximum in fracture toughness and fatigue resistance are required and thus justifies its use.
Date: June 1, 1993
Creator: Tiegs, T. N.; Ploetz, K. L.; Kiggans, J. O. & Yeckley, R. L.
Partner: UNT Libraries Government Documents Department

Enhancement of creep resistance of a sintered Si{sub 3}N{sub 4} ceramic by microwave annealing

Description: Creep behavior was investigated for a sintered Si{sub 3}N{sub 4} Ceramic microwave annealing at 1400 and 1500 C for 20 h. Results of creep tests at 1200 C showed that microwave annealing can enhance the creep resistance in terms of lowering creep rate and, hence, extending creep rupture life, but the 1400 C annealing was most effective. X-ray diffraction analyses showed that the crystalline second phase was transformed as a result of microwave annealing from single phase Y{sub 10}Al{sub 2}Si{sub 3}O{sub 18}N{sub 4} to several different phases. The situation was further complicated by evolution of additional phases during high temperature creep experiments.
Date: September 1, 1994
Creator: Liu, K. C.; Stevens, C. O.; Brinkman, C. R.; More, K. L.; Kiggans, J. D. & Tiegs, T. N.
Partner: UNT Libraries Government Documents Department

Enhancement of creep resistance of a sintered Si{sub 3}N{sub 4} ceramic by microwave annealing

Description: Creep behavior was investigated for a sintered Si{sub 3}N{sub 4} ceramic following microwave annealing at 1400 and 1500C for 20 h. Results of creep tests at 1200C showed that microwave annealing can enhance the creep resistance in terms of lowering creep rate and, hence, extending creep rupture life, but the 1400C annealing was most effective. X-ray diffraction analyses showed that the crystalline second phase was transformed as a result of microwave annealing from single phase Y{sub 10}Al{sub 2}Si{sub 3}O{sub 18}N{sub 4} to several different phases. The situation was further complicated by evolution of additional phases during high temperature creep experiments.
Date: September 1, 1994
Creator: Liu, K. C.; Stevens, C. O.; Brinkman, C. R.; More, K. L.; Kiggans, J. D. & Tiegs, T. N.
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: May 1, 1993
Creator: Blake, R. D. & Katz, J. D.
Partner: UNT Libraries Government Documents Department

Metal recovery from porous materials

Description: The present invention relates to recovery of metals. More specifically, the present invention relates to the recovery of plutonium and other metals from porous materials using microwaves. The United States Government has rights in this invention pursuant to Contract No. DE-AC09-89SR18035 between the US Department of Energy and Westinghouse Savannah River Company.
Date: January 1, 1991
Creator: Sturcken, E. F.
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

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

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

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

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 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

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