Field leaching studies were carried out in granite at the Stripa site in Sweden and also in salt in the Materials Interface Interaction Test at the Waste Isolation Pilot Plant (MIIT/WIPP) in New Mexico. The goal of these studies is to assess the durability of various glass compositions engineered to isolate high-level nuclear waste from the biosphere. An additional goal of the MIIT study is to determine how the glasses interact with a wide array of proposed materials that may be a part of the multi-barrier waste package. These substances include metals, geological host specimens,, as well as engineered backfill and overpack materials. p]Two year data on the SRLY (165/TDS) glass compositions has been extracted from both studies (Stripa and WIPP/MIIT) and five year data has recently become available from the MIIT study. Results from SEM/EDS, SIMS and FTIRRS analyses on glass/glass interfaces are presented in this paper.

The drying process is one of the most vital steps in the manufacturing of ceramics. The presence of different pore sizes affects the rate of drying in conventional convective heating and if not properly controlled can result in cracking. Experimentally it has been found that microwave heating can result in faster drying times for ceramics. Although the mechanisms of drying are the same, the duration of the drying stages differs. This research compares microwave and conventional drying of silica filters with differing pore sizes and proposes a model to explain the more rapid drying observed with the use of microwave energy.

Numerous reports presented in the literature have shown that microwave sintering results in reduction of processing temperature/time required for densification in some materials when compared to conventional sintering. While faster sintering regimes may look promising, it is important to understand why microwaves appear to enhance the sintering phenomena. It is speculated that the electric field associated with microwave energy is enhancing flux, leading to accelerate densification. Enhancement in flux is a result of an increase in driving force, in the transport coefficient, or both. This study examines the sintering behavior of 8 mol% yttria-zirconia at various values of electric field intensity (frequency being constant, 2.45GHz) to understand whether the driving force or transport coefficient terms in the flux equation lead to enhanced densification. The transport coefficient term shows an increasing trend with an increase in electrical field intensity. These results indicate that the underlying reason for the increase in the transport coefficient term is due to a shift in diffusion path, from volume to grain boundary diffusion.

Fourier transform infrared reflectance spectroscopy (FTIR-RS) was investigated as a potential tool for determining the volume fraction of crystals in partially-crystallized lithium disilicate (LS2) glasses. The LS2 glass samples were partially-crystallized at two temperatures, 583°C and 595°C, as a function of time. These temperatures were selected based on thermal analysis of LS2 glass. The FTIR spectra of the polished sample surfaces were obtained in specular reflectance mode. The volume fraction of crystals in the samples was obtained via a point-count stereology technique. A relation between FTIR-RS peak intensities and the volume fraction of crystals in the partially-crystallized LS2 glasses was then determined. This relation can provide a convenient quality control process for glass-ceramic industry.

The activation energies were estimated for conventional and microwave sintering of Zirconia‐8 mol% Yttria (8YZ). The results were analyzed to explain the mechanisms responsible for enhancing flux/mass transport during microwave sintering. The activation energies were evaluated using isothermal and nonisothermal methods. The nonisothermal sintering resulted in higher values of activation energies, as compared to isothermal methods. This behavior may be due to the presence of more than one type of diffusion mechanism dominating throughout the process. The nonisothermal method represented activation energy values close to a single densification mechanism (either volume or grain boundary diffusion). A value of 500 ± 25 kJ/mol was observed for nonisothermal sintering of 8YZ with conventional heating. This value was close to the volume diffusion of Zr ion (500 kJ/mol). The microwave sintering (using nonisothermal method) resulted in activation energy values of 200 ± 27 kJ/mol, a value close to the grain boundary diffusion of the Zr ion.

The 1988 Spring Meeting of the Materials Research Society will be held at Bally's in Reno, Nevada, with events spanning April 4-10. Program Chairs David Clark, Clif Draper, and Chain T. Liu have planned the most diversified topical symposia coverage to date. In addition to a thorough examination of the popular and “hot news” areas, the meeting will also offer a selection of intriguing specialty topics never before offered at an MRS meeting. This year's Spring meeting will feature 16 topical symposia, a program of 23 short courses, and an equipment show. Highlights of the symposia are described below. The names of the short courses and equipment exhibitors are listed elsewhere in this issue. For details see the 1988 MRS Spring Meeting Preliminary Program mailed to all MRS members.During the Plenary and Student Awards session, Raymond D. Tuminaro of AT&T Bell Laboratories will present the Plenary Address on “Materials Aspects of the SL Undersea Optical Cable Design.” Tuminaro will focus on the fiber and cable materials, review their vulnerabilities to degradation mechanisms, and explore methods currently being used to assure acceptable performance levels for the projected 25-year service life of these systems.A special feature is being planned for the 1988 MRS Spring Meeting. A major photomicrography exhibition—Microscapes: The Hidden Art of High Technology—will focus on the seldom-seen world of advanced developments in microelectronics and lightwave communications.

The crystallization of lithium disilicate (LS2) glass using a variable frequency microwave (VFM) processing technique was investigated. Lithium disilicate glass samples were prepared from commercial frit using a conventional glass melting and casting technique. A two-stage heat-treatment regime was used to crystallize the glass samples. The nucleation and crystallization temperatures were determined by the thermal analysis of the prepared LS2 glass. The LS2 glass samples were nucleated by conventional heating, followed by the crystallization step using two different techniques: conventional and microwave crystallization. Characterization of the prepared glass-ceramic samples by both techniques was conducted using X-ray diffraction, Fourier transform infrared reflectance spectroscopy, Raman spectroscopy, and scanning electron microscopy. Variable frequency microwave processing was successfully used to crystallize LS2 glass. Enhanced kinetics and slightly different crystallization mechanisms were observed in the VFM crystallization process as compared with the conventional one.

A team associated with a Federal Laboratory, academia, and industry has been actively developing new microwave technology for treatment and remediation of a variety of potentially hazardous materials for almost a decade. This collaboration has resulted in unique equipment and processes with potential applicability to many fields, including disposition of electronic circuitry and components, medical wastes, radioactive materials and recycling of used tires.

The effects of waste composition and percent loading in a borosilicate glass designed for US defense high level wastes (HLW) have been evaluated. Three types of simulated wastes were investigated; high alumina, high iron and a composite representative of an average waste composition from Savannah River Plant (SRP) waste tanks. Corrosion resistance of the borosilicate glass is significantly enhanced by the presence of any of the three types of wastes. Additionally, corrosion resistance is improved as the % waste loading is increased in the glass. The best corrosion performance was obtained with the high alumina waste in deionized water.

The effects of repository material and a tailored backfill or overpack on the leaching behavior of glass have been studied. Two types of glasses were used in this investigation: 1) Model glasses comprised of 33 mol% alkali oxide-67 mol% SiO2, and 2) alkali borosilicate glasses with and without simulated wastes. Several types of repository material were placed in the same containers as the glasses to determine if their presence would alter the extent of leaching. A backfill material consisting of phosphate slime/sand mixtures was evaluated with the same procedure. The results indicate that the leaching behavior of the glass may be influenced by the presence of some materials. Preliminary results of a 16½ month burial experiment in Florida are also discussed.

Three Savannah River Laboratory (SRL) simulated nuclear waste glasses were buried in granite boreholes 345 meters deep. Included in the same boreholes were other potential waste package components including stainless steel and bentonite. Samples were maintained at either ambient mine temperature (8–10°C) or 90°C. Differences in glass leaching performances were observed among the three compositions, with SRL 165 being more durable than SRL 131, both with 29.8% TDS waste. Likewise, the presence of some package components affected the leaching performances. Bentonite resulted in accelerated attack on the glass while the presence of stainless steel did not appear to have much effect. Results obtained through one year of burial are presented in this paper.

Master sintering curves were developed to provide a viable database for industries for predicting the sintering behavior of ceramics. A dilatometer is required to construct these curves. Due to the non-availability of dilatometers that use microwave energy as the heating source, a push-rod microwave dilatometer was developed. A TE103 single-mode microwave cavity was altered to incorporate heating elements and a dial gauge. The heating elements were used to determine the sensitivity of the experimental setup. The validity of the measurement and the calibration procedure was verified by measuring the expansion of the following materials: sapphire, alumina, copper and fused quartz. The experimental setup was able to determine the coefficient of thermal expansion to an accuracy of ±3%. Microwave heating was then used to construct a master sintering curve for sintering cubic-zirconia.

Fully stabilized-zirconia is proposed as an inert matrix for next-generation nuclear fuels. This study presents the application of microwave technology for lowering the sintering temperature of 8mol% yttria-zirconia (8YZ) to minimize the loss of volatile actinides that will be incorporated into the fuels. Direct microwave sintering results were compared with microwave-hybrid and conventionally sintered samples. Direct Microwave Sintering of 8YZ showed a reduction of 300 degrees C in temperature required for full densification when compared with conventional sintering. A difference of 200 degrees C was observed with microwave-hybrid sintering. Despite these differences in processing temperatures, the variations in resulting properties were negligible.

Short ceramic fibers or whiskers may be ideally suited for the fabrication of ceramic-ceramic composites using the sol-gel process. The fibers can be uniformly dispersed in a low viscosity sol and then frozen into the matrix through gelation. Several ceramic composites were prepared by synthesizing an Al2O3 precursor from aluminum sec-butoxide and then dispersing fibers of either zirconia, graphite or SiC. The composites were dried at room temperature and fired up to 1200°C. The fibers reduce the volume shrinkages in comparison to that obtained with pure Al2O3 during processing. Structures with dimensions of several cm2 can be rapidly produced with this method without cracking.

A variety of surface sensitive techniques has been used to assess surface layers formed on SRL 165 waste glass specimens from the Stripa burial study and from a laboratory study designed to simulate conditions of the Stripa environment. The laboratory study included static and slow flow tests carried out for periods up to 6 and 24 months, respectively. Comparisons of leached layers formed in the two studies are based upon secondary ion mass spectrometry (SIMS), Fourier transform infrared reflection spectroscopy (FTIRRS), and scanning electron microscopy-electron microprobe (SEM-EMP) analysis. Results demonstrate that surface layers having similar trends in elemental profiles were developed in both lab and field tests. It was also found that both sets of samples showed similar changes in FTIRR spectra. One significant difference between the lab and field samples was that surface alteration, as indicated by changes in FTIRR spectra and leached layer thickness (from SIMS), occurred more rapidly in the lab tests.

Throughout the three-year project funded by the Department of Energy (DOE) and lead by Virginia Tech (VT), project tasks were modified by consensus to fit the changing needs of the DOE with respect to developing new inert matrix fuel processing techniques. The focus throughout the project was on the use of microwave energy to sinter fully stabilized zirconia pellets using microwave energy and to evaluate the effectiveness of techniques that were developed. Additionally, the research team was to propose fundamental concepts as to processing radioactive fuels based on the effectiveness of the microwave process in sintering the simulated matrix material.

Microwave processing was utilized to decompose oxides to their constituent metal. Samples were processed in a microwave transparent, porous silica refractory in a self-sustaining non-oxidizing atmosphere. Processing parameters were carefully controlled and resulted in metal discs. The Richardson-Ellingham chart of the oxidation of metals was used to determine the temperatures and atmosphere required to induce decomposition. This technique offers a unique method to produce a wide range of ceramic-metal composites.

Alternative processing methods are being considered for rapid sintering of inert matrix fuel (IMF) at low temperatures to minimize the loss of volatile actinides. Previous studies on microwave-hybrid sintering of the matrix material, 8mol.% yttria–zirconia (8YZ), showed rapid densification at lower temperatures when compared with a conventional process. The current study examines the applicability of dysprosia (Dy2O3) as a surrogate for americia (Am2O3) in investigating the microwave-hybrid sintering of a simulated IMF, 20wt.% Dy2O3 dispersed in 8mol.% yttria–zirconia (8YZ-20D). The results show that 8YZ-20D is sintered to 93% of its theoretical density (TD) at 1300°C with a soak time of 100min in a multimode microwave-hybrid furnace. A similar heating schedule in a conventional furnace resulted in 87% TD. The enhancement in densification of 8YZ-20D due to microwave-hybrid sintering did not alter any of the resulting microstructures. Based on these experiments, it was found that low-temperature microwave-hybrid sintering was suitable for fabricating IMF pellets.

This study focused on reducing overall processing time and temperature for fully stabilized zirconia, an inert matrix material candidate, to minimize the loss of actinides (that will be incorporated into the matrix material), while maintaining at least 90% theoretical density (TD). The effects of different processing routes on bulk density and microstructure were evaluated. The results obtained by adopting microwave sintering for 8mol% Y2O3–ZrO2 were compared to conventional sintering. A 20min soak time at 1300°C resulted in pellets with 90% TD for microwave-processed samples, compared to 77% TD for pellets processed conventionally. A similar density was obtained at lower temperature (1200°C) by increasing the soak time to 100min in microwave processing. This time and temperature resulted in 60% TD conventionally processed pellets. Compressive strength values obtained for a 1300°C (20min soak time) microwave-processed sample were higher (1600MPa) as compared to a conventionally processed sample (1300MPa).