Thomas T. Meek

Microwave sintering of some oxide materials using sintering aids

Etude du frittage de poudres de zircone stabilisee par CaO ou Y 2 O 3 , de Y 2 O 3 et de Al 2 O 3 en presence de divers additifs

Ceramic—ceramic seals by microwave heating

Several conclusions may be drawn from this work. First, less energy is required to form a glass-ceramic seal by microwave heating than by conventional heating. Second, less time is required to form the seal by microwave heating, and third, the seal composition is different, and the bonding is different. The micostructure of the seal formed by microwave heating reflects extensive diffusion of the glass constitients throughout the alumina substrate; and alumina throughout the seal glassy matrix. Fourth, higher heating rates are possible with microwave heating than with conventional heating. Last, the energy is coupled differently to the reactants using microwave heating, and thus the reaction kinetics may be different, as indicated by the vastly different microstructures obtained.

Fabrication of nylon-6/carbon nanotube composites

A new technique to fabricate nylon-6/carbon nanotube (PA6/CNT) composites is presented. The method involves a pretreatment of carbon nanotubes synthesized by catalytic pyrolysis of hydrocarbon and an improved in-situ process for mixing nanotubes with the nylon 6 matrix. A good bond between carbon nanotubes and the nylon-6 matrix is obtained. Mechanical property measurements indicate that the tensile strength of PA6/CNT composites is improved significantly while the toughness and elongation are somewhat compromised. Scanning electron microscopy (SEM) analysis of the fractured tensile specimens reveals cracking initiated at the wrapping of the CNTs PA6 layer/PA6 matrix interface rather than at the PA6/CNT interface.

Characterization of ZrO2-Al2O3 composites sintered in a 2.45 GHz electromagnetic field

The microwave heating process has shown potential for uniform material heating with rapid heating rates possible. The ceramic composite 80 wt % ZrO2 (+3 mol % Y2O3) 20 wt % Al2O3 was sintered in a Cober S6F microwave oven operating at 2.45 GHz even though it was considered to be microwave transparent at room temperature. The microwave-sintered sample was densified more rapidly and in a short time and lower temperature than the conventionally sintered sample. The fracture of the conventionally sintered sample was intergranular, but one of the microwave-sintered samples was transgranular. The fraction of the monoclinic-phase zirconia was different in the conventionally and microwave-sintered samples. The unusual microstructure of microwave-processed materials is explained by a microwave heating theory.

Cation diffusion in glass heated using 2.45 GHz radiation

Etude de la diffusion des ions Co, Na, Ni, Cu, Zn dans un verre pyrex a differentes temperatures par retrodiffusion electronique

Adhesive bonding via exposure to variable frequency microwave radiation

Adhesive bonding through the application of variable frequency microwave (VFM) radiation has been evaluated as an alternative curing method for joining composite materials. The studies showed that the required cure time of a thermosetting epoxy adhesive is substantially reduced by the use of VFM when compared to conventional (thermal) curing methods. Variable frequency microwave processing appeared to yield a slight reduction in the required adhesive cure time when compared to processing by the application of single frequency microwave radiation. In contrast to the single frequency processing, the variable frequency methodology does not readily produce localized overheating (burnt or brown spots) in the adhesive or the composite. This makes handling and location of the sample in the microwave oven less critical for producing high quality bonds and allows for a more homogeneous distribution of the cure energy. Variable frequency microwave processing is a valuable alternative method for rapidly curing thermoset adhesives at low input power levels.

Thermal processing of ilmenite and titania-doped haematite using microwave energy

To test the potential for microwave processing of lunar materials the heating of ilmenite-rock mixtures, and TiO2-doped haematite were investigated using microwave radiation, llmeniterich rocks will couple, without a coupling agent, to microwave radiation. The microwave experiments are repeatable. Attempts to couple TiO2-doped haematite to microwave radiation were very successful, with susceptibility increasing with TiO2 content. Scanning electron microscopy (SEM) showed increased grain size and particle size with increased TiO2 content in the microwave-heated products of the haematite-TiO2 system. The differences between microwave and furnace melts of ilmenite-rich rocks were also investigated. Petrographic analysis revealed a large amount of titanomagetite in microwave melts while furnace melts contained a large amount of haematite, but the cause of this difference is not fully understood.

Ultrasonic modification of alumina powder during wet-ball milling☆

The comminution of unagglomerated alumina powders was enhanced by applying ultrasonic energy during wet-ball milling for 16 h. The resulting powders had significantly finer mean and median particle sizes, narrower particle-size distributions, and less angular morphologies than powders which were conventionally wet-ball milled.

Processing of Thermoset Prepreg Laminates Via Exposure to Microwave Radiation

Studies of microwave-assisted curing of neat resins (epoxy) and unidirectional glass and carbon fiber laminates have shown that a substantial reduction in the curing time was obtained. This may be explained by the penetration of microwave energy directly and throughout the laminate with enhancement of the kinetics of the chemical reaction. Results of this work indicate that the microwave assisted curing of glass fiber laminates also shows a substantial reduction of the required curing time. Microwave radiation of 2.45 GHz has been demonstrated to be an acceptable method to cure unidirectional carbon fiber laminates. Also, effective curing of crossply (0/90) laminates through this method was observed when proper rotation of the parts accompanied the curing process. This is in accordance with previous work. Multidirectional carbon fiber/epoxy laminates demonstrate a lack of coupling during the curing process. A direct curing of these laminates was not possible by microwave radiation with the experimental approach used, in agreement with previous work. Nevertheless, a moderate reduction in the curing time of these thin laminates was observed due to hybrid curing.

Semiconductor Neutron Detectors Using Depleted Uranium Oxide

This paper reports on recent attempts to develop and test a new type of solid-state neutron detector fabricated from uranium compounds. It has been known for many years that uranium oxide (UO2), triuranium octoxide (U3O8) and other uranium compounds exhibit semiconducting characteristics with a broad range of electrical properties. We seek to exploit these characteristics to make a direct-conversion semiconductor neutron detector. In such a device a neutron interacts with a uranium nucleus, inducing fission. The fission products deposit energy-producing, detectable electron-hole pairs. The high energy released in the fission reaction indicates that noise discrimination in such a device has the potential to be excellent. Schottky devices were fabricated using a chemical deposition coating technique to deposit UO2 layers a few microns thick on a sapphire substrate. Schottky devices have also been made using a single crystal from UO2 samples approximately 500 microns thick. Neutron sensitivity simulations have been performed using GEANT4. Neutron sensitivity for the Schottky devices was tested experimentally using a 252Cf source.