Secondary sulfate minerals from Alum Cave Bluff: Microscopy and microanalysis

Microcrystals of secondary sulfate minerals from Alum Cave Bluff, Great Smoky Mountains National Park, were examined by scanning electron microscopy and identified by X-ray fluorescence (XRF) in the SEM. Among the samples the author discovered three new rare-earth sulfates: coskrenite-(Ce), levinsonite-(Y), and zugshunstite-(Ce). Other minerals illustrated in this report include sulfur, tschermigite, gypsum, epsomite, melanterite, halotrichite, apjohnite, jarosite, slavikite, magnesiocopiapite, and diadochite. Additional specimens whose identification is more tentative include pickeringite, aluminite, basaluminite, and botryogen. Alum Cave is a ``Dana locality`` for apjohnite and potash alum, and is the first documented North American occurrence of slavikite

Development of Low Cost Sensors for Hydrogen Safety Applications

We are developing rugged and reliable hydrogen safety sensors that can be easily manufactured. Potential applications also require an inexpensive sensor that can be easily deployed. Automotive applications demand low cost, while personnel safety applications emphasize light-weight, battery-operated, and wearable sensors. Our current efforts involve developing and optimizing sensor materials for stability and compatibility with typical thick-film manufacturing processes. We are also tailoring the sensor design and size along with various packaging and communication schemes for optimal acceptance by end users

Irradiation performance of pyrolytic silicon carbide coatings on fissile fuel particles

Fuel particles for the High Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission product barrier. Optimization of the SiC coating with respect to fuel performance involves four areas of study: (a) characterization of as-deposited SiC coatings; (b) thermodynamics and kinetics of chemical reactions between SiC and fission products; (c) irradiation behavior of SiC in the absence of fission products; and (d) the combined effects of irradiation and fission product interactions. This paper reports the behavior of SiC deposited on fissile fuel particles and irradiated to fast neutron fluences typical of HTGR fuel at end-of-life

Irradiation behavior of pyrolytic silicon carbide. [HTGR]

Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission-product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: characterization of as-deposited SiC coatings; thermodynamics and kinetics of chemical reactions between SiC and fission products; irradiation behavior of SiC in the absence of fission products; and combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast-neutron fluences typical of HTGR fuel at end-of-life

Development of Low-cost Hydrogen Sensors

This research was aimed at understanding and improving the speed and reproducibility of our resistive hydrogen sensor, along with complementary efforts in manufacturability and further design improvements. Maskworks were designed to allow for the printing and firing of multi-sensor layouts (15 per substrate) and a large batch of these sensors was produced using standard thick-film manufacturing lines. Piece-to-piece variations of both the as-made resistance and the response of these sensors to hydrogen were within acceptable tolerances, and the sensor design has now been released for commercial prototyping. Automated testing was begun in order to develop long-term performance data. Dynamic response of selected sensors was measured before and after exposures to methane, hydrogen sulfide, and carbon monoxide, in order to assess the effects of interference gases and surface poisoning. As expected, H{sub 2}S degrades the sensor somewhat, whereas CH{sub 4} and CO do not create significant interference when air is present

Amphibole ceramics: conceptual development and preliminary experiments

Certain natural silicate minerals, commonly called jade, are well known for their resistance to brittle fracture. One type of jade, nephrite, is a compacted form of the amphibole mineral series tremolite-actinolite. Nephrite is tough because the naturally acicular crystal habit of these amphibole minerals produces an interwoven fibrous microstructure that impedes crack propagation. Object of this work was to duplicate the fibrous microstructure of nephrite by pulverizing natural tremolite or actinolite and then compacting it by hot pressing to form a dense body. Two other materials were also investigated, namely, clinochrysotile (serpentine asbestos) and synthetic fluor-tremolite. For each material, the milling characteristics and densification were studied. The resulting microstructures were characterized, and fracture toughness was measured for a limited number of samples. The most ''fibrous'' microstructure was obtained by hot pressing clinochrysotile 15 min a 1000/sup 0/C. Actinolite, hot pressed 15 min at 1100/sup 0/C, had a critical fracture toughness K/sub IC/ = 4.5 MPa m/sup 1/2/, which compares favorably with the toughness of nephrite jade (K/sub IC/ = 3.6). Decomposition of tremolite and actinolite to more stable phases occurred to some degree during hot pressing. Results suggest that hot isostatic pressing at high water vapor pressure should yield a dense product without causing amphibole decomposition. 28 figs., 7 tabs

Interaction of silver and palladium with silicon carbide in HTGR fuel particles. Preliminary report

Fuel particles for the High-Temperature Gas-Cooled Reactor contained a layer of pyrolytic silicon carbide, which acts as a pressure vessel and provides containment for metallic fission products. The SiC layer is deposited by the thermal decomposition of methyltrichlorosilane (CH/sub 3/SiCl/sub 3/ or MTS) in an excess of hydrogen. Certain fission products, notably silver and palladium, can cause degradation of the SiC during irradiation. The purpose of this study is to develop a quantitative data base to better understand noble-metal attack as well as to evaluate the relationship between SiC deposition conditions and noble-metal release. The interaction between SiC and noble-metal fission product elements was investigated in the temperature range 1200 to 1500/sup 0/C

New materials for thick-film electronics

Certain ceramic compounds such as rare-earth perovskites and transition-metal diborides that exhibit metallic conductivity are readily available or can be easily synthesized. Some are stable in air firing temperatures typical of hybrid-circuit processing. The work described is part of an exploratory program to determine whether these materials can be used as low-cost alternatives to precious metals for thick-film conductor and low-resistor inks or as substitutes for copper in nitrogen-fireable compositions. 8 refs., 13 figs., 3 tabs

Metallic phase-change materials for solar dynamic energy storage systems

Solar (thermal) dynamic power systems for satellites require a heat storage system that is capable of operating the engine during eclipse. The conventional approach to this thermal storage problem is to use the latent heat of fluoride salts, which would melt during insolation and freeze during eclipse. Although candidate fluorides have large heats of fusion per unit mass, their poor thermal conductivity limits the rate at which energy can be transferred to and from the storage device. System performance is further limited by the high parasitic mass of the superalloy canisters needed to contain the salt. This report describes a new thermal storage system in which the phase-change material (PCM) is a metal (typically germanium) contained in modular graphite canisters. These modules exhibit good thermal conductivity and low parasitic mass, and they are physically and chemically stable. Prototype modules have survived over 600 melt/freeze cycles without degradation. Advanced concepts to further improve performance are described. These concepts include the selection of ternary eutectic alloys to provide a wider range of useful melting temperatures and the use of infiltration to control the location of liquid alloy and to compensate for differences in thermal expansion. 13 refs., 18 figs