Compaction behavior of ceramic particles
Ceramic particle compaction as function of size, shape, loading rate and hardness for fused alumina, magnesia and mullite
Leiser, D. B.↗
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Determining and analyzing the strength and impact resistance of high modulus glass
A number of new glass compositions have been prepared with increased emphasis on compositions without beryllia. Glass preparations have been much more broadly based and have included the eutectic glass fields, and the mullite-rare earth glass systems. Of the new glasses, the best non-toxic composition is UARL 472 with a bulk modulus of only 18.20 million psi. A second experimental glass, UARL 417, was chosen for research in making large quantities of fiber in monofilament form. Tests of these UARL 417 epoxy resin samples in comparison to similar composites made with the DuPont organic fiber, PRD-49-1, show that the UARL composites have a compressive strength 41/2 times higher and a specific compressive strength at least 21/2 times greater. Much of the research effort attempted to answer the question of why a given glass should have an impact strength superior to other glasses. No definitive answer to the question was found.
Bacon, J. F.↗
Status of reusable surface insulation thermal protection system technology programs
The development of three low-density rigidized insulation materials for the shuttle TPS application is reported. These materials consist of one high purity silica system and two systems based on mullite, an aluminum silicate. Both systems consist of fibers joined together with appropriate binders to obtain a rigidized insulation composite. Both material systems require the application of a glassy coating to provide a wear resistant, high emittance surface and to prevent the absorption of water by the fiber matrix. The technology program has addressed the development of water impervious coatings, methods of assembling the materials in design concepts while minimizing the thermal stress in the insulation, achieving compatibility between the RSI material and the structural system, and test evaluations to demonstrate the feasibility of the surface insulation concept.
Greenshields, D. H.↗
Symposium on Reusable Surface Insulation for Space Shuttle. Volume 1: RSI fabrication, improvement, morphology and properties
Production of silica, mullite, and alumino silicate reusable surface insulation materials for space shuttle orbiters
Source record↗
Effects of sea salts on the physical characteristics of reusable surface insulation
Test results show that sea salt contamination and thermal cycles cause significant changes in the morphology of surface insulation coatings with increased melting. Sea salt contamination and thermal cycles do not have a significant effect on emittance of mullite and silica composite coatings at high temperatures (1300 K). At the lower temperatures there is apparently some effect on emittance but the evidence is inconclusive because of the absence of multiple tests.
Ransone, P. O.↗
Silica RSI for Application to the Shuttle Orbiter
Silica reusable surface insulation is analyzed for its cold soak properties, bond properties at low temperature, gap and step heating effects, and aerodynamic surface roughness effects to determine space shuttle weight and cost sensitivity to structure subsystem weights. Computerized simulation studies show that total program cost savings of silica (vs. mullite) exceed thermal protection system design and development costs and that an early introduction of silica increases total program cost savings.
Forsberg, K. J.↗
The infrared properties of reusable surface insulations.
The total infrared scattering and absorption cross sections of both flexible and rigidized high temperature fibrous insulations have been measured. The methods for accomplishing these measurements are described. Infrared reflection and transmission spectra were obtained to study the dependence of the total cross sections on the spectral characteristics of the transported radiation. These results are applied to steady-state effective thermal conductivity measurements via a four-flux model of radiative heat transfer to separate the radiative component and to calculate the effective thermal conductivity under transient heating conditions. Data for both silica and mullite fibers are presented.
Schmitt, R. J.↗
Radiative contribution to the thermal conductivity of fibrous insulations
An approach is shown for using a simple two-flux model to interpret infrared transmission data for a variety of reuseable surface insulations materials and to calculate the radiation transmission. A description is given of preliminary experiments on mullite and silica-based materials. The calculated parameters are compared with the measured values of the total thermal conductivity, as determined on guarded hot plate equipment. It is pointed out that for many samples the newly developed four-flux model must be utilized because the scattering properties of the fibers are often dependent on the wavelength of the radiation.
Linford, R. M. F.↗
Feasibility and process scale-up low cost alumina fibers for advanced Re-usable Surface Insulation (RSI)
The objective of this program was to establish feasibility of a process to produce low cost aluminum oxide fibers having sufficient strength, flexibility, and thermal stability for multiple re-use at temperatures to 1480 C in advanced RSI type heat shields for reentry vehicles. Using bench-scale processing apparatus, the Alcoa 'Saphiber' process was successfully modified to produce nominally 8 microns diameter polycrystalline alpha-alumina fiber. Thermal stability was demonstrated in vacuum reheating tests to 1371 C and in atmospheric reheating to 1483 C. Individual fiber properties of strength, modulus, and flexibility were not determined because of friability and short length of the fiber. Rigidized tile produced from fiber of nominally 8, 20 and 40 micron diameter had thermal conductivities significantly higher than those of RSI SiO2 or mullite at relatively low temperature but became comparable above about 1000 C. Tile densities were high due to short fiber length, especially in the coarser diameter fiber. No significant effect of fiber diameter on thermal properties could be determined form the data. Mechanical properties of tiles deteriorated as fiber diameter increased.
Pearson, A.↗
Fundamental studies on the nature and properties of ceramic fiber insulation
Silica and mullite fibers used to fabricate reusable surface insulation (RSI) for the space shuttle orbiter may devitrify/recrystallize within the temperature range anticipated upon reentry. This is shown to be dependent upon impurity level, temperature, and time at temperature. It is determined that the effects of the material improvement and optimization program are positive. The degree of crystallinity is shown to have a predominant effect upon the strength of fabricated RSI tile, and limits are determined. Models are developed to predict tensile strengths and shrinkage rates of silica tile based upon readily measurable parameters. Thermal cycling which simulates reentry results in an increase in the crystallinity and in the porosity of tile coatings.
Mueller, J. I.↗
Improved ceramic heat exchange material
Improved corrosion resistant ceramic materials that are suitable for use as regenerative heat exchangers for vehicular gas turbines is reported. Two glass-ceramic materials, C-144 and C-145, have superior durability towards sulfuric acid and sodium sulfate compared to lithium aluminosilicate (LAS) Corning heat exchange material 9455. Material C-144 is a leached LAS material whose major crystalline phase is silica keatite plus mullite, and C-145 is a LAS keatite solid solution (S.S.) material. In comparison to material 9455, material C-144 is two orders of magnitude better in dimensional stability to sulfuric acid at 300 C, and one order of magnitude better in stability to sodium sulfate at 1000 C. Material C-145 is initially two times better in stability to sulfuric acid, and about one order of magnitude better in stability to sodium sulfate. Both C-144 and C-145 have less than 300 ppm delta L/L thermal expansion from ambient to 1000 C, and good dimensional stability of less than approximately 100 ppm delta L/L after exposure to 1000 C for 100 hours. The glass-ceramic fabrication process produced a hexagonal honeycomb matrix having an 85% open frontal area, 50 micrometer wall thickness, and less than 5% porosity.
Mccollister, H. L.↗
Dip-coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project
The objective of this research program is to investigate the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. The past quarter demonstrated significant progress in several areas. Seeded growth of silicon-on-ceramic (SOC) with an EFG ribbon seed was demonstrated. Different types of mullite were successfully coated with silicon. A new method of deriving minority carrier diffusion length, L sub n from spectral response measurements was evaluated. ECOMOD cost projections were found to be in good agreement with the interim SAMIS method proposed by JPL. On the less positive side, there was a decrease in cell performance which we believe to be due to an unidentified source of impurities.
Zook, J. D.↗
Dip-coated sheet silicon solar cells
A cost-effective method is being developed for producing solar cell quality sheet silicon by dip coating inexpensive ceramic substrates with a thin layer of large grain silicon. Mullite (Aluminum Silicate) ceramic substrates coated with a thin layer of graphite have been dipped into molten silicon to produce 20-150 micron thick layers having grain sizes as large as .4 cm x 4 cm. With these silicon layers photovoltaic diodes have been fabricated with measured and inherent conversion efficiencies of 4% and 7%, respectively.
Heaps, J. D.↗
Continuous coating of silicon-on-ceramic
Growth of sheet silicon on low-cost substrates has been demonstrated by the silicon coating with inverted meniscus (SCIM) technique. A mullite-based ceramic substrate is coated with carbon and then passed over a trough of molten silicon with a raised meniscus. Solidification occurs at the trailing edge of the downstream meniscus, producing a silicon-on-ceramic (SOC) layer. Meniscus shape and stability are controlled by varying the level of molten silicon in a reservoir connected to the trough. The thermal conditions for growth and the crystallographic texture of the SOC layers are similar to those produced by dip-coating, the original technique of meniscus-controlled growth. The thermal conditions for growth have been analyzed in some detail. The analysis correctly predicts the velocity-thickness relationship and the liquid-solid interface shape for dip-coating, and appears to be equally applicable to SCIM-coating. Solar cells made from dip-coated SOC material have demonstrated efficiencies of 10% on 4-sq cm cells and 9.9% on 10-sq cm cells.
Heaps, J. D.↗
Development, solar test, and evaluation of a high-temperature air receiver for point-focusing parabolic dish applications
A high temperature solar receiver was fabricated and tested in excess of 1370 C on an 11-meter-diameter test bed concentrator at the Jet Propulsion Laboratory Parabolic Dish Test Site, Edwards, California. The 60-kilowatt thermal receiver design utilizes state-of-the-art silicon carbide honeycomb matrix panels to receive and transfer the solar energy and mullite elements for thermal buffer storage. Solar tests were conducted with indicated air exit temperatures ranging from 885 C (1625 F) to 1427 C (2600 F), mass flow rates of 75 to 105 g/sec (0.16 to 0.23 lbm/sec), and pressures up to 265 kPa absolute (38.4 psia). Estimates of efficiency are 59.7% at 1120 C (2048 F) to 80.6% at 885 C (1625 F) when aperture spillage losses are considered separately. Results are presented which demonstrate the feasibility of this innovative receiver concept for point-focusing parabolic dish applications over a wide temperature range.
Hanseth, E. J.↗
Low cost silicon-on-ceramic photovoltaic solar cells
A technique has been developed for coating low-cost mullite-based refractory substrates with thin layers of solar cell quality silicon. The technique involves first carbonizing one surface of the ceramic and then contacting it with molten silicon. The silicon wets the carbonized surface and, under the proper thermal conditions, solidifies as a large-grained sheet. Solar cells produced from this composite silicon-on-ceramic material have exhibited total area conversion efficiencies of ten percent.
Koepke, B. G.↗
Ceramic technology for solar thermal receivers
The high-temperature capability, resistance to corrosive environments and non-strategic nature of ceramics have prompted applications in the solar thermal field whose advantages over metallic devices of comparable performance may begin to be assessed. It is shown by a survey of point-focusing receiver designs employing a variety of ceramic compositions and fabrication methods that the state-of-the-art in structural ceramics is not sufficiently advanced to fully realize the promised benefits of higher temperature capabilities at lower cost than metallic alternatives. The ceramics considered include alumina, berylia, magnesia, stabilized zirconia, fused silica, silicon nitride, silicon carbide, mullite and cordierite, processed by such methods as isostatic pressing, dry pressing, slip casting, extrusion, calendaring and injection molding.
Kudirka, A. A.↗
Large-area silicon-on-ceramic substrates for low-cost solar cells
The SCIM (Silicon-Coating-By-Inverted Meniscus) process to produce SOC (silicon-on-ceramic) substrates has been investigated for various growth conditions and substrate velocities (4-30 cm/min). Slotted mullite-based substrates (10-cm-wide by 100-cm-long) have been coated with smooth, continuous silicon layers, with thicknesses in the range from 100 to 300 microns. Thermal stress (which can be a problem at low velocities) is prevented by proper thermal design. The highest SCIM-coated SOC cell efficiencies to date are 7.5% (AM1, AR) as compared to 10.5% (AM1, AR) for dip-coated SOC cells. Substantial improvements in cell efficiency are expected when high purity parts are installed in the SCIM-coater.
Schuldt, S. B.↗