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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Cyclic arc plasma tests of RSI materials using a preheater

The results of a test program are reported in which a preheater was used with an arc plasma stream to study the thermal response of samples of candidate reusable surface insulation materials for the space shuttle. The preheater simulated the shuttle temperature history during the first and last portions of the test cycle, which could not be simulated by the air arc plasma flow. Pre- and post-test data taken for each of the materials included magnified views, optical properties, and chemical analyses. The test results indicate that the mullite base samples experience higher surface temperatures than the other materials at heating rates greater than 225 kw/sq m. The ceramic fibrous mullite and silica coatings show noncatalytic wall behavior. Internal temperature response data for the materials are compared and correlated with analytical predictions.

Stewart, D. A.↗
NASA NTRS1973

Results of RSI Thermal-structural Analysis

Thermostructural comparisons of mullite and silica reusable surface insulation materials for space shuttle application show that mullite is much more subject to thermal stress failure than silica composite materials.

Pigg, O. E.↗
NASA NTRS1972

Thermal characterization of reusable external insulation for the space shuttle.

Thermal protection systems utilizing reusable ceramic external insulations are under study for application to the orbiter vehicle of NASA's space shuttle system which is to be launched by an expendable booster, remain in orbit for a week or two, reenter the earth's atmosphere, and land like a conventional aircraft. The required reuse capability is for 100 missions. The thermal characterization of the reusable external insulation (REI) is described. Thermal conductivity measurements are described for a series of mullite-based REIs with densities ranging from 100 to 300 kg/cu m, including opacified variations of the mullite material designed for reduction of the radiant component of heat transport. The results of thermal conductivity measurements performed on guarded-hot-plate equipment from 150 to above 1200 K in different vacuum and gaseous environments are described. Measurements were also made with exceptionally large temperature differences to detect transparency effects in the unopacified REIs. These measurements were made to provide design data for the flight conditions, and to aid in theoretical computations aimed at separating and optimizing the heat transport components.

Brazel, J. P.↗
NASA NTRS1975

Theoretical study of production of unique glasses in space

The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.

Larsen, D. C.↗
NASA NTRS1975

Evaluation of low cost/high temperature insulation, July 1974 - June 1975

Six fiber products and six insulation blankets comprising silica, alumina, zirconia, mullite, and mixed ceramic systems were subjected to furnace exposures up to 500 hours at temperatures of 1000 to 1600 C and evaluated for chemical and dimensional stability and for changes in thermal conductivity. Alumina, zirconia, and mullite fibers were fabricated into reusable surface insulation (RSI) tile by water-felting and reimpregnation with ethyl silicate. Specimens were exposed to 25 thermal cycles at 1200 C and 1400 C and a pressure of 10 and 32 torr, respectively. Production costs for 930 sq m (10,000 sq ft) of blanket insulation and of alumina RSI tile were developed.

Strauss, E. L.↗
NASA NTRS1976

Dip coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

To date, an experimental dip-coating facility was constructed. Using this facility, relatively thin (1 mm) mullite and alumina substrates were successfully dip-coated with 2.5 - 3.0 ohm-cm, p-type silicon with areas of approximately 20 sq cm. The thickness and grain size of these coatings are influenced by the temperature of the melt and the rate at which the substrate is pulled from the melt. One mullite substrate had dendrite-like crystallites of the order of 1 mm wide and 1 to 2 cm long. Their axes were aligned along the direction of pulling. A large variety of substrate materials were purchased or developed enabling the program to commence a substrate definition evaluation. Due to the insulating nature of the substrate, the bottom layer of the p-n junction may have to be made via the top surface. The feasibility of accomplishing this was demonstrated using single crystal wafers.

Heaps, J. D.↗
NASA NTRS1976

Dip coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

The technical and economic feasibility of producing solar cell quality sheet silicon by dip-coating one surface of carbonized ceramic substrates with a thin layer of large grain polycrystalline silicon was investigated. The dip-coating methods studied were directed toward a minimum cost process with the ultimate objective of producing solar cells with a conversion efficiency of 10% or greater. The technique shows excellent promise for low cost, labor-saving, scale-up potentialities and would provide an end product of sheet silicon with a rigid and strong supportive backing. An experimental dip-coating facility was designed and constructed, several substrates were successfully dip-coated with areas as large as 25 sq cm and thicknesses of 12 micron to 250 micron. There appears to be no serious limitation on the area of a substrate that could be coated. Of the various substrate materials dip-coated, mullite appears to best satisfy the requirement of the program. An inexpensive process was developed for producing mullite in the desired geometry.

Heaps, J. D.↗
NASA NTRS1981

Early development of ceramic fiber insulation for the Space Shuttle

The evolution of reusable surface insulation is described, with attention to the mullite and other aluminosilicates, zirconia, and silicon carbide-coated carbon compositions experimented with in the late 1960s and early 1970s. Evaluation and development concentrated in this period on such aspects of design and material properties as cold soak performance, attachment, shock impingement, surface coating cracks, and tile gap design and heating. In addressing the central problem of heat-shield thermal conductivity, it was found that for a given density, silica fibers had a lower conductivity than those of mullite. This was due to the one-micron, as opposed to 4.7-micron, diameter of the silica fibers, which resulted in smaller pores and therefore less convective and radiative heat transfer. Attention is also given to tile coating materials and the high-temperature processes by which they were applied.

Buckley, J. D.↗
NASA NTRS1989

Friction and wear of oxide-ceramic sliding against IN-718 nickel base alloy at 25 to 800 C in atmospheric air

The friction and wear of oxide-ceramics sliding against the nickel base alloy IN-718 at 25 to 800 C were measured. The oxide materials tested were mullite (3Al2O3.2SiO2); lithium aluminum silicate (LiAlSi(x)O(y)); polycrystalline monolithic alpha alumina (alpha-Al2O3); single crystal alpha-Al2O3 (sapphire); zirconia (ZrO2); and silicon carbide (SiC) whisker-reinforced Al2O3 composites. At 25 C the mullite and zirconia had the lowest friction and the polycrystalline monolithic alumina had the lowest wear. At 800 C the Al2O3-8 vol/percent SiC whisker composite had the lowest friction and the Al2O3-25 vol/percent SiC composite had the lowest wear. The friction of the Al2O3-SiC whisker composites increased with increased whisker content while the wear decreased. In general, the wear-resistance of the ceramics improve with their hardness.

Sliney, Harold E.↗
NASA NTRS1989

Crystallization of a barium-aluminosilicate glass

The crystallization of a celsian glass composition was investigated as a possible high-temperature ceramic matrix material. Heat treatments invariably resulted in crystallization of the hexaclesian phase unless a flux, such as lithia, was added or a nucleating agent used (e.g., celsian seeds). TEM analysis revealed complex microstructures. Glasses with Mo additions contained hexacelsian, mullite, and an Mo-rich glass. Li2O additions stabilized celsian but mullite and Mo-rich glass were still present.

Drummond, C. H., III↗
NASA NTRS1991

The high temperature creep behavior of oxides and oxide fibers

A thorough review of the literature was conducted on the high-temperature creep behavior of single and polycrystalline oxides which potentially could serve as fiber reinforcements in ceramics or metal matrix applications. Sapphire when oriented with the basal plane perpendicular to the fiber axis (c-axis oriented) is highly creep resistant at temperatures in excess of 1600 C and applied loads of 100 MPa and higher. Pyramidal slip is preferentially activated in sapphire under these conditions and steady-state creep rates in the range of 10(exp -7) to 10 (exp -8)/s were reported. Data on the creep resistance of polycrystalline beryllia suggest that C-axiz oriented single crystal beryllia may be a viable candidate as a fiber reinforcement material; however, the issure of fabricability and moisture sensitivity must be addressed for this material. Yttrium aluminum garnet (YAG) also appears to be a fiber candidate material having a high resistance to creep which is due to it's complex crystal structure and high Peierl resistance. The high creep resistance of garnet suggests that there may be other complex ternary oxides such as single crystal mullite which may also be candidate materials for fiber reinforcements. Finally, CVD and single crystal SiC, although not oxides, do possess a high resistance to creep in the temperature range between 1550 and 1850 C and under stresses of 110 to 220 MPa. From a review of the literature, it appears that for high creep resistant applications sapphire, silicon carbide, yttrium aluminum garnet, mullite, and beryllia are desirable candidate materials which require further investigation.

Jones, Linda E.↗
NASA NTRS2000

Internally Cooled Monolithic Silicon Nitride Aerospace Components

A set of rapid prototyping (RP) processes have been combined with gelcasting to make ceramic aerospace components that contain internal cooling geometry. A mold and core combination is made using a MM6Pro (Sanders Prototyping, Inc.) and SLA-250/40 (3Dsystems, Inc.). The MM6Pro produces cores from ProtoBuild (trademarked) wax that are dissolved in room temperature ethanol following gelcasting. The SLA-250/40 yields epoxy/acrylate reusable molds. Parts produced by this method include two types of specimens containing a high density of thin long cooling channels, thin-walled cylinders and plates, as well as a model hollow airfoil shape that can be used for burner rig evaluation of coatings. Both uncoated and mullite-coated hollow airfoils has been tested in a Mach 0.3 burner rig with cooling air demonstrating internal cooling and confirming the effectiveness of mullite coatings.

Best, Jonathan E.↗
NASA NTRS2003

Sintering and Interface Strain Tolerance of Plasma-Sprayed Thermal and Environmental Barrier Coatings

Ceramic thermal and environmental barrier coatings will be more aggressively designed to protect gas turbine engine hot section SiC/SiC Ceramic Matrix Composite (CMC) components in order to meet future engine higher fuel efficiency and lower emission goals. A coating system consisting of a zirconia-based oxide topcoat (thermal barrier) and a mullite/BSAS silicate inner coat (environmental barrier) is often considered a model system for the CMC applications. However, the coating sintering, and thermal expansion mismatch between the zirconia oxide layer and the silicate environmental barrier/CMC substrate will be of major concern at high temperature and under thermal cycling conditions. In this study, the sintering behavior of plasma-sprayed freestanding zirconia-yttria-based thermal barrier coatings and mullite (and/or barium-strontium-aluminosilicate, i.e., BSAS) environmental barrier coatings was determined using a dilatometer in the temperature range of 1200-1500 C. The effects of test temperature on the coating sintering kinetics were systematically investigated. The plasma-sprayed zirconia-8wt.%yttria and mullite (BSAS) two-layer composite coating systems were also prepared to quantitatively evaluate the interface strain tolerance of the coating system under thermal cycling conditions based on the dilatomentry. The cyclic response of the coating strain tolerance behavior and interface degradation as a function of cycle number will also be discussed.

Zhu, Dongming↗
NASA NTRS2016

Environmental Barrier Coatings for Ceramic Matrix Composites - An Overview

Ceramic Matrix Composites (CMCs) are increasingly being considered as structural materials for advanced power generation equipment. Broadly speaking the two classes of materials are oxide-based CMCs and non-oxide based CMCs. The non-oxide CMCs are primarily silicon-based. Under conditions prevalent in the gas turbine hot section the water vapor formed in the combustion of gaseous or liquid hydrocarbons reacts with the surface-SiO2 to form volatile products. Progressive surface recession of the SiC-SiC CMC component, strength loss as a result of wall thinning and chemical changes in the component occur, which leads to the loss of structural integrity and mechanical strength and becomes life limiting to the equipment in service. The solutions pursued to improve the life of SiC-SiC CMCs include the incorporation of an external barrier coating to provide surface protection to the CMC substrate. The coating system has become known as an Environmental Barrier Coating (EBC). The relevant early coatings work was focused on coatings for corrosion protection of silicon-based monolithic ceramics operating under severely corrosive conditions. The development of EBCs for gas turbine hot section components was built on the early work for silicon-based monolithics. The first generation EBC is a three-layer coating, which in its simplest configuration consists of a silicon (Si) base coat applied on top of the CMC, a barium-strontium-aluminosilicate (BSAS) surface coat resistant to water vapor attack, and a mullite-based intermediate coating layer between the Si base coat and BSAS top coat. This system can be represented as Si-Mullite-BSAS. While this baseline EBC presented a significant improvement over the uncoated SiC-SiC CMC, for the very long durations of 3-4 years or more expected for industrial operation further improvements in coating durability are desirable. Also, for very demanding applications with higher component temperatures but shorter service lives more rugged EBCs will be necessary. A second generation of EBCs incorporates rare earth silicates which have extremely favorable resistance against environmental attack and a higher temperature capability. Performance data for this class of EBCs is more limited and especially field data are not as extensive as for the first generation EBCs. Extensive laboratory, rig and engine testing, including testing of EBC coated SiC-SiC CMCs in actual field applications is in progress. The development of next generation EBCs with even higher temperature capability than the second generation EBC is also underway. This paper will discuss the current status of EBC technology and future direction based on literature survey.

Laboratory↗
NASA NTRS1972

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.↗
NASA NTRS1972

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.↗