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At least 235 records · Page 13

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NASA NTRS1981

Use of ceramics in point-focus solar receivers

One of the research and development efforts in the Solar Thermal Energy Systems Project at the Jet Propulsion Laboratory has been focused on application of ceramic components for advanced point-focus solar receivers. The impetus for this effort is a need for high efficiency, low cost solar receivers which operate in a temperature regime where use of metal components is impractical. The current status of the work on evaluation of ceramic components at JPL and elsewhere is outlined and areas where lack of knowledge is currently slowing application of ceramics are discussed. Future developments of ceramic processing technology and reliability assurance methodology should open up applications for the point-focus solar concentrator system in fuels and chemicals production, in thermochemical energy transport and storage, in detoxification of hazardous materials and in high temperature process heat as well as for electric power generation.

Smoak, R. H.↗

NASA NTRS1981

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.↗

NASA NTRS1982

Ceramic applications in turbine engines

In the past the potential of vehicular gas engines could not be realized because component materials served to limit the turbine operating temperature, thereby restricting fuel economy and initial cost. It was, therefore, not possible for the vehicular gas turbine to compete with more conventional engines. The emergence of low-cost, high-temperature ceramic components has the potential to reverse this situation. For example, the Allison GT404 engine, operating with ceramic components at turbine inlet temperatures up to 2350 F to 2500 F, has the potential of a fuel economy which is better than that of current Diesel engines. The Allison AGT100 engine operating with ceramic components offers the possibility of a 30% improvement in fuel economy over 1985 spark ignition engines. The materials considered for an employment in the ceramic components include silicon carbide, silicon nitride, aluminum silicate, and lithium aluminum silicate.

Byrd, J. A.↗

NASA NTRS1983

Absorbable-Susceptor Welding of Ceramics

Susceptor becomes part of joint. Susceptor is heated to high temperature by RF energy, then melts adjacent ceramic material. Susceptor dissolves in molten ceramic. When cooled, ceramic parts form moloithic assembly. Suitable for joining complex subassemblies in heat exchangers or other ceramic process equipment for high temperatures.

Schroeder, J. E.↗

NASA NTRS1982

High-temperature ceramic heat exchanger element for a solar thermal receiver

A study was performed by AiResearch Manufacturing Company, a division of The Garrett Corporation, on the development a high-temperature ceramic heat exchanger element to be integrated into a solar receiver producing heated air. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is to be fabricated by an innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. The unit is sized to produce 2150 F ar at 2.7 atm pressure, with a pressure drop of about 2 percent of the inlet pressure. This size is compatible with a solar collector providing a receiver input of 85 kw(th). Fabrication of a one-half scale demonstrator ceramic receiver has been completed.

Strumpf, H. J.↗

NASA NTRS1982

A high temperature ceramic heat exchanger element for a solar thermal receiver

The development of a high-temperature ceramic heat exchanger element to be integrated into a solar receiver producing heated air was studied. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is to be fabricated by a innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. The unit is sized to produce 2150 F air at 2.7 atm pressure, with a pressure drop of about 2 percent of the inlet pressure. This size is compatible with a solar collector providing a receiver input of 85 kw(th). Fabrication of a one-half scale demonstrator ceramic receiver was completed.

Strumpf, H. J.↗

NASA NTRS1985

Experimental and analytical study of ceramic-coated turbine-tip shroud seals for small turbine engines

The results of an experimental and analytical evaluation of ceramic turbine tip shrouds within a small turbine engine operating environment are presented. The ceramic shrouds were subjected to 1001 cycles between idle and high power and steady-state conditions for a total of 57.8 engine hr. Posttest engine inspection revealed mud-flat surface cracking, which was attributed to microcracking under tension with crack penetration to the ceramic and bond coat interface. Sections and micrographs tend to corroborate the thesis. The engine test data provided input to a thermomechanical analysis to predict temperature and stress profiles throughout the ceramic gas-path seal. The analysis predicts cyclic thermal stresses large enough to cause the seal to fail. These stresses are, however, mitigated by inelastic behavior of the shroud materials and by the microfracturing that tensile stresses produce. Microfracturing enhances shroud longevity during early life but provides the failure mechanism during life but provides the failure mechanism during extended life when coupled with the time dependent inelastic materials effects.

Biesiadny, T. J.↗

NASA NTRS1985

Ceramics for advanced O2/H2 application

Ceramics are prime candidate materials for advanced rocket engines because they possess high-temperature capability, a tolerance for aggressive environments, and low density. A program was conducted to assess the applicability of structural ceramics to advanced versions of the Space Shuttle main engine (SSME). Operating conditions of ceramic turbine components were defined and each component in the hot-gas path was assessed in regard to materials selection, manufacturing process and feasibility, and relative structural reliability. The conclusion is that ceramic components would be viable in advanced SSME turbopumps.

Carpenter, H. W.↗

NASA NTRS1984

Plastic flow of plasma sprayed ceramics

The plastic flow of plasma-sprayed ZrO2-8Y2O3 ceramic has been measured at temperatures up to 1250 C and compared to the plastic flow of pressed and sintered ZrO2-8Y2O3. Plasma spraying of binary oxide ceramics is found to result in a metastable state which is inelastic at high temperature but can also be stabilized or devitrified through heat treating so as to decrease plastic properties. The mechanical properties of the as-plasma sprayed and devitrified ceramic sheet material was measured. An improved algorithm that incorporates the inherently nonlinear thermomechanical field equations was used to determine the influence of inelastic material behavior on the thermomechanical response of ceramic coated seal components. Significant creep was found during the thermal shock and steady heating periods with insufficient time during thermal quench to reverse the process, thereby inducing significant residual stresses into the components.

Padovan, J.↗

NASA NTRS1985

Ceramic automotive Stirling engine study

A conceptual design study for a Ceramic Automotive Stirling Engine (CASE) is performed. Year 1990 structural ceramic technology is assumed. Structural and performance analyses of the conceptual design are performed as well as a manufacturing and cost analysis. The general conclusions from this study are that such an engine would be 10-26% more efficient over its performance map than the current metal Automotive Stirling Reference Engine (ASRE). Cost of such a ceramic engine is likely to be somewhat higher than that of the ASRE but engine cost is very sensitive to the ultimate cost of the high purity, ceramic powder raw materials required to fabricate high performance parts. When the design study is projected to the year 2000 technology, substantinal net efficiency improvements, on the order of 25 to 46% over the ASRE, are computed.

Musikant, S.↗

NASA NTRS1985

Capsulation of moldings made from silicon ceramic material

Ceramic articles are potted for hot isostatic pressing by porous glass and/or ceramic coating which is sintered to a pressure-tight coating in vacuo. Thus, a powdered SiO2 glass mixture with saturated alcohol sterin is sprayed on a SI3N4 ceramic, dried, introduced into the press which is evacuated to less than 0.013 mbar and heated to approximately 1200 C to drive off the organic binder and leave a powdered glass coating on the ceramic. The coating is sintered by heating to approximately 1200 C for 0.5 to 2 hours and forms a tight gass-impermeable layer. The press is heated to approximately 1700 C at 1000-300 bar and isostatic pressing is performed in the conventional manner.

Rossmann, A.↗

NASA NTRS1986

Ceramic automotive Stirling engine program

The Ceramic Automotive Stirling Engine Program evaluated the application of advanced ceramic materials to an automotive Stirling engine. The objective of the program was to evaluate the technical feasibility of utilizing advanced ceramics to increase peak engine operating temperature, and to evaluate the performance benefits of such an increase. Manufacturing cost estimates were also developed for various ceramic engine components and compared with conventional metallic engine component costs.

Source record↗

NASA NTRS1987

Ceramic matrix and resin matrix composites: A comparison

The underlying theory of continuous fiber reinforcement of ceramic matrix and resin matrix composites, their fabrication, microstructure, physical and mechanical properties are contrasted. The growing use of organometallic polymers as precursors to ceramic matrices is discussed as a means of providing low temperature processing capability without the fiber degradation encountered with more conventional ceramic processing techniques. Examples of ceramic matrix composites derived from particulate-filled, high char yield polymers and silsesquioxane precursors are provided.

Hurwitz, Frances I.↗

NASA NTRS1988

Fast Measurements Of Thermal Diffusivities Of Ceramics

Temperature rises of samples compared with reference sample. Apparatus quickly measures thermal diffusivities of ceramics at high temperatures. Produces data on relative thermal diffusivities of as many as six ceramic specimens per hour. Thermal-diffusivity tester makes it easy to determine thermal diffusivities of ceramics. Pronounced effects of processing parameters on thermal properties of ceramics evaluated quickly.

Smith, Marnell↗

NASA NTRS1986

Thermal cyclic durability testing of ceramic materials for turbine engines

The thermal cyclic durability of commercial ceramic materials for turbine engines was under evaluation since 1978. Ceramic materials are exposed to cyclic diesel-fired burner exhaust at either 1204 or 1371 C (2200 or 2500 F) for up to 3500 hours. The test conditions are selected to simulate the environment experienced by the hot flow path components in an automotive gas turbine engine. The silicon nitride and silicon carbide materials tested are the same ceramic materials currently used on the AGT100 and AGT101 ceramic turbine engine program.

Lindberg, L. J.↗

NASA NTRS1986

Polymer precursors for ceramic composites

The fiber composite approach to reinforced ceramics provides the possibility of achieving ceramics with high fracture toughness relative to monolithics. Fabrication of ceramic composites, however, demands low processing temperatures to avoid fiber degradation. Formation of complex shapes further requires small diameter fibers as well as techniques for infiltrating the matrix between fibers. Polymers offer low temperature processability, control of rheology not available with ceramic powders, and should serve as precursors to matrix fibers. In recent years, a number of polysilanes and polysilezanes were investigated as potential presursors. A review of candidate polymers is presented, including recent studies of silsesquioxanes.

Hurwitz, Frances I.↗

NASA NTRS1987

Ceramic matrix and resin matrix composites - A comparison

Hurwitz, Frances I.↗

NASA NTRS1989

A review of failure models for unidirectional ceramic matrix composites under monotonic loads

Ceramic matrix composites offer significant potential for improving the performance of turbine engines. In order to achieve their potential, however, improvements in design methodology are needed. In the past most components using structural ceramic matrix composites were designed by trial and error since the emphasis of feasibility demonstration minimized the development of mathematical models. To understand the key parameters controlling response and the mechanics of failure, the development of structural failure models is required. A review of short term failure models with potential for ceramic matrix composite laminates under monotonic loads is presented. Phenomenological, semi-empirical, shear-lag, fracture mechanics, damage mechanics, and statistical models for the fast fracture analysis of continuous fiber unidirectional ceramic matrix composites under monotonic loads are surveyed.

Tripp, David E.↗