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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Silica-Aerogel Composites Opacified with La(0.7)Sr(0.3)MnO3

As part of an effort to develop improved lightweight thermal-insulation tiles to withstand temperatures up to 1,000 C, silica aerogel/fused-quartz-fiber composite materials containing La0.7Sr0.3MnO3 particles as opacifiers have been investigated as potentially offering thermal conductivities lower than those of the otherwise equivalent silica-aerogel composite materials not containing La(0.7)Sr(0.3)MnO3 particles. The basic idea of incorporating opacifying particles into silica-aerogels composite to reduce infrared radiative contributions to thermal conductivities at high temperatures is not new: it has been reported in a number of previous NASA Tech Briefs articles. What is new here is the selection of La(0.7)Sr(0.3)MnO3 particles as candidate opacifiers that, in comparison with some prior opacifiers (carbon black and metal nanoparticles), are more thermally stable. The preparation of a composite material of the present type includes synthesis of the silica-aerogel component in a sol-gel process. The La(0.7)Sr(0.3)MnO3 particles, made previously in a separate process, are mixed into the sol, which is then cast onto fused-quartz-fiber batting. Then the aerogel-casting solution is poured into the mold, where it permeates the silica fiber felt. After the sol has gelled, the casting is aged and then subjected to supercritical drying to convert the gel to the final aerogel form. The separate process for making the La(0.7)Sr(0.3)MnO3 particles begins with the slow addition of corresponding proportions of La(CH3COOH)3, Mn(CH3COOH)3, and Sr(NO3)2 to a solution of H2O2 in H2O. The solution is then peptized by drop-wise addition of NH4OH to obtain a sol. Next, the sol is dried in an oven at a temperature of 120 C to obtain a glassy solid. The solid is calcined at 700 C to convert it to La(0.7)Sr(0.3)MnO3. Then La(0.7)Sr(0.3)MnO3 particles are made by ball-milling the calcined solid. The effectiveness of La(0.7)Sr(0.3)MnO3 particles as opacifiers and thermal-conductivity reducers depends on the statistical distribution of particle sizes as well as the relative proportions of La(0.7)Sr(0.3)MnO3 and aerogel. For experiments performed thus far, samples of aerogel/fiber composites were formulated to have, variously, silica target density of 0.07 or 0.14 g/cu cm and to contain 30 percent of La(0.7)Sr(0.3)MnO3 in average particle size of 0.3 or 3 microns. The thermal conductivities of the samples containing the 3 micron La(0.7)Sr(0.3)MnO3 particles were found to be lower than those of the samples containing the 0.3 micron La(0.7)Sr(0.3)MnO3 particles. The optimum particle size is believed to be between 1 and 5 microns.

Rhine, Wendell↗
NASA NTRS1968

Preparation of silver-activated zinc sulfide thin films

Silver improves luminescence and reduces contamination of zinc sulfide phosphors. The silver is added after the zinc sulfide phosphors are deposited in thin films by vapor evaporation, but before calcining, by immersion in a solution of silver salt.

Feldman, C.↗
NASA NTRS1972

High strength high modulus ceramic fiber

Low cost method was developed for producing high strength, high modulus, continuous ceramic oxide fibers. Process transforms inexpensive metallic salts into syrup-like liquids that can be fiberized at room temperatures. Resulting salt fibers are then converted to oxides by calcination at relatively low temperatures.

Fetterolf, R. N.↗
NASA NTRS1974

Infrared transmission spectra of Sea of Fertility regolith

Transmission spectra in the 2-25 micrometer region were obtained for samples of lunar regolith returned by the Luna 16 automatic station. A comparison of the Luna 16, Apollo 11, and Apollo 12 samples showed that the infrared transmission spectra of regolith samples from the mare regions are similar and characteristic of basic basaltic rocks. The absorption bands show up in the vibration region of the SiO4 groups. No water and OH groups were found in the samples based on the spectrum. Spectra of regolith samples calcined at 1000C showed changes that can be interpreted as changes in the spectra of irradiated crystals (especially distinctly for the Luna 16 samples).

Akhmanova, M. V.↗
NASA NTRS1978

Adsorption and chemical reaction of gaseous mixtures of hydrogen chloride and water on aluminum oxide and application to solid-propellant rocket exhaust clouds

Hydrogen chloride (HCl) and aluminum oxide (Al2O3) are major exhaust products of solid rocket motors (SRM). Samples of calcination-produced alumina were exposed to continuously flowing mixtures of gaseous HCl/H2O in nitrogen. Transient sorption rates, as well as maximum sorptive capacities, were found to be largely controlled by specific surface area for samples of alpha, theta, and gamma alumina. Sorption rates for small samples were characterized linearly with an empirical relationship that accounted for specific area and logarithmic time. Chemisorption occurred on all aluminas studied and appeared to form from the sorption of about a 2/5 HCl-to-H2O mole ratio. The chemisorbed phase was predominantly water soluble, yielding chloride/aluminum III ion mole ratios of about 3.3/1 suggestive of dissolved surface chlorides and/or oxychlorides. Isopiestic experiments in hydrochloric acid indicated that dissolution of alumina led to an increase in water-vapor pressure. Dissolution in aqueous SRM acid aerosol droplets, therefore, might be expected to promote evaporation.

Cofer, W. R., III↗
NASA NTRS1978

The disposal of nuclear waste in space

The important problem of disposal of nuclear waste in space is addressed. A prior study proposed carrying only actinide wastes to space, but the present study assumes that all actinides and all fission products are to be carried to space. It is shown that nuclear waste in the calcine (oxide) form can be packaged in a container designed to provide thermal control, radiation shielding, mechanical containment, and an abort reentry thermal protection system. This package can be transported to orbit via the Space Shuttle. A second Space Shuttle delivers an oxygen-hydrogen orbit transfer vehicle to a rendezvous compatible orbit and the mated OTV and waste package are sent to the preferred destination. Preferred locations are either a lunar crater or a solar orbit. Shuttle traffic densities (which vary in time) are given and the safety of space disposal of wastes discussed.

Burns, R. E.↗
NASA NTRS1976

Energy Conservation Alternatives Study (ECAS): Conceptual Design and Implementation Assessment of a Utility Steam Plant with Conventional Furnace and Wet Lime Stack Gas Scrubbers

A study was performed to estimate the technical/economic characteristics of a steam power plant (3500 pounds per square inch gauge, 1000 degrees Fahrenheit / 1000 degrees Fahrenheit) with a coal-burning radiant furnace and a wet lime stack gas scrubber to control sulfur emissions. Particulate emissions were controlled by an electrostatic precipitator operating at 300 degrees Fahrenheit. The stack gas from the scrubber was reheated from 125 degrees Fahrenheit to 250 degrees Fahrenheit as a base case, and from 125 degrees Fahrenheit to 175 degrees Fahrenheit as an alternate case. The study was performed on a basis consistent with the General Electric ECAS Phase II evaluation of advanced energy conversion systems for electric utility baseload applications using coal or coal-derived fuels. A conceptual design of the power plant was developed, including the on-site calcination of limestone to lime and the provision of sludge ponds to store the products of flue gas scrubbing. From this design, estimates were derived for power plant efficiency, capital cost, environmental intrusion characteristics, natural resource requirements, and cost of electricity at an assumed capacity factor of 65 percent. An implementation assessment was performed where factors affecting applicability of the conceptual design power plant in electric utility generation systems were appraised. At 250 degrees Fahrenheit and 175 degrees Fahrenheit stack gas temperatures respectively, the plants showed a cost of electricity of 39.8 and 37.0 mills per kilowatt-hours and overall plant efficiencies of 32 percent and 34 percent.

Brown, Dale H.↗
NASA NTRS1980

Modification of the ECAS reference steam power generating plant to comply with the EPA 1979 new source performance standards

Detailed capital cost estimates for the ECAS and modified reference plants in mid-1978 dollars for both 250 and 175 F (394 and 353 K) stack gas reheat temperatures based on the cost estimates developed for the ECAS study are presented. The scope of the work included technical assessment of sulfur dioxide scrubber system design, on site calcination versus purchased lime, reheat of stack gas, effect of sulfur dioxide scrubber on particulate emission, and control of nitrogen oxides.

Fogelson, S. A.↗
NASA NTRS1983

Thermal and mechanical properties of advanced, high temperature ceramic-composite insulation

It is found that the mechanical properties of fibrous refractory composite insulation (FRCI) can be improved if a higher calcination temperature is used before final processing. The results also reveal that a higher density FRCI containing 60 wt pct aluminoborosilicate fibers will exhibit minimal surface recession at 1480 C in a convective-heating environment. Another finding is that the material performance in the convective-heating environment is limited by the coating and the temperature capability of its emittance agent. A table is included giving the coating compositions used with the composite insulation and tested in the convectively heated environment at a surface temperature of 1480 C.

Leiser, D. B.↗
NASA NTRS1984

Silicon nitride sintered body

The sintering of silicon carbide and it production are described. The method of production is by calcination in which molding is followed by sintering without compression. The invention improves the composition of the silicon carbide ceramic. Six examples of the invention are illustrated and discussed.

Suzuki, K.↗
NASA NTRS1984

Structural changes during milling of aluminum oxide powders

The mechanical activation of four fused corundum powders and a calcined Al2O3 powder was studied. The milled powders were characterized by their structural properties, crystallite size, and lattice distortions. Structural changes during milling, detected by X-ray line broadening analysis, gave information about the enhanced activity of the powders caused by the lattice distortions and by the decreasing crystallite size during milling. The structural changes during milling, under the same milling conditions, can be quite different for the same ceramic material, but with different characteristics in the as received state.

Ziepler, G.↗
NASA NTRS1989

Process for making a noble metal on tin oxide catalyst

A quantity of reagent grade tin metal or compound, chloride-free, and high-surface-area silica spheres are placed in deionized water, followed by deaerating the mixture by boiling and adding an oxidizing agent, such as nitric acid. The nitric acid oxidizes the tin to metastannic acid which coats the spheres because the acid is absorbed on the substrate. The metastannic acid becomes tin oxide upon drying and calcining. The tin-oxide coated silica spheres are then placed in water and boiled. A chloride-free precious metal compound in aqueous solution is then added to the mixture containing the spheres, and the precious metal compound is reduced to a precious metal by use of a suitable reducing agent such as formic acid. Very beneficial results were obtained using the precious metal compound tetraammine platinum(II) hydroxide.

Upchurch, Billy T.↗
NASA NTRS1990

The oxidation of carbon monoxide using tin oxide based catalysts

The preparation conditions for precious metal/tin oxide catalysts were optimized for maximum carbon monoxide/oxygen recombination efficiency. This was achieved by controlling the tin digestion, the peptization to form the sol, the calcination process and the method of adding the precious metals. Extensive studies of the tin oxide structure were carried out over the temperature range 20 to 500 C in air or hydrogen environments using Raman scattering and X ray diffraction. Adsorbed species on tin oxide, generated in an environment containing carbon monoxide, gave rise to a Raman band at about 1600 cm(exp -1) which was assigned to carbonaceous groups, possible carbonate.

Sampson, Christopher F.↗
NASA NTRS1992

An acetate precursor process for BSCCO (2223) thin films and coprecipitated powders

Since the discovery of high temperature superconducting oxides much attention has been paid to finding better and useful ways to take advantage of the special properties exhibited by these materials. One such process is the development of thin films for engineering applications. Another such process is the coprecipitation route to producing superconducting powders. An acetate precursor process for use in thin film fabrication and a chemical coprecipitation route to Bismuth based superconducting materials has been developed. Data obtained from the thin film process were inconclusive to date and require more study. The chemical coprecipitation method of producing bulk material is a viable method, and is preferred over the previously used solid state route. This method of powder production appears to be an excellent route to producing thin section tape cast material and screen printed devices, as it requires less calcines than the oxide route to produce quality powders.

Haertling, Gene H.↗
NASA NTRS1993

Development of high Tc (greater than 100 K) Bi, Tl and Y-based materials as superconducting circuit elements

Results on this project over the past three years have shown that the Bi and Tl-based superconducting materials in bulk form are noticeably different from the Y-based 123 material in that superconductivity is considerably harder to achieve, maintain and reproduce. This is due primarily to the difficulty in obtaining the higher Tc phase in pure form since it commonly co-exists with other undesirable, lower Tc phases. In particular, it has been found that long processing times for calcining and firing (20 - 200 hrs.) and close control of temperatures which are very near the melting point are required in order to obtain higher proportions of the desirable, high Tc (2223) phase.

Haertling, Gene↗
NASA NTRS1992

Regenerative Life Support Systems Test Bed performance - Lettuce crop characterization

Two crops of lettuce (Lactuca sativa cv. Waldmann's Green) were grown in the Regenerative Life Support Systems (RLSS) Test Bed at NASA's Johnson Space Center. The RLSS Test Bed is an atmospherically closed, controlled environment facility for the evaluation of regenerative life support systems using higher plants. The chamber encloses 10.6 m 2 of growth area under cool-white fluorescent lamps. Lettuce was double seeded in 480 pots, each containing about 250 cm 3 of calcined-clay substrate. Each pot was irrigated with half-strength Hoagland's nutrient solution at an average total applied amount of 2.5 and 1.8 liters pot -1 , respectively, over each of the two 30-day crop tests. Average environmental and cultural conditions during both tests were 23°C air temperature, 72% relative humidity, 1000 ppm carbon dioxide (CO 2 ), 16h light/8h dark photoperiod, and 356 μmol m -2 s -1 photosynthetic photon flux. After 30 days from seeding, average yield (g pot -1 ) for the first and second crop tests were 72 and 49 edible (shoot) fresh mass, 3.65 and 2.56 edible dry mass, and 0.44 and 0.45 inedible (root) dry mass, respectively. Averaging over both crop tests, the test bed met the requirements of 2.1 person-days of oxygen production, 2.4 person days of CO 2 removal and 129 person days of potential potable water production. The satisfactory growth of both crops demonstrates the potential of lettuce for air revitalization and water production in a controlled ecological life support system. Differences in crop performance resulting from engineering system effects provides evidence of the resilience of biological systems.

Life support systems↗
NASA NTRS1992

A modified sulfate process to lunar oxygen

A modified sulfate process which produces oxygen from iron oxide-bearing minerals in lunar soil is under development. Reaction rates of ilmenite in varying strength sulfuric acid have been determined. Quantitative conversion of ilmenite to ferrous sulfate was observed over a range of temperatures and concentrations. Data has also been developed on the calcination of by-product sulfates. System engineering for overall operability and simplicity has begun, suggesting that a process separating the digestion and sulfate dissolution steps may offer an optimum process.

Sullivan, Thomas A.↗