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Simplified configuration and procedure developed for assembly of stacks of solid-electrolyte cells separating oxygen from air electrochemically. Reduces number of components and thus reduces probability of such failures as gas leaks, breakdown of sensitive parts, and electrical open or short circuits. Previous, more complicated version of cell described in "Improved Zirconia Oxygen-Separation Cell" (NPO-16161).
The invention is particularly concerned with sealing thermal barrier coating systems of the type in use and being contemplated for use in diesel and other internal combustion engines. The invention also would find application in moderately high temperature regions of gas turbine engines and any other application employing a thermal barrier coating at moderate temperatures. Ni-35Cr-6Al-1Y, Ni-35Cr-6Al-1Yb, or other metallic alloy denoted as MCrAlx is applied over a zirconia-based thermal barrier overlayer. The close-out layer is glass-bead preened to densify its surface. This seals and protects the thermal barrier coating system.
The objective is to optimally design the thermal components of a system that uses carbon dioxide (CO2) from the Martian atmosphere to produce oxygen (O2) for spacecraft propulsion and/or life-support. Carbon dioxide is thermally decomposed into carbon monoxide (CO) and O2 followed by the electrochemical separation of O2. The design of the overall system and its various individual components depends on, among other things, the fraction of the stoichiometric yield of O2 that can be realized in the system and the temperature of operation of the electrochemical separation membrane. The analysis indicates that a substantial reduction could be obtained in the mass and power requirements of the system if the unreacted CO2 were to be recycled. The concepts of an optimum temperature of the zirconia cell and impracticality of plant operation at low cell efficiencies are also discussed. The design of the thermal equipment is such that the mass and power requirements of the individual components and of the overall system are optimized.
There is considerable interest in in-situ propellant manufacturing on the moon and Mars. One of the concepts of oxygen production that is being actively pursued is the processing of atmospheric carbon dioxide on Mars to produce oxygen by means of thermal decomposition and electrochemical separation. The key component of such a production facility is the electrochemical separation cell that filters out the oxygen from the gas mixture of carbon dioxide, carbon monoxide, and oxygen. Efficient design of the separation cell and the selection of electrolyte and electrode materials of superior performance for the cell would translate to significant reduction in the power requirement and the mass of the production facility. The objective is to develop the technology required to produce the cells in-house and test various electrolyte and electrode materials systematically until the optimal combination is found. An effective technique was developed for the fabrication of disk shaped cells. Zirconia and Ceria cells were made in-house. Complete modules of the electrochemical cell and housings were designed, fabricated, and tested.
Glasses in the yttria-silica system with 20 to 40 mol pct Y2O3 were subjected to recrystallization studies after melting at 1900 to 2100 C in W crucibles in 1 and 50 atm N2. The TEM and XRD results obtained indicate the presence of the delta, gamma, gamma prime, and beta-Y2Si2O7 crystalline phases, depending on melting and quenching conditions. Heat treatment in air at 1100 to 1600 C increased the amount of crystallization, and led to the formation of Y2SiO5, cristabalite, and polymorphs of Y2Si2O7. Also investigated were the effects of 5 and 10 wt pct zirconia additions.
The program at NASA Lewis Research Center to develop a high temperature static strain gage system for the hypersonic vehicle and turbine engine research has emphasized a palladium-13 wt pct chromium (PdCr) alloy. Gages made from this alloy are being developed in both fine wire and thin film form. The wire gage system had platinum wire as a temperature compensator and was coated with a special alumina and zirconia mixture overcoat. This PdCr compensated wire gage responded linearly to the imposed strain to at least 1000 microstrain. The apparent strain varied within 300 microstrain from room temperature to 800 C with a reproducibility within 50 microstrain between thermal cycles to 800 C. The sputtered thin film PdCr strain gage, whose size was 8 x 8 mm and 10 microns thick, has demonstrated the possibility of extending the use of the PdCr strain gage to a temperature of approximately 1000 C.
The paper provides an overview of the short history, current status, and future prospects of ceramic thermal barrier coatings for gas turbine engines. Particular attention is given to plasma-sprayed and electron beam-physical vapor deposited yttria-stabilized (7 wt pct Y2O3) zirconia systems. Recent advances include improvements in the spallation life of thermal barrier coatings, improved bond coat composition and spraying techniques, and improved component design. The discussion also covers field experience, life prediction modeling, and future directions in ceramic coatings in relation to gas turbine engine design.
Sandwich geometry superconductor/normal metal/superconductor structures have been fabricated on LaAlO3 and cubic zirconia with laser-ablated, c-axis-oriented YBa2Cu3O(7-delta) base electrodes, 100-600 A of Au, and Nb counter electrodes, all formed in situ without breaking vacuum. Junctions range in size from 5 to 50 micron on a side. Four probe I-V measurements at 4.2 K show RnA products as low as 6 x 10 to the -9th sq cm and critical current densities up to 5.2 kA/sq cm. AC Josephson steps were observed with the application of 10-GHz radiation. The temperature dependence of Jc and the observation of the AC Josephson effect suggest that true supercurrents are present and that they do indeed represent the characteristics of the YBa2Cu3O(7-delta)/Au/Nb structure. The best results were obtained when the devices were annealed at about 450 C in O2 for 30 min after Au deposition.
A study focusing on oxygen production using resources indigenous to Mars is presented. A bank of solid zirconia electrolytic cells that will electrochemically separate oxygen from a high temperature stream of carbon dioxide is at the center of the oxygen production system. The experimental data are discussed with attention given to the cell operating temperature, the carbon dioxide flow rate, and the voltage applied across the cell.
Experimental PdCr temperature-compensated resistance static-strain gages are described. The gages are developed in both fine-wire and thin-film forms. It is found that a PdCr wire strain gage coated with a flame-sprayed mixture of alumina and 4 wt pct zirconia demonstrates the smallest variation in and the best repeatability of apparent strain among the existing gages used at temperatures up to 800 C. Results of preliminary tests indicate uncompensated uncoated thin-film gages have potential usefulness at temperatures up to 1000 C.
A temperature compensated static strain gauge, which is fabricated from Pd13Cr alloy and a Pt compensator, is being developed and has been tested over a temperature range to 1500 F at NASA-Lewis. The PdCr compensated strain gage has significantly lower apparent strain to 500 F than other high temperature strain gages. The PdCr compensated gage is protected from oxidation by a flame-sprayed alumina-4 wt pct zirconia overcoating. Test Results to 1500 F indicate apparent strain variations of less than 250 micro-epsilon and reproducibility between thermal cycles within 50 micro-epsilon. The apparent strain of the coated PdCr compensated gage can be predicted and cancelled due to its reproducibility and low value.
Thick films of fluorine-doped YBa2Cu3O(y) were screen printed on highly polished alumina, magnesia spinel, strontium titanate, and yttria-stabilized zirconia (YSZ) substrates. They were annealed at 1000 C and soaked in oxygen at 450 C, followed by slow cooling to room temperature. The films were characterized by electrical resistivity measurements as a function of temperature and x-ray diffraction. The film on YSZ showed the best characteristics with a T sub c (onset) of 91 K, T sub c (R equals 0) of 88.2 K, and a transition width, delta T sub c (10-90 percent), of approximately 1.7 K. The film adhesion, probably controlled by interdiffusion of cations between the film and the substrate, was good in all cases except on strontium titanate where the film completely detached from the substrate.
This investigation had two objectives: (1) to determine the effects of space radiation on superconductor parameters that are most important in space applications; and (2) to determine whether this effect can be simulated with Co-60 gamma rays, the standard test method for space materials. Thin films of yttrium barium copper oxide (YBCO) were formed by coevaporation of Y, BaF2, and Cu and post-annealing in wet oxygen at 850 C for 3.5 h. The substrate used was (100) silicon with an evaporated zirconia buffer layer. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were the zero resistance transition temperature T(sub c) and the room temperature resistance. The samples were then exposed to Co-60 gamma-rays in air and in pure nitrogen, and to 780 keV electrons, in air. The parameters were then remeasured. The results are summarized. The results indicate little or no degradation in the parameters measured for samples exposed up to 10 Mrads of gamma-rays in nitrogen. However, complete degradation is preliminarily attributed to the high level of ozone generated in the chamber by the gamma-ray interaction with air. It can be concluded that: (1) the electron component of space radiation does not degrade the critical temperature of the YBCO films described, at least for energies around 800 keV and doses similar to those received by surface materials on spacecraft in typical remote sensing missions; and (2) for qualifying this and other superconducting materials against the space-radiation threat the standard test method used in the aerospace industry, namely, exposure to Co-60 gamma-rays in air, may require some further investigation. As a minimum, the sample must be either in vacuum or in positive nitrogen pressure.
Thin films of YBa2Cu3O(7-x) (YBCO) were temperature cycled to simulate conditions of a low earth orbit satellite. In one series of tests, epitaxial and polycrystalline YBCO films were cycled between temperatures of +/- 80 C in vacuum and in nitrogen for hundreds of cycles. The room temperature resistance of an epitaxial YBCO film increased by about 10 percent, but the superconducting transition temperature was unchanged. The largest changes were for a polycrystalline YBCO film on oxidized silicon with a zirconia buffer layer, for which the transition temperature decreased by 3 K. An extended test was carried out for epitaxial films. After 3200 cycles (corresponding to about 230 days in space), transition temperatures and critical current densities remained unchanged.
After delivering a significant data base on boilerplate and prototype advanced nickel cadmium (Ni/Cd) battery cells, Hughes decided to start using the Advanced Ni/Cd batteries on several of their flight programs. The advanced cell can been operated at 80 percent depth of discharge (DOD) for more than 10 years, and possibly 15 years, in geosynchronous earth orbit (GEO) applications. This cell offers an important weight saving over the standard Ni/Cd cell that is usually only operated at 50 to 60 percent DOD in GEO applications. The negative and positive electrodes are manufactured using electrochemical deposition methods which reduce the sinter corrosion problems encountered by the chemical deposition process used in the standard cells. The degradable nylon separators used in standard cells was replaced by polymer impregnated Zirconia separators.
High T sub C superconducting thick film were prepared by a screen printing process. Y-based (YBa2Cu3O(7-x) superconducting thick film were printed on 211/Al2O3, SNT/Al2O3, and YSZ substrates. Because of poor adhesion of the superconductor thick films to 211/Al2O3 and SNT/Al2O3 substrates, relatively low T sub C and J sub C values were obtained from the films printed on these substrates. Critical temperatures (T sub C) of YBa2Cu3O(7-x) thick films deposited on 211/Al2O3 and SNT/Al2O3 substrates were about 80 K. The critical current densities (J sub C) of these films were less than 2 A/sq cm. Higher T sub C and J sub C YBa2Cu3O(7-x) thick films were printed on YSZ substrates. A YBa2Cu3O(7-x) thick film with T sub C=86.4 and J sub C= 50.4 A/sq cm was prepared by printing the film on YSZ substrate and firing at 990 C for 10 minutes. Multiple-lead samples were also prepared on the YSZ substrates. The multiple-lead samples showed lower T sub C and/or J sub C values than those of the plain samples. The electrical properties of YBa2Cu3O(7-x) thick films were determined by the microstructures of the films. The YBa2Cu3O(7-x) thick films printed on the YSZ substrates, which had the best properties among the films printed on the three different kinds of substrates, had the highest density and the best particle interconnection. The YBa2Cu3O(7-x) thick films with preferred orientation in (001) direction were obtained on the YSZ substrates. Cracks, which retard the properties of the films, were found from the films deposited on the YSZ substrates. Currently, a MSZ (Magnesium Stabilized Zirconia) substrate, which had higher thermal expansion coefficient than the YSZ substrate, is used as substrate for the YBa2Cu3O(7-x) thick film in order to eliminate the cracks on the film. Bi-based superconductor thick films were printed on polycrystalline MgO and YSZ substrates. Interactions between BSCCO thick films and the YSZ substrates were observed. Various buffer layer materials were applied onto the substrates in order to avoid the interactions between the BSCCO thick films and the ZrO2-based substrates. So far, a BSCCO printed on MgO substrate with T Sub C=89K was obtained. The J sub C of the film was lower than 0.1 A/sq cm by reason of poor interconnectivity of the BSCCO particles.
It is pointed out that an advanced NiCd cell based on a Hughes Aircraft Company design appears to show the most promise in the current generation of aerospace NiCd batteries. The cell was designed to ameliorate the major failure mechanisms of NiCd cells. This required cell design and process modifications and the use of alternate materials for some of the components (the most notable one being the substitution of zirconia cloth for nylon as the separator material). Recent reports in the literature indicate that the improvement in the performance of this technology appears to have been verified for GEO (geosynchronous)-type applications. The authors report on initial results of the evaluation of the advanced NiCd technology for applications of interest to NASA. They summarize the characteristics of cells based on the advanced technology from the time of manufacture to their current cell cycling status.
Addition of some rare-earth oxides to prior alumina (only) coating material increases maximum service temperature of palladium/chromium-wire strain gauges. Pd/Cr wires used at temperatures up to 800 degrees C without excessive drift in electrical resistance. Oxides used: zirconia (ZrO2), yttria (Y2O3), ceria (CeO2), and hafnia (HfO2). Addition of one of these oxides to decrease oxidation of wire at high temperature. Protection against oxidation increases with concentration of rare-earth oxide. Addition of ZrO2 at 4 to 6 weight percent or Y2O3 at 1 weight percent results in smallest drift in electrical resistance.