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At least 145 records · Page 8

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NASA NTRS1975

Formation mechanism of a silicon carbide coating for a reinforced carbon-carbon composite

Results are presented for a study to determine the mechanisms involved in a high-temperature pack cementation process which provides a silicon carbide coating on a carbon-carbon composite. The process and materials used are physically and chemically analyzed. Possible reactions are evaluated using the results of these analytical data. The coating is believed to develop in two stages. The first is a liquid controlled phase process in which silicon carbide is formed due to reactions between molten silicon metal and the carbon. The second stage is a vapor transport controlled reaction in which silicon vapors react with the carbon. There is very little volume change associated with the coating process. The original thickness changes by less than 0.7%. This indicates that the coating process is one of reactive penetration. The coating thickness can be increased or decreased by varying the furnace cycle process time and/or temperature to provide a wide range of coating thicknesses.

Rogers, D. C.↗

NASA NTRS1976

Linear polarimeter with rapid modulation, achromatic in the 0.3-1.1-micron range

A polarimeter is described, which provides achromatic modulation over the spectral range 0.3 to 1.1 microns, with very small light losses. The instrument is the first one to use superachromatic half-wave plates; such a plate is made of three achromatic half-wave plates of quartz and magnesium fluoride cemented with the optical axis of the central plate making an angle of 1.00 rad with the axes of the parallel-oriented outer half-wave plates. Wavelength dependence of the axis direction of the optical axis was eliminated by using two identical such plates in front of a Wollaston prism. The plate closer to the prism is stationary, while the other is continuously rotated by a stepper motor. In the polarimeter constructed, the range of instrumentally induced wavelength dependence of the plane of polarization did not exceed 0.002 rad. Using the polarimeter on a 228-cm telescope, a 10-min integration through the blue filter of the UBV photometric system for a star of magnitude 10.0 gives the percentage polarization with a mean error of + or - 0.014%.

Frecker, J. E.↗

NASA NTRS1976

Potential biomedical applications of ion beam technology

Electron bombardment ion thrusters used as ion sources have demonstrated a unique capability to vary the surface morphology of surgical implant materials. The microscopically rough surface texture produced by ion beam sputtering of these materials may result in improvements in the biological response and/or performance of implanted devices. Control of surface roughness may result in improved attachment of the implant to soft tissue, hard tissue, bone cement, or components deposited from blood. Potential biomedical applications of ion beam texturing discussed include: vascular prostheses, artificial heart pump diaphragms, pacemaker fixation, percutaneous connectors, orthopedic pros-thesis fixtion, and dental implants.

Banks, B. A.↗

NASA NTRS1977

Reinforced Carbon Carbon (RCC) oxidation resistant material samples - Baseline coated, and baseline coated with tetraethyl orthosilicate (TEOS) impregnation

Reinforced carbon-carbon material specimens were machined from 19 and 33 ply flat panels which were fabricated and processed in accordance with the specifications and procedures accepted for the fabrication and processing of the leading edge structural subsystem (LESS) elements for the space shuttle orbiter. The specimens were then baseline coated and tetraethyl orthosilicate impregnated, as applicable, in accordance with the procedures and requirements of the appropriate LESS production specifications. Three heater bars were ATJ graphite silicon carbide coated with the Vought 'pack cementation' coating process, and three were stackpole grade 2020 graphite silicon carbide coated with the chemical vapor deposition process utilized by Vought in coating the LESS shell development program entry heater elements. Nondestructive test results are reported.

Gantz, E. E.↗

NASA NTRS1977

Scanning-electron-microscopy observations and mechanical characteristics of ion-beam-sputtered surgical implant alloys

An electron bombardment ion thruster was used as an ion source to sputter the surfaces of orthopedic prosthetic metals. Scanning electron microscopy photomicrographs were made of each ion beam textured surface. The effect of ion texturing an implant surface on its bond to bone cement was investigated. A Co-Cr-W alloy and surgical stainless steel were used as representative hard tissue implant materials to determine effects of ion texturing on bulk mechanical properties. Work was done to determine the effect of substrate temperature on the development of an ion textured surface microstructure. Results indicate that the ultimate strength of the bulk materials is unchanged by ion texturing and that the microstructure will develop more rapidly if the substrate is heated prior to ion texturing.

Weigand, A. J.↗

NASA NTRS1976

Potential biomedical applications of ion beam technology

Banks, B. A.↗

NASA NTRS1976

Inorganic analyses of Martian surface samples at the Viking landing sites

Elemental analyses of fines in the Martian regolith at two widely separated landing sites, Chryse Planitia and Utopia Planitia, produced remarkably similar results. At both sites, the uppermost regolith contains abundant Si and Fe, with significant concentrations of Mg, Al, S, Ca, and Ti. The S concentration is one to two orders of magnitude higher, and K (less than 0.25% by weight) is at least 5 times lower than the average for earth's crust. The trace elements Sr, Y, and possibly Zr have been detected at concentrations near or below 100 parts per million. Pebble-sized fragments sampled at Chryse contain more S than the bulk fines and are thought to be pieces of a sulfate-cemented duricrust.

Clark, B. C.↗

NASA NTRS1977

Labyrinth and cerebral-spinal fluid pressure changes in guinea pigs and monkeys during simulated zero G

This study was undertaken to explore the hypothesis that shifts of body fluids from the legs and torso toward the head contribute to the motion sickness experienced by astronauts and cosmonauts. The shifts in body fluids observed during zero-G exposure were simulated by elevating guinea pigs' and monkeys' torsos and hindquarters. Cerebral-spinal fluid pressure was recorded from a transducer located in a brain ventricle; labyrinth fluid pressure was recorded from a pipette cemented in a hole in a semicircular canal. An anticipated divergence in cerebral-spinal fluid pressure and labyrinth fluid pressure during torso elevation was not observed. The results of this study do not support a fluid shift mechanism of zero-G-induced motion sickness. However, a more complete test of the fluid shift mechanism would be obtained if endolymph and perilymph pressure changes were determined separately; we have been unable to perform this test to date.

Parker, D. E.↗

NASA NTRS1976

Coatings for directional eutectics

Coatings developed to provide oxidation protection for the directionally-solidified eutectic alloy NiTaC-B (4.4 weight percent Cr) were evaluated. Of seven Co-, Fe- and Ni-base coatings that were initially investigated, best resistance to cyclic oxidation was demonstrated by duplex coatings fabricated by depositing a layer of NiCrAl(Y) by vacuum evaporation from an electron beam source followed by deposition of an Al overlayer using the pack cementation process. It was found that addition of carbon to the coating alloy substantially eliminated the problem of fiber denudation in TaC-type eutectic alloys. Burner rig cycled NiTaC-B samples coated with Ni-20Cr-5Al-0.1C-0.1Y+Al and rupture-tested at 1100 deg C performed as well as or better than uncoated, vacuum cycled and air-tested NiTaC-13; however, a slight degradation with respect to uncoated material was noted in air-stress rupture tests at 870 deg C for both cycled and uncycled samples.

Rairden, J. R.↗

NASA NTRS1978

Fabrication of sea-floor models

Sea-floor models are fabricated simply and inexpensively by utilizing milling machine programmed with data tapes from ocean sounding surveys, and cement vermiculite mixture.

Hale, G. L.↗

NASA NTRS1977

Injection of coal by screw feed

The use of the screw feeder for injecting solids through a 20 to 30 psi barrier is common practice in the cement making industry. An analytical extrapolation of that design, accounting for pressure holding characteristics of a column of solids, shows that coal can be fed to zones at several hundred psi with minimal or no loss of gas. A series of curves showing the calculated pressure gradient through a moving column of solids is presented. Mean particle size, solids velocity, and column length are parameters. Further study of this system to evaluate practicality is recommended.

Fisher, R.↗

NASA NTRS1977

Reliability analysis of forty-five strain-gage systems mounted on the first fan stage of a YF-100 engine

The reliability of 45 state-of-the-art strain gage systems under full scale engine testing was investigated. The flame spray process was used to install 23 systems on the first fan rotor of a YF-100 engine; the others were epoxy cemented. A total of 56 percent of the systems failed in 11 hours of engine operation. Flame spray system failures were primarily due to high gage resistance, probably caused by high stress levels. Epoxy system failures were principally erosion failures, but only on the concave side of the blade. Lead-wire failures between the blade-to-disk jump and the control room could not be analyzed.

Holanda, R.↗

NASA NTRS1978

High temperature surface protection

Alloys of the MCrAlX type are the basis for high temperature surface protection systems in gas turbines. M can be one or more of Ni, Co, or Fe and X denotes a reactive metal added to enhance oxide scale adherence. The selection and formation as well as the oxidation, hot corrosion and thermal fatigue performance of MCrAlX coatings are discussed. Coatings covered range from simple aluminides formed by pack cementation to the more advanced physical vapor deposition overlay coatings and developmental plasma spray deposited thermal barrier coatings.

Levine, S. R.↗

NASA NTRS1978

Advanced solid electrolyte cell for CO2 and H2O electrolysis

A solid electrolyte cell with improved sealing characteristics was examined. A tube cell was designed, developed, fabricated, and tested. Design concepts incorporated in the tube cell to improve its sealing capability included minimizing the number of seals per cell and moving seals to lower temperature regions. The advanced tube cell design consists of one high temperature ceramic cement seal, one high temperature gasket seal, and three low temperature silicone elastomer seals. The two high temperature seals in the tube cell design represent a significant improvement over the ten high temperature precious metal seals required by the electrolyzer drum design. For the tube cell design the solid electrolyte was 8 mole percent yttria stabilized zirconium oxide slip cast into the shape of a tube with electrodes applied on the inside and outside surfaces.

Shumar, J. W.↗

NASA NTRS1978

Thermal energy storage for industrial waste heat recovery

The potential is examined for waste heat recovery and reuse through thermal energy storage in five specific industrial categories: (1) primary aluminum, (2) cement, (3) food processing, (4) paper and pulp, and (5) iron and steel. Preliminary results from Phase 1 feasibility studies suggest energy savings through fossil fuel displacement approaching 0.1 quad/yr in the 1985 period. Early implementation of recovery technologies with minimal development appears likely in the food processing and paper and pulp industries; development of the other three categories, though equally desirable, will probably require a greater investment in time and dollars.

Hoffman, H. W.↗

NASA NTRS1977

The Viking X ray fluorescence experiment - Sampling strategies and laboratory simulations

Ten samples of Mars regolith material (six on Viking Lander 1 and four on Viking Lander 2) have been delivered to the X ray fluorescence spectrometers as of March 31, 1977. An additional six samples at least are planned for acquisition in the remaining Extended Mission (to January 1979) for each lander. All samples acquired are Martian fines from the near surface (less than 6-cm depth) of the landing sites except the latest on Viking Lander 1, which is fine material from the bottom of a trench dug to a depth of 25 cm. Several attempts on each lander to acquire fresh rock material (in pebble sizes) for analysis have yielded only cemented surface crustal material (duricrust). Laboratory simulation and experimentation are required both for mission planning of sampling and for interpretation of data returned from Mars. This paper is concerned with the rationale for sample site selections, surface sampler operations, and the supportive laboratory studies needed to interpret X ray results from Mars.

Baird, A. K.↗

NASA NTRS1978

Possible fossil H2O liquid-ice interfaces in the Martian crust

The extensive chaotic and fretted terrains in the equatorial regions of Mars are explained on the basis of the vertical distribution of H2O liquid and ice which once existed in the crust. This account assumes that below the permafrost containing water ice, there was a second zone in which liquid water resided for at least a time. Diagenetic alteration and cementation characterized the material in the subpermafrost zone; above, pristine fragmented material with various ice concentrations was found. Later, the ice-laden zone was stripped away by a number of erosional processes, exposing the former ice-liquid water interface.

Soderblom, L. A.↗

NASA NTRS1980

High-temperature high-pressure magnetic pickup

Magnetic-pickup transducers operate at temperature as high as 1,100 C and pressures in excess of 2.5 kilobars. Transducers obtain simulated seismic data in laboratory experiments at high temperatures and pressure. They also have potential applications in industrial instrumentation for measurements under similarly difficult conditions. Transducers use high-temperature cement to bond parts together and high-temperature-insulated copper or aluminum wire for windings.

Ahlberg, L. A.↗