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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

700 F properties of autoclave cured PMR-II composites

Studies were conducted to develop autoclave processing parameters for graphite reinforced PMR-2 resin composite materials intended for use in applications at temperatures up to 371 degrees (700 F). The effect of resin composition on autoclaveability was investigated. The effect of various graphite fibers and resin composition on 343 C (650 F) and 371 C (700 F) thermo-oxidative stability and mechanical properties was also investigated. The results of the processing studies show that PMR-2 resin composites can be easily fabricated under autoclave conditions. Autoclaved laminates exposed to 1 atm of air at 343 C (650 F) and 371 C (700 F) exhibited less than 5 percent weight loss after 750 hr exposure to 650 F air and 8 percent weight loss during exposure to 700 F air for 500 hr. After 500 hr exposure, autoclaved laminates exhibited greater than 90 percent retention of initial 650 and 700 F flexural and interlaminar shear strengths. The effect of resin formulated molecular weight and postcure conditions on laminate glass transition temperature is also discussed.

Cifani, Diane↗
NASA NTRS1961

Titanium Nitride: An Oxidizable Coating for the High-Temperature Protection of Graphite

A titanium nitride coating for graphite, prepared by deposition process, protected test specimens for 60 seconds the vapors in a supersonic ceramic-heated air jet with a stagnation temperature of approximately 2,250 K. For the same test conditions, coated specimens showed no damage to the graphite body for the 60-second test, whereas uncoated specimens were very severely damaged after 20 seconds and were destroyed toward the end of the test. A discussion of the coating of these graphite specimens and of some of the conditions necessary for the utilization of oxidizable substances as oxidation-protective coatings for bodies facing high convective heat transfer in the atmosphere is presented.

Wakelyn, N. T.↗
NASA NTRS2005

Analysis of Carbon/Carbon Fragments From the Columbia Tragedy

The extensive investigation following the Space Shuttle Orbiter Columbia accident of February 1, 2003 determined that hot gases entered the wing through a breach in the protective reinforced carbon/carbon (RCC) leading edge. In the current study, the exposed edges of the recovered RCC from the vicinity of the breach are examined with scanning electron microscopy and Raman spectroscopy. Electron microscopy of the exposed edges revealed regions of pointed carbon fibers, characteristic of exposure to high temperature oxidizing gases. The Raman technique relates the observed 1350 and 1580 to 1600 cm(-1) bands to graphitic dom ains and their corresponding temperatures of formation. Some of the regions showed evidence of exposure temperatures beyond 2700 ?C during the accident.

Tallant, David R.↗
NASA NTRS2016

12Cao-7Al2o3 Electride Hollow Cathode

The use of the electride form of 12CaO-7Al.sub.2O.sub.3, or C12A7, as a low work function electron emitter in a hollow cathode discharge apparatus is described. No heater is required to initiate operation of the present cathode, as is necessary for traditional hollow cathode devices. Because C12A7 has a fully oxidized lattice structure, exposure to oxygen does not degrade the electride. The electride was surrounded by a graphite liner since it was found that the C12A7 electride converts to it's eutectic (CA+C3A) form when heated (through natural hollow cathode operation) in a metal tube.

Rand, Lauren P.↗
NASA NTRS2017

12CaO-7Al2O3 Electride Hollow Cathode

The use of the electride form of 12CaO-7Al2O3, or C12A7, as a low work function electron emitter in a hollow cathode discharge apparatus is described. No heater is required to initiate operation of the present cathode, as is necessary for traditional hollow cathode devices. Because C12A7 has a fully oxidized lattice structure, exposure to oxygen does not degrade the electride. The electride was surrounded by a graphite liner since it was found that the C12A7 electride converts to it's eutectic (CA+C3A) form when heated (through natural hollow cathode operation) in a metal tube.

Rand, Lauren P.↗
NASA NTRS1978

Glass matrix composites. I - Graphite fiber reinforced glass

An experimental program is described in which graphite fibers of Hercules HMS and HTS, Thornel 300, and Celanese DG-12 were used to reinforce, both uniaxially and biaxially, borosilicate pyrex glass. Composite flexural strength distribution, strength as a function of test temperature, fracture toughness and oxidative stability were determined and shown to be primarily a function of fiber type and the quality of fiber-matrix bond formed during composite fabrication. It is demonstrated that the graphite fiber reinforced glass system offers unique possibilities as a high performance structural material.

Prewo, K. M.↗
NASA NTRS2002

High-Temperature Intercalated Graphite Fiber Conductors Fabricated

Composites of intercalated graphite fibers show promise to significantly reduce the weight of electromagnetic interference shielding in spacecraft and aircraft. Bromine intercalated pitch-based fibers have been among the most heavily studied systems because of their attractive electrical and thermal conductivities and their stability over a wide range of environmental conditions. Previous studies found that the resistivity of bromineintercalated graphite fibers began to increase when the fibers were exposed to temperatures in excess of about 200 C in air for long periods of time. If the temperature was as high as 450 C, the resistivity increased dramatically within a few hours. It remained unclear, however, whether the increase was due to deintercalation of the bromine or to air oxidation of the fibers. Studies were initially directed toward determining the temperature at which bromine would deintercalate from the fibers, and perhaps become a hazard to both personnel and equipment. So the mass of bromine-intercalated graphite fibers was carefully monitored as it was heated in an inert atmosphere, since the fibers are known to oxidize at a lower temperature than they deintercalate. What was found was that the fibers, which are about 18-wt% bromine, did not lose any appreciable mass even at temperatures approaching 1000 C. X-ray diffraction studies showed that there were also no changes in the overall structure of the compound. Resistivity measurements indicated that there is some slight degradation in the electronic structure, in that the resistivity increased by a few percent. Overall, the results show that these materials may be suitable for applications at temperatures at least this high, provided oxygen is excluded. This may enable their use in carbon-ceramic, and perhaps even carbon-carbon composites.

Gaier, James R.↗
NASA NTRS1972

Development of seal ring carbon-graphite materials (tasks 5, 6, and 7)

Carbon-graphite seal ring bodies for operation at air temperatures to 1300 F(704 C) were manufactured from three select formulations. Mechanical and thermal properties, porosities, and oxidation rates were measured. The results have shown that: (1) Major property improvements anticipated from the screening studies were not realized because of processing problems associated with the scale-up in material size and probable deterioration of a phenolic resin binder; (2) the mechanical properties of a phenolic resin-bonded, carbon-graphite material can be improved by applying high pressure during carbonization; and (3) the textile form of graphite fiber used as the minor filler component in a carbon-graphite material can beneficially affect mechanical properties.

Fechter, N. J.↗
NASA NTRS1997

Mineralogy of Meteorite Groups

Approximately 275 mineral species have been identified in meteorites, reflecting diverse redox environments, and, in some cases, unusual nebular formation conditions. Anhydrous ordinary, carbonaceous and R chondrites contain major olivine, pyroxene and plagioclase; major opaque phases include metallic Fe-Ni, troilite and chromite. Primitive achondrites are mineralogically similar. The highly reduced enstatite chondrites and achondrites contain major enstatite, plagioclase, free silica and kamacite as well as nitrides, a silicide and Ca-, Mg-, Mn-, Na-, Cr-, K- and Ti-rich sulfides. Aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates, complex organic compounds, magnetite, various sulfates and sulfides, and carbonates. In addition to kamacite and taenite, iron meteorites contain carbides, elemental C, nitrides, phosphates, phosphides, chromite and sulfides. Silicate inclusions in IAB/IIICD and lIE iron meteorites consist of mafic silicates, plagioclase and various sulfides, oxides and phosphates. Eucrites, howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides. Ureilttes .are made up mainly of calcic, chromian olivine and low-Ca clinopyroxene embedded in a carbonaceous matrix; accessory phases include the C polymorphs graphite, diamond, lonsdaleite and chaoite as well as metallic Fe-Ni, troilite and halides. Angrites are achondrites rich in fassaitic pyroxene (i.e. , AI-Ti diopside); minor olivine with included magnesian kirschsteinite is also present. Martian meteorites comprise basalts, Iherzolites, a dunite and an orthopyroxenite. Major phases include various pyroxenes and olivine; minor to accessory phases include various sulfides, magnetite, chromite and Ca-phosphates. Lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase. Several meteoritic phases were formed by shock metamorphism. Martensite (a2-fe,Ni) has a distorted body-centered-cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling. The C polymorphs diamond, lonsdaleite and chaoite formed by shock from graphite. Suessite formed in the North Haig ureilite by reduction of Fe and Si (possibly from olivine) via reaction with carbonaceous matrix material. Ringwoodite, the spinel form of (Mg,Fe)2Si04, and majorite, a polymorph of (Mg,Fe)Si03 with the garnet structure, formed inside shock veins in highly shocked ordinary chondrites. Secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hy-. droxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by alteration of troilite.

Rubin, Alan E.↗
NASA NTRS1977

Thermionic converter studies at Thermo Electron

The Thermionic Energy Converter (TEC) development program includes theoretical and experimental surface studies, diode evaluation, enhanced mode converter investigations and system studies, as well as materials fabrication and testing. The primary effort has been concentrated on increasing converter performance via improved electrodes. Diodes with oxide collectors (i.e., tungsten oxide, titanium oxide, zinc oxide and barium oxide) have provided the best performance. Emitters requiring reduced cesium pressure (such as oxygenated tungsten, lanthanum hexaboride, platinum and graphite) are being tested. Converter configurations using particle spacing are under investigation. Experiments with auxiliary electrode thermionic converters are in progress. Both silicon carbide and alloy hot shells (i.e., barriers to isolate the converter from the combustion environment) have been fabricated and tested.

Huffman, F. N.↗
NASA NTRS1998

Adjusting Measured Weight Loss of Aged Graphite Fabric/PMR-15 Composites

The purposes of this study were to evaluate the growth of the surface damage layer in polymer matrix composites (PMC's) fabricated with graphite fabric reinforcement and to determine the effects of the cut-surface degradation on the overall thermo-oxidative (TOS) stability of these materials. Four important conclusions were made about the TOS behavior of T650-35/PNIR- 15 fabric-reinforced composites: (1) Three stages of composite weight loss were seen on the plot of weight loss versus aging time; (2) the depth of the cut-edge damage is related to the composite thickness; (3) the actual weight loss realized by a mechanical test specimen that has had all the aging-induced cut-edge damage removed during the preparation process is significantly less than the weight loss measured using specimens with a high percentage of cut edges exposed to the damaging environment; and (4) an extrapolation of a section of the weight loss curve can be used to obtain a more correct estimate of the actual weight loss after extended periods of aging at elevated temperatures.

Bowles, Kenneth J.↗
NASA NTRS2012

Advanced Ceramics for Use as Fuel Element Materials in Nuclear Thermal Propulsion Systems

With the recent start (October 2011) of the joint National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) Advanced Exploration Systems (AES) Nuclear Cryogenic Propulsion Stage (NCPS) Program, there is renewed interest in developing advanced ceramics for use as fuel element materials in nuclear thermal propulsion (NTP) systems. Three classes of fuel element materials are being considered under the NCPS Program: (a) graphite composites - consisting of coated graphite elements containing uranium carbide (or mixed carbide), (b) cermets (ceramic/metallic composites) - consisting of refractory metal elements containing uranium oxide, and (c) advanced carbides consisting of ceramic elements fabricated from uranium carbide and one or more refractory metal carbides [1]. The current development effort aims to advance the technology originally developed and demonstrated under Project Rover (1955-1973) for the NERVA (Nuclear Engine for Rocket Vehicle Application) [2].

Valentine, Peter G.↗
NASA NTRS1962

PYROLYTIC GRAPHITE ROCKET THRUST CHAMBER INVESTIGATION PROJECT. MONTHLY LETTER

This is the Monthly Letter Progress Report for the eighth month of a twelve month technical study directed toward the following objectives: A. Determining analytically and experimentally the feasibility and attractiveness of using free-standing pyrolytic graphite for a radiation cooled liquid rocket thrust chamber and exit nozzle for space application. B. Establishing through analysis and experimental demonstration, a set of design principles to facilitate the design of a reliable pyrolytic graphite thrust chamber assembly for a specific range of operating conditions. C. Demonstrate by means of test firings of complete thrust chamber assemblies, the validity of the design data and principles developed during the program. Preparations have been completed for test firing the two 100 lb. thrust Boron Pyralloy chambers at Marquardt during the first week in March 1962. These two chambers will first be static pressure checked with water to a pressure of 135 psig. The chambers will then be test fired with N204/N2H4-MMH propellants . Test samples of eleven different pyrolytic carbide and nitride materials have been ordered for high temperature oxidation tests and should be delivered by the end of March for evaluation in the plasma torch facility. The specific materials ordered in free- standing condition in thicknesses from 0.030 inch to 0.065 inch were as follows: (a) Pyrolytic graphite (on hand) (b) Pyrolytic graphite-boron alloy (on hand) (c) Pyrolytic graphite-tungsten alloy (d)Boron nitride (e) Titanium nitride (f) Silicon carbide (g) Titanium carbide (h) Zirconium carbide (i) Hafnium carbide (j) Niobium carbide (k) Tantalum carbide (l) High density (1 1-90) graphite (m) High density graphite (heat treated) These materials were ordered from Raytheon, HTM, and American Meta 1 Products . A summary of the available data on the oxidation rates of pyrolytic materials under slow air and rocket motor conditions is shown in Figure 1. High Temperature Materials, Inc. has been contacted relative to providing Pyrographite thrust chambers with extra-thick walls . They believe they can deliver chambers with substantially thicker walls than were possible a short time ago. Such a configuration, with acceptable residual stresses, would provide a longer firing life since it is ultimately limited by the oxidation rate of the chamber wall material. Stress and structural studies have continued. The analytical stress studies point out some of the problems associated with the experimental determination of the elastic constants of this highly anisotropic material. Further analysis may shed light on improved techniques for making these experimental determinations. The large potential weight saving available with the use of pyrolytic graphite as a thrust chamber wall material in a radiation cooled rocket motor has been calculated and is shown graphically in Figure 2. Figure A presents the program progress schedule and the actual expenditures as of 7 February 1962.

ROCKET ENGINE↗
NASA NTRSDate not supplied

Monitoring of Ionic Silver Biocide with Capacitively-Coupled Contactless Conductivity Detection (C4D)

Monitoring of biocide dosing in spacecraft potable water systems is desirable to ensure dosing system operation and resultant microbial control. Electrolytic conductivity is linearly related to the concentration ionic silver (Ag+, the baseline biocide for future NASA missions) chemically dosed into highly purified water, and could serve as a proxy measurement. Traditional conductivity cells rely on immersed metal or graphite electrodes, which may potentially be subject to significant current-induced or auto-galvanic deposition of Ag+. Furthermore, oxide fouling may potentially induce measurement errors. Capacitively-coupled contactless conductivity detection (C4D) is a promising alternative. C4D uses electrodes placed outside an inert, non-conductive flow path, potentially mitigating such problems. We identified and purchased a commercial C4D system with claimed performance (conductivity range: 20 nS/cm to 4 µS/cm) appropriate for this application. We characterized the instrument’s performance with conductivity standards and Ag+ solutions. We began investigations considering practical and long-term detector operation, including potential current-induced deposition of conductive deposits at the tubing wall. In addition, we designed a side-stream flow system to provide liquid flow through the narrow tubing (1/16” outer diameter) required by the detector and characterized the performance of the combined C4D detector/flow system. Finally, we completed theoretical modeling of expected conductivity change with multiple dosing techniques and water chemistries.

Lance Dean Delzeit↗
NASA NTRS1990

Aeolian removal of dust from radiator surfaces on Mars

Simulated radiator surfaces made of arc-textured Cu and Nb-1 percent-Zr and ion beam textured graphite and C-C composite were fabricated and their integrated spectral emittance characterized from 300 to 3000 K. A thin layer of aluminum oxide, basalt, or iron (III) oxide dust was then deposited on them, and they were subjected to low pressure winds in the Martian Surface Wind Tunnel. It was found that dust deposited on simulated radiator surfaces may or may not seriously lower their integrated spectral emittance, depending upon the characteristics of the dust. With Al2O3 there is no appreciable degradation of emittance on a dusted sample, with basaltic dust there is a 10 to 20 percent degradation, and with Fe2O3 a 20 to 40 percent degradation. It was also found that very high winds on dusted highly textured surfaces can result in their abrasion. Degradation in emittance due to abrasion was found to vary with radiator material. Arc-textured Cu and Nb-1 percent Zr was found to be more susceptible to emittance degradation than graphite or C-C composite. The most abrasion occurred at low angles, peaking at the 22.5 deg test samples.

Gaier, James R.↗
NASA NTRS1991

Pretreatment of lubricated surfaces with sputtered cadmium oxide

Cadmium oxide is used with a dry solid lubricant on a surface to improve wear resistance. The surface topography is first altered by photochemical etching to a predetermined pattern. The cadmium oxide is then sputtered onto the altered surface to form an intermediate layer to more tightly hold the dry lubricant, such as graphite.

Fusaro, Robert L.↗
NASA NTRS1992

Structure-to-property relationships in addition cured polymers. 4: Correlations between thermo-oxidative weight losses of norbornenyl cured polyimide resins and their composites

Relationships are identified between the thermo-oxidative stability (TOS) at 316 C of a wide variety of PMR (polymerization of monomeric reactants) addition cured polyimide resins and their corresponding graphite fiber composites. Weight loss results at 316 C confirmed the expected relationship of increasing aliphatic endcap content with decreasing TOS. Moreover, the resin TOS study also showed an unexpected linear correlation of decreasing weight loss to increasing ratio of benzylic diamine to aliphatic endcap in the range of the stoichiometries studied. Only after long term 316 C aging does the dianhydride used with the benzylic diamines become an additional factor in influencing the amount of PMR resin and composite weight losses. Also, the benzylic systems consistently showed much lower resin and composite weight losses at 316 C than the corresponding nonbenzylic norbornenyl resins and composites, except when the nonbenzylic diamine monomer does not contain a connecting group. Instead, this diamine resulted in a 316 C resin and composite weight loss that was only competitive with benzylic type diamines. Results show excellent correlation between TOS of all graphite fiber PMR composites and resins.

Alston, William B.↗