Engineering topics

Gaier, J. R.

Publications and source records attributed to Gaier, J. R..

At least 19 records

NASA NTRS2014

Conductivity and Ambient Stability of Halogen-Doped Carbon Nanotube Fibers

Carbon nanotube fibers were fabricated using a variety of spinning conditions and post-spinning processing with the goal of creating a high-conductivity yet environmentally stable fiber. These fiber variants were then doped with bromine, iodine, iodine chloride, or iodine bromide and their electrical and microstructural properties were characterized. Environmentally stable compounds were synthesized with electrical conductivity greater than 50,000 Scm.

carbon fibers↗

NASA NTRS2009

What We Do Not Know and Probably Need to Know

By far the most important database to help us determine the engineering questions we need to address comes from the Apollo experience. In combing through the Apollo Mission Reports and Technical Debriefings there are numerous references to the problems caused by lunar dust during the missions. These have been sorted into nine classes of difficulties.

Gaier, J. R.↗

NASA NTRS1994

Durability of Carbon-Carbon Composites to a Simulated Martian Atmosphere

A new facility was designed and constructed to investigate the effects of the Martian atmosphere on high temperature radiator components. Preliminary experimental results from carbon-carbon composite radiator samples suggest that carbon is unstable in the simulated Martian atmosphere at a temperature of 600 C, consistent with previous thermodynamic modeling. However, more work is needed to identify the exact mechanism. The versatile design of the facility permits additional study of materials stability in the presence of other atmospheres.

Jaworske, D. A.↗

NASA NTRS1991

Effects of Martian dust on power system components

Before large power systems for manned exploration of the Martian surface can be put into place, it must be determined how their performance will be affected by the Martian environment. A program was started to assess the impact of these environmental factors on power system performance, and to find ways to mitigate the degradative effects. The effects of blowing dust on photovoltaic (PV) and radiator surfaces is studied. Extensive use was made of the Martian Surface Wind Tunnel (MARSWIT) located at NASA-Ames to simulate Martian winds. Two basic types of experiment sets were run. In the first, the threshold clearing velocity of dust deposited on PV coverslip material and high emissivity radiator materials in clear Martian-like winds was examined. In the second, dust was dropped near the inlet of the wind tunnel and the winds were allowed to carry the dust past the samples, simulating a dust storm. A summary of results is given.

Gaier, J. R.↗

NASA NTRS1989

Properties of Pb(1-x)Bi(x)/Ba2YCu3O(x) composites - Reaction of Ba2YCu3O(x) with Pb and Bi

This paper describes experiments conducted with a purpose of fabricating superconducting composites from Pb, Bi, and Ba2YCu3O(x), together the results of SEM examinations and energy dispersive spectroscopy performed on products. Results showed a limited utility of Pb and Pb(1-x)Bi(x) as matrices for ceramic superconductors. It was found that cold pressing followed by sintering at 200 C resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal superconducting transition. Processing at 400 or 950 C resulted in oxygen depleted perovskite and/or metal oxides; these materials displayed greatly degraded superconducting properties. Finally, processing at 800 C resulted in high Tc only for composites containing more than 90 wt pct ceramic.

Hepp, A. F.↗

NASA NTRS1988

Synthesis and structural chemistry of Au(III)-substituted Ba2YCu3O(7-delta)

Gold-substituted superconductors, Ba2Y(Au(x)Cu(1-x))3O(7-delta) (x = 0-0.1) were synthesized. For x = 0.1, there was no change in the a and b lattice parameters (a = 3.826 A and b = 3.889 A) but a 0.06 A c axis expansion to 11.75 A was observed. Substituted gold is found to be trivalent by XPS. Replacing Cu(1) in the copper oxide chain with a slight reordering of oxygen is consistent with c axis expansion. The formal charge of the site remains trivalent; remaining Cu in the chains may be reduced resulting in an oxygen stoichiometry is less than or equal to 7. A small effect on T(sub c)(89 K for x = 0.10) is observed upon gold substitution.

Hepp, A. F.↗

NASA NTRS1988

Advantages of barium peroxide in the powder synthesis of perovskite superconductors

This paper compares reaction chemistry, material processing, and material characteristics for the solid state reaction using BaCO3 or BaO2 in the synthesis of perovskite superconductors. Results are presented for weight loss and X-ray diffraction, sample morphology and homogeneity as monitored by SEM and EDS, and the superconductivity critical temperature and ac susceptibility. Greater mass density, increased sample homogeneity, lower resistance, and improved reproducibility for material are found when BaO32 is used.

Hepp, A. F.↗

NASA NTRS1988

Characterization of Ba2YCu3O(7-x) prepared in an inert atmosphere

Reaction data, X-ray data, and critical temperature measurements have been used to show that superconducting Ba2YCu3O(7-x) can be produced in an inert atmosphere using BaO2 as the barium source. Weight loss data are presented for samples produced in O2 and N2. The use of BaO2 is found to result in decreased levels of intergrain BaCO3. The necessity for total inert atmosphere handling and tighter control of the carbon content of starting materials is pointed out. It is shown that materials made with BaO2 and handled in inert atmospheres can be used to improve the J sub c of melt processed materials.

Hepp, A. F.↗

NASA NTRS1988

Structural chemistry of Au(III)-substituted Ba2YCu3O(7-delta)

A series of gold-substituted perovskite superconductors Ba2Y(Cu/1-x/Aux)3O(7-delta)(x = 0-0.1) was synthesized. For x = 0.1, there was no change in the a and b lattice parameters (a = 3.826 A and b = 3.889 A), but a 0.06 A c-axis expansion to 11.75 A was observed. Substituted gold was found to be trivalent by X-ray photoelectron spectroscopy. Replacing Cu(1) in the copper oxide chain with a slight reordering of oxygen is consistent with c-axis expansion. The formal charge of the site remains trivalent, while remaining Cu in the chains is reduced to Cu(I), resulting in an oxygen stoichiometry of less than 7. Finally, no large effect on Tc is observed (Tc = 89 K for x = 0.10), in contrast to the effect of a number of other metal ion dopants. These results are discussed relative to the chemistry of Au(III) and to the use of the metal in structures containing gold and ceramic superconductors.

Hepp, A. F.↗

NASA NTRS1988

Interaction of Au, Ag, and Bi ions with Ba2YCu3O(7-y) - Implications for superconductor applications

Results are presented on the reactions of Au, Ag, and Bi ions with Ba2YCu3O(7-y) oxides and on the properties of the resultant materials. The results indicate that Au(3+) structural chemistry makes gold an excellent candidate for multiphase structures of the Ba2Y(Cu/1-x/Au/x/)3O(7-y)-type substituted superconductors. Silver is structurally and chemically compatible with the perovskite structure, but when it forms a second phase, it does so without the destruction of the superconducting phase, making silver a useful metal for metal/ceramic applications. On the other hand, bismuth was shown to degrade Tc phase or to form other phases, indicating that it may not be useful in applications with rare-earth-based superconductors.

Hepp, A. F.↗

NASA NTRS1988

Improved synthesis of ceramic superconductors with alkaline earth peroxides - Synthesis and processing of Ba2YCu3O(7-x)

Synthesis processes for the preparation of ceramic conductors Ba2YCu3O(7-x) from BaO2 or BaCO3 in flowing O2 or N2 are described, and the characteristics of the materials produced in these processes are compared. Results of EDAX, XRD, SEM, and dc resistivity analyses demonstrated that superconducting materials made from BaO2 were more homogeneous, denser, and more metallic than materials produced from BaCO3, because of the higher reactivity of BaO2. Potential applications of this processes are discussed.

Hepp, A. F.↗

NASA NTRS1987

Microstructure-derived macroscopic residual resistance of brominated graphite fibers

The microscopic bromine distribution in pitch-based brominated graphite fibers has been measured with a scanning transmission electron microscope by monitoring the Br K alpha1 X-ray intensity. An imhomogeneous distribution of Br along the fiber is found with two distinct cross-sectional distributions, namely, a uniform distribution in Br-rich regions and a Gaussian-like distribution in Br-poor regions. A model based on these Br distribution measurements is proposed to understand the relation between the Br microstructure and the macroscopic residual resistance of the fiber. This model yields semiquantitative agreement with experimental results.

Qian, X. W.↗

NASA NTRS1987

Differential scanning calorimetric survey of brominated PAN, pitch-based and vapor-grown fibers

A differential scanning calorimetric survey of brominated PAN, pitch-based and vapor-grown fibers revealed that only vapor-grown fibers heat-treated to temperatures of 2250 C or above exhibited the phase change at 100 C associated with the two-dimensional melting of bromine, similar to that observed in HOPG. All the pitch-based fibers tested, as well as vapor-grown fibers annealed to 2250 C, showed a substantial decrease in resistivity upon bromination but gave no indication of a phase change, suggesting that the bromine in these fibers does not have the long-range order needed to undergo two-dimensional melting. The brominated PAN fibers and unannealed vapor-grown fibers showed no phase change and no change in resistivity, indicating that these fibers do not intercalate bromine.

Jaworske, D. A.↗

NASA NTRS1986

Properties and potential applications of brominated P-100 carbon fibers

A review of the properties and potential applications of bromine-intercalated pitch-based carbon fibers is presented. The dynamics of the intercalation reaction are summarized, and characteristics, such as resistivity, density, and stability, are discussed. In addition, the mechanical and electrical properties of bromine-intercalated fiber-epoxy conposites will be addressed. With conductivities comparable to stainless steel, these brominated carbon fibers may be used in a number of composite applications, such as electromagnetic interference shielding containers, large conductive space structures, lightning strike-tolerant aircraft surfaces, and aircraft deicing applications.

Jaworske, D. A.↗

NASA NTRS1986

The milling of pristine and brominated P-100 graphite fibers

Techniques were developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubrication properties of graphite, large ball loads (50 percent by volume) were required. Use of 2-propanol as a milling medium enhanced the efficiency of the process. Milled brominated P-100 fibers had resistivities which were indistinguishable from milled pristine P-100 fibers. Apparent loss of bromine from the brominated fibers suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. Other intercalates which do not degas may be more appropriate for a milled fiber application. These same results, however, do provide evidence that bromine molecules leave the fiber surface when removed from overpressure of bromine. While exploring possible solvent media for milling purposes, it was found that brominated fibers are stable in a wide variety of organic solvents.

Dillehay, M. E.↗

NASA NTRS1986

A comparison of the bromination dynamics of pitch-based and vapor-grown graphite fibers

The electrical resistance of pitch based P-100 fibers and experimental organic vapor grown fibers was recorded in-situ during bromination and subsequent exposure to ambient laboratory air. The results indicate that the bromination and debromination reactions proceed much slower for vapor grown fibers than for pitch based. While this may be due in part to the larger diameter of the vapor grown fibers, the majority of the effect can probably be attributed to the differences in graphene plane orientation between the fiber types. Although the reactions are slower in the vapor grown than in the pitch based fibers, the extent of reaction as measured by the change in electrical resistance is essentially the same, with comparable (or larger) decreases in resistivity. The bromination reaction proceeds with one or more plateaus in the resistance versus time curves, which suggests staging and strengthens the argument that these fibers produce true intercalation compounds.

Gaier, J. R.↗

NASA NTRS1986

Effects of graphitization on the environmental stability of brominated pitch-based fibers

The residual bromine graphite intercalation compounds of high modulus pitch-based fibers (Amoco P-55, P-75, P-100, and P-120) were formed and their resistances were monitored under a variety of environmental conditions. A threshold graphitization was observed below which the bromination reaction does not occur to an appreciable extent. The graphitization of the P-55 fibers falls below that threshold, precluding an extensive reaction. The P-75, P-100, and P-120 fibers all form bromination compounds which are stable at ambient conditions, under vacuum, and under high humidity (100 percent humidity at 60 C). The thermal stability of the resistivity increased with decreasing graphitization, with the stable temperature for P-120 being 100 C; for P-100, 200 C; and for P-75, 250 C. When cost is a consideration, bromination of pitch-based fibers is an economical way to achieve low resistivities.

Gaier, J. R.↗

NASA NTRS1985

Environmental stability of intercalated graphite fibers

Graphite fibers intercalated with bromine, iodine monochloride, ferric chloride, and cupric chloride were subjected to stability tests under four environments which are encountered by engineering materials in the aerospace industry: ambient laboratory conditions, as would be experienced during handling operations and terrestrial applications; high vacuum, as would be experienced in space applications; high humidity, as would be experienced in marine applications; and high temperature, as would be experienced in some processing steps and applications. Monitoring the resistance of the fibers at ambient laboratory conditions revealed that only the ferric chloride intercalated fibers were unstable, due to absorption of water from the air. All four types of intercalated fibers were unstable, due to absorption of water from the air. All four types of intercalated fibers were stable for long periods under high vacuum. Ferric chloride, cupric chloride, and iodine monochloride intercalated fibers were sensitive to high humidity conditions. All intercalated fibers began to degrade above 250 C. The order of their thermal stability, from lowest to highest, was cupric chloride, iodine monochloride, bromine, and ferric chloride. Of the four types of intercalated fibers tested, the bromine intercalated fibers appear to have the most potential for application, based on environmental stability.

Gaier, J. R.↗