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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Diamond-Coated Carbon Nanotubes for Efficient Field Emission

Field-emission cathodes containing arrays of carbon nanotubes coated with diamond or diamondlike carbon (DLC) are undergoing development. Multiwalled carbon nanotubes have been shown to perform well as electron field emitters. The idea underlying the present development is that by coating carbon nanotubes with wideband- gap materials like diamond or DLC, one could reduce effective work functions, thereby reducing threshold electric-field levels for field emission of electrons and, hence, improving cathode performance. To demonstrate feasibility, experimental cathodes were fabricated by (1) covering metal bases with carbon nanotubes bound to the bases by an electrically conductive binder and (2) coating the nanotubes, variously, with diamond or DLC by plasma-assisted chemical vapor deposition. In tests, the threshold electric-field levels for emission of electrons were reduced by as much as 40 percent, relative to those of uncoated- nanotube cathodes. Coating with diamond or DLC could also make field emission-cathodes operate more stably by helping to prevent evaporation of carbon from nanotubes in the event of overheating of the cathodes. Cathodes of this type are expected to be useful principally as electron sources for cathode-ray tubes and flat-panel displays.

Dimitrijevic, Stevan↗
NASA NTRS2016

Fabrication of High Thermal Conductivity NARloy-Z-Diamond Composite Combustion Chamber Liner for Advanced Rocket Engines

NARloy-Z alloy (Cu-3 percent, Ag-0.5 percent, Zr) is a state of the art alloy currently used for fabricating rocket engine combustion chamber liners. Research conducted at NASA-MSFC and Penn State – Applied Research Laboratory has shown that thermal conductivity of NARloy-Z can be increased significantly by adding diamonds to form a composite (NARloy-Z-D). NARloy-Z-D is also lighter than NARloy-Z. These attributes make this advanced composite material an ideal candidate for fabricating combustion chamber liner for an advanced rocket engine. Increased thermal conductivity will directly translate into increased turbopump power and increased chamber pressure for improved thrust and specific impulse. This paper describes the process development for fabricating a subscale high thermal conductivity NARloy-Z-D combustion chamber liner using Field Assisted Sintering Technology (FAST). The FAST process uses a mixture of NARloy-Z and diamond powders which is sintered under pressure at elevated temperatures. Several challenges were encountered, i.e., segregation of diamonds, machining the super hard NARloy-Z-D composite, net shape fabrication and nondestructive examination. The paper describes how these challenges were addressed. Diamonds coated with copper (CuD) appear to give the best results. A near net shape subscale combustion chamber liner is being fabricated by diffusion bonding cylindrical rings of NARloy-Z-CuD using the FAST process.

Bhat, Biliyar N.↗
NASA NTRS2016

Fabrication of High Thermal Conductivity NARloy-Z-Diamond Composite Combustion Chamber Liner for Advanced Rocket Engines

This paper describes the process development for fabricating a high thermal conductivity NARloy-Z-Diamond composite (NARloy-Z-D) combustion chamber liner for application in advanced rocket engines. The fabrication process is challenging and this paper presents some details of these challenges and approaches used to address them. Prior research conducted at NASA-MSFC and Penn State had shown that NARloy-Z-40%D composite material has significantly higher thermal conductivity than the state of the art NARloy-Z alloy. Furthermore, NARloy-Z-40 %D is much lighter than NARloy-Z. These attributes help to improve the performance of the advanced rocket engines. Increased thermal conductivity will directly translate into increased turbopump power, increased chamber pressure for improved thrust and specific impulse. Early work on NARloy-Z-D composites used the Field Assisted Sintering Technology (FAST, Ref. 1, 2) for fabricating discs. NARloy-Z-D composites containing 10, 20 and 40vol% of high thermal conductivity diamond powder were investigated. Thermal conductivity (TC) data. TC increased with increasing diamond content and showed 50% improvement over pure copper at 40vol% diamond. This composition was selected for fabricating the combustion chamber liner using the FAST technique.

Bhat, Biliyar N.↗
NASA NTRS2015

High Thermal Conductivity NARloy-Z-Diamond Composite Liner for Advanced Rocket Engines

NARloy-Z (Cu-3Ag-0.5Zr) alloy is state-of-the-art combustion chamber liner material used in liquid propulsion engines such as the RS-68 and RS-25. The performance of future liquid propulsion systems can be improved significantly by increasing the heat transfer through the combustion chamber liner. Prior work1 done at NASA Marshall Space Flight Center (MSFC) has shown that the thermal conductivity of NARloy-Z alloy can be improved significantly by embedding high thermal conductivity diamond particles in the alloy matrix to form NARloy-Z-diamond composite (fig. 1). NARloy-Z-diamond composite containing 40vol% diamond showed 69% higher thermal conductivity than NARloy-Z. It is 24% lighter than NARloy-Z and hence the density normalized thermal conductivity is 120% better. These attributes will improve the performance and life of the advanced rocket engines significantly. The research work consists of (a) developing design properties (thermal and mechanical) of NARloy-Z-D composite, (b) fabrication of net shape subscale combustion chamber liner, and (c) hot-fire testing of the liner to test performance. Initially, NARloy-Z-D composite slabs were made using the Field Assisted Sintering Technology (FAST) for the purpose of determining design properties. In the next step, a cylindrical shape was fabricated to demonstrate feasibility (fig. 3). The liner consists of six cylinders which are sintered separately and then stacked and diffusion bonded to make the liner (fig. 4). The liner will be heat treated, finish-machined, and assembled into a combustion chamber and hot-fire tested in the MSFC test facility (TF 115) to determine perform.

Bhat, Biliyar↗
NASA NTRS2004

The L1 diamond affair

The L1 Diamond is a configuration of four solar sail spacecraft traveling in approximately a diamond arrangement and situated on the Sun side of the Sun-Earth L1 Lagrange point. The purpose of this diamond arrangement will be to determine the large scale three-dimensional structure of solar disturbances propagated toward the Earth. These spacecraft will have a wide separation of 100 to 500 Earth radii and solar sails will maintain this separation in non-Keplarian orbits. In this paper equations are derived to calculate the solar sail characteristic acceleration as a function of the position in the L1 Diamond formation.

Sauer, Carl G. Jr.↗
NASA NTRS1979

Experiments with diamond-turned metal X-ray mirrors

It is noted that the primary advantages of diamond turning technology for the fabrication of X-ray telescope mirrors is in the smoothness of the finished surface and the control of the position of the cutter afforded by the precision slides and computer-assisted positioners which form the surface. The paper summarizes the Caltech work in attempting to make Wolter Type I telescope mirrors using the diamond turning facilities at the Oak Ridge Y-12 laboratory. Attention is given to such factors as the use of aluminum with copper plating and electroless nickel coating. It is found that although the diamond turning capability of the Y-12 lab is capable of making good X-ray mirror contours, there are problems in the process which have limited the accuracy achieved by this technique.

Garmire, G. P.↗
NASA NTRS1982

The uses of Man-Made diamond in wafering applications

The continuing, rapid growth of the semiconductor industry requires the involvement of several specialized industries in the development of special products geared toward the unique requirements of this new industry. A specialized manufactured diamond to meet various material removal needs was discussed. The area of silicon wafer slicing has presented yet anothr challenge and it is met most effectively. The history, operation, and performance of Man-Made diamond and particularly as applied to silicon wafer slicing is discussed. Product development is underway to come up with a diamond specifically for sawing silicon wafers on an electroplated blade.

Fallon, D. B.↗
NASA NTRS1981

The failure strengths of perfect diamond crystals

Finite elasticity analysis is extended to the 110 direction, where off axis strain symmetry is not present, and the third order elastic data are obtained for diamond. The compressive yield strengths of perfect diamond crystals loaded in the 100, 110, and 111 directions are predicted to be 2.2, 5.6, and 2.8 Mbars, respectively, while the corresponding tensile fracture strengths are 1.0, 0.5, and 0.5 Mbars. From these results and from Hertz theory it is predicted that ring fracture of spherically tipped diamonds pressed against a flat will occur at pressures of 1.8-1.9 Mbars, substantially below the yield pressure (above 3 Mbars). Modification of the tip shape leads to a predicted increase in the pressure at which fracture occurs.

Whitlock, J.↗
NASA NTRS1984

Diamond shines in high-power devices

The 20-W S-band power amplifiers aboard the GOES E and F spacecraft exemplify the problems that type-IIa diamond heat sinks have been developed to solve, including the requirement for junction temperatures to be kept below 125 C. Diamond heat sinks allow high power S-band semiconductors to operate at a flange temperature of 70 C without exceeding the stipulated maximum junction temperature. Type-IIA diamond, which is an excellent electrical insulator, possesses a thermal conductivity four times better than pure copper at 100 C, and outperforms BeO by an even greater margin. Higher costs are offset by high reliability. Attention is presently given to the results of tests conducted by the NASA Goddard Space Flight Center.

Line, L.↗
NASA NTRS1986

A new method for fabrication of diamond-dust blocking filters

Thermal embedding of diamond dust onto a polyethylene-coated Al plate has been used to make a blocking filter for FIR applications. The Al plate is sandwiched between two Mylar 'blankets' and the air between the layers is removed by means of a small vacuum pump. After the polyethylene is heated and softened, the diamond dust is applied to the polyethylene coating using a brush. The optimum diamond dust grain sizes corresponding to polyethylene layer thicknesses of 9-12 microns are given in a table, and the application of the blocking filter to spectrometric measurements in the FIR is described. An exploded view diagram of the layered structure of the blocking filter is provided.

Collard, H. R.↗
NASA NTRS1986

High-pressure ruby and diamond fluorescence - Observations at 0.21 to 0.55 terapascal

A diamond-anvil, high-pressure apparatus was used to extend the upper pressure limit of static laboratory experiments. Shifts of the R1 strong fluorescent line of ruby were observed that correspond to static pressures of 0.21 to 0.55 terapascal (2.1 to 5.5 megabars) at 25 C. Sensitive spectroscopic techniques in the pressure range 0.15 to 0.28 terapascal were used to observe ruby and diamond fluorescence separately; these two fluorescent emissions overlap strongly at high pressures. At pressures greater than approximately 0.28 terapascal, the diamond fluorescence diminished and the ruby fluorescence reappeared strongly. Pressure was determined by extrapolation of the calibrated shift of the ruby R1 line.

Xu, J. A.↗
NASA NTRS1987

Are small diamonds thermodynamically stable in the interstellar medium?

Very small diamond particles (50 A diameter) are shown to be thermodynamically stable with respect to similar sized graphite particles for reasonable values of the surface free energies of diamond and graphite. Small diamonds are likely to be stable against both thermal evaporation and chemical attack in the general interstellar medium. A few of the consequences of these conclusions are examined.

Nuth, Joseph A., III↗
NASA NTRS1988

The nature and origin of interstellar diamond

The C-delta component of the Allende meteorite is a microscopic diamond some of whose properties seem in conflict with those expected of diamond. High spatial resolution analytical data are presented here which may help explain such results. Surface and interfacial carbon atoms in the component, which may comprise as much as 25 percent of the total, impart an 'amorphous' character to some spectral data. These data support the proposed high-pressure conversion of amorphous carbon and graphite into diamonds due to grain-grain collisions in the ISM, although a low-pressure mechanism of formation cannot be ruled out.

Blake, David F.↗
NASA NTRS1988

Growth of diamond by RF plasma-assisted chemical vapor deposition

A system has been designed and constructed to produce diamond particles by inductively coupled radio-frequency, plasma-assisted chemical vapor deposition. This is a low-pressure, low-temperature process used in an attempt to deposit diamond on substrates of glass, quartz, silicon, nickel, and boron nitride. Several deposition parameters have been varied including substrate temperature, gas concentration, gas pressure, total gas flow rate, RF input power, and deposition time. Analytical methods employed to determine composition and structure of the deposits include scanning electron microscopy, absorption spectroscopy, scanning Auger microprobe spectroscopy, and Raman spectroscopy. Analysis indicates that particles having a thin graphite surface, as well as diamond particles with no surface coatings, have been deposited. Deposits on quartz have exhibited optical bandgaps as high as 4.5 eV. Scanning electron microscopy analysis shows that particles are deposited on a pedestal which Auger spectroscopy indicates to be graphite. This is a phenomenon that has not been previously reported in the literature.

Meyer, Duane E.↗
NASA NTRS1988

Elimination of pressure-induced fluorescence in diamond anvils

At pressures above one megabar (100 GPa) in high-pressure diamond anvil cell experiments, the ruby fluorescence signal needed for pressure calibration is increasingly difficult to measure. A primary cause of this difficulty is the presence of an intense pressure-induced diamond fluorescence. A tentative identification of this pressure-induced fluorescence is given, a technique for the elimination of this fluorescence is reported. It is demonstrated that weak ruby signals, completely hidden by diamond fluorescence, are now easily measured with this technique.

Eggert, Jon H.↗
NASA NTRS1989

Diamond films for laser hardening

Laser-damage experiments were performed on free-standing polycrystalline diamond films prepared by plasma-enhanced CVD. The high laser-induced stress resistance found for this material makes it useful for thin-film coatings for laser optics. Results for diamond-coated silicon substrates demonstrate the enhanced damage threshold imparted by diamond thin-film coatings to materials susceptible to laser damage.

Albin, S.↗
NASA NTRS1990

Ubiquitous interstellar diamond and SiC in primitive chondrites - Abundances reflect metamorphism

It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains.

Huss, Gary R.↗