Search NASA⌕ Search

SEARCH · Search NASA

Results for “Atmospheric sintering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Friction and wear of sintered Alpha SiC sliding against IN-718 alloy at 25 to 800 C in atmospheric air at ambient pressure

The sliding friction and wear of the SiC-nickel based alloy IN-718 couple under line contact test conditions in atmospheric air at a linear velocity of 0.18 m/sec and a load of 6.8 kg (67N) was investigated at temperatures of 25 to 800 C. It was found that the coefficient of friction was 0.6 up to 350 C then decreased to 0.3 at 500 and 800 C. It is suggested that the sharp decrease in the friction in the range of 350 to 550 C is due to the lubrication value of oxidation products. The wear rate reaches a minimum of 1 x 10 to the -10 to 2 x 10 to the -10 cu cm/cm/kg at 400 to 600 C.

Deadmore, Daniel L.↗
NASA NTRS1984

Silicon carbide material sintered bodies manufacturing

A method is described for producing a high density silicon carbide sintering substance which contains aluminum oxide. The sintering is done in CO gas atmosphere, which is kept at 2 to 20 atmospheric pressures.

Suzuki, K.↗
NASA NTRS1991

Synthesis of Y1BaCu3O(x) superconducting powders by intermediate phase reactions

A procedure for synthesizing Y1Ba2Cu3O(x) by solid state reactions was developed. The method is based on the use of barium compounds, previously synthesized, as intermediate phases for the process. The reaction kinetics of this procedure were established between 860 C and 920 C. The crystal structure and the presence of second phases were studied by means of XRD. The sintering behavior and ceramic parameters were also determined. The orthorhombic type-I structure was obtained on the synthesized bodies after a cooling cycle in an air atmosphere. Superconducting transition took place at 91 K. Sintering densities higher than 95 percent D sub th were attained at temperatures below 940 C.

Moure, C.↗
NASA NTRS1986

Sintering, microstructural, radiographic, and strength characterization of a high-purity Si3N4-based composition

A commercially available high purity alpha-Si3N4 powder (UBE SN-E10) was characterized, milled with additives, and sintered in a high-pressure nitrogen atmosphere at temperatures ranging from 1750 to 2140 C. The composition selected for this study has been previously examined using a different alpha-Si3N4 powder. Densification behavior, microstructure characteristics, X-radiographic appearance, room- and high-temperatures flexural strength, and fracture-initiating flaw sites were determined. The high-temperature flexural strengths significantly exceeded those observed in the earlier studies using an identical composition (different alpha-Si3N4 powder) and similar processing techniques.

Kiser, J. D.↗
NASA NTRS1986

Effect of impregnation method on cycle life of the nickel electrode

The nickel electrode has been identified as the life limiting component for individual pressure vessel (IPV) nickel-hydrogen cells when cycled under a low earth orbit (LEO) cycle regime at deep depths of discharge. As a part of an overall program to develop a long life nickel electrode for nickel-hydrogen cells, the effect of two different methods of electrochemical impregnation on the cycle life of the nickel electrode was investigated. One method was the Pickett (aqueous/ethanolic) process. The other was the modified Bell (aqueous) process. The plaques for both impregnation methods were made by sintering dry carbonyl nickel powder in a reducing atmosphere. The plaques contain a nickel screen substrate. Electrodes made from both processes were cycle tested in Air Force design IPV nickel-hydrogen cells. The only factor different for this test was the method of plaque impregnation; all other factors were the same. The cells were cycled to failure under a 90 min LEO cycle regime at a deep depth of discharge (80 percent DOD). Failure for this test was defined to occur when the cell voltage degraded to 1.0 V prior to the completion of the 35 min discharge.

Smithrick, J. J.↗
NASA NTRS1986

Effect of impregnation method on cycle life of the nickel electrode

The nickel electrode has been identified as the life limiting component for individual pressure vessel (IPV) nickel-hydrogen cells when cycled under a low earth orbit (LEO) cycle regime at deep depths of discharge. As a part of an overall program to develop a long life nickel electrode for nickel-hydrogen cells, the effect of two different methods of electrochemical impregnation on the cycle life of the nickel electrode was investigated. One method was the Pickett (aqueous/ethanolic) process. The other was the modified Bell (aqueous) process. The plaques for both impregnation methods were made by sintering dry carbonyl nickel powder in a reducing atmosphere. The plaques contain a nickel screen substrate. Electrodes made from both processes were cycle tested in Air Force design IPV nickel-hydrogen cells. The only factor different for this test was the method of plaque impregnation; all other factors were the same. The cells were cycled to failure under a 90 min LEO cycle regime at a deep depth of discharge (80 percent DOD). Failure for this test was defined to occur when the cell voltage degraded to 1.0 V prior to the completion of the 35 min discharge.

Smithrick, J. J.↗
NASA NTRS1984

Sinterability, strength and oxidation of alpha silicon carbide powders

An investigation is made of pressureless sintering of commercially available alpha-SiC powders at temperatures between 1900 and 2150 C for periods of 10 to 240 min under one atmosphere of argon pressure. It is found that alpha-SiC powder containing boron and carbon sintering aids is sinterable at 2150 C for a period of 30 min to a high final density (greater than 96 percent of theoretical). In alpha-SiC powder containing aluminum and carbon sintering aids, the final density achieved is only about 80 percent of theoretical. Determinations are made of room temperature and high temperature (1370 C) flexure strength and oxidation resistance on sintered high density (more than 96 percent of theoretical) alpha-SiC (boron, carbon) material. It is found that both the strength and the resistance to oxidation are equivalent and comparable to those of the sintered alpha-SiC which represents the state of the art.

Dutta, S.↗
NASA NTRS1994

Ultra high purity, dimensionally stable INVAR 36

An INVAR 36 material having long-term dimensional stability is produced by sintering a blend of powders of nickel and iron under pressure in an inert atmosphere to form an alloy containing less than 0.01 parts of carbon and less than 0.1 part aggregate and preferably 0.01 part individually of Mn, Si, P, S and Al impurities. The sintered alloy is heat treated and slowly and uniformly cooled to form a material having a coefficient of thermal expansion of less than 1 ppm/C and a temporal stability of less than 1 ppm/year.

Sokolowski, Witold M.↗
NASA NTRS1995

Ultra high purity, dimensionally stable INVAR 36

An INVAR 36 material having long-term dimensional stability is produced by sintering a blend of powders of nickel and iron under pressure in an inert atmosphere to form an alloy containing less than 0.01 parts of carbon and less than 0.1 part aggregate and preferably 0.01 part individually of Mn, Si, P, S and Al impurities. The sintered alloy is heat treated and slowly and uniformly cooled to form a material having a coefficient of thermal expansion of less than 1 ppm/C and a temporal stability of less than 1 ppm/year.

Sokolowski, Witold M.↗
NASA NTRS1979

Formation of porous surface layers in reaction bonded silicon nitride during processing

An effort was undertaken to determine if the formation of the generally observed layer of large porosity adjacent to the as-nitride surfaces of reaction bonded silicon nitrides could be prevented during processing. Isostatically pressed test bars were prepared from wet vibratory milled Si powder. Sintering and nitriding were each done under three different conditions:(1) bars directly exposed to the furnance atmosphere; (2) bars packed in Si powder; (3) bars packed in Si3N4 powder. Packing the bars in either Si of Si3N4 powder during sintering retarded formation of the layer of large porosity. Only packing the bars in Si prevented formation of the layer during nitridation. The strongest bars (316 MPa) were those sintered in Si and nitrided in Si3N4 despite their having a layer of large surface porosity; failure initiated at very large pores and inclusions. The alpha/beta ratio was found to be directly proportional to the oxygen content; a possible explanation for this relationship is discussed.

Shaw, N. J.↗
NASA NTRS1986

Silicon carbide sintered products and a method for their manufacturing

SiC based sinters are produced by pressureless sintering from a SiC-AlN solid solution containing Al2 to 20, N 0.2 to 10, O 0.2 to 5, a Group IIIB element 0 to 15 percent, the remainder being Si and C. Thus, a 90:10 mixture of SiC and AlN powders were cold pressed at 2000 kg/sq cm and sintered for 5 hours at 2100 C in a nitrogen atmosphere. The resulting product had density of 3.11 g/cu cm and bending strength at ambient and 1400 C at 68.5 and 66.3 kg/sq mm.

Suzuki, K.↗
NASA NTRS1984

Gas pressure sintering of Beta-Sialon with Z=3

An experiment conducted on beta-sialon in atmospheric pressure, using a temperature of 2000 C and 4 MPa nitrogen atmosphere, is described. Thermal decomposition was inhibited by the increase of the nitrogen gas pressure.

Tani, E.↗
NASA NTRS1975

Fluid transport on earth and aeolian transport on Mars

Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars - in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect.

Sagan, C.↗
NASA NTRS1985

Manufacture of dense sintered bodies containing silicon nitride

Sintered bodies containing 1-32.5 Si oxide and 1.5 wt.% SiC (Si oxide/SiC wt. ratio 3/2) are prepared and kept in a 10-3000 kg/2 sq. cm. N (g) atmosphere at 1500-2300 degrees, while simultaneously maintaining the CO (g) partial pressure around the body lower than the nitrogenation equil. pressure to give a dense sintered body. The prepared dense sintered body has high strength at high temperatures. Thus, SiC 40, oxide 30 and Si3N4 30 wt% were fired to a body which was kept in 1500 kg/sq. cm. N (g) for 20 h at 2000 degrees to give a dense sintered body having high bending strength at high temperatures.

Hirota, K.↗
NASA NTRS1982

Study of alumina-trichite reinforcement of a nickel-based matric by means of powder metallurgy

Research was conducted on reinforcing nickel based matrices with alumina trichites by using powder metallurgy. Alumina trichites previously coated with nickel are magnetically aligned. The felt obtained is then sintered under a light pressure at a temperature just below the melting point of nickel. The halogenated atmosphere technique makes it possible to incorporate a large number of additive elements such as chromium, titanium, zirconium, tantalum, niobium, aluminum, etc. It does not appear that going from laboratory scale to a semi-industrial scale in production would create any major problems.

Walder, A.↗
NASA NTRS1985

Hot corrosion of sintered alpha-SiC at 1000 C

The hot corrosion of sintered alpha-SiC by thin films of Na2SO4 and Na2CO3 was studied at 1000 C in controlled gas atmospheres. Under all conditions, corrosion led to 10 to 20 times the amount of SiO2 formed in pure oxidation after a 48-h exposure. In addition, small amounts of sodium silicate formed. Melts of Na2SO4/SO3 caused uniform pitting of the SiC substrate; Na2CO3/CO2 melts caused localized pitting and grain-boundary attack. In all cases, the protective SiO2 layer dissolved to form silicate, leading to corrosion. In the sulfate case, free carbon in the SiC promotes this process. In all cases the presence of liquid films is responsible for rapid transport rates and the subsequent rapid reaction.

Jacobson, N. S.↗
NASA NTRS2016

Atmospheric Pressure Plasma Jet as a Dry Alternative to Inkjet Printing in Flexible Electronics

We have developed an atmospheric pressure plasma jet printing system that works at room temperature to 50 deg C unlike conventional aerosol assisted techniques which require a high temperature sintering step to obtain desired thin films. Multiple jets can be configured to increase throughput or to deposit multiple materials, and the jet(s) can be moved across large areas using a x-y stage. The plasma jet has been used to deposit carbon nanotubes, graphene, silver nanowires, copper nanoparticles and other materials on substrates such as paper, cotton, plastic and thin metal foils.

Printable electronics↗