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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

The catalytic removal of ammonia and nitrogen oxides from spacecabin atmospheres

Investigations were made on methods for the removal of ammonia and to a lesser extent nitrogen oxides in low concentrations from air. The catalytic oxidation of ammonia was studied over a temperature range of 250 F to 600 F and a concentration range 20 ppm to 500 ppm. Of the catalysts studied, 0.5 percent ruthenium supported on alumina was found to be superior. This material is active at temperatures as low as 250 F and was found to produce much less nitrous oxide than the other two active catalysts, platinum on alumina and Hopcalite. A quantitative design model was developed which will permit the performance of an oxidizer to be calculated. The ruthenium was found to be relatively insensitive to low concentrations of water and to oxygen concentration between 21 percent and 100 percent. Hydrogen sulfide was found to be a poison when injected in relatively large quantities. The adsorption of ammonia by copper sulfate treated silica gel was investigated at temperatures of 72 F and 100 F. A quantitative model was developed for predicting adsorption bed behavior.

Gully, A. J.↗
NASA NTRS1973

Alloy composition effects on oxidation products of VIA, B-1900, 713C, and 738X: A high temperature diffractometer study

High temperature X-ray diffraction studies were performed to investigate isothermal and cyclic oxidation at 1000 and 1100 C of the nickel-base superalloys VIA, B-1900, 713C, and 738X. Oxidation was complex. The major oxides, Al2O3, Cr2O3, and the spinels, formed in amounts consistent with alloy chemistry. The alloys VIA and B-1900 (high Al, low Cr alloys) tended to form Al2O3 and NiAl2O4; 738X (high Cr, low Al) formed Cr2O3 and NiCr2O4. A NiTa2O6 type of oxide formed in amounts approximately proportional to the refractory metal content of the alloy. One of the effects of cycling was to increase the amount of spinels formed.

Garlick, R. G.↗
NASA NTRS1973

Observation of oxide particles below the apparent oxygen solubility limit in tantalum

The apparent solubility of oxygen in polycrystalline tantalum as determined by the X-ray diffraction lattice parameter technique is about 1.63 atomic percent at 820 C. However, oxide particles were identified in samples containing as low as 0.5 atomic percent of oxygen. These oxide particles were present at the grain boundaries and within the grains. The number of oxide particles increased with increasing oxygen concentration in tantalum. The presence of oxide particles suggests that the true solubility of oxygen in the polycrystalline tantalum metal is probably significantly lower than that reported in the literature.

Stecura, S.↗
NASA NTRS1973

Application of diffusion barriers to the refractory fibers of tungsten, columbium, carbon and aluminum oxide

A radio frequency powered ion-plating system was used to plate protective layers of refractory oxides and carbide onto high strength fiber substrates. Subsequent overplating of these combinations with nickel and titanium was made to determine the effectiveness of such barrier layers in preventing diffusion of the overcoat metal into the fibers with consequent loss of fiber strength. Four substrates, five coatings, and two metal matrix materials were employed for a total of forty material combinations. The substrates were tungsten, niobium, NASA-Hough carbon, and Tyco sapphire. The diffusion-barrier coatings were aluminum oxide, yttrium oxide, titanium carbide, tungsten carbide with 14% cobalt addition, and zirconium carbide. The metal matrix materials were IN 600 nickel and Ti 6/4 titanium. Adhesion of the coatings to all substrates was good except for the NASA-Hough carbon, where flaking off of the oxide coatings in particular was observed.

Douglas, F. C.↗
NASA NTRS1973

A stochastic model of turbulent mixing with chemical reaction: Nitric oxide formulation in a plug-flow burner

A stochastic model of turbulent mixing was developed for a reactor in which mixing is represented by n-body fluid particle interactions. The model was used to justify the assumption (made in previous investigations of the role of turbulent mixing on burner generated thermal nitric oxide and carbon monoxide emissions) that for a simple plug flow reactor, composition nonuniformities can be described by a Gaussian distribution function in the local fuel:air equivalence ratio. Recent extensions of this stochastic model to include the combined effects of turbulent mixing and secondary air entrainment on thermal generation of nitric oxide in gas turbine combustors are discussed. Finally, rate limited upper and lower bounds of the nitric oxide produced by thermal fixation of molecular nitrogen and oxidation of organically bound fuel nitrogen are estimated on the basis of the stochastic model for a plug flow burner; these are compared with experimental measurements obtained using a laboratory burner operated over a wide range of test conditions; good agreement is obtained.

Flagan, R. C.↗
NASA NTRS1974

Effect of chlorine purification on oxidation resistance of some mechanical carbons

Oxidation experiments were conducted with some experimental and commercial mechanical carbons at 650 C in dry air flowing at 28 cc/sec (STP). In general, purification of these carbon-graphites with chlorine at 2800 C improved oxidation resistance. Additional improvements in oxidation resistance were obtained from purification followed by an antioxidant (zinc phosphate) treatment. For the commercial materials, purification alone gave greater oxidation resistance than the antioxidant treatment alone. The reverse, however, was the case for the experimental materials.

Wisander, D. W.↗
NASA NTRS1974

Dynamic oxidation behavior at 1000 and 1100 C of four nickel-base cast alloys, NASA-TRW VIA, B-1900, 713C, and 738X

The superalloys NASA-TRW VIA, B-1900, 713C, and 738X were tested cyclically and isothermally for resistance to oxidation in high velocity gas streams for 100 hours at specimen temperatures of 1000 C and 1100 C. Alloys VIA and B-1900, which were the most oxidation resistant, displayed slight and very similar weight changes and metal losses. Alloy 713C also sustained only slight metal losses, but it exhibited some tendency to spall. Alloy 738X was found to be the most susceptible to cyclic oxidation; this resulted in heavy spalling, which in turn caused high weight losses and high metal losses. Oxidation test results are related to the amounts of chromium aluminum, and the refractory metals in the alloys investigated.

Sanders, W. A.↗
NASA NTRS1973

Cyclic and isothermal oxidation behavior on some Ni-Cr alloys

It is shown experimentally that 3 wt.% Si and 3 wt.% Mn additions can substantially improve the oxidation resistance of Ni-20Cr under both isothermal and cyclic conditions at 1100 and 1200 C. This is especially true in cyclic oxidation. In all cases, Si offers a greater improvement than Mn; however, the advantage of Si is substantial only during cyclic oxidation at 1200 C. The Si additions which lead to alloys of improved oxidation resistance suppress the formation of NiO and NiCr2O4 even under the most severe test conditions. The mechanism of improvement afforded by Mn appears to be the formation of MnCr2O4 at the expense of NiO and NiCr2O4.

Lowell, C. E.↗
NASA NTRS1975

A study of the oxide dispersion and recrystallization in NiCrAl prepared from preoxidized powder

The sintered aluminum powder (SAP) technique of dispersion strengthening (formation of an oxide dispersion by preoxidation of metal powders) was applied to atomized powder of a nickel alloy containing, by weight, 17% Cr, 5% Al, and 0.2% Y. The SAP-NiCrAl alloy (without the ytterbium removed by oxdation) was worked by extrusion and rod rolling at 1205 C and by swaging at 760 C. Annealing treatments were applied after working to determine the recrystallization response. The NiCrAlY alloy, similarly prepared from atomized powder, but without a preoxidation treatment, was examined for comparison. The SAP-NiCrAl alloy exhibited oxide particle size and spacing much larger than that usually observed in oxide dispersion strengthened alloys; nonetheless, it was possible to achieve abnormal (secondary) recrystallization in the SAP-NiCrAl alloy as has been reported for other oxide dispersion strengthened alloys. In contrast, the unoxidized NiCrAlY alloy exhibited only primary recrystallization.

Glasgow, T. K.↗
NASA NTRS1975

Satellite measurements of nitric oxide in the polar region

Ultraviolet measurements of the (1, 0) gamma band of nitric oxide in fluorescence by a satellite at high latitudes show nitric oxide concentrations which are highly variable in both time and space. The average nitric oxide concentration is 3 to 4 times higher at high latitudes than at midlatitudes. If auroral activity is responsible for the larger nitric oxide densities and if the reaction N(2D) + O2 is the source of NO, then auroral processes must be more efficient in the production of N(2D) atoms than dayglow processes.

Rusch, D. W.↗
NASA NTRS1975

A study of the oxide dispersion and recrystallization in NiCrAl prepared from preoxidized powder

The SAP technique of dispersion strengthening (formation of an oxide dispersion by preoxidation of metal powders) was applied to atomized powder of the alloy Ni-17Cr-5Al-0.2 Y. SAP-NiCrAl was worked by extrusion and rod rolling at 1205 C and by swaging at 760 C. A variety of annealing treatments were applied after working to determine the recrystallization response. NiCrAlY, similarly prepared from atomized powder, but without a preoxidation treatment, was examined for comparison. The SAP-NiCrAl of this study exhibited oxide particle size and spacing much larger than that usually observed in oxide dispersion strengthened alloys; nonetheless, it was possible to achieve abnormal (secondary) recrystallization in the SAP-NiCrAl as has been reported for other oxide dispersion strengthened alloys. In contrast, unoxidized NiCrAlY exhibited only primary recrystallization.

Glasgow, T. K.↗
NASA NTRS1975

Sulfur poisoning of hydrocarbon oxidation by palladium

Using a differential bed recycle reactor the oxidation of ethane and diethyl ketone by a Pd catalyst was studied at the 0-30 ppm level in air. In both cases first order kinetics were observed. The ethane oxidation rate was characterized n the Arrhenius form by a pre-exponential of 1.0 x 10 to the 8th power cm/sec and an E sub a of 27 kcal/mole. The diethyl ketone oxidation rate was characterized by a pre-exponential of 5.7 x -1000 cm/sec and E sub a of 14 kcal/mole. Poisoning of ethan oxidation was also investigated by hydrogen sulfide and to a smaller extent by the refrigerants Freon 22 and Gentron 142-B. Poisoning by Gentron 142-B was much more severe than by hydrogen sulfide. Kinetic experiments indicated that only the pre-exponential was changing.

Baumgartner, A. J.↗
NASA NTRS1977

The effect of delta T /oxidizing temperature minus cooling temperature/ on oxide spallation

Several alloys (one iron base and five nickel base) were cyclically oxidized in a series of tests in which the higher temperature (1100 or 1200 C) of the cycle was fixed at a level to allow ample oxidation in reasonable time and the lower temperature was variable to allow cycle temperature differences of up to 1400 C. For all nickel alloys, as delta T increased the extent of spallation increased. This effect was attributed to thermal expansion mismatches between the oxide and the nickel substrate. The FeCrAl alloy was not sensitive to delta T and resisted spalling at delta T levels to 1400 C. FeCrAl, and the Al2O3 scale which forms on it, have thermal expansion coefficients which are substantially more alike than any of the other oxide-metal combinations tested.

Deadmore, D. L.↗
NASA NTRS1977

Volatile products from the interaction of KCl(g) with Cr2O3 and LaCrO3 in oxidizing environments

Cooled target collection techniques and high pressure mass spectrometric sampling were used to measure the relative rates of oxidative vaporization and to identify the volatile products emanating from samples of chromia and Mg-doped lanthanum chromite. The materials were exposed to partial pressures of KCl with and without H2O in one atmosphere of slowly flowing oxygen at elevated temperatures. Chromia and fresh samples of lanthanum chromite exhibited enhanced rates of oxidative vaporization upon exposure to these reactants. Mass spectrometric identification showed that the enhancements resulted from the heterogeneous formation of complex molecules of the type KCl sub 1,2,3 CrO3 and KOH sub l,2 CrO3. Lanthanum chromite that had undergone prolonged oxidative vaporization exhibited no enhanced oxidation upon exposure to the reactants.

Kohl, F. J.↗
NASA NTRS1977

Volatile products from the interaction of KCl/g/ with Cr2O3 and LaCrO3 in oxidizing environments

Based on cooled target collection methods and high pressure mass spectrometer sampling, oxidative vaporization rates and emanating volatile products were evaluated for interactions of KCl(g) with Cr2O3 and LaCrO3 in oxidizing environments. It was found that: (1) increased rates of oxidative vaporization upon exposure to the reactants are exhibited by chromia and fresh lanthanum chromite samples, and (2) these increased rates result from the heterogeneous formation of complex molecules such as KCl sub 1,2,3CrO3 and KOH sub 1,2CrO3. No increased rates were observed for lanthanum chromite subjected to prolonged oxidative vaporization.

Kohl, F. J.↗
NASA NTRS1978

Effects of ultrathin oxides in conducting MIS structures on GaAs

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

Childs, R. B.↗
NASA NTRS1978

Nitric oxide production by Tunguska meteor

The nonequilibrium chemical processes of nitric oxide formation are computed for the wake of the Tunguska meteor of 1908. The wake characteristics are derived by carrying out an optically-thick radiation field analysis for ablation of the meteoroid. The wake flow field is approximated by a one-dimensional, well-stirred reactor model. Known characteristics of the Tunguska event are imposed as constraints, and three controlling parameters - chemical composition, density, and velocity - are varied over a range around the values derived by Korobeinikov et al. (1976) and Petrov and Stulov (1975). The calculation shows that at least 19 million tons of nitric oxide is produced between the altitudes of 10 and 50 km. The anomalous atmospheric phenomena following the event are attributed to the reactions involving nitric oxide thus produced and atmospheric ozone. It is speculated that the nitric oxide produced by the event fertilized the area near the fall, causing the observed rapid plant growth.

Park, C.↗
NASA NTRS1979

The effect of surface oxide layer on the rate of hydrogen emission from aluminum and its alloys in a high vacuum

The influence of surface oxide layers on the kinetics of hydrogen emission at the high vacuum of 10 to the minus 8th power torr was investigated at temperatures from 20 to 450 C using samples of pure AB00 aluminum and the cast alloy AMg. Cast and deformed samples of AMts alloy were used to study the effect of oxide film thickness on the rate of hydrogen emission. Thermodynamic calculations of the reactions of the generation and dissociation of aluminum oxide show that degasification at elevated temperatures (up to 600 C) and high vacuum will not reduce the thickness of artificially-generated surface oxide layers on aluminum and its alloys.

Makarova, V. I.↗