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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Use of radiation in preparative chemistry

A summary and updating of previous work on the use of radiation chemistry for the preparation of pure materials are presented. Work was chiefly concerned with the reduction of metal salts in solution to the free metal using 2 MeV electrons. Metals deposited from aqueous solution are copper, silver, zinc, cadmium, thallium, tin, lead, antimony, iron, nickel, cobalt, and palladium. Dry organic solvents were evaluated for the deposition of metals based on a study involving deposition of antimony from soltions of antimony (III) chloride. The use of organic liquids for the preparation of anhydrous metal halides is also presented. Reaction mechanisms for both organic liquids and aqueous system are discussed.

Philipp, W. H.↗
NASA NTRS1971

Induction plasma calcining of pigment particles for thermal control coatings

Induction plasma heating techniques were studied for calcining zinc orthotitanate particles for use in thermal control coatings. Previous studies indicated that the optimum calcining temperature is between 1400 and 1750 C. An intermediate temperature (1670 C) was chosen as a reference point for running a temperature series at the reference point and 220 C on both sides. The effect of varying chamber temperature on the reflectance spectra, before and after vacuum UV irradiation, is presented. The correlation between Zn2Ti04 paramagnetic resonance activity and its susceptibility to vacuum UV damage is discussed.

Farley, E. P.↗
NASA NTRS1971

Space thermal control development

The results of experimental investigations on a number of various phase change materials (PCMs) and PCMs in combination with metals and other materials are reported. The evaluations include the following PCM system performance characteristics: PCM and PCM/filler thermal diffusivities, the effects of long-term thermal cycling, PCM-container compatibility, and catalyst effectiveness and stability. Three PCMs demonstrated performance acceptable enough to be considered for use in prototype aluminum thermal control devices. These three PCMs are lithium nitrate trihydrate with zinc hydroxy nitrate catalyst, acetamide, and myristic acid. Of the fillers tested, aluminum honeycomb filler was found to offer the most increase in system thermal diffusivity.

Hoover, M. J.↗
NASA NTRS1972

Hair radioactivity as a measure of exposure to radioisotopes

Since many radioisotopes accumulate in hair, this tropism was investigated by comparing the radioactivity of shaved with plucked hair collected from rats at various time intervals up to 24 hrs after intravenous injection of the ecologically important radioisotopes, iodine-131, manganese-54, strontium-85, and zinc-65. The plucked hair includes the hair follicles where biochemical transformations are taking place. The data indicate a slight surge of each radioisotpe into the hair immediately after injection, a variation of content of each radionuclide in the hair, and a greater accumulation of radioactivity in plucked than in shaved hair. These results have application not only to hair as a measure of exposure to radioisotopes, but also to tissue damage and repair at the hair follicle.

Strain, W. H.↗
NASA NTRS1971

Investigation of environmental effects on coatings for thermal control of large space vehicles

The objective of significantly advancing the state-of-the-art of white, spacecraft-radiator coatings has been realized in a comprehensive goal-oriented, pigmented-coatings research program. Considered were inorganic pigments and coatings, silicone polymers and coatings, the design and construction of a combined ultraviolet-plus-proton irradiation facility, the development of zinc orthotitanate pigment and coatings, and the effects on several low alpha sub s/epsilon paints of combined ultraviolet and proton irradiation.

Zerlaunt, G. A.↗
NASA NTRS1972

Nonleaking battery terminals

Three different terminals were designed for usage in a 40 ampere/hour silver zinc battery which has a 45 percent KOH by weight electrolyte in a plastic battery case. Life tests, including thermal cycling, electrical charge and discharge for up to three years duration, were conducted on these three different terminal designs. Tests for creep rate and tensile strength were conducted on the polyphenylene oxide (PPO) plastic battery cases. Some cases were unused and others containing KOH electrolyte were placed on life tests. The design and testing of nonleaking battery terminals for use with a potassium hydroxide (KOH) electrolyte in a plastic case are discussed.

Snider, W. E.↗
NASA NTRS1971

Development of space stable thermal control coatings for use on large space vehicles

The evaluation and environmental testing of zinc orthotitanate pigments for use as space stable thermal control coatings on large space vehicles are discussed. Electron paramagnetic resonance spectra of the pigments and their precursor compounds are examined. A continuing study of the spectral intensity of mercury-argon and mercury-xenon sources in reported. Results of long term environmental testing of commercially available, strippable, protective coatings are discussed.

Gilligan, J. E.↗
NASA NTRS1972

Development and testing of a high cycle life 30 A-h sealed AgO-Zn battery

A two-phase program was initiated to investigate design parameters and technology to develop an improved AgO-Zn battery. The basic performance goal was 100 charge/discharge cycles (22 h/2 h) at 50 percent depth of discharge following a six-month period of charged stand at room temperature. Phase 1, cell evaluation, involved testing 70 cells in five-cell groups. The major design variables were active material ratios, electrolyte concentrations, separator systems, and negative plate shape. Phase 1 testing showed that cycle life could be improved 10 percent to 20 percent by using greater ratios of zinc to silver oxide and higher electrolyte concentrations. Wedge-shaped negatives increased cycle life by nearly 100 percent. Phase 2 battery evaluation, which was initiated before the Phase 1 results were known completely, involved evaluation of six designs as 19-cell batteries. Only one battery exceeded 100 cycles following nine months charged stand.

Bogner, R. S.↗
NASA NTRS1972

Corrosion study of bare and coated stainless steel

A program was conducted at Kennedy Space Center from February 1968 to February 1971 to evaluate the performance of austenitic stainless steel alloys used in fluid systems lines. For several years, there had been numerous failures of stainless steel hardware caused by pitting and stress corrosion cracking. Several alloys were evaluated for effectiveness of certain sacrificial-type protective coverings in preventing corrosion failures. Samples were tested in specially designed racks placed 91 meters (100 yards) above high-tide line at Cape Kennedy. It is concluded that: (1) unprotected tubing samples showed evidence of pitting initiation after 2 weeks; (2) although some alloys develop larger pits than others, it is probable that the actual pitting rate is independent of alloy type; (3) the deepest pitting occurred in the sheltered part of the samples; and (4) zinc-rich coatings and an aluminum-filled coating have afforded sacrificial protection against pitting for at least 28 months. It is believed that a much longer effective coating life can be expected.

Morrison, J. D.↗
NASA NTRS1972

Population inversion calculations using near resonant charge exchange as a pumping mechanism

Near resonance charge exchange between ions of a large ionization potential gas such as helium or neon and vapors of metals such as zinc, cadmium, selenium, or tellurium has produced laser action in the metal ion gas. The possibility of obtaining population inversions in near resonant charge exchange systems (Xe-Ca, Xe-Mg, Xe-Sr, Xe-Ba, Ar-Mg, N-Ca) was investigated. The analysis is an initial value problem that utilizes rate equations for the densities of relevant levels of the laser gas (Ca, Ba, Mg, or Sr) and an electron energy equation. Electron excitation rates are calculated using the Bohr-Thomson approximation for the cross section. Approximations to experimental values of the electron ionization cross section and the ion-atom charge exchange cross section are used. Preliminary results have been obtained for the Ca-Xe system and show that it is possible to obtain gains greater than 10 to the 14th power/m with inversion times up to 8x10 to the minus 7th power second. A possible charge exchange laser system using a MPD arc plasma accelerator is also described.

Chubb, D. L.↗
NASA NTRS1972

Time-of-flight mobility and trapping results for ZnSe.

Results of measurements of time-of-flight mobility and trapping for zinc selenide. The data were obtained at room temperature for electric fields in the range from 30,000 to 800,000 V/cm. A relatively constant hole mobility (about 50 sq cm/V sec) was found for the entire range of investigated fields. The electron mobility was approximately constant (about 400 sq cm/V sec) up to approximately equal to 300,000 V/cm, above which the drift velocity remained constant. No obvious negative differential mobility was observed, even though the Gunn effect has been reported for the field range investigated. Trapping and detrapping times in the vicinity of 1 nsec are reported for both holes and electrons. The field dependence of the electron-trapping times is unusual and remains unexplained.

Heaton, J. L., III↗
NASA NTRS1972

Pulsed metallic-plasma generators.

A pulsed metallic-plasma generator is described which utilizes a vacuum arc as the plasma source. The arc is initiated on the surface of a consumable cathode which can be any electrically conductive material. Ignition is accomplished by using a current pulse to vaporize a portion of a conductive film on the surface of an insulator separating the cathode from the ignition electrode. The film is regenerated during the ensuing arc. Over 100 million ignition cycles have been accomplished by using four 0.125-in. diameter zinc cathodes operating in parallel and high-density aluminum-oxide insulators. Among the applications being investigated for the generator are metal deposition, vacuum pumping, electric propulsion, and high-power dc arc interruption.

Gilmour, A. S., Jr.↗
NASA NTRS1972

Progress in electrochemical storage for battery systems

Efforts to improve electrochemical systems for space use relate to: (1) improvement of conventional systems; (2) development of fuel cells to practical power systems; and (3) a search for new systems that provide gains in energy density but offer comparable life and performance as conventional systems. Improvements in sealed conventional systems resulted in the areas of materials, charge control methods, cell operations and battery control, and specific process controls required during cell manufacture. Fuel-cell systems have been developed for spacecraft but the use of these power plants is limited. For present and planned flights, nickel-cadmium, silver-zinc, and silver-cadmium systems will be used. Improvements in nickel-cadmium batteries have been applied in medical and commercial areas.

Ford, F. E.↗
NASA NTRS1972

A proposed magnetic digital temperature transducer, volume 1

A study has been made of the feasibility of using the discontinuous permeability versus temperature characteristics of some magnetic materials for a digital temperature transducer and a thermally controlled ON-OFF switch. Simple logic converts the number of output pulse to a digital word recognizable by the system. Efforts have been concentrated on materials with Curie temperatures between 0 and 100 C. One compound has the composition Mn(5-x)Fe(x)Ge3 where the amount of iron determines the transition temperature. The other compound is Ni-Zn ferrite and has the compositon Ni(1-x)Zn(x)Fe(1.95)O4 where the nickel: zinc ratio determines the transition temperature. A detailed report of materials prepared is presented. Toroidal inductors of the material have been constructed and the change in inductance with temperature measured. In view of these initial measurements, it is felt that a transducer utilizing the permeability versus temperature characteristics of these materials has promise as a reliable and sensitive solid state digital temperature transducer.

Collier, T. E.↗
NASA NTRS1972

Preparation of pigments for space-stable thermal control coatings

The identification and control of vapor phase reaction kinetics to produce pigments by homogeneous nucleation were achieved. A vapor phase apparatus was designed, fabricated, and calibrated through 1800 C. Vapor phase reactions were analyzed, calculations made, and powders of alumina, rutile, zinc orthotitanate (in a mixed phase), calcium tungstate, and lanthana were produced by homogeneous nucleation. Electron microscopy shows uniform particle morphology and size, and supports anticipated advantages of vapor-phase homogeneous nucleation; namely, purity, freedom from defects, and uniform particle sizing without grinding.

Campbell, W. B.↗
NASA NTRS1973

Study of CO2 sorbents for extravehicular activity

Portable life support equipment was studied for meeting the requirements of extravehicular activities. Previous studies indicate that the most promising method for performing the CO2 removal function removal function were metallic oxides and/or metallic hydroxides. Mgo, Ag2, and Zno metallic oxides and Mg(OH)2 and Zn(OH)2 metallic hydroxides were studied, by measuring sorption and regeneration properties of each material. The hydroxides of Mg and Zn were not regenerable and the zinc oxide compounds showed no stable form. A silver oxide formulation was developed which rapidly absorbs approximately 95% of its 0.19 Kg CO2 Kg oxide and has shown no sorption or structural degeneration through 22 regenerations. It is recommended that the basic formula be further developed and tested in large-scale beds under simulated conditions.

Colombo, G. V.↗
NASA NTRS1973

Oxidation resistance of selected mechanical carbons at 650 deg C in dry flowing air

Oxidation experiments were conducted with several experimental mechanical carbons at 650 C in air flowing at 28 cu cm/sec (STP). Experiments indicate that boron carbide addition and zinc phosphate treatment definitely improved oxidation resistance. Impregnation with coal tar pitch before final graphitization had some beneficial effect on oxidation resistance and it markedly improved flexure strength and hardness. Graphitization temperature alone did not affect oxidation resistance, but with enough added boron carbide the oxidation resistance was increased although the hardness greatly decreased.

Allen, G. P.↗