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Sodium chloride, used with proper solvent-dispersant combination, forms very durable reflective coatings. Several other inorganic salts, such as barium sulfate, barium carbonate, sodium fluoride, potassium chloride, sodium hexafluorosilicate, and aluminum oxide, are also suitable. Sodium chloride may also be used with other formulations to produce same type of coating.
Composition consists of dispersion of barium sulphate in aqueous solution of water-soluble inorganic binder. Binder is selected from group consisting of alkali metal sulphates. Coating exhibits high reflectance of ultraviolet light to wavelengths of approximately 200.0 nm, which compares favorably with high reflectance of virgin barium sulphate power.
Barium and lithium vapors were released from sounding rockets in the thermosphere and observed from aboard the NASA Convair 990 at an altitude of 40,000 ft. The purpose of the releases was to (1) check out observational and operational procedures associated with the large high altitude barium release from a Scout rocket (BIC); (2) develop an all-weather technique for observing chemical releases; (3) evaluate methods of observing daytime releases, and (4) investigate the possibilities of observations from a manned satellite. The initial analysis indicates that the previous limitations on the usage of the vapor release method have been removed by the use of the aircraft and innovative photographic techniques. Methods of analysis and applications to the investigation of the thermosphere are discussed.
Samples of ASTM type A jet fuel were analyzed for trace-element content by instrumental neutron activation techniques. Forty-nine elements were sought. Only ten, aluminum, gold, indium, lanthanum, titanium, vandium, barium, dysprosium, tellurium, and uranium, were observed at levels above the detection limits encountered; of these only aluminum, titanium, and barium were present at concentrations greater than 0.1 ppm. Estimates of exhaust gas concentrations are made, and the ambient contribution at or near airports is calculated by using the Los Angeles International Airport dispersion model. It is shown that the ambient contribution is about an order of magnitude below typical urban levels for virtually all elements sought.
An experimental study of starting and operating characteristics of conventional hollow cathodes and of hollow cathodes without alkaline earth emissive materials demonstrated that the emissive mix is essential to obtain the desired cathode operation. Loss of the emissive mix by evaporation and chemical reaction was measured. New insert designs consisting of emissive mix supported on nickel and of barium impregnated porous tungsten were studied. Cathodes with a modified orifice geometry operated in a low voltage, 'spot' mode over a broad range of discharge current. Thermal degradation tests on cathode heaters showed the flame sprayed SERT II type to be the most durable at high temperatures. Thermal shock was observed to be a significant factor in limiting cathode heater life. A cathode having a barium impregnated porous tungsten tip and a heater which is potted in sintered alumina was found to have favorable operating characteristics.
Samples of ASTM type A jet fuel were analyzed for trace element content by instrumental neutron activation techniques. Forty-nine elements were sought. Only ten, aluminum, gold, indium, lanthanum, titanium, vanadium, barium, dysprosium, tellurium, and uranium, were observed at levels above the detection limits encountered; of these only aluminum, titanium, and barium were present at concentrations greater than 0.1 ppm. Estimates of exhaust gas concentrations are made, and the ambient contribution at or near airports is calculated by using the Los Angeles International Airport dispersion model. It is shown that the ambient contribution is about an order of magnitude below typical urban levels for virtually all elements sought.
Measurements of the thermospheric neutral wind and ionospheric drift made at Eglin AFB, Florida and Kwajalein Atoll are discussed. The neutral wind measurements at Eglin had little variation over a period of four years for moderate magnetic activity (Kp 4); the ionospheric drifts are small. Evidence is presented that indicates that increased magnetic activity has a significant effect on the neutral wind magnitude and direction at this midlatitude station. The neutral wind at dusk near the equator is generally small although in one case out of seven it was significantly larger. It is described how observations of large barium releases can be used to infer the degree of electrodynamic coupling of ion clouds to the background ionosphere. Evidence is presented that indicates that large barium releases are coupled to the conjugate ionosphere at midlatitudes.
Shaped charge barium release data and high-speed auroral image data show the likely existence of anomalously large (about 1 V/m referred to the 100-km level) electric fields at distances the order of one earth radius above the earth. A model of the electrostatic field above an auroral arc is proposed in which the magnetic field lines are not all equipotentials. Use is made of recent theoretical work on oblique current-driven electrostatic shocks to demonstrate the plausibility of nonequipotential field lines. The model is addressed to the structure of inverted-V electron spectra, current continuity between magnetosphere and ionosphere, and the results of recent shaped charge barium experiments. The model is used to identify specific gaps in our understanding of auroral phenomena.
Thermionic converters using a variety of metal oxide collector surfaces have been fabricated and tested. Both work function and power output data are presented and evaluated. Oxides of barium, strontium, zinc, tungsten and titanium have been incorporated into a variable spacing converter. Tungsten oxide was found to give the highest converter performance and to furnish oxygen for the emitter at the same time. Oxygenated emitters operate at reduced cesium pressure with an increase in electrode spacing. Electron spectroscopy for chemical analysis (ESCA) performed on several tungsten oxide collectors showed cesium penetration of the oxide layer, possibly forming a cesium tungstate bronze. Titanium oxide showed high performance but did not furnish oxygen for the emitter; strontium oxide, in the form of a sprayed layer, appeared to dissociate in the presence of cesium. Sprayed coatings of barium and zinc oxides produced collector work functions of about 1.3 eV, but had excessive series resistance. Lanthanum hexaboride, in combination with oxygen introduced through a silver tube, and cesium produced a low work function collector and better than average performance.
Sodium and barium fluorosilicates precipitated and thermally decomposed into silicon tetrafluoride. Barium fluorosilicate thermally decomposes at lower temperatures in shorter times, to give same percentage yield of silicon tetrafluoride gas, than sodium fluorosilicate. Salt byproducts of decompositions recycled to precipitate fluorosilicates from hexafluorosilicic acid, the primary reactant.
In order to study the access of solar wind ions to the magnetosphere, together with the processes that transport and accelerate magnetospheric particles, the Active Magnetospheric Particle Tracer Explorers (AMPTE) mission will release and monitor lithium and barium tracer ions in both the solar wind and the magnetosphere. A single, massive release of barium in the dawn magnetosheath will in addition create a visible artificial comet in the flowing solar wind plasma, within which studies of a range of different plasma effects will be undertaken. The AMPTE will obtain comprehensive measurements of natural magnetospheric particle populations' elemental composition and dynamics. AMPTE comprises three spacecraft: the Ion Release Module, the Charge Composition Explorer, and the United Kingdom Subsatellite.
The hydrated surfaces of a zirconium barium fluoride glass, which has potential for application in optical fibers and other optical elements, were observed by scanning electron microscopy. Crystalline zirconium fluoride was identified by analysis of X-ray diffraction patterns of the surface crystals and found to be the main constituent of the surface material. It was also found that hydrated zirconium fluorides form only in highly acidic fluoride solutions. It is possible that the zirconium fluoride crystals form directly on the glass surface as a result of its depletion of other ions. The solubility of zirconium fluoride is suggested to be probably much lower than that of barium fluoride (0.16 g/100 cu cm at 18 C). Dissolution was determined to be the predominant process in the initial stages of the reaction of the glass with water. Penetration of water into the glass has little effect.
Numerous plasma wave effects were detected by the AMPTE/IRM spacecraft during the artificial comet experiment on December 27, 1984. As the barium ion cloud produced by the explosion expanded over the spacecraft, emissions at the electron plasma frequency and ion plasma frequency provided a determination of the local electron density. The electron density in the diamagnetic cavity produced by the ion cloud reached a peak of more than 5 x 10 to the 5th per cu cm, then decayed smoothly as the cloud expanded, varying approximately as t exp-2. As the cloud began to move due to interactions with the solar wind, a region of compressed plasma was encountered on the upstream side of the diamagnetic cavity. The peak electron density in the compression region was about 1.5 x 10 to the 4th per cu cm. Later, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region. This noise has characteristics very similar to noise observed in the earth's bow shock, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons.
NASA Goddard Space Flight Center, Wallops Flight Facility has developed, flown, and recovered a unique plasma physics payload. This sounding rocket payload was developed to measure varying aspects of Alfven's critical velocity effect in a space plasma by using conical-shaped barium explosives. These measurements could possibly duplicate conditions that existed in the early solar system. This paper provides details of the payload and subpayload development, with specific emphasis on the extensive dynamic analysis of the barium release modules. Other key elements which are expanded on in the paper are: (1) design, development, and testing acceptance for the science/inertia booms using a viscous damping system for high spin rate deployment; (2) vehicle dynamic analysis; (3) apogee and impact dispersion analysis to satisfy the science and NASA safety requirements; (4) a comparison of predicted versus actual flight events.
The Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft performed a series of eight chemical releases in essentially comparable pairs. There were two lithium releases in the solar wind, two lithium and two barium releases in the near-Earth magnetotail, and two barium releases to simulate artificial comets, one in the solar wind and the other in the magnetosheath. A variety of plasma waves were observed in conjunction with each of the releases. Although there were unique features associated with some of the individual releases, the comparable releases generally produced similar wave emissions. This paper discusses the similarities and differences among the releases.
Thin films of YBa2Cu3O(7-beta) have been grown by sequential evaporation of Cu, Y, and BaF2 on SrTiO3 and MgO substrates. The onset temperatures were as high as 93 K while T sub c was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hr, while the annealing temperatures used ranged from 850 C to 900 C. A good correlation was found between transition temperature (T sub c) and the annealing conditions; the films annealed at 900 C on SrTiO3 had the best T sub c's. There was a weaker correlation between composition and T sub c. Barium poor films exhibitied semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis of the films and the correlations are reported.
Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.
Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.