Calculation of the temperature and the purity dependence of sound attenuation in superconducting Nb
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Sung, C. C.↗
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Purity test for copper-plating solutions
Electrode configuration can be used to measure extent of impurities in acid-copper plating solution. It can be inserted into any plating tank and will show whether bath is clean or contaminated, within fifteen minutes.
Mansfeld, F. B.↗
High purity silica reflective heat shield development
Measurements were made of reflectance in the vacuum ultraviolet down to 0.15 micron. Scattering coefficients (S) and absorption coefficients (K) were also measured. These coefficients express the optical properties and are used directly in a thermodynamic analysis for sizing a heat shield. The effect of the thin silica melt layer formed during entry was also studied from the standpoint of trapped radiant energy.
Blome, J. C.↗
Targets for producing high purity I-123
Tellurium powder in improved targets is bombarded with a cyclotron beam to produce Xe-123. Flowing gas streams carry the Xe-123 through one cold trap which removes Xe-123 that subsequently decays to I-123. During this bombardment energy is deposited in the target material causing its temperature to rise. Some of the tellurium vaporizes and subsequently condenses on surfaces that are cooler than the vaporization temperature. Provision is made for the repeated bombardment of this condensed tellurium.
Blue, J. W.↗
Diagnostics and control of wavenumber stability and purity of tunable diode lasers relevant to their use as local oscillators in heterodyne systems
Initial operation of the tunable diode lasers (TDL) showed that it was not possible to adjust the wavenumber to one selected a priori in the TDL tuning range. During operation, the operating point would change by 0.1/cm over the longer term with even larger changes occurring during some thermal cycles. Most changes during thermal cycling required using lower temperatures and higher currents to reach the former wavenumber (when it could be reached). In many cases, an operating point could be selected by changing TDL current and temperature to give both the desired wavenumber and most of the power in a single mode. The selection procedure had to be used after each thermal cycling. Wavenumber nonlinearities of about 10% over a 0.5 cm tuning range were observed. Diagnostics of the single mode selected by a grating monochromator showed wavenumber fine structure under certain operating conditions. The characteristics due to the TDL environment included short term wavenumber stability, the instrument lineshape function, and intermediate term wavenumber stability.
Poultney, S.↗
Producing High-Purity Silicon With Sodium
Simple technique for producing silicon for solar cells employs solid sodium to reduce silicon fluoride. Since solid rather than liquid sodium is used, careful temperature control is unnecessary, and simple feed equipment is used. Technique is energy-efficient, since reaction produces enough heat to sustain itself.
Sanjurjo, A.↗
High purity low dislocation GaAs single crystals
Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm.
Chen, R. T.↗
Growing Single Crystals From Low-Purity Silicon
Heat exchanger method continuously moves impurities to outside of growth interface. Silicon heated in crucible to above melting point, and melted silicon then solidified by extracting heat from bottom of crucible by means of heat exchanger.
Schmid, F.↗
Bread board float zone experiment system for high purity silicon
A breadboard float zone experimental system has been established at Westech Systems for use by NASA in the float zone experimental area. A used zoner of suitable size and flexibility was acquired and installed with the necessary utilities. Repairs, alignments and modifications were made to provide for dislocation free zoning of silicon. The zoner is capable of studying process parameters used in growing silicon in gravity and is flexible to allow trying of new features that will test concepts of zoning in microgravity. Characterizing the state of the art molten zones of a growing silicon crystal will establish the data base against which improvements of zoning in gravity or growing in microgravity can be compared. 25 mm diameter was chosen as the reference size, since growth in microgravity will be at that diameter or smaller for about the next 6 years. Dislocation free crystals were growtn in the 100 and 111 orientations, using a wide set of growth conditions. The zone shape at one set of conditions was measured, by simultaneously aluminum doping and freezing the zone, lengthwise slabbing and delineating by etching. The whole set of crystals, grown under various conditions, were slabbed, polished and striation etched, revealing the growth interface shape and the periodic and aperiodic natures of the striations.
Kern, E. L.↗
High purity, low dislocation GaAs single crystals
Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.
Chen, R. T.↗
Preliminary study of a radiantly heated fluidized bed for the production of high purity silicon
The preparation of very pure silicon from silane (SIH4) using radiant heating of the hot silicon particles of a fluidized bed is discussed. The fraction of electrical energy supplied to the heater which is actually absorbed by the particles and the heat transfer coefficient between the hot bed and the cool distributor plate were investigated. The experimental design is presented and the results of the study are summarized.
Levenspiel, O.↗
Containerless high purity pulling process and apparatus for glass fiber
Apparatus and method for pulling optical glass fibers in a containerless environment is disclosed which includes a single axis acoustical levitation furnace in which a specimen is levitated and melted. A reflector unit is carried in the interior of the furnace and includes a reflector disposed centrally about the acoustical axis of the levitator. The reflector unit includes a circular shroud of insulation and a copper sleeve inserted in the unit which is hollow at for receiving a cooling medium. A fiber pulling bore is formed centrally in the reflector unit surrounded by cooling jacket to enhance solidification and formation of a fiber. A starting fiber strand is introduced into the melt and pulled outwardly through bore whereby the specimen fiber is started and formed as pulled therethrough. In order to replenish the melt and thus enable a continous process, a movable secondary reflector is provided which captures a supplemental specimen pellet and by movement of the reflector transfers it to the melt.
Naumann, R. J.↗
High-purity silicon crystal growth investigations
The study of silicon sheet material requirements for high efficiency solar cells is reported. Research continued on obtaining long lifetime single crystal float zone silicon and on understanding and reducing the mechanisms that limit the achievement of long lifetimes. The mechanisms studied are impurities, thermal history, point defects, and surface effect. The lifetime related crystallographic defects are characterized by X-ray topography and electron beam induced current.
Ciszek, T. F.↗
Turbulent flow model for vapor collection efficiency of a high-purity silicon reactor
In this study a mathematical model and a computer code based on this model was developed to allow prediction of the product distribution in chemical reactors for converting gaseous silicon compounds to condensed-phase silicon. Specifically, the model formulated describes the silicon vapor separation/collection from the developing turbulent flow stream within reactors of the Westinghouse type. Migration of the silicon vapor to the reactor walls was described by the parametric solutions presented here, in order to reduce the experimentation necessary in the design of such reactors. Calculations relating to the collection efficiencies of such reactors are presented as a function of the reactor throughflow and distance along its length.
Srivastava, R.↗
Phase purity of NiCo2O4, a catalyst candidate for electrolysis of water
NiCo2O4 is shown to be difficult to obtain as a pure phase, and may never have been so obtained. High resolution x-ray diffractometry is required for its precise characterization. Film XRD is not likely to show the asymmetry in the spinel diffraction lines, caused by poorly crystallized NiO, as seen in diffractometer traces. The Co3O4 which is expected to accompany NiO as an impurity in NiCo2O4 syntheses has the same diffraction pattern as the binary oxide. Firings of the co-precipitated hydroxides at 300, 350, and 400 C, including one in pure O2, failed to produce single phase cobaltate. Scanning electron microscopy showed all the sintered products to range over several orders of magnitude in agglomerate/particle size. Surface areas by BET were all in the range 40 to 110 m sq/g, equivalent to particles of 200 to 100 Angstrom diameter. The spinel diffraction line breadths were compatible with those approximate dimensions.
Singer, J.↗
Development in tunable solid state lasers with high spectral purity, high efficiency and long lifetime for differential absorption lidar
The paper presents a review of tunable vibronic solid state lasers for DIAL measurements and provides new experimental results for tunable Ti:sapphire lasers, materials development, and spectral bandwidth narrowing through injection control. Pulsed injection control of a Ti:sapphire laser with a 2.5-pm narrow band pulsed dye laser and with another Ti:sapphire laser is demonstrated with nearly complete energy extraction, indicating homogeneous line broadening. The status of tunable solid state lasers in the 1.6-2.3 micron range for DIAL measurements of trace gases, and development trends for lasers with reduced cryogenic cooling needs, are included. The effects of laser gain on optical damage, energy extraction, and amplified spontaneous emission are indicated for several tunable lasers.
Hess, R. V.↗
Oxygen transport through high-purity, large-grain Ag
The permeability of oxygen through pure, large-grain Ag membrames has been found to be linear and repeatable over the 400-800 C range, but only at a magnitude that is a factor of 3.2 smaller than ascribed by prior research. AES data indicate the pertinence of grain-boundary considerations, due to the virtual undetectability of intragranular oxygen. Vacuum-desorption of oxygen-saturated Ag is found to occur at the critical temperature of 630 C; this is consistent with the increased mobility of oxygen atoms in the higher temperature regime.
Outlaw, R. A.↗
Some properties of high-purity sintered wrought molybdenum metal at temperatures up to 2400 F
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TITANIUM CARBIDE-COBALT ALLOYS↗