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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.

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At least 145 records · Page 8
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NASA NTRS1985

Processing Science and Technology

The heat capacity at constant pressure,Cp, of poly-p-xylylene (PPX) was measured from 220 to 625 degrees K using differential scanning calorimetry. The heat capacities at constant volume, Cv, of both PPX and its isomer polystyrene (PS were interpreted using literature data on full normal mode calculations for PS and estimates from low molecular weight analogues for PPX for the 39 group vibrations. Nine skeletal vibrations were used with theta sub 1 and theta sub 3 temperatures of 534.5 degrees K and 43.1 degrees K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48-vibration theta sub 1 temperatures of 3230 degrees K for PS and 2960 degrees K for PPX are sufficient to describe Cv above 220 degrees K. Below 140 deg K, PS heat capacity shows deviations from the Tarasov treatment.

Source record↗
NASA NTRS1985

Aerosol seeding systems for the NSWC wind tunnels

Four types of laskin nozzles which are used to generate the primary aerosol mist are illustrated. This mist may be used directly as laser doppler velocimeters (LDV) particles. However, in general, a wide range of particle size exists at this stage and requires the use of some type of mono-dispersion refinement technique. These nozzles rely on the shearing action of high speed air near a column of seeding liquid. Typically, olive oil or dioctyl phthalate (DOP) is used, but within the past year solid polystyrene particles in an alcohol suspension have been used with great success. Air, at a typical pressure of five psig, is supplied to the top of the nozzle which is merely a hollow tube. This air issues radially from one or more small jets located near the collar close to the bottom of the tube. When the collar is submerged in the seeding liquid, the hollow columns located in the collar become filled with liquid. The air from the jet shears the liquid into the fine mist.

Yanta, W. J.↗
NASA NTRS1985

Development of a new laser Doppler velocimeter for the Ames High Reynolds Channel No. II

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. 2 is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to position the laser beams in the channel flow. Techniques used to seed the flow with 0.5-micron-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.

Seegmiller, H. L.↗
NASA NTRS1985

Direct observation of the excited-state proton transfer and decay kinetics of internally hydrogen-bonded photostabilizers in copolymer films

The excited-state dynamics of a 2-hydroxyphenylbenzotriazole (HPB) photostabilizer copolymerized with polystyrene are reported. HPB fluorescence from these copolymer films is observed at approximately 630 nm, characteristic of the proton-transferred excited state of HPB, and it has a risetime of less than 10 ps and a decay time of 28 + or - 4 ps at room temperature. Measurement of the relative fluorescence quantum yield as a function of temperature gives the activation energy for nonradiative decay of this state to be E/hc = 259 + or 25/cm.

Oconnor, D. B.↗
NASA NTRS1986

Comet coma sample return

The feasibility of capturing comet dust with polymer foam, dense gas, and fiber collectors is discussed. Polystyrene foams seem suitable. For volatile capture, chemically active getters are suggested. A scenario for a low speed flyby sample return mission is outlined.

Tsou, P.↗
NASA NTRS1987

Interfacial adhesion of carbon fibers

Relative adhesion strengths between AS4, AS1, and XAS carbon fibers and thermoplastic polymers were determined using the embedded single filament test. Polymers studied included polycarbonate, polyphenylene oxide, polyetherimide, polysulfone, polyphenylene oxide blends with polystyrene, and polycarbonate blends with a polycarbonate polysiloxane block copolymer. Fiber surface treatments and sizings improved adhesion somewhat, but adhesion remained well below levels obtained with epoxy matrices. An explanation for the differences between the Hercules and Grafil fibers was sought using X ray photon spectroscopy, wetting, scanning electron microscopy and thermal desorption analysis.

Bascom, Willard D.↗
NASA NTRS1987

Advances in solid polymer electrolyte fuel cell technology with low-platinum-loading electrodes

The Gemini Space program demonstrated the first major application of fuel cell systems. Solid polymer electrolyte fuel cells were used as auxiliary power sources in the spacecraft. There has been considerable progress in this technology since then, particularly with the substitution of Nafion for the polystyrene sulfonate membrane as the electrolyte. Until recently the performance was good only with high platinum loading (4 mg/sq cm) electrodes. Methods are presented to advance the technology by (1) use of low platinum loading (0.35 mg/sq cm) electrodes; (2) optimization of anode/membrane/cathode interfaces by hot pressing; (3) pressurization of reactant gases, which is most important when air is used as cathodic reactant; and (4) adequate humidification of reactant gases to overcome the water management problem. The high performance of the fuel cell with the low loading of platinum appears to be due to the extension of the three dimensional reaction zone by introduction of a proton conductor, Nafion. This was confirmed by cyclic voltammetry.

Srinivasan, Supramaniam↗
NASA NTRS1986

Development and testing of a space-flight dilatometer/reactor

A stainless-steel piston cylinder dilatometer (volume about 100 cu cm), designed for use in microgravity, was tested and modified for the purpose of obtaining the polymerization kinetics of monodisperse polystyrene latexes, as well as the latexes themselves. A low-speed, oscillatory agitation (10 rpm, 30 deg of arc/per cycle) and redesigned stir paddle were selected for the low shear requirements of the microgravity experiments. Conversion histories accurate to within 2 percent were obtained after apparatus modification and procedural changes were implemented.

Sudol, E. D.↗
NASA NTRS1987

Electrodeposition of metals and metal/cermet composites in low gravity

Electrodeposition experiments were carried out on the bench and a KC-135 aircraft at 0.01 g in anticipation of microgravity flights on NASA's Space Transportation System Shuttle. Experimental results obtained by interferometry compare concentration gradients as a function of time in the vicinity of a reducing electrode (cathode) for Cu(+2) and Co(+2) electrodeposition cells. No difference was found between bench and 0.01 g produced gradients for a .1M CuSO4 cell, but a significant difference was noted between the gradients in a 1M CoSO4 cell even though the bench cells were operated in a nonconvecting shielded (cathode over anode) mode. The gradient for Co(+2) depletion produced at 0.01 g was greater and the entire layer was thicker than found on the bench. Neutral buoyancy/matched density codeposition experiments were performed on the bench in an attempt to physically duplicate the results of metal/cermet codepositions in microgravity. Polystyrene spheres with average diameter 11.8 microns and density approximately matching that of 1M CoSO4 were utilized to emulate nonsedimenting cermets in microgravity. The cells were operated in a shielded convectionless mode. Comparison with literature data on codeposition with stirred cells indicate significant improvement in volume percent neutral occluded in the depositing metal matrix. A multicell electrodeposition flight apparatus that has been designed, constructed and is undergoing testing is discussed.

Riley, Clyde↗
NASA NTRS1986

Stopping of relativistic heavy ions in various media

The residual ranges of (900 + or - 3)-MeV/amu gold nuclei accelerated at the Lawrence Berkeley Laboratory Bevalac have been measured in several different media. The energy of the beam of nuclei was measured directly using a new time-of-flight system. The ranges were measured by absorption in linear wedges of polyethylene, carbon, aluminum, copper, tin, and lead and in circular wedges of polystyrene, aluminum, and gold, and by total absorption in nuclear emulsion. The measured ranges were significantly different from those calculated from the best available theoretical estimates of the energy loss of highly charged nuclei. It is concluded that at present energy losses and residual ranges of relativistic heavy ions in an arbitrary medium cannot be predicted with better than an approximately 2 percent accuracy.

Waddington, C. J.↗
NASA NTRS1986

An analysis for crack layer stability

The problem of uncontrolled crack propagation and crack arrest is considered with respect to crack layer (CL) translational stability. CL propagation is determined by the difference between the energy release rate and the amount of energy required for material transformation, and necessary and sufficient conditions for CL instability are derived. CL propagation in polystyrene is studied for two cases. For the case of remotely applied fixed load fatigue, the sufficient condition of instability is shown to be met before the necessary condition, and the necessary condition controls the stability. For the fixed displacement case, neither of the instability conditions are met, and CL propagation remains stable, resulting in crack arrest.

Sehanobish, K.↗
NASA NTRS1987

Control of electroosmosis in coated quartz capillaries

The effectiveness of various coatings for controlling the electroosmotic fluid flow that hinders electrophoretic processes is studied using analytical particle microelectrophoresis. The mobilities of 2-micron diameter glass and polystyrene latex spheres (exhibiting both negative and zero effective surface charge) were measured in 2-mm diameter quartz capillaries filled with NaCl solutions within the 3.5-7.8 pH range. It is found that capillary inner surface coatings using 5000 molecular weight (or higher) poly(ethylene glycol): significantly reduced electroosmosis within the selected pH range, were stable for long time periods, and appeared to be more effective than dextran, methylcellulose, or silane coatings.

Herren, Blair J.↗
NASA NTRS1984

Preparation of large-particle-size monodisperse latexes in space - Polymerization kinetics and process development

Monodisperse polystyrene latexes are prepared by seeded emulsion polymerization; however, sizes larger than 2 microns are difficult to prepare because of the creaming and settling of the particles and their sensitivity to mechanical shear. Preparation in space would obviate the creaming and settling, and allow agitation just sufficient for good heat transfer and mixing. Three polymerizations yielding 3-5 micron size particles were carried out successfully on the third flight of the 'Columbia' launched Mar. 22, 1982; however, four polymerizations yielding sizes up to 10 microns on the fourth flight launched June 27, 1982 were incomplete owing to apparatus malfunction. The results of these polymerizations and the prospects of developing a preparative space process are reviewed.

Vanderhoff, J. W.↗
NASA NTRS1988

Acrolein Microspheres Are Bonded To Large-Area Substrates

Reactive cross-linked microspheres produced under influence of ionizing radiation in aqueous solutions of unsaturated aldehydes, such as acrolein, with sodium dodecyl sulfate. Diameters of spheres depend on concentrations of ingredients. If polystyrene, polymethylmethacrylate, or polypropylene object immersed in solution during irradiation, microspheres become attached to surface. Resulting modified surface has grainy coating with reactivity similar to free microspheres. Aldehyde-substituted-functional microspheres react under mild conditions with number of organic reagents and with most proteins. Microsphere-coated macrospheres or films used to immobilize high concentrations of proteins, enzymes, hormones, viruses, cells, and large number of organic compounds. Applications include separation techniques, clinical diagnostic tests, catalytic processes, and battery separators.

Rembaum, Alan↗
NASA NTRS1987

Continuous flow electrophoresis system experiments on shuttle flights STS-6 and STS-7

A space continuous flow electrophoresis system (CFES) was developed that would incorporate specific modifications to laboratory instruments to take advantage of weightlessness. The specific objectives were to use a model sample material at a high concentration to evaluate the continuous flow electrophoresis process in the CFES instrument and compare its separation resolution and sample throughput with related devices on Earth and to expand the basic knowledge of the limitations imposed by fluid flows and particle concentration effects on the electrophoresis process by careful design and evaluation of the space experiment. Hemoglobin and polysaccharide were selected as primary samples. The results from space show a large band spread of the high concentration of the single species of hemoglobin that was due to the mismatch of electrical conductivity between the sample and the buffer. On STS-7 the major objective was to evaluate the influence of the electrical properties of the sample constituents on the resolution of the CFES. As expected, the polystyrene latex microspheres dispersed in a solution with 3 times the electrical conductivity of the curtain buffer separated with a larger band spread than in the 2nd experiment.

Snyder, Robert S.↗
NASA NTRS1987

Curvilinear crack layer propagation

An account is given of an experiment designed to allow observation of the effect of damage orientation on the direction of crack growth in the case of crack layer propagation, using polystyrene as the model material. The direction of crack advance under a given loading condition is noted to be determined by a competition between the tendency of the crack to maintain its current direction and the tendency to follow the orientation of the crazes at its tip. The orientation of the crazes is, on the other hand, determined by the stress field due to the interaction of the crack, the crazes, and the hole. The changes in craze rotation relative to the crack define the active zone rotation.

Chudnovsky, Alexander↗
NASA NTRS1987

On self-similarity of crack layer

The crack layer (CL) theory of Chudnovsky (1986), based on principles of thermodynamics of irreversible processes, employs a crucial hypothesis of self-similarity. The self-similarity hypothesis states that the value of the damage density at a point x of the active zone at a time t coincides with that at the corresponding point in the initial (t = 0) configuration of the active zone, the correspondence being given by a time-dependent affine transformation of the space variables. In this paper, the implications of the self-similarity hypothesis for qusi-static CL propagation is investigated using polystyrene as a model material and examining the evolution of damage distribution along the trailing edge which is approximated by a straight segment perpendicular to the crack path. The results support the self-similarity hypothesis adopted by the CL theory.

Botsis, J.↗
NASA NTRS1989

Unpressurized Container For Cryogenic Testing

Unpressurized cryostat makes mechanical testing of materials at low temperature more convenient. Maintains specimens at temperatures of -400 to -450 degree F without sealing them in gastight, vacuum-insulated container. Easy to insert and remove specimens and attach instrumentation wiring to them. Vents vapor continuously, so no danger of buildup of internal pressure from evaporating cryogenic liquid. Includes two concentric chambers with stainless-steel walls and fiber insulation. Specimen mounted in inner chamber, and such instruments as extensometers and thermocouples attached. Loose lid of polystyrene foam or other suitable material placed over vessel.

Walker, Susan B.↗