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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Acoustically Enhanced Electroplating Being Developed

In cooperation with the NASA Glenn Research Center, Alchemitron Corp. is developing the Acoustically Enhanced Electroplating Process (AEEP), a new technique of employing nonlinear ultrasonics to enhance electroplating. The applications range from electroplating full-panel electronic circuit boards to electroplating microelectronics and microelectromechanical systems (MEMS) devices. In a conventional plating process, the surface area to be plated is separated from the nonplated areas by a temporary mask. The mask may take many forms, from a cured liquid coating to a simple tape. Generally, the mask is discarded when the plating is complete, creating a solid waste product that is often an environmental hazard. The labor and materials involved with the layout, fabrication, and tooling of masks is a primary source of recurring and nonrecurring production costs. The objective of this joint effort, therefore, is to reduce or eliminate the need for masks. AEEP improves selective plating processes by using directed beams of high-intensity acoustic waves to create nonlinear effects that alter the fluid dynamic and thermodynamic behavior of the plating process. It relies on two effects: acoustic streaming and acoustic heating. Acoustic streaming is observed when a high-intensity acoustic beam creates a liquid current within the beam. The liquid current can be directed as the beam is directed and, thus, users can move liquid around as desired without using pumps and nozzles. The current of the electroplating electrolyte, therefore, can be directed at distinct target areas where electroplating is desired. The current delivers fresh electrolyte to the target area while flushing away the spent electrolyte. This dramatically increases the plating rate in the target area. In addition, acoustic heating of both the liquid in the beam and the target surface increases the chemical reaction rate, which further increases the plating rate. The combined effects of acoustic streaming and heating accelerate the deposition of plating in that area and, thus, provide an effect similar to a mask but without the costs of masking. AEEP further improves the plating process by clearing debris and bubbles from the surface by acoustic radiation pressure and acoustic streaming.

Oeftering, Richard C.↗
NASA NTRS1979

Metal-dielectric interactions

There is a wide variety of situations wherein metals are in solid state contact with dielectric materials. The paper reviews some of the factors that influence solid state interactions for metals in contact with dielectric surfaces. Since surfaces play an important part in these reactions, the use of analytical tools in characterizing surfaces is discussed. Adhesion, friction, and wear are utilized as indicators of the nature of interfacial bonding between metals and dielectrics can be effectively determined with adhesion and friction force measurements. Films present on the surface, such as oxygen or water vapor, markedly alter adhesive bond strength which in turn affects friction force and interfacial fracture when attempts are made to separate the contact regions. Analytical surface tools such as the field ion microscope, Auger emission spectroscopy, and X-ray photoelectron spectroscopy are very effective in providing insight into the effect of contact on the surfaces of metals and dielectrics.

Buckley, D. H.↗
NASA NTRS2006

Grain Surface Chemistry and the Composition of Interstellar Ices

Submicron sized dust grains are an important component of the interstellar medium. In particular they provide surface where active chemistry can take place. At the low temperatures (-10 K) of the interstellar medium, colliding gas phase species will stick, diffuse, react, and form an icy mantle on these dust grains. This talk will review the principles of grain surface chemistry and delineate important grain surface routes, focusing on reactions involving H, D, and O among each other and with molecules such as CO. Interstellar ice mantles can be studied through the fundamental vibrations of molecular species in the mid-infrared spectra of sources embedded in or located behind dense molecular clouds. Analysis of this type of data has provided a complex view of the composition of these ices and the processes involved. Specifically, besides grain surface chemistry, the composition of interstellar ices is also affected by thermal processing due to nearby newly formed stars. This leads to segregation between different ice components as well as outgassing. The latter results in the formation of a so-called Hot Core region with a gas phase composition dominated by evaporated mantle species. Studies of such regions provide thus a different view on the ice composition and the chemical processes involved. Interstellar ices can also be processed by FUV photons and high energy cosmic ray ions. Cosmic ray processing likely dominates the return of accreted species to the gas phase where further gas phase reactions can take place. These different chemical routes towards molecular complexity in molecular clouds and particularly regions of star formation will be discussed.

Tielens, A. G. G. M.↗
NASA NTRS1965

Porous glass makes effective substrate for ozone-sensing reagent

Porous-glass substrate is used for absorption of a dye used in measuring the concentration of atmospheric ozone at high altitudes. This measurement is based on the chemiluminescence produced in the reaction between ozone and the dye, rhodamine B. The porous glass provides a large interstitial surface area which promotes this reaction.

Source record↗
NASA NTRS1997

Atomic Oxygen Treatment Technique for Removal of Smoke Damage from Paintings

Soot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy.

Rutledge, S. K.↗
NASA NTRS1996

Combustion Processes in Hybrid Rocket Engines

In recent years, there has been a resurgence of interest in the development of hybrid rocket engines for advanced launch vehicle applications. Hybrid propulsion systems use a solid fuel such as hydroxyl-terminated polybutadiene (HTPB) along with a gaseous/liquid oxidizer. The performance of hybrid combustors depends on the convective and radiative heat fluxes to the fuel surface, the rate of pyrolysis in the solid phase, and the turbulent combustion processes in the gaseous phases. These processes in combination specify the regression rates of the fuel surface and thereby the utilization efficiency of the fuel. In this paper, we employ computational fluid dynamics (CFD) techniques in order to gain a quantitative understanding of the physical trends in hybrid rocket combustors. The computational modeling is tailored to ongoing experiments at Penn State that employ a two dimensional slab burner configuration. The coordinated computational/experimental effort enables model validation while providing an understanding of the experimental observations. Computations to date have included the full length geometry with and with the aft nozzle section as well as shorter length domains for extensive parametric characterization. HTPB is sed as the fuel with 1,3 butadiene being taken as the gaseous product of the pyrolysis. Pure gaseous oxygen is taken as the oxidizer. The fuel regression rate is specified using an Arrhenius rate reaction, which the fuel surface temperature is given by an energy balance involving gas-phase convection and radiation as well as thermal conduction in the solid-phase. For the gas-phase combustion, a two step global reaction is used. The standard kappa - epsilon model is used for turbulence closure. Radiation is presently treated using a simple diffusion approximation which is valid for large optical path lengths, representative of radiation from soot particles. Computational results are obtained to determine the trends in the fuel burning or regression rates as a function of the head-end oxidizer mass flux, G=rho(e)U(e), and the chamber pressure. Furthermore, computation of the full slab burner configuration has also been obtained for various stages of the burn. Comparisons with available experimental data from small scale tests conducted by General Dynamics-Thiokol-Rocketdyne suggest reasonable agreement in the predicted regression rates. Future work will include: (1) a model for soot generation in the flame for more quantitative radiative transfer modelling, (2) a parametric study of combustion efficiency, and (3) transient calculations to help determine the possible mechanisms responsible for combustion instability in hybrid rocket motors.

Venkateswaran,S.↗
NASA NTRS2004

Fuel Oxidizer Reaction Products (FORP) Contamination of Service Module (SM) and Release of N-nitrosodimethylamine(NDMA)in a Humid Environment from Crew EVA Suits Contaminated with FORP

The Service Module (SM) is an element of the Russian Segment of the International Space Station (ISS). One of the functions of the SM is to provide attitude control for the ISS using thrusters when the U.S. Control Moment Gyros (CMG's) must be desaturated. Prior to an Extravehicular Activity (EVA) on the Russian Segment, the Docking Compartment (DC1) is depressurized, as it is used as an airlock. When the DC1 is depressurized, the CMG's margin of momentum is insufficient and the SM attitude control thrusters need to fire to desaturate the CMG's. SM roll thruster firings induce contamination onto adjacent surfaces with Fuel Oxidizer Reaction Products (FORP). FORP is composed of both volatile and non-volatile components. One of the components of FORP is the potent carcinogen N-nitrosdimethylamine (NDMA). Since the EVA crewmembers often enter the area surrounding the thrusters for tasks on the aft end of the SM and when translating to other areas of the Russian Segment, the presence of FORP is a concern. This paper will discuss FORP contamination of the SM surfaces, the release of NDMA in a humid environment from crew EVA suits, if they happen to be contaminated with FORP, and the toxicological risk associated with the NDMA release.

Schmidl, William↗
NASA NTRS1979

Development of silicon nitride of improved toughness

The application of reaction sintered Si2N4 energy absorbing surface layers to hot-pressed Si3N4 was investigated. The surface layer was formed by in-place nitridation of silicon powder. It was found that reaction sintered Si3N4 layers of 1 mm thickness, fabricated from either -100, +200, -200, or -325 mesh Si powder and nitrided in 96% N2/4% H2 so that approximately 20-25 vol % unnitrided Si remained in the layer, resulted in a sevenfold increase in ballistic impact resistance of a 0.64 cm thick hot-pressed SI3N4 substrate from RT 1370 C. Both NC-132 SI3N4, with MgO additive, and NCX-34 Si3N4, with Y2O3 additive, were evaluated as substrate material. The finer grain size -200 and -325 mesh nitrided Si layers were for their smoothness and relatively high density. It was found that nitriding in N2/H2 mixtures, rather than pure N2, resulted in a microstructure that did not substantially degrade the strength of the hot-pressed Si3N4 substrate. Thermal cycling tests on the RSSN/HPSN combinations from 200 C to 1370 C for 75 cycles in air did not degrade the impact resistance nor the interfacial bonding, although a large amount of internal silica formation occurred within the RSSN layer. Mach 0.8, 5 hr, hot gas erosion tests showed no surface recession of RSSN layers at 1200 C and slight surface recession at 1370 C.

Brennan, J. J.↗
NASA NTRS2015

TPSAS-NF1676L-21180-DND

Ablative materials are used as the Thermal Protection System (TPS) for space vehicles that enter a planetary atmosphere. During the entry phase, the vehicle experiences high rates of aerodynamic heating. These ablative materials, acting as a heat shield, protect the vehicle from the harsh environment and ensure a safe entry. Ablative materials reduce the incoming heat flux through various phenomena such as near-surface oxidation, pyrolysis chemical reaction, vaporization, and other erosive processes, collectively known as ablation. Spallation is one such ablative process, in which solid particles are ejected from the material into the flow field. The many conditions leading to spallation, however, are not well understood and cannot be described accurately by simple phenomenological models. However, the spallation phenomenon might impact the aerodynamic heating rates of re-entry vehicles using ablative heat shields. For example, the solid particles ejected from the surface can modify the near surface chemical processes and flow field. To investigate spallation effects, a code was developed to compute the dynamics of spalled particles. The code uses a finite-rate chemistry model to study the chemical interactions of the particles with the flow field. The spallation code is dynamically coupled to a CFD solver that models the time accurate hypersonic flow field around an ablative sample. An experimental investigation was also performed at the NASA Langley HYMETS facility. HYMETS is a 400 kW arcjet that can simulate hypersonic flight and Earth or Martian entry conditions. Using high speed cameras, an IR camera, NIR and UV-VIS spectrometers, and other diagnostic instruments, test data on various graphite, LI-900, FiberForm, and PICA test samples were obtained, using target heat flux conditions of 100, 200, and 400 W/cm 2 . From the test campaign, measurements of particle velocity, acceleration and trajectory are obtained.

A Martin↗
NASA NTRS1978

Enhanced hydrophilicity of chlorided aluminum oxide particulates

An enhancement of hydrophilicity for chlorided aluminas was demonstrated by the results obtained from gaseous H2O sorptions at 70-, 80-, and 86-percent relative humidity on alpha and gamma aluminum oxide particulates and on alpha and gamma aluminum oxide particulates with a chemisorbed surface chloride phase (produced by reactions of gaseous HCl + H2O on alumina). Continuous sorption histories for H2O on chlorided aluminas having specific surface areas that range from 7 to 227 sq m/g before chloriding indicated that initial sorption rates were directly linked to the extent of chemisorbed chlorided coverage and implied the same relationship for sorption capacities. The initial sorption rate on chlorided aluminas was found to be slower for the first exposure to H2O than for subsequent exposures (which reached equilibrated H2O coverages much faster), suggesting that slow chemical reactions between H2O and chlorided alumina may have been operative during initial exposures. Chlorided alumina particles were found to remain very hydrophilic (relative to nonchlorided analogs) for several H2O sorption/desorption cycles.

Cofer, W. R., III↗
NASA NTRS1998

Energetics of amino acid synthesis in hydrothermal ecosystems

Thermodynamic calculations showed that the autotrophic synthesis of all 20 protein-forming amino acids was energetically favored in hot (100 degrees C), moderately reduced, submarine hydrothermal solutions relative to the synthesis in cold (18 degrees C), oxidized, surface seawater. The net synthesis reactions of 11 amino acids were exergonic in the hydrothermal solution, but all were endergonic in surface seawater. The synthesis of the requisite amino acids of nine thermophilic and hyperthermophilic proteins in a 100 degreesC hydrothermal solution yielded between 600 and 8000 kilojoules per mole of protein, which is energy that is available to drive the intracellular synthesis of enzymes and other biopolymers in hyperthermophiles thriving in these ecosystems.

NASA Discipline Exobiology↗
NASA NTRS1992

Effect of non-equilibrium flow chemistry on the heating distribution over the MESUR forebody during a Martian entry

Effect of flow field properties on the heating distribution over a 140 deg blunt cone was determined for a Martian atmosphere using Euler, Navier-Stokes (NS), viscous shock layer (VSL), and reacting boundary layer (BLIMPK) equations. The effect of gas kinetics on the flow field and the surface heating distribution were investigated. Gas models with nine species and nine reactions were implemented into the codes. Effects of surface catalysis on the heating distribution were studied using a surface kinetics model having five reactions.

Chen, Yih-Kang↗
NASA NTRS1996

Stratospheric Heterogeneous Chemistry and Microphysics: Model Development, Validation and Applications

The objectives of this project are to: define the chemical and physical processes leading to stratospheric ozone change that involve polar stratospheric clouds (PSCS) and the reactions occurring on the surfaces of PSC particles; study the formation processes, and the physical and chemical properties of PSCS, that are relevant to atmospheric chemistry and to the interpretation of field measurements taken during polar stratosphere missions; develop quantitative models describing PSC microphysics and heterogeneous chemical processes; assimilate laboratory and field data into these models; and calculate the extent of chemical processing on PSCs and the impact of specific microphysical processes on polar composition and ozone depletion. During the course of the project, a new coupled microphysics/physical-chemistry/ photochemistry model for stratospheric sulfate aerosols and nitric acid and ice PSCs was developed and applied to analyze data collected during NASA's Arctic Airborne Stratospheric Expedition-II (AASE-II) and other missions. In this model, detailed treatments of multicomponent sulfate aerosol physical chemistry, sulfate aerosol microphysics, polar stratospheric cloud microphysics, PSC ice surface chemistry, as well as homogeneous gas-phase chemistry were included for the first time. In recent studies focusing on AASE measurements, the PSC model was used to analyze specific measurements from an aircraft deployment of an aerosol impactor, FSSP, and NO(y) detector. The calculated results are in excellent agreement with observations for particle volumes as well as NO(y) concentrations, thus confirming the importance of supercooled sulfate/nitrate droplets in PSC formation. The same model has been applied to perform a statistical study of PSC properties in the Northern Hemisphere using several hundred high-latitude air parcel trajectories obtained from Goddard. The rates of ozone depletion along trajectories with different meteorological histories are presently being systematically evaluated to identify the principal relationships between ozone loss and aerosol state. Under this project, we formulated a detailed quantitative model that predicts the multicomponent composition of sulfate aerosols under stratospheric conditions, including sulfuric, nitric, hydrochloric, hydrofluoric and hydrobromic acids. This work defined for the first time the behavior of liquid ternary-system type-1b PSCS. The model also allows the compositions and reactivities of sulfate aerosols to be calculated over the entire range of environmental conditions encountered in the stratosphere (and has been incorporated into a trajectory/microphysics model-see above). Important conclusions that derived from this work over the last few years include the following: the HNO3 content of liquid-state aerosols dominate PSCs below about 195 K; the freezing of nitric acid ice from sulfate aerosol solutions is likely to occur within a few degrees K of the water vapor frost point; the uptake and reactions of HCl in liquid aerosols is a critical component of PSC heterogeneous chemistry. In a related application of this work, the inefficiency of chlorine injection into the stratosphere during major volcanic eruptions was explained on the basis of nucleation of sulfuric acid aerosols in rising volcanic plumes leading to the formation of supercooled water droplets on these aerosols, which efficiently scavenges HCl via precipitation.

Turco, Richard P.↗
NASA NTRS1990

Gaseous optical contamination of the spacecraft environment: A review

Interactions between the ambient atmosphere and orbiting spacecraft, sounding rockets, and suborbital vehicles, and with their effluents, give rise to optical (extreme UV to LWIR) foreground radiation which constitutes noise that raises the detection threshold for terrestrial and celestial radiations, as well as military targets. Researchers review the current information on the on-orbit optical contamination. Its source species are created in interaction processes that can be grouped into three categories: (1) Reactions in the gas phase between the ambient atmosphere and desorbates and exhaust; (2) Reactions catalyzed by exposed ram surfaces, which occur spontaneously even in the absence of active material releases from the vehicles; and (3) Erosive excitative reactions with exposed bulk (organic) materials, which have recently been identified in the laboratory though not as yet observed on spacecraft. Researchers also assess the effect of optical pumping by earthshine and sunlight of both reaction products and effluents.

Tran, N. H.↗
NASA NTRS1974

Cold-air investigation of a turbine for high temperature-engine application. 5: Two-stage turbine performance as affected by variable stator area

The stator areas of the design two-stage turbine were both decreased and increased by nominally 30 percent, and the performances of the two turbines are compared with that of the design stator area turbine. Turbine efficiency decreased with stator area changes. Closing the stator area resulted in the more severe efficiency loss. The decrease in efficiency for both turbines is attributable to rotor incidence, off-design blade-surface velocities, and adverse reaction changes across the blade rows.

Behning, F. P.↗
NASA NTRS1974

A mass spectrometric system for analyzing thermal desorption spectra of ion-implanted argon and cesium in tungsten

A mass spectrometric system for determining the characteristics of materials used in instrumental development and aerospace applications was developed. The desorption spectra of cesium that was ion-implanted into polycrystalline tungsten and the effects on the spectra of bombardment of the tungsten by low energy (70 eV) electrons were investigated. Work function changes were measured by the retarding potential diode method. Flash desorption characteristics were observed and gas-reaction mechanisms of the surface of heated metal filaments were studied. Desorption spectra were measured by linearly increasing the sample temperature at a selected rate, the temperature cycling being generated from a ramp-driven dc power supply, with the mass spectrometer tuned to a mass number of interest. Results of the study indicate an anomolous desorption mechanism following an electron bombardment of the sample surface. The enhanced spectra are a function of the post-bombardment time and energy and are suggestive of an increased concentration of cesium atoms, up to 10 or more angstroms below the surface.

Wood, G. M., Jr.↗
NASA NTRS1977

Surfactant-assisted coal liquefaction

Improved process of coal liquefaction utilizing nonaqueous surfactant has increased oil yield from 50 to about 80%. Asphaltene molecule formation of colloid particles is prevented by surfactant. Separated molecules present more surface area for hydrogenation reaction. Lower requirements for temperature, pressure, and hydrogen lead to reduction in capital and operation costs.

Hsu, G. C.↗