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NASA NTRS1990

Development of pitch angle anisotropy and velocity diffusion of pickup ion shell distribution by solar wind turbulence

The evolution of pitch angle anisotropy in initially isotropic spherical shell distribution of pickup ions subjected to a continuous influence of weak or moderate intrinsic solar wind turbulence is investigated using a physical model which assumes that the wave of the solar wind turbulence is propagating mainly in the direction parallel to the ambient magnetic field. It is shown that, because of the pitch angle dependence of the velocity diffusion process, a significant pitch angle anisotropy of pickup ion shell distribution develops in the early stage of the diffusion process. Although it is smeared out later on, the result can be of significant importance, especially if the pickup ion density is large, because the pitch angle anisotropy can excite collective instabilities and increase the wave level, thus accelerating the diffusion process.

Yoon, Peter H.↗

NASA NTRS1976

Microscopic aspects of interfacial reactions in diffusion bonding processes

Microscopic aspects of interfacial reactions are discussed, such as interdiffusion, formation of intermetallic phases, generation and annihilation of lattice defects, effect of temperature, grain size, etc., which normally occur in diffusion bonding processes. Relationships between properties and microstructure in thin film couples are examined utilizing a unique combination of contact resistance measurements and characterization by transmission electron microscopy.

Shearer, M. P.↗

NASA NTRS1990

[NASA/DOD Aerospace Knowledge Diffusion Research Project. Paper 7:] The NASA/DOD Aerospace Knowledge Diffusion Research Project: The DOD perspective

This project will provide descriptive and analytical data regarding the flow of STI at the individual, organizational, national, and international levels. It will examine both the channels used to communicate information and the social system of the aerospace knowledge diffusion process. Results of the project should provide useful information to R and D managers, information managers, and others concerned with improving access to and use of STI. Objectives include: (1) understanding the aerospace knowledge diffusion process at the individual, organizational, and national levels, placing particular emphasis on the diffusion of Federally funded aerospace STI; (2) understanding the international aerospace knowledge diffusion process at the individual and organizational levels, placing particular emphasis on the systems used to diffuse the results of Federally funded aerospace STI; (3) understanding the roles NASA/DoD technical report and aerospace librarians play in the transfer and use of knowledge derived from Federally funded aerospace R and D; (4) achieving recognition and acceptance within NASA, DoD and throughout the aerospace community that STI is a valuable strategic resource for innovation, problem solving, and productivity; and (5) providing results that can be used to optimize the effectiveness and efficiency of the Federal STI aerospace transfer system and exchange mechanism.

Pinelli, Thomas E.↗

DOE OSTI2023

Product selectivity and mass transport in levulinic acid transfer hydrogenation by monolithic MIL-100, MIL-88B and ZIF-8@Pd MOFs

The diffusion processes between adsorbent and adsorbate naturally play a significant role in the efficiency and selectivity of the heterogenous catalytic process. This paper considers the importance of diffusion processes in the transfer hydrogenation reaction of levulinic acid to γ-valerolactone by MIL-88B, MIL-100, and ZIF8@Pd monolithic catalysts. Over a period of five catalytic cycles, it was shown that the Fe-based catalysts can achieve similar conversions to the ZIF-8 supported Pd, with the only current limitation being the lower aqueous stability of these MOFs. Diffusion constants were calculated using the ZLC method, with micropore diffusion limitation found for ZIF-8 and MIL-100 monolithic frameworks at 2.7 x 10 -8 and 4.6 x 10 -8 cm 2 s -1 respectively. This diffusion limitation was also confirmed by IR spectroscopy with an increasing concentration of C—H bands on the MOF substrate post-reaction. Mass transfer coefficients, also calculated by ZLC, revealed increased mass transport for the hydrophobic ZIF-8 framework, which perhaps aids in the γ-valerolactone selectivity over side products that are produced in the absence of catalytic material, as seen for MIL-88B and MIL-100 after multiple uses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1992

Tidal evolution of globular clusters. II - The effects of Galactic tidal field and diffusion

The tidal evolution of globular clusters subject to various degrees of the internal diffusion process is investigated. In cases of negligible diffusion, clusters are found to be tidally truncated to the theoretical tidal radius at perigalacticon. There is no apparent orbital phase dependence of the tidal radius for clusters with eccentric orbits. In clusters with moderately short two-body relaxation time scales, diffusion processes significantly modify the structure of the outer regions in such a way that the limiting radius may be comparable to the tidal radius at apogalacticon. The Galactical tidal torque induces isotropy in the velocity dispersion of the outer regions of the cluster. For relaxed clusters, the velocity dispersion may be isotropic in the core, anisotropic in the envelope and isotropic near the limiting radius. Disk shocking is also very efficient for isotropizing the orbits of stars in the outer cluster regions. Stars with direct orbits are less stable, so that prolonged tidal interaction can lead to apparent retrograde rotation in the outer regions of the cluster.

Oh, K. S.↗

DOE OSTI2021

Theoretical Analysis of Experimental Data of Sodium Diffusion in Oxidized Molybdenum Thin Films

In this work, the diffusion process of sodium (Na) in molybdenum (Mo) thin films while it was deposited on soda lime glass (SLG) was studied. A small amount of oxygen was present in the chamber while the direct-current (DC) magnetron sputtering was used for the deposition. The substrate temperatures were varied to observe its effect. Such molybdenum films, with or without oxidations, are often used in thin film solar cells, either as back contact or as hole transport layers. Secondary ion mass spectrometry (SIMS) was used to quantify the concentration of the species. A grain diffusion mechanistic model incorporating the effect of grain and grain boundary geometrical shape and size was developed. The model was used to provide an in-depth theoretical analysis of the sodium diffusion in molybdenum thin films that lead to the measured SIMS data. It was observed that not only diffusion coefficients should be considered when analyzing diffusion processes in thin films but also the ratio of grain boundary size to grain size. Both depend on substrate temperature and directly affect the amount of diffused species in the film. The data were analyzed under the light of the film growth speed versus diffusion front speed, the effect of oxygen content, and the effect of substrate temperature on the overall diffusion process. The temperature inversely affects the ratio of grain boundary size and grain size and directly affects the diffusion coefficient, which leads to a preferable temperature at which the highest amount of alkali can be found in the film.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Effect of indium concentration on electrochemical properties of electrode-electrolyte interface of CuIn{sub 1-x}Ga{sub x}Se{sub 2} prepared by electrodeposition

Highlights: • CIGS thin film was electrodeposited on a molybdenum (Mo) electrode from a non-pH buffered chloride-based electrolyte. • The electrodeposited time and the concentration of In{sup 3+} control the growth of CIGS thin film prepared in this electrodeposition system. • The kinetic of electrodeposition system was gradually dominated by the diffusion process with the electrodeposition time. - Abstract: In this study, the electrochemical impedance spectroscopy (EIS) technique was used to investigate the electrochemical behavior of the interface between the Mo electrode and the Cu-In-Ga-Se electrolyte. In this electrodeposition system, the main parameters include (1) various deposition times, and (2) the effect of In{sup 3+} concentration on the diffusion processes, electrical double layer, charge transfer resistance, and Warburg impedance. Experimental results revealed that the electrochemical kinetic behavior of CIGS thin film is strongly influenced by (1) the electrical double layer existing between the substrate, and (2) the electrolyte with different concentrations of In{sup 3+}. With an increase in the electrodeposition time, the kinetic behavior of this electrodeposition system was gradually dominated by the diffusion process rather than charge transfer process.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Diffusion behavior of Ag in TiO2 nanofilms

Highlights: • We prepared Ag/TiO{sub 2} bilayer nanofilms and heat treatment at 400 °C lead to the formation of Ag nanoparticles, which evenly distributed inside TiO{sub 2} nanofilms. • Ag is not oxidized during the heat treatment. • The morphology and size of Ag nanoparticles after heat treatment is temperature related, higher temperature lead to larger Ag nanoparticles on the surface of the film. • The diffusion process is of Ag much easier in amorphous than in anatase structure. - Abstract: Using magnetron sputtering, Ag/TiO{sub 2} bilayer nanofilms were deposited on glass substrates. Heat-treating the Ag/TiO{sub 2} nanofilms at 400 °C led to the formation of Ag nanoparticles, which dispersed inside the TiO{sub 2} films as well as the free surface of the TiO{sub 2} films. After heat treatment the sample at 500 °C, larger Ag nanoparticles could be observed on the surface, which means the particle size after heat treatment is temperature related. Anatase TiO{sub 2} phase was formed after the Ag/TiO{sub 2} films were heat-treated at 400 °C. SEM and TEM were used to investigate the morphology and structure of the films and it was found that Ag was not oxidized during heat treatment. The diffusion process of Ag in TiO{sub 2} film is also related to the order of Ag layer and TiO{sub 2} layer on glass substrate. Moreover, the diffusion process is much easier in amorphous than that in anatase structure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS2001

Turbulent Flame Processes Via Diffusion Flame-Vortex Ring Interactions

Flame-vortex interactions are canonical configurations that can be used to study the underlying processes occurring in turbulent reacting flows. This configuration contains many of the fundamental aspects of the coupling between fluid dynamics and combustion that could be investigated with more controllable conditions than are possible under direct investigations of turbulent flames. Diffusion flame-vortex ring interaction contains many of the fundamental elements of flow, transport, combustion, and soot processes found in turbulent diffusion flames. Some of these elements include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, soot formation and oxidation, and heat release effects. Such simplified flowfield allows the complex processes to be examined more closely and yet preserving the physical processes present in turbulent reacting flows. Furthermore, experimental results from the study of flame-vortex interactions are useful for the validation of numerical simulations and more importantly to deepen our understanding of the fundamental processes present in reacting flows. Experimental and numerical results obtained under microgravity conditions of the diffusion flame-vortex ring interaction are summarized in this paper. Results are obtained using techniques that include Flame Luminosity Imaging (FLI), Laser Soot-Mie Scattering (LSMS), Computational Fluid Dynamics and Combustion (CFDC), and Diode Laser Spectroscopy/Iterative Temperature with Assumed Chemistry (DLS/ITAC).

Dahm, Werner J. A.↗

NASA NTRS1980

Recent progress in high-output-voltage silicon solar cells

The status of the technology associated with the development of high output voltage silicon solar cells is reported. The energy conversion efficiency of a double diffusion process is compared to that of a single diffusion process. The efficiency of a 0.1 ohm/cm solar cell is characterized both before and after covering.

Muelenberg, A.↗

DOE OSTI2021

Aging power spectrum of membrane protein transport and other subordinated random walks

Single-particle tracking offers detailed information about the motion of molecules in complex environments such as those encountered in live cells, but the interpretation of experimental data is challenging. One of the most powerful tools in the characterization of random processes is the power spectral density. However, because anomalous diffusion processes in complex systems are usually not stationary, the traditional Wiener-Khinchin theorem for the analysis of power spectral densities is invalid. Here, we employ a recently developed tool named aging Wiener-Khinchin theorem to derive the power spectral density of fractional Brownian motion coexisting with a scale-free continuous time random walk, the two most typical anomalous diffusion processes. Using this analysis, we characterize the motion of voltage-gated sodium channels on the surface of hippocampal neurons. Our results show aging where the power spectral density can either increase or decrease with observation time depending on the specific parameters of both underlying processes.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Diffusion in intact secondary cell wall models of plants at different equilibrium moisture content

Secondary plant cell walls are composed of carbohydrate and lignin polymers, and collectively represent a significant renewable resource. Leveraging these resources depends in part on a mechanistic understanding for diffusive processes within plant cell walls. Common wood protection treatments and biomass conversion processes to create biorefinery feedstocks feature ion or solvent diffusion within the cell wall. X-ray fluorescence microscopy experiments have determined that ionic diffusion rates are dependent on cell wall hydration as well as the ionic species through non-linear relationships. In this work, we use classical molecular dynamics simulations to map the diffusion behavior of different plant cell wall components (cellulose, hemicellulose, lignin), ions (Na + , K + , Cu2 + , Cl - ) and water within a model for an intact plant cell wall at various hydration states (3-30 wt% water). From these simulations, we analyze the contacts between different plant cell wall components with each other and their interaction with the ions. Generally, diffusion increases with increasing hydration, with lignin and hemicellulose components increasing diffusion by an order of magnitude over the tested hydration range. Ion diffusion depends on charge. Positively charged cations preferentially interact with hemicellulose components, which include negatively charged carboxylates. As a result, positive ions diffuse more slowly than negatively charged ions. Measured diffusion coefficients are largely observed to best fit piecewise linear trends, with an inflection point between 10 and 15% hydration. These observations shed light onto the molecular mechanisms for diffusive processes within secondary plant cell walls at atomic resolution.

09 BIOMASS FUELS↗

NASA NTRS1978

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

The extent to which diffusion-thermal heat flow affects H(+) temperatures in the high-latitude topside ionosphere is studied. Such a heat flow occurs whenever there are H(+)-O(+) relative drifts. From our study we have found that at high-latitudes, where H(+) flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H(+) temperatures by 500-600 K at altitudes above about 900 km.

Schunk, R. W.↗

DOE OSTI2024

Toward a Universal Model of Hyporheic Exchange and Nutrient Cycling in Streams

In this paper we demonstrate that several ubiquitous hyporheic exchange mechanisms can be represented simply as a one-dimensional diffusion process, where the diffusivity decays exponentially with depth into the streambed. Based on a meta-analysis of 106 previously published laboratory measurements of hyporheic exchange (capturing a range of bed morphologies, hydraulic conditions, streambed properties, and experimental approaches) we find that the reference diffusivity and mixing length-scale are functions of the permeability Reynolds Number and Schmidt Number. These dimensionless numbers, in turn, can be estimated for a particular stream from the median grain size of the streambed and the stream's depth, slope, and temperature. Application of these results to a seminal study of nitrate removal in 72 headwater streams across the United States, reveals: (a) streams draining urban and agricultural landscapes have a diminished capacity for in-stream and in-bed mixing along with smaller subsurface storage zones compared to streams draining reference landscapes; (b) under steady-state conditions nitrate uptake in the streambed is primarily biologically controlled; and (c) median reaction timescales for nitrate removal in the hyporheic zone are 0.5 and 20 hr for uptake by assimilation and denitrification, respectively. While further research is needed, the simplicity and extensibility of the framework described here should facilitate cross-disciplinary discussions and inform reach-scale studies of pollutant fate and transport and their scale-up to watersheds and beyond.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1987

Crack diffusion coefficient - A candidate fracture toughness parameter for short fiber composites

In brittle matrix composites, crack propagation occurs along random trajectories reflecting the heterogeneous nature of the strength field. Considering the crack trajectory as a diffusive process, the 'crack diffusion coefficient' is introduced. From fatigue crack propagation experiments on a set of identical SEN polyester composite specimens, the variance of the crack tip position along the loading axis is found to be a linear function of the effective 'time'. The latter is taken as the effective crack length. The coefficient of proportionality between variance of the crack trajectory and the effective crack length defines the crack diffusion coefficient D which is found in the present study to be 0.165 mm. This parameter reflects the ability of the composite to deviate the crack from the energetically most efficient path and thus links fracture toughness to the microstructure.

Mull, M. A.↗

DOE OSTI2017

Electrochemical force microscopy

A system and method for electrochemical force microscopy are provided. The system and method are based on a multidimensional detection scheme that is sensitive to forces experienced by a biased electrode in a solution. The multidimensional approach allows separation of fast processes, such as double layer charging, and charge relaxation, and slow processes, such as diffusion and faradaic reactions, as well as capturing the bias dependence of the response. The time-resolved and bias measurements can also allow probing both linear (small bias range) and non-linear (large bias range) electrochemical regimes and potentially the de-convolution of charge dynamics and diffusion processes from steric effects and electrochemical reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Atomic Diffusion, Segregation, and Grain Boundary Migration in Nickel-Based Alloys from Molecular Dynamics Simulations

Grain boundary diffusion and metal mobility in alloys control material performance in many applications and yet remain poorly understood at a mechanistic level. With advances in accessible time and length scales for computational molecular simulations, and recent force field developments, we now possess tools to help unravel those mechanisms. Using large-scale molecular dynamics simulations, here we examined vacancy-mediated diffusion processes in Ni-5Cr alloy with low and high-energy grain boundaries. We show that atomic diffusion inside the grain boundary plane is about four times higher than bulk diffusion, at any temperature, and exhibits a typical Arrhenius behavior with a very small energy barrier (0~.8 eV for Cr and 0.7 eV for Ni within 1300-1600 K). Additionally, the fastest diffusing species inverts; Cr diffusion was faster than Ni in the bulk but slower in the grain boundaries. This is attributed to the creation of high cohesive energy clusters of Cr at the grain boundary. Grain boundary migration was also observed to be temperature dependent and appears to be two times higher in the 5% Cr alloy than in pure Ni, highlighting the important role of the alloying element on grain boundary motion.

Simonnin, Pauline GN↗

DOE OSTI2018

Tritium Diffusion Pathways in y-LiAlO2 Pellets Used in TPBAR: A First-Principles Density Functional Theory Investigation

With superior thermophysical and thermochemical properties, gamma-LiAlO2 has high compatibility with other blanket materials and is used in the form of an annular pellet in tritium-producing burnable absorber rods (TPBARs) to produce tritium by thermal neutron irradiation of Li-6. In radiation damaged gamma-LiAlO2, different types of vacancies, defects of its constituent elements, and other trapping sites hinder the diffusion process of tritium. In this study, the first-principles density functional theory approach is used to study the diffusion mechanisms of tritium defect and its species, such as interstitial and substitutional tritium defects, oxygen-tritium vacancy defects, and interaction of tritium with oxygen vacancies in defective and nondefective gamma-LiAlO2. The obtained results provide an understanding of how such defects hamper the diffusivity and solubility of tritium. By calculating several different diffusion pathways, our results show that the smallest activation energy barrier is 0.63 eV for substitutional tritium diffusion with a diffusion coefficient of 3.25 X 10(-12) m(2)/s. The smallest oxygen-tritium diffusion barrier is found to be 2.17 eV, which is around 3.5 times higher than the tritium diffusion barrier alone.

Paudel, Hari↗