Lunar Dust Levitation

Observations of a lunar “horizon glow” by several Surveyor spacecraft on the lunar surface in the 1960s and detections of dust particle impacts by the Apollo 17 Lunar Ejecta and Meteoroid Experiment have been explained as the result of micron-sized charged particles lifting off the surface. The surface of the Moon is exposed to the solar wind and solar UV radiation causing photoemission, so it develops a surface charge and an electric field near the surface. Dust particles injected into this plasma from the lunar regolith, whether from human and mechanical activity or from meteoroid impacts or electrostatic forces, may be stably levitated above the surface and may undergo preferential deposition onto areas of the lunar surface (or equipment) with different electrical properties. This can lead to a net transport as well as contamination of sensitive equipment. This paper reports on new experimental measurements and numerical simulations of the plasma environment above the lunar surface and the related behavior of charged dust.     

EBSD-Based Microscopy: Resolution of Dislocation Density

Consideration is given to the resolution of dislocation density afforded by EBSD-based scanning electron microscopy. Comparison between the conventional Hough- and the emerging high-resolution cross-correlation-based approaches is made. It is illustrated that considerable care must be exercised in selecting a step size (Burger's circuit size) for experimental measurements. Important variables affecting this selection include the dislocation density and the physical size and density of dislocation dipole and multi-pole components of the structure. It is also illustrated that simulations can be useful to the interpretation of experimental recoveries.     

Electrospun Nanoparticle–Nanofiber Composites via a One‐Step Synthesis

A facile approach to synthesize and incorporate metal nanoparticles (NPs) into electrospun polymer nanofibers (NFs) wherein the electrospinning polymer acts as both a reducing agent for the metal salt precursor, as well as a protecting and templating agent for the ensuing NPs, is reported. Such a true one‐step process at ambient conditions and free of organic solvents is demonstrated using a system comprising AgNO₃ and poly(ethylene oxide) (PEO) at electrospinnable molecular weights of 600, 1000, or 2000 kDa. The PEO transforms Ag⁺ into AgNPs, a phenomenon that has not been previously possible at PEO molecular weights less than 20 kDa without the addition of a separate reducing agent and stabilizer or the application of heat. Results from X‐ray photoelectron spectroscopy and UV–Vis absorption spectrophotometry analyses support the formation of pseudo‐crown ethers in high molecular weight PEO as the mechanism in the development of NPs. The AgNPs reduce fiber diameter and enhance fiber quality (reduced beading) due to increased electrical conductivity. Interestingly, several of the NFs exhibit AgNP‐localized nanochain formation and protrusion from the NF surface that can be attributed to the combined effect of applied electrical field on the polymer and the differences between the electrical conductivity and polarizability of the polymer and metal NPs.     

Emission modeling of styrene from vinyl ester resins with low hazardous air pollutant contents

Styrene is a commonly used co-monomer in vinyl ester (VE) resins, which acts as a reactive diluent and is required in most liquid molding fabrication methods to reduce viscosity and improve overall resin performance. Resins containing low hazardous air pollutant contents have been developed to reduce the styrene emissions during composite fabrication. VE monomers with a bimodal molecular weight distribution have been used to effectively decrease the amount of styrene in the system while maintaining low resin viscosities. Fatty acid vinyl ester (FAVE) resins partially replace styrene with non-volatile fatty acid monomers to reduce styrene emissions. The emissions from bimodal and FAVE resins were measured as a function of time and various parameters, including styrene content, VE molecular weight, and fatty acid monomer content and chain length. The initial emission rate from VE resins is only dependent on styrene content for constant evaporation geometry. Furthermore, the evaporation rate constant was the same regardless of VE molecular weight, styrene content, or the use of co-reactive diluent (MFA monomers). The diffusivity was not dependent on the styrene content in the resin, but decreased linearly as the VE molecular weight increased because of a corresponding increase in the resin viscosity. The diffusivity also increased as the content of MFA increased because of a decrease in the resin viscosity with high MFA content at high emission time. Furthermore, the emission profiles were accurately modeled using a modified version of 1D diffusion through a planar sheet that accounts for the depth change as a function of styrene evaporation. Overall, the model predicted emission profiles similar to the experimentally measured profiles as a function of time for various styrene contents, VE molecular weights, and fatty acid monomer contents.     

Modeling efficiency and water balance in PEM fuel cell systems with liquid fuel processing and hydrogen membranes

Integrating PEM fuel cells effectively with liquid hydrocarbon reforming requires careful system analysis to assess trade-offs associated with H₂ production, purification, and overall water balance. To this end, a model of a PEM fuel cell system integrated with an autothermal reformer for liquid hydrocarbon fuels (modeled as C₁₂H₂₃) and with H₂ purification in a water–gas-shift/membrane reactor is developed to do iterative calculations for mass, species, and energy balances at a component and system level. The model evaluates system efficiency with parasitic loads (from compressors, pumps, and cooling fans), system water balance, and component operating temperatures/pressures. Model results for a 5-kW fuel cell generator show that with state-of-the-art PEM fuel cell polarization curves, thermal efficiencies >30% can be achieved when power densities are low enough for operating voltages >0.72 V per cell. Efficiency can be increased by operating the reformer at steam-to-carbon ratios as high as constraints related to stable reactor temperatures allow. Decreasing ambient temperature improves system water balance and increases efficiency through parasitic load reduction. The baseline configuration studied herein sustained water balance for ambient temperatures ≤35 °C at full power and ≤44 °C at half power with efficiencies approaching ∼27 and ∼30%, respectively.     

Sodium borohydride hydrolysis kinetics comparison for nickel,cobalt, and ruthenium boride catalysts

Hydrolysis tests have been performed at a constant temperature of 60 °C over a range of sodium borohydride (2.5–30 wt%) and sodium hydroxide (2.5–30 wt%) concentrations. Catalysts used to initiate the hydrolysis reaction were developed through the metal salt reduction method with sodium borohydride. These catalysts were identified as nickel boride, cobalt boride, and ruthenium with each catalyst having similar morphology. Catalysts were tested in loose, powder form free of binders or substrates. Hydrolysis rate comparisons show that reaction rates decrease linearly with increasing NaBH₄ concentrations due to mass transfer limitations. Increasing NaOH concentration has been shown to drive a non-catalyzed intermediate reaction with the rate of the overall reaction hindered by the catalysts’ ability to bind hydrogen to active sites. Maximum hydrogen production rates for the Ni₃B, Co₃B, and Ru catalysts were found to be 1.3, 6.0, and 18.6 L min⁻¹ g_cat⁻¹, respectively.     

The synthesis, characterization and biocompatibility of poly(ester urethane)/polyhedral oligomeric silesquioxane nanocomposites

The primary goal of this study is to develop a facile and inexpensive synthesis method for a new biodegradable and biocompatible poly(ester urethane) (PEU)/polyhedral oligomeric silesquioxanes (POSS) nanocomposite via in situ homogeneous solution polymerization reaction into prescribed macromolecular structure and properties including improved biocompatibility, thermal and hydrolytic stability, and stiffness and strength. Cell culture studies, nuclear magnetic resonance spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetry, and dynamic mechanical analysis measurements were used to confirm the structure and property improvements. The results show that the targeted PEU/POSS nanocomposites (which are remarkably different from conventional polymers, polymer nanocomposites and microcomposites) have significant improvements in mechanical properties and degradation resistance at small POSS concentrations (≤6 wt%). The nanocomposites exhibited excellent support for cell growth without any toxicity. POSS concentration did not affect cell adhesion or cell growth, but it significantly changed the surface structure of the PEU into a 3-dimensional matrix with regular pores that may allow cells to better access the growth factors/nutrients, waste exchange, and tissue remodeling. The PEU/POSS nanocomposites were resistant to degradation over a period of six months when exposed to a buffer solution. These desirable characteristics suggest that the nanocomposites may hold great promise for future high-end uses such as in biomedical devices, especially at cardiovascular interfaces.     

Fischer-Tropsch catalyst testing in a continuous bench-scale coal gasification system

A bench-scale oxygen-blown fluid-bed gasifier was coupled to a modular fixed-bed Fischer-Tropsch (FT) reactor system for testing an FT catalyst under syngas. Various blends of subbituminous coal, torrefied biomass, and untreated biomass were gasified at 22 bar absolute, 800°-860 °C, and 4 kg/h. Syngas exiting the fluid bed passed through a cyclone, candle filter, and sulfur sorbent to reduce fine particulate and H₂S to levels well below 1 ppmv. The syngas was cooled to condense out moisture and volatiles and then reheated to temperatures required for FT synthesis. The clean syngas then flowed into the FT reactor with a 5:1 ratio of recycled FT product gas-to-fresh syngas feed. A 70% overall conversion of CO and H₂ was achieved at 269 °C and 18.9 bar over an iron-based catalyst supported on gamma-alumina pellets.     

A Novel Processing Route to Develop a Dense Nanocrystalline Alumina Matrix (<100 nm) Nanocomposite Material

A dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) toughening alumina matrix nanocomposite with a nanocrystalline (<100 nm) matrix grain size has been successfully developed by a novel processing method. A combination of very rapid sintering at a heating rate of 500°C/min and at a sintering temperature as low as 1100°C for 3 min by the spark-plasma-sintering technique and mechanical milling of the starting γ-Al₂O₃ nanopowder via a high-energy ball-milling process can result in a fully dense nanocrystalline alumina matrix ceramic nanocomposite. The grain sizes for the matrix and the toughening phase were 96 and 265 nm, respectively. A great increase in toughness almost 3 times that for pure nanocrystalline alumina has been achieved in the dense nanocomposite. Ferroelastic domain switching without undergoing phase transformation in nanocrystalline t -ZrO₂ is likely as a mechanism for enhanced toughness.     

Highly Textured BaTiO3 via Templated Grain Growth and Resulting Polarization Reversal Dynamics

Samples of bulk textured polycrystalline BaTiO₃ ceramics were fabricated using a templated grain growth (TGG) approach in order to investigate effects of polycrystallinity and texture related to ferroelectric domain reversal under high‐power drive conditions. Barium titanate platelets were formed via two‐step topochemical conversion of bismuth titanate platelets grown via molten salt synthesis, then aligned via tape casting within a matrix of fine BaTiO₃ powder. The coarse‐grained parts showed a high degree of crystallographic texture after sintering. Combined with ceramics of similar density and polycrystallinity, but random orientation and commercial single‐crystal specimens, this sample set enabled direct isolation of crystallographic texture and polycrystallinity as the primary variables for high‐power polarization reversal studies. These studies have also demonstrated a link between grain size and polarization reversal time that strongly suggests that grain boundaries serve effectively as nucleation sites during the ferroelectric switching process.