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A Quantitative Examination of Catalyst Component Impacts on Hydrogen Adsorption and Spillover
Hydrogen spillover is a widely recognized but poorly understood surface phenomenon. We coupled volumetric chemisorption with Fourier transform infrared spectroscopy, thermogravimetric analysis, and acid–base titrations to quantify the roles of metal (Pt, Au) and support chemistry (anatase, rutile, P25 titania) on spillover. We show that metal identity has little to no impact on the amount of spillover hydrogen. Spillover pressure dependence is essentially the same on Au/TiO 2 and Pt/TiO 2 , indicating H 2 adsorption is equilibrated across both the metal and support. Conversely, spillover is highly sensitive to support surface chemistry, as rutile TiO 2 stabilizes ∼5× more surface hydrogen than anatase TiO 2 . This change is due to a combination of factors, including the rutile surface’s higher proton affinity, stabilized surface electronic states, and larger surface entropy. This work highlights the utility of Au/MO x catalysts as control materials for spillover, as they enable quantitative evaluation of H 2 adsorption on active metals and spillover onto the support.
Stochastic stability of the liquid free surface in vertically excited cylinders
Stochastic stability of heavy liquid free surface enclosed in partly filled prismatic cylinder subjected to random vertical acceleration
Fabrication of Metallic Hollow Nanoparticles
Metal and semiconductor nanoshells, particularly transition metal nanoshells, are fabricated using dendrimer molecules. Metallic colloids, metallic ions or semiconductors are attached to amine groups on the dendrimer surface in stabilized solution for the surface seeding method and the surface seedless method, respectively. Subsequently, the process is repeated with additional metallic ions or semiconductor, a stabilizer, and NaBH.sub.4 to increase the wall thickness of the metallic or semiconductor lining on the dendrimer surface. Metallic or semiconductor ions are automatically reduced on the metallic or semiconductor nanoparticles causing the formation of hollow metallic or semiconductor nanoparticles. The void size of the formed hollow nanoparticles depends on the dendrimer generation. The thickness of the metallic or semiconductor thin film around the dendrimer depends on the repetition times and the size of initial metallic or semiconductor seeds.
Effect of thickness and surface composition on the stability of polarization in ferroelectric Hf x Zr 1 - x O 2 thin films
Using density functional theory, we find that tailoring the surface composition provides a route to stabilize the polar phases of the promising ferroelectric material, Hf x Zr 1-x O 2 . First, we show that for pure Hf O 2 , controlling the positively polarized surface to be relatively oxygen rich adequately screens the ferroelectric surface charges and stabilizes the polar orthorhombic phase. We then demonstrate that the ferroelectric polarization, as measured by the structural polar displacements, increases with decreasing thickness, leading to the emergence of a polar rhombohedral-like phase at the ultrathin limit (1.5 unit cells). Our findings extend to the cases of Hf 0.5 Zr 0.5 O 2 and Zr O 2 , both of which have surface energy landscapes similar to that of Hf O 2 . In conclusion, these findings are consistent with and offer insights into the observed absence of a ferroelectric thickness limit in Hf x Zr 1-x O 2 -based thin films.
A model of wind shear and turbulence in the surface boundary layer
A model of wind and turbulence has been described for the surface boundary layer. The wind structure in the surface layer is considered to be a function of the surface parameters, stability, and height. The surface parameters considered are: (1) the surface roughness length; (2) the surface friction velocity; and (3) the zero plane displacement height. The stability parameter, Z/L, where L is the Monin-Obukov stability length, describes the thermal effect on the wind profile. The logarithmic wind profile is used to describe the mean wind field in the neutral boundary layer, and a logarithmic profile with a stability defect is used to describe the stable and unstable atmospheric conditions. For the very stable conditions, the logarithmic wind law does not hold. Under this condition, the layers of the atmosphere become disconnected and large scale frontal motions are the predominate factor in defining the wind profile. Figures are presented which represent some typical wind profiles in the very stable condition.
Low-speed Investigation of the Effect of Small Canard Surfaces on the Directional Stability of a Sweptback-wing Fighter-airplane Model
Low-speed free flight tunnel testing of swept wing fighter aircraft for determining effect of small canard surfaces on directional stability
Differential Surface Elemental Distribution Leads to Significantly Enhanced Stability of PtNi-Based ORR Catalysts
Not provided.
Ultraviolet stability of some modified metal phosphates for thermal-control surfaces.
Modified metal phosphates for thermal-control surfaces investigating stability to ultraviolet, thermal and vacuum environments
Cavity stability during gas jet impingement on liquid surfaces in weightlessness
Cavity stability during gas jet impingement on liquid surfaces in weightlessness
Low Force Penetration of Icy Regolith
A percussive cone penetrometer measures the strength of granular material by using percussion to deliver mechanical energy into the material. A percussive cone penetrometer was used in this study to penetrate a regolith ice mixture by breaking up ice and decompacting the regolith. As compared to a static cone penetrometer, percussion allows low reaction forces to push a penetrometer probe tip more easily into dry regolith in a low gravity environment from a planetary surface rover or a landed spacecraft. A percussive cone penetrates icy regolith at ice concentrations that a static cone cannot penetrate. In this study, the percussive penetrator was able to penetrate material under 65 N of down-force which could not be penetrated using a static cone under full body weight. This paper discusses using a percussive cone penetrometer to discern changes in the concentration of water-ice in a mixture of lunar regolith simulant and ice to a depth of one meter. The rate of penetration was found to be a function of the ice content and was not significantly affected by the down-force. The test results demonstrate that this method may be ideal for a small platform in a reduced gravity environment. However, there are some cases where the system may not be able to penetrate the icy regolith, and there is some risk of the probe tip becoming stuck so that it cannot be retracted. It is also shown that a percussive cone penetrometer could be used to prospect for water ice in regolith at concentrations as high as 8 by weight.
Mitigation of rapid capacity decay in silicon-LiNi 0.6 Mn 0.2 Co 0.2 O 2 full batteries
Silicon (Si)-based materials have been considered as the most promising anode materials for high-energy-density lithium-ion batteries because of their higher storage capacity and similar operating voltage, as compared to the commercial graphite (Gr) anode. But the use of Si anodes including silicon-graphite (Si-Gr) blended anodes often leads to rapid capacity decay in Si-Gr/LiNixMnyCo z O 2 (x+y+z=1) full cells, which has been attributed to surface instability of the Si component. In addition to stabilizing the surface, this work investigates the potential of the Si-Gr blended anodes in a full-cell configuration and its impact on the capacity contribution from active components. Using dQ/dV plots of the full cells, a powerful but simple-to-implement differential potential approach is developed to decouple the capacity contribution and degradation from the graphite and silicon components. Data collected from three-electrode cells confirm the results from the differential potential approach, which suggests a voltage slippage to a higher voltage at the blended anode side. Additionally, the voltage slippage causes a reduced utilization of the Gr component and exacerbates side reactions between the Si-Gr anode and carbonate electrolytes. Furthermore, based on these failure mechanisms, we adopted a mitigation strategy to tune the open circuit voltage of the prelithiated anode while stabilizing the surface. As a result, the full cells with the modified Si-Gr anodes (mass loading, 2.5 mAh/cm 2 ) offer a highly reversible full-cell energy density of 390 Wh/kg (based on the mass of both anode and cathode materials in a full cell) with a cycling CE of 99.9% over 200 cycles.
Catalytic Activity and Water Stability of the MgO(111) Surface for 2-Pentanone Condensation
Nanomaterials derived from earth-abundant metal oxides have gained tremendous interest as catalysts; although, water stability remains a challenge. This study examines MgO(111) surfaces for 2-pentanone condensation and their evolution during D2O hydration. Catalyst screening confirmed the high activity of fresh MgO(111) for 2-pentanone condensation relative to conventionally prepared MgO(100). Computational modeling suggests that the (111) surface is readily hydroxylated, and that surface hydroxyls help stabilize the surface and reduce the barrier for 2-pentanone condensation. Vapor-phase D2O hydration after 3 min increased MgO(111) hydroxyls and retained surface area and activity; however, after 1 h, deuteroxide formation reduced the surface area and activity by >30 %. After 24 h, deuteroxide growth slowed down, and surface area and activity remained stable. This suggests MgO(111)-derived hydroxide may be the dominant surface responsible for 2-pentanone condensation following water exposure. Thermal regeneration of the 24-h sample restored 86 % of the surface area and 94 % of the activity.
The effects of the variations in sea surface temperature and atmospheric stability in the estimation of average wind speed by SEASAT-SASS
The average wind speeds from the scatterometer (SASS) on the ocean observing satellite SEASAT are found to be generally higher than the average wind speeds from ship reports. In this study, two factors, sea surface temperature and atmospheric stability, are identified which affect microwave scatter and, therefore, wave development. The problem of relating satellite observations to a fictitious quantity, such as the neutral wind, that has to be derived from in situ observations with models is examined. The study also demonstrates the dependence of SASS winds on sea surface temperature at low wind speeds, possibly due to temperature-dependent factors, such as water viscosity, which affect wave development.
Space shuttle: Static stability characteristics and control surface effectiveness of the Boeing .00435 scale model space shuttle booster H-32
Experimental aerodynamic investigations were made in the Grumman 36-inch hypersonic wind tunnel on a .00435 scale model of the H-32 reusable space shuttle booster. The objectives of the test were to determine the static stability characteristics and control surface effectiveness at hypersonic speeds. Data were taken at M = 8.12 over a range of angles of attack between -5 and 85 deg at beta = 0 deg and over a range of side slip angles between -10 and 10 deg at alpha = 0 and 70 deg. Six component balance data and base-cavity pressure data were recorded.
Coinage Metal–Sulfur Complexes: Stability on Metal(111) Surfaces and in the Gas Phase
We introduce a comprehensive theoretical assessment at the level of density functional theory (DFT) of the stability of various coinage metal–sulfur complexes, both in the gas phase and also for the complexes adsorbed on the (111) surface of the same coinage metal. Our primary interest lies in the latter where earlier scanning tunneling microscopy (STM) experiments were interpreted to imply the existence of adsorbed S-decorated metal trimers, sometimes as a component of more complex adlayer structures. Recent STM studies at 5 K directly observed other isolated adsorbed metal–sulfur complexes. For these adsorbed species, we measure various aspects of their energetics including a natural measure of stability corresponding to their formation energy from sulfur adsorbed on terraces and from metal atoms that are in thermal equilibrium with the substrate. From this perspective, our DFT analysis shows that all of Ag 2 S 3 , Ag 3 S 3 , and many larger complexes on Ag(111) are strongly stable, Cu 2 S 3 is stable, and some larger complexes are marginally stable on Cu(111), but only Au 4 S 4 on Au(111) is stable. Results are consistent with STM observations for Cu(111) and Ag(111) surfaces but appear to deviate slightly for Au(111). A systematic analysis relating stability in the gas phase with that of adsorbed species is achieved within the framework of Hess’s law. This analysis also unambiguously elucidates various energetic contributions to stability.
A study of the photodegration of selected thermal-control surfaces
Ultraviolet stability of thermal control coatings and Alodine 401 chemical conversion coating
Tailoring the Surface of Silicon Nanoparticles for Enhanced Chemical and Electrochemical Stability for Li-Ion Batteries
Organic monolayers of epoxy-containing oligo(ethylene oxide)s were grafted to the surface of silicon nanoparticles via a hydrosilylation reaction. The surface functional groups suppressed the chemical and electrochemical reactivity of the as-grown and lithiated silicon nanoparticles with high material utilization. A robust Si/electrolyte interphase was formed with the participation of the grafted organic groups with facilitated Li+ transfer and was further enforced by electrode integrity via the epoxy/poly(acrylic acid) (PAA) binder reaction. The improved cycling stability and post-test analysis indicate that surface functionalization on the Si particle level is a feasible approach to enabling a Si anode in high-energy-density lithium-ion batteries.