Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector
Explore the source record for details and available documents.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
SEARCH · Engineering Papers
Results for “Pt”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Understanding Platinum Ionomer Interface Properties of Polymer Electrolyte Fuel Cells
A well-designed cathode catalyst layer with optimal ionomer distribution is critical to minimizing amount of Platinum (Pt) content in polymer electrolyte fuel cells (PEFCs). The impact of Pt loading, ionomer content and carbon support types on the catalyst/ionomer interface were also investigated at dry and wet conditions. Higher Pt loadings resulted in higher double layer capacity (C dl ) and similar electrochemical surface area (ECSA) due to well dispersed ionic phase material. Higher ionomer content resulted in higher ionic conductivity but also showed similar SO 3 − group coverage. High surface area (HSA) carbon support had larger ECSA and C dl at both dry and wet conditions, as less agglomerated Pt was well dispersed in the meso-pores of the support. Lower SO 3 − group coverages were observed for HSA carbon than for Vulcan carbon due to Pt particles being buried within the porous HSA carbon support. The effect of cell conditioning and voltage recovery on the PEFC cathode catalyst layer was shown to have minimal impact on SO 3 − group coverage despite a decrease in C dl and ECSA due to the size increase of Pt particles. At dry condition, a significant increases in SO 3 − group coverage were observed for all MEAs due to higher adsorptivity of ionomer in dry conditions.
25 ENERGY STORAGE↗
Modeling Nanoscale Ohmics in Carbon Supports of Fuel Cell Cathodes
Here, reducing platinum (Pt) loading in polymer electrolyte fuel cells (PEFCs) while meeting performace requirements is critical to their widespread deployment. However, significant polarization losses manifest at higher current densities in cathodes with lower Pt content. The morphology of the carbon supports in PEFC cathodes affects the location of Pt deposition into the micropits or onto the surface of the carbon support, translating into different kinetic and transport resistances. In this work, we derive an agglomerate scale model that differentiates the sink terms for Pt on the surface and in the pits of carbon supports. We develop an approach to assess the impact of nanoscale ohmic resistance to Pt in the micropits arising from weakly ionic solution in the carbon support on PEFC performance. Effectiveness factors relating the actual reaction rate to the maximum reaction rate (had all the Pt been exposed) are derived and embedded into a one-dimensional catalyst layer model. Parameters in the catalyst layer model are tuned based on experimental local oxygen transport resistances. Subsequently, we estimate bounds for the micropore resistances based on geometric and physical arguments. Lastly, polarization curves are simulated to assess the effect of the micropore resistance in fully-humidified and oxygen-rich environments.
25 ENERGY STORAGE↗
An Improved Pathway to Ethylene Glycol via CO 2
This report describes our efforts to develop a partial electrochemical oxidation process to produce formaldehyde selectively from methanol. The effort examined numerous potential anode materials in pursuit of 70% Faradaic efficiency for conversion of methanol to formaldehyde. Among the various electrode materials tested herein both Pt and PtRu were identified as the most promising catalysts in this process as the Faradaic efficiency obtained in these cases are 40% and >70% respectively. Several other 3d transition metals, Pt group metals and their alloys were also studied in which the Faradaic efficiency was obtained within 5-30%. In case of Pt and PtRu bulk metal electrode shows higher selectivity to formaldehyde compared to their nanostructured materials. Based on the literature, nanostructured Pt and PtRu are considered as active catalysts for methanol fuel cells, thus, lower selectivity to formaldehyde with nano Pt and PtRu in our case was attributed to their preferential oxidation of methanol to CO 2 . Severe catalyst deactivation was noted when 0.5 (M) sulfuric acid was used as the electrolyte irrespective of catalyst formulation. On the other hand, much higher activity and selectivity for formaldehyde was noted when alkaline electrolyte was employed during oxidation. Considering selective electrochemical oxidation of methanol to formaldehyde is an area which is underexplored as of today, our findings about catalyst formulation and process condition is noteworthy in this direction. Both bulk metal electrodes of Pt and PtRu may be cost prohibitive and thus present challenges to the scale up this technology. Therefore, we recognize that additional efforts are needed to develop catalysts with high activities and Faradaic efficiencies similar to bulk electrodes for the electrooxidation of methanol to formaldehyde.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mechanical Properties of High-Temperature Fiber-Reinforced Thermoset Composites with Plain Weave and Unidirectional Carbon Fiber Fillers
Fiber-reinforced thermoset composites are a class of materials that address the arising needs from the aerospace and hypersonic industries for high specific strength, temperature-resistant structural materials. Among the high-temperature resistant thermoset categories, phenolic triazine (PT) cyanate esters stand out thanks to their inherent high degradation temperature, glass transition temperature, and mechanical strength. Despite the outstanding properties of these thermosets, the performance of carbon fiber composites using PT cyanate esters as matrices has not been thoroughly characterized. This work evaluated PT and carbon fiber composites’ compressive properties and failure mechanisms with different fiber arrangements. A PT resin with both plain weave (PW) and non-crimped unidirectional (UD) carbon fiber mats was analyzed in this research. Highly loaded thermoset composites were obtained using process temperatures not exceeding 260 °C, and the composites proved to retain compressive strength at temperatures beyond 300 °C. Compressive testing revealed that PT composites retained compressive strength values of 50.4% of room temperature for UD composites and 61.4% for PW composites. Post-compressive failure observations of the gage section revealed that the mechanisms for failure evolved with temperature from brittle, delamination-dominant failure to shear-like failure promoted by the plastic failure of the matrix. This study demonstrated that PT composites are a good candidate for structural applications in harsh environments.
Hall, Samuel Ernesto↗
Progressive transmission of pseudo-color images. Appendix 1: Item 4
The transmission of digital images can require considerable channel bandwidth. The cost of obtaining such a channel can be prohibitive, or the channel might simply not be available. In this case, progressive transmission (PT) can be useful. PT presents the user with a coarse initial image approximation, and then proceeds to refine it. In this way, the user tends to receive information about the content of the image sooner than if a sequential transmission method is used. PT finds application in image data base browsing, teleconferencing, medical and other applications. A PT scheme is developed for use with a particular type of image data, the pseudo-color or color mapped image. Such images consist of a table of colors called a colormap, plus a 2-D array of index values which indicate which colormap entry is to be used to display a given pixel. This type of image presents some unique problems for a PT coder, and techniques for overcoming these problems are developed. A computer simulation of the color mapped PT scheme is developed to evaluate its performance. Results of simulation using several test images are presented.
Hadenfeldt, Andrew C.↗
Re-Evaluation of HSE DATA in Light of High P-T Partitioning Data: Late Chondritic Addition to Inner Solar System Bodies Not Always Required for HSE
Studies of terrestrial peridotite and martian and achondritic meteorites have led to the conclusion that addition of chondritic material to growing planets or planetesimals, after core formation, occurred on Earth, Moon, Mars, asteroid 4 Vesta, and the parent body of the angritic meteorites. One study even proposed that this was a common process in the final stages of growth. These conclusions are based al-most entirely on the 8 highly siderophile elements (HSE; Re, Au, Pt, Pd, Rh, Ru, Ir, Os), which have been used to argue for late accretion of chondritic material to the Earth after core formation was complete. This idea was originally proposed because the D(metal/silicate) values for the HSE are very high (greater than 10,000), yet their concentration in the terrestrial mantle is too high to be consistent with such high Ds. The HSE in the terrestrial mantle also are present in chondritic relative abundances and hence require similar Ds if this was the result of core-mantle equilibration. The conclusion that late chondritic additions are required for all five of these bodies is based on the chondritic relative abundances of the HSE, as well as their elevated concentrations in the samples. An easy solution is to call upon addition of chondritic material to the mantle of each body, just after core formation; however, in practice this means similar additions of chondritic materials to each body just after core formation which ranges from approximately 4-5 Ma after T(sub 0) for 4 Vesta and the angrites, to 10-25 Ma for Mars, to 35 to 60 Ma for Moon and perhaps the Earth. Since the work of there has been a realization that high PT conditions can lower the partition coefficients of many siderophile elements, indicating that high PT conditions (magma ocean stage) can potentially explain elevated siderophile element abundances. However, detailed high PT partitioning data have been lacking for many of the HSE to evaluate whether such ideas are viable for all four bodies. Re-cent partitioning studies have covered P, T, fO2, and compositional ranges that allow values to be predicted at conditions relevant to these five inner solar system bodies. Because the D(HSE) metal/silicate are lowered substantially at higher PT conditions and natural com-positions (FeNi metallic liquids and peridotites) it is natural to re-examine the role of core formation on the HSE patterns in a variety of inner solar system bodies. Here I will discuss other processes (including high PT core formation for Mars, Moon and Earth) that can produce the observed HSE patterns, and demonstrate that there are viable hypotheses other than the "one size fits all" hypothesis of late chondritic additions.
Righter, K.↗
Assessing the Role of Interfacial and Metal Sites in Pt/TiO2-Catalyzed Acetic Acid Hydrodeoxygenation
Thermochemical conversion of biomass to produce drop-in quality biofuels typically involves hydrodeoxygenation (HDO) steps following catalytic fast pyrolysis (CFP) to remove excess oxygen and create a more stable bio-oil product. HDO involves co-feeding the CFP vapor-phase product and H2 gas over a bi-functional catalyst. Reducible metal oxide-supported noble-metal catalysts (e.g., Pt/TiO2) are promising materials for HDO chemistry, with recent work aiming to elucidate the role of various Pt/TiO2 actives sites (i.e., Pt-metal, TiO2-support, Pt-TiO2-interfacial sites) in the competing desired deoxygenation and undesired decarboxylation/decarbonylation reactions for important classes of CFP vapor model compounds. Carboxylic acids are one important class of bio-derived compounds that has not been studied extensively for HDO on Pt/TiO2, particularly at the atomic level. Past experimental work evaluating Pt/C and Pt/TiO2 catalysts for acetic acid HDO (AA-HDO) demonstrated selectivity toward C-C and C-O bond-dissociation products, respectively. This work utilizes atomic-scale modeling to discern the role of Pt-metal and Pt-TiO2-interfacial sites in promoting key C-C bond-breaking, C-O bond-breaking, and (de)hydrogenation steps in AA-HDO. Using Pt(111) and Pt-TiO2-interface surface models, adsorption and reaction energetics calculated by density functional theory provide fundamental insights into the role of interfacial sites and oxygen vacancies in promoting desired deoxygenation pathways over undesired decarboxylation/decarbonylation pathways.
BIOMASS FUELS,INORGANIC, ORGANIC, PHYSICAL, AND AN↗
X-Ray Absorption Spectroscopy (XAS): Surface Structural Determination of Alloy Nanoparticles
In catalysis since reactions occur on the surface of nanoparticles (NP), it is essential to determine the composition of this structure, rather than that of the nanoparticles, since the two may be, and often are, different. Conventional techniques including X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are powerful techniques, but these data reflect the average composition of the entire particle. In this chapter, we introduce the method of EXAFS analysis, which isolates the surface atoms of nanoparticles based on its sensitivity to chemical reactions, specifically surface oxidation. As shown in our case studies, if the surface of a Pt-based nanoparticle is contacted by air at room temperature, the surface will selectively oxidize, resulting in the loss of Pt-Pt and Pt-M bonds to the formation of Pt-O bonds. The difference between the completely reduced and surface-oxidized nanoparticle allows for the isolation of signal from the catalytic surface. Although these examples highlight Pt alloys, similar analysis is also possible for other group 8 and IB bimetallic catalysts.
Zhang, Guanghui↗
Baselining Activity and Stability of ORR Catalysts and Electrodes for Proton Exchange Membrane Fuel Cells for Heavy-Duty Applications
Activity and stability of electrodes with Pt and PtCo alloy catalysts supported on high surface area carbon, hereafter to as a-Pt/C and d-PtCo/C, were evaluated for heavy-duty applications. Both catalysts had nearly identical Pt loading (50-wt% Pt on carbon and 0.25 mg Pt cm −2 ) and had undergone thermal treatment to stabilize them by growing the average particle size to 4–5 nm. Both were subjected to 90,000 (90 k) standard accelerated stress tests (AST) cycles consisting of 0.6–0.95 V square wave potentials, 3-s hold at upper and lower potential limits in H 2 /N 2 at 1.5 atm, 80 °C and 100% RH. Test protocols were developed to monitor the performance losses and characterize them in terms of activity for the oxygen reduction reaction (ORR), oxygen transport in the electrode and proton transport in the membrane and cathode catalyst layer. Despite the nearly double initial ORR activity, the PtCo/C electrode degraded faster due to the leaching of Co from the catalyst that had started even before the imposition of the AST potential cycles. Commensurate with Co leaching, Co poisoning of ionomer is responsible for the inferior performance of d-PtCo/C electrode at high current densities both before and after AST.
30 DIRECT ENERGY CONVERSION↗
Materials Data on USnPt by Materials Project
UPtSn is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. U is bonded to four equivalent Pt and six equivalent Sn atoms to form a mixture of distorted corner and face-sharing USn6Pt4 tetrahedra. All U–Pt bond lengths are 2.87 Å. All U–Sn bond lengths are 3.31 Å. Pt is bonded in a body-centered cubic geometry to four equivalent U and four equivalent Sn atoms. All Pt–Sn bond lengths are 2.87 Å. Sn is bonded in a 10-coordinate geometry to six equivalent U and four equivalent Pt atoms.
36 MATERIALS SCIENCE↗
Materials Data on MgSbPt by Materials Project
MgPtSb is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mg is bonded to four equivalent Pt and six equivalent Sb atoms to form a mixture of distorted face and corner-sharing MgSb6Pt4 tetrahedra. All Mg–Pt bond lengths are 2.75 Å. All Mg–Sb bond lengths are 3.18 Å. Pt is bonded in a body-centered cubic geometry to four equivalent Mg and four equivalent Sb atoms. All Pt–Sb bond lengths are 2.75 Å. Sb is bonded in a 10-coordinate geometry to six equivalent Mg and four equivalent Pt atoms.
36 MATERIALS SCIENCE↗
Materials Data on HfSiPt by Materials Project
HfPtSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Hf is bonded in a 11-coordinate geometry to six equivalent Pt and five equivalent Si atoms. There are a spread of Hf–Pt bond distances ranging from 2.98–3.11 Å. There are three shorter (2.75 Å) and two longer (2.85 Å) Hf–Si bond lengths. Pt is bonded in a 12-coordinate geometry to six equivalent Hf and four equivalent Si atoms. There are a spread of Pt–Si bond distances ranging from 2.48–2.58 Å. Si is bonded in a 9-coordinate geometry to five equivalent Hf and four equivalent Pt atoms.
36 MATERIALS SCIENCE↗
Materials Data on CeBPt2 by Materials Project
CePt2B crystallizes in the hexagonal P6_222 space group. The structure is three-dimensional. Ce3+ is bonded to eight equivalent Pt and four equivalent B3- atoms to form a mixture of corner, edge, and face-sharing CeB4Pt8 cuboctahedra. There are four shorter (3.10 Å) and four longer (3.13 Å) Ce–Pt bond lengths. All Ce–B bond lengths are 3.05 Å. Pt is bonded in a distorted bent 120 degrees geometry to four equivalent Ce3+ and two equivalent B3- atoms. Both Pt–B bond lengths are 2.12 Å. B3- is bonded in a 4-coordinate geometry to four equivalent Ce3+ and four equivalent Pt atoms.
36 MATERIALS SCIENCE↗
Materials Data on MnAlPt by Materials Project
MnPtAl crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mn is bonded in a 6-coordinate geometry to two equivalent Mn, six equivalent Pt, and six equivalent Al atoms. Both Mn–Mn bond lengths are 2.73 Å. All Mn–Pt bond lengths are 2.85 Å. All Mn–Al bond lengths are 2.85 Å. Pt is bonded in a 11-coordinate geometry to six equivalent Mn and five equivalent Al atoms. There are three shorter (2.51 Å) and two longer (2.73 Å) Pt–Al bond lengths. Al is bonded to six equivalent Mn and five equivalent Pt atoms to form a mixture of distorted face and corner-sharing AlMn6Pt5 trigonal bipyramids.
36 MATERIALS SCIENCE↗
Materials Data on MnAlPt2 by Materials Project
MnPt2Al is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Mn is bonded in a body-centered cubic geometry to eight equivalent Pt atoms. All Mn–Pt bond lengths are 2.69 Å. Pt is bonded in a body-centered cubic geometry to four equivalent Mn and four equivalent Al atoms. All Pt–Al bond lengths are 2.69 Å. Al is bonded in a body-centered cubic geometry to eight equivalent Pt atoms.
36 MATERIALS SCIENCE↗
Materials Data on Sc2Pt by Materials Project
Sc2Pt is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Sc sites. In the first Sc site, Sc is bonded in a 3-coordinate geometry to three equivalent Pt atoms. There are one shorter (2.70 Å) and two longer (2.89 Å) Sc–Pt bond lengths. In the second Sc site, Sc is bonded to four equivalent Pt atoms to form a mixture of edge and corner-sharing ScPt4 tetrahedra. There are a spread of Sc–Pt bond distances ranging from 2.70–2.78 Å. Pt is bonded in a 7-coordinate geometry to seven Sc atoms.
36 MATERIALS SCIENCE↗
Materials Data on Tb2Pt by Materials Project
PtTb2 is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Tb sites. In the first Tb site, Tb is bonded to four equivalent Pt atoms to form a mixture of edge and corner-sharing TbPt4 tetrahedra. There are one shorter (2.90 Å) and three longer (2.97 Å) Tb–Pt bond lengths. In the second Tb site, Tb is bonded in a 3-coordinate geometry to three equivalent Pt atoms. There are one shorter (2.83 Å) and two longer (3.07 Å) Tb–Pt bond lengths. Pt is bonded in a 7-coordinate geometry to seven Tb atoms.
36 MATERIALS SCIENCE↗