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Results of an atomistic calculation supporting two-dimensional diffusion of a Pt atom on a Pt(110) surface are presented. The calculations for diffusion energies indicate that interchannel diffusion by the replacement of a channel-wall atom by the adatom is energetically favorable.
Neutron activation analysis is used to ascertain the proportions of Ru, Re, Os, and Pt refractory siderophiles, and moderately volatile Au, in 41 iron meteorites. The Ni-element trends defined for groups IID and IIIF support a magmatic origin; in addition, the results obtained for groups IAB and IIICD contrast with trends observed in magmatic groups, where the Ru and Pt slopes are substantially less steep. In group IIIAB, at Ni concentrations above 90 mg/g, the steep decrease of Re, Os, and Ir with Ni levels off, and the interelement ratios exhibit considerable scatter. These observations may be explained in terms of the contamination of the residual molten core with small amounts of late primitive melts draining from the mantle.
New observations of the spectrum of Pt II have been made with hollow-cathode lamps. The region from 1032 to 4101 A was observed photographically with a 10.7-m normal-incidence spectrograph. The region from 2245 to 5223 A was observed with a Fourier-transform spectrometer. Wavelength measurements were made for 558 lines. The uncertainties vary from 0.0005 to 0.004 A. From these measurements and three parity-forbidden transitions in the infrared, accurate values were determined for 28 even and 72 odd energy levels of Pt II.
Niobium-platinum samples of compositions ranging from 16 to 32 at. pct have been undercooled to as much as 540 K in the low gravity, containerless environment of a 105 meter drop tube. Undercooling was terminated in the Nb-Pt samples by the nucleation and growth of the Nb3Pt phase. In the 16-18 at. pct Pt samples, this resulted in samples which are completely Nb3Pt, in contrast to both the equilibrium phase diagram and the nonundercooled samples which formed with Nb dendrites and interdendritic Nb3Pt. Undercoolings for the Nb-Si samples were up to 670 K, which corresponds to 27 percent of the liquidus temperature or 80 percent of the estimated hypercooling limit. In the Nb-Si system, a coupled zone was identified as well as a metastable extension of the solubility limit of Si in Nb due to deep undercooling.
Scanning electron microscopy of certain partially melted Y-Ba-Cu-O materials containing minority metal oxide species (Y:Tb:Ba:Cu = 1:0.1:2:3 or Y:Ba:Cu with Pt impurities), accompanied by both EDX and EMP analysis, indicates that the minority species (Tb or Pt) is quantitatively concentrated in a relatively small number of 123-type grains. High magnetic susceptibility and magnetization observed for these materials indicate that such elemental distribution is not detrimental to superconducting behavior.
Heterogeneous nucleation and its effects on the crystallization of lithium disilicate glass containing small amounts of Pt are investigated. Measurements of the nucleation frequencies and induction times with and without Pt are shown to be consistent with predictions based on the classical nucleation theory. A realistic computer model for the transformation is presented. Computed differential thermal analysis data (such as crystallization rates as a function of time and temperature) are shown to be in good agreement with experimental results. This modeling provides a new, more quantitative method for analyzing calorimetric data.
Re-187 - Os-187 and Pt-190 - Os-186 isotope systems are applied to dating evolved iron meteorites. The Re-Os systematics of some evolved irons may indicate late stage system closure. This conclusion appears to be supported by a "young" Pt-Os isochron age.
Small Hf additions were incorporated into a Pt aluminide coating during chemical vapor deposition (CVD) on single crystal RENE N5 substrates. Standard yttria-stabilized zirconia top coats were subsequently deposited onto the coated substrates by electron beam-physical vapor deposition (EB-PVD). The coated substrates underwent accelerated thermal cycle testing in a furnace at a temperature in excess of 1121 C (2050 F) (45 minute hot exposure, 15 minute cool to approximately 121 C (250 F)) until the thermal barrier coating (TBC) failed by spallation. Incorporating Hf in the bond coat increased the TBC life by slightly more than three times that of a baseline coating without added Hf. Scanning electron microscopy of the spalled surfaces indicated that the presence of the Hf increased the adherence of the thermally grown alumina to the Pt aluminide bond coat. The presence of oxide pegs growing into the coating from the thermally grown alumina may also partially account for the improved TBC life by creating a near-surface layer with a graded coefficient of thermal expansion.
A method for scaled-up synthesis of PtNi nanoparticles. Synthesizing a Pt nanoparticle catalyst comprises the steps of: synthesizing PtNi nanoparticles, isolating PtNi/substrate nanoparticles, acid leaching the PtNi/substrate, and annealing the leached PtNi/substrate nanoparticles, and forming a Pt-skin on the PtNi/substrate nanoparticles.
Combined survey analyses of galaxy clustering and weak gravitational lensing (3x2-pt studies) will allow new and accurate tests of the standard cosmological model. However, careful validation is necessary to ensure that these cosmological constraints are not biased by uncertainties associated with the modelling of astrophysical or systematic effects. In this study we validate the combined 3x2-pt analysis of the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) spectroscopic galaxy clustering and overlapping weak lensing datasets from the Kilo-Degree Survey (KiDS), the Dark Energy Survey (DES), and the Hyper-Suprime-Cam Survey (HSC). By propagating the modelling uncertainties associated with the non-linear matter power spectrum, non-linear galaxy bias and baryon feedback, we design scale cuts to ensure that measurements of the matter density and the amplitude of the matter power spectrum are biased by less than 30% of the statistical error. We also test the internal consistency of the data and weak lensing systematics by performing new measurements of the lensing shear ratio. We demonstrate that the DESI-DR1 shear ratios can be successfully fit by the same model used to describe cosmic shear correlations, and analyse the additional information that can be extracted about the source redshift distributions and intrinsic alignment parameters. This study serves as crucial preparation for the upcoming cosmological parameter analysis of these datasets.
Pb2PtO4 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. Pt4+ is bonded to six O2- atoms to form edge-sharing PtO6 octahedra. There are two shorter (2.04 Å) and four longer (2.07 Å) Pt–O bond lengths. There are two inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 4-coordinate geometry to three O2- atoms. There are two shorter (2.24 Å) and one longer (2.37 Å) Pb–O bond lengths. In the second Pb2+ site, Pb2+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are a spread of Pb–O bond distances ranging from 2.23–2.69 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Pt4+ and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Pt4+ and one Pb2+ atom. In the third O2- site, O2- is bonded in a trigonal planar geometry to one Pt4+ and two Pb2+ atoms.
PtF6N2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of eight ammonia molecules and four PtF6 clusters. In each PtF6 cluster, Pt4+ is bonded in an octahedral geometry to six equivalent F1- atoms. All Pt–F bond lengths are 1.91 Å. F1- is bonded in a single-bond geometry to one Pt4+ atom.
PtS6N2 crystallizes in the monoclinic C2/m space group. The structure is zero-dimensional and consists of four ammonia molecules and two PtS6 clusters. In each PtS6 cluster, Pt2+ is bonded in a square co-planar geometry to four equivalent S2- atoms. All Pt–S bond lengths are 2.30 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in an L-shaped geometry to two equivalent S2- atoms. Both S–S bond lengths are 2.03 Å. In the second S2- site, S2- is bonded in an L-shaped geometry to one Pt2+ and one S2- atom.
PtO2(I)4 crystallizes in the tetragonal P4_2/mnm space group. The structure is zero-dimensional and consists of eight hydriodic acid molecules and two platinum hydroxide (pt(oh)2) molecules.
PtI6N2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of eight ammonia molecules and four PtI6 clusters. In each PtI6 cluster, Pt4+ is bonded in an octahedral geometry to six equivalent I1- atoms. All Pt–I bond lengths are 2.67 Å. I1- is bonded in a single-bond geometry to one Pt4+ atom.
PtCl6N2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of eight ammonia molecules and four PtCl6 clusters. In each PtCl6 cluster, Pt4+ is bonded in an octahedral geometry to six equivalent Cl1- atoms. All Pt–Cl bond lengths are 2.32 Å. Cl1- is bonded in a single-bond geometry to one Pt4+ atom.
Supported transition metal catalyzed, chemical upcycling of polyolefins by hydrogenolysis typically occurs in a polymer melt phase at elevated temperatures (T > 200 ºC). Currently, the impact of the melt phase on the catalytic activity and selectivity of the transition metal is largely unknown. Herein, we use a hybrid quantum mechanical/molecular mechanical (QM/MM) approach to investigate the melt-phase effects on the adsorption free energy (∆∆G$^{gas→liq}_{Adsorbate}$) of atomic hydrogen, 12 hydrocarbon molecules, and 4 transition states in the hydrogenolysis mechanism of butane on a Pt(111) catalyst surface at 573 K in the presence of a polyethylene surrogate melt consisting of C 36 H 74 chains. The smallest and largest endergonic melt phase effects, (∆∆G$^{gas→liq}_{Adsorbate}$), belong to hydrogen (0.045 eV) and butane (1.357 eV). Altogether, we find melt-phase effects are significant and change the activity of transition metal catalysts. Beyond an overall reduced adsorption strength, elementary surface reactions are also affected by the melt phase.
Here, in-situ to ex-situ evolution of the Cs + in-plane structure in electrochemical Stern layers are investigated on Pt(111) surface with surface X-ray scattering studies. The Cs + single-sublattice (2 x 2) structure of the Stern layer formed in situ in 0.1 M CsF electrolyte evolves eventually to the two-sublattice (2 x 2) structure upon emersion from the electrolyte. While the Cs+ layers maintain the (2 x 2) symmetry, the ex situ layer increases the density progressively over several minutes by incorporating Cs + ions of the electrolyte during the emersion process.