Vibrational relaxation in the HF-HCl, HF-HBr, HF-HI, and HF-DF systems.
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Ahl, J. L.↗
SEARCH · Engineering Papers
Results for “Hf”
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Investigation of the 176 Yb Interference Correction during Determination of the 176 Hf/ 177 Hf Ratio by Laser Ablation and Solution Analysis on the Neoma MC-ICP-MS
We utilized the Neoma™, a recently released MC-ICP-MS platform offered by ThermoFisher Scientific, to assess the behavior of the Lu-Yb-Hf system during laser ablation analyses of various zircon standards as well as solution-based analyses of the JMC-475 Hf standard doped with varying quantities of Yb and Lu. The primary goal of this work was to characterize the behavior of the Yb interference correction on the Neoma™ platform since this is one of the biggest issues in the Hf isotope analysis community and because the Neoma™ platform will supplant the Neptune™ series instrument. During laser ablation analysis, we found that the overall data quality scales proportionally with the total Hf signal intensity, with higher signal analyses producing extremely accurate (within 1 ε Hf unit) and precise (sub ε Hf unit within-run standard errors) data. At low Yb signals (<0.1 V 173 Yb), we were not able to produce an accurate internal Yb mass bias factor. However, utilizing an empirical approach allows for the application of session-specific relationships between the Yb and Hf mass bias factors, determined by analysis of standards of varying Yb content, to produce accurate ε Hf values from zircons with higher Yb/Hf ratios even where the total Hf signal intensity is relatively low. Similar behavior was observed in the solution analyses. Lastly, while the behavior of the Yb interference correction on the Neoma™ platform appears comparable to the Neptune™ series MC-ICP-MS, further work will help refine the understanding of the controls on mass bias behavior, oxide formation, session-to-session stability, etc.
36 MATERIALS SCIENCE↗
Role of Hf on Phase Formation in Ti45Zr(38-x)Hf(x)Ni17 Liquids and Solids
Hafnium and zirconium are very similar, with almost identical sizes and chemical bonding characteristics. However, they behave differently when alloyed with Ti and Ni. A sharp phase formation boundary near 18-21 at.% Hf is observed in rapidly-quenched and as-cast Ti45Zr38-xHfxNi17 alloys. Rapidly-quenched samples that contain less than 18 at.% Hf form the icosahedral quasicrystal phase, whiles samples containing more than 21 at.% form the 3/2 rational approximant phase. In cast alloys, a C14 structure is observed for alloys with Hf lower than the boundary concentration, while a large-cell (11.93 ) FCC Ti2Ni-type structure is found in alloys with Hf concentrations above the boundary. To better understand the role of Hf on phase formation, the structural evolution with supercooling and the solidification behavior of liquid Ti45Zr38-xHfxNi17 alloys (x=0, 12, 18, 21, 38) were studied using the Beamline Electrostatic Levitation (BESL) technique using 125keV x-rays on the 6ID-D beamline at the Advanced Photon Source, Argonne National Laboratory. For all liquids primary crystallization was to a BCC solid solution phase; interestly, an increase in Hf concentration leads to a decrease in the BCC lattice parameter in spite of the chemical similarity between Zr and Hf. A Reitveld analysis confirmed that as in the cast alloys, the secondary phase that formed was the C14 below the phase formation boundary and a Ti2Ni-type structure at higher Hf concentrations. Both the liquidus temperature and the reduced undercooling change sharply on traversing the phase formation boundary concentration, suggesting a change in the liquid structure. Structural information from a Honeycutt-Anderson index analysis of reverse Monte Carlo fits to the S(q) liquid data will be presented to address this issue.
Wessels, V.↗
Ferroelectric Phase Content in 7 nm Hf (1- x ) Zr x O 2 Thin Films Determined by X-Ray-Based Methods
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99 GENERAL AND MISCELLANEOUS↗
Ab Initio Calculations of Anharmonic Vibrational Spectroscopy for Hydrogen Fluoride (HF)n (n=3,4) and Mixed Hydrogen Fluoride/Water (HF)n(H20)n (n=1,2,4) Clusters
Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n with n=3,4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n=1,2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the MP2 potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.
Chaban, Galina M.↗
Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF)n (n = 3, 4) and mixed hydrogen fluoride/water (HF)n(H2O)n (n = 1, 2, 4) clusters
Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n, with n = 3, 4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n = 1, 2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the Moller-Plesset (MP2) potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.
Water/chemistry↗
Temperature dependence of vibrational relaxation in the HF, DF, HF-CO2, and DF-CO2 systems
The laser excited fluorescence method has been employed to determine rate constants for V to V, R and V to R, T relaxation HF (nu = 1) and DF(nu = 1) by CO2 over the temperature range from 295 to 670 K. The self-deactivation rates for HF(nu = 1) and DF(nu = 1) by ground state molecules and the rate of V to V, R transfer from HF(nu = 1) and DF(nu = 1) to the CO2 (00/0/1) state exhibit a marked decrease with increasing temperature. The results provide additional evidence for the conversion of the large vibrational energy defects of the present systems into rotational motion of the hydrogen halide under the influence of a sizable attractive intermolecular potential well.
Lucht, R. A.↗
Temperature dependence of vibrational relaxation in the HF-DF, HF-CO2, and DF-CO2 systems. II
Measurements of vibrational energy transfer probabilities are presented for the temperature range 205-360 K for HF-DF, HF-CO2, and DF-CO2 gas mixtures. The present results provide an accurate determination of the inverse temperature dependence of the energy transfer probabilities exhibited by these systems. Large deactivation effects caused by HF (DF) polymers were observed for temperatures below 220 K.
Lucht, R. A.↗
M IV /Co –I (M = Zr, Hf) Bis(phosphinoamide) Complexes with η 6 - and η 4 -Arenes
Despite their relevance to catalysis, low-/subvalent cobalt complexes are difficult to synthesize and isolate. Consequently, very few “cobaltate” complexes are known and there is a lack of architectural diversity in this field. Lewis acidic d 0 group IV metals have been demonstrated to stabilize Co –I centers via metal–metal bonds. Herein, we report the synthesis of bis(phosphinoamide) heterobimetallic M IV /Co –I arene complexes (M = Zr, Hf). The driving force to maintain the aromaticity of the arenes dictates the hapticity of the Co-bound arene ligands and influences the binding arrangement of the phosphinoamide ligands. Benzene and toluene were observed to bind η 6 to the Co –I center, forcing dissociation of one of the phosphinoamide ligands, whereas η 4 -coordination of anthracene allows both phosphinoamide ligands to remain bound to the Co center. The identity of both the arene and the group IV metal ion starkly influence the lability of the arene. For instance, the Co-bound benzene ligand in the Zr IV /Co –I benzene complex rapidly exchanges with C 6 D 6 in solution, whereas toluene/C 6 D 6 exchange is much slower and appreciable C 6 H 6 /C 6 D 6 exchange is not observed for the Hf analogue. The Zr IV /Co –I benzene complex loses benzene upon repeated exposure to vacuum to form an arene-free tetrametallic dimer.
aromatic compounds↗
Computational exploration of biomedical HfNbTaTiZr and Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr refractory high-entropy alloys
Refractory high entropy alloys (RHEAs) have been proven to be a potential candidate in the biomedical field due to their balanced mechanical properties and biocompatible composition. Recent experimental findings show that RHEAs like HfNbTaTiZr and Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr have good mechanical properties such as high polarization and wear resistance than others which establish them as potential materials for biomedical application. In this work, we performed first-principles density functional theory calculations on the mechanical and thermal properties of HfNbTaTiZr and Hf 0.5 Nb 0.5 Ta 0.5 Ti 1.5 Zr. The predicted lattice constant, density, Young's modulus, and Vickers hardness are consistent with the available experimental report, which verifies the accuracy of the applied model. The thermal coefficient of linear expansion of both RHEAs has been investigated by utilizing the Debye theory. The present methods could be applied to study other future RHEAs on exploration of their physical properties.
36 MATERIALS SCIENCE↗
H-phase precipitation and its effects on martensitic transformation in NiTi-Hf high-temperature shape memory alloys
Not provided.
Materials Science↗
Influence of eutectoid structures on the mechanical properties and oxidation behavior of Hf-27%Ta and Hf-42%Ta alloys
Not provided.
Materials Science↗
Purely chemical laser operation in the HF, DF, HF-CO2, and DF-CO2 systems
CW chemical operation in IR for hydrogen fluoride, deuterium fluoride, hydrogen fluoride- carbon dioxide and deuterium fluoride-carbon dioxide systems
Cool, T. A.↗
Identification and quantification of distinct active sites in Hf-Beta zeolites for transfer hydrogenation catalysis
Despite the significant progress made in characterizing different framework heteroatom sites that exist in Lewis acidic zeolites with probe molecule adsorption and spectroscopy, methods to reliably quantify site counts remain indefinite and have been primarily limited to Sn and Ti Lewis acid sites. Here, methods to quantify framework Lewis acidic Hf 4+ sites in zeolite Beta (Hf-Beta) with two Lewis base titrants (pyridine, deuterated acetonitrile) were developed using infrared (IR) spectroscopy. Lewis acid site counts for Hf-Beta zeolites were validated by measuring integrated molar extinction coefficients (IMECs; ε, cm μmol –1 ) on Sn-Beta zeolites using identical Lewis base titrants to benchmark site counts with established literature procedures to quantify Lewis acid sites in Beta zeolites from IR spectra. Highlighting the importance of benchmarking active site counts against well-established experimental protocols, IMECs of CD 3 CN bound to open (ε(Sn; 2316 cm –1 ): 1.80 ± 0.25) and closed (ε(Sn; 2308 cm –1 ): 3.76 ± 0.33) Sn sites were ~1.8x larger than those previously reported while total Lewis acid site counts agreed with those measured by pyridine (ε(Sn; 1451 cm –1 ): 1.58 ± 0.16) on six different Sn-Beta zeolites. IMECs measured for IR peaks reflecting pyridine bound to Lewis acidic Hf sites (ε(Hf; 1448 cm –1 ): 1.54 ± 0.21) and CD 3 CN bound to open (ε(Hf; 2313 cm –1 ): 2.40 ± 0.22) and closed (ε(Hf; 2307 cm –1 ): 3.55 ± 0.41) Hf sites, gave similar counts for the total number of Lewis acidic sites across six Hf-Beta zeolites (Si/Hf = 100–413). Consistent with previous reports with Sn-Beta catalysts where open Sn sites are responsible for catalytic turnover, apparent first and zero-order MPVO rate constants (0.01–1 M cyclohexanone in 2-butanol; per total Hf, 373 K) correlated with the total number of open Hf sites, per total Hf, but not with the total number of closed Hf sites or total Lewis acid site counts. Measured initial MPVO rates (0.1 M cyclohexanone in 2-butanol, per open Hf, 373 K) were ~25x higher on hydrophobic Hf-Beta-F than on hydrophilic Hf-Beta-OH zeolites. Overall, the apparent first-order MPVO rate constants (2-butanol solvent, per open Hf, 373 K) were ~6x higher on Hf-Beta-F than on Hf-Beta-OH zeolites. The characterization methods reported here enable normalization of MPVO turnover rates on Sn- and Hf-Beta zeolites by their number of open sites. Finally, this enables performing quantitative rate comparisons across Lewis acid zeolites of varying active site identity, solvation, and pore topology used in liquid-phase catalysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Materials Data on Hf(ClO4)4 by Materials Project
Hf(O4Cl)4 crystallizes in the monoclinic Cc space group. The structure is zero-dimensional and consists of four Hf(O4Cl)4 clusters. Hf is bonded to eight O atoms to form distorted HfO8 hexagonal bipyramids that share edges with four ClO4 tetrahedra. There are a spread of Hf–O bond distances ranging from 2.19–2.22 Å. There are fifteen inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the second O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.55 Å. In the third O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the fourth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.53 Å. In the fifth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the sixth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.53 Å. In the seventh O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the eighth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.41 Å. In the ninth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.54 Å. In the tenth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.53 Å. In the eleventh O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.54 Å. In the twelfth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. In the thirteenth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.54 Å. In the fourteenth O site, O is bonded in a water-like geometry to one Hf and one Cl atom. The O–Cl bond length is 1.53 Å. In the fifteenth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.42 Å. There are four inequivalent Cl sites. In the first Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share an edgeedge with one HfO8 hexagonal bipyramid. In the second Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share an edgeedge with one HfO8 hexagonal bipyramid. In the third Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share an edgeedge with one HfO8 hexagonal bipyramid. In the fourth Cl site, Cl is bonded to four O atoms to form ClO4 tetrahedra that share an edgeedge with one HfO8 hexagonal bipyramid.
36 MATERIALS SCIENCE↗
Materials Data on Hf by Materials Project
Hf crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 11-coordinate geometry to eleven Hf atoms. There are a spread of Hf–Hf bond distances ranging from 2.89–3.28 Å. In the second Hf site, Hf is bonded in a 2-coordinate geometry to fourteen Hf atoms. Both Hf–Hf bond lengths are 3.09 Å.
36 MATERIALS SCIENCE↗
Investigation and Development of Data-Driven D-Region Model for HF Systems Impacts
Space Environment Corporation (SEC) and RP Consultants (RPC) are to develop and validate a weather-capable D region model for making High Frequency (HF) absorption predictions in support of the HF communications and radar communities. The weather-capable model will assimilate solar and earth space observations from NASA satellites. The model will account for solar-induced impacts on HF absorption, including X-rays, Solar Proton Events (SPE's), and auroral precipitation. The work plan includes: I . Optimize D-region model to quickly obtain ion and electron densities for proper HF absorption calculations. 2. Develop indices-driven modules for D-region ionization sources for low, mid, & high latitudes including X-rays, cosmic rays, auroral precipitation, & solar protons. (Note: solar spectrum & auroral modules already exist). 3. Setup low-cost monitors of existing HF beacons and add one single-frequency beacon. 4. Use PENEX HF-link database with HF monitor data to validate D-region/HF absorption model using climatological ionization drivers. 5. Develop algorithms to assimilate NASA satellite data of solar, interplanetary, and auroral observations into ionization source modules. 6. Use PENEX HF-link & HF-beacon data for skill score comparison of assimilation versus climatological D-region/HF absorption model. Only some satellites are available for the PENEX time period, thus, HF-beacon data is necessary. 7. Use HF beacon monitors to develop HF-link data assimilation algorithms for regional improvement to the D-region/HF absorption model.
Eccles, J. V.↗
Materials Data on Hf(PO5)2 by Materials Project
Hf(PO4)2O2 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of two water water molecules and one Hf(PO4)2 sheet oriented in the (0, 0, 1) direction. In the Hf(PO4)2 sheet, Hf is bonded to six O atoms to form HfO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Hf–O bond distances ranging from 2.01–2.11 Å. There are two inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four equivalent HfO6 octahedra. The corner-sharing octahedra tilt angles range from 4–35°. All P–O bond lengths are 1.54 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with two equivalent HfO6 octahedra. The corner-sharing octahedra tilt angles range from 13–29°. There is two shorter (1.52 Å) and two longer (1.57 Å) P–O bond length. There are eight inequivalent O sites. In the first O site, O is bonded in a linear geometry to one Hf and one P atom. In the second O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the third O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Hf and one P atom. In the sixth O site, O is bonded in a linear geometry to one Hf and one P atom. In the seventh O site, O is bonded in a single-bond geometry to one P atom. In the eighth O site, O is bonded in a single-bond geometry to one P atom.
36 MATERIALS SCIENCE↗