Showing papers on "Hafnium published in 2015"

Relativistic many-body calculations on wavelengths and transition probabilities for forbidden transitions within the $3{{{\rm d}}^{k}}$ ground configurations in Co- through K-like ions of hafnium, tantalum, tungsten and gold

Abstract: Wavelengths and transition probabilities have been computed for forbidden lines within the 3dk(k = 1-9) ground configurations in ions of hafnium, tantalum, tungsten and gold, employing the second-order relativistic many-body perturbation theory (RMBPT). For comparison, the relativistic configuration-interaction (RCI) calculations have also been performed. Comparing to the previously published theoretical wavelengths and the present RCI ones, the present RMBPT results are in much better agreement with the experimental values measured recently by using the electron beam ion trap facility, reproducing these observed wavelengths to within 0.2% for all transitions only with one exception. In addition, it removes dramatically the systematic underestimation/overestimation for shorter/longer wavelengths existing in the present RCI and other calculations.

Nanostructured titanium, zirconium and hafnium diborides: the synthesis, properties, size effects and stability

Abstract: The review is concerned with methods of synthesis of nanopowders, nanowires and films based on titanium, zirconium and hafnium diborides. Methods for consolidation of nanoparticles in order to prepare bulk nanostructured samples are analyzed. Information on the physicochemical and physicomechanical properties of these systems is generalized and the role of the size effects is analyzed. Data on the thermal stability and influence of radiation, deformation and corrosion on the TiB2-, ZrB2- and HfB2-based nanostructures are presented. Poorly studied aspects of the title field of research are pointed out. The bibliography includes 130 references.

Zirconium carbide, hafnium carbide and their ternary carbide nanoparticles by an in situ polymerization route

Abstract: An in situ polymerizable complex method to produce zirconium carbide, hafnium carbide and their ternary carbides at a relatively low temperature (1300 °C) using simple and mainly nontoxic starting reagents is presented. In this aqueous process, citric acid (CA) was used to chelate the metal ion and ethylene glycol (EG) to form a polymerized complex resin. We suggest that, based on the results of FT-IR and 13C NMR spectroscopies, a very stable metal–CA chelate complex formed in the starting solution, which was thermally stable upon gelation even up to 350 °C. Immobilization of the metal ion in a rigid polymer can largely guarantee the in situ charring, resulting in carbon adjacent to the metal oxide in the pyrolysed product. The contiguous carbon and metal oxide led to in situ reaction (1100 °C) with a minimum of diffusion, which involved the formation of large numbers of metastable phases. Afterwards, well-defined binary and ternary carbide nanoparticles (∼100 nm) were formed through localized particle coarsening by Ostwald ripening.

Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition

Abstract: The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys with 1, 2, and 4 at. pct Hf addition at 1173 K (900 °C). Microstructural characterizations using aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal high density of HfO2 nanoparticles with sizes of ~4 nm dispersed throughout the ferritic matrix. This indicates that kinetic stabilization by HfO2 nanoparticle pinning is primarily responsible for the observed high thermal stability. In addition, some Hf and Cr segregation on grain boundaries is observed in the Fe-14Cr-4Hf, suggesting the existence of thermodynamic stabilization at high Hf content. Second-phase precipitations such as hafnium carbide, M23C6, and Fe-Cr-Hf intermetallic phase are also found in the Fe-14Cr-4Hf, but their large sizes and inter-spacing suggest that their contribution to stabilization is minimal.

Optical properties and bandgap evolution of ALD HfSiOx films

Abstract: Hafnium silicate films with pure HfO2 and SiO2 samples as references were fabricated by atomic layer deposition (ALD) in this work. The optical properties of the films as a function of the film composition were measured by vacuum ultraviolet (VUV) ellipsometer in the energy range of 0.6 to 8.5 eV, and they were investigated systematically based on the Gaussian dispersion model. Experimental results show that optical constants and bandgap of the hafnium silicate films can be tuned by the film composition, and a nonlinear change behavior of bandgap with SiO2 fraction was observed. This phenomenon mainly originates from the intermixture of d-state electrons in HfO2 and Si-O antibonding states in SiO2.

Effect of hafnium doping on density of states in dual-target magnetron co-sputtering HfZnSnO thin film transistors

Abstract: This study investigates the effect of hafnium doping on the density of states (DOSs) in HfZnSnO thin film transistors fabricated by dual-target magnetron co-sputtering system. The DOSs is extracted by temperature-dependent field-effect measurements, and they decrease from 1.1 × 1017 to 4.6 × 1016 eV/cm3 with increasing the hafnium concentrations. The behavior of DOSs for the increasing hafnium concentration HfZnSnO thin film transistors can be confirmed by both the reduction of ΔVT under bias stress and the trapping charges calculated by capacitance voltage measurements. It suggests that the reduction in DOSs due to the hafnium doping is closely related with the bias stability and thermal stability.

In situ determination of hafnium isotopes from rutile using LA-MC-ICP-MS

Abstract: The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals (zircon/baddeleyite/calzirtite/eudialyte), however, little work has been reported on Hf-poor (<100 ppm) minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from rutile using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with 176Hf/177Hf=0.281795±0.000015 (2SD, n=33) and 176Lu/177Hf=0.000018±0.000004 (2SD, n=17) that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material (R10, Sugluk-4 and PCA-S207) and the 176Hf/177Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought.

Kinetics for extraction of zirconium and hafnium in DIBK-P350 system

Abstract: The extraction kinetics of zirconium and hafnium from the mixtures of diisobutyl ketone (DIBK) and di-(1-methyl-heptyl) methyl phosphonate (P350) were studied by using a Lewis cell. The results show that the extraction of zirconium and hafnium fit with pseudo-first order reaction, and the extraction kinetic of zirconium is governed by chemical reactions at bulk phase with activation energy (E a, Zr) of −10.412 kJ/mol, while for hafnium, it is proved to be controlled by mixed-control, whose activation energy (E a, Hf) is calculated to be −34.362 kJ/mol.

Screw Dislocation Assisted Spontaneous Growth of HfB2 Tubes and Rods

Abstract: The mechanism of anisotropic growth of HfB2 rods has been discussed in this study. HfB2 powder has been synthesized via a sol–gel-based route using phenolic resin, hafnium chloride, and boric acid as the source of carbon, hafnium, and boron respectively, though a small number of comparative experiments involved amorphous boron as the boron source. The effects of calcination dwell time and Hf:C and Hf:B molar ratio on the purity and morphology of the final powder have been studied and the mechanism of anisotropic growth of HfB2 has been investigated. It is hypothesized that imperfect oriented attachment of finer HfB2 particles results in screw dislocations in the coarser particles. The screw dislocation facilitates dislocation-driven growth of particles into anisotropic HfB2 rods.

Computer modelling of hafnium doping in lithium niobate

Abstract: Lithium niobate, LiNbO3, is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. Doping LiNbO3 with hafnium, Hf has been shown to improve the resistance of the material to optical damage. Computer modelling provides a useful means of determining the properties of doped and undoped LiNbO3, including its defect chemistry, and the effect of doping on the structure. In this paper, Hf doped LiNbO3 has been modelled, and the final defect configurations are found to be consistent with experimental results.

Aperture-time of oxygen-precursor for minimum silicon incorporation into the interface-layer in atomic layer deposition-grown HfO2/Si nanofilms

Abstract: Hafnium oxide nanofilms were grown with atomic layer deposition on H-terminated Si (001) wafers employing tetrakis dimethyl amino hafnium (TDMA-Hf) and water as precursors. While the number of cycles (30) and the aperture-time for TDMA-Hf (0.08 s) were kept constant, the aperture-time ( τH2O) for the oxidant-agent (H2O) was varied from 0 to 0.10 s. The structure of the films was characterized with robust analysis employing angle-resolved x-ray photoelectron spectroscopy. In addition to a ∼1 nm hafnium oxide layer, a hafnium silicate interface layer, also ∼1 nm thick, is formed for τH2O > 0. The incorporation degree of silicon into the interface layer (i.e., the value of 1 − x in HfxSi1−xOy) shows a minimum of 0.32 for τH2O = 0.04 s. By employing the simultaneous method during peak-fitting analysis, it was possible to clearly resolve the contribution from the silicate and from oxide to the O 1s spectra, allowing for the assessment of the oxygen composition of each layer as a function of oxidant aperture ti...

Oxidation behavior of vacuum plasma-sprayed hafnium–tantalum nitrides

Abstract: A series of (HfN)1−x(TaN)x, ceramics with x representing the starting powder blend compositions of 0.0, 18.8, 28.1, and 46.7 at.%, have been fabricated by vacuum plasma spraying. During the plasma spraying, the mixture lost approximately 25 at.% nitrogen facilitating the precipitation of metallic and metal-rich nitride phases. These specimens underwent static air oxidation exposure up to 1700 °C. In general, it was found that the addition of tantalum nitrides to the hafnium nitrides resulted in poorer oxidation behavior. However, the 18.8 at.% specimen deviated from this trend and had the lowest observed mass change. This specimen formed a dark-colored oxide scale, indexed as Hf6Ta2O17, which acted as a passivation layer. Within the scale, hafnium oxynitride phases were observed. A transformation pathway in forming these rhombohedral oxynitride phases is proposed by the filling in of oxygen in the light element interstitial locations of the rhombohedral e-Hf3N2 and ζ-Hf4N3 structures.

Hafnium or Zirconium Oxide Coating

Abstract: The invention concerns an optical coating ( 3, 3 ′), having a high refractive index and good optical properties (i.e., low absorption and scatter) and limited internal stresses in a spectral range extending from the visible to the near UV range (i.e., up to a wavelength of 220 nm). The coating ( 3, 3 ′) according to the invention consists of a hafnium- or zirconium-containing oxide Hf x Si y O z or Zr x Si y O z , containing an silicon fraction (y) between 1 at. % and 10 at. %, especially between 1.5 at. % and 3 at. %.

Zirconium and hafnium germanate-based thin films on SiC fibers

Abstract: A technique has been developed for producing coatings from sols of hydrous zirconium and germanium dioxides or hafnium and germanium dioxides on SiC microfibers The technique allows one to produce homogeneous, dense nanocoatings of controlled phase composition SiC fiber surface modification under optimal conditions has been shown to have no significant effect on the mechanical tensile strength of the fibers Zirconium germanate and hafnium germanate coatings on SiC fibers favor fiber debonding and pullout from the SiC matrix

A theoretical approach to the sublimation separation of zirconium and hafnium in the tetrafluoride form

Abstract: Synopsis The separation of zirconium and hafnium is essential in the nuclear industry, since zirconium alloys for this application require hafnium concentrations of less than 100 ppm. The separation is, however, very difficult due to the numerous similarities in the chemical and physical properties of these two elements. Traditional methods for separation of zirconium and hafnium rely predominantly on wet chemical techniques, e.g. solvent extraction. In contrast to the traditional aqueous chloride systems, the AMI zirconium metal process developed by Necsa focuses on dry fluoride-based processes. Dry processes have the advantage of producing much less hazardous chemical waste. In the proposed AMI process, separation is effected by selective sublimation of the two tetrafluorides in an inert atmosphere under controlled conditions, and subsequent selective desublimation. Estimates are made for the sublimation rates of the two tetrafluorides based on the equilibrium vapour pressures. A sublimation model, based on the sublimation rates, was developed to determine if the concept of separation by sublimation and subsequent desublimation is theoretically possible.

Recovery of uranium, hafnium and zirconium from petroleum ash leach liquor

Abstract: We investigated the optimum adsorption conditions of uranium, hafnium and zirconium elements from petroleum fly ash leach liquor using Dowex 1×8 as a strong basic anion exchange. Uranium was precipitated from the acidic solution by adding either NaOH or H2O2 solutions at different pH. The remaining concentrate containing hafnium and zirconium was firstly precipitated by using NaOH solution followed by dissolution in HCl solution and individually separated from each other by a solvent extraction technique using Alamine 336 as the extractant. On the other hand, the loaded zirconium was stripped with HCl while hafnium was scrubbed by using H2SO4 acid.

Influence of Dilute Hf Additions on Precipitation and Martensitic Transformation in Ni-Ti-Pd Alloys

Abstract: The effect of Hf (0–1 at.%) additions in a Ni-Ti-Pd alloy on P-phase precipitation and martensitic transformations was studied. The addition of hafnium resulted in the refinement of precipitates with an increase in number density. The overlapping strain fields created due to the decrease in inter-precipitate spacing are suspected to reduce the matrix volume to be less than the critical free volume size needed for the martensitic transformation over the temperature range studied (183–573 K). Hafnium was also found to delay the aging time to achieve peak hardness, suggesting a reduction in growth and coarsening kinetics.

Electrical Properties of Lead-Free Na1/2Bi1/2TiO3 Relaxor Ferroelectric Ceramics Doped with Hafnium or Zirconium

Abstract: Ferroelectric (Na1/2Bi1/2)TiO3 and its various solid solutions have been drawing special attention as a new candidate for their lead-based counterparts. In this study, therefore, hafnium- or zirconium-doped grain-oriented (Na1/2Bi1/2)TiO3 ceramics with pc orientation were fabricated by templated grain growth method using anisotropically shaped SrTiO3 template particles. These molten salt synthesized SrTiO3 platelets were tape cast with calcined (Na1/2Bi1/2)TiO3 powders, and then sintered at 1200°C for 6 h. Texture fractions up to 70% have been obtained. Unipolar strains up to >0.25% were measured. Doped ceramics showed a “relaxor-like” ferroelectric behavior. A broad dielectric peak with a slim hysteresis loop was present for hafnium- or zirconium-doped samples. Electrostrictive coefficient of hafnium-doped (Na1/2Bi1/2)TiO3 ceramics were found to be 0.032 m4/C2, which is much larger than that of PMN-based electrostrictive materials. Electromechanical properties of hafnium- and zirconium-doped (Na1/2Bi1/2)TiO3 ceramics under electric bias were studied as well.

Piezoelectric thin film and method for manufacturing the same, and piezoelectric element

Abstract: A piezoelectric thin film comprising aluminum nitride containing magnesium and hafnium, wherein a content of the hafnium based on 100 atomic % of the magnesium is 8 atomic % or more and less than 100 atomic %, and a total content of the magnesium and hafnium based on a sum of a content of the magnesium, hafnium, and aluminum is in a range of 47 atomic % or less.

Hafnium nitride film of cubic phosphating thorium single-phase structure and preparing method thereof

Abstract: The invention relates to a hafnium nitride film of a cubic phosphating thorium single-phase structure and a preparing method of the hafnium nitride film The hafnium nitride film is characterized in that the nitrogen content of the film ranges from 571% to 615%, the pressure stress of the film ranges from 20 GPa to 40 GPa, and the hafnium nitride film is obtained through argon ion bombardment in the preparing process A radio frequency reactive sputtering method is adopted, high-purity Hf serves as a target source, Ar and N2 serves as discharging gas, the hafnium nitride film is deposited on a single-crystal Si substrate and optical glass, the nitrogen flow speed ratio ranges from 50% to 80%, argon ion bombardment is introduced into the film growing process, and the negative voltage applied on a sample tray ranges from -70 V to -90 V The preparing method is simple in process and high in efficiency The obtained hafnium nitride film is completely composed of cubic phosphating thorium, does not contain other phases, has the visible light-infrared transparent characteristic, has a reflection reducing function for a typical infrared window material Ge and is a novel infrared reflection reducing protective film material and capable of applied to surface protection of aeronautics and astronautics optical devices under an extreme service condition

Special features of preparation of nanosized hafnium diboride of different dispersity

Abstract: X-ray diffraction analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, and elemental analysis have been applied to study the products of interaction of powder hafnium with fine-crystalline boron in the Na2B4O7 ionic melt at 600–850°C and of HfCl4 with NaBH4 at 300–700°C.

Nanoscale Potential Fluctuation in Non-Stoichiometric Hafnium Suboxides

Abstract: We study the structure of nonstoichiometric HfOx films with variable composition using methods of X-ray photoelectron spectroscopy and spectroscopic ellipsometry. HfOx, to a first approximation, is a mixture of HfO2 and Hf metal with a small amount (~10–15%) of hafnium sub-oxide HfOy (y < 2).