Hafnium Metal Research Articles

Synthesis and Structural Study of Tetravalent (Zr4+, Hf4+, Ce4+, Th4+, U4+) Metal Complexes with Cyclic Hydroxamic Acids

AbstractSix‐ and seven‐membered cyclic hydroxamic acids, such as 1‐hydroxypiperidine‐2‐one (1H, 1,2‐PIPOH) and 1‐hydroxyazepan‐2‐one (2H), have recently been identified in some mixed siderophores as one of their three chelating subunits. Compared to their ubiquitous noncyclic counterparts, cyclic hydroxamates are preorganized for metal binding. Surprisingly, the coordination chemistry of these bidentate, monoanionic ligands remains virtually unknown, even in the case of iron(III). We report herein the first structural study of the complexes of 1– and of 6–, an unsaturated seven‐membered ring analog of 2–, with tetravalent cations of transition metals (zirconium and hafnium), lanthanide (cerium), and actinides (thorium and uranium). Structural characterization by means of X‐ray crystallography of the corresponding ML4 complexes evidenced distorted square antiprismatic coordination geometries with the exception of U4+, which favors a dodecahedral arrangement.

MORPHOFUNCTIONAL STATUS OF REGIONAL LYMPH NODES IN CONDITIONS OF INTRAMEDULLARY OSTEOSYNTHESIS BY RETAINERS WITH COAT BASED ON SUPERHARD COMPOUNDS

Objective: to evaluate the morphofunctional state of the popliteal lymph nodes of the operated and intact pelvic rabbit limbs in conditions of intramedullary fixation of the tibia fracture with the implant coated with titanium nitride and hafnium. A morphological study of two groups of experimental animals was conducted. Osteoclasis of tibia and subsequent osteosynthesis with medical steel needles coated with and without titanium nitride and hafnium was made. In the lymph nodes of the animals in the comparison group both inflammatory (acute and chronic lymphadenitis) and immunomorfologycal (hyperplasia of T-and B-dependent areas, sinus histiocytosis) reactions were observed, with the latter being more common in the operated limb, and the inflammatory - in the intact one. The obtained data have proved the feasibility of using metal structures coated with nitrides of group IV metals (titanium and hafnium) for external osteosynthesis.

Design and performance projection of symmetric bipolar charge‐plasma transistor on SOI

A novel symmetric structure of bipolar charge-plasma transistor (BCPT) is presented. It consists of symmetrical gates with platinum on top of a thin intrinsic silicon film, which forms hole plasma in emitter and collector regions. The base contact is formed with hafnium metal to induce electron plasma; hence, a p-n-p charge-plasma transistor is formed without any doping. The collector area that is chosen is the same as an emitter to make the device symmetrical. 2D simulation results revealed that the proposed BCPT possesses higher collector current and higher current gain than conventional p-n-p bipolar junction transistor (BJT) and almost the same characteristics such as asymmetrical p-n-p BCPT for different geometries. The major challenge of poor cut-off frequency ( f T ) of BCPT is also addressed by optimising the silicon film thickness and intrinsic gaps.

Electrochemical reduction behavior of Hf(IV) in molten NaCl–KCl–K2HfCl6 system

The electrochemical reduction mechanism of hafnium ion(IV) was studied in NaCl–KCl–K2HfCl6 melts on a molybdenum electrode. The cyclic voltammetry study shows that Hf(IV) is reduced to hafnium metal in double two-electron process, that is: Hf(IV) + 2e− → Hf(II) and Hf(II) + 2e− → Hf, and the electrochemical reduction of Hf(IV) process was diffusion-controlled. The diffusion coefficients were calculated at several temperatures, and the results obey the Arrhenius law. According to the relationship of lnD versus 1/T, the corresponding activation energy was determined to be 158.8 kJ·mol−1. The square wave voltammetry results further confirm the reduction mechanism of hafnium.

Reinvestigation of high pressure polymorphism in hafnium metal

There has been a recent controversy about the high pressure polymorphism of Hafnium (Hf). Unlike, the earlier known α→ω structural transition at 38 ± 8 GPa, at ambient temperature, Hrubiak et al. [J. Appl. Phys. 111, 112612 (2012)] did not observe it till 51 GPa. They observed this transition only at elevated temperatures. We have reinvestigated the room temperature phase diagram of Hf, employing x-ray diffraction (XRD) and DFT based first principles calculations. Experimental investigations have been carried out on several pure and impure Hf samples and also with different pressure transmitting media. Besides demonstrating the significant role of impurity levels on the high pressure phase diagram of Hf, our studies re-establish room temperature α→ω transition at high pressures, even in quasi-hydrostatic environment. We observed this transition in pure Hf with equilibrium transition pressure Po = 44.5 GPa; however, with large hysteresis. The structural sequence, transition pressures, the lattice parameters, the c/a ratio and its variation with compression for the α and ω phases as predicted by our ab-initio scalar relativistic (SR) calculations are found to be in good agreement with our experimental results of pure Hf.

Oxygen and nitrogen diffusion in α-hafnium from first principles

We use a combination of density functional theory and multistate diffusion formalism to analyze the diffusion of oxygen and nitrogen in technologically important hafnium metal. Comparing the local density approximation and the Perdew-Burke-Ernzerhof version of the generalized gradient approximation, we find that a better description of the hafnium lattice in the latter results in the correct sequence of stable and transition states for oxygen interstitials leading to essentially quantitative agreement with experiment. For oxygen diffusion, we find an isotropic temperature-dependent diffusion coefficient of D=0.082e−2.04/kBTcm2s−1 utilizing interstitial sites with hexahedral and octahedral coordination. For the diffusivity of nitrogen, we find that an additional stable interstitial site, the crowdion site, exists and that the diffusion coefficient is D=0.15e−2.68/kBTcm2s−1. Our results also reproduce the experimental observation that nitrogen diffusivity is lower than that of oxygen in hafnium.

Assessing hafnium on hafnia as an oxygen getter

Hafnium dioxide or hafnia is a wide band gap dielectric used in a range of electronic applications from field effect transistors to resistive memory. In many of these applications, it is important to maintain control over oxygen stoichiometry, which can be realized in practice by using a metal layer, specifically hafnium, to getter oxygen from the adjacent dielectric. In this paper, we employ density functional theory to study the thermodynamic stability of an interface between (100)-oriented monoclinic hafnia and hafnium metal. The nudged elastic band method is used to calculate the energy barrier for migration of oxygen from the oxide to the metal. Our investigation shows that the presence of hafnium lowers the formation energy of oxygen vacancies in hafnia, but more importantly the oxidation of hafnium through the migration of oxygen from hafnia is favored energetically.

Metal and nanoparticle occurrence in biosolid-amended soils

Metals can accumulate in soils amended with biosolids in which metals have been concentrated during wastewater treatment. The goal of this study is to inspect agricultural sites with long-term biosolid application for a suite of regulated and unregulated metals, including some potentially present as commonly used engineered nanomaterials (ENMs). Sampling occurred in fields at a municipal and a privately operated biosolid recycling facilities in Texas. Depth profiles of various metals were developed for control soils without biosolid amendment and soils with different rates of biosolid application (6.6 to 74dry tons per hectare per year) over 5 to 25years. Regulated metals of known toxicity, including chromium, copper, cadmium, lead, and zinc, had higher concentrations in the upper layer of biosolid-amended soils (top 0–30cm or 0–15cm) than in control soils. The depth profiles of unregulated metals (antimony, hafnium, molybdenum, niobium, gold, silver, tantalum, tin, tungsten, and zirconium) indicate higher concentrations in the 0–30cm soil increment than in the 70–100cm soil increment, indicating low vertical mobility after entering the soils. Titanium-containing particles between 50nm and 250nm in diameter were identified in soil by transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDX) analysis. In conjunction with other studies, this research shows the potential for nanomaterials used in society that enter the sewer system to be removed at municipal biological wastewater treatment plants and accumulate in agricultural fields. The metal concentrations observed herein could be used as representative exposure levels for eco-toxicological studies in these soils.

Estudio DFT de los componentes de una interfaz de tres capas Hf/HfO2/TiN

En el presente estudio, las celdas unitarias del hafnio metálico (Hf), óxido de hafnio (HFO2), y nitruro de titanio (TiN), que son los componentes de una interfaz innovadora de tres capas: Hf/HFO2/TiN, que posee gran potencial para aplicaciones en nanoelectrónica, es descrita teóricamente mediante la aproximación de pseudopotenciales y ondas planas como se encuentra implementado en el Paquete de Simulación Ab Initio de Vienna (VASP).
 Todos los cálculos se realizan usando la Aproximación del Gradiente Generalizado (GGA), con el funcional de Perdew-Burke-Ernzerhof (PBE). Como resultado del presente estudio, se propone un procedimiento sistemático para la simulación mecánico cuántica de cada sistema, resumido de la siguiente manera: (i) la construcción del modelo a partir de datos experimentales, (ii) determinación del valor óptimo de la energía de corte para las ondas planas, (iii) optimización del parámetro que determina el número de puntos κ en el espacio recíproco, y (iv) la optimización de la geometría de las posiciones atómicas y de los parámetros de celda. En el caso específico del HfO2, se aplica el método de correcciones coulómbicas localizadas (GGA+U) para calcular un bandgap de energía más exacto.

Recoil Induced Room Temperature Stable Frenkel Pairs in a-Hafnium Upon Thermal Neutron Capture

Ultrapure hafnium metal (110 ppm zirconium) was neutron activated with a thermal neutron flux of 6:6 · 1012 cm-2s-1 in order to obtain 181Hf for subsequent time differential perturbed angular correlation (TDPAC) experiments using the nuclear probe 181Hf(β-) 181Ta. Apart from the expected nuclear quadrupole interaction (NQI) signal for a hexagonal close-packed (hcp) metal, three further discrete NQIs were observed with a few percent fraction each. The TDPAC spectra were recorded for up to 11 half lives with extreme statistical accuracy. The fitted parameters vary slightly within the temperature range between 248 K and 373 K. The signals corresponding to the three additional sites completely disappear after ‘annealing’ at 453 K for one minute. Based on the symmetry of the additional NQIs and their temperature dependencies, they are tentatively attributed to Frenkel pairs produced by recoil due to the emission of a prompt 5:694 MeV -ray following thermal neutron capture and reported by the nuclear probe in three different positions. These Frenkel pairs are stable up to at least 373 K.

Domestic and International Present Status and Utilization of Hafnium Resource

Metal hafnium has research significance as a rare metal. Metal hafnium, hafnium alloy and hafnium compounds are made a simple introduction, the distribution of hafnium resource is summarized at home and abroad, and the processing method of hafnium resource and the development prospect of comprehensive performance of hafnium resource are discussed.

Effect of Advanced Plasma Source bias voltage on properties of HfO2 films prepared by plasma ion assisted electron evaporation from metal hafnium

HfO2 films, using metal hafnium as starting material, are deposited by plasma-ion assisted electron evaporation with different Advanced Plasma Source (APS) bias voltages. The refractive index and extinction coefficient are calculated, the chemical state and composition, as well as the stress and aging behavior is investigated. Laser induced damage threshold (LIDT) and damage mechanism are also evaluated and discussed. Optical, structural, mechanical and laser induced damage properties of HfO2 films are found to be sensitive to APS bias voltage. The film stress can be tuned by varying the APS bias voltage. Damage morphologies indicate the LIDT of the HfO2 films at 1064nm and 532nm are dominated by the nodular-defect density in coatings, while the 355nm LIDT is dominated by the film absorption. HfO2 films with higher 1064nm LIDT than samples evaporated from hafnia are achieved with bias voltage of 100V.

Improved Growth Behavior of Atomic-Layer-Deposited High-k Dielectrics on Multilayer MoS2 by Oxygen Plasma Pretreatment

We report on the effect of oxygen plasma treatment of two-dimensional multilayer MoS2 crystals on the subsequent growth of Al2O3 and HfO2 films, which were formed by atomic layer deposition (ALD) using trimethylaluminum and tetrakis-(ethylmethylamino)hafnium metal precursors, respectively, with water oxidant. Due to the formation of an ultrathin Mo-oxide layer on the MoS2 surface, the surface coverage of Al2O3 and HfO2 films was significantly improved compared to those on pristine MoS2, even at a high ALD temperature. These results indicate that the surface modification of MoS2 by oxygen plasma treatment can have a major impact on the subsequent deposition of high-k thin films, with important implications on their integration in thin film transistors.

Oxidation of Hafnium and Diffusion of Hafnium Atoms in Hexagonal Close-Packed Hafnium; Microscopic Investigations by Perturbed Angular Correlations

Time-differential perturbed angular correlation (TDPAC) studies in hafnium metal (~5%Zr) have been carried out at different temperatures. It is found that hafnium metal on heating at 873 K continuously for two days in air, transforms partially and abruptly to HfO2 while no component of oxide has been observed for heating up to 773 K and during initial heating at 873 K for 1 day. This result is strikingly different to that expected from the Arrhenius theory. Also, a strong nuclear relaxation effect has been observed at 873 K due to rapid fluctuation of hafnium atoms in hexagonal closepacked (hcp) hafnium. At this temperature, ~ 5% probe nuclei experience static perturbation due to monoclinic HfO2, ~ 50% experience fluctuating interaction, and ~ 5% produce static defect configuration of hcp hafnium. With lowering of temperature, defect configurations of hafnium increase at the cost of fluctuating interaction. An almost total fluctuating interaction observed in hcp hafnium at a temperature much lower than its melting point is another interesting phenomenon.

Viscosity measurements of molten refractory metals using an electrostatic levitator

Viscosities of several refractory metals (titanium, nickel, zirconium, niobium, ruthenium, rhodium, hafnium, iridium and platinum) and terbium have been measured by the oscillation drop method with an improved procedure. The measured data were less scattered than our previous measurements. Viscosities at their melting temperatures showed good agreement with literature values and some predicted values.

Electro-deoxidation of hafnium dioxide and niobia-doped hafnium dioxide in molten calcium chloride

This paper investigates the capability of the FFC-Cambridge process of producing metallic hafnium powder that can meet commercial standards. The results show that the reduction in the core of the pellet is hindered in an intermediate step associated with the formation of CaHfO3. Doping the initial hafnium oxide with niobium oxides in the initial pellet prevents this blocking. The charge passed is much higher than that observed with undoped HfO2. The powder obtained after 36h of electro-deoxidation is an Hf–Nb alloy cubes with 0.8wt.% oxygen content and 5–20μm size.

A Hafnium Material Control Rod Design and Manufacture

Because the metallic hafnium has good combination properties, that makes it the preferred material for control rods of nuclear reactors. To prevent the irradiation deformation and the mechanical property decrease of hafnium plates, and to increase the service life of the control rods, a new type of square-tube control rod is developed. The elemental composition, mechanical property, the corrosion resistance and the physical characteristics of hafnium are researched. Several tests are carried out after the product manufactured, which prove that the design and manufacture of the control rod meet the requirement of the technical conditions.

The Properties Research of Hafnium Plate for Control Rod

Metallic hafnium has good comprehensive performance that makes it the preferred material for control rods of nuclear reactors. The elemental composition, mechanical properties, the corrosion resistance and the physical characteristics of hafnium plate are researched during the development of control rod for reactors. It proved the manufacturing method of hafnium plate is appropriate, characteristic of materials meet the requirement of a control rod.

High pressure study on the phonon spectra and thermal properties in hafnium nitride and zirconium nitride

We report ab initio calculations of the thermal properties for transition metal nitrides, hafnium and zirconium nitride at ambient and high pressures. The assessment of thermodynamical properties like lattice specific heat, vibrational energy, internal energy and entropy for two nitrides has been carried out. The basic calculations of ingredient phonon density of states for the determination of thermal properties have been done using density functional perturbation theory including external perturbations like strains and electric fields in periodic systems. The ground state properties such as equilibrium lattice constants and bulk modulus obtained for two nitrides are in good agreement with the available experimental value. The calculated pressure variation of the phonon density of states shows trend similar to the experimental pressure dependent Raman spectra. The lattice specific heat, internal energy, entropy and Helmholtz energy increases with pressure.

Effects of substrate temperatures on the structure and properties of hafnium dioxide films

Different HfO2 monolayers under different deposition conditions, such as substrate temperature and oxygen partial pressure, were prepared from metal hafnium using the reactive electron beam evaporation method. X-ray diffraction was applied to determine the crystalline phase of these films, the surface morphology of the samples was examined by atomic force microscopy, and the optical properties were analyzed using a spectrophotometer and the surface thermal lens technique. The relationship between substrate temperature and film characteristic was investigated, and the correlation between the observed film properties and the laser damage threshold was also discussed.