Hafnium Metal Research Articles

Dissimilar micro beam welding of titanium to Nitinol and stainless steel using biocompatible filler materials for medical applications

In the present investigation, thin sheet geometries of commercially pure titanium (cp, grade 4) are butt-welded to AISI 316L stainless steel as well as Nitinol by means of micro electron beam welding using filler materials. In order to avoid mixing of the base materials, the refractory metals tantalum, niobium and hafnium are applied as intermediate layers. Owing to the biocompatibility of these filler materials, the final products are suitable for medical technology applications. In combination with low energy inputs and precise beam alignments, it is demonstrated that high-quality and crack-free joints can be produced using micro electron beam welding. The welded joints are analysed using nanoindentation to identify critical weld areas, e.g. high concentrations of intermetallic compounds, and to evaluate the compatibility of the base and filler materials. To correlate the hardness mappings with the microstructural evolution of the welds, an exemplary joint is analysed by means of electron backscatter diffraction and energy dispersive X-ray spectroscopy with special emphasis on intermixing and the formation of intermetallic compounds. Based on the generated hardness mappings as well as the ultimate tensile strengths of the joints, it will be concluded which filler material provides the most promising results for the given material combinations.

Structure Tuning of Hafnium Metal–Organic Frameworks through a Mixed Solvent Approach

The recent development of water-stable metal–organic frameworks (MOFs) has significantly broadened the application scope of this emerging type of porous material. Structure tuning of hafnium MOFs is less studied compared with zirconium MOFs. In this work, we report the synthesis of a mesoporous hafnium MOF, csq-MOF-1, through finely tuning the solvent mixture ratio. The successful synthesis of csq-MOF-1 also relies on the linker flexibility as linker bending and a symmetry decrease were observed in this framework as compared to its structural isomer NPF-300 (Hf). The mesoporous feature and permanent porosity were determined by the N2 adsorption at 77 K. Such a hierarchical pore feature is expected to enable a variety of applications through encapsulation of large functional molecules. The synthetic strategy of utilizing a mixed solvent and flexible linker is expected to inspire the development of new hafnium MOFs with diverse topological structures.

High Protonic Conductivity of Three Highly Stable Nanoscale Hafnium(IV) Metal-Organic Frameworks and Their Imidazole-Loaded Products.

Attracted by the exceptional structural rigidity and inherent porous structures of the Hf-based metal-organic frameworks (MOFs), we adopted a rapid synthesis approach to preparing three nanoscale MOFs, Hf-UiO-66 (1), Hf-UiO-66-(OH)2 (2), and Hf-UiO-66-NH2 (3), and systematically explored the water-assisted proton conductivities of the original ones and the post-modified products. Interestingly, the proton conductivities (σ) of all three MOFs exhibit significant temperature and humidity dependence. At 98% RH and 100 °C, their optimal σ values can reach up to 10-3 S·cm-1. Consequently, imidazole units are loaded into 1-3 to obtain related MOFs, Im@1, Im@2, and Im@3, and the σ values of the imidazole-loaded products are boosted to 10-2 S·cm-1. Note that these modifications not only do not change the frameworks of the pristine MOFs but also do not affect their high chemical and water stability. The proton-conductive mechanisms of these MOFs before and after modification have been thoroughly discussed based on structural analyses, N2 and H2O vapor adsorptions, and activation energy values. The excellent structural stability as well as the durability and stability of their proton conduction ability indicate that these MOFs can be used in the field of fuel cells and so on.

A Developed Plasmatron Design to Enhance Production of Hydrogen in Synthesis Gas Produced by a Fuel Reformer System

Feeding IC engines with hydrogen-rich syngas as an admixture to hydrocarbon fuels can decrease pollutant emissions, particularly NOx. It offers a potential technique for low-environmental impact hydrocarbon fuel use in automotive applications. However, hydrogen-rich reformate gas (syngas) production via fuel reforming still needs more research and optimization. In this paper, we describe the effect of a plasma torch assembly design on syngas yield and composition during plasma-assisted reforming of gasoline. Additionally, erosion resistance of the cathode-emitting material under the conditions of gasoline reforming was studied, using hafnium metal and lanthanated tungsten alloy. The gasoline reforming was performed with a noncatalytic, nonthermal, low-current plasma system in the conditions of partial oxidation in an air and steam mixture. To find the most efficient plasma torch assembly configuration in terms of hydrogen production yield, four types of anode design were tested, i.e., two types of the swirl ring, and two cathode materials while varying the inlet air and fuel flow rates. The experimental results showed that hydrogen was the highest proportion of the produced syngas. The smooth funnel shape anode design in Ring 1 at air/fuel flow rates of 24/4, 27/4.5, and 30/5 g/min, respectively, was more effective than the edged funnel shape. Lanthanated tungsten alloy displayed higher erosion resistance than hafnium metal.

Therapeutic Advancements in Metal and Metal Oxide Nanoparticle-Based Radiosensitization for Head and Neck Cancer Therapy.

Simple SummaryThough radiation therapy remains a primary modality for head and neck cancer (HNC) management, the collateral damage to normal surrounding tissues and tumor relapse represent major challenges. Hence, it is imperative to develop safer and more effective HNC therapies. Metal and metal oxide nanoparticle-based radiosensitizers have been explored for their potential to overcome these challenges. The key impetus of this review was to shed light on ongoing metal and metal oxide nanoparticle-based radiosensitizers’ development and to address their success in in vitro and in vivo HNC models and in clinical translation.Although radiation therapy (RT) is one of the mainstays of head and neck cancer (HNC) treatment, innovative approaches are needed to further improve treatment outcomes. A significant challenge has been to design delivery strategies that focus high doses of radiation on the tumor tissue while minimizing damage to surrounding structures. In the last decade, there has been increasing interest in harnessing high atomic number materials (Z-elements) as nanoparticle radiosensitizers that can also be specifically directed to the tumor bed. Metallic nanoparticles typically display chemical inertness in cellular and subcellular systems but serve as significant radioenhancers for synergistic tumor cell killing in the presence of ionizing radiation. In this review, we discuss the current research and therapeutic efficacy of metal nanoparticle (MNP)-based radiosensitizers, specifically in the treatment of HNC with an emphasis on gold- (AuNPs), gadolinium- (AGdIX), and silver- (Ag) based nanoparticles together with the metallic oxide-based hafnium (Hf), zinc (ZnO) and iron (SPION) nanoparticles. Both in vitro and in vivo systems for different ionizing radiations including photons and protons were reviewed. Finally, the current status of preclinical and clinical studies using MNP-enhanced radiation therapy is discussed.

Highly Stable Artificial Synapses Based on Ferroelectric Tunnel Junctions for Neuromorphic Computing Applications

AbstractOwing to the limited processing speed and power efficiency of the current computing method based on the von Neumann architecture, research on artificial synaptic devices for implementing neuromorphic computing capable of parallel computation is accelerating. The potential application of artificial synapses composed of ferroelectric tunnel junctions based on metal–hafnium zirconium oxide–metal structure for neuromorphic computing is investigated. Multiple resistance levels are implemented through partial polarization switching control, and synaptic plasticity is successfully imitated based on a high level of device stability and reproducibility. In addition, this device exhibits linear symmetric long‐term potentiation and long‐term depression using a highly variable pulse driving scheme. Finally, the artificial neural network applied with this synaptic device shows high classification accuracy (95.95%) for the Mixed National Institute of Standards and Technology handwritten digits.

Apatite formation on electrochemically modified surface of hafnium metal in simulated body environment

ABSTRACT Biomedical application of Hf for hard tissue repair may be expanded if it can be imparted with bone-bonding ability. Apatite formation in the body is required for artificial materials to bond to bone. We have shown that apatite can form on NaOH- and heat-treated Hf in simulated body fluid, although the degree of apatite formation is not high. In this study, we investigated apatite formation on surface-modified Hf metal in simulated body fluid. Hf substrates were soaked in NH4F solution or electrochemically polarized in H2SO4 or NH4F solution, followed by heating at 600°C. The sample soaked or cathodically polarized in NH4F solution had porous structure, and the anodically polarized sample had nanotube aggregates on its surface. F was incorporated into the sample polarized in NH4F solution, but not the sample merely soaked in the solution. NH4F was more effective than H2SO4 in facilitating apatite formation. Remarkably, the sample soaked in NH4F solution had the highest apatite-forming ability. Its porous structure was considered to play a dominant role in apatite formation. Furthermore, there was little correlation between surface energy and apatite formation. Notably, NH4F treatment is more effective than the previously reported NaOH and heat treatments in promoting apatite formation.

Effect of Hafnium Coating on Osseointegration of Titanium Implants: A Split Mouth Animal Study

The behaviour of hafnium as surface coating in biological environments has not been studied. Little is known about osseointegration of hafnium-coated titanium implants. Thus, further studies of hafnium coating under biological conditions are required in order to determine the suitability of this material, as a surface coating for biomedical application. The aim of the study is to analyse the difference between hafnium-coated titanium and uncoated titanium by evaluating the osseointegration ability of hafnium metal and mechanism of which promotes better bone integration. The study was conducted with a split mouth design on 16 Wistar Albino rats of both sexes, at the age of 6-7 months, weighing 2526.5 ± 74.4 g . Self-tapping titanium osteosynthesis screws ( 4 mm × 2 mm ) (LeForte System Bone Screw®) were implanted in the mandible of rats: Group A (pure titanium screws, n = 12 ) and Group B (hafnium-coated screws, n = 12 ). The implanted screws’ stability was checked and noted with a specially customised torque apparatus during insertion and removal of implant. The tissue sections were then processed for hematoxylin and eosin and Masson’s trichrome for bone and connective tissue examination, after 4 and 8 weeks of placement. Hafnium coating appears to have offered similar biocompatibility (aspartate transaminase (AST), alanine aminotransferase (ALT), and creatine kinase (CK) enzyme assay), statistically significant improvement (independent Student’s t -test, p < 0.05 ) in insertion torque ( 25.42 ± 3.965 ) and removal torque ( 29.17 ± 2.887 ) than commercially pure titanium with insertion torque ( 22.08 ± .575 ) and removal torque ( 25.42 ± 2.575 ). Hafnium coating in the rat mandible showed promising osseointegration with good tissue biocompatibility. Further human trials of hafnium-coated implants are needed to understand the biological behaviour better to enhance clinical performance.

Mathematical modeling and simulation of MHD electro-osmotic flow of Jeffrey fluid in convergent geometry

The multiphase flow of Jeffery fluid under the impact of Magnetohydrodynamic is examined in this analysis. The nanoparticles of Hafnium metal are mixed up in the base fluid along with the impact of the electroosmotic phenomenon having a great significance in the present decade. Two different models, namely particulate and fluid phases, are considered for a convergent geometry with numerous usages in practical life, especially in modern technologies like microfluidic devices, chemical analysis, soil analysis, and other industries. The set of partial differential equations are converted into ordinary differential equations by using the non-dimensional quantities and obtained the exact solution of the resulting boundary value problem. The impact of physical parameters involving in the study is highlighted through graphs. To observe the flow pattern, the streamlines are also constructed. The Hartman number and Jeffrey fluid parameter slow down the velocity of fluid and particle phases. The Helmholtz-Smoluchowski parameter reduces the streamlines while the flow pattern remains unchanged via U HS . Moreover, the results are also compared with the previously published literature and noted excellent agreement with each other. The developed mathematical will be helpful in the diverse geometries used widely in medical and engineering walks to incorporate the fluid in complicated places like species separation, biomedical lab-on-a-chip devices, DNA sequences and stimulated drugs in diverse veins colliers, etc.

Enhanced Reactant Activation and Transformation for Efficient Photocatalytic Acetone Degradation on SnO2 via Hf Doping

AbstractIntensified photocatalytic performance through reducing the recombination of electron–hole pairs and enhancing the oxidation capacity is a key challenge in the field of photocatalytic removal of volatile organic compounds (VOCs). Acetone, as one of the emblematical contaminants VOCs, is a general solvent and widely applied in the pharmaceutical industry, contributing severely to air pollution. Most studies of photocatalysis have focused on the photocatalyst efficiency toward pollutant degradation, but the detailed mechanisms of charge separation as well as transfer and photocatalytic acetone oxidation pathways are not revealed clearly. In this work, it is found that hafnium metal doping on the n‐type semiconductor SnO2 can modify the electronic structures, restrain the recombination of electron–hole pairs, where the hafnium metal ion acts as the activation site, leading to improved oxidation ability to realize efficient acetone degradation. In addition, the specific path toward the acetone degradation is revealed by closely combined active radical detection, in situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculation methods. It provides a new perspective about the detailed and comprehensive reaction mechanism of photocatalytic acetone degradation and carriers transfer between pollutants and photocatalysts, which is expected to promote the practical usage of photocatalytic technology for the expeditious removal VOCs.

Pressure dependent ultrasonic properties of hcp hafnium metal

Abstract The elastic and ultrasonic properties have been evaluated at room temperature between the pressure 0.6 and 10.4 GPa for hexagonal closed packed (hcp) hafnium (Hf) metal. The Lennard-Jones potential model has been used to compute the second and third order elastic constants for Hf. The elastic constants have been utilized to calculate the mechanical constants such as Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio, and Zener anisotropy factor for finding the stability and durability of hcp hafnium metal within the chosen pressure range. The second order elastic constants were also used to compute the ultrasonic velocities along unique axis at different angles for the given pressure range. Further thermophysical properties such as specific heat per unit volume and energy density have been estimated at different pressures. Additionally, ultrasonic Grüneisen parameters and acoustic coupling constants have been found out at room temperature. Finally, the ultrasonic attenuation due to phonon–phonon interaction and thermoelastic mechanisms has been investigated for the chosen hafnium metal. The obtained results have been discussed in correlation with available findings for similar types of hcp metals.

Osseointegration of Hafnium when Compared to Titanium - A Structured Review

Aim: This systematic review was conducted to analyse osseointegration of hafnium over conventional titanium. Materials and Methods: Search methodology was comprehended using PICO analysis and a comprehensive search was initiated in PubMed Central, Medline, Cochrane, Ovid, Science Direct, Copernicus and Google Scholar databases to identify the related literature. Randomised control trials, clinical studies, case control studies and animal studies were searched for osseointegration of hafnium coated titanium implants versus conventional titanium implants. Timeline was set to include all the manuscripts published till December 2018 in this review. Clinical Significance: Hafnium is a very promising surface coating intervention that can augment osseointegration in titanium implants. If research could be widened, including in vivo studies on hafnium as a metal for coating over dental implants or as a dental implant material itself to enhance better osseointegration, it could explore possibilities of this metal in the rehabilitation of both intra and extra oral defects and in medically compromised patients with poor quality of bone. Results: Out of the 25 articles obtained from the PICO based keyword search, 5 studies were excluded based on title and abstract. Out of the remaining 20 studies, 16 were excluded based on the inclusion and exclusion criteria of our interest and finally, 4 were included on the basis of core data. Conclusion: This systematic review observed hafnium metal exhibited superior osseointegration than titanium. Owing to its biocompatibility, hafnium could be an alternative to titanium, in the near future.

The forgotten chemistry of group(IV) metals: A survey on the synthesis, structure, and properties of discrete Zr(IV), Hf(IV), and Ti(IV) oxo clusters

• Group IV metal oxo clusters (MOCs) applications in materials and catalysis are rapidly expanding. • Group IV MOCs are prepared in aqueous or organic medium with a variety of ligands. • Ligands influence structure and properties, thus impacting materials syntheses and catalysis. • Ligand-exchanged happens with or without rearrangement of the inorganic core. Group (IV) metal oxo clusters are a diverse class of compounds with rapidly growing applications in catalysis, materials chemistry, electronics and optics. They possess unique structural stability, reactivity and electronic properties; however, their potential remains underexplored due to the gaps in fundamental understanding about their structure, intrinsic features, and nuances in their synthesis that overall would allow for great tunability of their properties. In this context, here we review the chemistry of discrete zirconium, hafnium, and titanium metal oxo clusters reported in the literature in order to provide a critical overview of the structural features, properties and reactivity disclosed to date. While a comprehensive summary of Zr and Hf clusters is presented, only the most recent Ti oxo clusters are discussed in addition to some key compounds that have been revised elsewhere. Envisioning the growing relevance group (IV) metal oxo clusters for the synthesis of nanostructure materials and in catalysis, we also summarize key principles of their surface chemistry, and the photoactivity of Ti oxo clusters, given the paramount importance of these properties for the development of future applications.

Determination of Hafnium Zirconium Oxide Interfacial Band Alignments Using Internal Photoemission Spectroscopy and X-ray Photoelectron Spectroscopy.

Doped ferroelectric HfO2 is highly promising for integration into complementary metal-oxide semiconductor (CMOS) technology for devices such as ferroelectric nonvolatile memory and low-power field-effect transistors (FETs). We report the direct measurement of the energy barriers between various metal electrodes (Pt, Au, Ta, TaN, Ti/Pt, Ni, Al) and hafnium zirconium oxide (Hf0.58Zr0.42O2, HZO) using internal photoemission (IPE) spectroscopy. Results are compared with valence band offsets determined using the three-sample X-ray photoelectron spectroscopy (XPS) as well as the two-sample hard X-ray photoelectron spectroscopy (HAXPES) techniques. Both XPS and IPE indicate roughly the same dependence of the HZO barrier on metal work function with a slope of 0.8 ± 0.5. XPS and HAXPES-derived barrier heights are on average about 1.1 eV smaller than barrier heights determined by IPE, suggesting the presence of negative charge in the HZO.

Hf metal powder synthesis via a chemically activated combustion-reduction process

The present study demonstrates the synthesis of fine hafnium (Hf) metal powders via a chemically activated combustion synthesis (CS) approach, which develops temperatures in the range of 1000–1600 °C. The current CS approach can be employed to obtain Hf powders with a single-crystalline hexagonal close-packed (hcp) structure in addition to high compositional uniformity and average particle sizes ranging from 0.05 to 2.0 μm. The mechanism of Hf particle formation can be understood by analyzing the process thermodynamics, including adiabatic temperatures and equilibrium reaction phases. In addition, analytical methods, including X-ray diffraction, SEM/TEM BET, FTIR, and oxygen analysis, were employed to characterize the synthesized Hf powders. Theoretical analysis was also conducted to predict the oxygen content according to Hf particle size. To the author's best knowledge, this work is the first known report demonstrating the preparation of hafnium micro- and nanopowders by the combustion synthesis method.

Development in the Production of Hafnium Wire Conforming to ASTM B737 Standard

Despite the sufficient exploration of industrial methods for the manufacturing of products from metal hafnium, the public domain has a limited number of reports that highlight the technological aspects of hafnium wire manufacturing and their effect on the structure and mechanical properties of the products formed [1, 2]. This article describes the methods employed in the manufacturing of hafnium wire from the ingots of its own production, which have been tested by Chepetsk Mechanical Plant (CMP) under industrial conditions, as well as the advantages and disadvantages of each tested method for producing the wire. The stages of hafnium wire drawing are described in detail. During the experiments, the relationships between the technological, energy–power parameters, surface quality, and material structure were studied. The effects of the type of drawing tool on the wire surface quality and drawing force were revealed, as well as the effects of the wire diameter on the amount of permissible deformation between the annealed products and the grain size of the metal. The paper reports the results of studies conducted on the structure, mechanical, and corrosion properties of the experimental samples of wires manufactured in compliance with the ASTM B737 standard specification for hot rolled and/or cold-drawn hafnium rods and wire. Currently, CMP can manufacture wires with a diameter of 1 mm or more from hafnium ingots of its own production, in compliance with the ASTM B737 standard.

The chemistry and applications of hafnium and cerium(iv) metal-organic frameworks.

The coordination connection of organic linkers to the metal clusters leads to the formation of metal-organic frameworks (MOFs), where the metal clusters and ligands are spatially entangled in a periodic manner. The immense availability of tuneable ligands of different length and functionalities gives rise to robust molecular porosity ranging from several angstroms to nanometres. Among the large family of MOFs, hafnium (Hf) based MOFs have been demonstrated to be highly promising for practical applications due to their unique and outstanding characteristics such as chemical, thermal, and mechanical stability, and acidic nature. Since the report of UiO-66(Hf) and DUT-51(Hf) in 2012, less than 200 Hf-MOFs (ca. 50 types of structures) have been reported. Besides, tetravalent cerium [Ce(iv)] has been proven to be capable of forming similar topological MOF structures to Zr and Hf since its first discovery in 2015. So far, ca. 40 Ce(iv) MOFs with 60% having UiO-66-type structure have been reported. This review will offer a holistic summary of the chemistry, uniqueness, synthesis, and applications of Hf/Ce(iv)-MOFs with a focus on presenting the development in the Hf/Ce(iv)-clusters, topologies, ligand structures, synthetic strategies, and practical applications of Hf/Ce(iv)-MOFs. In the end, we will present the research outlook for the development of Hf/Ce(iv)-MOFs in the future, including fundamental design of Hf/Ce(iv)-clusters, defect engineering, and various applications including membrane development, diversified types of catalytic reactions, irradiation absorption in nuclear waste treatment, water production and wastewater treatment, etc. We will also present the emerging computational approaches coupled with machine-learning algorithms that can be applied in screening Hf and Ce(iv) based MOF structures and identifying the best-performing MOFs for tailor-made applications in future practice.

Fabrication of Tantalum and Hafnium Carbide Fibers via ForcespinningTM for Ultrahigh‐Temperature Applications

In this work, a novel method for producing ultrafine tantalum and hafnium carbide fibers using the ForcespinningTM technique via a nonhalide‐based sol‐gel process was investigated. An optimal solution viscosity range was systematically determined via rheological studies of neat PAN/DMF as a function of fiber formation. Subsequently, ForcespinningTM parameters were also systemically studied to determine the optimal rotational velocity and spinneret‐to‐collecting rod distance required for ideal fiber formation. TaC and HfC fibers were synthesized via ForcespinningTM utilizing a mixture of PAN and refractory transition metal alkoxides (i.e., tantalum (V) ethoxide and hafnium (IV) tert‐butoxide) in DMF solution based on optimal conditions determined from the neat PAN/DMF. In all instances after calcination, powder X‐ray diffraction (PXRD) and energy dispersive spectroscopy (EDS) indicated that TaC and HfC fibers were produced. TGA/DSC confirmed the chemical stability of the resulting fibers.

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

Summary Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

Low-temperature Hf-silicate prepared with various thermal budgets

In this study, the influence of thermal budget on preparing hafnium silicate (HfSiO) and metal–insulator–semiconductor (MIS) structures with tetragonal hafnium oxide (HfO2) films was investigated. Amorphous silicon (a-Si) was used as a sacrificial layer for HfSiO formation. Rapid thermal annealing (RTA) could efficiently drive the oxidation of a-Si with HfO2. The RTA-produced HfSiO film thicker than that produced through furnace annealing could suppress gate leakage in MIS devices, and aid in maintaining a high dielectric constant of the gate insulator. The combination of sacrificial a-Si film use and RTA application resulted in a HfSiO/HfO2 structure (named as hybrid HfO2), which demonstrated a high dielectric constant and strength (29.5 and 21.2 MV cm−1, respectively). MIS devices integrated with this hybrid HfO2 achieved a hysteresis value of only 0.11 V on a flat-band voltage measured at a 50 mV s−1 sweep rate with an applied voltage between −5 and 5 V.