Tantalum Powder Research Articles

Fabrication of Metallic Tantalum Powder by Magnesium-gas Reduction of Tantalum Oxide

Fabrication of Metallic Tantalum Powder by Magnesium-gas Reduction of Tantalum Oxide

Magnesiothermic Reduction of Mg4Ta2O9 in the Combustion Regime

We have studied the magnesium reduction of the Mg4Ta2O9 tantalate in the combustion regime and assessed the influence of starting mixture parameters on the combustion speed and temperature, the degree of reduction, and characteristics of the resultant tantalum powders. The use of Mg4Ta2O9 as a precursor for the reduction process has made it possible to increase the degree of reduction and the specific surface area of tantalum powders. We have obtained powders with a specific surface area of up to 21 m2/g, which is a factor of 4–5 larger than in the case of the reduction of Ta2O5 under the same conditions.

Niobium Powders of Mesoporous Structure

The mesoporous structure of niobium powders of specific surface areas from 32 to 150 m2/g obtained through reduction of niobium-oxide compounds by magnesium vapors has been investigated. A doubling of the specific surface area of magnesium-thermic niobium powders in comparison to tantalum powders has been shown to be caused by the larger volume and smaller size of pores. For a powder with a specific surface area of 150 m2/g, 90% of the surface is governed by pores of sizes smaller than 5 nm. Although the X-ray pattern of the powder corresponds to the metal niobium, 96.5% of this powder weight consists of a natural surface-oxide film, according to the TGA data. The thickness of this oxide decreases in comparison with the surface oxide on the compact metal depending on the powder mesoporous structure.

Niobium and Tantalum Powders from Lithium Niobate and Lithium Tantalate Production Waste

The preparation of tantalum and niobium powders with a low content of impurities and a large specific surface area by magnesium-thermic reduction directly from the lithium tantalate and lithium niobate single crystal production waste without preliminary conversion is described. It is shown that the resulting tantalum powders can be used for manufacturing anodes of capacitors with a specific charge of 100000–130000 μC/g.

Quantification of tantalum sedimentation rates in liquid embolic agents

Background Endovascular treatment (EVT) of brain arteriovenous malformations has evolved from cyanoacrylate derivatives such as N-butyl cyanoacrylate, an adhesive glue, to ethylene vinyl copolymer-based liquid embolics such as Onyx® and SQUID® dissolved in dimethyl sulfoxide. Although these agents offer several advantages, their rapidly decreasing radiopacity, as a result of the sedimentation of tantalum powder, compromises visual control during EVT. This study aims to quantify and compare tantalum sedimentation rates of several liquid embolic agents, and determine their effects on radiopacity. Methods The rate of sedimentation of liquid embolics Onyx 18®, SQUID 12®, and SQUID 18® was measured after preparation by single x-ray exposures for a period of 30 minutes. The signal-to-noise ratios (SNRs) of the suspension of each liquid embolic was calculated at various time points as tantalum settled out of the suspension. Precipitating Hydrophobic Injectable Liquid (PHIL®) was imaged as a control. Results Onyx 18® demonstrated the fastest sedimentation rate of the liquid embolics analyzed and demonstrated a threefold faster drop in SNR compared to SQUID 18® over 30 minutes. Onyx 18® demonstrated a one and a half times faster drop in SNR compared to SQUID 12®. Although PHIL 25® maintained constant SNR over the same time, it was lower at baseline immediately after preparation compared to tantalum-based liquids. Conclusion Caution during long injections using tantalum-based agents is advised. Onyx 18® has a significantly faster drop in radiopacity compared to SQUID 12® and SQUID 18®. Covalently bonded iodine-based embolics like PHIL® demonstrate constant radiopacity over time.

Detonation spraying behaviour of refractory metals: Case studies for Mo and Ta-based powders

In thermal spraying of refractory metal powders, two major issues need to be solved: particles of materials having high melting temperatures should be heated to reach a semi-molten/molten state or temperatures close to the melting point, while oxidation of the metals should be prevented. It has long been believed that it is rather difficult, if not impossible, to produce high-quality refractory metal coatings by detonation spraying. In this work, we demonstrated the capability of the detonation spraying method to produce tantalum-based and molybdenum coatings of low porosity. Using a computer-controlled detonation spray (CCDS2000) facility, the detonation spraying behaviour of a molybdenum powder and a partially oxidized tantalum powder was studied. Spraying was conducted onto steel substrates using an acetylene-oxygen mixture with O2/C2H2 = 1.1. The spraying process was studied by means of analyzing the splat morphology and calculating the particle temperatures and velocities. According to the X-ray diffraction phase analysis, the metals did not experience oxidation during the deposition. Rather, partial reduction of the oxide phase contained in the Ta-based powder occurred during spraying.

Effect of concentrated light on morphology and vibrational properties of boron and tantalum mixtures

Heating a mixture of boron (impurities: carbon ∼ B50C2, boric acid – H3BO3) and tantalum (Ta) powders in nitrogen flow in a xenon high-flux optical furnace was performed. As-received powder composed of h-BN, H3BO3, TaB2, B9H11 and a number of other phases including β-rhombohedral boron, apparently, heavily doped with Ta. FT–IR examination of any sample of the material reveals the complicated vibration spectrum containing, in particular, an absorption band near 2260 cm−1. The shapes of these bands are different for samples because powders were synthesized at different temperatures. Known, that in β-rhombohedral boron lattice, there are nano-sized voids of different types, which allow an accommodation of single atoms or small groups of atoms. Theoretical calculations performed by the method of quasi-classical type yields the same value, 2260 cm−1, for the vibrations frequency of Ta atoms in D-type crystallographic voids in β-rhombohedral boron lattice. Since, Ta atoms are known to prefer accommodation just in D-voids the experimentally detected bands can be identified with localized vibrations of Ta atoms.

Karakterizacija tantal prevlake deponovane vakuum plazma sprej procesom

Tantalum is a very popular material for the industry as a whole because of very important characteristics such as: high melting point, significant thermal and electrical conductivity, high toughness and resistance to corrosion and good biocompatibility. Since the tantalum metal is sensitive to O, N and H gases, tantalum coating layers are deposited only using the vacuum plasma spray process (VPS), which has, in the past few years been used successfully for preparing coatings which are widely used in the preparation of metal implants. The aim of this paper was to, at a low pressure inert gas eliminate the influence of the surrounding atmosphere on the melted Ta powder particles and produce coatings with mechanical and structural characteristics which will find application in biomedicine. For depositing the coating a commercial tantalum powder AMPERIT® 151065 grain size of 10 - 30 μm was used. The powder was deposited with a plasma F4 gun at a distance of substrates at 300 mm. The Ta coating layers were deposited with a thickness of 60 to 70 μm on steel substrates. As the plasma gas used was a mixture of Ar and He inert gases. The microhardness of the coating was tested using the HV0.3 method and the tensile strength of the coatings bond was tested by the tensile method in accordance with the ASTM C633-1 standard. The microstructure of the coating in deposited state and after etching was studied on an optical microscope (OM) and scanning electron microscope (SEM). Etching the coating was carried out in the reagent which consisted of two parts of nitric acid, two parts hydrofluoric acid, and five parts water (2HNO3: 2HF: 5H2O). The structure of the coating consists solely of a tough αTa phase with a body centered cubic lattice. Tests have shown that layers of VPS - Ta coatings have the microstructure and mechanical properties which completely support the use of the coating in the process of making implants.

The dynamic mechanical characteristics of Zr-based bulk metallic glasses and composites

In the current study, Zr-based metallic glass matrix composites (MGMCs) were prepared by doping high-melting point of tantalum powders and investigated by dynamic mechanical analysis. The results suggest that the relaxation processes are changed by modifying the chemical composition. The influence of crystalline phase on the dynamic mechanical response of Zr-based MGMC has been analyzed. The master curves of loss modulus can be well fitted by the Kholrausch-Williams-Watts (KWW) model, decreasing of the parameter βKWW implies that the Zr-based MGMC doped with more tantalum powders has higher dynamic heterogeneity. To better understand the dynamic mechanical properties of the MGMCs, quasi-point defects (QPD) theory is adopted, the kinetic characteristics of glass transition of Zr-based MGMCs are analyzed in a quantitative manner. The experimental results provide an insightful information on the complex structural relaxation of the metallic glass matrix composite.

Heat Treatment of Tantalum and Niobium Powders Prepared by Magnesium-Thermic Reduction

Changes in the specific surface area and porous structure of tantalum and niobium powders, which were prepared by magnesium-thermic reduction of Ta2O5, Mg4Ta2O9, and Mg4Nb2O9 oxide compounds and subjected to heat treatments at temperatures of 600–1500°C, have been studied. It is noted that, owing to the mesoporous structure of the magnesium-thermic powders, the decrease in the surface area during heat treatment, first of all, is related to a decrease in the amount of pores less than 10 nm in size. The heat treatment of a reacting mass is shown to allow us to correct the specific surface area of the powder without any increase in the oxygen content in it. Data on the effect of heat treatment conditions on the specific charge of capacitor anodes are reported.

Production of high-porous electrodes from tantalum powder

Production of high-porous electrodes from tantalum powder

A Morphological Approach to the Modeling of the Cold Spray Process

A coating buildup model was developed, the aim of which was simulating the microstructure of a tantalum coating cold sprayed onto a copper substrate. To do so, first was operated a fine characterization of the irregular tantalum powder in 3D, using x-ray microtomography and developing specific image analysis algorithms. Particles were grouped by shape in seven classes. Afterward, 3D finite element simulations of the impact of the previously observed particles were realized. To finish, a coating buildup model was developed, based on the results of finite element simulations of particle impact. In its first version, this model is limited to 2D.

Synthesis and photocatalytic properties of mesoporous tantalum oxynitride

The effect of the conditions of ammonolysis of mesoporous magnesiothermic tantalum powders with the specific surface area of 56–63 m2 g–1 on phase composition and specific surface area of the products is studied in the temperature range of 400–900°C. The ammonolysis products are shown to be X-ray amorphous at 400–600°C. At the heating rate of 20 K/min, the nitrogen content in these products is 5.4–7.3% and the specific surface area is 42–35 m2 g–1, while at heating rate of 8 K/min these parameters are 2.4–5.4% and 56–49 m2 g–1, respectively. The crystalline phase of tantalum oxynitride TaON is formed at a temperature of 700°C and above. The resulting materials exhibit a high photocatalytic activity in the reactions of ferroin and methylene blue degradation under irradiation with visible light (λ ≥ 420 nm).

X-ray diffraction study of magnesiothermic tantalum powders

We have studied the effect of specific surface area and reaction product leaching conditions on the crystal structure of mesoporous tantalum powders prepared by reducing tantalum oxide compounds with magnesium vapor.

Unprecedented simultaneous enhancement in damage tolerance and fatigue resistance of zirconia/Ta composites

Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO2 and lamellar metallic powders of tantalum or niobium (20 vol.%) as starting materials. The present study has demonstrated the unique and unpredicted simultaneous enhancement in toughness and strength with very high flaw tolerance of zirconia/Ta composites. In addition to their excellent static mechanical properties, these composites also have exceptional resistance to fatigue loading. It has been shown that the major contributions to toughening are the resulting crack bridging and plastic deformation of the metallic particles, together with crack deflection and interfacial debonding, which is compatible with the coexistence in the composite of both, strong and weak ceramic/metal interfaces, in agreement with predictions of ab-initio calculations. Therefore, these materials are promising candidates for designing damage tolerance components for aerospace industry, cutting and drilling tools, biomedical implants, among many others.

In Vitro Quantification of the Radiopacity of Onyx during Embolization.

PurposeOnyx has been successfully applied in the treatment of various neurovascular lesions. However, some experience is required to get accustomed to its unpredictable fluoroscopic visibility during injection. This in vitro study aimed to evaluate the characteristics of radiopacity change in a simulated embolization procedure.Materials and MethodsUsing a bench-top Onyx injection experiment simulating a typical brain arteriovenous malformation embolization, nine cycles of casting modes (continuous injection) and plugging modes (injection with intermittent pauses) were performed. Radiodensity of Onyx droplets collected from the microcatheter tip and the distal head portion of the microcatheter were measured as time lapsed. Distribution of droplet radiodensity (radiodensity) and distribution of radiographic grade (grade) were analyzed and compared by repeated measurements.ResultsWithin-group analysis revealed no significant radiodensity change with time (P>0.05). The radiodensity was significantly higher in the casting mode than in the plugging mode (P<0.01). The lateral radiograph of the microcatheter showed higher radiopacity (P<0.01) and better evenness (P<0.01) in the casting mode than in the plugging mode. A significant difference in microcatheter attenuation (both radiographic grade mean and SD; P<0.01) was noted between the two modes. Radiodensity had a significant influence on the radiopacity and radiopacity evenness of the microcatheter.ConclusionThe radiopacity of the Onyx can vary significantly over time because of early precipitation of tantalum powder. Radiopacity decreased significantly during plugging modes, characterized by pauses between injections.

Solid State Manufacture of High Entropy Alloys-Preliminary Studies

For the past ten years Metalysis have produced tantalum, titanium and titanium alloy powders for high performance applications using their solid state salt electrolysis process. This low energy and environmentally friendly process is now being used to manufacture the next generation of High Entropy Alloys (HEAs). In most cases the manufacture of HEAs involves high temperatures which put all of the alloying elements into the liquid phase. This can lead to numerous problems and restrict the number of HEAs which can be made, particularly the alloys where one needs to combine low melting point elements with refractory elements and also where there are significant liquid density differences between the constituents causing melt segregation. The aim is to present the preliminary work carried out by Metalysis and to show how the solid state diffusion process based on molten salt electrolysis lends itself to the industrial scale manufacture of the next generation of HEAs. This study will focus on the HEAs whose constituent alloying elements have large differences in both their melting points and liquid densities, for example, chromium, niobium, tantalum, titanium and aluminum.

A modeling of tobacco smoking and smoke and resin microparticles deposition in the airways

The aim of this study was smoking modeling with visualization of microparticles of the smoke deposed on the walls of the digestive and the respiratory tracts. Methods. Patients with tuberculosis and chronic non-infectious lung diseases participated in the study. All the patients underwent bronchoscopy. Powdered tantalum mircoparticles with the size of &lt; 1 µm were used as markers of tobacco smoke microparticle deposition. The tantalum powder was administered orally and intratracheally. Tantalum microparticles deposed in the airways were identified using the chest X-ray examination immediately and in 4 h after the insufflation. Results. In most patients (64.3%), 95% of microparticles deposed in the mouth, the oropharingeal area, the pharynx, the pyriform sinuses and the larynx just after the insufflation and only 5% achieved the lower airways. Conclusion . We investigated factors facilitating deposition of microparticles into the bronchi. Such deposition could lead to bronchial obstruction and further penetration of microparticles into the alveoli. We also determined three types of optical density of the deposed smoke microparticles that could characterize microparticle layer thickness, a mechanism of deposition (impaction, sedimentation, or diffusion) and its distinct location.

Ammonolysis of magnesiothermic tantalum powders

Tantalum nitrides are synthesized by ammonolysis of a mesoporous magnesiothermic tantalum powders. The effect of specific surface area of the powders and synthesis temperature on product composition is shown. Nitrogen content in the ammonolysis product of tantalum powder with a specific surface area of 56 m2 g–1 corresponds to oxynitride TaON exposed to 600°C for 1 h. The specific surface area of the oxynitride is 35 m2 g–1.

Capacitance Stability in Polymer Tantalum Capacitors with PEDOT Counter Electrodes

Polymer Tantalum capacitors with PEDOT cathodes fabricated with an aqueous pre-polymerized PEDOT dispersion (slurry PEDOT) were investigated for stability with temperature. In particular, capacitance dependence on temperature was investigated in humidified and dry capacitors fabricated with both coarse and fine tantalum powders, variable thicknesses of the Ta2O5 dielectric, and in-situ vs. slurry PEDOT cathodes. Electrical measurements along with scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) were used to characterize the samples. The capacitance of all samples was observed to increase with temperature; however, the extent and nature of this increase depends significantly on the nature of the polymer cathode and its interface with the dielectric. Humidified devices showed less capacitance variation above room temperature while dry devices showed less capacitance variation below room temperature for both coarse and fine powders. These results cannot be explained by the inherent variation of the dielectric constant with temperature. A model was developed for the capacitance dependence on relative humidity and temperature based on surface area changes due to heating or cooling, complimented by changes in the dielectric constant, which is in good agreement with the experimental data. The results of this work demonstrate the critical impact of the dielectric-polymer interface on capacitance stability in these capacitors.