Tantalum Powder Research Articles

Composite fabrication in cast Al A206 via friction stir processing

Using friction stir processing (FSP) in forming localised or surface composites in castings can be very advantageous and has significant potential for many applications. Consequently, this study was initiated at ACRC to investigate the feasibility of fabricating composites in Al alloy castings via FSP. The study started with the Al A206 alloy matrix via an ex-situ technique, using a pre-machined groove with emplaced reinforcements. Three reinforcement materials (nanosized tantalum powders, nanosized SiC powders, and discontinuous reinforced aluminium) and several key processing parameters (number of FSP passes, the amount of the reinforced materials) were investigated and localised composites were produced successfully. This paper will present the experimental set-up, procedure, the microstructure and properties of the resulting composites, and a discussion of the formation mechanism of the composite and the influences of materials and process on the microstructure and properties.

Effect of the conditions of sintering of sodium-reduced tantalum powders on their characteristics

The effect of the granulation and heat treatment of sodium-reduced tantalum powders with a specific surface area of 2.5–3.6 m2/g on the bulk density, the powder flow time, and the specific surface area of the powders and the specific capacitance of the anodes made of them is studied. It is shown that heat treatment of a granulated powder in vacuum at 1100°C or in a mixture with magnesium at 800°C makes it possible to achieve the required powder flow time.

Deoxidation of the tantalum powder produced by self-propagating high-temperature synthesis

The possibility of removal of oxygen and magnesium from the products of the magnesium reduction of tantalum pentoxide under self-propagating high-temperature synthesis conditions that contain 30 wt % Mg4Ta2O9 is studied. Additional reduction of this material can decrease the magnesium content to 30 m2/g during the reduction of Mg4Ta2O9.

Effect of doping on microstructure and technical usage property of tantalum wire

Effect of different dopants and various dopants quantity at different annealing temperatures on microstructure of tantalum wire, bending of tantalum wire after sintering and bending after pressing into tantalum powder and sintering were investigated through observation of microstructure and testing of bending of tantalum wire after sintering and bending after pressing into tantalum powder and sintering. The results show that the recrystallization temperature of tantalum wire increases and the grain of microstructure can be reduced with the increase of dopants quantity. At the same time, the effect of dopant Ce on reduction of the grain is more obvious than that of dopant Ge. The bending time of tantalum wire after sintering increases with the increase of dopant Ge or Ce quantity. Under the same condition, the bending time of tantalum wire after pressing into tantalum powder and sintering worsens with the increase of oxygen content in tantalum powder. The bending time of tantalum wire doped with Ge and Ce after pressing into tantalum powder and sintering is better than that of tantalum wire doped with Ge, while that of tantalum wire doped with Ge is better than that of pure one when oxygen content in tantalum powder is not too high.

Effect of tantalum capacitor powder preparation conditions on the dielectric loss tangent of anodes

We have studied the effect of the preparation and agglomeration conditions of tantalum powders produced by sodium reduction on the frequency dependences of the specific capacity and dielectric loss tangent for anodes fabricated from the powders.

X-ray diffraction study of sodium metal reduction tantalum powders

This paper examines the effect of sodiothermic reduction conditions on the crystal structure of tantalum and the structural changes induced by subsequent modification of the tantalum powder.

Low-temperature combustion waves in low-energy K2TaF7–Si-additive systems

This work presents the use of a thermocouple technique for measuring temperature profiles in a condensed K2TaF7–Si system blended with a small amount of Teflon [(C2F4)n] or potassium chlorate (KClO3). A base experiment is described in detail to demonstrate the ability of the system to react under a low-rate self-sustaining mode at ambient temperature. The ignition temperatures, temperature–time profiles, combustion parameters, and final products are presented with respect to the additive concentration. The combustion processes begin at 340 and 450°C for the KClO3 and (C2F4)n-containing mixtures, respectively. The maximum temperatures of both KClO3 and (C2F4)n-containing mixtures range from 470 to 960°C and the combustion self-propagates along the sample at a speed of 0.01–0.08cm/s. The solid combustion products produced under the optimized conditions include fine powders of tantalum, tantalum carbide, and tantalum silicides. The chemical mechanism of the combustion process and reaction parameters responsible for low-speed wave propagation are presented and discussed.

SU‐E‐T‐415: Dosimetric Measurements of An N‐Butyl Cyanoacrylate Embolization Material for Arteriovenous Malformations

Purpose: The therapeutic regimen for cranial arteriovenous malformations (AVMs) often involves both stereotactic radiosurgery and adjunct endovascular embolization. Embolization agents often contain radiopaque contrast to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these contrast agents. This study investigated dosimetric properties of n‐butyl cyanoacrylate (n‐BCA) plus lipiodol (NPL) with and without tantalum powder. Methods: The NPL was provided cured from the manufacturer (Codman Trufill; Codman & Shurtleff, Inc., Raynham, MA) with and without tantalum. Attenuation measurements were made for the samples with and without tantalum powder and compared to the attenuation of a water substitute using a 6MV photon beam. Effective linear attenuation coefficients (ELAC) were derived from the attenuation measurements and measured sample thicknesses. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units were measured using our department's standard stereotactic radiosurgery CT protocol. Results: For a 3cm square field, the ELAC was 0.0428 1/cm and 0.0474 1/cm for NPL without and with tantalum respectively, compared to 0.0461 1/cm for the water substitute. Non‐density corrected dose calculations would Result in errors of −0.33% and 0.13% per cm thickness of NPL without and with tantalum, respectively. Interface effects compared to water were less than 1.3% for both embolization materials. CT values at 120 kVp were 2082 HU and 2358 HU for NPL without and with tantalum, respectively. Conclusion: The dosimetric properties of NPL are very close to those of water for therapeutic energies. Therefore, treating the entire intracranial space as uniform in composition will Result in typically less than 1% dosimetric errors. However, due to the high attenuation of both embolization agents for diagnostic energies, artifacts may occur that necessitate MR imaging to accurately identify the spatial extent of the region to be treated.

Influence of Ta on microstructure and abrasive wear resistance of laser clad NiCrSiB coating

A mixture of NiCrSiB alloy powder and tantalum (Ta) powder was used as laser clad material to improve abrasive wear resistance of the Ni-based coating. The microstructure and wear resistance of the coating were investigated. Addition of Ta element works to suppress the growth of coarse M7C3 carbide in the coating, resulting in a decrease in aspect ratio of coarse carbide. In the abrasive wear test, in situ synthesized TaC particles well bond with Ni-based matrix, and are hardly pull out from wear surface. Grooves on the worn surface of NiCrSiB coating are much deeper and sharper than those in the NiCrSiB+Ta composite coating. Also, a weight loss of the composite coating is much lower than that of the NiCrSiB coating. The wear resistance of the laser clad Ni-based coating is enhanced to a much greater extent through the addition of Ta. This is attributed to the in situ synthesized hard TaC particles of nearly equiaxed shape, the Ni-based matrix strengthened by Ta and the decrease in aspect ratio of the coarse brittle carbides.

Atmospheric electron-beam surface alloying of titanium with tantalum

This paper presents the results of studies of the structure and properties of coatings produced by cladding 10mm thick titanium plates with titanium–tantalum powder mixtures using an electron beam extracted into air. A mixture of CaF2 and LiF salts was used as a flux that protected the heated material from the air atmosphere. The electron beam power was 33.5kW, the velocity of the sample relative to the beam 10mm/s, and the beam scanning frequency 50Hz. High-performance titanium–tantalum layers 2–2.5mm thick with a tantalum content of 3.9–22.4wt% were obtained. The surface layers have a dispersed α(α′)+β structure. The tensile strength of the alloy containing 3.9% tantalum is 620MPa. Increasing the Ta content to 22.4% increases the tensile strength to 735MPa. For the coating material containing 22.4wt% Ta, the rate of corrosion in a 68% solution of boiling nitric acid was 190 times lower than that for unclad titanium. The conditions of formation of the layer structure by high-velocity electron-beam cladding of powder materials are significantly different from equilibrium. For this reason, the resulting materials are characterized by a number of features, including a high degree of dispersion of the structural components and inhomogeneous chemical composition.

Preparation of ultrahigh purity cylindrical tantalum ingot by electron beam drip melting without sintering process

A two-step process was used to obtain an ultrahigh purity cylindrical tantalum ingot from tantalum powder. Generally, powders cannot be used as raw materials in processes employing electron beam (EB) drip melting. We designed a process that could indeed use powders. The first step reduced the impurities in tantalum by the repeated EB melting of tantalum buttons fabricated from tantalum powder. An ultrahigh purity tantalum ingot was then fabricated by repeated EB drip melting of the refined tantalum buttons. A cylindrical ingot (Ø80×100 mm) with purity of 99·9998% was obtained. The purity of the raw tantalum powder was 99·9944%, while those of tantalum buttons remelted twice and four times were 99·9989 and 99·9994% respectively. The concentration of gas impurities such as C, N and O was reduced to <10 ppm from an initial level of 3340 ppm.

Flüssigembolisate – Onyx als Problemlöser

Liquid embolic agents are used for permanent occlusion of capillaries but optimal administration properties are lacking. The lack of visualization by fluoroscopy and the risk of serious complications are disadvantages of conventional embolic agents, such as ethanol and Histoacryl. Onyx is a liquid embolic agent consisting of ethylene vinyl alcohol copolymer dissolved in various concentrations of dimethyl sulfoxide (DMSO) and suspended micronized tantalum powder to provide contrast for fluoroscopy. The physicochemical characteristics of Onyx allow controlled application, forming a defined cast and permanent occlusion. Disadvantages are the high costs. Furthermore, the solvent DMSO requires special catheter material and causes pain during Onyx application. Onyx has been primarily used for interventional neuroradiological treatment but peripheral applications are becoming increasingly more common. Currently, Onyx is mainly used for embolotherapy of endoleaks after endovascular aortic aneurysm repair, for treatment of acute arterial bleeding and for treatment of arteriovenous malformations.

Tantalum Powder Preparation from Ta2O5 by Calciothermic Reduction

Tantalum Powder Preparation from Ta2O5 by Calciothermic Reduction

Preparation of high-purity tantalum powders by sodium-thermal reduction

This paper examines the possibility of preparing high-purity sodium-reduced tantalum powders with a large specific surface area. We demonstrate that such powders have a larger specific surface area when prepared using potassium heptafluorotantalate based melts containing tantalum oxyfluoride compounds. The purity and specific surface area of powders thus prepared are suitable for the development of capacitor powders with a specific capacity of up to 100000 μFV/g.

Sodium-reduced tantalum powders produced from plumbomicrolite raw materials

Effect of various extractive systems (triisoamyl phosphate/HF+H2SO4, n-octanol/HF+H2SO4, n-octanol/HF+HNO3) used to obtain potassium heptafluorotantalate from plumbomicrolite-based raw materials on the purity and characteristics of sodium-reduced tantalum powders was studied. Application of the extractive systems provides production of high-purity potassium heptafluorotantalate from raw materials based on products formed in processing of the plumbomicrolite concentrate.

SU-E-I-112: Pre-Clinical Imaging with an Ultra-High Resolution X-Ray Detector.

To explore the possible applications for a newly developed ultra-high resolution, small field-of-view (FOV) micro-solid state x-ray image intensifier (micro-SSXII) detector. The micro-SSXII is based on an 8 micron, 1004 by 1002 electron-multiplying CCD (EMCCD) optically coupled to a 100-micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm with a resolution limit of more than 20 lp/mm. The system has the capability of providing real-time images at low exposures because of the high variable gain of the EMCCD. Several phantoms were prepared by filling catheter tubes of 470 micron internal diameter with separate mixtures of a casting resin with different ratios of three different contrast agents (Omnipaque 350, barium sulphate, tantalum powder). These were imaged with the micro-SSXII at 50 kVp to help select the best mixture for use in making a cast of a rat kidney whose vasculature would then be made radiopaque and visualized. The images of all phantoms showed clumping of these contrast agents within the resin resulting in a non-uniform mix. The image of the phantom filled with Omnipaque and resin in a 1:4 ratio showed the best mixture although large bubble formation of the iodine was observed. This combination was used to make a cast of a rat kidney vasculature and imaged with the micro-SSXII. Small iodine bubbles with diameters as small as 25 microns were clearly delineated in the rat kidney vessels confirming the sharp detail capability of the micro-SSXII. The micro-SSXII in combination with a soft x-ray spectrum can provide excellent images of small animal casts prepared with an appropriate radiopaque resin to study finer details of the vasculature. This new imager has the potential to be used for region-of-interest x-ray image guidance for interventional studies in small animals. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

The chemical state and control of oxygen in powder metallurgy tantalum

Abstract Tantalum powders containing different oxygen concentrations have been vacuum hot-pressed in graphite dies to study the dissolution and precipitation of oxygen and carbon in powder metallurgy (PM) tantalum. Various types of oxide and carbide precipitates were observed using microscopy and analyzed by X-ray microdiffraction. An in situ contact gettering method using zirconium has been coupled with hot-pressing to control oxygen. This method is effective at removing oxygen from the solid solution, while the precipitation behavior is not significantly altered. Hardness profiles with distance from Zr contact agree well with those expected from oxygen concentration profiles predicted by analysis assuming a diffusion-limited rate of gettering. Corresponding lattice parameter measurements by microdiffraction indicate that oxygen prefers to stay in supersaturated solid solution, even under slow cooling, where it is much more effective in hardening than in the form of precipitates.

Plasmochemical process for the production of niobium and tantalum nanopowders

Niobium and tantalum powders used in modern manufacturing are materials with nanostructure. The authors have studied and optimized the process of the production of niobium and tantalum nanopowders (adjusted in the range of the particle size of 20-150 nm) at pilot scale. The process is based on the reduction reaction of pentachlorides of tantalum and niobium with hydrogen in a plasma generator at about 3500 K. To stabilize the structure and adjust the granulometric composition of the produced nanopowders thermal treatment at 1373 K under vacuum was applied. The powders are characterized by very high purity with regard to oxygen and metallic admixtures and by low bulk density (0.1-0.3 g/cm 3 ). The specimens had a high specific surface area (10-30 m 2 /g). The process of compacting and sintering of powders was tested at temperatures from 1173 to 1373 K. The porosity of the specimens was 0.55-0.75 from the theoretical. The pore diameter was adjusted to 0.5-0.05 µm.

High-flow Neonatal Macrocerebral Arteriovenous Fistulas in Hereditary Hemorrhagic Telangiectasia

Although some cases of vein of Galen aneurysmal malformation (VGAM) present initial clinical symptoms such as cardiopulmonary disturbance in the neonatal period, pial arteriovenous fistula is very seldom present as a clinical symptom immediately after birth. A neonatal patient, the first-born to his family, presented with tachypnea postpartum. This baby had a family history of hereditary hemorrhagic telangiectasia. A cerebral MR image revealed multiple macrocerebral arteriovenous fistulas (MCAVFs), resulting in a large partially thrombosed venous pouch within the cerebral cortex. Trans-arterial embolizations of the main two fistulas were performed using N-butyl cyanoacrylate (NBCA) with tantalum powder six months after birth. Post-embolization angiography confirmed the obliteration of the fistulas and magnetic resonance imaging (MRI) revealed thrombosis and reduction in size of the venous component. His tachypnea disappeared completely. There were no neurological complications due to the treatment. The prognosis of multiple MCAVFs mainly depends on the presence of medullar signs and symptoms and a delay before treatment. Pure glue endovascular intervention, as used in our case, is considered to be the first therapeutic choice to decrease the risk of neurological consequences.

Manufacture of sodium-reduced tantalum powders with a specific capacity up to 100000 CV/g

The characteristics of the tantalum powders produced by sodium thermal reduction from salt melts based on potassium heptafluotantalate K2TaF7 with additions of oxygen-containing tantalum compounds and sodium chloride are studied. The oxygen sources in a melt during sodium thermal reduction are represented by oxyfluoride compounds K3TaOF6, KTaOF4, and K2Ta2O3F6. The produced tantalum powders can be used as initial materials for the production of capacitor powders with a capacity up to 100 000 μC/g.