Liquid metals niobium

Similar relationships can be written for the dissolution of hydrogen and oxygen. These relationships are expressions of Sievert s law which can be stated thus the solubility of a diatomic gas in a liquid metal is proportional to the square root of its partial pressure in the gas in equilibrium with the metal. The Sievert s law behaviour of nitrogen in niobium is illustrated in Figure 3.8. The law predicts that the amount of a gas dissolved in a metal can be reduced merely by reducing the partial pressure of that gas, as for example, by evacuation. In practice, however, degassing is not as simple as this. Usually, Sievert s law is obeyed in pure liquid metals only when the solute gas is present in very low concentrations. At higher concentrations deviations from the law occur. 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

Pure niobium has relatively poor mechanical properties and readily oxidizes in air to niobium pentoxide (Nb205) at elevated temperatures. Various niobium-containing alloys such as Nb-lZr and C-103 have been successfully used in specific liquid-metal based nuclear applications and in the fabrication of various rocket components, see also Inorganic Chemistry. 

Refractory metals and alloys are generally dissolution-resistant in liquid metals and corrosion is often controlled by reactions with impurity/interstitial elements [13,14,27]. In the case of refractory metal alloys based on niobium or tantalum, the concentration of oxygen in the alloy is an important parameter with respect to corrosion in alkali metals, particularly lithium [34-38]. As little as 300 wppm of oxygen in niobium will induce catastrophic penetration of the niobium by lithium. Interstitial oxygen will also cause penetration of niobium tmd tantalum by sodium or potassium, but the threshold of oxygen concentration is higher. 

Static isothermal capsules are also useful for studying dissimilar metal mass transfer. DiStef o [79] studied the interactions of type 316 stainless steel with niobium or Nb-1 % Zr in Na and NaK by exposing tension specimens of the niobium or Nb-1 % Zr to the liquid metal in a stainless steel container (Fig. 10). A transfer of carbon and nitrogen from the stainless steel to the niobium or Nb-1 % Zr was noted. The carbon and nitrogen transfer depended on temperature, time, and the surface tirea ratios of stainless steel to niobium (varied by changing the number of spacers shown in Fig. 10). 

Maximum Liquid-Metal Temperature to Which Niobium Is... 

Niobium is also resistant to attack by many liquid metals such as Li < 1000°C, Na, K -h NaK < lOOO C, ThMg < 850 = C, U < 1400 = C, Zn < 450°C, Pb< 850°C, Bi < 500 = C, and Hg < 600 = C. Niobium has the ability to form stable, passive oxides, and therefore, it can provide unique solutions to many corrosion problems. However, niobium cannot be used in air at temperatures exceeding 200°C. Table 8.27 contains corrosion rates for niobium exposed to various chemical environments. 

Bismuth Niobium is resistant to bismuth at temperatures up to 560°C but is attacked at higher temperatures and is therefore not considered a suitable container for handling liquid bismuth even under oxygen-free conditions Furthermore, the stress-rupture properties of niobium are significantly lowered when the metal is tested in molten bismuth at 815°C . 

Another point is related to the high acidity level of the final solution, which leads to certain limitations in the subsequent technological steps. Specifically, the high acidity of the initial solution eliminates any possibility for selective extraction, i.e. sequential separation of tantalum and then of niobium. Due to the high concentration of acids, only collective extraction (of tantalum and niobium together) can be performed, at least at the first step. In addition, extraction from a highly acidic solution might cause additional contamination of the final products with antimony and other related impurities. In order to reduce the level of contaminants in the initial solution, some special additives are applied prior to the liquid-liquid extraction. For instance, some mineral acids and base metals are added to the solution at certain temperatures to cause the precipitation of antimony [455 - 457]. 

The liquid-liquid extraction (solvent extraction) process was developed about 50 years ago and has found wide application in the hydrometallurgy of rare refractory and rare earth metals. Liquid-liquid extraction is used successfully for the separation of problematic pairs of metals such as niobium and tantalum, zirconium and hafnium, cobalt and nickel etc. Moreover, liquid-liquid extraction is the only method available for the separation of rare earth group elements to obtain individual metals. 

Modem refining technology uses tantalum and niobium fluoride compounds, and includes fluorination of raw material, separation and purification of tantalum and niobium by liquid-liquid extraction from such fluoride solutions. Preparation of additional products and by-products is also related to the treatment of fluoride solutions oxide production is based on the hydrolysis of tantalum and niobium fluorides into hydroxides production of potassium fluorotantalate (K - salt) requires the precipitation of fine crystals and finishing avoiding hydrolysis. Tantalum metal production is related to the chemistry of fluoride melts and is performed by sodium reduction of fluoride melts. Thus, the refining technology of tantalum and niobium involves work with tantalum and niobium fluoride compounds in solid, dissolved and molten states. 

Sample. This source places no restrictions on target material. Clusters of metals, produced. For example, polyethylene and alumina have been studied as well as refractory metals like tungsten and niobium. Molecular solids, liquids, and solutions could also be used. However the complexity of the vaporization process and plasma chemistry makes for even more complex mixtures in the gas phase. To date the transition metals(1-3) and early members of group 13 (IIIA) and 14 (IVA)( 11-16) have been the most actively studied. 

Preparation of Niobium(V) and Tantalum(V) Halides. The niobium(V) and tantalum (V) chloride and bromide were prepared in a system of sealed, evacuated bulbs by reacting the pure metal with gaseous halogen. For the chlorides the metal was maintained at 300° to 350° under a chlorine pressure of approximately 70 mm. of Hg the chlorine pressure was maintained By keeping the liquid chlorine immersed in a dry ice-acetone bath. For the bromides the metal was maintained at a temperature of 400° to 450° under a bromine pressure of approximately 250 mm. of Hg, maintained by leaving the liquid bromine at room temperature. 

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