Melting points tantalum fluorides

Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below ISOoC, and is attacked only by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety... 

Fused Salt Electrolysis. Only light RE metals (La to Nd) can be produced by molten salt electrolysis because these have a relatively low melting point compared to those of medium and heavy RE metals. Deposition of an alloy with another metal, Zn for example, is an alternative. The feed is a mixture of anhydrous RE chlorides and fluorides. The materials from which the electrolysis cell is constmcted are of great importance because of the high reactivity of the rare-earth metals. Molybdenum, tungsten, tantalum, or alternatively iron with ceramic or graphite linings are used as cmcible materials. Carbon is frequently used as an anode material. 

Another anhydrous solvent that is frequently used for the synthesis of tantalum and niobium fluoride compounds is bromine trifluoride, BrF3. At ambient temperature, bromine trifluoride is light yellow liquid characterized by a boiling point of 126°C, a melting point of 9°C and a density of 2.84 g/cm3 at melting temperature. 

Table 50 lists melting points of some tantalum-containing fluoride compounds. 

The method based on a net melt-holder is used successfully for materials with relatively low melting points and is less promising for the investigation of fluoride melts containing tantalum and niobium. 

Fluorides are nonhygroscopic, and their melting points are higher than those of the corresponding chlorides. Besides, the fluoride reduction reactions are considerably more exothermic. The prime examples of the use of fluorides as intermediates are the reduction of uranium tetrafluoride by calcium or magnesium the reduction of rare earth fluorides by calcium, reduction of beryllium fluoride by magnesium and the reduction of potassium tantalum double fluoride by sodium. 

The fluoride salt is reduced to dysprosium by heating above the melting point of dysprosium with calcium in argon atmosphere in a tungsten or tantalum vessel ... 

Neodymium, along with lanthanum, cerium and praseodymium, has low melting points and high boiling points. The fluorides of these and other rare earth metals are placed under highly purified helium or argon atmosphere in a platinum, tantalum or tungsten crucible in a furnace. They are heated under this inert atmosphere or under vacuum at 1000 to 1500°C with an alkali or alkaline earth metal. The halides are reduced to their metals ... 

K. Tantalum. (Tantalum mp 2,996°C), is an extremely chemically resistant metal which is hard but ductile. Because of its high melting point and good corrosion resistance, tantalum is frequently used as a container for high-temperature melts. It is attacked by HF and other fluorides, as well as sulfur trioxide and nitrogen oxides. 

Refractory metals, such as tantalum and zirconium, can be deposited from their fluorides in a molten salt bath. In the case of zirconium, for example, the bath consists of ZrF or ZrF in a KF/NaF/LiF mixture. The alkali fluorides are employed to increase conductivity and decrease the melting point. Even so, these baths are operated at about 800 C. Good deposits have been reported as long as the right valency was chosen for each metal (3 for Mo and V, 4 for Nb and Zr, 5 for Ta). The bath must be operated in a pure argon atmosphere, and impurities must be strictly excluded. It siiould be obvious that the operation of such baths is expensive and control is difficult. Thus their use is limited either for research purposes or for highly specialized applications, where cost is of secondary importance. 

---