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Tantalum Preparation
Sep 12, 2017

Tantalum Ta, metal elements, mainly in tantalite, with niobium symbiosis. Tantalum hardness is moderate, full of ductility, can be drawn into thin filament thin film. Its thermal expansion coefficient is very small. Tantalum has a very good chemical properties, with high corrosion resistance. Whether in cold and hot conditions, hydrochloric acid, concentrated nitric acid and "aqua regia" do not respond. Can be used to manufacture evaporative containers, etc., can also do the tube electrode, rectifier, electrolytic capacitor. Medical used to make thin slices or thin lines, sew the damaged organization. Although the corrosion resistance of tantalum is very strong, but its corrosion resistance is due to the surface of the stable tantalum pentoxide (Ta2O5) protective film.

Physical properties

Chemical symbol Ta, steel gray metal, in the periodic table is a VB family, atomic number 73, atomic weight 180.9479, body-centered cubic crystal, the common parity is +5. Tantalum hardness is low, and with the oxygen content, ordinary pure tantalum, annealed Vickers hardness of only 140HV [1]. Its melting point of up to 2995 ℃ [1], in the elemental [1], second only to carbon, tungsten, rhenium and osmium, ranked fifth. Tantalum is highly ductile and can be drawn into thin filaments. Its thermal expansion coefficient is very small. Each rose one degree Celsius only expansion of 6.6 points per million. In addition, its toughness is stronger than copper.

Chemical properties

Tantalum also has a very good chemical properties, with a high degree of corrosion resistance, whether in cold and hot conditions, hydrochloric acid, concentrated nitric acid and "aqua regia" do not respond. But tantalum in the hot concentrated sulfuric acid can be corroded at 150 ℃ below, tantalum will not be concentrated sulfuric acid corrosion, only at this temperature will react, in the 175 degrees of concentrated sulfuric acid in 1 year, the corrosion of the thickness 0.0004 mm, the tantalum into 200 ℃ sulfuric acid soak for one year, the surface damage only 0.006 mm. At 250 degrees, the corrosion rate increased for the corrosion of the annual thickness of 0.116 mm, at 300 degrees, the corrosion rate is faster, soaking for 1 year, the surface was corrosion 1.368 mm. In the fuming sulfuric acid (containing 15% SO3) corrosion rate is more serious than concentrated sulfuric acid, 130 degrees in the solution soak for 1 year, the surface corrosion thickness of 15.6 mm. Tantalum at high temperatures will be corrosion of phosphoric acid, but the reaction is generally more than 150 degrees occurred in the 250 degrees of 85% phosphoric acid, soaking for 1 year, the surface was corrosion 20 mm, in addition, tantalum in hydrofluoric acid and nitric acid Of the mixed acid can quickly dissolve in hydrofluoric acid can also be dissolved. But tantalum is more afraid of strong alkali, in the 110 degrees 40% concentration of caustic soda solution, tantalum will be quickly dissolved in the same concentration of potassium hydroxide solution, as long as 100 degrees will be quickly dissolved. In addition to the above mentioned circumstances, the general inorganic salt in the 150 degrees below the general can not corrosion tantalum. Experiments show that tantalum at room temperature, the alkaline solution, chlorine, bromine, dilute sulfuric acid and many other agents do not work, only in the hydrofluoric acid and heat concentrated sulfuric acid under the reaction. This situation is relatively rare in the metal.

But at high temperatures, the oxide film on the surface of tantalum is destroyed, so it can react with a variety of substances, tantalum can react with fluorine at room temperature. At 150 ° C, tantalum is inert to chlorobromide at 250 ° C. Tantalum is still resistant to dry chlorine and is heated to 400 ° C in water containing steam. It remains bright at 500 ° C It began to be corroded, more than 300 degrees of tantalum and bromine reaction, the iodine vapor when the temperature reached before the red hot were inert. Hydrogen chloride at 410 degrees and tantalum reaction, the production of pentachloride, hydrogen bromide at 375 degrees with tantalum reaction. When heated to a temperature of 200 degrees or less, S can interact with Ta, carbon and hydrocarbons at 800-1100 degrees with tantalum.

Preparation

Smelting method: Tantalum and niobium ore is often accompanied by a variety of metals, tantalum smelting the main steps is to decompose concentrate, purification and separation of tantalum, niobium, to produce tantalum, niobium pure compounds, and finally the preparation of metal.

Ore decomposition can be used hydrofluoric acid decomposition method, sodium hydroxide melting method and chlorination method. Tantalum and niobium separation can be solvent extraction method [commonly used extraction agent for methyl isobutyl ketone (MIBK), tributyl phosphate (TBP), sec-octanol and acetamide, etc.], step-by-step crystallization and ion exchange.

Separation: First, the tantalum and niobium ore concentrate with hydrofluoric acid and sulfuric acid decomposition of tantalum and niobium fluoride tantalate and fluorine niobate dissolved in leaching solution, while iron, manganese, titanium, tungsten, silicon and other associated elements are also soluble Leaching solution, the formation of very complex components of strong acid solution. Tantalum and niobium leaching solution Extraction of tantalum and niobium with methyl isobutyl ketone is simultaneously extracted into the organic phase, and the trace impurities in the organic phase are washed with sulfuric acid solution to obtain pure organic waste solution containing tantalum and niobium and the raffinate, Trace tantalum and niobium and impurity elements, is a strong acid solution, can be integrated recovery. The pure organic phase containing tantalum and niobium is back-extracted with dilute sulfuric acid solution to obtain an organic phase containing tantalum. Niobium and a small amount of tantalum into the aqueous phase and then extracting the tantalum with methyl isobutyl ketone to obtain a pure niobium-containing solution. The pure tantalum containing organic phase is back extracted with water to give a pure tantalum containing solution. The organic phase after extraction of tantalum is returned to the extraction cycle. The pure fluorotitanic acid solution or the pure fluoro niobic acid solution reacts with potassium fluoride or potassium chloride to produce potassium fluorotantalate (K2TaF7) and potassium fluorophosphate (K2NbF7), respectively, and react with ammonium hydroxide to form hydrogen Tantalum oxide or niobium hydroxide precipitation. Tantalum or niobium hydroxide is calcined at 900 to 1000 ° C to form an oxide of tantalum or niobium.

Preparation of tantalum:

① metal tantalum powder can be used metal thermal reduction (sodium heat reduction) method from the system. Reduction of Potassium Fluorotitanate with Metal Sodium in an inert atmosphere: K2TaF7 + 5Na - → Ta + 5NaF + 2KF. The reaction was carried out in a stainless steel tank and the reaction was quickly completed when the temperature was heated to 900 ° C. This method of preparation of tantalum powder, grain irregular, fine particle size, suitable for the production of tantalum capacitors. Metal tantalum powder can also be made by molten salt electrolysis method: with potassium fluoride potassium tantalate, potassium fluoride and potassium chloride mixture of molten salt as an electrolyte to tantalum pentoxide (Ta2O5) dissolved in 750 ℃ under the electrolysis, can be Purity of 99.8 ~ 99.9% of the tantalum powder.

② can be obtained by carbothermal reduction of Ta2O5 metal tantalum. Reduction is generally carried out in two steps: first, a mixture of Ta2O5 and carbon is prepared in a hydrogen atmosphere at 1800 to 2000C to form tantalum carbide (TaC), and then TaC and Ta2O5 are prepared in a predetermined ratio. Reduced to metal tantalum. Metal tantalum can also be used thermal decomposition or hydrogen reduction of tantalum chloride chloride method. Dense metal tantalum can be prepared by vacuum arc, electron beam, plasma beam smelting or powder metallurgy. Preparation of high purity tantalum single crystal with non - crucible electron beam region melting method.





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