Niobium pentachloride

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

Niobium Pent chloride. Niobium pentachloride can be prepared in a variety of ways but most easily by direct chlorination of niobium metal. The reaction takes place at 300—350°C. Chlorination of a niobium pentoxide—carbon mixture also yields the pentachloride however, generally the latter is contaminated with niobium oxide trichloride. The pentachloride is a lemon-yeUow crystalline soHd that melts to a red-orange Hquid and hydrolyzes readily to hydrochloric acid and niobic acid. It is soluble in concentrated hydrochloric and sulfuric acids, sulfur monochloride, and many organic solvents. 

Two main methods exist for the production of tantalum and niobium from the mineral raw material. The first method is based on the chlorination of raw material, followed by separation and purification by distillation of tantalum and niobium in the form of pentachlorides, TaCl5 and NbCl5 [24, 29]. Boiling points of tantalum and niobium pentachlorides (236°C and 248°C, respectively) are relatively low and are far enough apart to enable separation by distillation. 

Chlorination of ferroalloys (ferroniobium-tantalum) is a more economical and simple alternative [30]. The process is performed on a sodium chloride melt that contains iron trichloride, FeCU. Chlorine is passed through the melt yielding NaFeCl4, which interacts as a chlorination agent with the Fe-Nb-Ta alloy. Chlorination of ferroalloys allows for the production of pure tantalum and niobium pentachlorides, which are used further in the production of high purity oxides and other products. 

Li3(BN2) have already demonstrated the decomposition of (BN2) ions into boron nitride. The remaining nitride can lead to the formation of a binary metal nitride or reduce the transition metal ion under the formation of N2. Both mechanisms have been obtained experimentally, depending on the stability of the metal nitride. For instance niobium pentachloride forms NbN, titanium trichloride forms TiN, and nickel dichloride forms Ni, plus BN and nitrogen, respectively, in reactions with Li3(BN)2 (at 300-600°C) [24]. 

Niobium pentachloride mentioned on page 66 is another example. The Baur rules also express these facts (cf. p. 60). 

The metal reacts with chlorine at 300°C forming niobium pentachloride, NbCls. It reacts with hot concentrated hydrochloric acid, also forming the pentachloride. Niobium dissolves in hot concentrated sulfuric acid at 170°C. Fused alkalies such as caustic soda and caustic potash attack niobium, embrittling the metal. 

Niobium pentachloride is used in making niobium metal and several niobium compounds. 

Niobium pentachloride is obtained as an intermediate during extraction of niobium from its ores (see Niobium). Also, the pentachloride is obtained readily by direct chlorination of niobium metal at 300 to 350°C ... 

Also, niobium pentafluroide can be prepared by the reaction of fluorine with niobium pentachloride ... 

Pentaoxide also reacts with niobium pentachloride at elevated temperatures, forming the oxide trichloride ... 

Niobium pentoxide has been reduced to the metal by means of hydrogen at 7 atmospheres pressure and at 1910° C.,1 and a fairly pure sample has been obtained by the action of hydrogen on niobium pentachloride at a red heat.2... 

Atomic Weight of Niobium.—The first determinations were carried out by Hermann 8 and Rose,4 but these are now only of historical interest. In 1864 Blomstrand5 analysed niobium pentachloride but obtained... 

Niobium Pentafluoride, NbFs, is the only known compound of niobium and fluorine, and even this cannot be obtained in the free state by a wet method because of the extreme readiness with which it hydrolyses. Niobium pentoxide dissolves readily in hydrofluoric acid, but evaporation of the solution leaves a residue of the unchanged oxide. Niobium pentafluoride has been prepared synthetically 1 by passing dry fluorine over the gently heated metal contained in a boat in a platinum tube. The product is freed from platinum tetrafluoride, a little of which is formed at the same time, by distillation in vacuo at 100° to 110° . An alternative method consists in treating niobium pentachloride with anhydrous hydrogen fluoride in a freezing mixture and purifying by redistillation.3... 

Niobium Trichloride, NbCl3, is prepared by leading the vapour of niobium pentachloride through a heated tube.4 It is also formed in small quantity by the action of carbon tetrachloride vapour on niobium pentoxide contained in a hard-glass tube, and has probably been prepared in solution by the electrolytic reduction of the pentachloride.4 It forms a black, crystalline crust with an almost metallic lustre, which closely resembles the appearance of a film of sublimed iodine. It is not decomposed by water or ammonia, but is readily oxidised by dilute nitric add to niobium pentoxide. On being heated to a red heat in an atmosphere of carbon dioxide, a sublimate of niobium oxytrichloride, NbOCl3, is produced, the carbon dioxide undergoing reduction to the monoxide. 

Niobium Pentachloride, NbCl5, is the most important of the chlorides of niobium, and is the material from which the other chlorides are prepared. It can be obtained by several methods ... 

Double chlorides of niobium pentachloride with chlorides of other metals to correspond with the double fluorides given by niobium penta-fluoride are not known. A double compound mth piperidine, NbCl5. 

Niobium oxytrichloride is prepared by the action of chlorine on a mixture of niobium pentoxide and carbon, or on the lower oxide, NbO 5 or by the action of the vapours of carbon tetrachloride on the pentoxide. Some niobium pentachloride is produced in the same reaction, and this is removed either by distilling it away at the lowest temperature possible in an atmosphere of carbon dioxide, or by subliming the product in a current of chlorine over the ignited oxide.7 The oxychloride has also been prepared by passing the vapours of niobium pentachloride over niobium pentoxide at a red heat.8... 

Delafontaine and Linebarger, J. Amer. Ohem. Soc., 1896, 18, 532 Ohem. News, 1896, 74, 33 oompare preparation of niobium pentachloride. 

Hydrates of Niobium Pentoxide. Colloidal Niobium Pentoxide.— Niobium pentoxide does not combine directly with water to form acids of definite composition. Two hydrates of the oxide, namely, 3Nb20s.4H20 and 3Nb205.7H20, have been reported,8 but their existence is very improbable. The term nioUe acid, is applied to the more or less hydrated pentoxide. When niobium pentachloride or niobium oxytriehloride, NbOCla, is hydrolysed with excess of water there is produced a white, amorphous, hydrated gel, which can also be obtained by the action of sulphuric acid or hydrochloric acid on alkali niobates 10 the precipitate is redissolved by excess of acid. Similar solutions axe... 

Other nitrides of niobium of doubtful composition have been obtained by the action of ammonia on niobium pentoxide,4 niobium oxychloride 5 and niobium pentachloride. 

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