Niobium pentoxide

Niobium pentoxide can be reduced with carbon in a two-step process, called the Balke process. Formation of the carbide is the first step. The oxide is mixed with the stoichiometric amount of lamp black, placed in a carbon cmcible, and heated in vacuum to 1800°C ... 

Niobium pentoxide also is reduced to metal commercially by the aluminothermic process. The finely ground powder is mixed with atomized aluminum and an accelerator compound which gives extra heat during reaction, then is ignited. The reaction is completed quickly and, after cooling, the slag is broken loose to free the metal derby which is purified by electron-beam melting. 

Niobium Dioxide Fluoride. Niobium dioxide fluoride, Nb02F, is formed on dissolution of niobium pentoxide in 48 wt % aqueous hydrofluoric acid, evaporation of the solution to dryness, and heating to 250°C. 

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. 

Niobium Oxide Tribromide. Niobium oxide tribromide, NbOBr, is a yeUowbrown soHd which is readily hydrolyzed by moist air. It is prepared by reaction of bromine with a mixture of niobium pentoxide and carbon at 550°C. It decomposes in vacuum to the pentabromide and pentoxide at 320°C. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Lithium niobate [12031 -63-9] Nb20 or LiNbO, is prepared by the soHd-state reaction of lithium carbonate with niobium pentoxide. After... 

Roles of Niobium Pentoxide, Vanadium Pentoxide and Titanium Dioxide In The Grain Growth And Sintering of Uranium Dioxide ,... 

Niobium pentoxide gives rise to a very violent reaction when it is heated at... 

Having established the feasibility of niobium metal production by the carbothermic reduction of niobium pentoxide under temperature and pressure conditions readily attainable in the laboratory and in industry, the principles of efficient process execution may now be examined. In a high-temperature vacuum furnace operation, the quantity of gas that is to be pumped off can influence the choice of the vacuum process. When the reduction of niobium pentoxide with either carbon or niobium carbide is attempted according to the following overall equations ... 

Niobium is a multivalent metal and forms stable oxides of compositions represented as niobium pentoxide, niobium dioxide, and niobium oxide. The heats of reaction for the reduction of each of these oxides are... 

The reactor used for the aluminothermic reduction of niobium pentoxide is shown schematically in Figure 4.17 (A). It is a steel pipe, lined on the inside with alumina and provided with a pipe cap. The charge, consisting of stoichiometric amounts of niobium pentoxide and aluminum powder, is blended and loaded in the lined pipe, and covered with alumina. The cap is closed and the reaction initiated by placing the loaded bomb in a gas-fired furnace, preheated to 800 °C, and by raising the temperature of the furnace to 1100 °C. 

Figure 4.17 B Schematic of the reactor for open aluminothermic reduction of niobium pentoxide.

Lithium is used to reduce metallic oxides in metallurgical operations, and the reactions, after initiation at moderate temperatures, are violently exothermic and rapid. Chromium(III) oxide reacts at 185°C, reaching 965° similarly molybdenum trioxide (180 to 1400°), niobium pentoxide (320 to 490°), titanium dioxide (200-400 to 1400°), tungsten trioxide (200 to 1030°), vanadium pentoxide (394 to 768°) also iron(II) sulfide (260 to 945°), and manganese tclluridc (230 to 600°C)... 

Balke A process for making niobium by reducing niobium pentoxide with carbon in a carbon crucible, in vacuo, at 1,800°C. 

Figure 4.32 Niobium pentoxide block structures (a) H-Nb2Os, (b) Ti2Nb10O29 monoclinic, and (c) W3Nb14044. The shaded squares represent MOg octahedra at two different levels and the shaded spheres represent cations in tetrahedral coordination.

Figure 4.33 Electron micrograph showing disorder in a niobium pentoxide block structure. The phase was synthesized from Nb2Os and CoF3 (which is analogous to W03). The region at the lower center of the micrograph consists of blocks of 4 x 4 octahedra with the W3Nb14044 structure with a block size of approximately 1.5 nm. (Courtesy of Dr. J. Hutchison, University of Oxford.)...

The pentachloride also may be made by chlorination of niobium pentoxide in the presence of carbon at 300°C. The products, however, contain small amounts of niobium oxide trichloride, NbOCls. 

Niobium pentoxide is produced as an intermediate during recovery of Nb metal from ores (See niobium). 

Niobium pentoxide reacts with hydrogen chloride gas at 400 to 700°C to form niobium oxide trichloride, NbOCls [13597-20-1] ... 

Yellow-brown oxide called tribromide of niobium, NbOBrs [14459-75-7], is produced by reacting niobium pentoxide with bromine and carbon at 550°C ... 

Selective Oxidative Dehydrogenation of Propane on Promoted Niobium Pentoxide... 

We attempted to improve the V-Mg-O catalyst system by doping it with various elements (S, 11 but these attempts were not successful. We have therefore focused our attention on niobium pentoxide. In previous papers 9 ylO) we have shown that high selectivities towards propylene are possible using pure niobia, but that the conversions were low. 

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