Niobium sulphidation

Grzesik Z and Mrowec S, Defect structure and transport properties of non-stoichiometric niobium sulphide . High Temp Mater Processes, 2006 25 209-216. Tatsuki K, Wakihara M, Taniguchi M, Phase relations in the Nb-S system at high temperatures , J Less-Common Met, 1979 68 183-191. 

Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption and it is not suited for use with sodium sulphide. 

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

The reactions of 1,2,5-triphenylphosphole (tpp)(46), 1,2,5-triphenylphosphole oxide (tppO), sulphide (tppS), and selenide (tppSe), with niobium(v) and tan-talum(v) halides in dry, oxygen-free organic solvents have been studied. The complexes formed were characterized by i.r. and X-ray spectroscopy. The... 

Instead of lixiviating with water, the pyrosulphate fusion is followed in a recent process 7 by extraction with tartaric acid solution the insoluble residue contains silica, tin, and lead, and the solution, after being saturated with hydrogen sulphide for the precipitation of copper, antimony, etc., contains the hydroxides of niobium and tantalum as well as tungsten, titanium, zirconium, rare earth metals, etc. 

Addition of ammonium hydroxide or ammonium sulphide to solutions of niobic acid and tantalic acid in mineral acids reprecipitates the niobic and tantalic acids, which may, however, retain some of the ammonia. This test does not distinguish between niobium and tantalum, and it does not proceed in the presence of tartaric acid. 

The pentavalent halides and oxyhalides, as in the case of other niobium compounds, are the most stable. It is remarkable that the pentavalency is maintained with increase in the atomic weight of the halogen. All the halogen compounds are characterised by their ready tendency to undergo hydrolysis on the addition of water or even in damp air with precipitation of niobie acid and formation of the hydrogen halide. Their preparation can, therefore, be effected only in the dry way (a) synthetically, or (b) by the action of chlorine, carbon tetrachloride, or sulphur monochloride on the oxide or sulphide. They do not possess saline properties, and cannot be prepared by the action of the halogen acids on the oxide. 

It can be prepared by heating metallic niobium or any of the lower oxides, or the sulphide, carbide, or nitride of niobium, in air or oxygen. Ammonium niobium oxyfluoride, (NH4)jNbOFs, also yields the pentoxide on being heated in air. Solutions of the alkali niobates yield a white gel of the hydrated pentoxide when treated with mineral adds, sulphuric acid bring usually preferred. Insoluble niobates on fusion... 

Sulphides.—Definite sulphides of niobium have not been prepared. Solutions of alkali niobates do not yield precipitates with hydrogen... 

Oxysulphides.—The action of carbon bisulphide vapour or hydrogen sulphide on niobium pentoxide, sodium niobate or niobium oxytrichloride gives rise to a black powder which assumes a metallic appearance on being rubbed, and which conducts electricity well. This is probably an oxysulphide of niobium, Nba.OJ,Sz, but its exact composition varies with the experimental conditions, and its individuality is a matter of doubt.5 Oxysulphides of niobium of doubtful composition, mixed with potassium sulphide, are also produced by the action of carbon bisulphide vapour on potassium oxalo-niobate. ... 

The formulae and structures of the sulphides and a comparison with the oxides formed by these metals illustrate the general points noted at the beginning of this chapter. For example, at least nine crystalline Nb-S phases have been characterized, and none has its counterpart among niobium oxides. There are two forms of NbSi x temperature, NiAs superstructure, high temperature, MnP... 

The superconductivity and structure of some ternary molybdenum sulphides 258 the non-stoicheiometry of ZrS2 259 and the phase systems ZnCd-S, ZnHg-S, and CdHg-S260 have all been investigated. The reaction of carbon disulphide with the metals of the transition groups IV, V, and VI, has been studied.261 In most cases, the product of the reaction at 800—1000 °C is a sulphide (or more rarely a mixture of two sulphides), but in the case of the metals niobium and tantalum a mixture of carbides is produced. 

Micro- and mesoporous materials containing niobium in the framework or extra framework positions were studied in the oxidation of dibutyl sulphide with H2O2. Leaching of Nb from the solid to the liquid phase was considered. Some of the catalysts prepared via the impregnation with Nb-salts show some leaching of Nb to the liquid phase and the oxidation partially occurs homogeneously in the liquid phase. The reaction proceeds mainly on the catalyst surface when the mesoporous molecular sieves containing Nb in the framework are used. 

It is a vein type deposit, which is hosted within, and is genetically related to, a carbonatitic alkaline complex. The deposit is very similar to the Californian Mountain Pass deposit. The similarities are the high concentrations of bastnaesite and barite, low niobium content, and the presence of sulphides (Wang et al. 2001). It has proven reserves of 0.4 million tons of ore grading at 2 % REE oxides. The discovery of the deposit was described by Pu (1988). The age of the carbonatites related to the deposit is 27.8-40.3 Ma (Cheng et al. 2003 Mindat.Org 2015). 

Gerasimov et have provided a reference book on the thermodynamic properties of tungsten, molybdenum, titanium, zirconium, niobium, and tantalum, and their more important compounds, viz. oxides, sulphides, halides, carbides, nitrides, silicates, borides, and hydrides. 

Danielewski M, Sulphidation behaviour of niobium , in Proc. of European Corrosion Meeting Eurocorr 87, 1987 223-228. 

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