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Oxofluoro-complexes

Tantalum is severely attacked at ambient temperatures and up to about 100°C in aqueous atmospheric environments in the presence of fluorine and hydrofluoric acids. Flourine, hydrofluoric acid and fluoride salt solutions represent typical aggressive environments in which tantalum corrodes at ambient temperatures. Under exposure to these environments the protective TajOj oxide film is attacked and the metal is transformed from a passive to an active state. The corrosion mechanism of tantalum in these environments is mainly based on dissolution reactions to give fluoro complexes. The composition depends markedly on the conditions. The existence of oxidizing agents such as sulphur trioxide or peroxides in aqueous fluoride environments enhance the corrosion rate of tantalum owing to rapid formation of oxofluoro complexes. [Pg.894]

Oxofluoro complexes are formed much more readily for niobium than for tantalum. This difference, indeed, is the basis of the classical method of separation of the two metals. When, for example, a 2-3% HF solution of the oxides is concentrated, K2TaF7 precipitates first and K2(NbOF5) H20 only later.1... [Pg.626]

M0OF4, M0O2F2 WOF4 are solids they form many oxofluoro-complexes... [Pg.469]

The presence of oxides and the formation of oxofluoro-complexes in molten electrolytes may be sometimes unwanted, but in many cases they are the fundamental features of the system. For instance, the formation of oxide complexes in alkali-alkaline earth chloride melts may be mentioned. The formation of oxofluoride complexes in molten cryolite-alumina melts, used as electrolytes for aluminum production, is typical as well. On the other hand, the presence of oxofluoride complexes in electrolytes used for niobium production was initially regarded as unwanted. Recently, however, it has been proven that their presence in niobium electrolytes plays an important role in the niobium electrodeposition. In the following, some technologically important examples of systems containing halides and oxides will be described. [Pg.56]

The crucial problem in niobium deposition in molten salts is the presence of oxygen in the electrolyte, because it is extremely difficult to prepare a melt free of 0 ions, especially in the case of industrial applications. It was formerly assumed that the presence of ions might decrease the quality of Nb coatings or prevent the formation of Nb coatings completely. Therefore a great part of the research efforts was concentrated on the influence of ions on the reduction mechanism of Nb and the formation of niobium oxofluoro-complexes in the melt. [Pg.66]

The presence of oxide in the melt causes the formation of various niobium oxofluoro-complexes. It was shown that relatively pure Nb coatings can be obtained from FLINAK melts if no/wNb is less than 1. However, it has been shown by Konstantinov et al. (1981) and Khalidi et al. (1991) that, even a small amount of 0 ions can entirely change the mechanism of Nb deposition depending on the types of the niobium oxofluorides formed in the melt. [Pg.66]

When oxide ions are present in the melt, the formation of the oxofluoro-complex [NbOFs] " according to the reaction... [Pg.67]

It may be concluded that the successive ligand displacement in the [NbF7]" anion by oxygen and the formation of oxofluoro-complexes can be described by the following general scheme... [Pg.69]


See other pages where Oxofluoro-complexes is mentioned: [Pg.35]    [Pg.2933]    [Pg.56]    [Pg.60]    [Pg.66]    [Pg.67]    [Pg.67]    [Pg.68]    [Pg.69]    [Pg.70]    [Pg.2932]    [Pg.50]    [Pg.506]    [Pg.35]    [Pg.2933]    [Pg.56]    [Pg.60]    [Pg.66]    [Pg.67]    [Pg.67]    [Pg.68]    [Pg.69]    [Pg.70]    [Pg.2932]    [Pg.50]    [Pg.506]    [Pg.2430]    [Pg.67]   
See also in sourсe #XX -- [ Pg.56 ]




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