Other methods for precipitation of tantalum and niobium oxide precursors

Other methods for precipitation of tantalum and niobium oxide precursors 

Other methods exist for the precipitation of tantalum and niobium hydroxides for subsequent use as oxide precursors. Application of ammonium carbonate, (NH4)2C03, instead of ammonia solution, also seems to have potential for the precipitation of tantalum and niobium hydroxides. Ammonium carbonate is relatively stable in aqueous media at room temperature and does not initiate the precipitation of hydroxides. Increasing the temperature of the solution causes hydrolysis and decomposition of ammonium carbonate yielding hydroxyl ions and an increase in pH, as follows  

The interaction described in Equation (148), in which C02 separates from the solution and ammonia hydroxide is formed, reduces the acidity of the solution causing precipitation of tantalum or niobium hydroxide. The hydroxide powder precipitated using ammonium carbonate is usually coarser and has better filtering properties. Changing the ammonium carbonate concentration and temperature of the solution allows some control over the particle size and filtering properties of the precipitated hydroxides. 

In addition to the possibility of controlling the particle size of the hydroxides, application of ammonium carbonate affords several other advantages compared to traditional precipitation of hydroxides using ammonia solution. First, ammonium carbonate does not increase the total volume of the solution as much as does the addition of ammonia. Second, the method enables to perform the interaction so as to precipitate stoichiometric mixtures, which 

Another promising method for the preparation of tantalum and niobium oxide precursors involves the precipitation of peroxoniobate and peroxotantalate compounds. 

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