Dissolution Characteristics as the Basis for Forming CBPCs

When powders of metal oxides are stirred in solvent such as an acid-phosphate solution, they dissolve slowly in the solvent and release cations in the solution. These cations react with the phosphate anions within the solvent and form a precipitate of salt molecules. Under the right conditions, these molecules form an ordered structure and grow into crystals. This ordered crystalline solid of the reaction products is the CBPC. Thus, CBPC formation is a result of the following three steps  

The acid phosphates dissolve in water, release phosphate anions, and form an acid-phosphate solution of low pH. 

The oxides dissolve gradually in the low pH solution and release cations. 

The phosphate anions react with the newly released cations and form a coordinated network and consolidate into a CBPC. 

The right conditions to form a CBPC are governed by the rate of reactions that control each of these three steps. Since acid phosphates selected for use in the CBPC process are soluble, their dissolution rate is comparatively high and, hence, uncontrollable. The phosphate reaction between dissolved cations and anions described in step 3 is also inherently fast and, again, cannot be controlled. Thus, the only reaction that can be controlled is the dissolution of oxides given in step 2. By selecting suitable oxides with appropriate reaction rates for forming CBPCs, one may allow sufficient time to mix the components in water and pour the slurry in molds, or spray the slurry, or apply it in any other suitable manner to form a ceramic. On the other hand, an oxide that dissolves fast 

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