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Coprecipitation

Coprecipitation is a scalable technique for atomic-level mixing of reactants. In one example, soluble transition metal salts are dissolved in water, and then added to a concentrated solution of potassium hydroxide, causing the rapid precipitation of insoluble metal hydroxides, now uniformly mixed. Often, a chelating agent such as ammonium hydroxide is added to the potassium hydroxide solution to encourage uniform nucleation. Careful control of the pH will result in a significantly more uniform distribution of the reagents.

Equipment

 
Tank reactor for large scale coprecipitation

A highly primitive coprecipitiation can be performed simply using a burette, erlenmeyer flask, stir plate, and magnetic stir bar. A more advanced version of this technique relies upon a tank reactor, which enables careful control over both pH and the concentration of the chelating agent.

Simplified Synthesis

Synthesis of Ni0.25Mn0.75(OH)2

  1. Create 10ml of a 0.5M NiSO4-6H2O and 1.5M MnSO4-H2O solution in water. (Water content of these hydrates salts can be measured using TGA)
  2. Add this solution dropwise to 100ml of a 2M KOH 0.05 NH4OH solution in water.
  3. Collect and wash the precipitate via vacuum filtration or centrifiguation until the pH of the filtrate is neutral and all residual K2SO4 is removed.