Coprecipitation-a Simple Method to Produce Nanoparticle Spinel Materials

Easy, economical, and simple method to produce nanoparticles of zinc ferrites and zinc aluminates by coprecipitation method.

Coprecipitation method offers some advantages. They are:

  1. Simple and rapid preparation.
  2. Easy control of particle size and composition
  3. Various possibilities to modify the particle surface state and overall homogeneity.

Coprecipitation of various salts (nitrates, sulphates, chlorides, perchlorates etc.) under a fine control of pH by using NaOH or NH4OH solutions yields corresponding spinel oxide nanoparticles. For example to prepare ZnFe2O4, zinc nitrate and ferric nitrate are used as starting precursors. The pH of the medium should be above 8 to get the better end product. Particle size of the coprecipitated material is strongly dependent on pH of the precipitation medium and molarity of the starting precursors. Consequently particle size control can be easily achieved.

A crystalline phase is achieved even with a pH around 8 if we use a salt that contain Fe2+ ions (in the case of inverse spinel ferrite). The electron mobility between Fe2+ and Fe3+ acts as the driving force for the spinel phase formation. But when we have to deal with normal spinel ferrites that have only Fe3+ ions we have to increase the pH of the medium to achieve crystallinity. A pH = 12 is desired in this case.

If we increase molarity of the solution, particle size gets reduced. But this size reduction is achieved in the expense of large amount of chemicals. Hence a compromise between this leads us to prefer a moderate molarity for the starting solutions. In our synthesis, we preferred 0.1M and 0.2M solutions to begin the coprecipitation.

Synthesis of ZnFe2O4

0.1 m aqueous solution of zinc nitrate and 0.2m aqueous solution of ferric nitrate were prepared separately. Both the solutions were mixed together and stirred using a magnetic stirrer keeping the temperature at 3730K. While stirring this mixture, pure ammonium hydroxide solution was added until the pH of the solution becomes 12. The precipitate produced was dried at 3730K and annealed in air at 7730K which yielded crystalline zinc ferrite.

Synthesis of ZnAl2O4

0.1 m aqueous solution of zinc nitrate and 0.2m aqueous solution of aluminum nitrate were prepared separately. Both the solutions were mixed together and stirred using a magnetic stirrer keeping the temperature at 3730K. While stirring this mixture, pure ammonium hydroxide solution was added until the pH of the solution becomes 12. The precipitate produced was dried at 3730K and annealed in air at 7730K which yielded crystalline zinc aluminate.

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One Response to “Coprecipitation-a Simple Method to Produce Nanoparticle Spinel Materials”
  1. gayathri Says...

    On September 8, 2007 at 12:06 pm

    A correction please note:temperature for drying is 373 Kelvin and annealing temperature is 573 Kelvin


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