Precipitation from solutions

Precipitation is one of the conventional methods to prepare nanoparticles of metal oxide ceramics. This process involves dissolving a salt precursor, usually chloride, oxychloride or nitrate, such as AlCl3 to make Al2O3, Y(NO3)3 to make Y2O3, and ZrCl4 to make ZrO2, in water. The corresponding metal hydroxides are usually obtained as precipitates in water by adding a base solution such as sodium hydroxide or ammonium hydroxide solution. The remaining counter-ions are then washed away and the hydroxide is calcined after filtration and washing to obtain the final oxide powder. This method is useful in preparing ceramic composites of different oxides by coprecipitation of the corresponding hydroxides in the same solution. Solution chemistry is also used to prepare non-oxide ceramics or pre-ceramic precursors that can be converted to ceramics upon pyrolysis.

One of the disadvantages of this method is the difficulty in controlling the particle size and size distribution. Very often, fast and uncontrolled precipitation takes place resulting in large particles.

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