Basic Principles of Precipitation and Nucleation

Though the preparation of coprecipitated catalysts comprises a number of steps, for example, precipitation, filtration, washing, shaping, drying, calcination, and sometimes activation, precipitation is most important, as during that step the basic properties of the catalyst are established. Indeed, 

For more information on precipitation fundamentals we refer to the various textbooks [4-8]. 

there is in essence a critical supersaturation concentration below which nucleation is very slow and above which nucleation is very fast. The range between this critical supersaturation concentration and the solubility concentration is the domain of deposition-precipitation discussed elsewhere (Chapter 6), while impregnation (Chapter 4) is performed in the concentration range below the solubility limit. Especially for multicomponent systems, it is important to operate at high supersaturation levels so that the solubility product of all products is simultaneously exceeded, otherwise a possibly undesired sequential precipitation may occur. 

Supersaturation can be produced in a variety of ways both by physical and chemical methods cooling of the reaction mixture, evaporation of solvents. 

There are several mechanisms for crystal growth, but most of them lead to the simplified equation for the growth rate as shown in Equation 7.3 [9,10). 

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