Metal colloids initiating crystallization

It must be noted that the initiation of crystallization is achieved by metal colloids, which are generated by UV irradiation and heat treatment. To apply this glass-ceramic for the production of integrated lens arrays, its manufacturing procedure had to be refined, and Borrelli, et al. (1985) achieved this objective (Beall 1992, 1993). 

The current state of the art carbon supported electrocatalyst is made using variants of the colloidal approach. A common approach is to dissolve the metal salt solution in an appropriate solvent followed by reduction to form a colloid. A wide variety of recipes using reducing agents, organic stabilizers, or shell-removing approaches have also been developed in recent years. The patents most frequently referred to in this field are from United Technologies by Petrow and Allen.Sols of the metal are obtained for instance by an initial formation of a metastable platinum-sulfito complex, which is inert at ambient temperature but decomposes and produces the small Pt-crystallites at temperatures in excess of 60°C. Thus a relatively well-defined crystal size between 2 to 6 nm can be obtained. 

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