Adiabatic nucleation and crystallization of gels

Adiabatic Nucleation Theory (ANT) has been successfully applied to pure liquid metals, oxide glasses, metallic glasses and polymers. This paper shows that ANT gives an interesting correlation between the crystallization data of gels of both reluctant and good (dense) glass forming systems. For reluctant glass formers, one finds that T ch < T 14 − , whereas for good (dense) glass formers, T ch > T 14 − . T − 14 is the temperature predicted by ANT at which nucleation starts in cooling experiments or ceases during heating and T ch is the experimental temperature of crystallization on heating. For systems with T ch considerably lower than t − 14 , as observed for reluctant glass formers, it is doubtful that one can obtain dense glasses by heat treatment of gels. This conclusion is in diagreement with the often advanced idea that the gel route can lead to dense glasses of unusual, reluctant glass forming compositions.