▁scale , ▁arr anging ▁in ▁a ▁defined ▁and ▁periodic ▁manner ▁that ▁defines ▁the ▁cry stal ▁structure . ▁The ▁cry stal ▁growth ▁is ▁the ▁subsequent ▁growth ▁of ▁the ▁nuc lei ▁that ▁succeed ▁in ▁ach ieving ▁the ▁critical ▁cluster ▁size . ▁ ▁Super co ol ing ▁ ▁In ▁spite ▁of ▁the ▁second ▁law ▁of ▁therm od ynam ics , ▁cry st all ization ▁of ▁pure ▁liqu ids ▁usually ▁begins ▁at ▁a ▁lower ▁temperature ▁than ▁the ▁mel ting ▁point , ▁due ▁to ▁high ▁activation ▁energy ▁of ▁hom ogeneous ▁nucle ation . ▁The ▁creation ▁of ▁a ▁nucle us ▁implies ▁the ▁formation ▁of ▁an ▁interface ▁at ▁the ▁boundaries ▁of ▁the ▁new ▁phase . ▁ ▁Some ▁energy ▁is ▁exp ended ▁to ▁form ▁this ▁interface , ▁based ▁on ▁the ▁surface ▁energy ▁of ▁each ▁phase . ▁If ▁a ▁hypoth et ical ▁nucle us ▁is ▁too ▁small , ▁the ▁energy ▁that ▁would ▁be ▁released ▁by ▁forming ▁its ▁volume ▁is ▁not ▁enough ▁to ▁create ▁its ▁surface , ▁and ▁nucle ation ▁does ▁not ▁proceed . ▁Free zing ▁does ▁not ▁start ▁until ▁the ▁temperature ▁is ▁low ▁enough ▁to ▁provide ▁enough ▁energy ▁to ▁form ▁stable ▁nuc lei . ▁In ▁presence ▁of ▁irregular ities ▁on ▁the ▁surface ▁of ▁the ▁containing ▁vessel , ▁solid ▁or ▁g ase ous ▁imp ur ities , ▁pre - formed ▁solid ▁cry st als , ▁or ▁other ▁nucle ators , ▁heter ogeneous ▁nucle ation ▁may ▁occur , ▁where ▁some ▁energy ▁is ▁released ▁by ▁the ▁partial ▁destruction ▁of ▁the ▁previous ▁interface , ▁raising ▁the ▁super co ol ing ▁point ▁to ▁be ▁near ▁or ▁equal