In order to elucidate the mechanism of the elaboration of raw materials by freeze-drying, a characterization of alpha-Fe2O3 freeze-dried powders has been undertaken during the main phases of the preparation. The freezing of the salt solution and the salt solidification in amorphous form govern mainly the properties of the produced powder -ultrafine, pure and highly reactive particles- and its thermal behaviour. The usefulness of such unconventional process is the lowering of temperature of chemical reactions involving alpha-Fe2O3.