The effect of high energy milling on the solid-state reactions taking place in Mn3O4 has been studied. Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) have been employed to study the solid-state reaction occurring under air in the temperature range between room temperature (rt) and 1100 degreesC. X-ray Powder Diffractometry (XRPD) has been used to ascertain the chemical nature of the transformations brought into evidence by thermo-analysis. (C) 2003 Elsevier Ltd. All rights reserved.