2004 Volume 44 Issue 12 Pages 1981-1990
In previous study, the extremely high reaction rate obtained by the mechanical milling has been reported. It was found that the phenomena were quite complicated and the many factors were affected on the reactivity. Among these factors, the crystal state of hematite and atmosphere (air and argon) during the milling were quite important ones.
Milling of hematite and graphite mixture was carried out both in the air and in the argon. Rate constants for the reactions were obtained by kinetic analysis. The enthalpy ΔH* and entropy ΔS* of activation were estimated on the basis of transition state theory. The interpretation of ΔS* and ΔH* was performed to explain the effect of milling on the reactivity related to the milling conditions.
The temperature of peak of reaction curve decreased with increasing milling time. The reactivity of the sample milled in the argon atmosphere showed higher reactivity than that milled in the air. The enthalpy ΔH* and entropy ΔS* of activation were obtained from experimental rate constants. The variation of ΔH* and ΔS* with milling time showed opposite tendency between the sample milled in the air and in the argon. It was considered that the active complex having loose bonding would form during milling in the air atmosphere. On the other hand, the active complex having a structure closed to the product (metallic iron) might form.