Abstract:
Rare-earth oxides as Y2O3 and La2O3 evenly dispersed in Fe matrix constitute ODS alloys with potential applications in nuclear power plants .Dispersion of the above oxides can be obtained from various synthetic routes. However, kinetics , particle size and morphology are difficult to control. Mechanochemical activation of rare earth oxide precursors with either Fe2O3 (hematite ) or Fe3O4 (magnetite) was also used since diffusive processes are accelerated under ambient conditions. In the induced chemical reaction, AFeO3 oxides (A is a rare earth element) can also be produced. This last orthoferrite phase is also interesting for its wide magnetic applications.
In this work, Fe/ La2O3 composite powder has been fabricated by high energy ball milling. Powder mixtures were milled during different times 0, 5, 10h in a planetary ball mill where hardened steel vials were rotated at about 400 rpm under argon atmosphere and a ball to powder weight ratio of 16:1 . And phase evolution of the milled powder mixtures were analyzed during the mechanical treatment by X-ray diffraction, differential thermal analysis and scanning microscopy.
Results showed that for the Fe/10%wt. La2O3 composite, starting powders are Fe, La2O3 and La(OH)3. The last one is due to the highly hygroscopic of La2O3, that convert to La(OH)3 when exposed to air. Also, the best refinement of X-ray diffraction pattern shows that La2O3, is composed of two structures cubic and hexagonal. After 5h of milling, the formation of the perovskite LaFeO3 is observed with the presence of nanocrystalline Fe and La2O3 phases. Increasing the milling time transforms the oxide phase into an amorphous structure and the iron phase into a disordered phase with a grain size less than 20 nm. Above 10 h of milling, the orthoferrite LaFeO3 disappears . Thermal analysis showed the presence of two endothermic peaks of La(OH)3 at 350 and 500°C . Increasing the milling time to 10 h , the formation of a wide exothermic peak is observed due mainly to LaFeO3
