抄録
Reactive grinding using a planetary ball-mill has been applied to the mechanochemical synthesis of lanthanoid ferrites, LnFeO3 (Ln: La, Pr, Sm, Gd, Dy, Yb). Colloidal lanthanoid hydroxides, Ln(OH)3, have first been formed from their oxides in organic liquids under grinding. The hydroxides not only promote the size reduction of the other reactant Fe2O3 in acting as the grinding aid but react with Fe2O3 to form hydroxide-complexes. The hydroxide complexes can be converted to LnFeO3 by the following stress-induced dehydration-condensation reaction. The reactivity strongly depends on the free energy change of hydroxide formation (delta GR) for the lanthadoid oxides and an electrostatic parameter of lanthanoid ions (Z/r), where Z is the ionic charge number and r the ionic radius. Although the delta GR values for all Ln2O3 are negative, the high Z/r value disturbs the formation of hydroxide-complexes. The adequate combination of the starting materials and the influence of the grinding stress have been discussed.
