Reactive Multicomponent Powder Mixtures Prepared by Microencapsulation: Pb(Mg1/3Nb2/3)O3 Synthesis

Abstract

Microencapsulation of ceramic powders using metalloorganic stearate soaps was investigated as an economical means to increase solid‐state reactivity of multicomponent mixtures. The specific system investigated was lead magnesium niobate (PMN); however, the process may be applicable to a wide range of other compositions. The physical and chemical characteristics of the unfired powder mixtures and reactivity during subsequent calcination were studied as a function of batch composition and mixing method. Batch composition was varied by molar substitution of magnesium stearate for magnesium carbonate. Mixing method was investigated by comparing a dry‐mixing technique developed for particle coating (mechanofusion) with conventional wet ball milling. Both mixing processes resulted in surface coating of the ceramic particles by the stearate soap. In addition, the mechanofusion process produced densely packed spherical granules of coated particles (multicored microcapsules) in the 50‐ to 200‐μm range. Solid‐state reactivity was measured in terms of perovskite phase yield, increased yields being indicative of a more reactive mixture. The highest perovskite yields (95 to 98 vol%) were achieved at 100 mol% substitution of magnesium stearate for magnesium carbonate, independent of mixing method. However, when magnesium stearate was only partially substituted for magnesium carbonate, the mechanofusion process produced consistently higher perovskite yields than did ball milling. Compared to conventional mixed‐oxide processing, the increased reactivity of the microencapsulated mixtures can be attributed to higher chemical activity of the metallo‐organic precursor, finer scale of mixing achieved by particle coating, and a further reduction in segregation scale due to the dense intragranule packing of multicore microcapsules.