Wet media mills grind solids to the nanometric size and the performance of the mills depends on solids loading, particle morphology, surfactant concentration, and material characteristics. As the particle size decreases, they tend to form clusters that reduce the grinding efficiency. Ultrasound deagglomerates these clusters thereby increasing efficiency but, surprisingly, it can operate at higher solids concentrations. We processed suspensions of LiFePO4 (LFP) with a yttria stabilized zirconia media with a size from 0.3 mm to 0.4 mm, and surfactant-to-LFP mass ratio 0.008. The combined method ground the particle size from 35 mu m down to 0.2 mu m in 90 min with a throughput of 0.68 kgLFP/kgmedia/h. We also tested the improved wet media milling on two catalysts: (WO3/TiO2 and vanadyl pyrophosphate (VPP) precursor) to confirm the trends. We adopt a model for the steady state and repeatable micronizing process with ultrasonic assistance. According to TEM imaging the WO3/TiO2 catalyst primary particles (20 nm) are much smaller than the agglomerated ones measured by laser diffraction (470 nm). VPP precursor slurry is normally an unstable suspension that is hard to mill. It formed agglomerates with recrystallized silica and VPP flocculation. The ultrasound-assisted wet milling technique produced nanometer scale particles (180 nm), which is otherwise impossible. We developed and updated the steady state micronizing process with ultrasonic assistance using a simplified population balance model. The model accounts for R2>0.95 of the variance in the experimental data.