The aggregation rate and mechanism of 150 nm alumina particles in 1 mM 1KNO(3) with various additives used in chemical mechanical planarization of copper were investigated. The pH of each suspension was similar to 8 such that the aggregation rate was slow enough to be measured and analyzed over similar to 120 min. In general, an initial exponential growth was observed for most suspensions indicating reaction-limited aggregation. After aggregate sizes increase to >500 nm, the rate followed a power law suggesting diffusionlimited aggregation. Stability ratios and fractal dimension numbers were also calculated to further elucidate the aggregation mechanism. (C) 2013 Elsevier Inc. All rights reserved.