The SEM images of the powders provide insight
into the particle size distributions of the milled
samples (Fig. 1). The unmilled powders (Fig. 1(a))
are characterized by aggregated and irregular NiO
particles, with few particles below 200 nm in size.
After milling for 480 min with no additive (Fig. 1(b)),
the extent of aggregation increases while the particle
size distribution now includes many more particles in
the 100 nm range. Milling for 480 min with carbon
(Fig. 1(c)) also increases the frequency of small