Mechanical Milling. The first step for the impregnation of the catalyst over the support is the Milling process. The Sigma- Xxxxxxx provides cobalt oxide (III) (Co3O4) in the form of powders [9]. The Co3O4 was mixed into the milling chamber with distillate water and balls of zirconia (d = 0.7 mm). The zirconia balls allow good mixing and reduce the size of the grains. The amount needed for each ingredient was calculated taking into account the volume percentage between water and cobalt oxide and the volume of the chamber: • 80% distilled H2O – 20% Co3O4 powder • Weight of zirconia balls = 10*(weight of the Co3O4 powder) The internal volume of the chamber was 25 ml. The three ingredients were weighted in order to refill 3/4 of the total volume permitting a good degree of blending. The density of the water at ambient conditions was considered to be 1 g/cm^3. The bulk density of the zirconia balls (3.7 g/cm^3) and the apparent density of the Co3O4 power (6.11 g/cm^3) were taken from the datasheet [9] [10]. So, the quantity of each compound is calculated: • 8 g of H2O • 2 g of Co3O4 • 20 g of zirconia balls (d = 0.7 mm) The chamber is made of a heavy metal and it is internal covered by a layer of zirconia to avoid contamination and possible reaction with the metal (Figure 8). Figure 8- left) comparison of the dimension with a pen; right) chamber refill with zirconia balls and Co3O4 powder The filled chamber was inserted in the milling machine to mix the ingredients. The milling machine is composed of two arms, where it is possible to put two xxxxxxxx at the same time (Figure 9).
