Surface Oxide Content

Aluminum reacts readily with moisture or free oxygen in the air during manufacture to form an oxide coating on the powder surface. The amount of surface oxide formed during atomization is strongly dependent on the oxygen level of the atomizing atmosphere and particle size of the powder produced. The oxygen content of fine powders atomized in air can approach 1% level by weight (Fig. 18). For coarser powders, 0.4% oxygen is more typical. A mean oxide thickness can be calculated from the oxygen content of the powder if the specific surface area has also been determined. It is then found that the thickness of oxide is, in fact, greater for coarser powders despite the lower overall oxygen content (Fig. 19). Finest powders under 10 /''m show a mean oxide thickness of 4 to 5 nm, whereas with coarser powders, the thickness can reach 10 nm.

Fig. 18 Oxygen content for aluminum powders
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Mass median diameter, nm

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Mass median diameter, nm

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