One observes in Fig. 9 that the ZrB2/ZrO2 and ZrB2/B2O3 peak intensity ratios increase after the etching,
a clear sign that the ZrB2powder particles are covered by an oxide layer.
As can be seen in Fig. 10, the direct high resolution TEM observations also support the presence of an amorphous nano-film at the fringe of the agglomerates.
This oxide distribution is attributed to two factors: (i) the lower chemical affinity between the oxides and ZrB2 than between ZrB2 crystals themselves which would
promote cold-welding during the high-energy ball-milling via contacts of the type ZrB2–ZrB2; and (ii) the spontaneous surface passivation of ball milled powder particles when exposed to ambient conditions after the high-energy ball-milling.