Finally, it is worth mentioning that a recent spark-plasma sintering (SPS) study [21] has revealed that the greater oxygen content of this ZrB2 nano-powder
obtained by high-energy ball milling in air does not hinder its densification.
On the contrary, it exhibits improved SPS kinetics relative to powders with larger particles and less oxygen content,
which has been attributed to the large inter-particle boundary surface area1 that can greatly enhance grain-boundary diffusion at lower temperatures.
Whether the SPS results can or not be extrapolated to the pressureless sintering (PS) is something that has yet to be investigated experimentally.
Whichever the case, it is reasonable to think that the sinterability of this ZrB2 nano-powder (by SPS, PS, or hot-pressing) would improve further if the high-energy
ball-milling were performed in an inert atmosphere, although the comminution routine would be more tedious and costly.