A study of the oxidation of ZrB2 powders during high-energy ball-milling in air

Oxide impurities in ZrB2 powders promote coarsening, resulting in lower sinterability. Given its importance for sintering, we studied the oxidation of ZrB2 powders during high-energy ball-milling (the form of milling able to refine ZrB2 powders to the nanoscale) with the aid of various characterization techniques, namely fusion in inert gas, X-ray diffractometry, helium pycnometry, transmission electron microscopy, and Fourier-transform infrared, Raman, and X-ray photoemission spectroscopy. It was found that high-energy ball-milling in air introduces twice as much oxygen into the ZrB2 powders as the more conventional attrition milling. Also, this oxygen does not form solid-solutions with ZrB2, but amorphous oxides (i.e., ZrO2 and B2O3) that locate preferentially on the surface of the ultra-fine agglomerates resulting from cold-welding of the primary nano-particles that form during the ball-milling.