The influence of the rotation frequency of a planetary ball mill on the limiting value of the specific surface area of the WC and Co nanopowders

[Display omitted] •The specific surface area (SSA) of particles during milling is limited.•As the speed of the mill increases, the limit increases if hardening is the cause.•As the speed of the mill increases, the limit decreases if the cause is coalescence.•The frequency dependences of the limits for WC and Co were investigated. An increase in the hardness and wear resistance of WC-Co alloys with a decrease in the grain diameter of WC and Co makes it relevant to search for methods for producing powders with a maximum specific surface area (SSA). SSA growth is limited even when milling powders of WC and Co in the most high-energy mills. Effect of increasing the rotation speed of a planetary ball mill on the limiting value of the SSA of obtained nano sized WC and Co powders is studied. According to the developed model, an increase in the rotational speed of the mill leads to an increase in the limiting value of SSA if the cause is particle hardening. If the cause is coalescence, an increase in frequency leads to a decrease in the limiting value of the SSA. It was determined that the limiting value of SSA of WC particles increases from 1.0⋅108 m2/m3 to 2.2⋅108 m2/m3 (Sauter average diameter decreases from 60 to 27 nm) with increase of mill rotation frequencies from 2.5 to 4.2 rps due to a decrease in the volume of “indestructible” particles. And the limiting value of SSA of WC particles decreases from 2.2⋅108 m2/m3 to 1.1⋅108 m2/m3 (Sauter average diameter increases from 26 to 55 nm) with increase of mill rotation frequencies from 5 to 6.7 rps due to the increase of the coalescence rate. The experiment showed that the limiting value of SSA for Co powder decreases from 1.0⋅108 m2/m3 to 1.1⋅106 m2/m3 with increasing of the rotational speed of the mill from 2.5 rps to 6.7 rps (Sauter average diameter increases from 60 to 5450 nm) due to the increase of the coalescence rate. Studies have shown that the growth of SSA of WC grains is limited by a certain value (11.5 nm).