Grinding to nano-sizes: Effect of media size and slurry viscosity

•The concept of “grinding zone volume” between media is defined.•Grinding zone volume is proportional to (particle size/ball diameter)2.•For ultrafine milling it is essential to use very small media for long times.•Discrete Element Method contact model for slurry effects is derived. The growing trend towards ultrafine milling makes it worthwhile to study the effect of key variables on this process. The concept of the “grinding zone” is defined and analysed. It is found that (volume of grinding zone)/(volume of voids between media) is proportional to [(particle size)/(media size)]2. The interaction between media travelling towards each other is analysed and the pressure developed between media is shown to be very high. The pressure acts on a small area of the media surface, so only affects media behaviour significantly when slurry viscosity is high. The analysis provides a basis for the development of a DEM contact model for interaction between media in a viscous slurry.