Researchers: Dr Colin Hare, Lige Wang (The University of Edinburgh)
Principal Investigator: Dr Colin Hare
Co-Investigator(s): Prof. Jin Ooi (The University of Edinburgh)
Sponsor: International Fine Particle Research Institute (IFPRI)
Status: Complete (2013 – 2014)



Milling is a highly inefficient process that can be better understood by using appropriate grindability tests.  Milling can be achieved by a number of load application methods, e.g. shear, impact compression, however the interest here is on milling by the impact mechanism in a pin mill.  Particles enter a chamber within which a set of rigid pins rapidly rotate, thus leading to size reduction by repeated impact damage.  The portfolio of impact velocities and impact angles experienced by the particles are reported elsewhere (Labra et al., 2013).  To predict milling the breakage rate of particles under such conditions should be established.


The mechanical properties of spherical alumina and zeolite particles were measured to better understand their propensity for size reduction in a pin mill.  Young’s modulus and hardness were determined by nanoindentation and fracture toughness was assessed by microindentation and Scanning Electron Microscopy (SEM).  The three material properties were greatest for alumina, and increased in size for zeolite.  The mechanical property measurements lead to the prediction that alumina is less susceptible to impact breakage caused by a pin mill, whilst the larger zeolite particles were most prone.


The impact breakage of the smaller zeolite particles (1.4 – 1.7 mm) was assessed in a single particle impact rig under a range of impact angles and velocities.  The extent of breakage was found to be independent of impact angle at low-moderate impact velocities, with breakage instead correlating with normal impact velocity.  Since the influence of impact angle is material dependent, similar behaviour is expected for the larger zeolite particles, however further testing is required to understand the influence of impact angle on impact breakage of alumina.