pulverisette 7 NIST
Agate 2.65 good soft to medium-99.9 % SiO 2 hard samples Silicon nitride 3.1 extremely abrasive sam-91 % Si 3N 4 good ples, iron-free grinding Sintered corundum 3.8 fairly good medium-hard, 99.7 % Al 2O 3 fibrous samples Zirconium oxide 5.7 very good fibrous, abrasive 94.2 % ZrO 2 samples Stainless steel 7.8 fairly good medium-hard,