Scratch hardness tests are used to determine the hardness of a material to scratches and abrasion. The earliest test was developed by mineralogist Friedrich Mohs in 1820 (see Mohs scale). It is based on relative scratch hardness, with talc assigned a value of 1 and diamond assigned a value of 10. Mohs' scale had two limitations; it was not linear, and most modern abrasives fall between 9 and 10.
Ridgeway modified the Moh's scale by giving garnet a hardness of 10 and diamond a hardness of 15. Woodell extended the scale further by using resistance to abrasion, where diamond equals 42.5. Resistance to abrasion is less affected by surface variations than other methods of indentations.
There is a linear relationship between cohesive energy density (lattice energy per volume) and Woodwell wear resistance, occurring between corundum (H=9) and diamond (H=42.5).
|Material||Mohs' scale||Ridgeway's scale||Woodell's scale|
|cubic boron nitride|
- Ridgeway, R. R; Ballard, A. H. and Bailey, B. L. (1933). "A revised Mohs hardness scale". Trans Electrochem Soc 63: 369.
- Woodell, C.E (1935). "Method of Comparing the Hardness of Electric Furnace Products and Natural Abrasives". Trans. Electrochem. Soc. 68: 111–130. doi:10.1149/1.3493860.
- Plendl, J.N. (1962). "Hardness of Nonmetallic Solids on an Atomic Basis". Phys. Rev. 125 (3): 828–832. doi:10.1103/PhysRev.125.828.