Scratch hardness
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[1] modified the Mohs scale by giving garnet a hardness of 10 and diamond a hardness of 15. Wooddell[2] 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 Wooddell wear resistance, occurring between corundum (H=9) and diamond (H=42.5).[3]
| Material | Mohs' scale | Ridgeway's scale | Wooddell's scale |
|---|---|---|---|
| talc | 1 | ||
| gypsum | 2 | ||
| calcite | 3 | ||
| fluorite | 4 | ||
| apatite | 5 | ||
| orthoclase | 6 | 6 | |
| vitreous silica | 7 | ||
| quartz | 7 | 8 | 7 |
| topaz | 8 | 9 | |
| garnet | 10 | ||
| corundum | 9 | 9 | |
| fused ZrO2 | 11 | ||
| fused ZrO2/Al2O3 | |||
| fused Al2O3 | 12 | ||
| SiC | 13 | 14 | |
| boron carbide | 14 | ||
| cubic boron nitride | |||
| diamond | 10 | 15 | 42.5 |
References
- ^ Ridgeway, R. R; Ballard, A. H. and Bailey, B. L. (1933). "A revised Mohs hardness scale". Trans Electrochem Soc. 63: 369.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Wooddell, 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, Johannes N.; Gielisse, Peter J. (1 Feb 1962). "Hardness of Nonmetallic Solids on an Atomic Basis". Phys. Rev. 125 (3): 828–832. doi:10.1103/PhysRev.125.828.