Scratch hardness

Scratch hardness refers to the hardness of a material in terms of resistance to scratches and abrasion by a harder material forcefully drawn over its surface. Scratch hardness test or scratch test refers to any of a number of methods of measuring scratch hardness. Resistance to abrasion is less affected by surface variations than indentation methods. Scratch hardness is measured with a sclerometer.^[1]

Attempting to scratch a surface to test a material is a very old technique.^[2] The first scientific attempt to quantify materials by scratch tests was by mineralogist Friedrich Mohs in 1812 (see Mohs scale).^[3][4] The Mohs scale is based on relative scratch hardness of different materials; with talc assigned a value of 1 and diamond assigned a value of 10.^[5] Mohs's scale had two limitations: it was not linear, and most modern abrasives fall between 9 and 10.;^[6][7] so, later scientists attempted to increase resolution at the harder end of the scale.

Raymond R. Ridgway, a research engineer at the Norton Company, modified the Mohs scale by giving garnet a hardness of 10 and diamond a hardness of 15.^[6][8] Charles E. Wooddell, working at the Carborundum Company, extended the scale further by using resistance to abrasion, and extrapolating the scale based on 7 for quartz and 9 for corundum, resulting in a value of 42.4 for South American brown diamond bort.^[9][10]

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).^[11]

See also

• Scratch test (disambiguation)