Scratch hardness refers to the
hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion (mechanical), abrasion. In general, different materials differ in their hardn ...
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.
Attempting to scratch a surface to test a material is a very old technique.
The first ''scientific'' attempt to quantify materials by scratch tests was by mineralogist
Friedrich Mohs in 1820 (see
Mohs scale).
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.
Mohs's scale had two limitations: it was not linear, and most modern abrasives fall between 9 and 10.
; 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.
Charles E. Wooddell, working at the
Carborundum Company, extended the scale further by using resistance to abrasion, and extrapolating the scale based on seven for
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
and nine for
corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the ...
, resulting in a value of 42.4 for South American brown diamond
bort.
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).
See also
*
Scratch test (disambiguation) A Scratch test may refer to:
* The skin allergy test used in the medical diagnosis of allergies
* Scratch hardness tests, such as Mohs scale of mineral hardness, used to measure the scratch resistance of various minerals
* Liver scratch test, use ...
References
Hardness tests
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