How do we measure the hardness of materials?
Some metals are harder than others. How is hardness measured?
Hardness is a property of solid material, which is measured by its resistance to scratches when it is rubbed against another material. The hardness of the various materials is measured either on the ‘Mohs’ scale or the ‘Knoop’ scale.
Friedrich Mohs first devised the Mohs’ scale in 1822. it measures resistance to indentation as judged by the material that will scratch another. Mohs’ scale is numbered from 1 to 10, i.e, it gives ten grades of hardness. In this scale,, diamond is the hardest material and talc is the softest. Diamond has a hardness of 10 Mohs and talc has a hardness of 1 Mohs. Mohs’ scale, which assigns numbers to natural minerals, has been widely accedpted and is used by mineralogists.
This test however is not quantitative. For example, the hardness of sapphire is 9 on the Mohs’ scale but it does not mean that sapphire is 10% softer than diamond.
Mineralogists carry a box containing pieces of the above minerals for testing samples in the field.
To measure hardness in the Knoop scale, an elongated diamond shaped indenting device is employed to measure the indentation it makes in a given test material. Using this method, the hardness of extremely brittle materials, including glass and even diamond can be measured without damaging either the indenter or the test piece. The size of the indentation is taken as a measure of the material’s hardness. Reference C.K.B by Dr.C.L.Garg.
MOHS’ HARDNESS OF SCALE
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