**1: Mohs Scale (source: Wikipedia)
Friedrich Mohs (January 29, 1773 - September 29, 1839) was a German geologist/mineralogist. In 1812, using relatively common minerals, he created a hardness scale that is still used today, called the Mohs' scale of mineral hardness.
The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is almost four times as hard as corundum. Table 1.1 shows comparison with absolute hardness.
Table 1.1 - comparison between Mohs and Absolute hardness
|Mohs Hardness||Mineral||Absolute Hardness|
On the Mohs scale, a pencil lead has a hardness of 1; a fingernail has hardness 2.5; a copper penny, about 3.5; a knife blade, 5.5; window glass, 5.5; steel file, 6.5. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. Table 1.2 incorporates additional substances that may fall between levels.
Table 1.2 additional substances in Mohs scale
|Mohs Hardness||Substance or Mineral|
|2.5 to 3||Pure gold, silver, aluminum|
|3||Calcite, copper penny|
|4 to 4.5||Platinum|
|4 to 5||Iron|
|6.5||Iron pyrite, steel|
|6 to 7||Glass, vitreous pure silica|
|7 to 7.5||Garnet|
|7 to 8||Hardened steel|
|9 to 9.5||Carborundum (SiC)|
|< 10||Ultrahard fullerite|
|> 10||Aggregated diamond nanorods|
Sintering is a process that takes place at both high pressure and high temperature and is ment to create solid parts starting from powders (usually ceramic, but a mix of ceramic and metals or metals alone can be used as well). Solid state sintering is when the heating temperature is below the melting point of the powders, liquid state sintering when at least one (but not all) element melts during the process. Cemented WC is obtained from liquid state sintering.