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Technical Paper


www.ireng.org


5.4 Hardness and Erosion Resistance The abrasion resistance of ceramics depends largely on: • the nature (hardness) of the essential phases; • the quantity of the essential and hardest phases; • the binding between the crystalline components; • the porosity.


Friction wear due to vortex-formation a


fluidised medium


b flow pattern c


originally the plane surface


A location with strongest abrasion B


sharp edging


Hardness according to Mohs [Ha No:


1


2 3 4 5 6 7 8 9


10


Material Talc


Gypsum


Limestone Fluorite Apatite Feldspar Quarts Topaz Ruby


Diamond Hardness according to Vickers [MPa] [Ha


No: 1


2 3 4 5 6 7 8 9


10


Material Talc


Gypsum


Limestone Fluorite Apatite Feldspar Quarts Topaz Ruby


Diamond


Hardness <100


1500 – 1800 1300 – 1700 1800 – 2500 6000 – 7000 7000 – 8000 12000 – 13000 10000 – 160000 21000 – 26000 70000


Average hardness with fine (<mm) abrasives Figures between [ ] hardness of most durable phase to course abrasive (>mm) 20 ENGINEER THE REFRACTORIES ]


Material Soft steel


Centrifuged steel [Mn, Si] Laminated steel [Mn, Cr] Pig iron non-alloyed


Martensitic alloy Ni-hard Martensitic alloy Cr-Mo Glass


Fused-cast alumina-zircon-silica 85% Aluminium oxide Silicon-carbide


Hardness 1200 2500 3200


2300 [8000] 6500 [10000] 6200 [12000] 4500


17000 [20000] 17000 [20000] 20000 [26000]


[Hm ] ]


Formula (OH2 Mg3


Explanation


CaSO4.2H2 CaCO3 CaF2


Ca5.(PO4 )3


K (Al Si3O8 SiO2


Al2 (SiO4 Al2O3


C


.[Si4 O


O10 ]


Very weak, finger crushable Scratches


.(Cl, F) )


).(F, OH)2


easy with fingernail easy with copper-coin easy with knife with knife


difficult with knife in window glass easy in quartz


easy with diamond Cannot be scratched


There are tables containing data with hardness properties of materials. Well known are the terms as Rockwell Hardness, Mohs' Scale, Brinell Hardness, Vickers, etc. They all rate materials according to their individual or comparative hardness. Because no exact definition can be given for hardness, it was 'every bodies guess'.


Mohs' Scale gives the comparative hardness of minerals from 1 to 10, where an unknown mineral which cannot be scratched but will with a mineral next higher on the scale, it will be classified in between. In order to have insight in the hardness he classified certain minerals as targets:


March 2019 Issue


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