Moh’s hardness

High speed machines such as impact mills begin to suffer high wear rates when processing materials above Mohs s hardness 3, unless very special wear-resisting measures can be taken. 

Nickel. Ni, at wt 58.71, at no 28, valences +2 +3, five stable isotopes, 7 radioactive isotopes. Malleable, silvery metal readily fabricated by hot and cold working takes high polish excellent resistance to corrosion. Mp 1455° bp 2900° d 8.9Q8g/cc electrical resistivity (20°) 6.844 microhm-cm Moh s hardness 3.8 spec heat (100°) 0.1123 latent heat of fusion 73cal/g. 

Hard and tough Mica Scrap and powdered metals Jaw crushers Gyratory crushers Cone crushers Autogeneous mills Ball, pebble, rod and cone mills Tube mills Vibration mills Ball, pebble and cone mills Tube mills Vibration and vibro-energy mills Fluid-energy mills Moh s hardness 5-10, but includes other tough materials of lower hardness... 

Hard, abrasive Coke, quartz, Jaw crushers Ball, pebble, Ball, pebble and Moh s hardness... 

Reddish-hrown hexagonal crystal refractive index 2.91 density 5.25g/cm3 Moh s hardness 6.0 melts at 1565°C insoluhle in water dissolves in acids. 

Colorless orthorhombic crystals refractive index 1.804 Moh s hardness 3-3.5 density 6.60 g/cm decomposes on heating at 315°C practically insoluble in water (1.1 mg/L at 20°C) Ksp 1.46xlCLi3 at 25°C also insoluble in alcohol and ammonia soluble in acids and alkahes. 

The oxide exhibits two crystalline modifications, the reddish or orange-red alpha form, known as litharge, and the yellow beta form, massicot. The alpha form constitutes tetragonal crystals while the beta modification is a yellow amorphous powder of orthorhombic crystal structure. The alpha form is stable at ordinary temperatures, converting to the beta form when heated at 489°C density 9.35 g/cm (beta form) Moh s hardness 2 (alpha form) the oxide melts at 888°C vaporizes at 1,472°C with decomposition vapor pressure 1 torr at 943° C and 5 torr at 1,039°C practically insoluble in water (the solubdity of alpha form is 17 mg/L at 20°C and that of beta form 23 mg/L at 22°C) insoluble in ethanol soluble in dilute nitric acid and aUtahes. 

Colorless tetragonal crystals faint violet luminescence refractive index 1.378 density 3.148 g/cm Moh s hardness 6 melts at 1261°C vaporizes at 2,260°C practically insoluble in water (76 mg/L at 18°C) soluble in nitric acid slightly soluble in dilute acids and acetone insoluble in ethanol. 

Green cubic crystal refractive index 2.16 density 5.37 g/cm at 23°C Moh s hardness 5.5 melts at 1945°C insoluble in water. 

Black tetragonal crystal exhibits two allotropic modifications—a stable alpha phase, occurring in tetragonal crystalline form (as hausmannite) and an unstable beta modification density 4.85 g/cm Moh s hardness 5.5 melts at 1,567°C insoluble in water soluble in hydrochloric acid. 

Orthogonal crystalline powder refractive index (for montroydite) 2.37 density 11.14 g/cm3 Moh s hardness 2.5 insoluble in water and ethanol soluble in dilute acids and aqueous solutions of alkali iodides and cyanides. 

White granular powder or cubic crystals refractive index 2.071 darkens on exposure to hght density 5.56 g/cm Moh s hardness 2.5 melts at 455°C vaporizes at 1,547°C vapor pressure 1 and 5 torr at 912 and 1,019°C insoluble in water, alcohol and dilute acids soluble in ammonia solution and concentrated sulfuric acid, alkali cyanide, ammonium carbonate also soluble in potassium bromide and sodium thiosulfate solutions. 

The common form of asphalt is a black, compact, amorphous, brittle mass of dull luster, which breaks showing a polished surface and fuses at 188-90°F (ca 87°), d 1.40-1.42 at 77°F (25°C) and Moh s hardness 1 to 2... 

Moh s hardness number Temp of product °F Specific heat... 

SiC, a hard substance(Moh s hardness 9.17), which can be obcained by heating sand and coke. with some sawdust in an electric furnace at high temp. The name carborundum is also applied to other hard materials, such as fused alumina. These materials are used as abrasives for cutting, grinding or polishing(Refs 2,3,5,6 7). 

Moh s hardness 8.5) CBr2 (crysts, mp 1850°, d 5.15, hardness 2010 Knoop resists oxida-tion up to 1100°) and CBr3 (crysts, d 6.1 Moh s hardness 9+). Because of their high mp s, high hardness and corrosion resistance, they were proposed for use in jet and tocket engines (See also Borides in Vol 2,pB249-R) Re/ CondChem Diet (1961), 274... 

A commonly used scale is Moh s Hardness Scale . This is a scale of relative hardness, and is not quantitative. Something with a hardness of 6 is not twice as hard as a hardness of 3. All this scale says is that something with a hardness of 6 is harder than all those things having hardnesses of less than 6 (Table 1.2). 

Quantitative tests of hardness involve indenting a material with a ball, cone, or wedge of hardened steel or other metal under a pre-determined pressure for a specific amount of time. The size and depth of the cavity left in the material being tested is then measured and a formula applied. The resulting value is the hardness, which, like Moh s hardness, has no units of measure. 

Moh s hardness 5-10, but includes other tough materials of lower hardness... 

Wide range of Moh s hardness although mainly less than 3 Tends to clog Wet grinding employed except for certain exceptional cases... 

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