Refractory materials hardness

Representative Glasses, 10-250 Refractive index see Index of refraction Refractory materials hardness, 12-217... 

Refractoriness (Melting Temperature). Instantaneous grinding temperatures may exceed 3500°C at the interface between an abrasive and the workpiece being ground (14). Hence melting temperature is an important property. Additionady, for alumina, sdicon carbide, B C, and many other materials, hardness decreases rapidly with increasing temperature (7). Fortunately, ferrous metals also soften with increasing temperatures and do so even more rapidly than abrasives (15). 

Cemented carbides are fairly expensive owing to the use of hard, refractory materials. This is expected to become even more the case as some of the strategic materials used in these tools become more expensive or newer but more expensive materials such as HfC or HfN come into more common use. 

Cemented carbides belong to a class of hard, wear-resistant, refractory materials ia which the hard carbides of Group 4—6 (IVB—VIB) metals are bound together or cemented by a soft and ductile metal biader, usually cobalt or nickel. Although the term cemented carbide is widely used ia the United States, these materials are better known iatemationally as hard metals (see also Refractories Refractory coatings Refractory fibers). 

Bluish-black, very hard crystals. Used as an abrasive and refractory material. 

The most extensive group of nitrides are the metallic nitrides of general formulae MN, M2N, and M4N in which N atoms occupy some or all of the interstices in cubic or hep metal lattices (examples are in Table 11.1, p. 413). These compounds are usually opaque, very hard, chemically inert, refractory materials with metallic lustre and conductivity and sometimes having variable composition. Similarities with borides (p. 145) and carbides (p. 297) are notable. Typical mps (°C) are ... 

Lupton, D. and Aldinger, F., Possible Substitutes for Tantalum in Chemical Plant Handling Mineral Acids, in Trends in Refractory Metals, Hard Metals, and Special Materials and Their Technology, Proceedings of the 10th Plansee Seminar, Reutte, Austria 101-130 (1981)... 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

Titanium (TiC) is an important industrial material produced extensively by CVD. It is an excellent refractory material which is unusually hard with high strength and rigidity and outstanding wear resistance. Its properties are summarized in Table 9.8. 

Silicon carbide (carborundum) Talc Bluish-black, very hard crystals. Used as an abrasive and refractory material. A hydrous magnesium silicate used in ceramics, cosmetics, paint and pharmaceuticals. 

Aluminum oxide, which has the mineral name corundum, is a solid that has several important uses. Because it will withstand very high temperatures, it is a refractory material, and because of its hardness it is commonly used in abrasives. Corundum often contains traces of other metals that impart a color to the crystals, making them valuable as gemstones. For example, ruby contains a small amount of chromium oxide, which causes the crystal to have a red color. By adding a small amount of a suitable metal oxide, it is possible to produce gemstones having a range of colors. 

Alundum. A pure crystalline AlaOj in granular form, d 3.9-4.0, mp 2030-2050°, hardness on the Mohs scale 9- It has been used as an abrasive, a basic refractory material, as a component of low-expansion glasses, as a filtering material and for chemical apparatus. It is probably suitable as a component of primer compns in lieu of glass, etc... 

Oxide Aluminum oxide, alumina AI1O3, white solid, insoluble, melting point 2020 C. formed by heating aluminum hydroxide to decomposition when bauxite is fused in the electric furnace and then cooled, there results a very hard glass ( alundum ), used as an abrasive (hardness 9 Mohs scale) and heat refractory material. Aluminum oxide is the only oxide that reacts both 111 H20 medium and at fusion temperature, 10 form salts with both acids and alkalis. 

Solid borides have high melting points, exceptionally high hardness, excellent wear resistance, and good immunity to chemical attack, which make them industrially important with uses as refractory materials and in rocket cones and turbine blades. Some metal borides have been found to exhibit superconductivity. 

Corundum, a-Al203, is a hard and chemically inert material that is a useful abrasive and refractory material that has the composition A1203. When traces of other metals are present,... 

When carbon forms compounds with other atoms having rather high electronegativity (Si, B, etc.), the bonds are considered to be covalent. The compounds formed, especially SiC, have the characteristics of being hard, unreactive refractory materials. Silicon carbide has a structure similar to diamond, and it is widely used as an abrasive material. It is prepared by the reaction of Si02 with carbon ... 

Elemental crystalline boron is nearly inert—for example, it reacts with hot concentrated nitric acid only in finely powdered form, and not at all with boiling HF. The bulk solid is extremely hard and is a refractory material, the /3-rhombohe-dral form melting at 2180°C. 

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