Refractories chromite

In technological practice, refractories are usually classified according to content of SLO2 and divalent oxides, as acid, neutral or basic types. The acid types comprise silica refractories and siliceous fireclay neutral refractories are alumina, mullite and chromite refractories magnesite, chrome-magnesite and dolomite refractories are... 

Chromite refractories are employed in furnaces as partings between the silica and magnesite bricks and heiice are considered neutral. They consist principally of crushed and ground chromite, and bricks are molded from this material which may be bonded together with a small amount of clay or burnt magnesia by pressing under a heavy pressure. The bricks are then dried and fired to a temperature of about cone 16. The composition of these refractories fluctuates between the following values ... 

Figure 10.6. Capillary Impregnation of a magnesia chromite refractory by a calcic slag...

Neutral refractory materials include graphite, charcoal, coke, chromite and various carbides. 

The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure. 

During much of the nineteenth century, the United States was the principal world producer of chromite ore (37). However in the latter twentieth century the United States has become completely dependent on imports from South Africa and Turkey (chromite) South Africa, Zimbabwe, Turkey, and Yugoslavia (ferrochromium) and the Philippines (chromite for refractory brick). 

Refra.ctories, Refractory products are prepared from a wide variety of naturally occurring materials such as chromite [1308-31 -2] and magnesite [546-93-0] or from clays predominandy composed of kaolinite. Increasingly, higher purity synthetic materials are being used to obtain special properties. On the other hand, for many refractory uses, a somewhat lower fusion point than that provided by kaolinite may be adequate, so that clay materials having a moderate amount of other components as, for example, iUite, may be satisfactory. High alumina clays are also used extensively for the manufacture of special types of refractories. 

Magnesia-base refractories, 15 425 Magnesian quicklime, 15 28 Magnesia products, 15 323 Magnesioferrite, in chromite, 6 474 Magnesioriebeckite, 3 288-289 Magnesite, 15 321, 387, 389-390... 

Chromium metal is produced hy thermal reduction of chromium(III) oxide, Cr203 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr203 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with A1 powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen. 

Chromite or Chrome Iron Ore, (Chrome Iron Stone) (Chromerz, Chromeisenstein, Chromit or Ferrochrom in Ger), Q O. FeO or Fe2(Cr02)2- This ore, which is the most important commercial source of chromium and and its compds, is not found in nature in pure form but mixed with oxides of A1 and/or Mg. Its color varies from iron-blk to brn-blk or streak dr brn. There are several grades metallurgical, refractory, or chemical av d 4.6 and hardness 5.5. Several methods for production of chromium from chromite are known, such as silicothermic, alumino-thermic electrolytical... 

Krishnaswamy R. 1984. Study of availability and composition of metal bearing wastes (generated in titanium extraction and fabrication, aluminum smelters, chromite bearing refractory and foundry sands and mercury battery industries). Report to US Bureau of Mines, Washington, DC, by NH Parker, PE and Associates, La Crescenta, CA. NTIS No. PB84-207091. 

Acids do not attack chromite, but fusion with alkali hydrogen sulphates effects its decomposition. The Grecian ore, which occurs mainly in the Eastern Provinces and in the island of Skyros, is particularly refractory on account of the impurities it contains. Chrome iron ores containing some Fe203 may be regarded as mixtures of chromite and chromitite (p. 17). Platmiferous chromites are found in the Urals.1... 

Chromia Chromite Cr2Fe04 is the most commonly used chromium-containing mineral for ceramic formulations. This mineral has a spinel crystal structure, where the iron may be replaced by magnesium and aluminum. Chromite is used in ceramics largely as a refractory in the form of burned and chemically bonded bricks. For this purpose, a low-silica material is desired. When low silica is desired, chromic oxide is extracted from chromite by dissolution in add, removal of the iron impiu-ity by liquid—liquid extraction, and precipitation of the hydroxide, which is subsequently calcined to the oxide. Chromic oxide is used as a color additive to azes and enamels and in ferrite production to give magnetic materials. 

Chromite is used in steel works as a refractory material for lining and repairing basic hearth furnaces. In its resistance to corrosion, and durability, it is superior to magnesite and silica-alumina mixtures. It vithstands sudden temperature changes, resists abrasion, and its hardness is but little affected at high temperatures. 

Kamenetsky V. S., Sobolev A. V., Eggins S. M., Crawford A. J., and Arculus R. J. (2002) Olivine-enriched melt inclusions in chromites from low-Ca boninites, Cape Vogel, Papua New Guinea evidence for ultramafic primary magma, refractory mantle source and enriched components. Chem. Geol. 183, 287-303. 

Chrome-magnesite, 352—353, 383—385 Chrome Ore, 383 — 384 Chromite, 383—384 refractories, 385 Chromium oxide, 32, 389 Chrysotile, 48 Circular kiln, 299 Clay minerals, 33—34 Clays, 33-38, 313 Clinoensfatite, 46-48, 316-317 Coatings, 399—416 Coefficient of thermal expansion, see thermal expansion Coesite, 17 Colemanite, 142... 

The range of materials used as refractories is very wide and includes such substances as the fireclays and kaolins, quartzites, bauxites, schist, magnesite, dolomite, graphite, carborundum, fused alumina, chromite, magnesium aluminate, magnesium silicate, zirconium oxide, zirconium silicate, boron nitride, and others. 

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