Corundum number

The reference intensity ratio method is based on the experimentally established intensity ratio between the strongest Bragg peaks in the examined phase and in a standard reference material. The most typical reference material is corundum, and the corresponding peak is (113). The reference intensity ratio k) is quoted for a 50 50 (wt. %) mixture of the material with corundum, and it is known as the corundum number . The latter is commonly accepted and listed for many compounds in the ICDD s Powder Diffraction File. Even though this method is simple and relatively quick, careful account and/or experimental minimization of preferred orientation effects are necessary to obtain reliable quantitative results. 

The Fe—O distances in hematite are 1.99 and 2.06 A. The (Mn,Fe)—O distances in bixbyite are expected to be the same in case that (Mn, Fe) has the coordination number 6, and slightly smaller, perhaps 1.90 A, for coordination number 4. The radius of 0= is 1.40 A, and the average O—O distance in oxide crystals has about twice this value. When coordinated polyhedra share edges the O—O distance is decreased to a minimum value of 2.50 A, shown by shared edges in rutile, anatase, brookite, corundum, hydrargillite, mica, chlorite, and other crystals. Our experience with complex ionic crystals leads us to believe that we may... 

The growth of vanadium oxide overlayers on Rh(l 11) converges after a number of intermediate stages to the formation of a three-dimensional bulk-like epitaxial V203 film [90], which is oriented with the (0 0 01) plane of its corundum structure parallel to the Rh(l 1 1) substrate surface. The V203 phase is the thermodynamically stable... 

The number of oxide type minerals is quite large. Rostov (1956) has identified 160 specific minerals, grouped them into classes (chrysoberyl, spinel, corundum, periclase, etc.), and proposed a classification system. Only a few examples will be discussed here. 

Chromium(III) acetylacetonate, physical properties, 6 528t Chromium alloys, 6 468-523 Chromium alumina pink corundum, formula and DCMA number, 7 347t Chromium antimony titanium buff rutile, formula and DCMA number, 7 347t Chromium-based catalysts, 20 173 Chromium baths, 9 800-804... 

A number of different gas, oxide, and metal reference electrodes have been used in molten cryolite. The A1(III)/A1 couple produced by placing molten aluminum in a sintered corundum or boron nitride tube is the traditional reference electrode [33]. However, a CO2/C electrode has also been used. This electrode consists of a graphite-covered copper tube C02 gas is passed through the tube and allowed to bathe the graphite surface while it is immersed in the melt [32]. 

Corundum is aluminum oxide, q -A1203, which has a hexagonal crystalline structure that is analogous to hematite. However, water treatment systems most often use activated alumina, which is typically produced by thermally dehydrating aluminum (oxy)(hydr)oxides to form amorphous, cubic (y), and/or other polymorphs of corundum (Clifford and Ghurye, 2002, 220 Hlavay and Poly k, 2005 Mohan and Pittman, 2007). When compared with corundum, amorphous alumina tends to have higher surface areas, greater numbers of sorption sites, and better sorption properties. 

A number of oxides are economically important ore minerals, such as hematite (iron), chromite (chrome), zincite (zinc), and cassiterite (tin). Some gemstone species are oxides, including corundum (ruby and sapphire), spinel, and chrysoberyl. Corundum is the second hardest natural substance and is used as an abrasive. 

For a large number of cases and applications, a metal oxide is more important than the metal itself. Many oxides are found native in nature or are formed spontaneously (e.g., Ti02, which is used in white paint and in the whitening of paper), while others are artificially produced from the metal itself (e.g., AI2O3, which protects aluminum from surface mechanical damage and corrosion it is produced by an electrolytic industrial process, and it also occurs in nature as the mineral corundum). 

Diamond is indeed far harder than corundum, and recent modifications of the Mohs scale have been su ested which assign a much larger hardness number, such as 15, to diamond. 

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