Stannic Oxide is the dioxide SnO2 of tin that occurs in nature as cassiterite, is produced artificially as a crystalline powder when anhydrous, and is used chiefly in ceramic colors, in vitreous enamels and glazes as an opacifier, in glass, and in polishes
Stannic oxide is derived from tin. Widely known and used, tin comprises about 0.001 percent of the earth's crust. It is sometimes found alone, but generally is found as the oxide in the mineral cassiterite. Tin mines exist in England, Spain, Indonesia, Thailand, Zaire, Nigeria and China. Significant amounts of tin is also obtained through recycling. Tin is nontoxic, ductile, malleable, adheres to various metals and has a relatively low melting point. These properties lend to its usefulness as a rust-proofing material on iron, low-grade steels, copper, and copper alloys.
Tin forms two series of compounds, termed stannous and stannic. One of the most important compounds commercially is stannic oxide, which is useful as a catalyst in industrial processing, in ceramics and as a polishing powder for steel.
Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite. Cr2O3 adopts the corundum structure, consisting of a hexagonal close packed array of oxide anions with 2/3 of the octahedral holes occupied by chromium. Similar to corundum, Cr2O3 is a hard, brittle material (Mohs hardness 8-8.5). It is antiferromagnetic up to 307 K, the Neel temperature. It is not readily attacked by acids or bases, although molten alkali gives chromites (salts with the Cr2O2−4 anion, not to be confused with the related mineral chromite). It turns brown when heated, but reverts to its dark green color when cooled. It is also hygroscopic.
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