magnesium oxide(redirected from calcined magnesia)
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magnesium oxide:see magnesiamagnesia,
common name for the chemical compound magnesium oxide, MgO. It occurs as colorless, cubic crystals. It is refractory, melting at about 2,800°C;. It is very slightly soluble in pure water but is soluble in acids and solutions of ammonium salts.
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MgO, colorless crystals. Density, 3.58 g/cm3; melting point, 2800°C; boiling point, 3600°C. Magnesium oxide exhibits marked volatility at 2000°C. It is poorly soluble in water (6.2 ×10-4 g per 100 g H2O at 20°C). In the microcrystalline state (fine white powder), amorphous MgO absorbs water vapor and CO2 from the air to form Mg(OH)2 and MgCO3; it reacts readily with acids. Strongly calcined magnesium oxide loses its ability to combine with water and dissolve in acids.
Magnesium oxide occurs naturally as the rare mineral periclase. It is prepared industrially by calcination of magnesite and dolomite, as well as by the thermal dissociation of magnesium sulfate and basic magnesium carbonate, 3MgCO3.Mg(OH)2.3H2O. The properties of the commercial product, calcined magnesia, depend on the conditions of preparation, and the grades of the product are differentiated by apparent density (lightness), sorption, and chemical activity. Heavy magnesium oxides are used in the manufacture of refractories; lighter oxides are used in the preparation of magnesia cements and construction materials; and the lightest oxides are used to refine petroleum products and as fillers in the rubber industry. In medicine, magnesium oxide is prescribed for internal use as an alkali to counteract increased gastric acidity, and in cases of acid poisoning it has a mild laxative effect.