Magnesia hardness

Hard-burned magnesia is characterized by moderate crystaUite size and moderately low chemical reactivity. Hard-burned magnesia is readily soluble only in concentrated acids. 

Hard-burned magnesias may be used in a variety of appHcations such as ceramics (qv), animal feed supplements, acid neutralization, wastewater treatment, leather (qv) tanning, magnesium phosphate cements, magnesium compound manufacturing, fertilizer, or as a raw material for fused magnesia. A patented process has introduced this material as a cation adsorbent for metals removal in wastewater treatment (132). 

Supply of MU water for a medium-pressure (450 psig) WT boiler, from a surface water source with very variable suspended solids and hardness (sugar refinery, South Africa). The process used is a. carbonate removal using hot-lime precipitation softening coupled with silica adsorption by magnesia addition b. clarification in anthracite filters and c. cation ion-exchange for the balance of hardness removal. 

Manganese (Mn, [Ar]3t/S4.v2), name and symbol after the Latin magnesia nigra (black magnesia). Isolated (1774) by the Swedish chemist Johan Gottlieb Gahn. Silvery, hard, brittle metal. 

A similar decomposition lakes place with soluble salts of magnesia, and hence, when hard waters are used for washing, not a particle of 6oap will act as a detergent until the whole of the lime and magnesia is removed. 

Accelerators are second in importance only to sulphur. Their function is to accelerate the normally slow rubber-sulphur reaction, increase the rate of vulcanization, and increase productivity. Accelerators are classified into two main classes by types, namely organic and inorganic. The inorganic accelerators such as lime, litharge and other lead compounds and magnesia were employed extensively before the introduction of organic accelerators. They are still used mainly to produce hard rubber or ebonite products. Litharge is used in rubberized fabrics, insulated wires and cables and shoe compounds as well as chemical resistant rubber products... 

Very small gold particles can also be formed on magnesia and brucite (Mg(OH)2).55,83 Au/MgO made by deposition-precipitation contained particles smaller than 1 nm that were claimed to show icosahedral and fee cubo-octahedral structures,170 but this is hard to believe as the diameter of a single gold atom is already 0.29 nm, and lnm particles afflxed at the steps... 

The preparation of violet phosphorus may conveniently be carried out as follows —The air is displaced, by means of carbon dioxide, from a hard glass tube, which is then one quarter filled with ordinary phosphorus, the remainder of the tube containing pieces of lead, preferably those which have served for a previous preparation. The carbon dioxide is then removed, the tube sealed on the pump, and placed inside an iron tube, the space between the walls being filled with magnesia. The whole is heated in a tube furnace for 8 to 10 hours at a moderate red heat. After opening, with the usual precautions, the crystalline phosphorus is removed from the surface and the crystals from the interior are collected after dissolving the lead in 1 1 nitric acid. 

Xon-crystalline alloys of molybdenum and boron have been obtained by heating together molybdenum dioxide and boron in magnesia crucibles. These alloys, containing up to 46 per cent, of boron, decrease in density and increase in hardness with increase in the percentage of boron. They are not attacked by hydrochloric and hydrofluoric acids or by alkalies, but concentrated sulphuric acid acts on warming, and dilute nitric acid dissolves them in the cold. 

At higher lime contents, free lime is present in the clinkers. The Ca(OH)2 or Mg(OH)2 formed upon hydrating free lime (CaO or MgO) takes up more space than the original oxide. Therefore, CaO (or MgO) in coarse crystalline lumps gives rise to so-called lime bursting (or magnesia bursting ), since the reaction with water is very slow and continues after the cement is hard. 

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