Dead-burning

It is also used as a reducing agent in the production of pure uranium and other metals from their salts. The hydroxide (milk of magnesia), chloride, sulfate (Epsom salts), and citrate are used in medicine. Dead-burned magnesite is employed for refractory purposes such as brick and liners in furnaces and converters. 

Dead-burned dolomite is a specially sintered or double-burned form of dolomitic quicklime which is further stabilized by the addition of iron oxides. Historically, it was used as a refractory for lining steel furnaces, particularly open hearths, but as of this writing is used primarily in making dolomite refractory brick (see Refractories). 

PefractoTy lime is synonymous with dead-burned dolomite, an unreactive dolomitic quicklime, stabilized with iron oxides, that is used primarily for lining refractories of steel furnaces, particularly open hearths. 

Hardness. Most limestone is soft enough to be readily scratched with a knife. Pure calcite is standardized on Mohs scale at 3 aragonite is harder, 3.5—4. Dolomitic limestone is generally harder than high calcium. Dead-burned or sintered limes are 3—4 on this scale, whereas most commercial soft-burned quicklimes are 2—3 (see Hardness). 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

Except for dead-burned dolomite, all limes are much more reactive with acids than limestone. The high calcium types are the most reactive. 

In Germany and Japan, pulverized quicklime is used in making self-fluxing sinters, partially replacing limestone. Granular dead-burned dolomite is stiU used to protect the refractory lining of open-hearth and electric furnaces, but not the basic oxygen furnace. Refractory time has declined with the... 

Dead-burned magnesia, characterized by large crystaUite size and very low chemical reactivity, is resistant to the basic slags employed in the metals refining industry. It reacts very slowly with strong acids, and does not readily hydrate or react with carbon dioxide unless finely pulverized. 

Table 20. Purity of Dead-Burned Magnesia from Various Processes ...

Calcination or dead burning is used extensively to dehydrate cements (qv) and hygroscopic materials such as MgO, and to produce a less water sensitive product. Calcination is also used to decompose metal salts to base oxides and to produce multicomponent or mixed oxide powders for... 

Magnesium oxide. The natural minerals, i.e., magnesite (MgCO ), brucite [Mg(OH)9], etc., after being crushed to predetermined size, are calcined at temperatures varying from 1055 to 2000 K, depending upon whether a caustic or a dead-burned produc t (periclase) is being... 

Totpunkt, m, dead point, dead center, tot-reif, a. dead ripe, -rosten, t.t. dead-roast, dead-burn, -sicher, a. dead sure, cocksure, Totspulen, n. Petroleum) mudding off, water ing off. 

Dead burned magnesium oxide is suitable as an expanding additive [368-370]. The expansion occurs by a hydration mechanism. The additive is particularly effective when used at setting temperatures greater than approximately 150° C. Enhanced adhesion of expanded cements can be achieved by the addition of urea-formaldehyde resins [1720]. 

Dead-block coders, 7 691 Dead-burned dolomite, 15 27, 53 Dead-end filtration, 11 388 15 827, 829 Dead end hydrogenation reactor, 10 811, 812... 

Calcination temperature is very important in the production process and dictates the particle size, purity and reactivity of the product. A dead-burned, sintered dense microcrystaUine product is obtained at calcination temperature of 1,400 to 1,700°C. A caustic-burned product is obtained when magnesium carbonate or hydroxide is calcined at 600 to 700°C. A hght grade (specific gravity 2.9) highly reactive caustic-hurned magnesia that contains some moisture and carbon dioxide is obtained at about 600°C. A denser form from... 

Inert Simulants for High Explosives. In certain physical tests on weapons explosives, eg the effects of humidity and temp cycling on the dimensional stability of the weapon, it is desirable to simulate the explosive filler by an inert filler. Many such inert simulants have been proposed and tested (Refs 1, 2 3). Simulants for Comp B TNT have been patented (Ref 4). The simulant for Comp B consists of a mixt of 30% of 1,2 hydroxystearic acid, 5% wood rosin 65% dead-burned gypsum. The simulant for TNT is a 40/60 mixt of hydroxystearic acid dead-burned gypsum... 

II Anhydrite 11 insoluble anhydrite inactive anhydrite dead-burned gypsum chemical anhydrite mineral anhydrite Produced hy calcining at 250-1.000 C. Relatively inert. Reactivity depends upon calcining-time-lemperaiure relationship and particle size. 

Terra alba or dead-burned, fine white gypsum is used as a paper filler, in plastics, and as an exlender far titanium dioxide. Pharmaceutically pure gypsum can be added to bread and other bakery products, finds use in beer production, and as a pharmaceutical-tablet diluent. In Japan, calcium sulfate is used in making tofu, a soyabean curd. 

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