Magnesium oxide temperature

Brunauer and co-workers [129, 130] found values of of 1310, 1180, and 386 ergs/cm for CaO, Ca(OH)2 and tobermorite (a calcium silicate hydrate). Jura and Garland [131] reported a value of 1040 ergs/cm for magnesium oxide. Patterson and coworkers [132] used fractionated sodium chloride particles prepared by a volatilization method to find that the surface contribution to the low-temperature heat capacity varied approximately in proportion to the area determined by gas adsorption. Questions of equilibrium arise in these and adsorption studies on finely divided surfaces as discussed in Section X-3. 

Light or heavy magnesium carbonate is exposed to a red heat, and carbon dioxide and water are expelled leaving light or heavy magnesium oxide. The density is also influenced by the calcining temperature higher temperatures yield more compact forms. 

Thermal Properties. Because all limestone is converted to an oxide before fusion or melting occurs, the only melting point appHcable is that of quicklime. These values are 2570°C for CaO and 2800°C for MgO. Boiling point values for CaO are 2850°C and for MgO 3600°C. The mean specific heats for limestones and limes gradually ascend as temperatures increase from 0 to 1000°C. The ranges are as follows high calcium limestone, 0.19—0.26 dolomitic quicklime, 0.19—0.294 dolomitic limestone, 0.206—0.264 magnesium oxide, 0.199—0.303 and calcium oxide, 0.175—0.286. 

When magnesium oxide is chlorinated in the presence of powdered coke or coal (qv), anhydrous magnesium chloride is formed. In the production of magnesium metal, briquettes containing CaCl2, KCl, NaCl, MgO, and carbon are chlorinated at a temperature such that the electrolyte or cell melt collects at the bottom of the chlorinator, enabling the Hquid to be transferred directly to the electrolytic cells. 

Magnesium nitrate is prepared by dissolving magnesium oxide, hydroxide, or carbonate in nitric acid, followed by evaporation and crystallization at room temperature. Impurities such as calcium, iron, and aluminum are precipitated by pretreatment of the solution with slight excess of magnesium oxide, followed by filtration. Most magnesium nitrate is manufactured and used on site in other processes. 

A fourth alkalinity control additive is magnesium oxide [1309A8A], which is used in clay-free polymer-base fluids (47). Magnesium oxide provides an alkaline environment and, as it is only slightly soluble, also has a buffering effect. It enhances the thermal stabHity of polymer solutions by preventing a pH decrease to neutral or slightly acidic conditions at elevated temperatures. It is mainly appHed in completion or workover operations where clay-free acid-soluble fluids are desired. 

Isopropyl alcohol can be oxidized by reaction of an a,P-unsaturated aldehyde or ketone at high temperature over metal oxide catalysts (28). In one Shell process for the manufacture of aHyl alcohol, a vapor mixture of isopropyl alcohol and acrolein, which contains two to three moles of alcohol per mole of aldehyde, is passed over a bed of uncalcined magnesium oxide [1309-48-4] and zinc oxide [1314-13-2] at 400°C. The process yields about 77% aHyl alcohol based on acrolein. 

At room temperature, the bisulfite pH inflection poiat occurs at pH 4.5 and the monosulfite at pH 9. Analogous equations can be written for magnesium, calcium, and ammonia. The starting raw materials, ia addition to sulfur, are sodium hydroxide, magnesium oxide, calcium carbonate, or ammonia, depending on the base used. The four commercial bases used ia the sulfite process are compared ia Table 4. 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

MI Cables (mineral insulated cables. Fig. 10-181) are the electric heat tracers of choice for high-temperature applications. High-temperature applications are generally considered to maintain temperatures above 250°F or exposure temperatures above 420°F where self-regulating heaters cannot be used. MI cable consists of one or two heating wires, magnesium oxide insulation (from whence it gets its... 

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... 

This is an endothermic reaction in which a volume increase accompanies dehydrogenation. The reaction is therefore favoured by operation at reduced pressure. In practice steam is passed through with the ethylbenzene in order to reduce the partial pressure of the latter rather than carrying out a high-temperature reaction under partial vacuum. By the use of selected catalysts such as magnesium oxide and iron oxide a conversion of 35-40% per pass with ultimate yields of 90-92% may be obtained. 

The high heat resistance produced by adding phenolic resins to solvent-borne CR adhesives is due to the formation of the infusible resinate, which reduces the thermoplasticity of the adhesive and provides good bond strength up to 80°C (Table 11). The resinate also increases the adhesive bond strength development by accelerating solvent release. 4 phr of magnesium oxide for 40 phr of phenolic resin are sufficient to produce a room temperature reaction. A small amount of water (1-2 phr) is necessary as a catalyst for the reaction. Furthermore, the solvent... 

The reaction is carried out under an inert atmosphere in an open crucible at approximately 830°C. Figure 1 shows typical equipment used for direct oxide reduction. Vitrified magnesium oxide ceramic is commonly used as a container material, but tungsten and tantalum can also be used(3). If the latter are used, CaF2 is added to lower the temperature needed to liquify... 

Self-Test 7.23B Estimate the temperature at which magnesium carbonate can be expected to decompose to magnesium oxide and carbon dioxide. 

Metallic magnesium is produced by either chemical or electrolytic reduction of its compounds. In chemical reduction, first magnesium oxide is obtained from the decomposition of dolomite. Then ferrosilicon, an alloy of iron and silicon, is used to reduce the MgO at about 1200°C. At this temperature, the magnesium produced is immediately vaporized and carried away. The electrolytic method uses seawater as its principal raw material magnesium hydroxide is precipitated by adding slaked lime (Ca(OH)2, see Section 14.10), the precipitate is filtered off and treated with hydrochloric acid to produce magnesium chloride, and the dried molten salt is electrolyzed. 

A ceramic monolith catalyst support, cordierite, consisting of silica, alumina and magnesium oxide. The purpose of this is to provide support, strength and stability over a wide temperature range. 

---