Magnesium oxide thermal properties

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. 

By careful choice of the storage material, catalysts with differing storage capacities and thermal properties can be designed for applications with different temperature ranges. Typical adsorber materials are the alkali and alkaline-earth metal oxides, e.g. barium, magnesium, potassium and cesium. 

Applications of thermal radiation spectroscopy to expins and pyrots are readily apparent. As a consequence of the highly exothermic nature of explns and flares, significant thermal radiation is emitted which can serve to characterize the reaction processes. The photometric properties of pyrots have been treated in Vol 8, P505-R. In practice, thermal radiation characteristics of explns do not always closely approximate black body properties since the system is non-equilibrium in nature and is time dependent. In addition, some pyrotechnically related materials such as aluminum oxide and magnesium oxide behave as gray bodies with emissivities well below unity. For such systems the radiant emission is reduced as shown in Fig 4... 

The physical and chemical properties of magnesium oxide are primarily governed by the source of the precursor, that is, derived from magnesite or precipitated from brine or seawater. Other important factors include time and temperature of calcination and the presence of trace impurities. Electron microscope studies have revealed that the precursor particle morphology has a large impact on the morphology of the final MgO particle. It has been shown that when brucite and magnesite crystals are thermally decomposed at low temperatures, pseudomorphs of a size and shape similar to the parent crystal are formed. 

Reasons for use abrasion resistance, cost reduction, electric conductivity (metal fibers, carbon fibers, carbon black), EMI shielding (metal and carbon fibers), electric resistivity (mica), flame retarding properties (aluminum hydroxide, antimony trioxide, magnesium hydroxide), impact resistance improvement (small particle size calcium carbonate), improvement of radiation stability (zeolite), increase of density, increase of flexural modulus, impact strength, and stiffness (talc), nucleating agent for bubble formation, permeability (mica), smoke suppression (magnesium hydroxide), thermal stabilization (calcium carbonate), wear resistance (aluminum oxide, silica carbide, wollastonite)... 

When a PA is to be used in applications requiring self-extinguishing characteristics and flame retardant properties, it is necessary to resort to the addition of a flame retardant. Flame retardant formulations, known in the field of poly(ester)s, can be widely adapted to PAs. Brominated poly(styr-ene) in combination with an antimony compound, such as sodium antimon-ate, can be used." The performance is improved when a minor amount of calcium oxide is added. The thermal stability of these compositions is much better in comparison to formulations with magnesium oxide or zinc oxide. 

Itatani K, Tsujimoto T, Kishimoto A (2006) Thermal and optical properties of transparent magnesium oxide ceramics fabricated by post hot-isostatic pressing. J Eur Ceram Soc 26 639-645... 

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