Thermal magnesium compounds

Wet mixes are usually dried before calcination. Calcination is performed continuously in rotary or tunnel kilns, or batchwise in directly fired drum or box furnaces. The temperature at which the mixed metal oxide pigments are formed can be reduced by adding mineralizing agents [3.75]. In the case of chromium rutile pigments, addition of magnesium compounds [3.81] or lithium compounds [3.80] before calcination improves thermal stability in plastics. 

Magnesium oxide of high surface area can be produced by the thermal decomposition of various magnesium compounds. In the early work of Gregg and Packer (1955), a maximum specific area of about 200 m2g 1 was obtained by the calcination of Mg (OH) 2 at 380°C. This temperature was a little below the temperature required for the complete decomposition of the Mg(OH)2 under these experimental conditions. 

In view of the trend to more controlled and stereoselective reactions with readily available, less expensive and environmentally non-problematic reagents, the light-induced inner-sphere electron transfer between M-C bonds of less polar co-ordinating organometallics (Zn, Al) and the organic substrate seems to be a particularly attractive alternative to thermal reactions from organolithium or -magnesium compounds. 

The dicyclopentadienyl derivatives of these elements which are known at the present time (those of magnesium and calcium) are in many respects similar to those of the alkali metals, being colorless, saltlike compounds. The magnesium compound was successfully prepared by the interaction of sodium cyclopentadienyl and magnesium bromide in tetra-hydrofuran 214), by thermal decomposition of cyclopentadienyl magnesium bromide 214) and, recently, by the action of cyclopentadiene... 

Recently, the alkaline earth bis(tetraethylalanates) of calcium, strontium, and barium (see Table I) have been described 155). They are more stable thermally than the magnesium compounds, and those of calcium and strontium may be distilled without decomposition. The relatively high volatility of these substances indicates that they are less saltlike than the corresponding alkali compounds 155, 156). 

High-temperature The predominant industrial application of magnesium compounds is in the use of thermal insulation magnesite and dolomite in refractory bricks. Bricks of high-purity magnesia are (2%) exceptionally wear and temperature resistant, with high heat capacity and... 

The only really serious interference the authors found was that due to magnesium and, particularly, to calcium, as shown in Figure 8.10, which has been associated with the formation of stable magnesium and calcium phosphates in the air/acetylene flame. Huang et al. [69] found that titanium was the most efficient releasing agent, and that the addition of 1 g/L Ti removed all the interference completely, as shown in Figure 8.11. The mechanism was most likely the formation of a thermally stable compound with a Ti / Ca molar ratio of one. 

Tantalum. Numerous methods developed to extract tantalum metal from compounds included the reduction of the oxide with carbon or calcium the reduction of the pentachloride with magnesium, sodium, or hydrogen and the thermal dissociation of the pentachloride (30). The only processes that ever achieved commercial significance are the electrochemical reduction of tantalum pentoxide in molten K TaF /KF/KCl mixtures and the reduction of K TaF with sodium. 

Dibasic magnesium hypochlorite is more thermally stable than neutral or dibasic calcium hypochlorite. In addition, its decomposition, which starts at - 325° C, is endothermic rather than exothermic as in the case of the Ca compounds. 

In most instances, perfluoroaliphatic magnesium and lithium compounds exhibit less thermal stability than perfluoroaromatic compounds This instability imposes some stringent restrictions on their reactions A prior knowledge ol their stability at various temperatutes is fundamental to their subsequent use as or-... 

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