Magnesium oxide composition range

The powder is principally composed of zinc oxide (Table 6.2). Magnesium oxide is found in all current commercial brands in amounts that range from 3 to 10%. Alumina and silica are sometimes to be found. Present day compositions show less variation than formerly when bismuth, calcium and barium oxides, or sometimes no additives, were to be found in commercial examples (Paffenbarger, Sweeney Isaacs, 1933). 

At low temperatures magnesium oxide, MgO, which adopts the sodium chloride structure, is virtually a stoichiometric phase, but at high temperatures in the MgO-A1203 system this is not so. At 1800°C the approximate composition range is from pure MgO to 5 mol % A1203 95 mol % MgO. The simplest way to account for this composition range is to assume that point defects are responsible. For this, because both Mg2+ and Al3+ cations in this system have a fixed valence, electronic compensation is unreasonable. There are then three ways to account for the composition range structurally ... 

Kurzius and Boudart [58] have adopted the same approach as above specifically for the determination of fej by measuring first limits for mixtures of composition 2H2 + O2 and 9H2 + O2 in a 10.2 cm diameter vessel coated with magnesium oxide. Their analysis considered only reactions (i)—(iii) and the surface destruction of H atoms, for which they assumed the surface to have unit efficiency (the results for the two compositions studied seemed to support this). On this basis, however, their results do not appear to be completely consistent with those of Baldwin. Thus, at 520 °C the parameters derived by Baldwin for KCl coated vessels would predict a limit for 2H2 + O2 at ca. 5.7 torr in a 10.2 cm diameter vessel of unit efficiency. The observed limit was 4.56 torr. This difference is reflected in a h her value for namely 6.3 x 10 at 520 °C compared with Baldwin s f re of 4.6x10 l.mole. sec already quoted. Over the temperature range 800—1000 K, Kurzius and... 

Example 2-1 Wynkoop and Wilhelm studied the rate of hydrogenation of ethylene, using a copper-magnesium oxide catalyst, over restricted pressure and composition ranges. Their data may be interpreted with a first-order rate expression of the form r = (ki)pPH (A)... 

Colourless white flint soda glass has the following composition range silica (Si02) 59-75%, calcium oxide (CaO) 5-12%, sodium oxide (Na20) 12-17%, alumina (A1203) 0.5-3.0%, and possibly small quantities of ferric oxide, titanium dioxide, potassium and magnesium oxide. 

Therefore, the initial choice for an oxidizer is one with an exothermic heat of decomposition such as potassium chlorate (KCIO 3). However, mixtures of both chlorate and perchlorate salts with active metal fuels are too ignition-sensitive for commercial use, and the less-reactive - but safer - nitrate compormds are usually selected. Potassium perchlorate is used with aluminum and magnesium in some "photoflash" mixtures these are extremely reactive compositions, with velocities in the explosive range. 

The layered silicates hectorite and magadiite were synthesized using hydrothermal procedures based on those described in 111. For hectorite which contains lithium and magnesium atoms in octahedral sites between the silicate sheets, this synthesis procedure was modified. The crystallizations were carried out at temperatures ranging from 100°C to 200°C. The compositions of the reaction mixtures (expressed as molar ratios of the oxides) were ... 

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