Magnesium oxide particles

It is apparent, then, that the choice of cone surface area will give widely different results. Experiments in which fine magnesium oxide particles are dispersed in the gas stream have shown that the flow streamlines remain relatively unaffected until the Schlieren cone, then diverge from the burner axis before reaching the visible cone. These experiments have led many investigators to use the Schlieren cone as the most suitable one for flame speed evaluation. 

Direct experimental determinations of these quantities do not exist. The nearest approach seems to be in some observations made by Nicolson (26) in his work on surface tension. He found that when he made magnesium oxide particles by burning magnesium in air, their lattice constants were the same as those of the bulk material. When the crystals were made by the decomposition of magnesium carbonate in vacuo, the expected change in lattice parameter took place due to the surface tension. These negative results obtained in the first method of preparation were attributed to the presence of gases adsorbed from the air. 

Examination of 95 workers exposed to an unspecified concentration of magnesium oxide dust revealed slight irritation of the eyes and nose the magnesium level in the serum of 60% of those examined was above the normal upper limit of 3.5mg/dl. No evidence of any pulmonary inflammatory response was found in six volunteers after short-term (36min) exposure to high concentrations (137.0mg/m ) of fine and ultrafine magnesium oxide particles. ... 

Kuschner WG, Wong H, D Alessandro A et al Human pulmonary responses to experimental inhalation of high concentration fine and ultrafine magnesium oxide particles. Environ Health Perspect 105(11) 1234—1237, 1997... 

The extinction curves for magnesium oxide particles (Fig. 11.2) and aluminum particles (Fig. 11.4) show the dominance of surface modes. The strong extinction by MgO particles near 0.07 eV( - 17 ju.m) is a surface mode associated with lattice vibrations. Even more striking is the extinction feature in aluminum that dominates the ultraviolet region near 8 eV no corresponding feature exists in the bulk solid. Magnesium oxide and aluminum particles will be treated in more detail, both theoretically and experimentally, in this chapter. 

FIGURE 5.2. Photograph of a natural gas-air flame on a rectangular burner, with very small magnesium oxide particles introduced into the flow and illuminated stroboscopically in order to make the gas streamlines visible (from [11], courtesy of B. Lewis and of Academic Press). 

The annular air flow was seeded with magnesium oxide particles with a nominal diameter of 3-5 /un. Signiflcant droplets and particles were available in the main spray to obtain good signal-to-noise ratios. 

This reaction proceeds at a very high temperature(at low temperature it turns back). When we superfluously add shellac or another organic substance to a composition, this reaction takes place, and the generation of the magnesium oxide particles in the flame is reduced to decrease the continuous spectrum. This is clearly obs.erved on a spectroscopic photograph. At the end of the flame the reaction reverses, and MgO appears as white smoke and C is oxidized to CO or COi by the oxygen in the air. Too much organic material produces soot therefore the practical limit of the content may be of 15 > 20%. 

The reaction is exothermic, which occurs with the loss of some ammonia, and can be retarded by the addition of borax or sodium tripolyphosphate (STPP). The reactions described by Abdelrazig et al. (1988 and 1989). show that the solution of ADP in water forms ammonium and phosphate ions immediately, which react with the magnesium oxide particles in suspension. At the initial stages of the reaction, when phosphate concentration is at its highest, the intermediate tetrahydrate schertelite is formed. As the... 

Magnesium oxide particles in the 2- to 7-p.m median particle size range deposit in the convection pass preferentially, while finer sized particles are not deposited and tend to get carried into the back end of the boiler. When an MgO of 2-p.m median particle size is fed into the fuel at treatment rates of 0.5-1.0 parts by weight Mg to 1.0 part V in the oil, the quantity of MgO deposited on the superheater tubes is 2-3 times that of the V and Na. This treatment rate results in a high Mg V ratio, which is needed to raise the ash-melting point and reduce tube deposits. 

Goodman, A.L., Li, P., Usher, C.R., Grassian, V.H. Heterogeneous uptake of sulftn dioxide on aluminum and magnesium oxide particles. J. Phys. Chem. A 105, 6109-6120 (2001)... 

---