| Magnesium. In this investigation, it was demonstrated that magnesium can be removed from aluminum-based melts using dichloro-difluoromethane (CCl{dollar}sb2{dollar}F{dollar}sb2{dollar}). Experiments were performed in order to examine the effect of: (i) initial magnesium content of the alloy, (ii) bath temperature, (iii) total gas flowrate, (iv) initial gas composition, and (v) alloying elements on the reaction kinetics. It was found that as long as the magnesium content of the melt was greater than 0.5 mass percent, the rate of magnesium loss from the bath was a constant. For an 850 g melt containing 5 mass percent magnesium, and an initial gas composition of 10% CCl{dollar}sb2{dollar}F{dollar}sb2{dollar}-90% N{dollar}sb2{dollar}, the reaction rates ranged from 4.6 {dollar}times{dollar} 10{dollar}sp{lcub}-3{rcub}{dollar} %Mg/min at 685{dollar}spcirc{dollar}C to 3.1 {dollar}times{dollar} 10{dollar}sp{lcub}-2{rcub}{dollar} %Mg/min at 810{dollar}spcirc{dollar}C.; Based on kinetic considerations, it was postulated that a product layer surrounds the rising gas bubble. Using a high-temperature radiographic technique, it was possible to observe this product layer forming around the CCl{dollar}sb2{dollar}F{dollar}sb2{dollar} bubble.; The thermodynamic characteristics of the magnesium removal ("demagging") operation were modelled using the F{dollar}*{dollar}A{dollar}*{dollar}C{dollar}*{dollar}T computer package. Various dross samples generated during the demagging experiments were analyzed by X-ray diffreaction in order to confirm the computer predictions.; Silicon. An apparatus was designed and constructed to refine hypoeutectic aluminum-silicon alloys by fractional solidification of the melt. The best refinement obtained was a reduction from {dollar}sim{dollar}4.7 to {dollar}sim{dollar}0.9 mass percent silicon.; The refining ratios obtained were always greater than those predicted from theory. This may be due to entrapment of interdendritic liquid in the "cake." Any liquid not removed lowers the efficiency of the process. Also, the presence of iron in the sample may raise the observed refining ratio.; It was found that low fraction solids result in low refining ratios (i.e. a better refinement). Therefore, a compromise must be made between the purity of the product and the amount produced (i.e. yield). |
