It is of great importance to understand the mechanism and the rate of Al
2O
3 dissolution into cryolite melt. This study is mainly concerned with the direct observation of melt through microscope and mesuring the dissolution rate of various type of Al
2O
3 by using the hot-thermo couple technige. The experimental results indicated that the dissolution pattern of Al
2O
3 in cryolite melt is divided into three types due to difference in crystal form irrespective of shape and size of Al
2O
3 and mode of press. The dissolution pattern of θ, δ and κ-alumina obtained by calcination of boehmite and gibbsite at low temperature showed type I and these dissolution proceeded rapidly from top part of Al
2O
3 into melt. On the other hand, the dissolution rate of Al
2O
3 obtained from gibbsite was very small and showed type II or III. Such classification was dependent upon the content of α-alumina expressed by relative X-ray intensity of α-alumina in the calcined products. The effect of addition of other fluorides to the cryolite melt upon the dissolution rate has been also investigated. The addition of NaF was found effective to increase the dissolution rate of alumina.
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