Abstract
In this work crust samples were made in the laboratory. In the experimental part of this work it is shown that the crust formation is a heat transfer controlled process. Hence, the rate of penetration of bath into the loose alumina during crust formation is determined by the thermal diffusivity of the crust and the alumina. In the experiments a typical value for the rate of penetration was 0.5 mm/min for the lower part of the crust. The rate of penetration decreased as the crust thickness approached steady state, which was obtained after three to four hours. The bath phase inside the crust was partly liquid and partly solid, and it was shown that the bath segregated as it rose into the crust. Solid cryolite was precipitated in the lower parts of the crust, causing the remaining liquid bath to be enriched in AlF{sub 3} and CaF{sub 2}. In the top of the crust the NaF/AlF{sub 3} molar ratio (CR) of the bath phase had decreased to approximately 1.3, even though the CR of the bath flowing into the crust had a CR of approximately 2.4. A bath with a low CR deposited less solid cryolite inside the crust during
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Citation Formats
Rye, K Aa.
Crust formation in cryolite based baths.
Norway: N. p.,
1992.
Web.
Rye, K Aa.
Crust formation in cryolite based baths.
Norway.
Rye, K Aa.
1992.
"Crust formation in cryolite based baths."
Norway.
@misc{etde_10105843,
title = {Crust formation in cryolite based baths}
author = {Rye, K Aa}
abstractNote = {In this work crust samples were made in the laboratory. In the experimental part of this work it is shown that the crust formation is a heat transfer controlled process. Hence, the rate of penetration of bath into the loose alumina during crust formation is determined by the thermal diffusivity of the crust and the alumina. In the experiments a typical value for the rate of penetration was 0.5 mm/min for the lower part of the crust. The rate of penetration decreased as the crust thickness approached steady state, which was obtained after three to four hours. The bath phase inside the crust was partly liquid and partly solid, and it was shown that the bath segregated as it rose into the crust. Solid cryolite was precipitated in the lower parts of the crust, causing the remaining liquid bath to be enriched in AlF{sub 3} and CaF{sub 2}. In the top of the crust the NaF/AlF{sub 3} molar ratio (CR) of the bath phase had decreased to approximately 1.3, even though the CR of the bath flowing into the crust had a CR of approximately 2.4. A bath with a low CR deposited less solid cryolite inside the crust during formation than in crusts made with a bath with a normal CR. The proportion between liquid bath and solid cryolite was higher in all parts of crusts made with a low CR bath. It was hard to find experimental evidence that variations in the alumina parameters had any impact on the steady state thickness, overall density and overall thermal conductivity of crust. A statistical analysis of the experimental data indicated a lower crust thickness at high contents of fines and a high initial content of the alpha phase in the alumina. No significant correlations were found between the alumina parameters and the measured thermal conductivity of crust. A theoretical model indicated increasing thermal conductivity of crust with increasing content of fines in the range 0 to 35 wt%, however. 62 refs., 80 figs., 8 tabs.}
place = {Norway}
year = {1992}
month = {Apr}
}
title = {Crust formation in cryolite based baths}
author = {Rye, K Aa}
abstractNote = {In this work crust samples were made in the laboratory. In the experimental part of this work it is shown that the crust formation is a heat transfer controlled process. Hence, the rate of penetration of bath into the loose alumina during crust formation is determined by the thermal diffusivity of the crust and the alumina. In the experiments a typical value for the rate of penetration was 0.5 mm/min for the lower part of the crust. The rate of penetration decreased as the crust thickness approached steady state, which was obtained after three to four hours. The bath phase inside the crust was partly liquid and partly solid, and it was shown that the bath segregated as it rose into the crust. Solid cryolite was precipitated in the lower parts of the crust, causing the remaining liquid bath to be enriched in AlF{sub 3} and CaF{sub 2}. In the top of the crust the NaF/AlF{sub 3} molar ratio (CR) of the bath phase had decreased to approximately 1.3, even though the CR of the bath flowing into the crust had a CR of approximately 2.4. A bath with a low CR deposited less solid cryolite inside the crust during formation than in crusts made with a bath with a normal CR. The proportion between liquid bath and solid cryolite was higher in all parts of crusts made with a low CR bath. It was hard to find experimental evidence that variations in the alumina parameters had any impact on the steady state thickness, overall density and overall thermal conductivity of crust. A statistical analysis of the experimental data indicated a lower crust thickness at high contents of fines and a high initial content of the alpha phase in the alumina. No significant correlations were found between the alumina parameters and the measured thermal conductivity of crust. A theoretical model indicated increasing thermal conductivity of crust with increasing content of fines in the range 0 to 35 wt%, however. 62 refs., 80 figs., 8 tabs.}
place = {Norway}
year = {1992}
month = {Apr}
}