Defining bath ratio in the presence of LiF and MgF{sub 2}
Conference
·
OSTI ID:371955
When Lewis acids other than AlF{sub 3} and Lewis bases other than NaF are present, the ratio of NaF to AlF{sub 3} is no longer a good measure of the Lewis acidity of molten Hall-Heroult bath. The following equivalent bath ratio was derived to give the same Lewis acidity at the same bath ratio as conventional bath ratio does without LiF or MgF{sub 2}: R{sub eq} = 0.5[(NaF)/42 + 0.32(LiF)/25.4] / [(AlF{sub 3})/84 + 0.41 (MgF{sub 2})/62.3]. Equal values of R{sub eq} produce essentially equal values of bath vapor pressure. However, at a specific R{sub eq}, LiF lowers: liquidus temperature, metal solubility, alumina solubility and bath density while raising electrical conductivity. At a specific R{sub eq}, MgF{sub 2} lowers: liquidus temperature, alumina solubility and electrical conductivity but increases bath density. Many important properties of the bath are not related its Lewis acidity. Perhaps bath ratio should be dropped from the vocabulary.
- OSTI ID:
- 371955
- Report Number(s):
- CONF-960202--; ISBN 0-87339-312-0
- Country of Publication:
- United States
- Language:
- English
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