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Recrystallization of aluminium in the molten mixture of aluminium chloride and sodium chloride
2194
Short comrrxmioations
Much of the recent data of At-via et al applied to solutions containing glycerol, which was not used in our work, and examination of their paper reveals that the ratio Dq/T is distinctly viscosity-dependent, a fact that is not hidden but not pointed out. We have therefore ignored their statement that Dq/T is reasonably constant at (2.23 f 0.37) x N-lo cm2 poise/s”K since this does not accurately represent their glycerol-free data, nor is a percentage deviation of 16 per cent permissible. An average of their data for the glycerol-free solutions indicates Dq/T = 2.09 x 10-n’ and this expression has been employed in the present re-assessment. The groups affected by the revision are the Sherwood (k&JD) and Schmidt (g/pD) numbers, and the necessary alteration has been made to all the data, examples of the revision being given in Table 1. It can be seen that the revised diffusivities are lower by some 17 per cent than those used previously. The revised data are plotted in Fig. 1, in which the solid line represents (2) and the shaded area represents the data as previously calculated, and it is clear that there is now much closer coincidence with the theoretical line. CONCLUSIONS
1. The reason for the small but significant discrepancy between previous experimental and predicted mass transfer values has been diagnosed and corrected. 2. The reliability of the diffusivity data of Arvia et al has been substantiated by application to a different mass-transfer system. 3. The possibility of very close coincidence between experiment and prediction in electrochemical mass-transfer systems is emphasized. REFERENCES 1. T. K. Ross and A. A. WRAGG, Electrochim. Acta lo,1093 (1965). 2. A. J. A~VIA, J. C. BAZAN and J. S. W. CARROZZA,Electrochim. Acta 11,881 (1966). 3. J. C. BAZAN and A. J. A~VIA, Electrochim. Acta 10,1025 (1965). 4. A. J. ARVJA,S. L. MARCHIANOand J. J. PODESTA,Electrochim. Acta 12,259 (1967). 5. A. R. GORWN and A. COLE,J.phys. Gem. 40,733 (1936). 6. M. EISENBERG, C. W. TOBIAS and C. R. WILKE, J. electrochem. Sot. 103,413 (1956). 7. E. J. FENECHand C. W. TOBIAS,Electrochim. Acta 2,311 (1960).
Ekctrochimica Acta, 1968.Vol. 13,pp. 2194to 2195. Peqamon Press. Printedin NorthernIreland
RECRYSTALLIZATION OF ALUMINIUM IN THE MOLTEN MIXTURE OF ALUMINIUM CHLORIDE AND SODIUM CHLORIDE* T. NOTOYA Department of Metallurgy, Faculty of Engineering, Hokkaido University, Sapporo, Japan MID~RIKAWA~
found a crystallization phenomenon of aluminium in the molten mixture of aluminium chloride and sodium chloride in the temperature range from 100 to 200°C. The existence of low valency aluminium subhalide ions, Al(I) complexes for instance, in the bath was suggested to explain the phenomenon. We have now observed recrystallized aluminium in the bath in the temperature range 200 to 400°C.
Short communications
2195
Figure 1 shows an example of recrystallized aluminium deposited on a spiral wire of aluminium (2 mm in diamter and 1 m in length; main impurities, Cu OGlO6 %, Fe 0@003 %, Si 0@003 %) in the molten eutectic mixture of aluminium chloride (38 mol. %) and sodium chloride, the volume of which was about 11, in a glass vessel.
This was observed when the aluminium wire was immersed in the bath, which had been purified by adding small pieces of aluminium metal to reduce impurities for several days before use, and left for two days at 400 f 5°C. The recrystallized aluminium grew with time, as would be expected. Most crystals (cu 20 mg) were den dritic; there were a few whiskers. The cause of the recrystallization seems to lie not only in the oxidation-reduction process of subhalide ions of aluminium in the bath, but also in the corrosion resulting from temperature difference due to a thermoelectric cell* and/or from the difference of solubilities of Al(II1) in the bath. The morphology of the deposit and the factors influencing it are now under detailed investigation in our laboratory. author thanks Professor R. Midorikawa and Mr. T. Ishikawa, Faculty of Engineering, Hokkaido University, for helpful discussion.
Acknowledgements-The
REFERENCES I. R. 2. C.
h&XmIKAWA, J. electrochem. EDELMNLJ and J. G. GIBSON,
Sot. Japan 25,13 0957). J. Inst. Metals 88,321 (1959).
* Manuscript received I7 January 1968.
Short comrrxmioations
Much of the recent data of At-via et al applied to solutions containing glycerol, which was not used in our work, and examination of their paper reveals that the ratio Dq/T is distinctly viscosity-dependent, a fact that is not hidden but not pointed out. We have therefore ignored their statement that Dq/T is reasonably constant at (2.23 f 0.37) x N-lo cm2 poise/s”K since this does not accurately represent their glycerol-free data, nor is a percentage deviation of 16 per cent permissible. An average of their data for the glycerol-free solutions indicates Dq/T = 2.09 x 10-n’ and this expression has been employed in the present re-assessment. The groups affected by the revision are the Sherwood (k&JD) and Schmidt (g/pD) numbers, and the necessary alteration has been made to all the data, examples of the revision being given in Table 1. It can be seen that the revised diffusivities are lower by some 17 per cent than those used previously. The revised data are plotted in Fig. 1, in which the solid line represents (2) and the shaded area represents the data as previously calculated, and it is clear that there is now much closer coincidence with the theoretical line. CONCLUSIONS
1. The reason for the small but significant discrepancy between previous experimental and predicted mass transfer values has been diagnosed and corrected. 2. The reliability of the diffusivity data of Arvia et al has been substantiated by application to a different mass-transfer system. 3. The possibility of very close coincidence between experiment and prediction in electrochemical mass-transfer systems is emphasized. REFERENCES 1. T. K. Ross and A. A. WRAGG, Electrochim. Acta lo,1093 (1965). 2. A. J. A~VIA, J. C. BAZAN and J. S. W. CARROZZA,Electrochim. Acta 11,881 (1966). 3. J. C. BAZAN and A. J. A~VIA, Electrochim. Acta 10,1025 (1965). 4. A. J. ARVJA,S. L. MARCHIANOand J. J. PODESTA,Electrochim. Acta 12,259 (1967). 5. A. R. GORWN and A. COLE,J.phys. Gem. 40,733 (1936). 6. M. EISENBERG, C. W. TOBIAS and C. R. WILKE, J. electrochem. Sot. 103,413 (1956). 7. E. J. FENECHand C. W. TOBIAS,Electrochim. Acta 2,311 (1960).
Ekctrochimica Acta, 1968.Vol. 13,pp. 2194to 2195. Peqamon Press. Printedin NorthernIreland
RECRYSTALLIZATION OF ALUMINIUM IN THE MOLTEN MIXTURE OF ALUMINIUM CHLORIDE AND SODIUM CHLORIDE* T. NOTOYA Department of Metallurgy, Faculty of Engineering, Hokkaido University, Sapporo, Japan MID~RIKAWA~
found a crystallization phenomenon of aluminium in the molten mixture of aluminium chloride and sodium chloride in the temperature range from 100 to 200°C. The existence of low valency aluminium subhalide ions, Al(I) complexes for instance, in the bath was suggested to explain the phenomenon. We have now observed recrystallized aluminium in the bath in the temperature range 200 to 400°C.
Short communications
2195
Figure 1 shows an example of recrystallized aluminium deposited on a spiral wire of aluminium (2 mm in diamter and 1 m in length; main impurities, Cu OGlO6 %, Fe 0@003 %, Si 0@003 %) in the molten eutectic mixture of aluminium chloride (38 mol. %) and sodium chloride, the volume of which was about 11, in a glass vessel.
This was observed when the aluminium wire was immersed in the bath, which had been purified by adding small pieces of aluminium metal to reduce impurities for several days before use, and left for two days at 400 f 5°C. The recrystallized aluminium grew with time, as would be expected. Most crystals (cu 20 mg) were den dritic; there were a few whiskers. The cause of the recrystallization seems to lie not only in the oxidation-reduction process of subhalide ions of aluminium in the bath, but also in the corrosion resulting from temperature difference due to a thermoelectric cell* and/or from the difference of solubilities of Al(II1) in the bath. The morphology of the deposit and the factors influencing it are now under detailed investigation in our laboratory. author thanks Professor R. Midorikawa and Mr. T. Ishikawa, Faculty of Engineering, Hokkaido University, for helpful discussion.
Acknowledgements-The
REFERENCES I. R. 2. C.
h&XmIKAWA, J. electrochem. EDELMNLJ and J. G. GIBSON,
Sot. Japan 25,13 0957). J. Inst. Metals 88,321 (1959).
* Manuscript received I7 January 1968.