Undercooling of copper in refractory procelain crucible
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Undercooling of Copper in Refractory Porcelain Crucible Z.Y. JIAN, W. YAN, G.C. YANG, and Y.H. ZHOU Fig. 2—Current efficiency against volume fraction of CO2. Bold solid line: Eq. [10]; fine solid line: Eq. [12]; dashed line: Eq. [13] from Saakuan[5]; and line and crosses: Eq. [8] from Pearson and Waddington.[1]
with d 4 d 1 ⫽ and with CO2 equal to 1, ⫽ dCO2 (3 ⫹ CO2)2 dCO2 4 Eq. [11] reduces to
⫽ 0.25* (CO2) ⫹ 0.75
[12]
[5]
Saakyan, measuring volumes and CO2 concentration of anodic gas from industrial cells, proposed the empirical equation
⫽ 0.22* (CO2) ⫹ 0.73
[13]
This is very close to the proposed theoretical one (Figure 2). But the large gas volume measured (approximately 1.15 times the expected one) was attributed by the author to a large contribution by the Boudouard reaction. Measurement of current efficiency by oxygen balance in a laboratory aluminum cell can be easily performed and comparison with the Pearson and Waddington equation may also be done. Dorren et al.[6] and Hives et al.,[7] for example, did these types of measurements and both teams pointed out a discrepancy between these two approaches. However, reinterpretation of CO2 concentration in terms of carbide formation leads to excellent agreement between the two methods. The loss of current efficiency by the direct formation of carbide from the carbon of the anode implies that the Boudouard reaction and the primary formation of CO from the reduction of alumina are negligible in normal electrolysis conditions. It brings up again the question of the nature of the aluminum present in the bath that does not react with the carbon dioxide. The most dramatic implication of the carbide formation is that a larger portion of the excess carbon consumption is linked to the loss of current efficiency and that it cannot be reduced by improving anode performance and quality. REFERENCES 1. T.G. Pearson and J. Waddington: Disc. Faraday Soc., 1947, vol. 1, p. 307. 2. T.R. Beck: J. Electrochem. Soc., 1959, vol. 106, p. 710. 3. T.R. Beck: J. Electrochem. Soc., 1960, vol. 107, p. 577. 744—VOLUME 32B, AUGUST 2001
The first report of a large degree of undercooling in a bulk sample of metal was given by Bardenheuer and Blackmann,[1] who produced 258 ⬚C undercooling in a 150 g sample of iron by melting in a glass slag. Kattamis and Flemings[2] extended this technique to iron-nickel alloy. They made bulk samples of Fe-25 pct Ni alloy with weight of 1814 g undercooled to 300 ⬚C by melting in Pyrex glass. Subsequently, Powell and co-workers[3–6] applied the glass slag (soda lime glass) technique to bulk samples of silver, copper, and their alloys whose weights were in a range from 350 to 500 g. They made silver, Ag-0.12 pct O alloy, copper, Cu-0.08 pct O alloy, Cu-0.16 pct O alloy, and Cu-20 pct Ag alloy undercooled to 250 ⬚C, 251 ⬚C, 208 ⬚C, 218 ⬚C, 97 ⬚C, and 197 ⬚C, respectively. Kobayashi and Paul[7] obtained a undercooling of 236 ⬚C in a bulk sample of copper with weight of 30 g by using the similar glass slag as that of Powell (i.e., soda lime glass). Cob
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