Electrochemical Determination of the Standard Free Energy of Formation of Alumina at Steelmaking Temperatures

Abstract

<p>A high temperature electrochemical formation cell</p> <p>[equation removed]</p> <p>has been used to determine the standard free energy of formation of alumina at steelmaking temperatures. The temperature variation of the free energy was determined as</p> <p>[equation removed]</p> <p>in the temperature range 1700º-1850ºK. These results are in good agreement with those reported in the literature at ~1300ºK using a similar technique but are 3.3% more positive than the generally accepted thermochemical value at 1800ºK. In order to confirm the absence of any systematic errors in the above cell, the following cell was designed and operated in the temperature range 1641º-1785°K</p> <p>[equation removed]</p> <p>The results from this cell are in good agreement with those of the first cell within the experimental error.</p> <p>The Third Law analysis of the present data gives an average value of the standard heat of formation of alumina at 298ºK, Hº₂₉₈, of -392.6 (± 0.92) kcal/mole which is in good agreement with the Third Law analysis of lower temperature cell (~1300ºK) data and the values of ΔHº₂₉₈ calculated from phase equilibria and solution calorimetric data in mineralogical systems. All these values are at variance with the presently accepted "best" value of ΔHº₂₉₈ = -400.40 (± 0.3) kcal/mole from oxygen bomb calorimetry, although the average of all bomb calorimetric data is in agreement. Using the presently determined ΔGºf (Al₂O₃), the temperature dependence of K = h²Al h³₀, the aluminum deoxidation constant, can be calculated as</p> <p>[equation removed]</p> <p>The value of K = 4.7x10⁻¹³ at 1600ºC is in good agreement with the most recent work of Jacquemont et al. (1973) and is an order of magnitude higher than previous calculations. An independent calorimetric determination of ΔHº₂₉₈ using a method other than oxygen bomb calorimetry is therefore suggested.</p>