Thermodynamic studies in liquid Fe-Nb-O, Fe-AI-O, Fe-Al-Mn-O systems, using solid electrolytes

Abstract

<p>A high temperature electrochemical technique has been developed, to continuously monitor the oxygen activity in iron based melts.</p> <p>The electrochemical cell used, can be represented as:</p> <p>Mo | Cr(s) -Cr₂O₃(s) | Calcia stabilised zirconia | Fe-M-O(ℓ) |Mo-ZrO₂, Mo cermet</p> <p>The electrolyte was in the form of a crucible to hold the metallic melt.</p> <p>The standard free energy change for the reactions:</p> <p>FeNb₂O₆(s) ⇆ 2NbO₂(s) + Fe(ℓ) + 2O lw/o</p> <p>FeNb₂O₄(s) ⇆ Al₂O₃(s) + Fe(ℓ) + O lw/o</p> <p>and the influence of manganese content of the melt on the oxygen activity for the equilibrium:</p> <p>(Fe1-x, Mnx)O.Al₂O₃(s) ⇆ Al₂O₃(s) + (1-x)Fe(ℓ) + xMn lw/o + O lw/o</p> <p>were determined using the technique at a temperature range of 1550 - 1600ºC.</p> <p>The results can be summarized as:</p> <p>(a) ΔGºT[FeNb₂O₆(s) - NbO₂(s)] = 105870 - 42.64ºT (±600) cal/mole FeNb₂O₆ [1550ºC - 1600ºC]</p> <p>(b) ΔGºT[FeAl₂O₄(s) - Al₂O₃(s)] = 49910 - 21.50 T(±300) cal/mole FeAl₂O₄ [1550ºC - 1600ºC]</p> <p>(c) Increasing the manganese content in the melt decreases the value of logh₀ in equilibrium with the transition reaction.</p> <p>The nature of the deoxidation inclusions of the liquid systems Fe-Nb-O, Fe-Al-O and Fe-Al-Mn-O were studied by X-ray analysis and their morphology by scanning electron microscopy. In the Fe-Nb-O system the inclusions were identified as NbO₂ and FeNb₂O₆ and appeared to form agglomerates of small crystallites.</p> <p>In the Fe-Al-O and Fe-Al-Mn-O the inclusions were identified as Al₂O₃ clusters along with FeAl₂O₄ or (Fe,Mn) Al₂O₄ respectively. The thermodynamic data obtained by the present technique are believed to be of high accuracy and the method significantly contributes in the studies of complex deoxidation systems at steelmaking temperatures.</p> <p>An attempt was made to use the present electro-chemical technique in studying the liquid Fe-Ti-O system at high oxygen potentials. Further research is suggested to fully resolve the results.</p>