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Date of Award

1-1977

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Metallurgy

Supervisor

D.A.R. Kay

Abstract

A high temperature electrochemical technique has been developed, to continuously monitor the oxygen activity in iron based melts.

The electrochemical cell used, can be represented as:

Mo | Cr(s) -Cr₂O₃(s) | Calcia stabilised zirconia | Fe-M-O(ℓ) |Mo-ZrO₂, Mo cermet

The electrolyte was in the form of a crucible to hold the metallic melt.

The standard free energy change for the reactions:

FeNb₂O₆(s) ⇆ 2NbO₂(s) + Fe(ℓ) + 2O lw/o

FeNb₂O₄(s) ⇆ Al₂O₃(s) + Fe(ℓ) + O lw/o

and the influence of manganese content of the melt on the oxygen activity for the equilibrium:

(Fe1-x, Mnx)O.Al₂O₃(s) ⇆ Al₂O₃(s) + (1-x)Fe(ℓ) + xMn lw/o + O lw/o

were determined using the technique at a temperature range of 1550 - 1600ºC.

The results can be summarized as:

(a) ΔGºT[FeNb₂O₆(s) - NbO₂(s)] = 105870 - 42.64ºT (±600) cal/mole FeNb₂O₆ [1550ºC - 1600ºC]

(b) ΔGºT[FeAl₂O₄(s) - Al₂O₃(s)] = 49910 - 21.50 T(±300) cal/mole FeAl₂O₄ [1550ºC - 1600ºC]

(c) Increasing the manganese content in the melt decreases the value of logh₀ in equilibrium with the transition reaction.

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.

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.

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.

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