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Metallurgical and Materials Transactions B

, Volume 50, Issue 3, pp 1193–1203 | Cite as

Correlation of Oxygen and Aluminum Contents of Molten Titanium-Aluminum Alloys in Alumina and Calcia Crucibles

  • Mahdi FarhaniEmail author
  • Gereon Hils
  • Karl-Heinz Spitzer
Article
  • 74 Downloads

Abstract

As a key part of investigating a new proposed Ti-alloy production process, Ti-Al alloys were produced by aluminothermic reduction experiments at 1973 K in Al2O3 crucibles. Besides, pure Ti and Al were melted inside CaO crucibles at 1973 K to investigate the possibility of melt refining in equilibrium with CaO. The experiments were carried out in a vacuum induction furnace under argon gas at atmospheric pressure. The experimental results were proved by thermodynamic evaluations including also literature data. The correlation of oxygen and aluminum in Ti melt with 11 to 23 wt pct Al in contact with Al2O3 was assessed as \( 3\ln X_{\text{O}} = -\,2\ln X_{\text{Al}} - 9.1 \pm 0.4. \) This correlation in Ti melt with 3 to 10 wt pct Al in contact with CaO was \( 3\ln X_{\text{O}} = - \,2\ln X_{\text{Al}} - 14.9 \pm 0.3. \) Partial molar excess Gibbs free energies of mixing and combinations thereof in Ti-rich Ti-Al-O-Ca melt were assessed as \( RT \ln (\gamma_{\text{Al}}^{2} \cdot \gamma_{\text{O}}^{3} ) = - 894 \pm 6\,({\text{kJ}}/{\text{mol}}) \), \( RT \ln \left( {\gamma_{\text{Ca}} \cdot \gamma_{\text{O}} } \right) = - 195 \pm 4\,({\text{kJ}}/{\text{mol}}) \), \( RT \ln \gamma_{\text{O}} = - 258 \pm 6\,({\text{kJ}}/{\text{mol}}) \), \( RT \ln \gamma_{\text{Ca}} = 62 \pm 7\,({\text{kJ}}/{\text{mol}}). \) The activity of Al2O3 in CaO-saturated slag was assessed as 0.003 ± 0.001. The changes of Gibbs free energy for the dissolution of 1 wt pct oxygen and 1 wt pct calcium in Ti-Al melt were estimated as −630 ± 6 and −11 ± 7 (kJ/mol), respectively. A model was developed and applied to calculate the basic data for refining Ti-Al alloy.

Table of Symbols

〈i〉

Element or component ‘i’ in pure solid state

[i]

Element ‘i’ in dissolved state in metallic melt

[pct i]

Weight percent (mass pct, wt pct) of element ‘i’ dissolved in metallic melt

{i}

Element or component ‘i’ in gaseous state

(i)

Component ‘i’ in slag

\( a_{\text{i}} \)

Activity of ‘i’ with respect to Raoultian reference state (pure ‘i’ in its stable state) at 1 atm

Gi

Partial molar Gibbs free energy of ‘i’

Gi°

Molar Gibbs free energy of ‘i’ in its pure state

ΔGf,i°

Standard molar Gibbs free energy of formation of ‘i’

γi

Activity coefficient of ‘i’

Mi

Molar mass of ‘i’

ni

Amount of ‘i’ in moles

P

Pressure

Pi

Partial pressure of ‘i’

\( P_{\text{i}}^{^\circ } \)

Standard vapor pressure of ‘i’

R

The gas constant

T

Temperature

Xi

Mole fraction of ‘i’

Notes

Acknowledgment

The support of the German Research Foundation (DFG) within the research group 1372 (Grant No. SP492/5-1) is appreciated.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2019

Authors and Affiliations

  • Mahdi Farhani
    • 1
    Email author
  • Gereon Hils
    • 1
  • Karl-Heinz Spitzer
    • 1
  1. 1.Institute of MetallurgyClausthal University of TechnologyClausthal-ZellerfeldGermany

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