Titre du document / Document title

Synergistic use of thermogravimetric and electrochemical techniques for thermodynamic study of TiO_x (1.67 < x < 2.0) at 1573 K

Auteur(s) / Author(s)

JACOB K. T. ⁽¹⁾ ; MANJURA HOQUE S. ⁽¹⁾ ; WASEDA Y. ⁽²⁾ ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, INDE
⁽²⁾ Institute for Advanced Materials Processing, Tohoku University, Sendai 980-8577, JAPON

Résumé / Abstract

A thermodynamic study of the Ti-O system at 1573 K has been conducted using a combination of thermogravimetric and emf techniques. The results indicate that the variation of oxygen potential with the nonstoichiometric parameter δ in stability domain of TiO_2-δ with rutile structure can be represented by the relation, Δμ_O2 = -6RT In δ - 711970(±1600) J/mol. The corresponding relation between non-stoichiometric parameter δ and partial pressure of oxygen across the whole stability range of TiO_2-δ at 1573 K is δ P^-1/6_O2. It is therefore evident that the oxygen deficient behavior of nonstoichiometric TiO_2-δ is dominated by the presence of doubly charged oxygen vacancies and free electrons. The high-precision measurements enabled the resolution of oxygen potential steps corresponding to the different Magneli phases (Ti_nO_2n-1) up to n = 15. Beyond this value of n, the oxygen potential steps were too small to be resolved. Based on composition of the Magneli phase in equilibrium with TiO_2-δ, the maximum value of n is estimated to be 28. The chemical potential of titanium was derived as a function of composition using the Gibbs-Duhem relation. Gibbs energies of formation of the Magneli phases were derived from the chemical potentials of oxygen and titanium. The values of -2441.8(±5.8) kJ/mol for Ti₄O₇ and -1775.4(±4.3) kJ/mol for Ti₃O₅ obtained in this study refine values of -2436.2(±26.1)kJ/mol and -1771.3(±6.9)) kJ/mol, respectively, given in the JANAF thermochemical tables.

Revue / Journal Title

Materials transactions - JIM    ISSN  0916-1821 

Source / Source

2000, vol. 41, n^o6, pp. 681-689 (29 ref.)

Langue / Language

Anglais

Editeur / Publisher

Japan Institute of Metals, Sendai, JAPON  (1989-2000) (Revue)

Mots-clés anglais / English Keywords

Thermodynamic properties

;

TGA

;

Electrochemical method

;

Titanium oxides

;

Chemical potential

;

Gibbs free energy

;

Rutile

;

Experimental study

;

Mots-clés français / French Keywords

Propriété thermodynamique

;

TGA

;

Méthode électrochimique

;

Titane oxyde

;

Potentiel chimique

;

Energie libre Gibbs

;

Rutile

;

Etude expérimentale

;

Mots-clés espagnols / Spanish Keywords

Método electroquímico

;

Energía libre Gibbs

;

Localisation / Location

INIST-CNRS, Cote INIST : 10153, 35400009100042.0060