Phase equilibria and thermodynamics of (silver  +  rhodium  +  oxygen)

✍ Scribed by K.T. Jacob; ; T. Uda; ; T.H. Okabe; ; Y. Waseda

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 244 KB
• Volume: 32
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.2000.0690

✦ Synopsis

An isothermal section of the phase diagram for (silver + rhodium + oxygen) at T = 1173 K has been established by equilibration of samples representing twelve different compositions, and phase identification after quenching by optical and scanning electron microscopy (s.e.m.), X-ray diffraction (x.r.d.), and energy dispersive analysis of X-rays (e.d.x.). Only one ternary oxide, AgRhO 2 , was found to be stable and a three phase region involving Ag, AgRhO 2 and Rh 2 O 3 was identified. The thermodynamic properties of AgRhO 2 were measured using a galvanic cell in the temperature range 980 K to 1320 K. Yttria-stabilized zirconia was used as the solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa was used as the reference electrode. The Gibbs free energy of formation of the ternary oxide from the elements, f G o (AgRhO 2 ), can be represented by two linear equations that join at the melting temperature of silver. In the temperature range 980 K to 1235 K, f G o (AgRhO 2 )/(J • mol -1 ) = -249080 + 179.08 T /K (±120). Above the melting temperature of silver, in the temperature range 1235 K to 1320 K, f G o (AgRhO 2 )/(J • mol -1 ) = -260400 + 188.24 T /K (±95). The thermodynamic properties of AgRhO 2 at T = 298.15 K were evaluated from the high temperature data. The chemical potential diagram for (silver + rhodium + oxygen) at T = 1200 K was also computed on the basis of the results of this study.