„Zwischen den Zeiten” – Aphorismen über und aus Natur und Wisenschaft – von Hans-Jürgen Quadbeck-Seeger

✍ Scribed by W. Schütz

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 103 KB
• Volume: 27
• Category: Article
• ISSN: 0933-5137
• DOI: 10.1002/mawe.19960270909

✦ Synopsis

Table 3. Transfer coefficients ci and the steady state open-circuit potential E for various concentrations of Fe"+/Fe2+ on oxide covered Ti electrodes [oxides formed at 0.6 V vs HgIHgzSO4 in aerated NaZS04 + H2S04 (pH = 3 ) ] Redox conc.1M E n Rc EImV 2.5 x 10-4 0.301 0.65 1 -42 5.0 x 0.240 0.682 -41 7.5 x 10-4 0.210 0.699 -40 1.0 x 10-3 0.180 0.699 -42 2.0 x 10-3 0.132 0.699 -40 Tables. 2 and 3 show that the values of the transfer coefficient for the cathodic process (a,) remain with the normal value (0.5-0.7) and independent of the film thickness. On the other hand, the values of the transfer coefficient for the anodic process (a,) are always lower (0.16-0.34). The low values of a, show that the anodic electron transfer reactions through the oxide are being hindered. This reflects the semiconducting character of titanium oxides. Similar behaviour was observed for Ti oxides [ I , 41, for Sn oxides [8] and for Ta oxides [9]. No regular decrease of a, was found here with increaseing the oxide thickness.