Mössbauer study of the Impact of Hydrogen Fluoride on Tin Probe Ions Located on the Surface of Cr2O3 microcrystals

✍ Scribed by P.B. Fabritchnyi; M.I. Afanasov; I.S. Bezverkhy; M. Danot

• Book ID: 102604063
• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 311 KB
• Volume: 162
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9318

✦ Synopsis

Room-temperature exposure of tin-doped Cr 2 O 3 surfaces to HF induces in the 119 Sn MoK ssbauer spectra changes that depend on the valence state of the tin probe and show di4erences between the Sn(II)-and Sn(IV)-containing Cr 2 O 3 crystallite surfaces. In the Sn(II)-doped samples (Sn(II)/Cr 2 O 3 ), the Sn and Cr surface cations are coordinatively unsaturated, and upon exposure to HF chemical corrosion occurs. Preliminary contact of Sn(II)/Cr 2 O 3 with oxygen results in oxidation of Sn(II) to Sn(IV) and concomitant saturation of the coordination sphere of the surface cations; the apparent activity of HF then drastically decreases (passivation e4ect). Similar phenomena were previously observed for Sn(II)/ and Sn(IV)/Cr 2 O 3 samples exposed to HCl or H 2 S, i.e., acid gases containing anions much larger than F ؊ . Thus, the behavior of the dopant cations in the presence of acid gases should not be imputed to size incompatibility between oxygen vacancies and foreign anions coming onto the surface from its gaseous surrounding.