Internal chlorination of Ni-based alloys and its relation to volatilization corrosion

✍ Scribed by J. P. Tu; Z. Z. Li; Z. Y. Mao

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: German
• Weight: 711 KB
• Volume: 48
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19970480706

✦ Synopsis

Abstract

The kinetics of internal chlorination of Ni‐based alloys between 400°C and 700°C were investigated by optical and scanning electron microscopy. Internal chlorination of Ni‐4Cr and Ni‐4Cr‐0.5Ce alloy occurred by formation of solid precipitates such as CrCl~2~, and CeCl~3~ which are thermodynamically stable and have low vapor pressures at the temperatures within the alloy matrix. In the lower temperature range, the kinetics of internal chlorination nearly followed a parabolic rate law. The degree of internal chlorination increased with increasing temperature. In the higher temperature range, the internal attack was accompanied by the consumption of the alloy by volatilization. When the rate of internal chlorination equaled the rate of overall metal consumption, the depth of the internal chlorination zone would approach a steady state value. At high temperatures, where vaporization was predominant, the steady state depth of internal attack was even smaller than that at lower temperature. When an alloy specimen was subject to little volatilization, it showed more internal attack than when it was not, and vice versa.