Oxide scales metal dusting

Common failures are because of oxidation, carburization, metal dusting, sulfidation, chlorination, and nitridation. The most common high-temperature degradation mode is oxidation, and the protection against oxidation is achieved by the formation of chromium oxide scale. Small amounts of aluminum or silicon may improve the resistance of chromia alloy. The attack by chlorine and sulfur depends strongly on the partial pressure of oxygen in the system. 

The process also requires additions of chloriding agents now and then their effect was investigated using trichlorethylene (TCE). The presence of TCE enhances the metal dusting attack markedly, most probably due to destruction of protective oxide scales. Upon sufficient H2S addition, this effect can be eliminated, but again the additions of H2S would have to be too high at temperatures >620 °C. 

Current methods of protection against metal dusting are either direeted to the process conditions - temperature, gas composition and sulphur content -or the development of a dense adherent oxide layer on the surface of the alloy by selective oxidation [5, 10-12]. This is done by the addition of chromium, and to a lesser extent aluminium and silicon. However, carbon can still dissolve in the base metal via defects in the oxide scale, meaning that metal dusting is not stopped, but slowed and delayed. 

Nickel alloys containing Cu, even though they did not have any oxide scales to protect against CO gas, were demonstrated to improve the metal dusting... 

Beryllium and its alloys (e.g., beryllium copper) have gained interest in the aerospace industry and specialty sports equipment industry in recent years. Brazing or riveting can be used for joining, but these methods are expensive, and distortion or highly stressed areas may be encountered. The metal must be handled with care when the processing produces dust, chips, scale, slivers, mists, or fumes, since airborne particles of beryllium and beryllium oxide are toxic with latent health effects. Abrasives and chemicals used with beryllium must be disposed of properly. 

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