Sulfidation resistance

J. S. Dunning and S. C. Rhoads, Effects of Ml Additions on Sulfidation Resistance of Some Fe-Cr-NiMlloys, Bureau of Mines, 1989,19 pp. 

Sulfidation-Resistant Nickel-Base Superalloy for FCC Flue Gas Expanders... 

Sulfur compounds, whether organic or inorganic in nature, cause sulfidation in susceptible materials. The sulfide film, which forms on the surface of much con-stmction materials at low temperatures, becomes friable and melts at higher temperatures. The presence of molten sulfides (especially nickel sulfide) on a metal surface promotes the rapid conversion to metal sulfides at temperatures where these sulfides are thermodynamically stable. High-alloy materials such as 25% Cr, 20% Ni alloys are widely used, but these represent a compromise between sulfidation resistance and mechanical properties. Aluminum and similar diffusion coatings can be of use. 

Most sulfur compounds resist the action of active Mn02 at low temperature. For instance, organic sulfides resist active Mn02 during the oxidation of allylic and benzylic alcohols.57 Thiols, being sulfur compouds with a greater oxidation sensitivity, are oxidized to disulfides.56... 

Cr Improves oxidation resistance. Detrimental to nitriding and fluorination resistance Improves sulfidation resistance beneficial to carburization and metal dusting resistance... 

Co Reduces rate of sulfur diffusion helps with sulfidation resistance improves solid solution strength improves solid solution resistance ... 

Ni Improves carburization, nitriding, and chlorination resistance detrimental to sulfidation resistance ... 

Austenitic steels provide excellent corrosion, oxidation, and sulfidation resistance with high creep resistance, toughness, and strength at temperatures greater than 565 °C. Thus they are used in refineries for heater tubes, heater tube supports, and in amine, fluid catalytic cracking (FCC), catalytic hydro-desulfurization (CHD) sulfur, and hydrogen plants. 

Sulfide-resistant calendered film. [Data from Mark RFD. Technical data sheet. Cromptonl]... 

Less reactive metals such as copper, silver, and gold can be found as free elements. The somewhat more reactive metals are present as sulfides formed early in Earth s existence (e.g., GuS, PbS, and ZnS). Because of their extremely low water solubility, sulfides resist oxidation and reactions with water and other ions. The still more reactive metals have been converted over millennia into oxides (e.g., MnOg, A Oj, and Ti02) and are mined in that form. 

There has also been recent interest in Nb-Al compounds as sulfidation-resistant coatings (Grzesik et al., 1995 Mitsui et al., 1996 Kai and Huang, 1997). Rates of sulfidation are generally low for refractory metals such as Nb - see the review by Mrow-ec (1995), for example. It is, however, uncertain whether such alloys will be effective in combined oxidizing/sulfidizing environments because of inadequate oxidation-resistance. 

Improved corrosion resistance through barrier or sacrificial protection Improved oxidation and/or sulfidation resistance Improved wear resistance Reduced fiictional energy losses... 

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