Tairoring Amorphous Surface Alloys Resistant against High Temperature Corrosion

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One of the objectives of this work is to tailor amorphous surface alloys on conventional metals by sputter deposition in order to protect the underlying conventional metals against sulfidation and oxidation at high temperatures. Tailoring active catalysis from amorphous alloy precursors for hydrolytic decomposition of cholorofluorocarbon is another aim of this work. We succeeded to prepare amorphous Al-Mo, Al-Nb and Al-Ta alloys with high resistance against both sulfidation and oxidation. In addition, the above-mentioned alloys with small additions of silicon have been obtained for further enhancement of oxidation resisitance. It is the first time on the history of corrosion science that the alloys with low sulfidation rates which are comparable to the oxidation rates of oxidation-resistant conventional alloys are obtained. Sulfide scales formed on these alloys consist of an outer aluminum sulfide layr and an inner refractory metal sulfide layr, the latter of which has high protectiven … More ess against sulfidation. The amorphous alloys are converted to intermetallics at high temperatures where sulfidation and oxidation take place, but the formation of fine grained intermatallics is responsible for better adhesion of the alloys to the substrate metals. Silicone contained in the alloys form silicides with refractory elements in the alloys at high temperatures, and because the silicides are stable against oxidation, the presence of silicon suppresses oxidation of refractory elements. Amorphous surface alloys have been successfully prepared on 304 stainless steel and show high protectiveness against both sulfidation and oxidation at high temperatures.In the catalytic decomposition of a cholorofluorocarbon CCl_2F_2 by hydrolysis into CO_2, HCl and HF the catalyst should be exposed to very aggressive decomposition products. The active and durable catalysts have been obtained as a result of the catalystic reaction from amorphous Ni-Zr alloy precursors containing small amounts of chromium, molybdenum or tungsten. Less