Abstract
A new concept to inhibit Metal Dusting on the catalytically active surface of steel based on the application of tin was investigated. The target of this investigation is to reduce the affinity of high alloy steel surfaces towards carbon deposition and uptake in general. To avoid the reaction of carbon with iron or nickel its deposition has to be prevented by blocking the catalytically active centers on the metal on the atomic scale by an inhibitor, which has a stronger bonding to those metals. Tin was used because of its similarity with carbon concerning its position in the periodic system in the fourth main group. First trials to develop a diffusion coating on alloy 800, 690 and P91 tests show a good solubility of nickel in the tin-rich phase. All over the diffusion zone a stable almost 5:4 ratio of nickel and tin is present. On the surface crystallites of Ni3Sn2 develop at 650°C. The melting point of this phase with 40 at% Sn is 1264°C. In the crystal structure of this alloy, nickel is surrounded by tin, which can be interpreted as a blockage for carbon. In first tests in a Metal Dusting atmosphere (24% CO, 74% H2, 2% H2O) for 100 h and 330 h at 650°C no or very little coke deposition or carbide formation were observed on this modified surface.
