Coatings for corrosion protection of porous substrates in gasifier components

Deposition of several coatings by Chemical Vapor Deposition in a Fluidized Bed was studied inside porous coupons made of 409 steel. Four different coating systems were studied: TiAlSiN/TiAl/SS409, TiAlSiN/TiAlSi/SS409, TiAlN/Nb/TiAl/SS409 and TiSiN/Nb/TiSi/SS409. Though coating thickness decreased with depth inside the porous filter, the formation of Ti-based ceramic films with thicknesses around 1 micrometer was observed 0.5 mm inside the bulk of the samples. Coated substrates were exposed to a simulated coal gas at 643 K for 300 hours, in order to study their corrosion resistance under conditions that mimic a porous metal particulate filter of a coal gasification system. Some of the coatings did not provide enough protection against corrosion at the bulk of the porous coupons, and iron sulfide crystals were formed that plugged the pores. On the other hand, the TiSiN/Nb/TiSi/SS409 system showed no sign of corrosion.