Inhibitor Coatings against High Temperature Corrosion

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The main goal of the present proposal is to elaborate the described novel coating approach, which can prevent the deposit corrosion at high temperatures often observed in land, marine, and aero turbine engines and chemical processes firing low quality fuels. The novel, proposed inhibitor coating should be obtained by modifying diffusion coatings with nano- or microscale particles. The pursued coatings will consist of a matrix of a typical diffusion coating such as aluminide in which inhibitor or salt mediating particles or combinations of both particles are randomly distributed. The advantage of such coatings is that, when corrosive substances such as sulphates or vanadates dissolve the otherwise protective alumina scale, the salt comes in contact with the added particles. The inhibitor particles will be sacrificed to form high-melting species or the corrosion will be retarded by a change in the acidity, making the melt less aggressive. The major objective is to test this new approach by investigating the efficiency of the coating and its chemical resistance as well as the underlying corrosion mechanisms. As a reference, an industrial state of the art, non-modified diffusion coating manufactured by low activity pack cementation will be used. The coatings will be exposed under two salt deposits that represent vanadate-enhanced (60%V2O5-40%Na2SO4 salt) and classical Na2SO4 type II corrosion for up to 1000h. In addition, cyclic oxidation tests will be performed to validate if the modifications themselves would affect the lifetime, e.g. by inducing cracks. Detailed investigation of the different short-, medium-, and long-term (up to 1000h) exposed samples of the different tests will be carried out.