Abstract
During biomass combustion alkali chloride particles are formed, depositing on the metallic surface or on the already-formed oxide layer. Subsequently, they react with the metal or the oxide layer and accelerate the oxidation process. The goal of this work was to study the first formation and localized reactions of alkali chloride particles with iron and iron oxide surfaces at temperatures from 300°C to 500°C to establish models for particle-induced corrosion. To investigate these reactions, equipment for particle deposition by impactor and thermophoresis was installed and optimized for homogenous deposition. After deposition of potassium chloride (KCl), iron samples were exposed to N2-20 vol% O2 and N2-20 O2-0.05 vol% hydrochloric acid (HCl) atmospheres for short times at 300°C. In N2-20 vol% O2, some deformation and local spreading of the particles were observed, probably from melt formation in contact with the metal. Oxidation with HCl addition led to a significant increase of chlorine and oxygen contents on the KCl-deposited sample surfaces. Finally, thermogravimetric tests were conducted on deposits formed on iron at temperatures from 300°C to 400°C in Ar-5 vol% O2 atmospheres, with and without the addition of 0.05 vol% HCl. In the case of HCl addition, the mass increased rapidly in the beginning of oxidation. The iron chloride or chlorine-rich layer was formed directly at the metal scale and under the oxide layer.
