Reactions of potassium chloride with chromium as a first step towards high temperature corrosion in biomass combustion

Reactions between potassium chloride (KCl) and chromium oxide (Cr₂O₃) as well as pure chromium (Cr) have been studied as model reactions for high temperature corrosion. The compounds have been used as powders because of their big area-to-mass ratio, which results in clearer signals in thermogravimetric measurements. The changes in mass and heat of reaction were measured by means of differential thermal analysis and thermal gravimetry (DTA/TG). The runs were performed mainly in synthetic air, but also nitrogen was used. After the DTA/TG runs the samples were analyzed with a scanning electron microscope (SEM).

Chromium oxide seems to be inert in the used conditions, but pure chromium reacted with potassium chloride forming chromium oxide as product. In some runs, a yellow intermediate, probably potassium chromate (K₂CrO₄) was detected. The reaction needs both oxygen and potassium chloride to proceed, but already a tiny amount of potassium chloride is enough to maintain the oxidation of chromium.