Thermogravimetric studies of high temperature reactions between potassium salts and chromium

• Published in: Corrosion science Vol. 59; pp. 55 - 62
• Main Authors: Lehmusto, J., Lindberg, D., Yrjas, P., Skrifvars, B.-J., Hupa, M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2012; Elsevier
• Subjects: A. Molten salts; Applied sciences; B. SEM; C. High temperature corrosion; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy; B. SEM; C. High temperature corrosion; A. Molten salts; Scanning electron microscopy; Temperature; C High temperature corrosion; A Molten salts; Chromium; High temperature; B SEM; High temperature corrosion; Molten salt
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2012.02.013

► K2CO3 reacted with Cr2O3 forming K2CrO4. ► Presence of chlorine did not alone explain the initiation of accelerated oxidation. ► More light was shed to the role of chromates in accelerated oxidation. ► Accelerated oxidation of chromia protected steels occurs in two consecutive stages. ► Both potassium and chloride are required, so that both stages of reaction occur. This study compares the high temperature reactions of potassium chloride (KCl) and potassium carbonate (K2CO3), two salts found in fly ashes formed in biomass combustion, with both pure metallic chromium (Cr) and chromium oxide (Cr2O3). The reactions were investigated with thermogravimetric measurements and the results discussed based on thermodynamic calculations. In simple terms: potassium chloride reacted with chromium forming potassium chromate (K2CrO4) and chromium oxide. Potassium chloride did not react with chromium oxide. Potassium carbonate reacted with chromium oxide, but not with chromium. The presence of potassium is sufficient to initiate accelerated oxidation, but chloride is needed to sustain it.