By 2020 Finland targets to obtain at least 38% of its energy from renewable sources. Solid biomass is one of the most important energy sources for meeting these targets. However, fouling, slagging and corrosion threaten long-term operation availability and costs of biomass power plants. A high concentration of potassium in biomass fuel tends to result in the formation of compounds with low melting points. Significant amounts of highly corrosive alkali chloride in the flue gases emanate through these processes. Slags on superheaters often constitute a considerable percentage of the complex inorganic phases. However, thermodynamic properties of the complex inorganic compounds and their combined effect with the chlorides have been either poorly studied or not available. The current project will give new information concerning properties of the metallic sulfates, chlorides and their phase mixtures, which will help to solve slagging and high temperature corrosion related problems.