The operation behavior of ceramic surface filters was examined at temperatures between 300 degrees C and 500 degrees C with redispersed carbon-rich ashes from biomass and coal. The duration of the first 50 filtration cycles was used to derive it measure of operating stability. For the same ash materials, data on thermal expansion (by dilatometer) and weight loss (by TGA) were obtained from measurements of oxidizing and inert gas atmosphere. As a result, alkaline content in the ash changes the filtration behavior as well as a change of particle properties in conjunction with the oxidation reaction of the ash carbon. (C) 2007 Elsevier B.V. All rights reserved.