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Mineral wool products, composed of stone wool fibers and organic binder, are used in many construction applications. Among all their beneficial properties, the most important requirement is safety for human health, such as when fibers are inhaled. For determining long-term toxicity, biosolubility and biopersistence studies in vitro and in vivo are essential. In vitro fiber dissolution rate, which depends on the medium, fiber composition, and the surface available for dissolution, is a key parameter in determining biopersistence of the material in vivo. We investigated how organic binder (phenol-urea-formaldehyde), which can partially shield fiber surfaces from the solution, influences fiber dissolution kinetics in synthetic lung fluid (modified Gamble's solution) at pH 4.5 and temperature 37 °C, in vitro. Dissolution experiments were made in batch and continuous flow using stone wool fibers with typical insulation product binder amounts (0-6 wt %), applied by the standard industrial process. Dissolution rates were determined from element concentrations in the reacted solution, and changes in fiber surface composition and morphology were monitored. Stone wool fiber dissolution was close to stoichiometric and was similar, whether or not the material contained binder. The high dissolution rate (508 ng of fiber/cm2/h) is explained by Al and Fe complexing agents, that is, citrate and tartrate, in the synthetic lung fluid. The organic binder mainly forms micrometer-sized discrete droplets on the fiber surfaces rather than a homogeneous thick coating. During in vitro tests, fibers with organic binder preferentially dissolved in the areas free of binder, forming cavities, whereas the untreated fibers dissolved homogeneously. Propagation of cavities undermined the binder droplets, leading to complete fiber dissolution. Thus, presence of organic binder on stone wool fibers, produced by the standard industrial process, had no measurable effect on dissolution rate in synthetic

Glass-based sealants have been developed with emphasis on filler material and surface treatment of the sealing components in order to optimise their mechanical and functional behaviour during the initial sealing process as well as during thermal cycling of the SOFC-stack after exposure to operating conditions. The bonding strength and microstructure of the interfaces between composite seals and interconnect materials were investigated as a function of surface treatment of the sealing surfaces, glass matrix composition, sealing pressure and temperature. The initial sealing performance and resistance to thermal cycling were then investigated on selected combinations of materials after ageing. Strongest bonding between sodium aluminosilicate glass composite and steel surfaces was obtained for sealing at 850°C. For the strongest interface, having shear strength of 2.35 MPa, rupture occurred in the glass matrix, meaning that the glass-steel interfaces are, in this case, even stronger. Application of transition metal oxide coatings on etched surfaces of Crofer 22APU steel showed a significant improvement in the development of a seamless transition zone between metal and glass, whereas the same coatings on a sanded surface showed no influence on the bonding strength, which on the other hand were all recorded at a fairly high level, only 15-20% less than the 2.35 MPa seen for the glass. Ageing and thermal cycling of sealed samples did not deteriorate the recorded strength.