THE STABILITY OF THE SEALING GLASS AF 45 IN H_2/H_2O - AND O_2/N_2 - ATMOSPHERES

摘要

The commercially available AF 45 - (SiO_2-B_2O_3-BaO-Al_2O_3-As_2O_3) glass has been successfully used for sealing SOFC - stacks operating at temperatures between 850 and 950℃. This solder shows low viscosity at lower temperatures. At temperatures between 800 and 1000℃, it crystallizes in a number of possible -modifications of celsian and SiO_2. These crystallographic modifications depend on the time-temperature path chosen and the reaction of the glass with the surrounding atmosphere. The crystallization increases the viscosity sufficiently to insure a gas - tight seal. X - ray diffraction analysis of the solder after stack - operation shows a fully or almost fully crystallized state of the material. From this, it could be concluded that part of the glass-forming agent, most likely B_2O_3 is lost. Thermodynamic calculations performed for reaction of AF45-glass with H_(2-), H_2/H_2O-, O_2-gases and air yield a number of volatile gas - species as reaction products which could be responsible for the removal of B_2O_3 and As_2O_3 and also the formation of pores.