Dense Ceramic Membranes for Oxygen Separation
This chapter provides an overview of major membrane concepts and materials. It discusses besides membranes made from a mixed ionic–electronic conducting, other membranes incorporating an oxygen ion conductor and presents data from oxygen permeability measurements on selected membrane materials. The rate at which oxygen permeates through a nonporous ceramic membrane is essentially controlled by two factors: the rate of solid state diffusion within the membrane and that of interfacial oxygen exchange on either side of the membrane. The basic assumption of the theory is that the lattice diffusion of oxygen or the transport of electronic charge carriers through the bulk oxide determines the rate of overall oxygen permeation. Besides the possibility of surface exchange limitations, oxygen transport through dense ceramics is necessarily influenced by the presence of high-diffusivity paths along internal surfaces such as grain boundaries.