Co-extrusion of multilayered ceramic micro-tubes for use as solid oxide fuel cells

Abstract

Current methods to manufacture tubular solid oxide fuel cells (SOFCs) involve multiple steps of extrusion, layer deposition and sintering, leading to high manufacturing costs. The aim of the work presented in this paper is to reduce the cost of manufacturing SOFCs. This is achieved by developing a method for manufacturing a five-layered micro-tubular structure by a multi-billet co-extrusion process. With the implementation of continuous screw extrusion equipment, this co-extrusion process could easily be adapted into a fully continuous manufacturing process. The co-extrusion process presented initially involves rheologically unifying five pastes made up of individual powder compositions. It is shown that it is possible to formulate the pastes with in an optimum solids loading region where the die land rheological properties are relatively insensitive to small variations in solids loading, thus allowing for a more stable process. These pastes are then extruded as billets from separate extrusion barrels through a single nozzle. This uses a novel die design which does not require the use of a central mandrel to form the tubular structure. The sintered structure comprises four Ni/YSZ anode layers and a YSZ electrolyte layer, each layer being approximately 60 μm thick, forming a tube with an outer diameter of 3 mm and an inner diameter of 2.4 mm.