F. Snijkers

Aqueous tape casting of yttria stabilised zirconia using natural product binder

Abstract A new and simple tape cast process has been developed for e.g. the fabrication of YSZ-electrolyte for solid oxide fuel cells (SOFCs). The method is environmentally friendly since it is water-based and uses a natural compound as a binder. The tape cast suspension was formulated taking into account a maximal solids loading, a minimum of organic compounds, colloidal stability, rheological and wetting properties. Green sheets of variable thickness (50–400 μm) have been prepared. After sintering, dense and defect-free electrolyte material, as required for SOFCs, was obtained. The microstructure and the surface of the sintered sheet material were characterised with FESEM.

Ion Transport and Thermomechanical Properties of SrFe ( Al ) O3 − δ – SrAl2O4 Composite Membranes

Moderate additions of monoclinic SrAl 2 O 4 to perovskite-type SrFe(Al)O 3-δ mixed conductors improve the sinterability and thermomechanical properties, including the thermal shock resistance, Vickers hardness, and fracture toughness, and decrease thermal expansion. The iron solubility in SrAl 2 O 4 , a mixed ionic and n-type electronic conductor with insulating properties, is lower than 5%. The total conductivity of SrAl 2 O 4 ceramics in air varies in the range 10 -7 -10 -5 S/cm at 973-1223 K. The transport properties and phase stability of dual-phase (SrFe) 1-x (SrAl 2 ) x O 2 (x = 0.3-0.7) composite membranes, where the partial dissolution of strontium aluminate in the ferrite phase leads to formation of A-site-deficient Sr 1-y Fe 1-2y Al 2y O 3-δ (y ≈ 0.08-0.12), are determined by the perovskite component. The total conductivity and Seebeck coefficient oxygen partial pressure dependencies exhibit general trends typical for SrFeO 3 -based solid solutions. Although the conductivity and oxygen permeability of (SrFe) 1-x (SrAl 2 ) x O z composites decrease with increasing x, the permeation fluxes through (SrFe)o.7(SrAl 2 ) 0.3 O z ceramics are comparable to those through single-phase SrFe 0.7 Al 0.3 O 3-δ . Under high p O2 gradients such as air/(H 2 -H 2 O), the oxygen transport is limited by surface-related processes, enabling stable operation of (SrFe) 0.7 (SrAl 2 ) 0.3 O 2 membranes. This composition was selected for fabrication of tubular membranes by the cold isostatic pressing. Surface modification of (SrFe) 0.7 (SrAl 2 ) 0.3 O z in order to enhance the exchange kinetics was found inappropriate from a stability point of view.

1.11 – Basic Aspects in Inorganic Membrane Preparation

Nowadays, a large variety of inorganic membranes exist, which include ceramic as well as metal membranes. The earliest developments involved membranes with pores in the micrometer range. The latest developments include microporous and dense membranes on the one hand and macroporous foams on the other hand. Despite this wide pore-size range, the synthesis of inorganic membranes shows some common aspects. n nAll synthesis starts from suitable powder preparation from precursor material. Subsequently, these powder particles are packed in a green product with a certain shape. After shaping, the synthesis of all inorganic membranes involves one or more heat treatments, leading to the final porous or dense microstructure of the membrane. To make dense or fine-porous membranes suitable for real applications, these membranes consist of a multilayer composition with a coarse-porous support providing the necessary mechanical strength, and the fine-porous or dense top layer responsible for the separation aimed at. In this manner, the membranes can combine a high flux and a high separation factor. In specific cases, the inorganic membranes are further functionalized in order to change the affinity of the membrane surface, or to obtain catalytically active membranes. n nThis chapter gives a concise but broad overview of all synthesis methods used, with emphasis on new trends and recent developments in this highly evolving field.