Development of stable oxygen transport membranes

Abstract

Chapter 1 provides an introduction of relevant developments in the field of oxygen transport membranes, and presents the aims of the work described in this thesis. In Chapter 2, the development of a versatile one-pot auto-combustion method for the synthesis of powders of the perovskite oxide titanium-doped strontium ferrate, SrTi1-xFexO3-δ (STF) is described. The method produces an almost phase-pure oxide powder with an ultra- fine crystallite size between 20-40 nm, and with a low level of organic residues. Highly sinter- active powders are obtained after calcination and ball-milling of the powders. Chapter 3 presents the results of compressive creep tests on perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1-xZrxO3-δ (BSCF-Z100 ⋅ x). Observed activation energies and stress exponents point to diffusional creep as the predominant mechanism for creep in BSCF-Z100 ⋅ x ceramics at temperatures above 850 °C. This is further supported by the fact that the observed grain-size-normalized creep rate varies little for the different BSCF-Z100 ⋅ x compositions. In Chapter 4, the results of compressive creep tests on mixed ionic-electronic conducting perovskite-type oxides SrTi1-xFexO3-δ (STF100 ⋅ x) are presented. Observed activation energies and stress exponents indicate that the steady-state creep rate for STF50 and STF70 is predominantly limited by cation lattice diffusion (Nabarro-Herring creep). The effective stress exponents reflect a contribution of dislocation creep to the mechanism of creep in STF30 (x = 0.3). Chapter 5 presents a study on solid solutions of SrTi1-xFexO3-δ, investigating their potential use as oxygen transport membrane. Oxygen transport properties such as chemical diffusion, oxygen surface exchange, and oxygen permeability as well as structural properties such as sintering, thermal and chemical expansion are investigated. The best compromise between structural and oxygen transport properties is found for an iron substitution level between 25-35%. In Chapter 6, the results of a case study into the effectiveness of cooperative learning in Dutch chemistry secondary education are presented. Cooperative learning increases information processing as compared to teacher-oriented learning (individual learning). In this study it also surfaced that students’ communication skills, essential for successful cooperation towards a joint goal, are improved as well as the importance of student motivation to study a specific topic.