Thesis Assignments

MSc assignment: Microstructure and performance of dual phase oxygen transport membranes

Announcing Institution:
Forschungszentrum Jülich GmbH, IEK-1 – Materials Synthesis and Processing,
and University of Twente – Electrochemistry Research Group

Starting date: anytime
Duration: 7 Month

Field of activity
Oxygen transport membranes (OTM) show great potential in future oxygen supply for sustainable processes in energy applications, e.g. syngas production, fuel processing. OTM possess mixed ionic electronic conductivity (MIEC) and, hence, do not consume any electrical power.

Single-phase MIEC materials with perovskite structure show the highest permeability so far. However, high permeability comes along with limited stability. Therefore, dual phase composites attracted great interest to overcome this trade-off. Major advantage is the opportunity to choose two inherently stable materials with distinct conductivities. There is a great flexibility in materials selection, although it is (of course) constrained by several requirements. Major requirements are

-          Chemical compatibility (no undesired reactions between the two phases),

-          Comparable thermal expansion behaviour (to avoid internal cracks), and

-          Percolation of ionic and electronic pathways (defining the quantity limits of
           each phase).

The IEK-1 of Forschungszentrum Jülich GmbH developed dual phase composites based on Gadolinia doped Ceria (Ce0.8Gd0.2O2, CGO) and a cobalt rich spinel (FeCo2O4, FCO) as ionic and electronic conductors, respectively. It turned out that a third phase forms during sintering, i.e. Gd- and Fe-rich perovskite (Gd,Ce)(Fe,Co)O3. This phase is electronically conductive and therefore contributes to oxygen permeation. However, initial tests showed that different synthesis routes led to a significant change in the oxygen permeation rate. Therefore, a systematic study on the influence of synthesis and processing on microstructure and successive performance is required.

Description of work

The aim of this work is to systematically study the influence of different synthesis routes on the microstructure of the sintered “dual phase membrane”, which actually is a multiphase composite. Major routes are a Sol-Gel technique (Pechini-synthesis) as well as oxide mixing (CGO, Fe2O3, Co2O3) and subsequent (reactive) sintering. After a literature review, different powders are synthesized and sintered into dense pellets. The influence of the powder synthesis on the sintering process is investigated. The microstructure of the sintered specimens is determined by SEM quantitatively. The different microstructures will be correlated to the resulting performance, e.g. oxygen permeation in lab conditions, electrical conductivity relaxation etc.

Requirements

Knowledge in materials science ideally ceramics; ability of hands-on lab work; good English skills

Contact persons - Forschungszentrum Jülich
Prof. Dr. Wilhelm A. Meulenberg
Phone: +49 2461 61-6323
E-Mail: w.a.meulenberg@fz-juelich.de   

Dr.-Ing. Stefan Baumann
Tel: +49 2461 61-8961
E-Mail: s.baumann@fz-juelich.de

Contact persons - University of Twente
Prof. Dr. Henny Bouwmeester
E-Mail: h.j.m.bouwmeester@utwente.nl
Tel:+31 53 489 2202

The main work will be carried out at Forschungszentrum Jülich in Germany. Forschungszentrum Jülich GmbH will cover some living costs for the stay in Jülich.