Available online at www.sciencedirect.com Journal of the European Ceramic Society 32 (2012) 1041–1052 Optimization of the strength of SOFC anode supports H.L. Frandsen a,∗ , T. Ramos a , A. Faes b , M. Pihlatie c , K. Brodersen a a Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark b Design & Materials Unit, University of Applied Sciences Western Switzerland, CH-1950 Sion, Switzerland c VTT - Technical Research Centre of Finland, FI-02044 VTT, Finland Received 4 September 2011; received in revised form 3 November 2011; accepted 12 November 2011 Available online 14 December 2011 Abstract During operation solid oxide fuel cells are stressed by temperature gradients and various internal and external mechanical loads, which must be withstood. This work deals with the optimization of the strength of as-sintered anode supported half-cells by imposing changes to production parameters, such as powder milling and sintering temperature. The strength was measured with the ball-on-ring method, and analyzed with a large displacement finite element model. Weibull statistics were used to describe the distribution of strengths. The influence on the Weibull strength of the many different processing parameters was found to be quantifiable in terms of cell porosity to a large extent. The results were validated with an independent set of measurements of strength and stiffness by uniaxial tension and the impulse excitation technique, respectively. For application of the finding in relation to the SOFC technology a mathematical frame to determine the optimal porosity of a SOFC system is presented. © 2011 Elsevier Ltd. All rights reserved. Keywords: Strength; Fuel cells; Sintering; Porosity; Optimization 1. Introduction One of the main challenges with solid oxide fuel cell (SOFC) technology is to ensure durable and stable operation for higher economical feasibility. Hence, in the development of the technol- ogy, a great deal of attention is directed towards cell degradation, integrity of the sealings, and other processes that can affect system efficiency. 1,2 Failure of a cell in a stack will decrease the stack efficiency, as well as shorten the lifetime of the stack considerably. Thus, development should focus not only on elec- trochemical but also on mechanical performance of SOFCs. Half-cells consisting of a tape-cast anode support, sprayed YSZ electrolyte, and sprayed Ni/YSZ cermet are already pro- duced on a pre-pilot plant scale at the Fuel Cell and Solid State Chemistry Division, Risø DTU. Lately, in view of the expected advantages, an effort has been made to develop and optimize the manufacturing of fully tape cast half-cells. This offers, at first glance, the possibility of reducing the number of manufacturing steps, as it allows one-step sintering. Also, a reduction of overall production waste makes lower production costs feasible. During ∗ Corresponding author. Tel.: +45 4677 5668; fax: +45 4677 5858. E-mail address: hlfr@risoe.dtu.dk (H.L. Frandsen). this development, the strength of the cells has been measured as a function of different production parameters. Variations of one or several of these parameters may introduce different flaw distri- butions, resulting in varying mechanical strength. The strength and indirectly the flaw distribution are typically represented by a Weibull distribution, 3–5 which is also the case for this work. The present work shows how modification of various produc- tion parameters, shaping, sintering temperature, milling period, and material composition influences the strength. The interest- ing finding is that independent Weibull strength correlates very well to the as-sintered porosity independent of which process- ing parameter is varied. Thus the porosity can be considered as a convoluting parameter, which accounts for all the processing parameter variations. This is an important observation in relation to production optimization, as this to a great extent can be done in terms of porosity and consequently opens for non-destructive quality testing as the impulse excitation technique. Another important finding in this work is the high decrease of Weibull strength with porosity, which is only observed in few other ceramics. Thus an independent set of experiments are conducted to confirm the finding, and to test the validity of the non-destructive testing in the production aspect. This is done by measuring the strength with uniaxial tension and the stiffness by the impulse excitation technique. 0955-2219/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2011.11.015