Available online at www.sciencedirect.com Journal of Power Sources 177 (2008) 1–8 Optimal heating trajectories of controlling green tapes of YSZ electrolyte deformation using TMA during thermal processing Leo Chau-Kuang Liau ∗ , Chung-Chun Chen Yuan Ze Fuel Cell Center, Department of Chemical engineering and Materials Science, Yuan Ze University, Chung-Li 320, Taiwan Received 15 October 2007; received in revised form 9 November 2007; accepted 9 November 2007 Available online 21 November 2007 Abstract The optimal heating trajectories to minimize the time required for the organic additives removal in yttria-stabilized zirconia (YSZ) green tapes were determined using a dynamic optimization method. The removal process model was described by the mass transport of the volatile gas evolved from the thermal decomposition of the organic additives inside the tapes and the kinetics of the decomposition. The pressure buildup of the sample tapes formed by the volatile gas can be estimated by a numerical simulation method; meanwhile, the deformation (strain) of the tape caused by the pressure buildup was measured by a thermal mechanical analyzer (TMA) during the thermal processing. Results show that the formation of the maximum pressure buildup at the center of the cubic tape is influenced by the sample size and heating conditions. In addition, the dynamic strain at the center of the sample measured by TMA agrees with the formation of the pressure buildup estimated by the numerical calculation. Moreover, the optimal heating trajectories determined by the dynamic optimization scheme with the constraint of the formation of the maximum pressure buildup were verified from the tape deformation analysis by the TMA tests. © 2007 Elsevier B.V. All rights reserved. Keywords: Dynamic optimization; YSZ green tape; Organic additives burnout; Numerical simulation; Thermal mechanical analysis 1. Introduction Electrolytes are one of the essential components to trans- port oxide ions for solid oxide fuel cells (SOFCs). The quality and efficiency of SOFCs relies on the performances of the electrolytes when operated between 600 and 1000 ◦ C. The elec- trolytes have to be fabricated to achieve some requirements, such as high ionic conductivity, leaking prevention, and thermal- shock resistance. The manufacturing of the electrolyte of solid oxide fuel cells has been developed utilizing a ceramic pro- cessing method. The beginning of the process is to prepare slurry by mixing YSZ powders with solvents, powder disper- sants, plasticizers and polymer binders. The prepared slurry is coated on substrates to form green tapes of the ceramic components with desired thicknesses or devices using a shape forming technique, i.e. tape-casting. The produced green tapes ∗ Corresponding author. Tel.: +886 3 4638800x2573; fax: +886 3 4559373. E-mail address: lckliau@saturn.yzu.edu.tw (L.C.-K. Liau). are then to be thermally treated by a firing cycle, including binder (organic additives) burnout, ceramic sintering, and cooling steps [1]. Thermal removal of the organic components in green tapes of the organic/YSZ composite is one of the critical heating pro- cesses to fabricate high quality of the electrolytes for solid oxide fuel cells. During the removal process, the organic additives are decomposed into volatile gas which evolves through the ceramic component when the operation is above the decomposition tem- peratures. If a large amount of the evolving gas accumulates inside the ceramic, a large pressure buildup is generated to deform the ceramic body as depicted in Fig. 1. The pressure buildup to generate the defects was proposed due to the forma- tion of the evolving gas and the gas transport out of the ceramic body. Defects, such as cracks, can be formed inside the tapes due to the large buildup pressure formation [2]. Recent studies were focused on controlling the formation rate of the evolved gas (kinetics) with respect to the adopted heating strategy to avoid the forming of the pressure buildup inside ceramic com- ponents [3,4]. Therefore, the phenomena of the organic additives 0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2007.11.041