Materials Science and Engineering A 429 (2006) 266–271 Aqueous tape casting of 10 mol%-Gd 2 O 3 -doped CeO 2 nano-particles L.H. Luo, A.I.Y. Tok ∗ , F.Y.C. Boey School of Materials Science & Engineering, Nanyang Technological University, Nanyang Avenue, Singapore, Singapore Received 26 July 2005; received in revised form 4 May 2006; accepted 11 May 2006 Abstract The aqueous tape casting process was systematically developed and investigated for the tape casting of 10mol%-Gd 2 O 3 -doped CeO 2 nano- particles. This study focused on obtaining the optimum slurry formulations and on the effects of the processing parameters such as the stability, the rheology and the wetting properties on the tape characteristics. High solid loading (55 vol.%) and stable slurries of 10GDC nano-particles were achieved using poly(acrylic acid) (PAA) as a dispersant; poly(vinyl alcohol) (PVA) as a binder; poly(ethylene glycol) (PEG) as a plasticizer; octanol as a defoamer and 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate as a surfactant. The pH values of the slurries were maintained in the range of 9.0–10.0. Homogeneous, defect-free green tapes (thickness 150–200 m) with smooth surface and high relative green density (51.5%) were thus successfully obtained. © 2006 Elsevier B.V. All rights reserved. Keywords: Aqueous tape casting; Nano-particles; 10GDC; Fuel cells 1. Introduction Tape casting produces a thin layer (or coating) on a carrier surface via the doctor blade technique [1–3]. The applied coat- ing dries to form a flexible film that consists of a particle-filled, polymeric matrix with appreciable porosity, which can be cut, punched or stacked to produce multilayered structures. Some potential applications include solid-oxide fuel cells [4,5], multi- layered ceramic packages (MLCP) [6–8], multilayered ceramic capacitors (MLCC) [9–11], sensors/actuators and transducers. Traditionally, tape casting was done using organic solvents. However, due to environmental, health, safety and economic reasons, aqueous (water-based) tape casting is rapidly replac- ing the non-aqueous form of tape casting. Despite the above- mentioned advantages, several problems are often encountered. These include slow drying of the tape, higher crack sensitiv- ity, flocculation and poor wetting of the slips due to the high surface tension of water [12,13]. Therefore, the development of such formulations has been a subject of recent research [14–16]. However, the majority of research has still been focused on the development of aqueous tape casting systems using microme- ter or sub-micrometer ceramic particles. Research on the tape casting of nanosized ceramic powders have not been reported ∗ Corresponding author. Tel.: +65 67904935; fax: +65 67904935. E-mail address: miytok@ntu.edu.sg (A.I.Y. Tok). much in journal papers. The stability and rheological proper- ties of nanosized ceramic powders are more complex due to particle interactions as a result of the small inter-particle dis- tances [16,17]. A moderate increase in the ionic strength of these slurries will lead to a decrease in viscosity [18]. Dietrich and Neubrand [18] have observed that rheological properties of SiO 2 nano-particles depend strongly on the particulate size and the molecular weight of dispersant, which indicate strong steric effects. Dispersed slurries containing SiO 2 nano-particles can be prepared only within a very limited range of disper- sant concentration. However, nanoscale ceramic powders offer the possibility of manufacturing dense ceramic materials with few microstructural defects at low sintering temperatures. Thus, the research and development of aqueous tape casting of nano- particles have great significance in the field of high-performance ceramics. Gadolinium oxide-doped cerium oxide (fluorite structured), 10 mol% Gd 2 O 3 CeO 2 (hereafter referred to as 10GDC for convenience), is a solid solution formed by replacing the Ce 4+ sites of the CeO 2 lattice by Gd 3+ cations. A 10GDC has been recognized as a low temperature (500–700 ◦ C operating temper- ature) electrolyte material for applications in solid-oxide fuel cells (SOFC) as 10GDC has a higher ionic conductivity [19]. In order to increase the ionic conductivity of fuel cells, elec- trolytes of 10GDC are required to be multilayered. A 10GDC nano-particles can be sintered at a low temperature, therefore, they can be co-fired with the anode/cathode at low tempera- 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.05.073