Natural Silica Sand/Alumina Ceramic Composites: Promising Candidates for Fuel-Cell Sealants

Abstract

Abstract. An attempt has been developed to establish the prospect of the useful application of Indonesian natural silica sand, instead of commercially expensive materials, as a future fuel-cell sealant. The sand was initially washed and ball-milled at 150 rpm for 60 minutes and then heated at 1000 C for the same duration. The resulting powder was then mixed with alumina powder at various amounts and shaped into discs before sintering at 1150 C and 1250 C to produce compact ceramics. The diameter shrinkage, porosity, and density of the ceramics were evaluated by Archimedes method. Their crystalline phase composition was quantified by Rietveld refinement analysis on the X-ray diffraction (XRD) data and the phase weight fraction was then used for coefficient of thermal expansion (CTE) evaluation. It was observed that the bulk density increased while the porosity decreased with alumina addition. The XRD data analysis revealed that the prepared silica sand contains a very high purity of quartz-SiO 2 , i.e. 97.8(18)%. The sintering temperatures of 1150 C and 1250 C transformed some quartz-SiO 2 to crystobaliteSiO 2 . All the calcite-CaCO 3 exhibited reaction sintering with SiO 2 forming wollastonite-CaSiO 3 . Therefore, the ceramic composites contained SiO 2 /Al 2 O 3 /CaSiO 3 . Regarding CTE, all of the composites meet the criteria for fuel-cell sealants, in the range of 9-12 ppm/C.Keywords: Indonesian silica sand, alumina, phase quantification, coefficient of thermal expansion, fuel-cell sealant. [5]. The SOFCs, devices that convert the chemical energy of fuels into electricity, have been extensively studied to reduce CO 2 emission and fossil fuel consumption [6]. In spite of this, it is confronted with a challengeable task on preventing leakage when an SOFC operates at high temperature (800-1000 °C) [7]. Consequently, a proper gas-tight sealing material plays a decisive role to obtain the best operation and performance of SOFCs [8]. The very basic criteria for fuel cell sealing material are the CTE, which must be in the range of 9-12 ppm/°C [9], and thermo-mechanically and chemically stable [10]. The matching of CTE of the fuel-cell sealing materials to other cell components is essential to minimize the thermal stresses [11].Recently, ceramic-based composites and glass-ceramics have become highly recommended sealing materials for various SOFCs attributable to their superior characteristics compared with those of metallic sealants, mainly to resist both reducing and oxidizing environments [12,13]. Additionally, they also perform excellent gas tightness and provide CTE similar to those of the other stack components [14]. Numerous investigations have been conducted in search of great fuel cell sealants, e.g. 30CaO- . However, rarely has a research exclusively explored the use of natural silica-based materials as the SiO 2 source for fuel cell sealants production.In this present study, we introduce the prospect of using Indonesian silica sand as the fuel cell sealing material. This breakthrough is crucial not on...