Preparation of a Supported Si 3 N 4 Membrane for Gas Filters
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Preparation of a Supported Si3N4 Membrane for Gas Filters Fei Cheng, Stephen M. Kelly, Stephen Clark and John S. Bradley Department of Chemistry, University of Hull, Cottingham Road, Hull, HU6 7RX, UK Marc Baumbach and Andreas Schütze Saarland University, Lab for Measurement Technology, Saarbrücken, Germany
ABSTRACT A supported Si3N4 membrane was prepared via a non-aqueous sol-gel process using tris(dimethylamino)silylamine, H2NSi(NMe2)3, as a starting material. The SEM image indicated the formation of the Si3N4 membrane with thickness about 2.3 µm on the surface of the α-Al2O3 support. Nitrogen adsorption analysis indicated that, although most of the pores were similar to those of the α-Al2O3 disk, a new pore size distribution of 20–50 Å for the Si3N4 membrane was observed. The new membrane demonstrates high selective absorption of NO2, suggesting a potential application as a selective filter for gas sensors. INTRODUCTION Due to their chemical and thermal stabilities, porous inorganic membranes are highly promising for use in current separation technology and as gas sensors.[1, 2] The overwhelming majority of these membranes are oxide ceramics consisting of mesoporous, microporous, or a combination of both, thin films. With the development of new applications, it is important to synthesize novel inorganic membranes with controlled physical and chemical properties. Silicon nitride offers potential advantages as a novel membrane/filter, particularly in high temperature separation processes and/or chemically harsh conditions, because of its unique combination of superior high-temperature mechanical properties and resistance to oxidation [3, 4]. Sol-gel processing has the advantages of synthetic flexibility, high product purity and material homogeneity and is well established as an important route to prepare shapeable, as well as size-selective, microporous and mesoporous metal oxide materials.[5] This is potentially a very attractive approach for the preparation of ceramic membranes with a controllable shape for practical gas sensors applications. We have developed a novel non-aqueous sol-gel technique for the preparation of a high-surface-area, porous silicon diimide gel by the acid-catalyzed ammonolysis of tris(dimethylamino)silylamine, (Me2N)3SiNH2, TDSA.[6] Pyrolysis of the silicon diimide gel under NH3 flow at 1000 °C produces mesoporous Si3N4 with a high-surface-area (BET
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≥ 400 m2/g) and narrow pore-size distribution (20 – 60 Å), suggesting a potentially useful mesoporous material with good selectivity.[7] In the present paper, we report the preparation of a silicon nitride membrane via a non-aqueous sol-gel technique and its gas separation properties as part of the EU project NANOSENSOFLEX. The high sensitivity, good reliability and low cost have made semiconductor gas sensors attractive for a wide range of applications ranging from air quality control to safety applications like explosion warning or fire detection. In order to improve the sensors in terms of reproducibility, long-term stab
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