Tin Dioxide Nano-Powders for Gas Sensor Applications
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ABSTRACT SnO 2 nanoparticles are of interest for gas sensor applications because the surface area is much larger compared to conventional powders. Thus, interactions between the material and the gases, which occur on the surface sites of the particles, are increased considerably. The preparation of SnO 2 powders has been investigated following two forced precipitation systems: the hydrolysis reaction of SnC14 in an emulsion media and the hydrolysis reaction of Sn2 รท in the presence of a complexing ligand (CH 3COO-). Spherical nanoparticles in the 10 to 100 nm range and with a narrow size distribution were synthesized by both precipitating routes. In both cases, it has been demonstrated that the most important parameter which controlled the particle size was the nature of the associated anion. When this associated anion or ligand is able to form a strong complex with the colloidal subunits, a barrier against Van der Waals attraction is created which results in little growth. This greatly influences the agglomeration/growth kinetics during the precipitation. The effect of acetate chelating ligands which resulted in the SnO 2 nano-powders formed of 5-10 nm crystallites will be presented and discussed. Preliminary results on the gas (N2 , NO) adsorption studies on pellets formed from these powders are also presented.
INTRODUCTION The physical and chemical properties of tin dioxide (transparency in the visible region, high
conductivity, high thermal, chemical and mechanical stabilities) make this material a suitable candidate for many applications fields [1]. For example, this material is of interest for application in solar cells, optoelectronic devices, liquid crystal displays, catalyst and gas sensors. Since recent years, the latter application has been extensively studied principally for the detection of toxic and flammable gases. There are many factors that influence the sensing properties of tin dioxide. One of the most important factor is the microstructure of the starting powder since the gas detection is governed by a surface phenomenon that leads to changes in the electrical resistance [2]. Then, having SnO 2 nanoparticles made of nanocrystalline sub-units is of particular interest for the gas sensing element because the surface area is greatly increased compared to conventional powders. At the nanometer scale, interactions between the nanostructured material surface and gases becomes very important. By reducing the particle size to a few nanometers, the material used as sensor can be expected to be more sensitive to gases and to show shorter response times. Furthermore, the sintering of such nanocrystalline powders occurs at lower temperature compared to conventional powders, and the sinterability is greatly improved if the powder consists of monodispersed particles with a narrow size distribution [3]. Tin dioxide nanoparticles can be produced from several methods such as the forced hydrolysis [4, 5] and the chemical vapor deposition [6, 7]. Most of these techniques starts with SnCI4 as precursor and result
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