Synthesis and characterization of microspheres composed of SnO 2 nanoparticles processed via a chemical route T. Sequinel a, ⁎, S. Cava b , D. Berger a , S.M. Tebcherani a , S.A. Pianaro a , S. Schmidt a a Universidade Estadual de Ponta Grossa, Av. Gal. Carlos Cavalcanti, 4748, Campus de Uvaranas, 84035-900 Ponta Grossa, PR, Brazil b Itajara Minérios Ltda., R. Balduíno Taques, 170, 84010-050 Ponta Grossa, PR, Brazil abstract article info Article history: Received 10 March 2009 Received in revised form 5 June 2009 Accepted 24 July 2009 Available online 4 August 2009 Keywords: Nanostructures Chemical synthesis Nanofabrications Scanning and transmission electron microscopy SnO 2 microspheres were synthesized by a chemical route, heating the mixed Sn 2+ and sulfuric acid solution in the presence of pressurized oxygen at 900 °C in a designed calorimetric pump. Phase analysis was carried out by X-ray diffraction (XRD) and the results confirmed the SnO 2 microspheres as a single-phase tetragonal structure. Scanning electron microscopy (SEM) images indicated that these microspheres with average diameters of 0.9 μm were composed of SnO 2 nanoparticles with a diameter of about 4.7 nm and a crystallite size of 3.7 nm, as observed by transmission electron microscope (TEM) and calculated by Scherrer's equation from diffractograms, respectively. The formation mechanism of microspheres composed of SnO 2 nanoparticles and the influence of changes in processing are proposed and explained. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In this age of nanoscience, the properties of many exciting new materials and devices will depend on the details of their composition down to the level of single atoms. Thus, the characterization of the structure and electronic properties of matter at the atomic scale has become increasingly vital for economic, technological and scientific reasons [1,2]. The design of reproducible and more efficient nanofabrication routes has become a very active field of research in recent years. In particular, the development of new methods for micro- and nano- patterning materials surfaces has attracted the attention of many researchers in industry and academia as a consequence of the growing relevance of patterned surfaces in many areas of technology, ranging from optoelectronics to biotechnology [3,4]. Tin dioxide (SnO 2 ), an important n-type semiconductor with a wide band gap, is a key functional material that has a been extensively used for optoelectronic devices, gas sensors for detecting leakages, transparent conducting electrodes, catalyst supports, electrochemical modifiers on electrodes, solar cells, etc. This material exhibits varistor behavior with high energy absorption capacity, whose function is to restrict transitory over-voltages without being destroyed when it is doped with a variety of oxides [5]. Over the last several years, considerable efforts have focused on exploring new routes to synthesize SnO 2 nanorods, nanowires, nanowire arrays, and nanobelts or nanoribbons [6,7]. SnO 2 spheres have also been fabricated by hydrothermal-based methods [8–12]. Functional oxides today are investigated extensively in terms of their basic properties and their current and potential applications [13,14]. Current methods employed in the preparation of powdered nanocrystalline tin dioxide include the combination of several synthetic processes, such as hydrolysis of tin(IV) chloride [15], for- mation of nanocrystalline SnO 2 , and subsequent hydrothermal treat- ments. After annealing treatments of hydrothermally treated SnO 2 particles, their crystallite sizes remain small, indicating high thermal stability against particle growth and sintering [16,17]. In this paper, we report on the preparation of microspheres composed of SnO 2 nanoparticles by a new system that allows for the association of chemical and physical routes with the aerosol method [18] and characterization by X-ray diffraction (XRD). The morphology of microspheres composed of SnO 2 nanoparticles was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 2. Experimental The experimental set-up used for the synthesis consisted of a horizontal tube furnace with the injection of a controlled atmosphere. SnO 2 powder was formed by a vapor–solid mechanism from a sulfuric solution with pH controlled between 3 and 4, in the presence of Sn +2 0.25 mol.L -1 . This solution was deposited through a horizontal tube Powder Technology 196 (2009) 180–183 ⁎ Corresponding author. Tel.: +55 42 3220 3053; fax: +55 42 3220 3160. E-mail address: sequinel.t@gmail.com (T. Sequinel). 0032-5910/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2009.07.019 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec