An Experimental Investigation of Gas-Phase Combustion Synthesis of SiO 2 Nanoparticles Using a Multi-Element Diffusion Flame Burner M. S. WOOLDRIDGE*, P. V. TOREK, M. T. DONOVAN, D. L. HALL, and T. A. MILLER Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125, USA and T. R. PALMER and C. R. SCHROCK Department of Aerospace Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125, USA The current work presents the results of an experimental investigation of gas-phase combustion synthesis of silica (SiO 2 ) particles using a multi-element diffusion flame burner (MEDB, a Hencken burner). Silane (SiH 4 ) was added to hydrogen/oxygen/argon (H 2 /O 2 /Ar) flames to produce SiO 2 nanoparticles at various burner operating conditions ( = 0.47–2.16). To characterize the burner performance, temperature measurements were made using water absorption spectroscopy and uncoated, fine-wire thermocouples. The results demon- strated the non-premixed flow arrangement of the fuel tubes and oxidizer channels of the MEDB provided uniform, 1D conditions above the surface of the burner, with temperature variations of less than 3% in the transverse direction (parallel to the surface of the burner) for elevations above the mixing region (z = 0 –7 mm), extending to heights  30 mm. At heights above the mixing region, approximately constant axial temperatures are also observed. Silica particle formation and growth were examined for comparison with current understanding of the physical mechanisms important in combustion synthesis of SiO 2 . The particle properties were determined using transmission electron microscope (TEM) imaging. Geometric mean diameters of the primary particles varied from d  p = 9 to 18 nm. The current study demonstrates the utility of the MEDB in providing a controlled environment for fundamental studies of gas-phase combustion synthesis phenomena, as well as offering broad flexibility in experimental design with control over process variables such as temperature field, particle residence time, scalable reactant loading, and particle precursor selection. © 2002 by The Combustion Institute INTRODUCTION Nanostructured materials have the potential to revolutionize materials applications and perfor- mance. For example, nanostructured single- component powders have been demonstrated to have order-of-magnitude higher catalytic activity in comparison to microstructured single-compo- nent powders [1]. Nanocomposite powders (consisting of two or more condensed-phase materials) have been shown to improve catalytic performance beyond that of single-component nanostructured materials [1]. Similarly, gas-sen- sors with controlled nanostructure and compo- sition have exhibited superior stability and sen- sitivity [2, 3]. Superparamagnetic behavior [4], lower reaction sintering temperatures [5], and higher ductility [6] are all examples of benefits that have been derived from nanostructured materials. In addition, the unique attributes associated with the nanometer size domain have led to new devices and novel applications such as in vitro bioassay materials [7] and nanocom- posite lasing materials [8]. Furthermore, meth- ods such as liquid-feed flame spray pyrolysis, developed by Laine and co-workers [8], have demonstrated that commercial scale production rates of nanostructured powders are readily achievable. Gas-phase combustion synthesis (GPCS) of nanostructured powders is a powerful synthesis method, capable of generating a broad range of high purity materials [9 –11] with controlled particle size, particle size distribution, morphol- ogy (e.g., degree of agglomeration) and compo- sition [12–15]. However, many of the fundamen- *Corresponding author. E-mail: mswool@umich.edu COMBUSTION AND FLAME 131:98 –109 (2002) 0010-2180/02/$–see front matter © 2002 by The Combustion Institute PII S0010-2180(02)00403-0 Published by Elsevier Science Inc.