Phase segregation in binary SiO 2 /TiO 2 and SiO 2 /Fe 2 O 3 nanoparticle aerosols formed in a premixed flame
- PDF / 914,863 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 39 Downloads / 207 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Phase segregation in binary SiO2/TiO2 and SiO2/Fe2O3 nanoparticle aerosols formed in a premixed flame Sheryl H. Ehrmana) and Sheldon K. Friedlander Air Quality and Aerosol Technology Laboratory, Department of Chemical Engineering, 5531 Boelter Hall, University of California, Los Angeles, California 90095
Michael R. Zachariah Chemical and Science Technology Laboratory, Building 221, Room B312, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 23 January 1998; accepted 11 August 1999)
Binary SiO2/TiO2 and SiO2/Fe2O3 nanoparticle (diameter < 100 nm) aerosols of varying mole ratios of Ti or Fe to Si were generated in a premixed Bunsen-type aerosol flame reactor. The distribution of species within the particles was investigated using transmission electron microscopy, electron energy loss spectrometry, x-ray diffraction, and Fourier transform infrared spectroscopy. Phase segregation was observed to varying degrees in qualitative agreement with segregation expected from binary phase diagrams for the bulk systems. Differences between the SiO2/TiO2 and SiO2/Fe2O3 systems can be explained by considering the variation in the thermodynamically stable liquid-phase solubility and differences in the ability of iron and titanium ions to substitute for silicon ions in the network structure.
I. INTRODUCTION
Aerosol flame reactors have long been used for commercial scale production of single-component refractory oxide powders such as silica and titania.1 The production of germanium-doped silica-based optical fibers by vaporphase axial deposition is an example of an industrial scale multicomponent aerosol process.2 We have a fairly good understanding of single-component aerosol formation from gas phase precursors in high-temperature processes. Growth occurs by collisions between primary particles followed by coalescence by either a viscous flow mechanism for liquid particles, or by solid-state diffusion if the particles are solid phase.3–6 Final primary particle size has been shown experimentally to depend on the time–temperature history of the process and on the material properties of the aerosols: viscosity for liquid particles or solid-state diffusivity.6–10 Of particular interest in the formation of multicomponent aerosols is the arrangement of chemical species within the particles. For two-component systems many different arrangements are possible, some of which are shown in Fig. 1. These can range from differences in
a)
Address all correspondence to this author. Present address: Department of Chemical Engineering, University of Maryland, College Park, MD 20742-2111. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 12, Dec 1999
http://journals.cambridge.org
Downloaded: 11 Mar 2015
chemical homogeneity, described by either the complete solubility of one oxide in another or the formation of a mixed solid oxide phase, to chemically distinct primary particles or agglomerates. The desired arrangement of species depends upon the applicati
Data Loading...
