USAXS of Thermophoretically Sampled Oxides from Flames Greg Beaucage, Nikhil Agashe, Doug Kohls- Dept. of Chemical and Materials Engineering, University of Cincinnati. Hendrik Kammler, Soritis Pratsinis- Institute of Processing Engineering, ETH, Zurich. Jan Ilavsky Purdue University/UNICAT, Argonne "The UNICAT facility at the Advanced Photon Source (APS) is supported by the Univ. of Illinois at Urbana-Champaign, Materials Research Laboratory (U.S. DOE, the State of Illinois-IBHE-HECA, and the NSF), the Oak Ridge National Laboratory (U.S. DOE under contract with UT-Battelle LLC), the National Institute of Standards and Technology (U.S. Department of Commerce) and UOP LLC. The APS is supported by the U.S. DOE, Basic Energy Sciences, Office of Science under contract No. W ENG-38." Standard 1-D collimation setup * slit-smeared geometry (a.k.a. Bonse-Hart ** ) Post-measurement desmearing calculation J.A. Lake; Acta Cryst 23 (1967) Typical slit-length ~ 0.05 -1 ~25 m 0.3 1.0 m0.6 m * G. G. Long, A. J. Allen, J. Ilavsky, P. R. Jemian, and P. Zschack, in CP521, Synchrotron Radiation Instrumentation: 11 th US National Conference, P. Pianetta and H. Winick, Eds., AIP, College Park, 183 (2000). ** U. Bonse & M. Hart, Appl. Phys. Lett. 7, 238 (1965) and Zeit. f Phyzik 189, 151 (1966). USAXS instrument at UNICAT Abstract: Combustion of organo-metallic or halide vapors and aerosol liquid sprays can be controlled to produce enormous quantities of nano-structured powders. Such flame processes are common in the production of fumed silica, and pyrolytic titania on an industrial scale with primary particle sizes on the order of 10 nm. Pyrolytic processes can also be used with liquid phase specialty precursors through flame spray pyrolysis. Pyrolytic nano-particles are typically connected through sintering bridges, ionic bonds or van der Waals forces into ramified, mass-fractal aggregates. The study of this promising technology for nano-particle production has been hindered by the kinetics of particle growth, typically on the order of milliseconds, at high temperature, 2000C. Using the UNICAT USAXS camera we have recently studied samples collected by shooting a TEM grid or small metal substrate through the flame at high velocity. This substrate attracts a small number of particles as it passes through the flame. Particle deposition via thermophoresis in the free molecular regime has no dependence on particle size so a true sample can be obtained. Despite the small quantity of sample, third generation synchrotron sources coupled with USAXS cameras are capable of measuring a reasonable scattering pattern on such thermophoretic samples and a particle morphological mapping as a function of distance from the burner is possible. The results of a recent study of thermophoretic samples is shown. I0I0I0I0 2222 sample X-rays in USAXS instrument is too compact to photograph well UNICAT USAXS Camera Diffusion flame (DF)Sustained premixed flame (SPF) L/min Hendrik Kammler 10/02 Variable Oxygen-Flow Rate 17 g/h SiO 2 Flame Variable Oxygen-Flow Rate 17 g/h SiO 2 Flame Premixed Silica Flame Diffusion Carbon Sooting Flame Pyrolytic Particle Growth Has a Wide Range of Conditions: O 2 + FuelFuel O2O2 O2O2 O2O2 INTRODUCTION Nucleation: Gibbs-Thompson (Ostwald-Freudlich or Hoffman-Lauritzen or Kelvin) Equation Using pseudo-equilibrium thermodynamics: "Deep quench conditions give nanoparticles" Supersaturated vapor: High particle conc.: Deep quench: (Reaction rate is high due to temp. and Laplace Eqn. ) Particle Transport: Knudsen Number: k n >> 1Free Molecular Regime: Particles interact thermally with gas D ~ d p -1/2 k n