AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Crystal Structure of Nanosized Ice Particles Formed in a Supersonic Nozzle
ANDREW AMAYA, Viraj Modak, Harshad Pathak, Michael Bogan, Hartawan Laksmono, Claudiu Stan, Duane Loh, Jonas Sellburg, Raymond Sierra, Sebastien Boutet, Garth Williams, Marc Messerschmidt, Soenke Seifert, Randy Winans, Barbara Wyslouzil, The Ohio State University
Abstract Number: 469 Working Group: Aerosol Physics
Abstract Supersonic nozzle with cooling rates of about 10$^5 K/s are able to probe both vapor-liquid and liquid-solid phase transitions at extreme nucleation rates of ~10$^(17) cm$^(-3)s$^(-1) for vapor-liquid and up to ~10$^(22) cm$^(-3)s$^(-1) for liquid-solid. To examine the structure of ice nanocrystals requires wide angle x-ray scattering experiments with scattering vectors, q, between 1.5 A$^(-1) and 3.5 A$^(-1). Experiments at the Free Electron Laser, LCLS, generated 2-D x-ray scattering patterns of ice with concentric rings located at q = 1.72 A$^(-1), 2.79 A$^(-1), and 3.27 A$^(-1). The position and the relative intensities of the peaks suggest that nanometer sized ice crystals created in a supersonic nozzle have a crystal structure that is close to pure cubic ice. To support the FEL experiments, Fourier Transform Infrared Spectroscopy (FTIR) followed the liquid-solid transition for water in more detail, and Small Angle X-ray Scattering (SAXS) determined the size of the ice particles. The SAXS experiments, completed at the Advanced Photon Source (Argonne National Laboratory) on the BESSC 12-ID beamline, found particle sizes of ~10 nm radius. The spectra from FTIR are used to find the fraction of ice, F$_(ice), and together with the particle size to calculate the volume-based nucleation rates, J$_(ice,V). The nucleation rates measured here lie between 1.12 x 10$^(22) cm$^(-3)s$^(-1) and 3.17 x 10$^(22) cm$^(-3)s$^(-1). The formation of cubic ice is favored in a supersonic nozzle because of the extreme liquid-solid nucleation rates and the small size of the particles.