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Title: In situ imaging of ultra-fast loss of nanostructure in nanoparticle aggregates

The word “nanoparticle” nominally elicits a vision of an isolated sphere; however, the vast bulk of nanoparticulate material exists in an aggregated state. This can have significant implications for applications such as combustion, catalysis, and optical excitation, where particles are exposed to high temperature and rapid heating conditions. In such environments, particles become susceptible to morphological changes which can reduce surface area, often to the detriment of functionality. Here, we report on thermally-induced coalescence which can occur in aluminum nanoparticle aggregates subjected to rapid heating (10{sup 6}–10{sup 11} K/s). Using dynamic transmission electron microscopy, we observed morphological changes in nanoparticle aggregates occurring in as little as a few nanoseconds after the onset of heating. The time-resolved probes reveal that the morphological changes initiate within 15 ns and are completed in less than 50 ns. The morphological changes were found to have a threshold temperature of about 1300 ± 50 K, as determined by millisecond-scale experiments with a calibrated heating stage. The temperature distribution of aggregates during laser heating was modeled with various simulation approaches. The results indicate that, under rapid heating conditions, coalescence occurs at an intermediate temperature between the melting points of aluminum and the aluminum oxide shell, and proceeds rapidly once this threshold temperaturemore » is reached.« less
Authors:
 [1] ; ; ;  [2] ;  [3] ;  [4]
  1. Department of Materials Science, University of Maryland, College Park, Maryland 20742 (United States)
  2. Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550 (United States)
  3. Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742 (United States)
  4. (United States)
Publication Date:
OSTI Identifier:
22278011
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ALUMINIUM; ALUMINIUM OXIDES; COALESCENCE; COMPUTERIZED SIMULATION; EXCITATION; HEATING; MELTING POINTS; MORPHOLOGICAL CHANGES; NANOSTRUCTURES; PARTICLES; SURFACE AREA; TEMPERATURE DISTRIBUTION; TIME RESOLUTION; TRANSMISSION ELECTRON MICROSCOPY