Time Resolved Laser Induced Incandescence Analysis of Metal Aerosols
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Synthetic nanoparticles are finding widespread adoption in a growing number of commercial and research applications. Their size dependent properties offer researchers a variety of ranging including targeted drug delivery, catalysis, and environmental remediation. As these materials are being adopted into these applications, there is a pressing need for a diagnostic which allows the accurate real time measurement of the particle size since the functionality of the nanoparticles are size dependent. Time-resolved laser-induced incandescence (TiRe-LII) is an in situ technique which allows the non-destructive inference of the nanoparticle size in real time. This technique was developed as a particle size diagnostic for soot primary particles and has been modified to characterize synthetic nanoparticles. The aerosolized nanoparticles are heated with a laser pulse to its incandescence temperature and the incandescence is measured as the nanoparticles are allowed to thermally equilibrate with the surrounding gas. As nanoparticles of different sizes will cool at different rates, the nanoparticle size can be inferred by modeling the incandescence using a spectroscopic and heat transfer model. The present work summarizes experiments conducted on aerosolized iron, silver, and molybdenum nanoparticles using TiRe-LII analysis. This includes the spectroscopic and heat transfer models, TiRe-LII instrument calibration and operating conditions, the nanoparticle preparation, comparisons of the TiRe-LII derived particle sizes to existing ex situ techniques, and the associated error analysis. The models required to interpret the TiRe-LII data, the spectroscopic and heat transfer models, are presented with the optical and physical parameters to solve them, as well as simulate the expected heat transfer modes of each of the nanoparticles. The calibration of the apparatus used as well as the nanoparticle preparation, and TiRe-LII experimental measurement methods are discussed, as well as the error bounds on the results. A fluence study was conducted by looking at the peak temperatures measured as a function of the fluence of the TiRe-LII instrument laser to determine the accuracy of the optical properties and to compare the results to the trends to previous studies. The nanoparticle size and thermal accommodation coefficient (TAC) of each of the aerosolized nanoparticle mixtures were attempted to be recovered based on the heat transfer modes present in the TiRe-LII measurements. The aerosolized iron nanoparticles had sufficient evaporation and conduction heat transfer modes which allowed the recovery of both the nanoparticle size and thermal accommodations coefficient, while the aerosolized silver nanoparticles only had heat transfer due to evaporation which only allowed the recovery of the nanoparticle size, and the aerosolized molybdenum nanoparticles only had heat transfer due to conduction which only allowed the recovery of the nanoparticle size to TAC ratio. The molybdenum TAC was recovered by introducing the ex situ calculated molybdenum nanoparticle size and nanoparticle size distribution, using electron microscopy, into the models. Finally, the error bounds for the TiRe-LII measurements are presented, and a perturbation analysis was performed due to the lack of provided error bounds on the optical and physical properties used. It was shown that the optical properties had a significant impact on the recovered nanoparticle size and TAC for all of the materials, while there was a lesser but non-trivial impact on the recovered values from the nanomaterials’ physical properties.
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