Development of ion-mobility and mass spectrometry for probing the reactivity of nanoparticles and nanocomposites.

摘要

Aerosols of diameter smaller than 100 nm, usually are referred as nanoparticles or ultrafines, have received considerable interests lately as a source of building blocks to novel materials. However, our capabilities for charactering these materials are greatly limited by lack of appropriate diagnostic tools. The objective of this work is to develop new aerosol-based techniques for the characterization of nanoparticles and nanocomposites. Though the scope of this dissertation is focused on probing the reactivity of metal based nanoparticles/nanocomposites and their applications in energetic materials, the methods provide generic approaches for understanding the intrinsic reactivity of nanoparticles.;Real-time single particle mass spectrometry (SPMS) has been used to study the reactivity of aluminum nanoparticles. The SPMS is a powerful tool due to its ability to obtain quantitative information at the single particle level. Here in this work, we conducted extensive investigations on the quantification of the SPMS. Particle morphology and composition biases on quantifying the composition of nanoparticles were observed experimentally, was related to the high non-linear properties of the laser-particle interaction. To understand pulsed laser interaction with nanoparticles, as it applied to the implementation and quantification of SPMS, we employed a one-dimensional hydrodynamic model to determine the characteristic behavior of ions produced from the particle. In the simulation, the temporal evolution of the ionization state and energy were evaluated as a function of aluminum particle size that were heated and ionized by a nanosecond laser. The results are shown to be consistent with our experimental observation, and suggest that particle size-dependent energetic ions led to the power law relationship between peak area and particle size observed in our single particle mass spectrometer.;Another approach to probe the reactivity of the nanoparticles is an ion-mobility spectrometry method. The basic idea of the experimental approach is to prepare nanoparticles of well characterized size/shape, and monitor particle size and mass changes during oxidation in free-flight. In this work, we studied nickel nanoparticles oxidation. Particles of well-controlled sizes and structure were generated in-situ, and subsequently size selected using a differential mobility analyzer (DMA). These particles were oxidized in a flow reactor at various temperatures and the size and mass change of the reacted particle were measured by a second DMA, or an aerosol particle mass analyzer (APM). We found the experimental data can be divided into an oxidation region, and a phase transition region. On the basis of the diffusion-controlled rate equation in the shrinking core model, we obtained size-resolved activation energies for nickel nanoparticles oxidation, as well as the absolute burn time and the effective diffusion coefficient.;Finally, a new Time-of-Flight mass spectrometer (TOFMS) combined with a temperature jump (T-Jump) technique is developed for time resolved analysis of the ultrafast condensed phase reaction, with focus on the decomposition, ignition and combustion processes of solid energetic materials. As the first application of this instrument, nanocomposite thermite systems of aluminum/copper oxide (Al/CuO) and aluminum/iron oxide (Al/Fe2O3) were studied, and the possible reaction mechanism and reaction steps of nanocomposite thermites were discussed based on time-resolved mass spectra measurements obtained from T-Jump/TOF mass spectrometry.