Online assessment of the crystalline modification of nanoparticles in the gas phase

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The synthesis of nanoparticles from the gas phase is resource-efficient and common. Thanks to cause and effect studies, it is known that particle properties (size, morphology, degree of agglomeration, crystallinity) can be changed by a variation of process parameters. Presently, the properties of the synthesized particles are characterized offline with considerable time delay after sample extraction and preparation, thus yielding only scarce information about the process-to-product event chain and not allowing direct influence on it. Within the second funding phase of the DFG/AIF joint project - Multi parameter characterization of particle based functional materials by means of innovative online measurement systems (MPaC) - , hereby an online and in-situ method of measurement for the analysis of the CRYSTALLINITY of particles in the gas phase is to be developed and tested in a new sub-project. The crystallinity as an internal structural parameter of particles has enormous relevance for the means of application, such as the bioavailability of active agents or the conductivity of particles. With this project, the hitherto not covered aspect of the parameter CRYSTALLINITY complements the works for the analysis of morphology, size and structure of the other MPaC sub-projects. Aim of this project is the development of a new Raman measurement process for the online and in-situ assessment of the crystalline modification of nanoparticles in the gas phase, with the simultaneous analysis of the gas phase temperature and composition. This allows investigating into the influence of varied process parameters on the resulting product properties in corresponding gas phase particle processes. By means of Raman spectroscopy, it is possible to distinguish polymorphs in aerosols by their characteristic spectral signatures. Simultaneously the gas phase temperature is ascertained from the rotational Raman spectrum of nitrogen. Due to the relatively weak cross-section of Raman scattering compared to concurring light-matter interactions, particular attention is paid to the efficient excitation and detection of the Raman signals, at the same time minimizing concurring and interfering disturbing signals (chemiluminescence, fluorescence). This will be realized by optimizing and building up a custom-made spectrometer especially for this project, and the application of the Shifted Excitation Raman Difference Spectroscopy (SERDS) method. The measurement method will be developed on the basis of the particle systems Titanium dioxide, Zirconium dioxide, and Iron(III) oxide dispersed in the gas phase.