CARactérisation in-situ de MIcro et NAno systèmes particulaires (CARMINA) – CARMINA

Micro and nano scale particles system are the subject of intensive academic, applied and industrial researches. Due to their high chemical reactivity linked with their high Surface Specific Area and their ability to be easily transported by fluid systems, they are already at the origin of valuable applications. By now they are essential for the development of advanced ceramics or large electronic components, quantum dots based light sources, elements of fuel cells or micro heat-exchangers. For almost the same reasons, but with opposite consequences, the measurement and the control of these particles are key problems in energy, safety and environmental issues (e.g. soots, nuclear fusion operation, aerosols, allergens). Different pathways exist to produce ultra-fine dry powders or colloidal suspensions. Controlling the particle size distribution and concentration of such systems is a key process factor and a major open issue due to the size of the objects but also their properties (high volatility and high capacity to aggregate, to precipitate or flocculate). For this purpose and up to now, sampling and off-line analyses as electron scanning microscopy and diffractometry, electro-mobility measurements,' are the most widely used. However, for so chemically reactive and fragile objects the consistency of such analyses is always questionable. For instance, when soot produced by a premixed flame are collected on a substrate, there is always a strong controversy whether or not the particles analyzed in laboratory are still representative in shape, size and composition to the originally one formed within the flame. In a fusion device, the dust are collected with a manual sampling procedure. Here, the analyses are simply biased by the fact that most of the submicron particles remain trapped in the tiles micro roughness. Suction, dilution and particles counting based techniques appear to be more powerful but they also suffer from several major drawbacks. Thus, the aim of this research project is to develop, in fine, an optical diagnostic that fully satisfies the aforementioned objectives and requirements: the characterization of nano and micro particles systems without perturbating the ambient system itself, i.e. a long distance measurement with limited optical access requirements. This technique is the Light Extinction Spectrometry (LES). With LES, the concentration and the Particle Size Distribution (PSD) of a particle system is obtained by analysing the spectral transmission of a broadband and collimated light beam through the medium. Fundamental advantages of this techniques regarding to all other ones are that: it is specially adapted to small particles (i.e. particles smaller than the wavelength); it does not requires large and numerous optical accesses to the particle systems since the collection angle can be extremely small; It probes a large volume and it is an integrated measurement; It can be performed at very large distance from the system. In that sense it is very well adapted to the characterization of reactive systems like flames or plasma, or large reactors like tokamaks. The project work program is organized in five tasks: Task 1: The development of cluster aggregation and light scattering models (electromagnetic and wave-optics based) to predict the scattering of nano and micro particles aggregate, irregular particles. Task 2: Development of a plasma glow reactor generating and controlling nano particles. The reactor will be specially design to test the LES technique. Task 3: Development of two LES systems with their inversion procedure, a reference optical technique (Small-to-large-scattering-angle technique); Task 4: validation of the electromagnetic models, the LES systems and investigation of different nano/micri particle systems: dusty plasma, sloot flame, nanofluids, aerosols. Task 5: will be an overall synthesis of all results obtained in the CARMINA project.