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More on Characterization • Qualitative size distribution dynamics • Particle chemistry •Particle chemical characterization Size distributions may change over time Starter size distribution: Processes in which volume is conserved Coagulation, communition or breakup, restructuring Processes in which volume not conserved Condensation, evaporation, nucleation, sedimentation, In class project – changing shapes of distributions Chemical composition not always same Varying degrees of chemical homogenaity in particle mixtures •Particles all of one chemical species (ie salt granules) – chemically homogeneous •Particles are all of one chemical species, but the particles are mixed – externally mixed •Particles are of two or more chemical components, but composition of each particle is same – internally mixed •Individual particles have different compositions Chemical composition may vary with size Pharmaceutical powders for inhalation - want small drug particles mixed with and loosely bound to larger inert particles Emissions from incinerators – some high volatility compounds evaporate in high temperature zone and nucleate downstream forming ultrafine high surface area particles More examples How to measure chemical composition? Many techniques – survey of analytical chemistry Some need large sample of material, so need to take average over whole size distribution, and/or time Some need extremely small amounts of material so representative sampling is crucial Some can tell you composition on-line or nearly on-line Some require off-line analysis SADK – secret acronym decoder kit a. Atomic absorption spectroscopy (AAS) b. Inductively coupled plasma- atomic emission spectroscopy (ICP-AES) c. Laser induced breakdown spectrometry (LIBS) d. Time of Flight Mass spectrometry of aerosols (TOF-MS) e. X-ray Fluorescence (XRF) f. Proton Induced X-Ray Emission (PIXE) g. Neutron activation analysis (NAA) h. X-ray photoelectron spectroscopy (XPS) i. Auger spectroscopy j. X-ray diffraction (XRD) k. Energy dispersive X-ray spectroscopy (EDX or EDS) l. Electron energy loss spectrometry (EELS) Analytical situations: in class problem