More on Characterization

• Qualitative size distribution dynamics

• Particle chemistry

•Particle chemical characterization

Size distributions may change over timeStarter 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 kita. 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 spectroscopyj. X-ray diffraction (XRD)k. Energy dispersive X-ray spectroscopy (EDX or EDS)l. Electron energy loss spectrometry (EELS)

Analytical situations: in class problem