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- Colloidal analysis (1)
- Microalloyed steels (1)
- Niobium carbonitrides (1)
- Precipitate analysis (1)
- Titanium carbonitrides (1)
- field-flow fractionation (1)
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Scientific Unit
Nanoparticles with properties that deviate from the bulk are the basis of many innovations in nanotechnology. Analytical techniques for the reliable characterization of nanoparticles are gaining importance as nanoparticle fabrication and their use increase in research and industry. Field-flow fractionation is capable of analyzing particulate samples from different materials that have complex size distributions. Good analytical performances have been reported for field-flow fractionation of inorganic nanoparticles, but large particle losses have so far hampered its application. This thesis studies reference particles to identify and overcome particle loss mechanisms during field-flow fractionation. Silica and gold nanoparticles were synthesized as model particle cores, and their size was systematically varied. Different labeling strategies were tested to make the particles easy to identify. The particles surfaces were modified to tune colloidal behavior and adsorption properties. Losses of different reference particles during field-flow fractionation were then studied and correlated with the particles’ structure and colloidal stability. Particle losses due to destabilization of particles with loosely attached ligands or polymer-mediated bridging adsorption on the separation membrane were identified. Reference particles were tested in a complex matrix.
Different colloidal particle characterization methods are examined for their suitability to determine the particle size distribution of particles extracted from steels. Microalloyed steels are dissolved to extract niobium and titanium carbonitride particles that are important for the mechanical properties of these steels. Such particles have sizes ranging from several nanometers to hundreds of nanometers depending on the precipitation stage during the thermomechanically controlled rolling process. The size distribution of the particles is analyzed by dynamic light scattering (DLS), analytical ultracentrifugation (AUC), and hollow fiber flow field-flow fractionation (HF5) and compared to data obtained for reference particles as well as data from electron microscopy, the standard sizing technique used in metallurgy today. AUC and HF5 provide high-quality size distributions, average over large particle numbers that enables statistical analysis, and yield useful insights for alloy design; however, DLS fails due to a lack of resolution. Important aspects in the conversion and comparison of size distributions obtained for broadly distributed particle systems with different measurement principles and the role of surfactants used in sample preparation are discussed.
