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Stabilization of Microparticle Suspension by Means of Nanoparticle with Focus on the Optical Measurement Methods

Keramati, Hadi | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46101 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saidi, Mohammad Hassan; Mozafari, Ali Asghar
  7. Abstract:
  8. Many of industrial processes include suspension in their middle section of production, final product or residue. Majority of these two-phase mixtures are unstable due to their large particle size (larger than one micrometer). Therefore, Study of particle distribution in suspensions for generation of stabilized suspension becomes significant. In this study a new mechanism in stabilization of microparticle suspension known as nanoparticle halo mechanism has been assessed. Experiments have been conducted in dilute suspension and two-way coupling range. The effect of the presence of silica nanoparticle on zirconia microparticle suspension has been investigated. The effect of zeta potential of microparticles and nanoparticles on nanoparticle halo mechanism has been assessed. Turbidity and microscopic imaging have been used for testing stability. Experiments have been conducted in different pH and volume fraction of particles in order to achieve an inclusive result. Experimental results show that in all pH values, the addition of a slight silica volume fraction of nanoparticles do stabilize zirconia microparticle suspension. Stability Efficacy in different pH values changes due to the differences in zeta potential and particles interaction. When microparticles and nanoparticles had high negative zeta potential, the lowest stability was recorded by turbidity test. When zirconia microparticles were in isoelectric condition and silica nanoparticles had relatively adequate negative charge, higher stability was recorded. Scanning Electron Microscope imaging showed the presence of nanoparticle halo around microparticles surface. Nanoparticles segregate into the potential well at microparticles surface and form a halo as a result of repulsion between nanoparticles. This halo decreases van der walls force between microparticles and increase electrostatic force by increasing the charge of microparticles. Therefore, agglomeration and sedimentation of microparticles are postponed. Decrease in agglomeration and sedimentation has been accredited by microscopic imaging in qualitative and quantitative ways.An increase in nanoparticles volume fraction results in two different behaviors in two regions. An increase in volume fraction leads to an increase in stability up to a certain volume fraction. Increasing volume fraction over this certain amount leads to appearance of depletion force and instability. Attraction depletion force that appears because of osmotic pressure is the dominant force and leads to instability in high volume fraction of nanoparticles
  9. Keywords:
  10. Stability ; TURBIDITY ; Microparticle Suspension ; Nanoparticle Halo

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