The Deposition and Removal of Sub-Micron Particles of Magnetite at the Surface of Alloy 800

Abstract

The rate of isothermal deposition of sub-micron particles of magnetite onto the surface of Alloy 800 has been measured at pHs between 4.2 and 9.3 at Re = 10 000 and a fluid temperature of 25 degrees C. Deposition is modelled as a two-step process; transport of particles to the surface region followed by attachment to the surface. The deposition is limited by particle transport between pH 6.5 and 8.3, and by the rate of attachment for pH outside of this range. The rate of attachment has an Arrhenius dependence on surface temperature with an activation energy of 42 kJ/mole at pH 9.3. The rate of particle removal was negligible compared to the deposition rate, probably because the thickness of the viscous sub-layer was very much greater than the particle size.