The deposition behaviour of colloidal corrosionproduct particles under isothermal conditions and different modes of heat transfer at atmospheric pressure has been reported previously -under conditions where the particles and heat-transfer surface had opposite electrostatic charges so the fouling process was under transport control. Reported here are observations from a recirculating loop of the deposition of nickel ferrite from suspension in alkaline water during sub-cooled boiling at the

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... e of an Alloy-800 tube. Control was nominally by attachment. The experiment involved tracing the particles with radioactive 60 Co so that their accumulation on the tube could be monitored remotely. A radioactive scoping test lasting 147h was followed by a test with three continuous, sequential periods when the surface radioactivity was monitored. The first, for 117 h, involved exposure to a ~5-ppm suspension, followed by a 124-h exposure to a nominally identical but non-radioactive suspension, followed by a 68-h exposure to water nominally devoid of nickel ferrite. The deposition during the first period followed kinetics similar to those measured under transport control in previous experiments and could be described by a mechanistic model developed previously. The surface radioactivity during the second period decreased, even whilst non-radioactive particles continued to deposit, but tended towards an asymptotic value at a rate that suggested that consolidation of a large portion of the deposit occurred abruptly. The final period saw a further decrease in surface radioactivity, presumably due to dissolution and release of deposit in the solute-free environment. These results are described with a mathematical model and their implications discussed in the context of the previous experiments.