The aggregation of iron oxide nanoparticles in magnetic fields

Bradford, Peter (2012). The aggregation of iron oxide nanoparticles in magnetic fields. University of Birmingham. Ph.D.

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Abstract

The application of a magnetic field to a suspension of weakly magnetic nanoparticles should, based on previous work and theory, increase the aggregation between particles. This is due to the increase in the magnetic interaction in competition with repulsive forces due to the electric double layer.

This hypothesis was tested using suspensions of magnetite and hematite nanoparticles. Magnetite particles were used to characterise the aggregation behaviour of strongly magnetic particles, which then served as a basis of comparison with hematite particles in a magnetic field. The expectation was that applying the magnetic field to the suspensions of weakly magnetic hematite particles would alter their aggregation behaviour to be more like that of the strongly magnetic magnetite particles.

Experimental findings indicate this is not the case. No evidence was found indicating that the magnetic field altered particle interactions sufficiently to alter the aggregation. Aggregation behaviour was controlled by the chemical environment and shear forces. The magnetic field did influence the motion of the particles. In static experiments hematite particles were separated from suspension, the efficiency of which was related to the degree of aggregation and thus particle size. In stirred systems the balance between shear and Lorentz forces affected aggregate formation.

As observed in previous work, small aggregation increases are possible but once aggregates reach a certain size the magnetic field affects the movement of particles and does not change interactions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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