Neutron imaging of froth structure and particle motion

This article reports on the simultaneous measurement of foam structure and attached particles employing neutron imaging. An aqueous foam sample is placed in the NEUTRA beamline at PSI, enabling a spatial resolution of less than 200 micron to be achieved at a frame rate of more than 1 Hz. A forced drainage setup allows the liquid content of the foam to be controlled. The averaged attenuation of the neutrons is demonstrated to yield the liquid fraction of the foam. Hydrophobized gadolinium particles with a diameter of 200 microns are added to the foam. Using two surfactants, different levels of hydrophobicity are achieved. Depending on the drainage flow and the hydrophobicity, the particles are washed out of the foam at different rates. An avalanche-like motion of particle clusters is observed. Neutron radiography is demonstrated to yield unique insights into the unsteady froth flotation process.