Investigating the Dispersion State of Alumina Suspensions: Contribution of CryoFieldEmission Gun Scanning Electron Microscopy Characterizations

We illustrate in this paper the interest of cryo-field-emission gun scanning electron microscopy (cryo-FEGSEM) to investigate the stability of alumina suspensions. The stability is investigated through viscosity, zeta potential, total organic carbon measurements, and cryo-FEGSEM observations. We focus on two examples: the effect of the quantity of ammonium polyacrylate as dispersant and the effect of its chain length on alumina particles dispersion with a solid content of 32 vol%. In the first example for some suspensions, we measure values of viscosity or zeta potential too similar to discriminate the best state of dispersion. To overcome this problem, we directly observe the suspensions with cryo-FEGSEM. We take advantage of the recent developments of the technique, which provide now extremely high cooling rates and ensure that the freezing step does not induce observations artifacts related to the formation of ice. This technique provides an accurate vision of particles dispersion, agglomeration in ceramic suspensions, and it is possible to visualize the excess of dispersant. In the second example, the longer dispersant appears to be the more effective to obtain the best state of dispersion. Through both examples, we demonstrate that to have the best interpretation of results, it is useful to combine direct observations by cryo-FEGSEM and the usual properties measurements.