School of Engineering
Edith Cowan University
Ministry of Education and Training of Vietnam under the ECU-VIED join grant (No. 23646)
This work investigates the effect of inter-particle forces arising from adsorbed typical cationic and anionic surfactants on the morphology of ball milled gadolinium oxide (Gd2O3). The experimental outcomes are interpreted in terms of stabilization and interaction mechanisms of fine washed Gd2O3 particles (size diameter <1 μm) in aqueous medium under the variation of surface forces arising of adsorbed surfactant. After ball milling and washing, the point of zero charge or isoelectric point (IEP) of Gd2O3 particles suspension is at pH 11 where its maximum yield stress is observed. Because of hydrophobic interaction, the maximum yield stress increases by 30 times by adsorbed sodium dodecyl sulfate (SDS) and its IEP shifts slightly to a lower pH. By cetyl trimethyl ammonium bromide (CTAB), the yield stress also increases by a much smaller extent (3 times) and shifts to a higher pH of 12.5. Without surfactants, the microstructure of dried Gd2O3 displays the coarse particles of various shapes, i.e. rod, spherical and cubic shapes. This indicates that the milled particles remain agglomerated in dispersion. In the presence of adsorbed anionic SDS, the particles are refined together with numerous 2D nanowire or nano-rod particles at pH 8. In contrast, coarser particles with absence of nano-rods are found when cationic CTAB is used to modify the Gd2O3 surface at a pH of about 12.5. The SDS-modified suspension exhibits a much higher yield stress, which results from finer particles in suspension. This is invoked from an organic shell formed by the high adsorbability of negatively charged heads of SDS into the bare positive charge density of the particle. The organic SDS shell prevents the fine particles from re-welding during the dispersing and annealing route. This work develops an inexpensive ball-milling approach with assisted SDS surfactant for mass production of nanosized Gd2O3 from bulky gadolinium material.