Dispersion stability and sedimentation evolution of Gd-doped SiO2/CeO2 chemical mechanical polishing slurry via the low-field NMR technique

The application of rare earth micro-nano materials requires first formulating them into slurries with high dispersion stability, including polishing powders, catalysts, phosphors, ceramics, and other materials. To achieve this, it is essential not only to prepare monodisperse micro-nano particles but also incorporate appropriate dispersants to prevent particle aggregation. For this purpose, the study designed and synthesized a core-shell structured Gd 3 + -doped CeO 2 -coated SiO 2 composite abrasive: SiO 2 /CeO 2 :Gd. Low-field nuclear magnetic resonance technique was employed to investigate the sedimentation behavior of polishing slurries and explore the mechanism by which different dispersants enhance slurry dispersion stability, achieving real-time nuclear magnetic resonance imaging tracking of the sedimentation process. Results show that: The strong paramagnetic properties of Gd 3+ significantly enhance the relaxation efficiency of water molecules within the particle surface region, thereby serving as a sensitive probe for characterizing the liquid environment at the particle surface. Based on the T 2 distributions, settling can be divided into three stages: homogenization, sedimentation, and agglomeration. In polishing slurries, water molecules primarily exist in three forms: bulk water (P1), hydration layer water (P4) and surface-bound water (P5), attributing to different peaks of T 2 relaxation times. However, only one T 2 peak (P2) was observed for the homogenization slurry due to the rapid exchange among the three kind of water molecules. With the sedimentation proceeding, P2 transforms into two peaks of P1 and P3. The rate of change in the peak areas of P1 and P2 can reflect the sedimentation rate of the slurry. In the agglomeration stage, the overlapping of hydration layers forms interstitial water, leading to an increase in its T 2 relaxation time. Therefore, the P3 can further split into two peaks of P4 and P5, corresponding to interstitial water and surface-bound water in the sediment layer.