Effect of Chelating Agents on the Stability of Nano-TiO₂ Sol Particles for Sol–Gel Coating

Agglomeration of sol particles in a titanium alkoxide (tetrabutyl orthotitanate (TBOT), >97%) solution during the hydrolysis and condensation steps makes the sol solution difficult to use for synthesizing homogeneous sol–gel coating. Here, we have investigated the effect of stabilizing agents (acetic acid and ethyl acetoacetate (EAcAc)) on the agglomeration of Ti alkoxide particles during hydrolysis and condensation in order to determine the optimized conditions for controlling the precipitation of TiO2 particles. The study was conducted at R _AC ([acetic acid]/[TBOT]) = 0.1–5 and R_EAcAc([EAcAc]/[TBOT]) = 0.05–0.65. We also studied the effects of a basic catalyst ethanolamine (ETA), water, and HCl on sol stability. The chelating ligands in the precursor sol were analyzed with FT-IR. The coating properties were examined by focused ion beam. The stabilizing agents (acetic acid and EAcAc) significantly influenced the agglomeration and precipitation of TBOT precursor particles during hydrolysis. As R_AC and R_EAcAc increased, the agglomeration remarkably decreased. The stability of the sol with acetic acid and E_AcAc arises from the coordination of the chelating ligand to TBOT that hinders hydrolysis and condensation. A uniform fine coating (thickness: 30 nm) on stainless steel was obtained by using an optimized sol with R_AC = 0.5 and R_EAcAc = 0.65.