Preparation of High Hardness Transparent Coating with Controllable Refractive Index by Sol-Gel Technology

SiO2/ZrO2 and SiO2/ZrO2/Al2O3 composite organic–inorganic coatings were prepared by the sol-gel technology. The structure of the coating was characterized by IR, particle size analyzer, SEM, and AFM, respectively. The results showed that ZrO2, SiO2 (inorganic component), and siloxane had undergone a hydrolytic condensation reaction, and the composite organic–inorganic coatings were formed with -O-M-O- (M is Si, Zr) as molecular skeleton network structure. Adding an appropriate ratio of ZrO2 sol, no agglomeration and phase separation occurred, which could significantly improve the refractive index, hardness, and light transmittance of the coatings. Al2O3 sol could greatly improve the friction resistance of the composite organic–inorganic coatings, and the Bayer ratio of the composite coatings could reach 7.86. By adjusting the proportioning of composite sol solution, the refractive index of the composite transparent coatings could be controlled from 1.52 to 1.65.

Surface and Morphological Features of ZrO2 Sol-Gel Coatings Obtained by Polymer Modified Solution

Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2 8H2O solution, modified with polyethylene glycol (PEG) (Mw = 400). The films have thickness of 80 nm and refractive index of about 1.45, which varied with the amount of added PEG. The thermal behaviour of the precursor was studied with thermogravimetry and differential thermal analysis (TG-DTA). The X-ray diffraction (XRD) analysis revealed the presence of a mixture of monoclinic and tetragonal ZrO2 polycrystalline phases with nanosized crystallites. The formation of hydrogen bonds among the organic and inorganic components was proved by means of Fourier transform infrared spectroscopy (FT-IR) analysis, while the different defect centres were investigated with electron paramagnetic resonance (EPR) spectroscopy. The scanning electron microscopy (SEM) images showed that the samples are dense and crack-free, with ganglia-like nanostructure. It was established that the addition of polymer resulted in the introduction of free volume in the films, which also varied with the content of PEG in the precursor solution.