Synthesis, characterization and resistant performance of α-Fe2O3@SiO2 composite as pigment protective coatings

• Homogeneous silica nanoparticles over the surface of α-Fe2O3 at pH = 1.3 is obtained.
• Effect of pH on film morphology, thickness and nanoparticles distribution is discussed.
• Fe2O3@SiNP indicates good acid/alkali-resistance, color stability and UV shielding property.
• The obtained Fe2O3@SiNP reveals greater thermal stability at high temperature.
• The proposed methodology opens a new insight in preservation of cultural heritage.

The natural pigment of hematite (red ocher, α-Fe2O3) is coated homogenously with colloidal silica-nanoparticles (SiNP) by a sol-gel process to obtain a durable hematite pigment of Fe2O3@SiNP composite for artifacts preservation. The acid/alkali-resistance, color stability and UV shielding behavior of obtained Fe2O3@SiNP are investigated. The results indicate that 60 nm thickness of uniformed coating is acquired at pH = 1.3 with 90 nm particle size distribution. Fe2O3@SiNP reveals great thermal stability at 1400 °C with minor color variation and strong acid-alkali resistance properties compared to Fe2O3 after 6 months' accelerated UV weathering, based on that the surface morphology of Fe2O3@SiNP remains intact while pure Fe2O3 is faded with critical deterioration. Therefore, silica-nanoparticles coated on surface of Fe2O3 could form a durable Fe2O3 pigment against acid, alkali, thermal and long term of UV irradiation.