Study of the thermal treatment of SiO₂ aggregate

Crystalline quality and the silanoles defects (Si-OH) present within the structure of natural SiO₂ play an important role in its reactivity. In this work, the relationship between the loss of silanoles and the crystallinity improvement upon heating between 450 °C and 650 °C was shown using X-Ray Diffraction (XRD) and Fourier Transform mid Infrared Spectroscopy in Attenuated Total Reflection (ATR). A shift of the principal band Si-O-Si from 1078 cm⁻¹ to 1082 cm⁻¹ and the decrease of the intensity of the Si-OH bands at 555cm⁻¹and at 950cm⁻¹ upon heating between 450 °C and 650 °C were shown. The reduction of the band is correlated to the loss of silanoles. In agreement with FT-IR results, the decrease of the FWHM of the XRD peaks shows that the crystalline quality is improved upon heating. This result leads to a decrease of the reactivity of SiO₂ aggregate under chemical attacks.