Morphological Evolution of Low-Grade Silica Fume at Elevated Temperature

Abstract To solve the environmental pollution problem caused by low-grade silica fume (SiO₂, < 86 mass%) and further expand its application field, the morphological development of low-grade silica fume from room temperature to 900 °C in air was investigated using TG-DTA, SEM and TEM techniques. The structural development of silica fume was further analyzed using FT-IR and Raman spectrum. The results show that silica fume contains many defects of broken bands such as Si-O or ≡Si at room temperature. When exposed to the moister or water, the broken bonds tend to react with water and result in the formation of Si-OH and adjacent hydroxyl groups of Si-OH•OH-Si. At elevated temperature up to 900 °C, the structure of silica fume becomes compact due to the reconstruction of the broken bonds caused by the dehydration reaction.