Preparation of spherical silica powder by oxygen–acetylene flame spheroidization process

A novel economic oxygen–acetylene flame spheroidization process and special equipments to prepare spherical silica powders are presented. Before spheroidization treatment, the raw silica is purified by mixed acids. In this spheroidization process, oxygen is used both as the carrier gas to transport the purified silica powders to the flame region, and as the combustion-supporting gas. The crystallized silica powders are melted and then transformed to amorphous silica after oxygen–acetylene flame spheroidization treatment. The powder size analysis indicates that the powder size increases and the size distribution become narrower after spheroidization treatment. By optimizing the process parameters, spherical silica powders were obtained. A scanning electron microscope (SEM) investigation reveals that the spheroidization efficiency of the 5 μm diameter powder is more than 95% at feeding rates below 60 g/min. The closer the length–diameter ratio of raw silica powder is to 1, the higher the spheroidization efficiency of the sample is. The fluidity value and apparent density of the powder with the spheroidization efficiency 95% is 70 s/50 g and 0.88 g/cm3, respectively. Oxygen–acetylene flame spheroidization process is a promising low-cost alternative for large-scale production of spherical silica powder.