焼成籾殻中の脆性炭化物を利用した非晶質シリカ微粒子の生成プロセス

Abstract

In application of amorphous silica originated from rice husks to industrial raw materials, fine particles less than a few microns are strongly required in the market. A long-time mechanical milling process is necessary to refine raw silica materials due to their high hardness, and results in a remarkable advance of the products cost. In this study, high efficiency refining technique of silica materials using the conventional milling process was proposed. When burning rice husks at 450 600 without air supply, the organic elements such as cellulose, hemi-cellulose and lignin are completely changed to very brittle carbides, and resulted in formation of layer-structures consisting of silica and carbides in the ashes. These brittle carbides easily lead to the fragmentation of hard silica materials, and very fine particles are successfully prepared by milling process. Raman spectroscopy and SEM-EDS analysis was effective to optimize the burning temperature of rice husks to obtain the carbide layers in the ashes. For example, when more than 34 wt% carbonized elements are contained in the ashes, one hour conventional milling process is enough to prepare fine amorphous silica particles with a mean particle size less than 1 μm. In comparison with silica materials with no carbide, the above refining technique remarkably reduced the milling process time to about 1/10. Finally after the secondary combustion of the refined ashes to thermally resolve the carbides and remove the carbon elements, the application of the optimized combustion temperature from 750~850 resulted in high-purity fine silica particles with a low carbon content less than 0.06 wt%.