矽溶膠（Na_2O．n SiO_2）是由二氧化矽微粒所組成的水溶液，亦稱為矽酸膠。其具獨特之物理及化學特性，諸如：高比表面積、粒子帶負電性、具粘著性、耐高溫膠化穩定性等，廣泛運用於鑄造業、造紙工業、光電產業等。本研究嘗試將一般工業用途之矽溶膠，使用業界常見之水熱製程來製作出奈米等級之二氧化矽微粉。實驗乃固定200℃溫度，以不同pH值之矽溶膠液與改變水熱持溫時間為參數，探討對產物形貌影響之研究。實驗結果顯示，溶膠液pH值的調整的確會對水熱產物之形貌產生影響；至於持溫時間的增長，除了使反應產物之粒徑與晶構強度隨之變大與增強外，同時亦觀察到產物之形貌會由結球狀之奈米薄片，逐步轉換成為多面體之奈米晶質顆粒。

Silica sol (Na_2O．n SiO_2), also known as silica gel, is an aqueous solution composed of silica particles. The characteristics of silica sol include a large specific surface area, negative particle electronegativity, strong adhesion, high temperature resistance, and stable gelation. These characteristics make silica sol highly valuable in various industries, with applications in foundries, paper-making, and optoelectronics. This study produced nanograde silicon dioxide micropowder from commonly used industrial silica gel by using a hydrothermal process. The effects of the silica gel solution's acidity and hydrothermal holding time on the morphology of the nanograde silicon dioxide micropowder were examined. The acidity of the silica gel solution was found to significantly influence the micropowder's morphology. Extending the holding time not only resulted in larger particles and higher crystalline intensity of the reactive products but also caused a gradual transformation from spherical nanoflakes to polyhedral nanocrystalline particles.