Differences Between Fumed Silica and Precipitated Silica
Fumed silicaand precipitated silica exhibit significant differences in raw materials, production processes, physical properties, chemical properties, and applications. Below is a detailed analysis of these differences:
1. Raw Materials and Production Process
Fumed Silica:
Raw Materials: Typically derived from silica sources such as silicone tetrachloride (SiCl₄) or silane (SiH₄).
Process: In high-temperature environments, silicone source gases react with oxygen or ammonia, forming silicone particles. These particles are cooled and collected in an inert gas atmosphere to produce fumed silica.
Precipitated Silica:
Raw Materials: Derived from sodium silicate solutions.
Process: Acid or alkali solutions are added to the sodium silicate solution, causing precipitation of silica. The silica precipitate is then filtered, washed, dried, and calcined to obtain precipitated silica.
2. Physical Properties
Transparency and Color: Fumed silica is generally transparent, whereas precipitated silica is typically opaque white.
Particle Size and Shape: Fumed silica has smaller particle sizes, usually on the nanoscale, and particles are spherical or near-spherical, with fineness exceeding 1000 mesh. Precipitated silica particles are larger, typically on the microscale, with irregular shapes and fineness in the 300–400 mesh range.
Tensile Performance: Fumed silica exhibits higher tear strength and elongation, resists tearing easily, and does not whiten under tension. In contrast, precipitated silica whitens under tension and has lower elongation.
3. Chemical Properties
Purity and Chemical Stability: Due to high-temperature and inert gas conditions during its production, fumed silica has a higher purity and very low impurity content, offering excellent chemical stability. Precipitated silica, although chemically stable, has relatively lower purity and may contain impurities introduced during production.
4. Applications
Fumed Silica:
Its high specific surface area, superior purity, and chemical stability make it ideal for high-end applications. Examples include:
Catalyst supports.
High-performance adsorbents.
Advanced electronic and optical material fabrication.
High-pressure cooker seals, silicone wires, and products requiring high tear strength.
Precipitated Silica:
Due to its cost-effectiveness and versatility, precipitated silica is widely used in various applications, such as:
Desiccants.
Fillers for rubber and plastics.
Anti-caking agents and rheology control additives in the food industry.
Components like remote control buttons, phone keypads, and foot pads, where high impact resistance is needed.