Full definition
A synthetic, amorphous silicon dioxide (SiO₂) produced by precipitation from sodium silicate solution, used as a reinforcing filler in rubber compounds as an alternative or complement to carbon black. Key advantage: silica with a silane coupling agent (e.g., Si-69/TESPT) produces compounds with significantly lower rolling resistance (hysteresis) while maintaining wet grip — the foundation of "green tire" technology that has reduced automotive fuel consumption by 3-5% since the 1990s. Particle size: 10-30 nm primary particles (similar to reinforcing carbon blacks). Grades per surface area: standard (150-160 m²/g), highly dispersible HD (170-200 m²/g — preferred for tire treads). Dosage: 30-80 phr. Unlike carbon black, silica is hydrophilic (polar surface) and does not naturally bond to non-polar rubber — the silane coupling agent is essential to create a chemical bridge between silica and polymer. Applications: tire treads (low rolling resistance + high wet grip), shoe soles (transparent/colored compounds), food-grade rubber (white, no carbon black), and industrial products requiring light color. Per ASTM D6738 for silica testing. Also provides good tear and abrasion resistance. Suppliers: Evonik (Ultrasil), Solvay (Zeosil), PPG (Hi-Sil).