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What method is used for the high-temperature surface treatment of precipitated silica?

2022-02-19

Surface high-temperature treatment involves subjecting precipitated silica to elevated temperatures to remove adsorbed molecules—such as water and other low‑molecular‑weight species—from its surface. While this approach can modestly improve certain vulcanization properties, the effect is not substantial. Surface chemical treatment, on the other hand, entails reacting the active silanol groups on the silica surface with specific chemical reagents, thereby enhancing the compatibility and reactive activity of the silica with polymer matrices. A wide variety of reagents can be employed for such surface modifications, and numerous methods exist; extensive literature and patents address this topic. The following provides a brief overview of some key aspects.

The specific process methods employed are:

(1) Steam method: Dry precipitated silica is brought into direct contact with the vapor of an organic compound, allowing the desired reaction to occur.

(2) Reflux method: The precipitated silica is boiled and refluxed together with the reaction solution to facilitate the desired reaction.

(3) Pressurized Thermal Reaction Method: White carbon black is subjected to high-pressure thermal treatment in an autoclave together with the reaction solution, thereby inducing a specified chemical reaction. The specific chemical reactions involved are as follows: As the degree of hydration increases, isolated silanol groups gradually decrease, while vicinal silanol groups progressively increase. Vicinal silanol groups exhibit a stronger adsorption capacity for water and polar substances.

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Precipitated silica is a high-tech inorganic fine chemical product.

White carbon black, also known as silica, is scientifically termed precipitated hydrated silica. It is a high‑tech inorganic fine chemical product whose main constituent is SiO₂. Its physical properties resemble those of carbon black, appearing as a highly dispersed white amorphous powder or flocculent powder; it is also processed into granular forms for commercial use. Lightweight, with an original particle size below 0.3 μm and a relative density ranging from 2.319 to 2.653, it has a melting point of 1750°C. It is insoluble in water and most acids, but absorbs moisture from the air, forming hygroscopic fine particles. It is soluble in caustic soda and hydrofluoric acid, while remaining inert to other chemicals; it does not decompose at high temperatures nor does it burn. It is chemically inert toward substrates, active ingredients, and additives, and exhibits excellent compatibility with many active components commonly used in vitamins, hormones, fluorides, antibiotics, enzyme preparations, and cosmetics. It possesses high electrical insulation properties. Owing to its porosity and large specific surface area, it demonstrates strong dispersibility in raw rubber and imparts superior reinforcing performance in rubber compounds. Surface‑modified hydrophobic silica readily disperses in oils, rubbers, and plastics as a reinforcing filler, significantly enhancing mechanical strength and tear resistance. Due to variations in manufacturing processes, the physical and chemical characteristics, as well as the microstructure, of silica may differ, leading to distinct application areas and performance outcomes.