2. Precipitated Silica VS Fumed Silica
a. Method of production
Precipitated Silica is produced by reacting a silicon-containing compound with an acid to form a precipitate of silica, which is then collected, washed, dried, and ground to produce a fine, white powder. The idealized equation involving a trisilicate and sulfuric acid is:
Fumed silica is produced by heating a silicon-containing compound to high temperatures in an oxygen-free environment, which breaks down the compound into its individual elements releasing silicon, oxygen, and other gases.The silicon reacts with the oxygen in the air to create a fine, white powder that consists of microscopic particles of silica (SiO2).The reaction equation is as follows:
b. Difference Between Precipitated Silica and Fumed Silica
One of the main differences between fumed silica and precipitated silica is their particle size. Fumed silica is made up of extremely small particles that are less than 100 nanometers in diameter, while precipitated silica is made up of larger particles that are typically in the range of 10 to 50 micrometers in diameter. This difference in particle size gives fumed silica and precipitated silica different physical and chemical properties, which can make them more suitable for different applications.
Another difference between fumed silica and precipitated silica is their purity. Fumed silica is typically composed of 99.8% silica, while precipitated silica is typically composed of around 90% silica. Fumed silica also has a low moisture content, while precipitated silica has a high moisture content.
The last difference between fumed silica and precipitated silica is the cost. Fumed silica is more expensive than precipitated silica due to the differences in their production processes and the resulting properties of the silicone. In the rubber industry, fumed silicas are limited due to expense, mainly used as reinforcing fillers for silicone rubbers. As silicone rubber fillers, precipitated silica is an alternative to fumed silica in silicone rubber compounds by reducing cost and process in efficiencies for silicone rubber compounders.
3. The different impacts of Precipitated Silica and Fumed Silica on silicone
Precipitated silica and fumed silica can both be used as reinforcement fillers for silicone to improve its strength and durability. However, they have different impacts on the properties of silicone, due to the differences in their composition and physical properties.
Silicone with Fumed silica as filler has much better tensile strength, abrasion resistance, and Elongation than Precipitated silica.
Silicone with fumed silica as a reinforcement filler can have higher transparency. Fumed silica can produce translucent or even clear, non-yellowing silicone with minimal aging effect. silicone with precipitated silica as a reinforcement filler may have low transparency.
Silicone with precipitated silica as filler will turn white when stretched or twisted, but fume silica won’t.
Silicone with fumed silica as filler will have better quality than precipitated silica.
Why silicone with precipitated silica as the filler will turn white when pinched or twisted but fumed silica won’t?
Silicone products that are produced with precipitated silica as a filler will turn white when they are stretched or deformed. This is known as strain whitening, and it is a normal phenomenon that occurs when the outer layer of the silicone becomes strained and becomes more transparent, resulting in a white appearance. This is different from fumed silica, which does not typically cause strain whitening when used as a filler in silicone.
The reason for this difference is that precipitated silica has a relatively low surface area and a narrow range of particle sizes, which can make it more susceptible to strain whitening. Fumed silica, on the other hand, has a very high surface area and a wide range of particle sizes, which can help to prevent strain whitening.
Overall, strain whitening is not a problem with silicone products that are produced with fumed silica as a filler. However, it is something to be aware of when using silicone products that are produced with precipitated silica, as they may turn white when stretched or deformed.