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When selecting fumed silica for a formulation, BET surface area is often one of the first specifications customers compare.
However:
Two fumed silica grades with similar BET values do not necessarily produce the same rheological behavior.
Why?
Because BET is only one part of the material characteristics.
Fumed silica contains surface groups that influence how silica particles interact with each other and with the formulation.
Hydrophilic and hydrophobic fumed silica can therefore behave differently even when their BET values are relatively similar.
Hydrophobic grades are surface-treated to modify the silica surface and change its interaction with the formulation.
The same silica can behave differently depending on:
Poor dispersion may result in agglomeration and inconsistent rheology.
For sealants, fumed silica may be used to control:
If the silica grade changes, the formulation may need to be adjusted even when the BET value looks similar.
No.
BET remains an important specification.
The point is that BET should not be treated as the only basis for direct replacement.
A better evaluation is:
BET → surface treatment → dispersion → rheology → extrusion → finished-product testing
IOTASILICA currently offers several hydrophobic fumed silica grades, including IOTA HB7132, HB7135, HB7139 and HB7151.
For customers considering a hydrophobic fumed silica replacement, the most useful information is not simply:
“I need 200 m²/g silica.”
It is better to provide:
This information allows a more meaningful product evaluation.
Product Reference: IOTA Hydrophobic Fumed Silica Series
Final selection should be verified through formulation and application testing.
