ASTM D6845-12 Test Method for Silica, Precipitated, Hydrated—CTAB (Cetyltrimethylammonium Bromide) Surface Area
ASTM D6845-12 T method covers the measurement of the specific surface area of precipitated silicas exclusive of the area contained in micropores too small to admit hexadecyltrimethyl-ammonium bromide (cetyltrimethylammonium bromide, commonly referred to as CTAB) molecules. This test method is suitable for characterizing rubber-grade silicas of all types.
Scope:
ASTM D6845-12 T Test method used for surface area measurement of particle size. This method is used in the silica and rubber industries. Determination of cetyltrimethylammonium bromide adsorption – CTAB (adsorption of large molecules, which cannot enter microspores; it gives information about the effective outer surface that is accessible for rubber molecules)
Test Procedure:
It is a method for measuring external surface area that is more closely related to the area available to rubber. The CTAB adsorption by silica is independent of functional groups containing hydrogen and oxygen. It is based on covering the silica aggregate with a monolayer of CTAB molecules and then titrating the excess with dioctyl sodium sulfosuccinate (Aerosol OT). The amount of CTAB adsorbed can be related to the surface area available for reaction with rubber.
Specimen Size:
A sample of silica.
Data:
S = (2V0 – V) × 4774 / [V0 × W(100 – Vol)]
Where,
S = CTAB surface area of dried silica, 103m2/g,
V0 = volume of OT required to titrate 5cm3 of CTAB
(Blank),
V = aerosol OT solution required for the 10 cm3 sample,
W = sample mass, g, and
Vol = volatile matter of silica, %.
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