Physico Chemical Characteristics of Precipitated Silica
1. BET Surface area Brunauer, Emmett and Teller developed the process of calculating the surface area of precipitated silica. This method of calculating the surface area is popularly known as BET surface area.
2. pH value The pH value of precipitated silica is generally in neutral range. It is determined electrometrically with a glass electrode and pH meter.
3. Drying loss There is very small amount of physically bonded water content in precipitated silica. The major part of this water content is removed by drying in drying cabinet at 105oC for 2 hours.
4. Ignition Loss Precipitated silica contains chemically bonded water in the form silanol groups is also removed after 2 hours of ignition time at 1000oC. The ignition loss is determined with the substance that has previously been dried for 2 hours at 105oC.
5. SiO2 content Silicon dioxide content is determined gravimetrically by fuming off with hydrofluoric acid. The sulphate and chloride contents are determined by potentiometric titration.
6. SIEVE residue SIEVE residue is determined by using Mocker apparatus. In this process the silica suspension is washed through the sieve with 4 bar water pressure. 45 micron sieves (325 mesh) is used for this process. The sieve is then dried and sieves residue is weighed.
7. Tamped density The tamped density is calculated from the initial weight of the sample and the resulting volume, reported in g/l. It is used for the purpose of calculating weight of product in powder form.
8. DBP absorption The DBP absorption is a numerical value used to indicate absorptive capacity of filler. Owing to the automatic measurement process, however, this method can be carried out more accurately than the determination of the oil absorption. The DBP absorption capacity is influenced by other parameters, such as the particle size.