Silicomolybdenum Blue Method for the Determination of Total Separated Silica from the Cement Samples

Abstract

Anspectrophotometric method for the determination of silica in the cement samples was described. The method is based on converting silica into silicon tetrafluoride (SiF₄) gas using concentrated hydrofluoric acid (HF) and concentrated sulfuric acid (H₂SO₄) then the amount of generated silicon tetrafluoride gas was determined spectrophotometrically.

The method was simple, rapid, sensitive, selective, accurate and the final green solution was shown a maximum absorption at 747nm. Beers law was obeyed in the silica percentage range of 5-40 SiO₂% with a molar absorptivity (1.69 x10⁴) L.mol^-1.cm^-1, and Sandell’s sensitivity (1.16 x 10^-1) µg.cm^-2.  Limit of detection (LOD) and limit of quantification (LOQ) are 0.06 SiO₂% and 0.19 SiO₂%, respectively. This method shows accurate results and reduced the time of silica estimating compare with the gravimetric method.