DETERMINATION OF TRACE SILICON IN HIGH-PURITY TITANIUM AND CHROMIUM BY MOLYBDOSILICIC ACID BLUE SPECTROPHOTOMETRY AFTER FLUORIDE SEPARATION

Fluoride separation-molybdosilicic acid blue spectrophotometry was applied to the determination of trace silicon in high-purity titanium and chromium samples. The analytical procedure used is as follows: dissolve 1.0 g of the sample in 6 ml of hydrochloric acid by heating. After replacing the hydrochloric acid with 20 ml sulfuric acid by the aid of a nitrogen gas flow, add 0.5 ml of 0.05% hydrofluoric acid for the chromium matrix, or the same amount of 10% acid for the titanium matrix, to yield volatile silicon tetrafluoride. Transfer the fluoride completely into a boric acid solution by purging it with nitrogen. Then, move the solution into a 25 ml flask, and add hydrochloric acid and ammonium molybdate to form molybdosilicate. After adding oxalic acid and ascorbic acid, measure the light absorbance of the solution at 810 nm. By this method, ppm level silicon in commercial high-purity titanium and chromium samples were successfully determined. Recoveries (n = 10) of 10 mu g of silicon were 98% and 97%, respectively, for The detection limit (3 sigma) was 0.07 ppm for 1 g of both kinds of sample.