Abstract： The testing condition of determining silicon dioxide in magnesia by perchloric acid dehydration gravimetric method with acid dissolution was proposed. After 1 g sample was dissolved by 10 mL hydrochloric acid, only 10 mL perchloric acid was applied for the test. Sulfuric acid and nitric acid were used separately as expulsion acid for silicon vaporization test. It was found that when nitric acid was used as expulsion acid, the weight loss of silicon was the same as SiO2 in the residue while sulfuric acid was used as expulsion acid, the testing result of SiO2 was lower. The residue after the volatilization of silicon was melted by anhydrous sodium carbonate and boric acid mixed flux (msodium carbonate: mboric acid=2∶1) and leached by hydrochloric acid,then ICP-AES was used for determination. It was found its major component was MgO. To prevent the production of MgF2 which had high decomposition temperature, F- must be expelled. Meanwhile, ICP-AES was used to determine SiO2 in filtrate. It was found the content of non-aggregated SiO2 was 0.3% (relative amount) lower than the total SiO2 in the sample. Thus, hydrochloric acid can be dehydrated just for one time. Testing was conducted on different level of magnesia standard sample (to be released). The result was consistent with the candidate certified value with the RSD of 1.2%, 0.93% and 0.45%, respectively. The method had simplified operation compared with that of alkali fusion.
