Abstract：During the determination of silicon in aluminum-titanium-boron alloy by silicon molybdenum blue spectrophotometry, titanium in sample can reaction with ammonium molybdate to form titanium molybdate precipitation,which reduces the concentration of molybdate in solution and have an influence on the coloring of silicomolybdic acid.Meanwhile, the titanium molybdate precipitation can also change the absorbance due to the scattering effect,thus affecting the determination results. The sample was decomposed by sodium hydroxide and hydrogen peroxide in experiments. Under slightly acidic conditions, the addition of ammonium molybdate in the coloring stage of silicon molybdenum yellow with two-fold dosage of that in traditional silicon molybdenum blue spectrophotometry could realize the complete coloring of silicon molybdenum yellow. Before reducing silicon molybdenum yellow to silicon molybdenum blue,the mixture of oxalic acid and sulfuric acid were added to accelerate the dissolution of titanium molybdate due to the complexation between oxalic acid and titanium,thus eliminating the interference of titanium molybdate precipitation with the determination. The ascorbic acid was used to reduce silicon molybdenum yellow to silicon molybdenum blue. After stable for 30 min, the absorbance of solution was measured on spectrophotometer at wavelength of 660 nm. The method for direct determination of silicon in aluminum-titanium-boron alloy by spectrophotometry without separation of titanium was established.The result showed that the mass concentration of silicon in range of 50-250 μg had a good linear relationship with the corresponding absorbance under the optimized experimental conditions. The correlation coefficient was not less than 0.999. The limit of detection and limit of quantification was 0.002 8% (mass fraction) and 0.009 3% (mass fraction), respectively. The interference test of coexisting ions showed that when the contents of titanium,boron,aluminum, iron and vanadium in aluminum-titanium-boron alloy was at the upper limit,these elements did not interfere with the determination of silicon.The proposed method was applied for the determination of silicon in aluminum-titanium-boron alloy,and the found results were consistent with those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) or gravimetric method.The relative standard deviation (RSD, n=11) of the results was less than 1%.
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