Determination of niobium in titanium-aluminum-niobium alloy by tannic acid precipitation separation-ceric sulfate titration method
Titanium-aluminum-niobium(Ti-Al-Nb)alloy has been widely used in the field of aerospace be-cause of its good properties such as low density,oxidation resistance and high temperature resistance.The accurate determination of niobium content in Ti-Al-Nb alloy is of great significance.When niobium is titra-ted with ceric sulfate standard solution,the titration result will be influence by the coexisting titanium.In experiments,the Ti-Al-Nb alloy was dissolved with sulfuric acid,hydrofluoric acid and nitric acid.The tannic acid was added to precipitate niobium,realizing the separation from most of titanium.After dissol-ving the precipitate,hydrogen peroxide was added into sulfuric acid medium to form stable niobium-hydro-gen peroxide complex(1∶1)with niobium.Then excessive ammonium ferrous sulfate standard solution was added quantitatively to destroy the niobium-hydrogen peroxide complex,and the residual ammonium ferrous sulfate standard solution was titrated with ceric sulfate standard solution.Finally,the content of niobium could be calculated.Consequently,the method for the determination of niobium in titanium-alu-minum-niobium alloy was established.The interference of titanium with the determination of niobium was investigated.The results showed that the maximum allowable amount of titanium was 1.60 mg for the so-lution containing 4.00 mg of niobium.Since the content of titanium in the testing solution after tannic acid precipitation separation was much lower than 1.60 mg,the titration of niobium would be not affected.The content of niobium in Ti-Al-Nb alloy sample was determined according to the experimental method.The relative standard deviations(RSD,n=11)of determination results were between 0.21％and 0.25％,and the range was 0.30％-0.33％.The spiked recoveries were between 99％and 101％.
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