重铬酸钾滴定法测定硼铁合金中全铁

Determination of total iron in ferroboron by potassium dichromate titrimetric method

采用氢氧化钠和过氧化钠混合熔剂熔融分解试样,分解后的熔融物以热水浸取,30mL HNO3(1+1)酸化、硫磷混酸冒烟除去氮氧化物及过氧化氢、盐酸提取后,用二氯化锡先将大量的三价铁还原为二价铁,然后以钨酸钠为指示剂指示还原的终点,逐滴加7滴15g/L三氯化钛溶液至试液呈蓝色,进一步将剩余的三价铁全部还原为二价铁,同时采用重铬酸钾氧化至"钨蓝"褪去的方法消除了过量三氯化钛的影响。最后,以二苯胺磺酸钠为指示剂,用重铬酸钾标准滴定溶液对样品溶液中全铁进行滴定,实现了对硼铁合金中全铁量的测定。实验表明,硼铁合金中共存元素不干扰全铁的测定。方法已用于硼铁合金标准样品中全铁的测定,测定结果与认定值相符,相对标准偏差(n=7)均小于0.5%。

After the sample was melted and decomposed by mixed flux of sodium hydroxide and sodium peroxide,the fusion sample was leached with hot water and acidized by 30 mL HNO3 （1 ＋1）.Then sulfuric acid and phosphorus acid were added to eliminate nitrogen oxide and hydrogen peroxide.After the sample was further extracted by hydrochloric acid,stannous chloride was first added to reduce the majority of ferric iron into ferrous,then 7 drops of 15 g/L titanium trichloride solution was added until the solution turn blue in order to reduce the residue ferric iron into ferrous.Simultaneously,the impact of excess titanium trichloride was eliminated by the fading of tungsten blue oxidized by potassium dichromate.Finally,total iron in the sample solution was titrated by potassium dichromate standard titration solution with sodium diphenylamine as indicator to realize the determination of total iron in boron ferroalloy.Experiment indicated that the coexistence elements in ferroboron had no interference with the determination of total iron.The method was applied to determination of total iron in ferroboron certified reference materials.The results were conformed to the certified values,and the relative standard deviations （RSD,n =7） was smaller than 0.5％.