Photometric method for the determination of manganese in alloys containing chromium and vanadium

摘要

Mn in alloys is determined by dissolving said alloy in nitric acid, oxidising Mn present to MnO4- with bismuthate, forming tetraphenyl phosphonium permanganate, extracting the latter and subjecting the extract to photometric determination. If V is also present, the solution to be subjected to extraction should contain 1-3.5M H2SO4: if.Cr is present it should contain 2.5-3.5M H2SO4. In the described procedure, an alloy is dissolved in conc. HNO3, evaporated to dryness (in the case of ferroalloys H2SO4 being then added and the product heated to destroy any organic material due to any C present), the residue redissolved in water, dilute HNO3 added and oxidised with bismuthate. The excess bismuthate is filtered off and NaOH aq. added until the precipitate formed redissolves. H2SO4 is added to the final molarity referred to above. Tetraphenyl-phosphonium chloride solution is added and the corresponding permanganate extracted with chloroform or dichloroethane. Na2SO4 (solid) is added to the extract to clarify and photometry is performed with a green filter.