Abstract
With a view towards controlling the molten caustic salts used for descaling of stainless steel, the author has studied the systematic rapid volumetric analysis of sodium nitrate, sodium nitrite, chromium, and iron in the molten caustic salts, and has developed the following method: a sample is taken from the middle part of the bath, weighed, treated with warm water, and filtered.
Then iron is determined from the residue; and sodium nitrate, sodium nitrite, and chromium are determined from the filtrate according to the following procedures.
(1) Sodium nitrate is reduced with ferrous sulfate in a strong sulfuric acid solution in an atmosphere of carbon dioxide, and the excess of ferrous sulfate is titrated with potassium permanganate solution, the chromate have first been reduced by the ferrous sulfate and the excess of ferrous sulfate and the nitrite oxidized by the potassium permanganate solution.
(2) Sodium nitrite is titrated directly with potassium permanganate solution in a weak sulfuric acid solution without the effect of sodium chromate.
(3) Chromium is determined by the ferrous sulfate-permanganate method after oxidation with perchloric acid.
(4) Iron is determined by the Reinhardt method after treating the residue with hydrochloric acid.
(5) The time of determination is about 4050 min.
(6) By using these procedures the author was able to clarify the descaling mechanism of stainless steel, and to simplify the controlling method thereof.
