Ferroxyl Test for Free Iron

posted on 13 February 2008 | posted in Stainless steel

Ferroxyl Test for Free Iron A Ferroxyl Test for Free Iron, outlined in ASTM A 380-99, section 7.3.4, is a very highly sensitive test and should be used only when traces of free iron or iron oxide is "objectionable". It should be used only by personnel familiar with its limitations.

It consists of 94 weight % of distilled water, 3 weight % of nitric acid, and 3 weight % of potassium ferricyanide. The potassium ferricyanide can emit lethal fumes if they are exposed to concentrated acids, or heated to decomposition.
The solution is best used freshly made, as it has a limited shelf-life.

Highly trained personnel should only be permitted to perform this test. The preferred method of application is by atomizer spray, and inhalation of this spray should be avoided. Alternatively, a filter paper can be soaked with the solution and applied to the surface. The metal turns blue when iron is present.

It is not recommended for use on products destined for use in food, medical or pharmaceutical unless complete removal of the cyanide solution can be guaranteed.

Carbon steel will only contaminate the stainless steel if the passive layer of chromium is destroyed. Very few fabricators have the capability to fabricate in an operating room environment. There are many ways to remove free iron and free iron oxides by using for example, Antox 75E ( a phosphoric acid solution). A ferroxyl test is a test done only to "detect" contamination. Once contamination is detected, then a removal procedure is carried out.


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