White fuming nitric acid

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White fuming nitric acid (WFNA) is a storable liquid oxidizer used with kerosene and hydrazine rocket fuel. It consists of nearly pure nitric acid (HNO3). WFNA is commonly specified as containing no more than 2% water and less than 0.5% dissolved nitrogen dioxide or dinitrogen tetroxide.

WFNA was sometimes used with an inhibitor compound to reduce corrosiveness, often hydrogen fluoride. Without inhibitors, WFNA will corrode nearly all structural metals. Inhibited WFNA is often called IWFNA. The hydrogen fluoride addition causes the formation of a protective layer of fluoride on the metal surfaces.

WFNA as an oxidizer has somewhat less performance than red fuming nitric acid (RFNA) but is considerably safer (though extremely corrosive), as it has little to no dissolved nitrogen tetroxide, which is an extremely toxic and volatile chemical. If not inhibited, it will form nitrogen tetroxide on contact with most metals and some organic materials. RFNA can be converted to WFNA by simply leaving the RFNA out in low temperature for a couple of hours.

WFNA was once used in the manufacture of nitroglycerin, an explosive, by mixing it with concentrated sulfuric acid, and then by the slow addition of glycerol. This has now mostly been replaced by a less expensive process that uses a nearly 1:1 solution of oleum and azeotropic nitric acid (70%).

WFNA and IWFNA are hypergolic with a long list of other propellants, including: UDMH, hydrazine, furfuryl alcohol, and aniline.

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