fuming sulphuric acid

Red fuming nitric acid

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists mainly of nitric acid (3), also containing 13% dinitrogen tetroxide and 3% water. The color of the resulting red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form nitrogen dioxide. White fuming nitric acid does not contain free dinitrogen tetroxide.

It is usually used with an inhibitor (with various, sometimes secret, substances, including hydrogen fluoride; any such combination is called IRFNA) because nitric acid attacks most container materials.

It can also be a monopropellant; with substances like ammonium nitrates dissolved in it, it can be used as the sole fuel in a rocket. It is not normally used this way however.

During World War II, the German military used RFNA in some rockets. The mixtures used were called S-Stoff (96% nitric acid with 4% ferric chloride) and SV-Stoff (94% nitric acid with 6% dinitrogen tetroxide).

Inhibited RFNA, used in modified SS-1 Scud missiles as an oxidizer by the Iraqi military during the 1991 Persian Gulf War, was suggested as a possible factor causing Gulf War Syndrome. However, this theory was later refuted.


  • IRFNA IIIa: 83.4% HNO3, 14% NO2, 2% H2O, 0.6% HF
  • IRFNA IV HDA: 54.3% HNO3, 44% NO2, 1% H2O, 0.7% HF
  • S-Stoff: 96% HNO3, 4% FeCl3
  • SV-Stoff: 94% HNO3, 6% N2O4
  • AK20: 80% HNO3, 20% N2O4
  • AK20F: 80% HNO3, 20% N2O4, fluorine-based inhibitor
  • AK20I: 80% HNO3, 20% N2O4, iodine-based inhibitor
  • AK20K: 80% HNO3, 20% N2O4, unknown inhibitor
  • AK27I: 73% HNO3, 27% N2O4, iodine-based inhibitor
  • AK27P: 73% HNO3, 27% N2O4, unknown inhibitor


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