Red fuming nitric acid

Red fuming nitric acid

Names
IUPAC name Nitric acid
Other names Red fuming nitric acid
Identifiers
CAS Number	52583-42-3 Y
ChemSpider	None
CompTox Dashboard (EPA)	DTXSID5029685
Properties
Chemical formula	HNO3 + NO2
Appearance	Liquid, red fumes
Density	Increases as free NO2 content increases
Boiling point	83 °C (181 °F; 356 K)
Solubility in water	Miscible in water
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Skin and metal corrosion; serious eye damage; toxic (oral, dermal, pulmonary); severe burns
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid (HNO₃), 13% dinitrogen tetroxide (N₂O₄) and 1–2% water.^[1] The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form nitrogen dioxide. The nitrogen dioxide dissolves until the liquid is saturated, and produces toxic fumes with a suffocating odor. RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water.

It is usually used with an inhibitor (with various, sometimes secret, substances, including hydrogen fluoride;^[2]: 62 any such combination is called inhibited RFNA, IRFNA) because nitric acid attacks most container materials. Hydrogen fluoride for instance will passivate the container metal with a thin layer of metal fluoride, making it nearly impervious to the nitric acid.

It can also be a component of a monopropellant; with substances like amine nitrates dissolved in it, it can be used as the sole fuel in a rocket. This is inefficient and it is not normally used this way.

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 as an ignition catalyst^{[2]: 115–9}) and SV-Stoff (94% nitric acid with 6% dinitrogen tetroxide) and nicknamed Salbei (sage).

Inhibited RFNA was the oxidizer of the world's most-launched light orbital rocket, the Kosmos-3M. In former-Soviet countries inhibited RFNA is known as Mélange.

Other uses for RFNA include fertilizers, dye intermediates, explosives, and pharmaceutical acidifiers. It can also be used as a laboratory reagent in photoengraving and metal etching.^[3]