Red fuming nitric acid

Red fuming nitric acid
IUPAC name Nitric Acid
Other names Red Fuming Nitric Acid
Identifiers
CAS number	78989-43-2 Y
Properties
Molecular formula	HNO3 + NO2
Appearance	Liquid, Red fumes
Density	Increases as free NO2 content increases
Boiling point	120.5°C
Solubility in water	miscible in water
Hazards
Main hazards	Skin and metal corrosion; serious eye damage; toxic (oral, dermal, inhale); severe burns
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists mainly of nitric acid (HNO₃), also containing 13% dinitrogen tetroxide and 3% water. The dissolved nitrogen dioxide is very concentrated and can be found at room temperature. 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. RFNA gives off a suffocating odor. It increases the flammability of combustible materials and is highly exothermic when reacted with water.

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

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. 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.^{[citation needed]} However, this theory was later refuted.^{[citation needed]}

Other uses for RFNA include fertilizers, dye intermediates, explosives, and pharmaceutic aid as acidifier. It can also be used as a laboratory reagent in photoengraving, metal etching.

Compositions

• 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, fluorine-based inhibitor
• AK27I: 73% HNO₃, 27% N₂O₄, iodine-based inhibitor
• AK27P: 73% HNO₃, 27% N₂O₄, fluorine-based inhibitor

Experiments

• Hydrofluoric Acid Content of RFNA

When RFNA is used as an oxidizer for rocket fuels, it usually has a HF content of about .6%. The purpose of the HF is to act as a corrosion inhibitor. RFNA was tested for HF with a standard solution containing 12% of NO₂ and a density of 1.57. These experiments were performed using an electrometric method. It was determined that the hydrofluoric acid content was about .5% by weight. This is very close to the usually .6% in rocket fuels.

• Water content of RFNA

To test the water content, a sample of 80% HNO₃, 8-20% NO₂, and the rest H₂O depending on the varied amount of NO₂ in the sample. When the RFNA contained HF, there was an average H₂O% between 2.4% and 4.2%. When the RFNA did not contain HF, there was an average H₂O% between .1% and 5.0%. When the metal impurities from corrosion were taken into account, the H₂O% increased, and the H₂O% was between 2.2% and 8.8%

• Corrosion of metals in RFNA

Stainless steel, aluminum alloys, iron alloys, chrome plates, tin, gold and tantalum were tested to see how RFNA affected the corrosion rates of each. This is important to understand because the containers that RFNA is kept in will affect the RFNA. Experiments were performed using 16% and 6.5% RFNA samples and the different substances listed above. Many different stainless steels showed resistance to corrosion. Aluminum alloys did not hold up as well as stainless steels especially in high temperatures but the corrosion rates were not high enough to prohibit the use of this with RFNA. Tin, gold and tantalum showed high resistance such like that of stainless steel. These are better though because at high temperatures, the corrosion rates were still kept low. It is important to note that at higher temperatures and the presence of phosphoric acid, the corrosion rates increase while sulfuric acid helped the corrosion rates and kept the substances from corrosion.

Related

• White fuming nitric acid
• Nitric Acid

External links

• National Pollutant Inventory - Nitric Acid Fact Sheet
• http://www.astronautix.com/props/nitidjpx.htm