Red fuming nitric acid
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|Red fuming nitric acid|
|Molecular formula||HNO3 + NO2|
|Appearance||Liquid, Red fumes|
|Density||Increases as free NO2 content increases|
|Solubility in water||miscible in water|
|Main hazards||Skin and metal corrosion; serious eye damage; toxic (oral, dermal, pulmonary); severe burns|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid (HNO3), 13% dinitrogen tetroxide and 1–2% water. 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 evaporates off into 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; 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) and nicknamed Salbei (sage).
Inhibited RFNA was the oxidizer of the world's most-launched light orbital rocket, the Kosmos-3M.
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 and metal etching.
- 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
- When RFNA is used as an oxidizer for rocket fuels, it usually has a HF content of about 0.6%. 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 0.5% by weight. This is very close to the usually 0.6% in rocket fuels.
- 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 0.1% 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, aluminium 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. Aluminium 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 corrosion resistance similar to that of stainless steel. These materials are better though because at high temperatures the corrosion rates did not increase much. It is interesting to note that corrosion rates at elevated temperatures increase in the presence of phosphoric acid. Conversely, the presence of sulphuric acid decreased corrosion rates.
- Clark, John D. (1972). Ignition! An Informal History of Liquid Rocket Propellants. Rutgers University Press. p. 62. ISBN 0-8135-0725-1.
- O'Neil, Maryadele J. (2006). The Merck index: an encyclopedia of chemicals, drugs, and biologicals. Merck. p. 6576. ISBN 978-0-911910-00-1.
- Baker, B. B. (1958). "Rapid Estimation of Hydrofluoric Acid in Red Fuming Nitric Acid". Analytical Chemistry 30 (6): 1085–1086. doi:10.1021/ac60138a025.
- Burns, E. A.; Muraca, R. F. (1963). "Determination of Water in Red Fuming Nitric Acid by Karl Fischer Titration". Analytical Chemistry 35 (12): 1967–1970. doi:10.1021/ac60205a055.
- Karplan, Nathan; Andrus, Rodney J. (October 1948). "Corrosion of Metals in Red Fuming Nitric Acid and in Mixed Acid". Industrial and Engineering Chemistry 40 (10): 1946–1947. doi:10.1021/ie50466a021.