mixed oxides of nitrogen

{{Short description| Solutions of nitric oxide in dinitrogen tetroxide/nitrogen dioxide.}}

Mixed oxides of nitrogen (MON) are solutions of dinitrogen trioxide (N₂O₃) in dinitrogen tetroxide/nitrogen dioxide (N₂O₄ and NO₂). It may be used as an oxidizing agent in rocket propulsion systems.{{cite report |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA036741 |archive-url=https://web.archive.org/web/20160303225221/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA036741 |url-status=dead |archive-date=March 3, 2016 |title=USAF Propellant Handbooks. Nitric Acid/Nitrogen Tetroxide Oxidizers. Volume II |author=Wright, Alfred C. |work=USAF |publisher=Defense Technical Information Center |id=AFRPL-TR-76-76 (DTIC Accession Number ADA036741) |date=February 1977 |access-date=14 April 2013}}

Mixed oxides of nitrogen are produced by dissolving nitric oxide (NO) gas in liquid dinitrogen tetroxide. Nitric oxide reacts with nitrogen dioxide, present in dinitrogen tetroxide, to from dinitrogen trioxide. Resulting mixture is greenish blue, while dinitrogen tetroxide is colorless or brownish yellow. Liquid phase of MON contains no nitric oxide.{{Cite encyclopedia |title=Dinitrogen Tetroxide |chapter=N₂O₄/N₂O₃ Mixtures|encyclopedia=Encyclopedia of Oxidizers |publisher=De Gruyter |last= Schmidt |first=Eckart W. |volume=1|date=2022 |pages=437–453 |doi=10.1515/9783110750294-005 |isbn=978-3-11-075029-4}}

{{chem2|N2O4 <-> 2NO2}}

{{chem2|NO2 + NO <-> N2O3}}

A broad range of compositions is available, and can be denoted as MONi, where i represents the percentage of nitric oxide in the mixture (e.g. MON3 contains 3% nitric oxide, MON25 25% nitric oxide). An upper limit is MON40 (40% by weight). In Europe MON 1.3 is mostly used for rocket propulsion systems, while NASA seems to prefer MON 3. A higher percentage of NO decreases the corrosiveness of the liquid, but decreases oxidation potential and increases costs.

The addition of nitric oxide also reduces the freezing point to a more desirable temperature. The freezing point of pure nitrogen tetroxide is {{convert|-9|°C|°F}}, while MON3 is {{convert|-15|°C|°F}} and MON25 is {{convert|-55|°C|°F}}.{{cite web |url=http://www.braeunig.us/space/propel.htm |title=Rocket Propellants |author=Robert A. Braeunig |publisher=Rocket and Space Technology |year=2008 |access-date=14 April 2013 |archive-url=https://web.archive.org/web/20130521134626/http://www.braeunig.us/space/propel.htm |archive-date=21 May 2013 |url-status=dead }}