Nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, nitro, or nos,[4] is a chemical compound, an oxide of nitrogen with the formula N
2O. At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste.[5] At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen.
Nitrous oxide has significant medical uses, especially in surgery and dentistry, for its anaesthetic and pain-reducing effects.[6] Its colloquial name, "laughing gas", coined by Humphry Davy, is due to the euphoric effects upon inhaling it, a property that has led to its recreational use as a dissociative anaesthetic.[6] It is on the World Health Organization's List of Essential Medicines.[7] It is also used as an oxidiser in rocket propellants, and in motor racing to increase the power output of engines.
Nitrous oxide's atmospheric concentration reached 333 parts per billion (ppb) in 2020, increasing at a rate of about 1 ppb annually.[8][9] It is a major scavenger of stratospheric ozone, with an impact comparable to that of CFCs.[10] About 40% of human-caused emissions are from agriculture.[11][12] Nitrogen is added to the soil via animal urine and dung, and synthetic fertilisers: micro-organisms then release it in nitrous oxide.[13] Being the third most important greenhouse gas, nitrous oxide substantially contributes to global warming.[14][15] Reduction of emissions is a popular topic in the politics of climate change.[16]
Nitrous oxide is used as a propellant, and has a variety of applications from rocketry to making whipped cream. It is used as a recreational drug for its potential to induce a brief "high". When used chronically, nitrous oxide has the potential to cause neurological damage through inactivation of vitamin B12.
Uses[edit]
Rocket motors[edit]
Nitrous oxide may be used as an oxidiser in a rocket motor. It has advantages over other oxidisers in that it is much less toxic, and because of its stability at room temperature, it is also easier to store and relatively safe to carry on a flight. As a secondary benefit, it may be decomposed readily to form breathing air. Its high density and low storage pressure (when maintained at low temperatures) enable it to be highly competitive with stored high-pressure gas systems.[17]
In a 1914 patent, American rocket pioneer Robert Goddard suggested nitrous oxide and gasoline as possible propellants for a liquid-fuelled rocket.[18] Nitrous oxide has been the oxidiser of choice in several hybrid rocket designs (using solid fuel with a liquid or gaseous oxidiser). The combination of nitrous oxide with hydroxyl-terminated polybutadiene fuel has been used by SpaceShipOne and others. It also is notably used in amateur and high power rocketry with various plastics as the fuel.
Nitrous oxide also may be used in a monopropellant rocket. In the presence of a heated catalyst, N
2O will decompose exothermically into nitrogen and oxygen, at a temperature of approximately 1,070 °F (577 °C).[19] Because of the large heat release, the catalytic action rapidly becomes secondary, as thermal autodecomposition becomes dominant. In a vacuum thruster, this may provide a monopropellant specific impulse (Isp) of as much as 180 s. While noticeably less than the Isp available from hydrazine thrusters (monopropellant or bipropellant with dinitrogen tetroxide), the decreased toxicity makes nitrous oxide an option worth investigating.
Nitrous oxide is said to deflagrate at approximately 600 °C (1,112 °F) at a pressure of 309 psi (21 atmospheres).[20] At 600 psi, for example, the required ignition energy is only 6 joules, whereas N
2O at 130 psi a 2,500-joule ignition energy input is insufficient.[21][22]