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Hydrazine

physical science Maturity 9-11 Next article →

Hydrazine is an inorganic chemical compound with the formula N2H4. It is a colorless, flammable liquid that smells like ammonia.

Sample of hydrazine hydrate
Sample of hydrazine hydrate

Because pure hydrazine is highly hazardous, it is often handled in a solution. One common form is hydrazine hydrate, which is a 64% solution of hydrazine in water by weight. Around 120,000 tons of hydrazine hydrate are manufactured worldwide every year. This substance is vital for modern technology, ranging from space exploration to medicine.

One of the most important ways hydrazine works is as a monopropellant for spacecraft. In these engines, the liquid hydrazine is passed over a catalyst. A catalyst is a material that speeds up a chemical reaction without being consumed itself. Often, scientists use iridium metal supported by alumina, which is a type of aluminum oxide. When the hydrazine hits the catalyst, it decomposes into several gases. This process includes producing nitrogen gas, ammonia, and hydrogen gas.

Hypergolic Fuels test 1958
Hypergolic Fuels test 1958

These chemical reactions are extremely exothermic. This means they release a massive amount of heat very quickly. The reaction can reach high temperatures in just a few milliseconds. This heat turns a small amount of liquid into a very large volume of hot gas. This rapid expansion provides the thrust needed to move spacecraft. For example, the Viking landers in the 1970s used these engines. More recently, Mars landers like Phoenix, Curiosity, and Perseverance have used hydrazine for propulsion.

Hypergolic3
Hypergolic3

Hydrazine is also used in two-component rocket fuels. In these systems, the fuel reacts with an oxidizer. This reaction is hypergolic, meaning it starts burning instantly upon contact without needing an external spark.

Hypergolic Fuel for MESSENGER
Hypergolic Fuel for MESSENGER

A famous example is Aerozine 50. This is a 50:50 mixture of hydrazine and unsymmetrical dimethylhydrazine (UDMH). This specific blend was used in the Apollo Lunar Module. It was also used in the Titan II intercontinental ballistic missiles.

Beyond space, hydrazine serves as a precursor for many important chemicals. A precursor is a starting material used to create a more complex substance. Chemists convert hydrazine into heterocyclic rings, which are ring-shaped molecules containing nitrogen. These rings are found in many pharmaceuticals and pesticides. For instance, the antifungal medicine fluconazole is synthesized using hydrazine.

Fluconazole skeletal formula
Fluconazole skeletal formula

It is also used to create various insecticides, herbicides, and plant growth regulators.

Industrial uses for hydrazine are also quite diverse. It acts as a blowing agent to create polymer foams. It is also used to make sodium azide, which is the gas-forming agent in car airbags. In large industrial boilers, hydrazine acts as an oxygen scavenger. This means it removes dissolved oxygen from the water to reduce corrosion in the system. Some aircraft, like the F-16 fighter jet, use a 70% hydrazine mixture for emergency power. This system provides electrical and hydraulic power if an engine fails in flight.

Despite its many uses, hydrazine is a dangerous substance. It can be absorbed through the skin, eyes, or lungs. Exposure can cause skin burns, nausea, dizziness, and even organ damage to the liver or kidneys. Because of these risks, workers often wear specialized safety suits when handling it.

Hypergolic Fuel for MESSENGER
Hypergolic Fuel for MESSENGER

Some health organizations, such as the EPA, classify it as a probable human carcinogen. Because of these safety concerns, the aerospace industry is currently researching safer alternatives, such as nitrous oxide-based propellants.

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🖼️ Images & Media (7)
File:Fluconazole skeletal formula.svg
Fluconazole skeletal formula.svg
File:Puch MS 25 with hydrazine-air fuel cell, Technisches Museum Wien.jpg
Puch MS 25 with hydrazine-air fuel cell,...
File:Hypergolic Fuels test 1958.gif
Hypergolic Fuels test 1958.gif
File:Hypergolic Fuel for MESSENGER.jpg
Hypergolic Fuel for MESSENGER.jpg
File:Hypergolic3.gif
Hypergolic3.gif
File:Pechiney-Ugine-Kuhlmann process.png
Pechiney-Ugine-Kuhlmann process.png
File:Sample of hydrazine hydrate.jpg
Sample of hydrazine hydrate.jpg
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