Perfluoropolyether (PFPE) is a type of liquid lubricant that has been used in the aerospace industry for over 30 years. The main properties of PFPE are being temperature resistant between and (depending on specific composites), having very low outgassing compared to other fluids ( vapour pressure of ) and having a dielectric strength of around 15.7 MV/m. Perfluoropolyether consists of a

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

chain in which

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification ...

s consisting of perfluoro-

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloal ...

groups are joined by

ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...

linkages. The bonds between

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

or fluorine are strong. The thermal and chemical stability of PFPE along with a

vapor–liquid equilibrium In thermodynamics and chemical engineering, the vapor–liquid equilibrium (VLE) describes the distribution of a chemical species between the vapor phase and a liquid phase. The concentration of a vapor in contact with its liquid, especially a ...

of 230 °C when mixed with the right composites make it a suitable candidate for vapor phase

soldering Soldering (; ) is a process in which two or more items are joined by melting and putting a filler metal ( solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike welding, soldering does not in ...

technologies.

History

It's been developed in early 1960s at request of

USAF The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...

with a requirement to be non-reacting with

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, an ...

and gaseous oxygen (O₂).

Manufacture

Perfluoropolyether can be synthesized from

tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a ...

or hexafluoropropylene.

Properties

PFPE is chemically inert to many acids and

oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ...

s (like fuming sulfuric acid (oleum, SO₃),

chlorine gas Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

) and solvents, etc.. PFPE is non-toxic under normal conditions, nonflammable, and exhibit unusually high load carry capabilities. PFPE can withstand gamma ray degradation. Electrical resistivity is 10¹⁴ ohm/cm ()

Applications

Generally PFPE may be used as lubricant in all sorts of bearing, plug valves, gaskets, chains, and joint bearing applications, where oxygen inertness of a material is a requirement. Examples include aircraft fuel systems, mechanical components of devices used in

airspace Airspace is the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere. It is not the same as aerospace, which is the ...

, deep space or high vacuum and at cryogenic temperatures. PFPE may be used in mold release agent for plastic injection molding. As top coating lubricant on computer disc drives and Scanning Electron Microscope As anti-galling compounds. As fluid medium in ferrofluidic seals.

Semiconductor industry

In the semiconductor industry, PFPE may be used as a vacuum grease or in plasma etching equipment, or for robots used in seminconductor

wafer A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...

handling, clean rooms, and other commercial environments.

References