Chlorine trifluoride

Chlorine trifluoride is an interhalogen compound with the formula ClF₃. This colorless, poisonous, corrosive, and extremely reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room temperature). The compound is primarily of interest as a component in rocket fuels, in plasmaless cleaning and etching operations in the semiconductor industry, in nuclear reactor fuel processing, and other industrial operations.

Molecular Formula: ClF₃

Synonyms:

CHLORINE TRIFLUORIDE

Chlorotrifluoride

7790-91-2

Chlorine fluoride (ClF3)

Trifluorure de chlore

Molecular Weight: 92.45 g/mol

Chlorine trifluoride appears as a colorless gas or green liquid with a pungent odor. Boils at 53°F. It reacts with water to form chlorine and hydrofluoric acid with release of heat. Contact with organic materials may result in spontaneous ignition. It is corrosive to metals and tissue. Prolonged exposure to low concentrations or short term exposure to high concentrations may result in adverse health effects. Under prolonged exposure to fire or intense heat the container may violently rupture and rocket.

Physical Description

Chlorine trifluoride appears as a colorless gas or green liquid with a pungent odor. Boils at 53°F. It reacts with water to form chlorine and hydrofluoric acid with release of heat. Contact with organic materials may result in spontaneous ignition. It is corrosive to metals and tissue. Prolonged exposure to low concentrations or short term exposure to high concentrations may result in adverse health effects. Under prolonged exposure to fire or intense heat the container may violently rupture and rocket.

Reactions

Reactions with many metals give chlorides and fluorides; phosphorus yields phosphorus trichloride (PCl₃) and phosphorus pentafluoride (PF₅); and sulfur yields sulfur dichloride (SCl₂) and sulfur tetrafluoride (SF₄). ClF₃ also violently reacts with water, oxidizing it to give oxygen or, in controlled quantities, oxygen difluoride (OF₂), as well as hydrogen fluoride and hydrogen chloride:

ClF₃ + 2H₂O → 3HF + HCl + O₂

ClF₃ + H₂O → HF + HCl + OF₂

It will also convert many metal oxides to metal halides and oxygen or oxygen difluoride.

One of the main uses of ClF₃ is to produce uranium hexafluoride, UF₆, as part of nuclear fuel processing and reprocessing, by the fluorination of uranium metal:

U + 3 ClF₃ → UF₆ + 3 ClF

The compound can also dissociate under the scheme:

ClF₃ → ClF + F₂

Uses

Semiconductor industry

In the semiconductor industry, chlorine trifluoride is used to clean chemical vapour deposition chambers. It has the advantage that it can be used to remove semiconductor material from the chamber walls without the need to dismantle the chamber. Unlike most of the alternative chemicals used in this role, it does not need to be activated by the use of plasma since the heat of the chamber is enough to make it decompose and react with the semiconductor material

Rocket propellant

Chlorine trifluoride has been investigated as a high-performance storable oxidizer in rocket propellant systems. Handling concerns, however, severely limit its use. John Drury Clark summarized the difficulties:

It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the formation of a thin film of insoluble metal fluoride that protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

The discovery of chlorine pentafluoride rendered ClF₃ obsolete as an oxidizer.

Proposed military applications

Under the code name N-Stoff (“substance N”), chlorine trifluoride was investigated for military applications by the Kaiser Wilhelm Institute in Nazi Germany not long before the start of World War II. Tests were made against mock-ups of the Maginot Line fortifications, and it was found to be an effective combined incendiary weapon and poison gas. From 1938, construction commenced on a partly bunkered, partly subterranean 14,000 m² munitions factory, the Falkenhagen industrial complex, which was intended to produce 90 tonnes of N-Stoff per month, plus sarin. However, by the time it was captured by the advancing Red Army in 1945, the factory had produced only about 30 to 50 tonnes, at a cost of over 100 German Reichsmark per kilogram^a. N-Stoff was never used in war

Hazards

Chlorine trifluoride accident

The first accident involving chlorine trifluoride (ClF(3)) in the history of semiconductor fabrication processes occurred on 28 July 2006 at Hsinchu (Taiwan), resulting in a large release of the highly reactive material and causing the chemical burn to several workers. ClF(3) is used primarily as an in situ cleaning gas in the manufacture of semiconductor silicon-wafer devices in replacement of perfluorocompounds (PFCs) because they have the high potential to contribute significantly to the global warming. This article aimed at reviewing ClF(3) in the physicochemical properties, the industrial uses, and the environmental implications on the basis of its toxicity, reactivity, health hazards and exposure limits. The health hazards of probable decomposition/hydrolysis products from ClF(3) were also evaluated based on their basic physicochemical properties and occupational exposure limits. The occupational exposure assessment was further discussed to understand potentially hazardous risks caused by hydrogen fluoride and fluorides from the decomposition/hydrolysis products of ClF(3).

Chlorine trifluoride where to buy

https://www.worldofchemicals.com/chemicals/chemical-suppliers/chlorine-trifluoride.html

Source:

cameochemicals.noaa.gov/chemical/372

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