Fluorine materials used in national defense and military industry

This article is transferred from: Chemical Expertise Service System

The fluorine chemical industry rose in the 1930s and is a rapidly growing sub-industry in the chemical industry, which can be divided into inorganic fluoride, fluorinated polymer materials, fluorinated fine chemicals, HCFCs and substitutes. Due to its excellent properties such as chemical resistance, high and low temperature resistance, aging resistance, low friction, insulation, etc., fluorine chemical products are widely used in military, chemical, machinery and other fields, and the demand is growing rapidly.

The development of fluorine chemical industry has a historical origin with the national defense and military industry. After scientists successfully isolated elemental fluorine in 1886, for a long time, the study of fluorine chemistry was basically limited to the laboratories of a few chemists. Until the second world war, the United States implemented the famous Manhattan Project, in the uranium isotope separation and other sub-projects, discovered the special role of fluorine chemicals, and conducted in-depth research on it, the most important application is the separation of uranium-235. In addition, special corrosion-resistant materials and sealing materials are required when processing uranium hexafluoride, which promotes the invention and application of PTFE and fluoroelastomers.

After World War II, the American DuPont Company and 3M Company, which participated in the Manhattan Project, successfully transformed some of these new materials and technologies into civilian products, and fluorine chemical products are more and more recognized and accepted by the public because of their special utilities.

Although fluorinated chemicals have now reached a multi-billion dollar market and are used in everything from heavy industry to daily necessities, it has maintained a natural connection with the defense and military industry, and many new fluorine chemicals have been developed in response to the needs of the defense industry. This article attempts to provide a brief review of fluorine chemicals in the defense and military industries.

Uranium hexafluoride

As mentioned above, the primer for the great development of fluorine chemicals was the synthesis of uranium hexafluoride due to the separation of uranium isotopes. To this day, uranium hexafluoride remains the only way to separate uranium isotopes, and all countries engaged in military or peaceful applications of atomic energy must establish devices for the synthesis of uranium hexafluoride to separate its isotopes.

Uranium hexafluoride is the only suitable gas compound in uranium isotope separation. This compound is solid at room temperature and pressure, but is easily volatile at 56. At 4 °C, it sublimates into a gas. The difference in mass between the uranium hexafluoride molecules of uranium-235 and the uranium hexafluoride molecules of uranium-238 is less than one percent, but it turns out that this difference is enough to separate them.

Magnesium difluoride

Magnesium difluoride is a stable inorganic fluoride that can be synthesized by a special hot pressing method to synthesize optical crystals, which have a good polarization effect on infrared light. Therefore, magnesium difluoride will be used as a coating material for optical instrument lenses and filters, fluorescent materials for cathode ray screens, and antireflective agents for optical lenses.

In the national defense chemical industry, the crystals of high-purity magnesium difluoride are used as optical lenses to transmit infrared light as a window material for missile infrared trackers; in addition, they are also used as lens accessories for ultraviolet optical instruments of spacecraft.

Fluorine gas

The most important use of international production of fluorine gas is the production of uranium hexafluoride and sulfur hexafluoride, however, fluorine itself is a laser material, generally fluorine and inert gas such as argon, krypton, etc.; fluorine atom laser is a multi-wavelength laser, in recent years has achieved relatively rapid development.

In addition, fluorine gas is also used directly in the synthesis of fluorine grease and the treatment of engineering material surfaces.

Sealing material

In the national defense chemical industry, there are special requirements for sealing materials, especially in the special requirements of high corrosion resistance media, high temperature resistance, low temperature resistance, radiation resistance, aging resistance, etc., and some special requirements need fluorine materials to meet. For example, in the aircraft engine and fuel tank fuel circuit sealing, sometimes the need for fluorine silicone rubber and even special benzene fluorosilicone rubber for some structural sealing; transport vehicles and armored vehicles in the engine and fuel tank fuel circuit sealing, the use of high fluorine content of fluoroelastomer can solve the problem of fuel leakage; in the missile and spacecraft rocket fuel system sealing, the need for special N2O4 resistance and at the same time high and low temperature resistance materials, this occasion only perfluoroelastomer can be competent.

 Flame retardant materials

In aircraft, rockets, submarines and other special occasions, the power wire and signal wire foreskin have higher flame retardant requirements, the current better is the use of polyperfluoroethylene propylene, the material has non-flammability and high heat resistance, high insulation, at present at home and abroad has been developed to also be used in high-rise building power lines and computer network signal lines.

For the flame retardant processing of engineering plastics (PC/ABS, PP, PC,, ABS, HIPS), in recent years, it has been found that the specially processed PTFE powder has a special function of preventing the dripping of combustion, and has halogen-free environmental protection, and has been widely added and used. Used to improve the flame retardancy of products.

Three anti-film materials

For anti-biochemical clothing, although rubber materials have a good isolation effect, but because they are not breathable and moisture-permeable, the comfort of the wearers is very poor. Textiles made of 2-way stretched high molecular weight PTFE film have impermeable oil permeable but can be breathable and moisture-permeable, and have been applied in military equipment (three-proof clothing, combat clothing, military boots) and have been widely used in outdoor sports clothing in civilian areas. This textile is also applied to the rain-proof cloth of vehicles and aircraft, and due to its breathability, it can prevent the equipment from rusting due to excessive humid heat inside.

Similar membrane materials are also well used in water treatment fields such as seawater desalination.

Battery membrane material

The fuel cells developed earlier were used in satellites and spacecraft, and their diaphragm material was a composite perfluorinated ion exchange membrane.

At present, due to global oil problems, PFOS proton exchange membranes are also one of the key materials for hydrogen fuel cells with lower costs used in automobiles. In addition, the current widely used lithium battery, its separator material is the use of modified polyvinylidene fluoride, the main component of its electrolyte is also a fluorine-containing compound - lithium hexafluorophosphate; the newly developed electrolyte with higher performance uses organic fluoride, such as lithium trifluoromethanesulfonimide.

Optical materials

There are some special fluorinated polymer materials suitable for optical materials in the defense chemical industry, such as fluorine-containing polyacrylate is a good optical fiber outer material, Teflon AF type of transparent fluororesin is suitable for missile infrared window materials. α-fluoropropylenate is a - plexiglass material that the Soviet Union successfully used in the front windshield of high-speed fighter jets.

Piezoelectric materials

Modified polyvinylidene fluoride material is a good performance piezoelectric material, its piezoelectric constant is higher than quartz and piezoelectric ceramics, and easy to form, frequency sound, aging resistance and moisture resistance, chemical resistance is good, has been applied in the submarine detection network, hydrophone, sonar and other aspects.

Defense coatings

Fluorine-containing coatings have good corrosion resistance, aging resistance, low surface energy and other characteristics, in the national defense and military industry has been applied, such as fluorine-containing ship bottom coatings can reduce resistance and prevent marine life from adhering, fluorine-containing deck coatings have a good effect on salt spray corrosion resistance, fluorine-containing coatings have also been used as aircraft skin coatings; in addition, fluorine coatings are used as radar surface coatings, which can prevent rain and snow from adhering. China's fluorine coatings have developed rapidly and have been applied on new fighters.

Contains fluoride oils

Fluorine-containing oils and fats mainly include fluoroether oil, fluorochloride oil, fluorobromine oil and other fats. They mainly have the characteristics of specific weight, good viscosity temperature, oxidation resistance, aging resistance, radiation resistance, etc., can meet the application of special working conditions in the chemical industry, /semiconductor industry, automobile manufacturing industry, oxygen industry and other fields, and can meet the requirements of extremely harsh operating conditions in the aerospace industry in the national defense and military industry, and is also a necessary material in submarine oxygen systems and rocket navigation gyroscopes.

Artificial plasma and fluorine-containing anesthetics

Some fluorocarbons, such as perfluoronaphthalene, have good oxygen carrying properties and are biologically inert, so they have been developed as artificial plasma for temporary blood supply in special occasions. China has been successfully developed and has practical applications since the 1970s.

At present, the inhalation general anesthetics that are widely used in clinical practice are all fluorine-containing anesthetics, the main varieties are enflurane, isoflurane, heptaxane, deflurane, etc., which have small toxic side effects, fast anesthesia onset of action, short wake-up time, and have special advantages for small surgeries on the battlefield.

chemical weapon

As the last example of a fluorine-containing compound in this article, a chemical weapon is a special molecule. During World War II, Germany discovered that fluorine-containing phosphonate compounds are extremely toxic, and developed the first type of nerve gas sarin; since then, it has been found that the more toxic of this type of toxic gas Soman (inhalation toxicity is 2 to 4 times that of sarin, skin toxicity is 5 to 10 times that of sarin. Poisoning is fast and there is no specific antidote. The former Soviet Union was equipped. )VX (more toxic, typical persistent agent, long when the lethal effect lasts. It is the focus of chemical warfare agent equipment in the United States.)

The above makes a brief overview of the fluorinated chemicals in the national defense and military industry, in general, the development and application of fluorinated chemicals has always maintained a close relationship with the national defense and military industry, and should be developed in response to the needs of the national defense and military industry. The development path of China's fluorine chemicals is also exactly the same, the older generation of fluorine chemists selfless work, to provide a strong guarantee for the smooth development of China's two bombs and one satellite project, the early development and service of fluorine chemical products for the military industry gradually promoted civilian, has been greatly developed and grown.

At present, China's fluorine chemical industry is walking at a new key point, some of our primary fluorine chemical products have occupied a considerable proportion in the international market, but the added value is very low, some high-tech production is still dependent on imports, and the import of some high-tech products is also limited by Western countries, it is necessary to enhance the technical content of China's fluorine chemical industry, meet the needs of domestic industrial progress, meet the new needs of the national defense and military industry, and increase the value of foreign export products.