Low Temperature Insulating Film Materials And Properties

Low temperature insulation materials can be divided into polymer materials, composite materials and ceramic materials. For the application of superconducting power devices, low temperature insulation materials are mainly applied in the form of films, adhesives and structural materials.

In order to reduce the insulation duty, it is necessary to use thin film insulation materials with excellent mechanical properties. The higher tensile breaking strength can also reduce the thickness of the film and reduce the number of layers, thereby further reducing the duty of the insulating part. As mentioned in the previous chapter, the commonly used superconducting electrical insulation films include polyimide film (PI), polytetrafluoroethylene film (PTFE), polypropylene film (PP), polyester film (PET), naphthalene ester film (pen), polyethylene film (PE), etc. PI film is the most ideal low temperature insulating film material due to its excellent mechanical properties, high and low temperature resistance, high electrical breakdown strength, good chemical stability and other characteristics.

Among polymer insulating films, PI films and PTEE films have been widely used in cryogenic technologies such as superconductivity, cryogenic engineering and cryogenic physical experiments due to their excellent electrical properties and chemical stability at low temperatures. PTFE film can work in the range of - 250~250 ℃, with small dielectric loss, little change in wide temperature range and wide frequency band, and no carbonization under the action of arc; At high temperature, the tensile strength decreases and the elongation increases; at low temperature, the tensile strength increases and the elongation decreases. However, the obvious disadvantage of PTFE film is that its mechanical properties are low and anisotropic, and it is not easy to bond at low temperatures. In addition to the vast majority of advantages of PTFE film, PI film can maintain flexibility at the temperature of liquid nitrogen and liquid helium, can withstand almost all organic solvents and acids, and has good wear resistance, arc resistance, high energy radiation resistance and other characteristics. The PI film can still maintain good tensile strength and elongation after being irradiated with 1010 ERG / g gamma ray. PI film also has the characteristics of strong designability, easy processing and modification. These characteristics make PI thin film become the most used thin film in superconducting electrical insulation materials, especially the high temperature superconductivity at 77 K and low temperature superconductivity at 4.2 K have been more and more applied.