The effect of high vacuum on materials

    High vacuum has adverse effects on many materials, motion mechanisms, and components, as follows:

    1 Material evaporation

    Temperature-controlled coatings and various materials that rely on the absorption and radiation energy of the material surface will accelerate the evaporation of the surface in a vacuum environment for a long time, causing the surface heat radiation characteristics to change. Generally speaking, electrodeless materials (such as ceramics) composed of oxides of Al, Be, Cr, Mg, Si, Ti, Zn and other compounds have low vapor pressure and are suitable for long-term space applications.

    The stability of organic materials in high vacuum is particularly important, because the materials will produce volatiles that condense onto thermal control surfaces, optical devices, and electronic components that have low ambient temperature and optical requirements, causing surface contamination.

    2 Dry friction and cold welding occur

    For the moving parts of some thermal control mechanisms (such as the rotating shaft of shutters), due to the high vacuum, the state of the solid surface changes, and the liquid and solid materials with high vapor pressure evaporate, causing dry friction or even cold welding on the surface, causing damping or blocking of the motion mechanism Die and lose the thermal control function.

    3 The thermal resistance increases and the temperature difference increases

    In the presence of gas, when solids are in contact with each other, the gas fills each tiny interstitial space except for the contact of the material itself. When transferring heat, it can conduct heat through solid contact and solid gas contact. After the vacuum degree is increased, only solid point contacts exist between the heat transfer surfaces, the heat transfer path is reduced, and the thermal resistance increases, which causes the temperature difference at the interface to increase.

    4 Discharge between electrodes damages the material

    There is a voltage difference between adjacent surfaces, when the vacuum reaches a certain value, an inter-electrode discharge will occur, and the arc will damage the surface.

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