Overview of glass sintering (glass-to-metal sealing)

    The glass-metal sealing structure commonly used in vacuum systems must have air tightness, certain strength, baking resistance and certain electrical insulation properties. The types of sealing are as follows:

        1) Matching sealing: It means that the linear expansion coefficient of glass and metal are similar within a certain temperature range (less than 10%);

        2) Mismatched sealing: refers to the large difference in linear expansion coefficient between glass and metal (greater than 10%);

        3) Transitional sealing: When the linear expansion coefficients of glass and metal differ greatly, one or more types of transitional sealing can be used between the two.

        There are two sealing methods: enclosure sealing and tubular sealing.

        The enclosing and sealing structure is a structure in which tungsten rods, molybdenum rods, Kovar rods, etc. are sealed with glass with similar linear expansion coefficients. The glass and metal rods need to be cleaned before sealing, preferably after hydrogen-burning annealing, to remove stress and surface decarburization. In order to ensure the quality of the sealing, glass beads are generally burned on the rod first. After sintering, tungsten is golden yellow, molybdenum is light brown, Kovar is mouse gray, and oxygen-free copper is brick red. If the metal rod is over-oxidized or insufficiently oxidized, and the metal rod becomes white, black or metallic after sealing, the air-tightness cannot be maintained.

        The most common tubular matching sealing is the sealing of Kovar tube or Kovar flange joint and molybdenum group glass tube (DM305DM308, etc.). The diameter of the glass tube for this type of sealing is related to the wall thickness of the metal tube, and the wall thickness of the glass tube. There is a certain relationship between the welt length.

        Dimensional requirements for tubular matching sealing

    The most commonly used tubular mismatch sealing is the sealing of oxygen-free copper pipes (linear expansion coefficient of 16.8x10-6/℃) and glass pipes (linear expansion coefficient of 4x10-6/℃~11x10-6/℃). In order to reduce the stress of the glass tube caused by the difference in expansion coefficient, the sealing edge of the oxygen-free copper tube should be blade-shaped. The length of the welt on the inner side of the glass and the cutting edge should be greater than the length of the outer welt.

 (huiputech)