Purification and surface treatment of metal sealing parts

    The surface condition of the metal has a great influence on the quality of the sealing. Therefore, the metal parts must be purified and heat treated before sealing to remove the oil, oxide layer, impurities and gas on the surface of the parts, reduce the carbon content of the surface layer of the ferroalloy, and eliminate Stress and other purposes. The formation of a dense, low-valent oxide layer with a certain thickness on the metal surface is tightly combined with the metal matrix, which is a necessary condition for good sealing. In order to obtain a high-strength air-tight seal, the metal parts must be oxidized.

    (1) Cleaning treatment of metal materials

    After the metal parts and the sealed glass parts are made according to the requirements on the drawings, the metal parts must first be cleaned and dried to remove grease and dirt on the metal surface. The general cleaning treatment is carried out according to the following steps:

    Mechanical purification → degreasing cleaning → chemical cleaning → drying

                                                                           →Electrochemical cleaning

    ①Mechanical purification Partially remove various compounds and adhered dirt on the surface of the material by means of mechanical friction. The usual method is to wipe with sandpaper, and sometimes with soap.

    ②Degreasing The oil is usually degreasing with lye and organic solution. The lye contains sodium hydroxide and potassium hydroxide, which are heated to 70~80°C to saponify the oil, so as to achieve the purpose of degreasing.

    ③Chemical cleaning Use the dissolution of compound dirt on the surface of the part in a chemical liquid to achieve the purpose of cleaning, and a highly cleaned surface can be obtained.

    ④Electrochemical cleaning It is to immerse the parts in a specially configured solution to energize, so that the metal and metal compounds on the surface of the parts are separated from the parts, so as to obtain a highly cleaned surface.

    ⑤ Drying Rinse and dry the cleaned metal with distilled water.

    (2) Degassing treatment

    After the metal parts are cleaned, they must be degassed. Because metal materials often contain a lot of gas during the production process and storage period, such as C0, H, He, and CO, etc. The presence of these gaseous impurities will cause gaseous impurities in the electric vacuum devices and electronic components to decompose gaseous impurities at high temperatures, destroy the vacuum of the electronic devices, contaminate the working gas and working materials, and poison the cathode (or electrode). , And even make the tube or light source ineffective. Secondly, a large number of bubbles will be generated in the sealing part of the metal parts that have not been degassed, which will affect the air tightness and sealing strength, and even cause the sealing part to leak or burst. The so-called degassing treatment is to place the metal in hydrogen (wet hydrogen) or vacuum for high-temperature heating, so that the gas inside the metal quickly diffuses to the outside with a lower pressure; or the hydrogen diffuses into the metal to replace other gases. This process is called hydrogen burning treatment. During the hydrogen burning treatment, the hydrogen of the metal is easily exhausted during the vacuum exhaust, and the oxide layer on the metal surface can also be removed and reduced.

    (3) Oxidation treatment

    After the metal parts are cleaned and hydrogen-burned, the sealing part needs to be oxidized to improve the wettability of the metal and glass and ensure the bonding quality of the sealing interface. However, when performing flame heating oxidation treatment, the degree of oxidation must be strictly controlled, and the metal should not be burnt so that the metal is shiny, and the temperature is too high to cause excessive oxidation; on the contrary, if the oxidation is insufficient, the oxide film is too thin, and air leakage will occur after sealing. When flame heating is used for oxidation treatment, the best oxide layer is obtained by the judgment of the operator (for Kovar, the best thickness is 0.3~0.7mg/cm2 after oxidation), that is, the sealing can be controlled by experience Temperature and time. From the color of the sealing surface, we can know whether the degree of oxidation is appropriate and whether the sealing quality is good.

    After the metal parts are oxidized, they can be melt-sealed with glass before they are cooled down. In actual production, there are two situations: one is to fuse and seal with glass immediately after oxidation, as is the case in the manufacture of small stems; the other is to burn "glass beads" on the metal rod after oxidation treatment ( For example, burning "glass beads" on tungsten rods and molybdenum rods), and then fuse the glass beads with the glass parts. When the metal rod burned with "glass beads" is melted and sealed with glass, the metal rod will not continue to oxidize, which is beneficial to obtain a good sealing part.

(Huiputech)