Surface purification and polishing of vacuum materials

    The working principle of ultrasonic cleaning is that after introducing ultrasonic waves into the liquid, the intense movement of the liquid causes a local pressure difference. The part with low pressure will produce a lot of bubbles. When the pressure rises again, these bubbles will burst in an instant, thereby generating shock waves in the liquid. The shock wave will peel off the oil stains on the solid surface. The liquid used for ultrasonic cleaning generally uses alcohol or acetone. After ultrasonically cleaned parts are placed in the atmosphere, the alcohol or acetone will evaporate immediately without leaving scale on the surface of the parts.

    The amount of gas released from the vacuum chamber and internal components is directly related to the surface area of the material. The atomic density of the solid surface is approximately 2×10¹⁹/m². Considering the unevenness of the surface, the actual solid surface will adsorb a large number of gas molecules. By polishing the surface to be more flat, the surface area can be greatly reduced, thereby reducing the gas molecules adsorbed on the surface. Polishing mainly includes glass shot sandblasting and electrolytic polishing.

    The cost of glass shot sandblasting is low, but the surface roughness of the solid after the treatment is large, and there is still more gas released, and currently less and less are used.

    The principle of electrolytic polishing is to place the metal part in an acidic electrolyte, the metal part is connected to the anode, the electrode and the container are used as the cathode, and the raised part of the metal part facing the cathode is dissolved first, and the Fe and Ni atoms in the composition of the metal part are dissolved. Into the electrolyte, finally achieve the purpose of smoothing the surface. By flexibly setting the cathode electrode, both the inner and outer surfaces of the cylindrical metal parts can be polished, and the metal parts can also be selectively polished locally.

    Electrolytic polishing can eliminate the small irregularities (0.01um~a few um) on the metal surface, and make it appear metallic luster, but it cannot eliminate the relatively large irregularities. Electrolytic polishing is a typical electrochemical polishing method, and the oxide film formed on the surface will also reduce the adsorption of gas molecules.

    There is also a special surface treatment method, that is, special gas is introduced into the vacuum chamber to induce electric discharge in the chamber, and the generated ions strike the inner wall of the chamber to obtain a smooth surface.

    The surface-purified vacuum chamber and parts should not be directly touched by hand to avoid the pollution of hydrocarbons and chlorides in hand sweat; in addition, dust and water vapor and other pollutants should also be avoided as much as possible.

(huiputech)