Precautions before installation of piezoelectric ceramic:
When actually installing piezoelectric ceramics, special attention should be paid to electrode treatment. The electrode mainly uses silver plated silver electrode and nickel electrode through electroless nickel plating.
Silver plating is to mix the metal silver powder with a small amount of lead borosilicate glass frit with organic solvent to form a paste, which is coated on the ceramic surface with brush and wire mesh. Then the ceramic is heated to 500 ~ 800 ℃ to decompose the organic matter and melt the frit, and the silver particles are closely attached to the ceramic surface. The film thickness of the silver electrode is 8 [ μ M], the adhesion strength is 20 [n / mm2], and the pencil hardness is about 3 ~ 5B.
The nickel electrode immerses the degreased ceramic material in the first salted tin solution to make tin ions adsorb on the surface of the material. After water washing, it is immersed in the saline palladium solution, and the nickel ion reacts with the palladium ion in the solution to form metal palladium as a catalyst on the surface. Then it is immersed in a reducing agent electroplating bath such as dimethylamine balance to reduce and precipitate metal nickel with a purity of more than 99%. The thickness of the nickel electrode film formed in this way is 3 [ μ M], the adhesion strength is 10 [n / mm2], and the pencil hardness is equivalent to the strength of about 3H.
As mentioned above, although silver electrode and nickel electrode can obtain sufficient strength in practical application, due to welding, bonding method and chemical environment, the adhesion strength will be reduced and the surface will be corroded, so special attention should be paid.
(a) Welding method of electrode
Ordinary welding can be carried out through neutral grease filler metal (low-temperature filler metal and silver filler metal as far as possible). It is hoped that the soldering iron temperature is below 270 ℃ and the working time is within 5 seconds. If the adhesion of soft solder is poor, gently grind the surface with sandpaper above 400. The welding flux after welding is cleaned with solvents such as trichloroethane, fluorocarbon and toluene.
(b) Bonding method
As a pretreatment, grind the bonding surface with light abrasive paper above 400 and PVA grindstone, and then degrease and clean it with organic solvent by using ultrasonic cleaning machine. (after that, dehumidify with ethanol as much as possible.) Epoxide system is the most suitable adhesive. Harden it at 80 ℃, which is effective in time and strength. (pay attention to the thermoelectric phenomenon of heating.)
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