Study on the effect of additive composition of electroplating solution on palladium coating
The plating solution was prepared by using dichlorotetrammine palladium as main salt,wetting agent A,brightener B and stabilizer C as combined additives,and Hough cell tests were conducted to obtain a palladium coating by electrodeposition.The composition and content of additives were screened through orthogonal experiments,and the morphology and structure of palladium coatings were characterized by scanning electron microscopy and X-ray diffraction.The effects of additive composition and content on the apparent morphology,micro-morphology and hardness of the palladium coating were investigated.The results of orthogonal experimental research show that under the electroplating process with a current density of 0.85 A/dm2,a plating solution pH value of 8.0,and a plating time of 20 minutes at 50℃,the stabilizer content in the additive has a more significant impact on electrodeposition.Coatings with high stabilizer levels have better appearance and hardness,while brighteners and wetting agents play an auxiliary role.The stabilizer is complexed with palladium ion to prevent palladium ion from being reduced and improve the stability of the bath.The brightener adsorbed on the cathode surface,increased the cathode polarization value,formed an active site,improved the formation rate of crystal nucleus,and obtained a fine and compact crystalline coating.The wetting agent reduces the adhesion of hydrogen bubbles produced during cathode electrodeposition,expands the coating in the low current region,improves the anti-impurity interference ability and makes the coating bright and smooth.Each component of the additive collaboratively improves the levelling ability of the bath and the brightness of the coating in the low current density area,and the cathodic current density range of the pure palladium coating is wider.