Research On Electroless Silver Plating System

As a very important surface treatment technology, electroless plating has been widely applied because of its simple operation and no restrictions on the electrical conductivity of the based material. However, the silver bath was very unstable, causing a lot of waste of raw materials and environmental pollution because of the volatile formaldehyde and ammonia. Therefore, its application was limited. In this paper, the double complex system with sodium potassium tartrate as reducing agent and with ethylenediamine and ethylenediamine tetraacetic acid disodium as double complexing agent was studied to ensure the stability of the plating solution. Then, the bright silver film with low resistivity and high purity was obtained by filtering experiment condition and surfactant.First, the effects of different complexants on the silver plating were explored when C₄O₆H₄KNa was used as the reducing agent. When only Na₂EDTA or EN was added, the stability of the bath was poor. The bath would decompose quickly when raising the bath temperature. When both Na₂EDTA and EN were added, the stability of the bath increased and the silver film was bright. Research showed that the reduction potential of silver ions in the bath which used double-complexants was more negative compared with the bath which used only Na₂EDTA or EN as the complexant, indicating that the bath which used double-complexants was more stable and the optimal ratio of Na₂EDTA and EN was 3:2.The effects of temperature, pH on the deposition rate and the silver film were explored. The results showed that the deposition rate could increase with the increase of temperature and pH. However, the plating solution would become instable when the deposition rate increased to a certain degree. Then effects of bath temperature and pH on the polarization curves of electroless silver bath were also studied by LSV. The results showed that the deposition rate of electroless Ag bath was promoted by temperature and pH through their promotion on the cathodic and anode polarization reaction. The optimal composition of the silver bath:AgNO₃ (3.4 g·L^-1), Na₂EDTA (16.7 g·L^-1), EN (22.5 g·L^-1), C₄O₆H₄KNa (16.7 g·L^-1). The bath temperature was 45℃ and pH was 12.0. Under this condition, the bath was very stable and the deposition rate was high （4.2μm/h）. The effects of different additives on the silver deposition rate and the quality of the silver film were explored in this bath. The results showed that adding tiny amounts of cetyl pyridine bromide （Brpy） and 2,2-pyridine （Dipy） simultaneously could not only improve the surface morphology a lot, but also have a synergistic effect on maintaining the deposition rate and reducing the electrical resistivity of the silver film （3.05μΩ cm）.A new environmental friendly electroless silver bath with high stability was studied in this paper. This bath had good stability and an appropriate deposition rate. Beyond that, the silver film which obtained from this bath had high purity, good crystallinity and low resistivity. It changed the instability and defect which can only be limited under room temperature of the plating bath, so it would have good practicality in industry.Another content of this paper is depositing nanometer metal oxide by electroplating in ionic liquid microemulsion quaternary system to catalyze the decomposition of water. The ionic liquids could not only enhance the electrical conductivity to improve the efficiency of electroplating, but also could be used as a soft template agent to control the size of the nanometer materials effectively by preventing the agglomeration of nanoparticles.First, TX^-100, hexanol, Ni（NO₃）₂、Fe（NO₃）₃ solution and ionic liquid [BMIMJBF₄ was mixed uniformly according to certain proportion to form inverse ionic liquid micromulsion. Then, the nanoparticles were formed on the substrate by constant potential method. The nano Ni-Fe hydroxide with controllable particle size of 15-65nm was obtained by controlling the experimental condition and content of ionic liquids.Then, the effects of electroplating conditions and the content of ionic liquid in system on the catalytic performance were studied. The result showed that the optimum condition was:Hexyl alcohol （3g）, TX^-100 （3g）, nitrate concentration （0.15mol/L）, nitrate content （1.2g）, [BMIM]BF₄ （0.7g）, deposition potential (^-1.5V), deposition time （1500s）, the Ni-Fe ratio in water phase （1:1）. Under this condition, the nanometer materials had the best catalytic properties and its overpotential could be dropped to 280mV.Final, the effect of Ni-Fe ratio in water phase on Ni-Fe ratio of nanometer materials was studied. The result showed that these two ratios could be consistent only when the deposition potential and the content of ionic liquid were kept within a certain range because of the damage on the microemulsion which high voltage and high content of ionic liquid caused. Therefore, the nano Ni-Fe hydroxide with controllable ratio could be obtained when the deposition potential was kept below^-1.5V and the content of ionic liquid was kept below 0.7g.