| Nickel/graphite composite powder, possessing good conductivity of nickel and lubricity of graphite, had broad application prospects as electrical contact materials, conductive fillers and electromagnetic shielding materials and so on. Compared with nickel powder, Ni/graphite composite powder was widely used in conductive silicone rubber because of its low price. In this paper, electroless nickel plating was used to deposit nickel layer on graphite. The effect of electroless plating process on surface topography of Ni/graphite composite powder was investigated. The growth mechanism of Ni deposition on graphite powder surface was also studied. And the conductive silicone rubber with different kinds and contents of conductive fillers was prepared and were investigated the conductivity and mechanical properties.The effect of pretreatment of the graphite powder, bath composition and operating conditions on the morphology and particle size of Ni/graphite composite powder was investigated. Laser-diffraction, SEM and Mastersizer were employed to observe particle dimension, surface topography and particle size distribution of composite powder. The results showed that the crystal grain of nickel deposits was finer and homogeneous when PdCl2 mass concentration were 0.03g/L and 0.1 g/L. The deposition rate increased with the increase of NiSO4·6H2O and N2H4 concentration, but higher deposition rate could lead to rough coating. The suitable concentration were NiSO4·6H2O 20g/L and N2H42%.Improving the bath temperature could increase the energy of the reaction and the nickel particle deposition rate. Compared with 60℃and 70℃, the graphite surface was evenly covered by the nickel coating when the temperature was 65℃. PH increase could lead to higher reaction rate and reduce the induction period. When pH was 11.0, plating rate was moderate and the induction period was 10min, while the graphite had smooth and integral nickel coating. The Ni/graphite composite powder had a gray appearance with medium speed (200～400r/min). Based on experimental results, some conclusions can be drawn as below. The NiSO4·6H2O mass concentration was 20g/L, N2H4 volume fraction was 2%, C6H8O7 mass concentration was 40g/L, PEG mass concentration was 0.1 g/L, pH was 11.0, the temperature was 65℃and the stirring speed was medium speed (200-400r/min).The deposition and growth mechanism of nickel on the graphite was illustrated by analyzing the graphite surface morphology under different electroless plating periods. The nickel deposits growed firstly on activation center Pd and forms island structure, then it continued to extend outward growth along the island structure with the effect of the activation center and nickel particle as autocatalyst particle. Nickel particles coverded the whole surface of graphite particle as reaction proceeding. The main growth period of nickel deposits was 90 min to 120min from beginning.The Ni/graphite powder with nickel mass fraction of 20%,40% and 60% were prepared by the above electroless plating technology. Compared with graphite and nickel powder, Those composite powders were used as conductive fillers to make conductive silicone rubber. The conductivity and mechanical property of those samples with different conductive fillers were investigated. The results showed that the addition of conductive fillers could effectively improve the conductivity of silicone rubber. With the same volume fraction, capacity of fillers improved the conductivity of conductive silicone rubber were ranged as follows from small to large:graphite<20Ni/graphite |
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