Investigation of the influence of the organic compounds and the dispersion particles on the kinetic of electrodeposition of the hybrid composite Ni-SiC-fluoropolymer layers
Benigna Szeptycka, Anna Gajewska Instytut Mechaniki Precyzyjnej, ul. Duchnicka 3, 01-796 Warszawa
Annals 3 No. 6, 2003 pages 23-29
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abstract In present work the hybrid composite electrochemical coatings were prepared with nickel matrix and SiC as the ceramic particles and PTFE or CFx as polymer particles. Table 1 shows the particle’s character. X-ray diffraction pattern for the dispersed particles of SiC and polytetrafluoropolymer are given in Figures 1 and 2. Linear distribution of carbon (Fig. 3) and silicon (Fig. 4) in the hybrid composite coating Ni-SiC-PTFE was given. Studies were carried out in the low-concentration nickel bath (NS) containing the brightening agent HRN and the four surfactants (ZPC). Nickel with a surface of 1 cm2 was used as cathode, silver-silver chloride as reference electrode and platinum as auxiliary electrode. Cathodic voltammetric curves with continuously changing potential were recorded in the range from –0.6 to –1.2 V with a sweep rates of 5 mV/s. The temperature of bath was 45±1oC and pH was 4. The solution was stirred with a magnetic stirrer at a rate of 500 revolution/minute. The influence of the following factors on the kinetics of nickel ion reduction was studied: presence of SiC powder and teflon dispersion, addition of brightening and wetting agents. The dependence of the current deposition of nickel from a bath containing surfactants versus the current deposition from a bath without additives in the potential –950 mV from the surfactant concentration is given in Figure 5. This same dependence for a bath with brightening agent HRN as a comparative bath is presented in Figure 6. Introduction of SiC powder to the solution NS causes the shift of curves towards more negative potentials (Fig. 7). Addition of surfactants caused a shift of cathodic curve towards more positive potentials (Fig. 8). Similar dependencies are presented for the teflon dispersion in Figures 9 and 10. Curves of cathodic polarisation for five of the hybrid composite nickel bath (Tab. 2) are presented in Figure 11. Changes in kinetics of the nickel ion reduction from these baths are presented in Figure 12. In every case, the introduction of two species dispersed particles to the bath containing the brightening and wetting agent caused a lowering of the electrochemical reaction rate versus this rate for a bath without additives. In Table 3 is presented the potential deposition of layers in the current density 4 A/dm2 and the contents of the dispersed particles in the coating. This potential is least shifted for the bath containing SiC1000, CFx and WFK1 as wetting agent and most for the bath containing SiCnano, teflon dispersion and this same surfactant. The codeposition of a SiC and fluoropolymer with electrodeposited nickel coatings, are found to be affected by the brightening and wetting agents present in the electrolyte. Generally, the wetting agents caused a lowering or heightening of overpotential of nickel ion reduction, the brightening agent caused a lowering this overpotential and the dispersed particles too. Key words: nickel, composites, hybrid, electrochemical coatings, SiC, fluoropolymer