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The nanocrystalline composite electrochemical coatings prepared with nickel matrix
and PTFE particles were investigated. Nickel plating bath of low nickel(II) concentration
(0.75M) with organic compounds and dispersed PTFE particles content was used for coatings
electrodeposition. PTFE particles content was determined gravimetrically. The roughness of
the nickel foils was evaluated using a TR 100 prod. Elcometr Instruments Ltd. profilograph.
The microhardness of the deposited layers was measured using a Vickers' method at a load of
0.01 and 0.05 kG. The following dependencies were obtained:
Ra=0.056 Cp+0.002D111, HV0.01=25.65/D1111/2 Siemens D500 X-ray diffractometer with CuKα radiation was used to determine the preferred orientation, the dimension of nickel [111] crystallites and microstress. The size of [111] nickel crystallites in the Ni-PTFE coatings was from 11 to 39 nm. All coatings have the approximately random orientation. Decreasing of the crystallite size in the nickel coating influenced on the increase microstress. Voltammetric method was used for examination of the samples of composite coatings during tests in 0.5M NaCI, pH 7. Results were used for calculation of the free corrosion potential and current. The corrosion resistance of all of the composite coatings was superior to that of the nickel coating. Non-conducting PTFE particles incorporated into a nickel coating also occur on its surface, which should affect the corrosive behavior of the composite coating. The following dependence was obtained: P=26.3P111+1.5D111 The corrosion rate increase with increasing of the preferred orientation (111) content and with increasing of the dimension of nickel [111] crystallites. |
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