Influence of Doped Detonation Nanodiamonds on the Physical and Chemical Properties of Electrochemical Chromium Coatings

Abstract

Chromium deposition process regularities are analyzed in the standard chromium plating electrolytes, with and without detonation nanodiamonds additives modified with boron, phosphorus (DND-boron, phosphorus-DND) at a temperature of 50º to 55ºC while stirring the solution and without. It was studied by method of recording the partial polarization curves the concentration effect of additives DND-boron (in the range of 2,5 ÷ 10 g/l) on the kinetics of the chromate ion partial and full reducing. It has been shown that increasing the concentration of DND-boron leads to inhibition of the reaction Cr (VI) → Cr (III) and Cr polarization curves shift reaction (VI) → Cr (0) to a negative potential on the magnitude of 40-70 mV. While stirring the electrolyte chromium deposition occurs at more positive potentials than in quiescent electrolyte. Dependence of the electrode potential on the current density logarithm in all cases are linear with a slope close to 120 mV, indicating a limiting step of attaching the first electron. Mechanism of deposition of chrome in the presence of boron-DND does not change. Shiny, smooth, uniform coatings are deposited in electrolytes with DND-boron additives. Increased polarization in the chromium precipitation of electrolytes with DND-boron causes a change in precipitation structure, and as a consequence an increase in microhardness of chrome coatings from 955 kgf/mm² for pure chromium to 1430 kgf/mm² for chromium with embedded DND-boron nanodiamond particles. Wear resistance is increased: using DND-TAN - 2-3 times compared to standard chrome plating, using DND-phosphorus - in 3 times in comparison with DND-TAN, and using DCS (Si), doped silicon, wear is not detected (under the test conditions).