Influence of the Composition of Dilute Nickel-Plating Electrolytes on the Physicomechanical Properties of Electroplated Coatings

Abstract

The influence of the composition of dilute nickel-plating electrolyte containing luster-forming additives on the leveling, plasticity, and internal stresses of coatings being electroplated was studied. The possibility of combining nickel sulfate, sodium chloride, and boric acid as the main composition of a dilute nickel-plating electrolyte was analyzed.Technological solutions that would make lower the expenditure of nonferrous metals, such as nickel, tin, copper, and their alloys, are sought for in order to further develop the galvanic industries. Compositions of bright-nickel-plating electrolytes ensuring a common plating rate of 0.831.2 mm min !1 at the concentrations of salts of a metal being deposited lowered by a factor of 232.5 (with a total nickel concentration of up to 30 335 g l !1 ) have been suggested [134]. The rate of nickel plating depends not only on the anionic composition of an electrolyte [5], but also on the luster-forming formulations used. The nature and cathodic behavior of luster-forming additives may lead to a redistribution of the rates of nickel deposition and hydrogen evolution in favor of the latter process. In this case, formation of nickel hydroxide compounds in a near-cathode layer and their inhibiting effect on nickel electrodeposition become more likely, and the microstructure of the resulting coatings is changed. The considerable increase in the hydrogenation of the deposits deteriorates the physicomechanical properties of the coatings obtained [6 3 8]. To improve the main characteristics of the bright-nickel-plating process, acetylene compounds are used in combination with ethylene and organosulfur additives [9].The aim of this study, was to assess the influence exerted by the composition of a dilute nickel-plating electrolyte containing luster-forming additives based on b-oxyethyl cinnamide (OECAM) on the physicomechanical properties of the coatings being deposited. EXPERIMENTALThe study was performed in nickel-plating electrolytes containing (g l !1 ): no. 1: 140 NiSO 4 . 7H 2 O, 30 NiCl 2 . 6H 2 O, and 30 H 3 BO 3 ; no. 2: 33 NiSO 4 . 7H 2 O, 120 NiCl 2 . 6H 2 O, and 30 H 3 BO 3 ; no. 3: 150 NiSO 4 . 7H 2 O, 50 NaCl, and 30 H 3 BO 3 .The electrolytes prepared were subjected to selective purification. Chemically and analytically pure reagents were used in the experiments. OECAM was synthesized and purified 1 mp 87oC. 2-butyne-1,4-diol (YN) was twice recrystallized from chloroform, mp 58oC; 2-butene-1,4-diol (EN) was purified chromatographically, mp 113oC at a pressure of 5 mm Hg. Saccharin was recrystallized from ethanol, mp 2253 226oC. The temperature of the experiment was 50oC and pH 4.0. The pH value of the electrolytes was measured with an LPU-01 pH-meter and adjusted with hydrochloric acid or sodium hydroxide.The microleveling power was determined by measuring profilograms of a titanium substrate with triangular grooves cut to a depth of about 4 mm (angle 120o). The microleveling factor B (%) was calculated from data on the average depth of the grooves before and after th...