Experimental design in the electrodeposition process of porous composite Ni–P + TiO2 coatings

In this paper, an environmentally friendly electroplating process of the composite Ni–P + TiO2 coatings was developed. Such coatings were prepared by in situ codeposition of Ni–P with TiO2 powder (anatase) on a polycrystalline copper substrate from the nickel-plating bath in which titanium dioxide particles were held in suspension. The codeposition was carried out under galvanostatic conditions on a rotating disc electrode. To optimize the production conditions of the Ni–P coatings modified with TiO2 by the method of mathematical statistics, the Hartley's polyselective quasi D optimum plan of experiments was used. The relationship between the percentage content in the electrodeposited composite Ni–P + TiO2 coatings (z) and the electrodeposition parameters like cathodic current density (jdep), bath temperature (T) as well as content of TiO2 powder suspended in the galvanic bath (c), has been described by the adequate cubic polynomial equation and illustrated graphically. Based on the Hartley's plan it can be stated that the maximal TiO2 content of 28.7 at.% in the Ni–P + TiO2 coating can be obtained for the following optimal parameters of the electrodeposition process: jdep = 0.05 A cm−2, c = 99 g dm−3 and T = 40 °C. The chemical and physical characteristics of the coating obtained under such optimum conditions, have been presented. The deposit exhibits the presence of TiO2 particles embedded into the amorphous Ni–P matrix. It has been ascertained that embedding of TiO2 powder to the amorphous Ni–P matrix leads to the production of deposits with large surface area. Such electrochemical codeposition method may be a good alternative in the field of porous composite coatings used in gas evolution.

► The in situ composite electrodeposition process of the porous Ni–P + TiO2 coating has been developed.
► The production conditions of the Ni–P coating modified with TiO2 have been optimized by the method of mathematical statistics.
► The Hartley's polyselective quasi D optimum plan (PS/DS-P: O (D)) has been applied for three variables: temperature, TiO2 powder in the bath and cathodic current density.
► The evaluated equation of the approximating polynomial is the adequate mathematical model which describes the composition changes of the obtained coatings under the influence of changes of the investigated factors values.
► The physical and chemical characteristics of composite the Ni–P + TiO2 coating electrodeposited under the optimized conditions have been carried out.