Surface Functionalisation through Nanoscale Science

Electroless deposition of Ni–P–nano-ZrO2 composite coatings in the presence of various types of surfactants

Electroless deposition of Ni–P–nano-ZrO2 composite coatings in the presence of various types of surfactants

Katarzyna Zielińska, Alicja Stankiewicz, Irena Szczygieł

a Department of Chemistry, Wrocław University of Technology, 27, 50-370 Wrocław, Poland
b Wrocław University of Economics, Department of Inorganic Chemistry, ul. Komandorska 118/120, 53-345 Wrocław, Poland

Ni–P–nano-ZrO2 coatings were produced using the electroless deposition technique. To prevent agglom- eration of zirconia nanoparticles in the plating bath, various surfactant additives (anionic, cationic, and nonionic) were used. The most stable bath was obtained with the addition of dodecyltrimethylammo- nium bromide (DTAB). The impact of this surfactant on the deposition rate, coating composition, and topography, as well as f potential of particles, was examined. Surface morphology and composition of the Ni–P–nano-ZrO2 composite coatings was analyzed by various techniques including scanning electron microscopy (SEM) equipped with in situ energy-dispersive X-ray (EDX) spectroscopy. Coatings with a clearly greater amount of zirconia (21.88–22.10 wt.%) were obtained from baths containing DTAB in con- centrations equal to or above its critical micelle concentration (cmc). For these surfactant concentrations, the reduction of Ni and P content was observed.

1. Introduction

Technology development in the material engineering area has to meet the requirements of contemporary industry. It demands new materials with better mechanical properties, greater reliability, which will guarantee a longer exploitation of appliances, even if they work in aggressive conditions. One of the solutions could be the application of composite materials that possess a variety of use- ful attributes. Nowadays, composites underlie the expansion of plenty of innovative products of modern branches such as elec- tronic, automotive, chemical, mining as well and many others [1– 4]. Metallic coatings containing the second phase in the form of solid particles embedded during the technological process, which can modify remarkably the physicochemical properties of a coating, are the dominant group of composite compounds. There are plenty of examples that belong to the classical solutions in the industrial practice: covering the surface of engines, drills with layers enclosing diamond used in crude oil’s output or deposits with PTFE on the tex- tile fabrication equipment’s elements – just to name a couple of them. Most of coatings are deposited by the electrochemical or elec- troless methods. Some metals or alloys (mainly nickel) are used as the matrix. The expectations relating to composite coatings are still extensive as evidenced by wide research conducted in many re- search centers all over the world. The embedding of diverse inert particles from an electrolytic or electroless bath into a metal matrix can bring a new functionality to the metal based matrix [5,6]. The potential benefits of such particle reinforcement can only be real- ized if the solid phase is well dispersed in the metal coating. The solution can be the selection of a proper mixing method, an addition of a surface active substance to the bath or use of an innovative pro- cess such as sol–gel enhanced electroless plating [7]. The surfac- tants are often utilized in colloidal systems, where they are responsible for uniformity and stability, as well an adsorption capacity [8–12]. Being a component of electroless nickel baths, the surfactants influence the features of Ni–P matrix [13] and the amount of embedded solids [14]. This is related to modification of the surface charge of particles which the surfactant monomers or hemimicelles are adsorbed on. Sodium dodecylsulfate (SDS) is most often utilized in electroless nickel deposition [15–17]. Cethyltrime- thylammonium bromide (CTAB) [15,18], fluorosurfactants [19], or 1,3-toloyltriethanolammonium chloride (TTAC) [14] are also in use. The literature of interest covers the effect of surface active com- pounds on bath stabilization, the possibility of obtaining the uni- form nickel-based composite coatings and also on the properties of a coating [5,6,19–21]. However, there is a lack of data showing the influence of structure and micellization ability of surfactant on the composite coatings plating. Additionally, due to the complicated nature of the electroless Ni/particle codeposition process, the mech- anism of plating bath stabilization with surfactants is not currently understood and requires more careful consideration.

The aim of the present contribution was to correlate the changes induced by the addition of various amounts of surfactants with different charges, that is, nonionic, anionic, and cationic ones,with the deposition of Ni–P–nano-ZrO2 composite coatings as well as with the composition and morphology of layers. We used so- dium dodecylsulfate (SDS) as anionic, dodecyltrimethylammonium bromide (DTAB) as cationic, and tetraethyleneglycol dodecyl ether (Brij 30) as a nonionic surfactant. Having emphasized the micelli- zation process, the impact of this issue on the parameters men- tioned earlier was studied. The surfactants can increase or decrease the stability of the system, so additionally the depen- dence between zeta potential and the bath stability was examined.

2. Experimental

2.1. Materials

Zirconium(IV) oxide (cat. no. 544760) as well as sodium dodecylsulfate, dodecyltrimethylammonium bromide and tetra- ethyleneglycol dodecyl ether (Brij 30) were obtained from Sigma–Aldrich.

2.2. Methods

In this work, coatings were produced on the specimens of d = 14 mm made from an alloy steel of AISI 304. Samples were pre- pared using a 1200 grade abrasive paper and ultrasonically cleaned in acetone. All the specimens were then etched for 10 min in a 0.1 mol dm—3 SnCl2 solution and washed with distilled water. After that the samples were activated for 10 s in a PdCl2 solution (1.4 10—3 mol dm—3), washed with distilled water, and subjected to the bath.

The composition of the baths used for the preparation of Ni–P– nano-ZrO2 coatings is given in Table 1. Sigma–Aldrich reagents pure p.a. were used to prepare the solutions. Zirconium(IV) oxide with a grain size of up to 100 nm was selected for the composite coating deposition. Nickel coating deposition took place in a thermostated vessel with a capacity of 30 cm3. Magnetic stirring at a rate of 500 rpm was used. The bath temperature was 75 °C, pH 6.0, and plating time 1 h. Such composition and parameters were selected according to the results of our previous work [22].

The microstructures of the electroless deposits were observed using a scanning electron microscope of VEGA II SBH. In addition, the quantitative composition was determined by an EDS INCA Pen- taFET Oxford Instruments attachment.

The particle size and distribution were determined by dynamic light scattering (DLS) (Zetananosizer Nano series ZS, Malvern Instruments Ltd.). The average size of the zirconia particles was computed using the Stokes–Einstein law: DH = kBT/(3pgD), where DH, kB, T, g, and D are the hydrodynamic diameter of the particles, the Boltzmann constant, temperature, viscosity of the system, and the diffusion coefficient, respectively. The DTS (Nano) program was applied to data evaluation. The zeta potential (f) of nanoparticle suspensions was measured in solutions with and without the presence of surfactants. Due to technical requirements, it was necessary to prepare diluted suspensions, but the relation particle–surfactant was the same as in the plating bath. The zeta potential measurements of nanoparticles were determined by elec- trophoretic mobility using the Zetananosizer Nano series ZS instru- ment (Malvern Instruments Ltd.). Both size and zeta potential measurements were carried out at 25 °C and each value noted is an average of at least three measurements.

In the sedimentation, the transmission percent test was used to estimate the settling rate of the samples. A 3 cm3 amount of each bath was carefully added into a glass cell and the transmittance was measured using a UV–Vis spectrophotometer (U-2010 Hitachi).

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