ELECTRODEPOSITED NI-BASED

NANOCOMPOSITES

ELECTRODEPOSITION

• Electroplating is often also called "electrodeposition“.

• It’s a process using electrical current to reduce cations of a desired

material from a solution and coat that material as a thin film onto a

conductive substrate surface.

• The overall process is also known as electrolysis.

OBJECTIVE

• To apply thin films of material to the surface of an object to change

its external properties such as to increase corrosion protection,

increase abrasion resistance, improve decorative quality or simply to

deposit a layer which is part of a more complicated device.

• MECHANICAL PROPERTIES: Mechanical properties of the

electrodeposited film depend to a considerable extent on the types

and amounts of growth-inhibiting substance at the cathode surfaces.

• ADHESION: It is desirable that the substrate and the deposited

metal interdiffuse with interlocking grains to give a continuous

interfacial region.

APPLICATIONS

• Decoration: Coating a more expensive metal onto a base metal

surface in order to improve the appearance. Applications are

jewellery , furniture fittings, builders’ hardware and tableware.

• Protection: Corrosion-resistant coatings such as chromium plating of

automobile parts and domestic appliances, zinc and cadmium

plating of nuts, screws and electrical components. Wear-resistant

coatings such as nickel or chromium plating of bearing surfaces and

worn shafts and journals.

• Electroforming: Manufacture of sieves, screens, dry shaver heads,

record stampers, moulds, and dies.

• Enhancement: coatings with improved electrical and thermal

conductivity, solderability, reflectivity etc.

• nano-composite coatings can give various properties, such as wear

resistance, high-temperature corrosion protection, oxidation

resistance and self-lubrication, to a plated surface.

• Research on electrodeposition of nano-composite coatings has

been attention directed towards the determination of optimum

conditions for their production, i.e. current density, temperature,

particle concentration and bath composition.

ELECTRODEPOSITION OF NI–SIC NANO-COMPOSITE

COATINGS

• EXPERIMENTAL DETAILS:-

• Cathodes, made of copper were positioned in vertical plane with

anode. A platinum plate was used as the anode.

• Analytical reagents and distilled water were used to prepare the

plating solution. Prior to plating, the SiC nano-particulates of a mean

diameter 50 nm with concentration of 1–20 g L−1 were dispersed in

the electrolyte in the presence of saccharine.

• Ni–SiC composites have been commercialized for the protection of

friction parts, combustion engines and casting moulds.

• The effects of the incorporated SiC on the cathodic efficiency of

bath, corrosion and wear resistance of the nanocomposite coatings

were analyzed.

• The dependence of SiC nano-particulates amount in the nano-

composite coatings was investigated in relation to the SiC

concentration in bath, cathode current density, stir rate and

temperature of plating bath and it is shown that these parameters

strongly affected the volume percentage of SiC nano-particulates.

• This can be attributed to

polarization at surface of

cathode with increasing

current densityand temperature.

• When the SiC nano-

particulates collide at the

cathode surface, the conditions

for deposit formation are

established and so the cathode efficiency increases.

• where a higher particle

concentration in the electrolyte

increases the adsorption, thus

resulting in a higher weight

percent of SiC nano-particulates in

composite coatings, while the

decrease in the weight percent of

the SiC nano-particulates at a

concentration of SiC

nanoparticulates above 5 g/ L is

attributed to the agglomeration of

the SiC nano-particulates in the

electrolyte owing to their poor

wettability.

• Increasing the stirring rate up to 120 rpm causes to increase the

percent of SiC nano-particulates but when the stirring rate is too

high, the decreasing trend of the weight percent is principally caused

by the collision factor. At a high-stirring rate, because of turbulent

flow in bath, the SiC nano-particulates on the cathode surface are

washed away and thus the SiC nanoparticulates percent in

composite coating decreases.

• Before the maximum the increasing percent of SiC nano-particulates can be attributed to the increasing tendency for adsorbed particles to arrive in the cathode surface.Theprocess is controlled by the adsorption of the particles and the particle deposition is dominant.

• When current density is greater than 20 mA/cm2, the decreasing trend can be explained by the fact that an increase in current density results in more rapid deposition of the metal matrix and fewer particles are embedded in the coating. Hence, the metal deposition dominates the deposition process.

• Below 50 ◦C, the activity of particulates increases with increasing the temperature of bath. However, as the temperature of bath is higher than 50 ◦C, the thermodynamic movement of the ions is greatly enhanced, which results in increasing the kinetic energy of particulates. increasing the temperature leads to the decrease in the adsorpability of the particulates and hence to decrease the overpotential of the cathode and the electric field, which makes it harder for the particulates to be embedded in the matrix and subsequently leads to a decrease in the weight percent of the SiC nano-particulates in the composite coating.

SEM morphology of nickel coating.

SEM morphology of Ni–SiC nano-composite coating.

• The figure reveals that the pure nickel deposit has exhibited irregular polyhedral crystals. The incorporation of SiC nano-particulates has modified the surface to particulate like crystals. The change in the morphology can be associated to the change from preferred orientation to random oriented composite deposits.

• EDX analysis revealed the uniform distribution of SiC in the composite. In addition, many nodular agglomerated grains are seen on the nano-composite coating surface (Fig. 7c).

• It is supposed that the SiC nano-particulates of a uniform distribution and agglomeration to some extent may contribute to increase the wear resistance of the Ni–SiC nano-composite coating.

• Fig. shows the variation in the microhardness and wear rate of the

Ni–SiC nano-composite coatings with the content of SiC nano-

particulates. It is seen that the Ni–5% SiC nano-composite coating

has a maximum hardness and minimum wear rate.

• The microhardness of the nano-composite coatings increases with

increasing weight percent of the SiC nano-particulate.Since the SiC

nano-particulates deposited in the nickel matrix could restrain the

growth of the nickel grains and the plastic deformation of the matrix

under a loading, by way of grain fining and dispersive strengthening

effects. The grain fining and dispersive strengthening effects

become stronger with increasing SiC nano-particulates content, thus

the microhardness and wear resistance of the Ni–SiC nano-

composite coatings increase with increasing SiC nanoparticulates

content.

Electrodeposition and mechanical properties of Ni–carbon

nanotube nanocomposite coatings

• EXPERIMENTAL PROCEDURE

• Ni–CNT nanocomposite coatings were electrodeposited in a sulfate Watts bath of the following composition: 260 g/L nickel sulfate (NiSO4 6H2O), 45 g/L nickel chloride (NiCl2 6H2O), 15 g/L boric acid (H3BO3), and 0.5 g/L saccharine. To improve MWCNT dispersion, SDS and HPC were added into the electrodepositionsolutions by varying the amounts of SDS and HPC from 0 to 10 g/L.

• The total amount of SDS and HPC was always kept as10 g/L. MWCNTs of 10–15 nm diameter, produced by CVD, were used to form the Ni–CNT electrodeposition solutions.

• Ni–CNT nanocomposites of 50 mm thickness were electrodeposited on Cu substrates of 2 cm2 cm size at a current density of 40 mA/cm2. During electrodeposition of a Ni–CNT nanocomposite, the bath was maintained at 40C with mechanical stirring at 500 rpm.

FESEM micrographs of the Ni–CNT nanocomposite electrodeposited in a bath containing dispersion additive of (a) 10 g/L SDS, (b) 7.5 g/L SDS and 2.5 g/L HPC, (c) 5 g/L SDS and 5 g/L HPC, (d) 2.5 g/L SDS and 7.5 g/L HPC,

• Fig. 1 illustrates surface morphologies of the Ni–CNT nanocompositeselectrodeposited in solutions with different amounts of SDS and HPC as dispersion additives. The MWCNT concentration of the electrodepositionsolutions was maintained as 10 g/L and the total amount of SDS and HPC was also kept as 10 g/L. Comparing Fig. 1(a) with Fig. 1(e) indicates that SDS is more effective for MWCNT dispersion than HPC. As shown in Fig. 1(b) and (c), however, incorporation of MWCNTs into Ni matrix was greatly enhanced by using SDS–HPC mixture with the SDS–HPC weight ratios of 3:1 and 1:1. Such SDS–HPC mixture might modify the surface chemistry of MWCNTs more suitable for uniform dispersion in the electrolytic bath, resulting in great increase in the MWCNT content of the Ni–CNT nanocomposite. SDS–HPC mixture additive affected not only the MWCNT dispersion characteristics but also the properties of Ni matrix itself. While the hardness of a Ni coating electrodeposited without MWCNTs in a Watt bath containing SDS of 10 g/L was 430 Hv, the value of one processed in a solution with the SDS–HPC mixture of the 3:1 weight ratio increased to 527 Hv.

FESEM micrographs of the Ni–CNT nanocomposite electrodeposited in a bath containing an MWCNT concentration of (a) 1 g/L, (b) 2 g/L, (c)5 g/L, and (d) 10 g/L.

• shows SEM micrographs of the Ni–CNT nanocompositesprocessed in the electrodeposition solutions with the MWCNT concentrations of 0–10 g/L and the 10 g/L SDS–HPC mixture of the weight ratio of 3:1.

• The Ni–CNT nanocomposites were etched in nitric acidto remove the surface layer for observation of the internalmorphology. With increasing the MWCNT concentrationin the electrodeposition bath up to 5 g/L, more MWCNTswere incorporated into Ni matrix. However, microstructureof the Ni–CNT composite became porous with increasing the MWCNT concentration in the bath beyond 2 g/L.

• The MWCNT content in the Ni–CNT• nanocomposite became larger and reached a maximum of• 22.5 vol% with increasing the MWCNT concentration in• the bath up to 5 g/L. However, the MWCNT content in the• composite decreased with further increasing the MWCNT• concentration in the bath beyond 5 g/L, which could be due• to the agglomeration of MWCNTs in the bath containing• MWCNTs above the saturation concentration [4]. As the• MWCNT content decreased and the microstructure• became substantially porous for the nanocomposite• processed in the bath containing MWCNTs of 10 g/L,• mechanical characterization was not conducted for this• specimen.

• With increasing the MWCNT content of the Ni–CNT composite to 14.6 vol%, the fracture stress was improved from 607 to 780MPa. However, the fracture stress dropped drastically to 534MPa for the specimen with the MWCNT content of 22.5 vol% as fabricated in the bath of the MWCNT concentration of 5 g/L. This might be due to the porous microstructure ofthenanocomposite with MWCNT content of 22.5 vol%.

The morphology of electrodeposited pure nickel and Ni–CeO2 nanocomposite. (a) Pure nickel; (b) Ni–CeO2 nanocomposites

• A pyramid structure as shown in Fig. 1(a) is observed at the surface

of the pure nickel. Whereas, with the addition of CeO2

nanoparticles, the grain size is reduced and the morphology is

changed to the hemispherical grain structure, as shown in Fig. 1(b).

• In the electrocodeposition process, CeO2 particles adsorb cations in

the bath under the high potential gradient. They will then be

transported to the cathode surface by electrophoresis, and will be

further adsorbed onto the cathode surface. This phenomenon

results in: (a) an increase in electrocrystalline potential because the

incorporated nanoparticles decrease the electrical cathode surface;

and (b) the occurrence of new nuclei because the adsorbed

nanoparticles limit the growth of the original crystal grains . It is

considered that both of the factors are favorable for fine grains, and

good surface morphology of the composite.

• The microhardness of pure nickel is about 282.7 Hv. With an addition of 30 g/L CeO2 nanoparticles, the microhardnessof the deposit increased significantly to 446.2 Hv.

• The wear height loss of the composite was 18 micron as compared to 43 micron for pure nickel.

• It is known that the microstructure of the electrodeposit is refined when nanoparticles are embedded. It will increase the load carrying capacity and improve the resistance for plastic deformation.

• shows the corrosion potential and corrosion current• obtained from an immersion test with a 3.5 wt.% NaCl• solution. The results indicate that the nanocomposite• obtained from the bath containing 30 g l1 CeO2 nanoparticles• and at the current density of 1 Adm2 exhibits the• best corrosion resistance. Balathandan et al. reported that• the corrosion potential and corrosion current of Ni matrix• reinforced with micron CeO2 particles were 550 mV and• 4 lA cm2, respectively, which are superior to Ni–ZrO2,• Ni–PSZ, and pure Ni coatings [9]. In the present experiments,• the corrosion potential and corrosion current of• the nanocomposite were found to be 195.458 mV and• 1.020 lA cm2, respectively, illustrating a significant• improvement in corrosion resistance over the composite• with micro-sized particles. It is considered that when• CeO2 nanosized particles are embedded in the nickel• matrix, the corrosion path is more seriously distorted as• compared to micro-sized particles, which is favorable for• corrosion resistance. In fact, the fine grain structure arising• from the co-electrodeposition of CeO2 nanoparticles also• promotes good corrosion resistance as compared to coarse• grain structure [13,14].