Metallization Development of Multi-Walled Carbon Nanotubes

(MWCNTs) with Copper by an Electroless Plating

Dewa Made Pancarana and I Nyoman Budiartana

Mechanical Engineering Department, Bali State Polytechnic, Bukit Jimbaran, Indonesia

Keywords: Multi-Wall Carbon Nanotubes, Metallization, Colloidal Tin-Palladium, Activation, Acceleration, Copper,

Electroless.

Abstract: In this study, Multi Walled Carbon Nanotubes (MWCNTs) were coated with copper by an electroless plating

process. The aim is to form a strong bond between the MWCNTs and the Aluminum matrix. Aluminum in

liquid form has a high surface tension compared to the surface tension of MWCNTs, resulting in very poor

wettability. The surface of MWCNTs coated with metal (copper) will increase the dispersion and wettability

between MWCNTs and the Aluminum matrix. The research was conducted at the mechanical engineering

laboratory, Bali State Polytechnic. Coating MWCNTs with copper is carried out in three steps, namely:

activation, acceleration, and electroless. MWCNTs were activated using a Pd-Sn colloidal solution adapted

from the Plating on Plastics (POP) industry. The ingredients used in the activation process were a mixture of

37.5 ml of Pd-Sn colloid solution, 37.5 ml of HCl (37%), and 175 ml of DI water. In the acceleration process,

fluoride acid (HF 55%) is used as an accelerator. The last process is the electroless plating process, in which

the surface of the MWCNTs that has been catalyzed is inserted into the Copper-Cobalt (Cu-Co) electrolyte

solution. Copper-coated MWCNTs were characterized using scanning electron microscopy (SEM-EDX)

analysis using (JEOL-JSM 6510 A) at the Mechanical Engineering Materials Laboratory, Udayana

University. The results of the SEM-EDX test showed that the copper content was 84.1%, carbon 12.08%, and

the rest were other elements, such as: O, Na, K, Co, Pd, Sn. The increasing size of MWCNTs indicates the

presence of copper on the surface of MWCNTs. The average diameter of the 85 nm copper-clad MWCNTs

increased compared to the average diameter of the initial MWCNTs (10–20 nm).

1 INTRODUCTION

Multi-walled Carbon nanotubes (MWCNTs) have

been widely used in the manufacture of composites

with aluminum matrices because MWCNTs have a

high strength-to-weight ratio. Several previous

studies have shown that the use of MWCNTs to

strengthen the aluminum matrix is very effective.

Most of these studies report using powder

metallurgical techniques such as high energy ball

milling followed by conventional and unconventional

compaction and sintering techniques for sample

preparation (Esawi, 2010, 2009). Of course, the Al-

MWCNTs composite manufacturing process using

powder metallurgy techniques, requires relatively

expensive costs.

In the metal industry, casting is one of the

techniques that can be used for the manufacture of

metal matrix composites. The use of MWCNTs in the

fabrication of aluminum-MWCNTs composites by

casting process faces several obstacles. The main

constraints are poor wetting which limits the

dispersion of MWCNTs in molten aluminum as well

as the problem of oxidation of MWCNTs at high

temperatures which destroys the structure of

MWCNTs (So, 2011). Recently, electroless coating

has offered many advantages that enable it to work

in harmony with MWCNTs in foundry engineering.

Applying a metallic layer

on the surface of MWCNTs

can increase their

wettability in molten metal and also

helps in increasing their dispersion (So, 2011). In

addition, it protects MWCNTs from oxidation at high

temperatures.

In general, electrolytic plating has two main

reactions occurring simultaneously, the oxidation of

the reducing agent to generate electrons representing

the anodic partial reaction and the reduction reaction

of the metal ions present in the solution without

electricity by the resulting electrons representing the

cathodic partial reaction. Since electroplating occurs

only on catalytic surfaces, the surface of MWCNTs

1086

Pancarana, D. and Budiartana, I.

Metallization Development of Multi-Walled Carbon Nanotubes (MWCNTs) with Copper by an Electroless Plating.

DOI: 10.5220/0010959500003260

In Proceedings of the 4th International Conference on Applied Science and Technology on Engineering Science (iCAST-ES 2021), pages 1086-1090

ISBN: 978-989-758-615-6; ISSN: 2975-8246

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

must be catalytically made to be ready for

electrocoating. The general scheme for surface

catalyzing is the conventional two-step technique of

sensitization and activation through aqueous

solutions of Tin(II) chloride (SnCl2) and Palladium

(II) chloride (PdCl) (Feng, 2004). This approach

helps in depositing catalytic palladium particles on

top of the MWCNTs. However, the optimization

process of such catalyst deposition on MWCNTs is

difficult due to the need to control the four

main

factors represented by SnCl

concentration PdCl

concentration,

PH level for both solutions, and the

resulting catalytic particle size. Such a process would

be difficult to optimize when it comes to coating

MWCNTs supplied from different sources due to the

different surface area and volume ratios for different

MWCNTs. However, electroless nickel and copper

phosphorus have been reported in decorating

MWCNTs following the previously mentioned

catalyst system. After that, the coated MWCNTs were

placed in molten aluminum which reported a

promising improvement in the mechanical properties

of the resulting composite (So, 2011).

One of the problems reported in this study for the

previous zero-electric approach was the absence of a

reaction stop mechanism to stop further copper

deposition on top of the MWCNTs once the required

copper layer was reached. This appears to be

particularly important during the final filtration in the

absence of sonication and stirring. Further copper

deposits may lead to the formation of Cu-coated

MWCNTs aggregates. The presence of electrolytes

with low deposition rates makes it difficult to achieve

a precise reaction stop mechanism. For electroplating

copper, the key factor to increase the deposition rate

is to increase the anodic partial reaction kinetics. By

oxidizing more formaldehyde (reducing agent), more

electrons will be generated and more copper ions will

be reduced in the cathodic partial reaction.

The key parameter of formaldehyde oxidation is

the pH value which is controlled by NaOH. As the pH

value increases, the deposition rate increases.

However, the pH reaches a threshold where it starts

to fall when it reaches a value of 12.5. Conventional

copper electrolytes rely on pH values and heating to

control the reaction kinetics (Feng, 2004) and

(Mishra, 1996). In this work, a room temperature

copper-cobalt electrolyte having a high deposition

rate was used. A new catalytic strategy using

palladium-tin colloids was explored.

2 MATERIALS AND

EXPERIMENTAL

PROCEDURES

2.1 Materials

The multi-walled carbon nanotubes are widely

supplied by Chengdu Organic Chemicals Co. Ltd.,

China (OD: 10 - 20 nm, length: 10 - 30 m and purity

>98%) was used in this study. Colloidal palladium-

tin drive was prepared with a composition of 0.5 g of

palladium chloride (PdCl2), 50 ml of 37%

hydrochloric acid (HCl), 200 ml of deionized water,

25 g of stannous chloride. Cupric Sulphate

Pentahydrate (98.5% Assay) and Sodium Carbonate

Anhydrous (99.5% Assay) were supplied by Bofa

Laboratotium. Sodium Hydroxide (99% Assay) was

supplied by Bofa Laboratotium. Potassium Sodium

Tartrate Tetrahydrate otherwise known as Rochelle

salt (99% Assay) is supplied by Bofa Laboratotium.

Cobalt(II) Chloride Hexahydrate (99% Assay) was

supplied by Bofa Laboratotium. Formaldehyde 37%

in aqueous solution was supplied by Bofa

Laboratotium.

2.2 Experimental Procedures

The process of coating the surface of MWCNTs with

copper is carried out in three steps. Starting with the

surface activation process of MWCNTs using Pd-Sn

colloidal particles. The next step is the acceleration

process to remove stanno hydroxide deposits on the

surface of the activated MWCNTs. The last process,

electroplating of Cu-Co on the surface of the

catalyzed MWCNTs. The above procedure globally

is shown in Figure 1

Figure 1: General Scheme of cu-co Electroless Plating on

MWCNTs.

Metallization Development of Multi-Walled Carbon Nanotubes (MWCNTs) with Copper by an Electroless Plating

1087

2.3 Activation of MWCNT’s in Pd-Sn

Colloidal Solution

The amount of MWCNTs used in this process was set

to 0.1 gram MWCNTs. MWCNTs is used when

received without any function. MWCNTs were

activated using a Pd-Sn colloidal solution adapted

from the Plating on Plastics (POP) industry. The

activation process was carried out in a mixture of 37.5

ml of Pd-Sn colloid solution, 37.5 ml of HCl (37%),

and 175 ml of DI water. When using, mix 15%

palladium-tin colloidal catalyst solution and 15%

hydrochloric acid (37%) together, and balance with

deionized water, then heated to 50 - 60 °C to get a

better catalytic effect.

For activation, MWCNTs were dispersed with a

magnetic stirrer in a colloidal solution for 30 minutes.

After the stirring was completed, the treated

MWCNTs were filtered using a 0.22 lm PTFE filter

membrane on the microfiltration kit. The filtered

MWCNTs were re-dispersed in DI water and filtered

again to remove excess colloidal particles and

residual colloid solution from activated MWCNTs.

After filtration, MWCNTs were collected from the

membrane using tweezers.

2.4 Acceleration of MWCNTs in a

Mixture of Acids

The activated MWCNTs are then introduced into a

mixed acid solution known as an accelerator.

The

accelerator serves to remove excess tin hydroxide

the surface of the catalytic particles in the MWCNTs

allowing the palladium surface to be exposed. The

acceleration process will not remove lead from the

core of colloidal particles (Cohen, 1976). The

acceleration process uses 55% (50 mL) HF acid in

500 mL DI water.

After acceleration, the MWCNTs were re-

dispersed in water and filtered again to remove traces

of the previous solution. Following the previous step,

the MWCNTs surface becomes catalytic.

2.5 Electroless Cu-Co Plating of

MWCNTs

The catalyzed MWCNTs were put into a 1 liter

solution of Cu-Co electrolyte with concentrations as

shown in Table I.

Table 1: Typical Concentrations of Cu-Co electrolyte.

Copper-Cobalt electrolyte

Concentrations

CuSO

.6H

6.99 g/L

Na₂CO₃

CoCl

2 g/L

CoCl

1.09 g/L

KNaC

·4H

O (Rochelle

Salt)

22.57 g/L

NaOH 4.5 g/L

Formaldehyde 37% 6 ml/L

All precursor powders were dissolved in DI

water under magnetic stirrer for 5 min. After making

sure all the powder is dissolved in the solution,

formaldehyde is added to the solution. Subsequently,

the activated MWCNTs were placed in an electroless

bath under a magnetic stirrer for 10 min and the

reaction started on the catalytic surface of the Pd-

coated MWCNTs. Air bubbles began to emerge from

the solution after the MWCNTs were added. This

occurs due to the dissolution of hydrogen from the

surface of the palladium and the oxidation of

formaldehyde which produces hydrogen. Then the

solution in a glass beaker was stirred using a magnetic

stirrer for 30 minutes. When the air bubbles stop, it

gives a good indication that the copper has

completely covered the entire surface of the catalyst.

In this case the copper surface became auto-catalyzed

and the solution turned dark brown indicating the

coverage of MWCNTs by copper. After stirring is

complete, the copper-coated MWCNTs begin to

accumulate on the bottom of the glass due to their

increased density. Then the solution was filtered

using a 0.22 nm PTFE filter membrane. The color of

the filtered solution appears to be a light pink color

indicating the consumption of all copper ions in the

solution prior to filtration. The color of the copper-

coated MWCNTs powder obtained, is shown in

Figure 2.

The characterization of copper-clad MWCNTs

was carried out at the Mechanical Engineering

Materials Laboratory of Udayana University using

scanning electron microscopy (SEM) analysis using

(JEOL-JSM 6510 A).

iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science

1088

Figure 2: Copper Coated MWCNT’s of a Brown Color.

3 RESULT AND DISCUSSION

The addition of cobalt(II) chloride to an electroless

copper solution helps in the autocatalytic reduction of

copper ions in an electroless solution increasing the

deposition rate tremendously. The use of colloidal

Pd-Sn nanoparticle catalytic system limits the

catalyst optimization process to two factors (colloidal

particle concentration and solution volume relative to

the number of MWCNTs) rather than four factors in

the predecessor system. In addition, the new system

provides a fixed average size of the colloidal

nanoparticles for better coating fit over MWCNTs.

The optimized catalyst concentration and volume

required to cover the surface area of a fixed number

of MWCNTs helps in controlling the catalyst

concentration-dependent initial copper deposition

rate.

SEM image in Fig. 3 shows MWCNTs after being

coated with copper. The increase in the thickness of

the MWCNTs indicates the presence of copper on the

surface of the MWCNTs. The mean diameter of the

copper-clad MWCNTs was found to be 85 nm

compared to the diameter of the initial MWCNTs,

averaging 10-20 nm. The SEM images show a

uniform layer that completely covers all the surfaces

of the MWCNTs.

Figure 3: SEM Image of The Copper Coated MWCNT’s.

To determine the percentage of the elements

present, chemical analysis was carried out using

energy dispersive X-ray (EDX). The spectrum

obtained is shown in Figure 4.

The results of the analysis showed that the

weight of copper was 84.10 % and 12.08 % C . Other

elements such as Na, K, Co and Sn were found in

minimal percentages as listed in Table 2.

Figure 4: EDX Spectrum of Copper Coated MWCNTs.

Metallization Development of Multi-Walled Carbon Nanotubes (MWCNTs) with Copper by an Electroless Plating

1089

Table 2: Edx Elemental Analysis of Copper Coated Mwcnt’s.

Element (keV) Mass% Sigma Mol% Compound Mass% Cation K

C K 0.277 12.08 0.24 47.47 C 12.08 0.00 2.9938

O 17.81

Na K 1.041 1.30 0.12 1.34 Na

O 1.76 1.22 0.6077

K K 3.312 0.05 0.03 0.03 K

O 0.07 0.03 0.0754

Co K 6.924 1.53 0.09 1.23 CoO 1.95 0.56 2.7533

Cu K 8.040 67.19 0.71 49.92 CuO 84.10 22.80 93.5240

Pd L

Sn L 3.442 0.04 0.07 001 SnO 0.05 001 0.0458

Total 100.00 100.00 100.00 24.62

ZAF Method Standardless Quantitative Analysis (Oxide)

Fitting Coefficient : 0.0326

Total Oxide : 24.0

The process of coating MWCNTs with copper

produces different amounts of elements, compared to

the results of previous studies (Elsharkawi, 2018).

This is influenced by the type of catalyst, the type of

accelerator, and the concentration of the solution used

when immersing the MWCNTs. In this study, the

SEM-EDX results showed that there was no Pd in the

copper-coated MWCNTs powder. The use of a

commercial Pd-Sn Colloidal Solution catalyst from

Dupont gave a better effect, obtained elemental

content of Cu 98.56% and Pd 0.43% (Elsharkawi,

2018).

4 CONCLUSIONS

In the electroless plating process of MWCNTs with

Cu, it can be concluded that:

The factors that affect the morphology of the

sample are; the composition of the colloidal

palladium-tin catalyst, the type of catalyst, the

activation temperature, the volume of the HF acid

solution during the acceleration process, and the

volume of the electrolyte solution bath.

The volume of the electrolyte solution bath is more

in electrolytic coating, resulting in better samples.

REFERENCES

Esawi, A.M.K., Morsi, K., Sayed, A., Taher, M. & Lanka,

S. (2010). Effect of carbon nanotube (CNT) content on

the mechanical properties of CNT-reinforced

aluminium composites. Elsevier, Composites Science

and Technology, vol.70, issue 16, pp. 2237-2241,

Esawi, A.M.K., Morsi, K., Sayed, A., Gawad, A.A. & Borah,

P. (2009). Fabrication and properties of dispersed

carbon nanotube–aluminum composites. Elsevier,

Materials Science and Engineering: A, vol. 508, issues

1–2, pp.167– 173.

So, K.P., Lee, I.H., Duong, D.L., Kim, T.H., Lim, S.C.,

An, K.H. & Lee, Y.H. (2011). Improving the wettability

of aluminum on carbon nanotubes. Elsevier, Acta

Materialia, vol.59, pp. 3313–3320.

Mallory, G.O. & Hajdu, J.B. (2009), Electroless plating:

fundamentals and applications. Am Electroplaters Surf

Finish, New York.

Feng, Y. & Yuan, H. (2004). Electroless plating of carbon

nanotubes with silver. Kluwer Academic Publishers,

Journal of Materials Science vol. 39 pp. 3241 – 3243.

Mishra, K.G.(1996). Kinetics and mechanism of electroless

deposition of copper. J Electrochem Soc 143:510.

hpttps://doi.org/10.1149/1.1836473

Cohen, R. & Meek, R. (1976). The chemistry of

palladium—tin colloid sensitizing processes. J Colloid

Interface Sci 55:156–162.

Shacham-Diamand, Y., Sverdlov, Y., Friedberg, S.,

Yaverboim A. (2017). Electroless plating and printing

technologies, in nanomaterials for 2D and 3D printing.

In: S. Magdassi and A. Kamyshny (eds) Wiley-VCH

Verlag GmbH & Co. KGaA, Weinheim, Germany.

https:// doi.org/10.1002/9783527685790.ch3

Osswald, S., Havel, M. & Gogotsi, Y. (2007). Monitoring

oxidation of multiwalled carbon nanotubes by Raman

spectroscopy. J Raman Spectros 38:728–736.

https://doi.org/10.1002/jrs.1686

Mansoor, M. & Shahid, M. (2016). Carbon nanotube-

reinforced aluminum composite produced by induction

melting, Journal of Applied Research and Technology.

Singhal, S.K., Lal, M., Sharma, I. & Mathur, R.B. (2012).

Fabrication of copper matrix composites reinforced with

carbon nanotubes using a combination of molecular-

level-mixing and high energy ball milling. J Compos

Mater 47:613–621.

Agarwal, A., Bakshi, S.R. & Lahiri, D. (2011). Processing

techniques. Carbon nanotubes: reinforced metal matrix

composites. CRC Press- Taylor & Francis, Boca Raton,

Florida, pp 30– 33

Elsharkawi, M. & Esawi, A.M.K.(2018), Development of

an Electroless PlatingProcess for Multi-wall Carbon

Nanotubes to Improve Their Dispersion and Wettability

in Molten Aluminum, The Minerals, Metals &

Materials Society, pp.29-39

iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science

1090