Fabrication and Surface Roughness Analysis of Anodized Nanoporous Alumina Oxide

(1)

International Journal of Recent Advances in Engineering & Technology (IJRAET)

_______________________________________________________________________________________________

ISSN (Online): 2347 - 2812, Volume-5, Issue -8, 2017 20

Fabrication and Surface Roughness Analysis of Anodized Nanoporous Alumina Oxide

1Rajesh Beri, ²Manoj Kumar Kushwaha, ³Neelkanth Grover

1I. K. Gujral Punjab Technical University, Kapurthala-144603, Punjab, India

2Dept. of Mechanical Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur-152001, Punjab, India

3Dept. of Mechanical Engineering, I. K. Gujral Punjab Technical University, Kapurthala-144603, Punjab, India

Abstract- Porous Anodized Alumina Oxide (PAAO) is developed on aluminum surface by anodization using 0.3 M H₃PO₄electrolyte bath. Anodization was done at various voltages. The results elicits that well organized pores were developed at 140 V – 160 V. FE-SEM analysis was done to understand morphology of nanoporous oxide layer. Surface roughness of anodized specimens was examined by MITUTOYO (SJ-201) surface roughness tester. Anodization results an increase in surface roughness. Higher anodization voltage has shown higher surface roughness. Results show the surface becomes 2-3 times rougher after anodization.

The surface roughness of anodized alumina significantly depends on the chemical cleanup prior to anodization.

Index Terms— Anodization, morphology, nonoporous, surface roughness.

I. INTRODUCTION

Due to applications in electronics, optoelectronics, energy storage, photo catalysis, photonics and biosensors/biomaterials, interest in one dimensional nanostructures has grown significantly during the last decade. Anodization is done on aluminum electrochemically resulting in to formation of thick anodic oxide layer called PAAO (Porous Anodized Alumina Oxide). The anodization process has been used by industry to protect metal components from corrosion for approximately 90 years. By using an electro-chemical process the surface chemistry of the metal is changed, via oxidation, to produce an anodic oxide layer that is thick enough to stifle further oxidation. Aluminum metal (Al), because of its high strength to weight ratio, numerous engineering applications [1, 2] is a widely used metal and is also easily available. For nanostructures Al is generally used in form of AAO. Two types of anodic Al oxide exist;

the first is a non-porous barrier layer that is thin, hard, and wear resistant and behaves as an electrical insulator. The second, a thicker porous oxide structure, is called PAAO layer [1]. This layer structure has a high aspect ratio and consists of a porous structure. The structure of AAO, is very stable at high temperature and in organic solvents, and exhibits uniform pore density, and the pores are parallel and perpendicular to the surface, having an ideal

cylindrical shape. Thus anodization is increasingly becoming the subject of many investigations in several fields. The most recent advancement in application of PAAO is the fabrication of capacitive humidity sensors because the nano sized pores provides a large surface area for absorbing water vapors. A thick porous layer i.e.

structure having large pore diameter results an increase in sensitivity because of an increase in contact surface area [8]. Furthermore, the porous AAO membrane itself is employed for filtration, gas separation or as photonic crystals [3].

This PAAO layer has the advantage of preventing further dissolution of the Al and thus provides an effective protective barrier. During the anodization process, Al produces a highly impervious protective layer on its surface. In anodization Al work piece is attached to the positive side of a DC power supply and placing it into the suitable electrolyte called bath. Another electrically conductive metal, inert in the anodizing bath, is connected to the negative side of the power supply. On activating the power supply, electrons are pulled from the Al into the solution causing the Al to react with water to form an oxide layer. At the cathode, hydrogen gas is formed.

There is formation of nanopores on the oxide layer formed on the surface of aluminum. These pores are hollow hexagonal in shape and forms honey comb like structure as shown below in figure 1.

Figure1: (A) Structure of anodic porous alumina

(2)

_______________________________________________________________________________________________

(B) Cross-sectional view of the anodized layer. [3]

As the oxide layer develops, the phosphoric acid in solution continues to partially dissolve the aluminum substrate and oxide layer. This is replaced by the volume of oxide growing on the surface in the form of hexagonal cells with hollow pores as shown above in the figure 1. It is showing the idealized structure of anodic porous alumina and the cross-sectional view of the anodized layer.

II. EXPERIMENTAL

Sample Preparation - Commercial pure aluminium (97.3% pure) with 0.4mm thickness was cut into rectangular shapes of dimensions 10 cm × 2 cm. The samples were then degreased in ethanol for 200 seconds.

These samples were washed with deionized water and air dried. The samples were then covered with lacquer and an area of 1 cm × 1 cm was exposed for anodization. The chemical composition of samples is determined with X- ray spectrometer.

Anodization - One step anodization was carried out in 0.3M Phosphoric acid solution at constant temperature 30

± 5°C with varying potential range from 140 V to 170 V for 1 hr. Anodization was carried out with the help of commercial potentiostat and two electrode cell, having aluminum as a counter electrode with vigorous stirring by using pump system.

III. RESULTS AND DISCUSSION

To understand the morphology Porous Anodized Alumina Oxide the specimens were tested on FE-SEM. The microstructure of anodized samples at different voltages has been shown below in figure 2.

Figure 2: FE-SEM Microstructure of PAAO at (A) 140 V (B) 150 V (C) 160 V (D) 170 V

Above fig. shows the formation of nano pores on the

surface of oxide layer. Results obtained from PAAO specimens for various voltages are given in table 1. It shows the various pore parameters like pore length, pore diameter, inter-pore distance and porosity at various voltages ranging from 140 V to 170 V.

Table I: Specifications of pores obtained S.

No. Voltage Pore Length (µm)

Pore Diameter (µm)

Inter-Pore Distance (nm)

Porosity (%)

1 140V 133 101 205 24

2 150V 148 155 271 29

3 160V 150 170 285 30

4 170V Dissolution of oxide layer

As shown above in table I, there is an increase in pore length, pore diameter and inter-pore distance as the voltage increases from 140 V to 160 V. On further increasing the voltage beyond 160 V there starts dissolution of oxide layer.

Surface Roughness - The importance of prior surface treatment before anodization has been also analyzed, to examine its effect on surface roughness. The samples were electro polished using D.C. power source. The samples were connected to anode and at cathode lead metal was connected. The electrolyte used is the mixture of 1:5 ratios of H3PO4 and CH3OH. Samples were electro polished for a time period of 1 minute to 6 minutes. The samples were examined for surface roughness using MITUTOYO (SJ-201) surface roughness tester. The values obtained at various time periods are shown below in table II.

Table II: Surface roughness values at different time periods

Duration of

Electro-polishing (minutes)

Surface

Roughness Value (µm)

1 Minute 0.450

2 Minutes 0.300

3 Minutes 0.284

4 Minutes 0.290

5 Minutes 0.290

6 Minutes 0.291

The above table shows that there is decrease in surface roughness value when the electro polishing was done for time periods of 1 minute to 4 minutes but after four minutes there is very insignificant improvement is noticed in surface finish. The value of surface roughness almost becomes constant after 4 minutes. So 4 minutes is the optimum time for electro polishing aluminum samples and surface roughness values was found to be minimal for 4 minutes of electro polishing. The prior treatment of aluminum samples for better surface finish also seems to be helpful in producing well organized nano pores by anodization.

(3)

_______________________________________________________________________________________________

Effect of anodization on surface roughness - For analyzing the surface roughness after anodization samples of bare aluminum and anodized alumina are taken in to consideration. These alumina samples are anodized using same anodizing parameters. These samples were analyzed by setting the cut off distance as 0.8 mm and number of sampling lengths as 5 in the surface roughness tester. The values of Ra (Arithmetic mean roughness) and Rz (Ten point mean roughness) were obtained from samples and the values are shown below

Table III: Surface roughness of Aluminum vs. PAAO S.

No.

Aluminum Samples PAAO Samples Ra (µm) Rz (µm) Ra (µm) Rz (µm)

1 0.39 3.16 2.21 14.26

2 0.40 3.10 2.23 14.26

3 0.42 3.10 2.23 14.22

4 0.39 3.12 2.22 14.23

The above table shows that surface roughness increases after anodization. All the four samples have shown an increase in surface roughness value after anodization.

IV. CONCLUSIONS

Results show that in the present study 140 V – 160 V is the optimum voltage for anodization using H3PO4 electrolyte.

Well organized pores are obtained in this voltage range.

The surface roughness has shown a clear change after anodization. Surface roughness increases after anodization. It has been found that pretreatment like electro-polishing helps in reducing surface roughness and it also improves the shape of pores.

V. ACKNOWLEDGEMENTS

The first author Rajesh Beri, being a Research Scholar of I. K. Gujral Punjab Technical University, Kapurthala highly acknowledge this university for supporting this research work. Furthermore, author also acknowledges L.L.R.I.E.T. Moga and S.B.S.S.T.C. Ferozepur for providing the experimental setup and equipments.

REFERENCES

[1] Gerrard,J.P., Ali, N. and Fawcett, D. “Progress in nano-engineered anodic aluminium oxide membrane development” Materials 2011, 4, 487-526.

[2] Xia, Z., Riester, L., Sheldon, B.W., Curtin, W.A., Liang, J., Yin, A. “Mechanical poperties of highly ordered nanoporous anodic alumina membranes”.

Mater.Sci. 2004, 6, 131-139.

[3] Samantilleke, A.P., Carneiro, J.O., Alpuim, P., Teixeira, V. and Thuy, T.T.T. “Nanoporous alumina templates: Anodization and mechanical

characterization”. Nanomaterials and nanostructures, 4, 320-341.

[4] Sulka, G.D. “Highly ordered anodic porous alumina formation by self organized anodizing”.

Nanostructured materials in electrochemistry.

2008, 1, 1-116.

[5] Lee, W., Schwirn, K., Steinhard, M., Pippel, E., Scholz, R. and Gosele, U. “Structural engineering of nanoporous anodic aluminium oxide pulse anodization of aluminium”. Nature nanotechnology 2008, 3, 234-239.

[6] Han, X.F., Shamaila, S., Sharif, R., Chen, J.Y. and Liu, D.P. “Structural and magnetic properties of various ferromagnetic nanotubes”. Adv. Mater.

2009, 21, 1-6.

[7] Rana, K., Dogu, G.K. and Bengu, E. “Growth of vertically aligned carbon nanotubes over self ordered nano porous alumina films and their surface properties”. Applied surface science 2012, 258, 7112-7117.

[8] Diggle, J.W., Thomas, C.D., and Goulding, C.W.

“Anodic oxide films on aluminium”. Chemical Reviews. 1969, 69, 365-405.

[9] Aryslanova, E.M., Alfimov, A.V. and Chivilikhin, S.A. “Model of porous aluminium oxide growth in the initial stage of anodization”. Nanosystems, 2013, 4, 585-591.

[10] Miravete, E. G. “The effect of anodizing to minimize friction and wear of aluminium surfaces”. Friction and wear of materials, 2009, 2, 1-18.

[11] Su, Z. and Zhou, W. “A thesis on porous anodic metal oxides”. School of chemistry 2008, 1-20.

[12] Hwang, H. J., Kim, C. H. and Jang, Y. H. “Effect of Annealing on the Magnetic properties of Ni nanowires Prepared by Using an Anodized Aluminum Oxide Template”. Journal of the Korean Physical Society. 2011, 58, 654-658.

[13] Papadopoulos, J. Li, C., and Moskovits, M.

“Highly-ordered carbon nanotube arrays for electronics applications”. Applied Physics Letters, 1999, 75, 367-369.

[14] Ruoff, R. S. and Lorents, D. C. “Mechanical and thermal properties of carbon nanotubes”. Carbon, 1995, 33(7), 925-930.

[15] Abdul, M. M., Losic, D. & Voelcker, N. H.

“Nanoporous anodic aluminium oxide: Advances

(4)

_______________________________________________________________________________________________

in surface engineering and emerging applications”

Progress in Materials Science, 2013, 58, 636–704.

[16] Goueffona,Y., Arurault, L., & Guigue, P. “Black anodic coatings for space applications: Study of the process parameters, characteristics and mechanical properties” Journal of Materials Processing Technology, 2009, 209, 5145–5151.

[17] Brevnov, D.A., Rao, G.M., and López, G.P.

“Dynamics and temperature dependence of etching processes of porous and barrier aluminium oxide layers” Electrochimica Acta 2004, 49, 2487–2494.

[18] Piao, Y., Lim, H., Chang, J.Y., Lee, W.Y. and Kim, H. “Nanostructured materials prepared by use of ordered porous alumina membranes”

Electrochimica Acta, 2005, 50, 2997–3013.

[19] Lei, Y., Cai, c., and Wilde, G. “Highly ordered nanostructures with tunable size, shape and properties: A new way to surface nano-patterning using ultra-thin alumina masks” Progress in Materials Science, 2007, 52, 465–539.

[20] Poinern, G.E., Ali, N. and Fawcett, D. “Progress in Nano-Engineered anodic aluminum oxide membrane development” Materials, 2011, 4, 487-526.

[21] Brace, A. “Anodizing-Its development, status and future challenges” Weston-super-Mare, 2002, 100 (11-12), 59-70.

[22] Alcala, G., Skeldon, P., Thompson, G.E., Mann, A.B., Habazaki, H. & Shimizu, K. “Mechanical properties of amorphous anodic alumina and tantala films using nano indentation”

Nanotechnology, 2002, 13, 451-455.

[23] Mahdavian, S.M., Mai, Y.W. & Cotterell, B.“Friction, metallic transfer and debris analysis of sliding surfaces” Wear, 1982, 82, 221-232.

[24] Mahdavian S.M. & Mai, Y.W.“Further study in friction, metallic transfer and wear debris of sliding surfaces” Wear, 1984, 95, 35-44.

[25] Masuda, H. & Fukuda, K. “Ordered metal nanohole arrays made by a two step replication of honey comb structures of anodic alumina”

Science, 1995, 268, 1466-1468.

[26] Shimizu, K., Kobayashi, K., Thompson, G.E. &

Wood, G.C. “Development of porous anodic films on aluminium” Philosophical Magazine A, 1992, 66, 643-652.

[27] Thompson, G.E. “Porous anodic alumina:

fabrication, characterization and applications,”

Thin Solid Films, 1997, 297, 192-201.

[28] Wood, G.C. & O’Sullivan, J.P. “The anodizing of aluminium in sulphate solutions” Electrochimica, 1970, 15, 1865-1876.

