Aluminium anodization from ionic liquid and deep eutectic solvent: alternative routes to traditional surface treatment

Aluminium anodization from ionic liquid and

deep eutectic solvent: alternative routes to

traditional surface treatment

Lapo Gabellini,

Stefano M. Martinuzzi,

Francesca Borgioli,

Emanuele Galvanetto,

Nicoletta Ditaranto,

Rosaria A. Picca,

Massimo Innocenti,

and Stefano Caporali,

a Industrial Engineering Dept. DIEF, University of Florence, Via di S. Marta 3, 50139-Firenze, Italy b Chemistry Dept., University of Florence, Via Lastruccia 3, 50019-Sesto Fiorentino, Italy

c INSTM - National Interuniversity Consortium of Materials Science and Technology, Via Giusti 9, 50121 Firenze, Italy

d Chemistry Dept. and CSGI – Centre for Colloid and Surface Science, University of Bari, Via Orabona, 4, 70125-Bari, Italy

E-mail: stefano.caporali@unifi.it

Introduction:

Among the emerging non-aqueous solvents suitable for industrial applications Deep Eutectic Solvents (DES) and Ionic Liquids (ILs) are gaining tremendous interest in owe to their “green“ characteristics, i.e. to be ecologically safe, nontoxic, biodegradable and to be easily

prepared from renewable sources. The present study deals with the electrochemical growth of passive layer of aluminum oxide (anodization) in ILs media for decorative and technological purposes.

Discussion:

Anodization in ILs allows the formation of nm-sized pores (Fig. 1) which result larger than the ones obtained by traditional aqueous anodization. However, no evident chemical differences are detectable at the surface (Fig.2) and the neutral salt spray test (UNI ISO 9227, Fig.3) evidenced better aesthetical performances (no colour changes) in aggressive Cl-bearing environments for the samples obtained from non-aqueous treatment.

Acknowledgements:

The present study was funded by Regione Toscana within POR Creo FESR 2014-2020, “EL4ALL” project.

Figure 1: Pore size distribution and SEM image in the inset of the sample surface after anodization via traditional (1) and ILs (2 and 3) treatment.

Experimental:

Aluminium lamina were anodized by

traditional (1) H₂SO₄ treatment, (2) H₂SO₄ 36% + buthyl-ethyl imidazolium–

trifluoromethansulphonate (BEiM-TFMS), current density 10mA/cm2, and (3) H

2SO4

36% BEiM-TFMS at 20mA/cm2. Then the

samples were coloured using commercial dye (Sanodure® Fiery Red ML) and

sealed in boiling water for corrosion test.

Figure 3: Corrosion test of red-dyed anodized aluminium samples before (1) and after (2) 96h of exposure to NSS test.

1

2

1

2

Traditional aqueous ILs anodization

1

2

₃

Figure 2: XPS spectra of C, N, O, S, Al and F collected on anodized samples. Two spectra for every samples are displayed evidencing no appreciable chemical differences.