ORIGINAL PAPER
Electrochemical investigation of the passive behaviour
of biomaterials based on Ag–Sn and Cu–Zn–Al in carbonate
buffer in the absence and presence of chloride
Vale
´
ria A. Alves Æ Luı
´
s A. da Silva Æ Luı
´
s F. de F. Santos Æ
Dane T. Cestarolli Æ Alexandre Rossi Æ Leonardo M. da Silva
Received: 11 September 2006 / Accepted: 29 April 2007 / Published online: 24 May 2007
Ó
Springer Science+Business Media B.V. 2007
Abstract The electrochemical behaviour of biomaterials
based on Cu–Zn–Al (cubic Cu
3
Zn phase) and Ag–Sn
(orthorhombic Ag
3
Sn and hexagonal Ag
4
Sn phases) alloys
was investigated in carbonate buffer solutions (pH 9.66) in
the absence and presence of chloride, using different
electrochemical techniques. Analyses of the open circuit
potential and the potentiodynamic polarisation curves
showed that the passivation domain and the corrosion
parameters depend on alloy composition and chloride
concentration. Chronoamperometric studies showed that
passivation kinetics and corrosion of the passive film are
both well described by a linear ln(i) versus ln(t) relation.
The passive film formed on the Ag–Sn alloy is less sus-
ceptible to corrosion when compared to the Cu–Zn–Al
system. The impedance data obtained in the passive region
for the Cu–Zn–Al alloy showed that the passive layer is
compact. In contrast, the impedance data obtained for the
Ag–Sn alloy showed that the passive layer is formed by a
compact oxide layer covered by a porous oxide gel layer.
Mott–Schottky analysis showed that the passive film
formed on the Cu–Zn–Al alloy behaves as a p-type semi-
conductor.
Keywords Corrosion Á Ag–Sn Á Cu–Zn–Al Á Impedance
spectroscopy Á Passivation kinetics
1 Introduction
The current trend in implant science is the substitution of
high-cost alloys by cheaper ones coated with protective and
very stable biocompatible thin films [1–6]. The basic
requirements for these films include: (i) adequate hardness
and mechanical properties; (ii) considerable corrosion
resistance in the oral environment and a high bonding
strength with the base material [7, 8].
Besides the intrinsic mechanical properties of the bio-
material, it should be chemically inert in the oral envi-
ronment, since corrosion considerably affects the
biocompatibility and mechanical integrity of implants. In
fact, corrosion and surface oxide film dissolution are two
mechanisms that enable introduction of ions into the body
which may result in biological reactions and mechanical
failure of the device [9].
Corrosion of alloys in the oral environment finds its
origin in the presence of several species, such as Cl
–
, the
hydrogen ion (H
+
), sulphide compounds (S
2–
), dissolved
oxygen (O
2
), and micro organisms [1–9]. For instance,
chloride causes pitting corrosion, which destroys the pro-
tective passive oxide film.
Numerous surface modification treatments have been
done in order to improve the corrosion behaviour, as well
as the biocompatibility and mechanical properties of
metallic biomaterials [2, 10]. A simple method to generate
V. A. Alves (&) Á L. F. de F. Santos Á A. Rossi
Departamento de Farma
´
cia, Faculdade de Cie
ˆ
ncias Biolo
´
gicas e
da Sau
´
de, Universidade Federal dos Vales do Jequitinhonha e
Mucuri - UFVJM, Rua da Glo
´
ria, 187, Centro, Diamantina,
Minas Gerais 39100-000, Brazil
e-mail: valeria@fafeid.edu.br
L. A. da Silva Á D. T. Cestarolli
Departamento de Cie
ˆ
ncias Ba
´
sicas, Faculdade de Cie
ˆ
ncias
Agra
´
rias, Universidade Federal dos Vales do Jequitinhonha e
Mucuri - UFVJM, Rua da Glo
´
ria, 187, Centro, Diamantina,
Minas Gerais 39100-000, Brazil
L. M. da Silva
Departamento de Quı
´
mica, Faculdade de Cie
ˆ
ncias Exatas e
Sociais Aplicadas, Universidade Federal dos Vales do
Jequitinhonha e Mucuri - UFVJM, Rua da Glo
´
ria, 187, Centro,
Diamantina, Minas Gerais 39100-000, Brazil
123
J Appl Electrochem (2007) 37:961–969
DOI 10.1007/s10800-007-9336-y