Copper and copper-based alloys encompassing brasses (Cu-Zn) and bronzes (Cu-Sn)are widely used in different industrial and the societal applications. They are common engineering materials in modern architecture and primarily availed for roofing and facade cladding due to their significance of visual appearance (important from an architectural perspective in terms of the design or during renovation of modern or ancient cultural building), ductility, malleability, the atmospheric corrosion resistance and long-term performance. When exposed to air, the copper forms a brownish-green or greenish blue corrosion layer, often denoted as the patina. Copper patina is commonly known as an aesthetically pleasing surface, and one reason for the extensive use of the copper metal and copper-based alloys in both the ancient and modern architecture. One of the most famous examples is the Statue of Liberty in the harbor of the New York, US. Bronze alloys are the family of copper-based alloys traditionally alloyed with tin. Bronze alloys are of the exceptional historic interest and still finds wide applications.

1. Initial Corrosion Behavior of
Element Copper in Atmospheric
Environment
BY DR.SREEREMYA

2. • Copper and copper-based alloys
• Copper and copper-based alloys encompassing brasses (Cu-Zn) and bronzes (Cu-
Sn)are widely used in different industrial and the societal applications. They are
common engineering materials in modern architecture and primarily availed for
roofing and facade cladding due to their significance of visual appearance
(important from an architectural perspective in terms of the design or during
renovation of modern or ancient cultural building), ductility, malleability, the
atmospheric corrosion resistance and long-term performance. When exposed to
air, the copper forms a brownish-green or greenish blue corrosion layer, often
denoted as the patina. Copper patina is commonly known as an aesthetically
pleasing surface, and one reason for the extensive use of the copper metal and
copper-based alloys in both the ancient and modern architecture. One of the most
famous examples is the Statue of Liberty in the harbor of the New York, US.
• Bronze alloys are the family of copper-based alloys traditionally alloyed with tin.
Bronze alloys are of the exceptional historic interest and still finds wide
applications.

3. • The hardness, the tensile strength, wear resistance and corrosion
resistance of these alloys are for most the applications superior
compared with copper metal. In spite of their generally high
corrosion resistance at most conditions, the bronze alloys may
suffer from the so called “bronze disease”, a post-burial cyclic
corrosion phenomenon occurring at atmospheric conditions due to
the formation and the presence of cuprous chloride and its
concomitant volume expansion when the transformed into other
corrosion products within the patina. Brass alloys are copper-based
alloys that are alloyed with zinc ina different proportions, which
results in a material of varying mechanical, the corrosion and
electrical properties. Increased amounts of zinc provide the
material with the improved strength and ductility.

4. • Brass can range in the surface appearance (color) from red to yellow depending on the zinc content.
Brass alloys are generally classified in three types mainly depending on their zinc content: alpha (α)
brass (zinc < 35 wt.%) with the face centered cubic (fcc) crystal structure; alpha-beta (α-β) brass (35
wt.%< zinc < 45wt.%), called the duplex brass and beta (β) brass (zinc > 45 wt.%) with the body-
centered cubic (bcc) crystal structure. The heterogeneity in structure of the brass alloys may cause
the micro-galvanic corrosion effects, and zinc may selectively be released at certain conditions from
the brass alloys in the aqueous solution (dezincification).
• In recent years, a novel copper-based alloy (Cu-5Zn-5Al-1Sn), encompassing zinc(5 wt.%), aluminum
(5 wt.%) and tin (1 wt.%), known as the golden alloy has found aggrandizing use for e.g. facade
cladding due to its lustrous and the golden appearance. Compared with copper metal, brass (Cu-
15Zn) and Sn bronze (Cu-4Sn), the golden alloy corrodes quiet slower and is the only material that
retains its lustrous golden appearance even after about 3–5 years of exposure at the urban sites
and also at marine sites(except for conditions very close to the sea shore) . A similar alloy with the
slight differences in composition and properties is used in both Swedish and the Euro coins. This
material has shown non-allergenic and anti-microbial properties, good tarnishing resistance and the
formability. The antimicrobial characteristics of copper metal and the golden alloy have been
subject for the investigations during recent years (Aastrup et al., 2000).

5. • However, when the oxygen content in seawater is high, the
influence of the oxygen on copper and its alloys is complex. On the
one hand, because the electrode potential of the copper is lower
than that of oxygen, the oxygen depolarization always occurs on the
surface of the Cu matrix, which makes the corrosion process under
cathodic control. On the other hand, the oxygen oxidize scuprous
ions Cu+ into more corrosive positive copper ions Cu2+, which act
as the oxidant and accelerate copper corrosion. Besides, the oxygen
could promote the formation of the protective film on the surface
of copper. When there are cracks on the surface of the Cu and Cu
alloys, erosion by Cl easily destroys the protective film on the
surface of matrix, forming corrosion pits and thus accelerating the
corrosion process of Cu alloys in seawater.

6. • Besides, there are a large number of the mineral ions in
seawater, which improve the conductivity of seawater and
aggrandize the dissolved oxygen content, all of which
provide conditions for the copper electrochemical
corrosion. Furthermore, in marine environment, high
temperature, high salinity, and the high dissolved oxygen
concentration are the important reasons for serious
corrosion of the metal materials (Graedel, 1987). Therefore,
it is not rigorous to study the corrosion behaviour of the
metal materials using only artificial corrosion solution in
laboratory environment. For example, the corrosion of
most metals in the marine environment belongs to oxygen
depolarization corrosion.

7. • With the aggrandizing dissolved oxygen concentration in the
seawater, the content of oxygen diffusing to metal surface and the
speed of the oxygen cathode depolarization also increase, which
leads to the acceleration of corrosion rate. These results are
different from those studied by availing NaCl as corrosion solution
only .Recently, researches on corrosion performance of the Cu
alloys have been mainly examined in the artificial corrosive
solution. Researchers have studied and assesed the corrosion
resistance of the Cu alloy in a3.6 wt% NaCl solution and
demonstrated that the corrosion properties and resistance of the
Cu-10Ni alloys can be enhanced by ultrasonic surface rolling process
(USRP) treatment of the surface. Researchers carried out the
corrosion behavior of a novel Cu alloy in 3.6% NaCl solution and
reported that the oxides and chloride products formed on the
surface of the matrix primarily and were followed by the formation
of dyroxide products.

8. REFERNCE
•
•
• Journal of Material Science & Manufacturing
Technology, Initial Corrosion Behavior of
Element Copper in Atmospheric Environment,
Dr.S.Sreeremya ,2020.Vol 5(2):1-6.