Corrosion and corrosion inhibition of copper alloys in acid medium

1. Alazhar university of Gaza
Corrosion and corrosion inhibition of
copper alloys in acid medium
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Table of contents
title
page
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2. Introduction to copper and copper alloys
3
Effects of alloy compositions on corrosion
4
Corrosion inhibitors for copper
6
Inorganic copper corrosion inhibitors
6
the organic copper corrosion inhibitors
7
Corrosion inhibition of copper alloys in acid medium
8
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3. Copper is metal that has a wide range of applications due to its good properties. It is
used in electronics, for production of Conductive wire, pipes, currency, sheets, tubes, and
also to form alloys1.
Copper alloys are widely used in many environments and applications because of their
excellent corrosion resistance, which is coupled with combinations of other desirable properties,
such as superior electrical and thermal conductivity, ease of fabricating and joining, wide range of
attainable mechanical properties, and resistance to bio-fouling .
Copper alloys resist many saline solutions, alkaline solutions, and organic chemicals. However,
copper is susceptible to more rapid attack in oxidizing acids, oxidizing heavy-metal salts, sulfur,
ammonia (NH3), and some sulfur and NH3 compounds.
Copper and copper alloys provide superior service in many of the applications included in the
following general classifications:
1- Applications requiring resistance to atmospheric exposure, such as roofing and other
architectural uses, hardware, building fronts, grille work, hand rails, lock bodies, doorknobs, and
kick plates
2- Freshwater supply lines and plumbing fittings, for which superior resistance to corrosion by
various types of waters and soils is important
3- Marine applications - most often freshwater and seawater supply lines, heat exchangers,
condensers, shafting, valve stems, and marine hardware - in which resistance to seawater,
hydrated salt deposits, and biofouling from marine organisms is important
4- Heat exchangers and condensers in marine service, steam power plants, and chemical process
applications, as well as liquid-to-gas or gas-to-gas heat exchangers in which either process stream
may contain a corrosive contaminant
5- Industrial and chemical plant process equipment involving exposure to a wide variety of
organic and inorganic chemicals
6- Electrical wiring, hardware, and connectors; printed circuit boards; and electronic applications
that require demanding combinations of electrical, thermal, and mechanical properties, such as
semiconductor packages, lead frames, and connectors.
1
Bradley D. Fahlman; Chapter 3 metals; Material chemistry; Central Michigan University;springer 2007;p89
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4. Effects of alloy compositions on corrosion
Coppers and high-copper alloys have similar corrosion resistance.
They have excellent resistance to seawater corrosion and bio-fouling, but are susceptible to erosioncorrosion at high water velocities. The high-copper alloys are primarily used in applications that
require enhanced mechanical performance, often at slightly elevated temperature, with good thermal
or electrical conductivity. Processing for increased strength in the high-copper alloys generally
improves their resistance to erosion-corrosion.
Brasses :
are basically copper-zinc alloys and are the most widely used group of copper alloys. The resistance
of brasses to corrosion by aqueous solutions does not change markedly as long as the zinc content
does not exceed about 15%. Above 15% Zn, dezincification may occur.
Tin Brasses.
Tin additions significantly increase the corrosion resistance of some brasses, especially resistance to
dezincification.Cast brasses for marine applications are also modified by the addition of tin, lead, and,
sometimes, nickel. This group of alloys is known by various names, including composition bronze,
ounce metal, and valve metal.
Aluminum Brasses
An important constituent of the corrosion film on a brass that contains few percents of aluminum in
addition to copper and zinc is aluminum oxide , which markedly increases resistance to impingement
attack in turbulent high-velocity saline water.
Phosphor Bronzes.
Addition of tin and phosphorus to copper produces good resistance to flowing seawater and to most
nonoxidizing acids except hydrochloric (HCl).
Alloys containing 8 to 10% Sn have high resistance to impingement attack. Phosphor bronzes are
much less susceptible to SCC than brasses and are similar to copper in resistance to sulfur attack. Tin
bronzes-alloys of copper and tin-tend to be used primarily in the cast form, in which they are modified
by further alloy additions of lead, zinc, and nickel.
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5. Copper Nickels
has the best general resistance to aqueous corrosion of all the commercially important copper alloys it
offers good resistance at lower cost. They are superior to coppers and to other copper alloys in
resisting acid solutions and are highly resistant to stress-corrosion cracking SCC and impingement
corrosion.
Nickel Silvers.
They have good resistance to corrosion in both fresh and salt waters. Primarily because their relatively
high nickel contents inhibit dezincification, and much more resistant to corrosion in saline solutions
than brasses of similar copper content.
Copper-silicon alloys.
generally have the same corrosion resistance as copper, but they have higher mechanical properties
and superior weldability. These alloys appear to be much more resistant to SCC than the common
brasses. Silicon bronzes are susceptible to embrittlement by high-pressure steam and should be tested
for suitability in the service environment before being specified for components to be used at elevated
temperature.
Aluminum bronzes
containing 5 to 12% Al have excellent resistance to impingement corrosion and high-temperature
oxidation. Aluminum bronzes are used for beater bars and for blades in wood pulp machines because
of their ability to withstand mechanical abrasion and chemical attack by sulfite solutions.
Aluminum bronzes are generally suitable for service in nonoxidizing mineral acids, such as
phosphoric (H3PO4), sulfuric (H2SO4), and HCl; organic acids, such as lactic, acetic (CF3COOH), or
oxalic; neutral saline solutions, such as sodium chloride (NaCI) or potassium chloride (KCl); alkalies,
such as sodium hydroxide (NaOH), potassium hydroxide (KOH), and anhydrous ammonium
hydroxide (NH4OH); and various natural waters including sea, brackish, and potable waters.
Environments to be avoided include nitric acid (HNO3); some metallic salts, such as ferric chloride
(FeCl3) and chromic acid (H2CrO4); moist chlorinated hydrocarbons; and moist HN3. Aeration can
result in accelerated corrosion in many media that appear to be compatible2.
2
ASM Handbook Volume 13B, Corrosion: Materials (ASM International); Published: 2005;pp 125-163
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6. Corrosion inhibitors for copper alloys:
It is noticed that presence of heteroatoms such as nitrogen, sulphur, phosphorous in the
organic compound molecule improves its action as copper corrosion inhibitor. This is explained
by the presence of vacant d orbitals in copper atom that form coordinative bonds with atoms able
to donate electrons. Interaction with rings containing conjugated bonds, electrons, is also
present. Based on these results more and more compounds containing numerous
heteroatoms and functional groups are developed synthesized since it is noticed they are
responsible for good properties regarding corrosion inhibition because they e nable
chemisorption. Also molecular weight is larger due to its beneficial effect on physical
adsorption3.
Although a number of chemical compounds can be used as corrosion inhibitors for copper, only a
few have been tested for conservation and even fewer are currently in use. Unfortunately,
inhibitors used in industry where copper is relatively free of corrosion have different aims and
restrictions than those in conservation.
The use of inhibitors for conservation is also restricted by factors such as :
-composition alterations.
-colour changes.
-toxicity .
-inhibitor film stability.
INORGANIC COPPER CORROSION INHIBITORS4 :
The use of inorganic inhibitors as an alternative to organic compounds is based on the
possibility of degradation of organic compounds with time and temperature. Three different
inorganic inhibitors are investigated: chromate CrO4 2- , molybdate MoO4 2- and tetraborate B4O7 2in concentration of 0,033M in solution containing 850g/l LiBr and has pH 6,9. Chromate
is generally accapted as efficient corrosion inhibitor that can passivate metals by forming a
monoatomic or polyatomic oxide film at the electrode surface, but it is also known that it
can promote corrosion acting as a cathodic reactive. Possible process for chromates is the
reduction or decomposition of the inhibitor on the metal surface, followed by precipitation.
Chromates are reduced to Cr(III)hydroxide or oxyhidrixide on the metal surface that results
in corrosion current density decrease.
3
4
M. M. Antonijevic; M. B. Petrovic; Copper Corrosion Inhibitors; Int. J. Electrochem. Sci., 3 (2008);p2
A.Igual Muñoz, J. García Antón, J.L. Guiñón, V. Pérez Herranz, Electrochimica Acta 50(2004)957
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7. However, the main disadvantage is the toxicity of chromium (VI) oxidation state. This is the
reason for search for less toxic alternatives. The logical alternative can be analogue of
hexavalent chromium the molybdate species that is an environmentaly friendly inhibitor.
Nevertheless, molybdate and tetraborate showed no significant inhibition. The corrosion
resistance is not improved because the film formation is not favorised in the electrolyte
containing very aggressive anions such as bromides. Inhibion efficiency increases in the
following order: molibdate (1.56%)< tetraborate (51.0%)< chromate (78.6%) Inorganic
compounds act through oxide films formation..
THE ORGANIC COPPER CORROSION INHIBITORS :
organic compounds and their derivatives such as azoles 5 , amines6 , amino acids7 .
The main corrosion inhibitor used for the stabilisation of copper and copper alloy archaeological
artefacts is benzotriazole (C6H5N3); a nitrogen-containing organic heterocyclic compound.
Benzotriazole (BTA) was first used by Madsen in 1967 and has been used widely in the field
since then . For years the use of BTA was based on empirical assessment and the application
methodology varied accordingly.
Organic compounds mostly act via adsorption on metal surface and complex formation.
The chemical industry employs copper and its alloys extensively for condensers, evaporators,
fractionating columns, etc. Copper does not displace hydrogen from acid solution and it is
therefore unattacked in non-oxidizing acid environments. Nevertheless, most acidic solution
contains dissolved air that enables some corrosion to take place8.
BTA efficiency as well as film formation depends on a number of factors including the pH of the
solution. In low pH values the adsorption of BTA on copper is weakened.
This might explain why BTA fails to inhibit corrosion of heavily corroded copper artefacts where
the pH level is very low, such as in the case of pitting and active bronze disease.
BTA increases the corrosion potential, retarding the corrosion rate of copper. This implies that
benzotriazole primarily blocks the exodus of copper ions and acts as a barrier to oxygen diffusion.
The kinetics of the film formation, its thickness and the degree of polymerisation depend on the
pH of the solution. In very acidic solutions (pH<2) a thick film (up to 25 nm) grows quickly
5
E.M.Sherif, Su-Moon Park, Electrochimica Acta 51( 2006) 6556
E.M.Sherif, Su-Moon Park, Electrochimica Acta 51 (2006) 4665
7
G. Moretti, F.Guidi, Corrosion science 44 (2002) 1995
8
D.Altura, K. Nobe, Corrosion28 (1972) 345
6
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8. following a dissolution-precipitation mechanism and, as such, the polymerization is not complete.
Therefore, although the film is thick, it is not that protective. At a pH of around 7, the film grows
more slowly in a self-inhibiting manner. It is thinner (0.5-4 nm) and is completely polymerized
providing the best protection. Therefore the degree of protection is found to be proportional to the
degree of polymerization.
Finally different oxides give different films, and the structure of the film is dependent on the
copper oxides formed 9.
Table: Inhibitors tested and their observed general effects10.
9
S. Golfomitsou and J. F. Merkel, Synergistic effects of corrosion inhibitors for copper and copper alloy archaeological
artefacts, Published by the National Museum of Australia(2004), pp 344-345
10
S. Golfomitsou and J. F. Merkel, Synergistic effects of corrosion inhibitors for copper and copper alloy archaeological
artefacts, Published by the National Museum of Australia(2004), p 346
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9. influence of 2-amino-5-ethylthio-1,3,4-thiadiazole (AETD) on copper corrosion in aerated
HCl solution11 ,as well as the influence of 2-amino-5-ethylthio-1,3,4-thiadiazole (AETD) 12,
2-amino-5-ethyl-1,3,4-thiadiazole
(AETDA) 13 and
5-(phenyl)-4H-1,2,4-triazole-3-thiole
14
(PTAT) in NaCl solution. It is expected that these compounds show high inhibition
efficiency since they are heterocyclic compounds containing more donor atoms, besides that
they are non-toxic and cheap. AETD, AETDA and PTAT good mixed type copper
corrosion inhibitors .
Higher inhibitor concentration and longer exposure of copper in inhibitor solution lead to
inhibition efficiency increase.
The corrosion and corrosion inhibition of copper in freely aerated neutral and acidic chloride
solutions, namely 0.5 M NaCl and 0.5 M HCl, by 5-ethyl-1,3,4-thiadiazol-2-amine (ETDA)
were reported using potentiodynamic polarization, chronoamperometry, electrochemical
impedance spectroscopy and weight-loss measurements. It was found that the corrosion of copper
in HCl solutions proceeds faster than in NaCl ones. The presence of ETDA and the
increase of its concentration decrease the corrosion current and connectively the corrosion
rate of copper through increasing its corrosion resistance. The inhibition efficiency of ETDA
increases with the increase of its concentration from 1.0 mM to 5.0 mM and its value on the
copper surface in NaCl solutions was higher than that obtained in HCl solutions15.
Isatin acts as inhibitors for the corrosion of Cu-Zn of the two alloy samples (I, II) in 0.1 M
H2SO4 or HCl. The inhibition efficiency increases with the increasing of the concentration
of isatin. The presence of isatin inhibits the corrosion of alloy samples cathodically in 0.1 M
H2SO4 or anodically in HCl solutions in the order: H2SO4> HCl. The inhibition is due to the
adsorption of the isatin molecules on the sample surface 16.
It is noticed that higher inhibition efficiency is achieved by application of organic compounds
related to inorganic. Thiazoles, benzotriazole, triazoles give good protection except in strongly
acidic media, where tetrazoles and imidazoles are revealed to be good17.
11
E.M.Sherif, Su-Moon Park, Electrochimica Acta 51( 2006) 6556
El-Sayed M. Sherif, Applied surface science 252 (2006) 8615
13
E.M.Sherif, Su-Moon Park, Corrosion science 48 (2006) 4065
14
El-Sayed M.Sherif, A.M.Shamy, Mostafa M.Ramla, Ahmed O.H.El Nazhawy, Materials chemistry and physics 102 (2007) 231
15
El-Sayed M. Sherif, Inhibition of Copper Corrosion Reactions in Neutral and Acidic Chloride Solutions by
5-Ethyl-1,3,4thiadiazol-2-amine as a Corrosion Inhibitor; Int. J. Electrochem. Sci., 7 (2012) 2843
16
S. A. M. Refaey, A. M. Abd El Malak, F. Taha1and H. T. M. Abdel-Fatah; Corrosion and Inhibition of Cu-Zn Alloys in Acidic
Medium by Using Isatin; nt. J. Electrochem. Sci.,3 (2008) 175
17
M. M. Antonijevic;M. B. Petrovic; Copper Corrosion Inhibitors. A review; Int. J. Electrochem. Sci., 3 (2008) 26
12
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10. Figrue:
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11. Another copper corrosion inhibitor in acidic medium in acidic sulphate media by ecofriendly amino acid compound18.
Inhibition of corrosion of copper in nitric acid solution by some arylmethylene
cyanothioacetamide derivatives19 .
Corrosion inhibition of pyrazolylindolenine compounds on copper surface in acidic media
pyrazolylindolenine compounds with S-atom (with an amine group) have illustrated better
corrosion inhibition performance compared to hydrazine and phenyl group20.
18
Ana T. Simonović, Marija B. Petrović,;Chemical Papers 68(3) 362-371(2014)
A.S.Fouda,A.K. Mohamed ,H.A.Mostafa;J.Chim. Phys. (1998)95 , 45-55
20
Mehdi Ebadi, Wan Jeffrey Basirun, Hamid Khaledi; Chemistry Central Journal 6 (2012) 163
19
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12. L-methionine (MIT), L-methionine sulfoxide (MITO) and Lmethionine sulfone (MITO2)
were found to act as safe corrosion inhibitors for copper surface in 1.0 M nitric acid.
Potentiodynamic polarization studies have shown thatL-mithionine derivatives act as
mixed-type inhibitors and their inhibition mechanism is adsorption assisted by hydrogen
bond formation 21.
Inhibition of Corrosion of Copper in HCl by Tea Leaves Extracts, Methanol extracts of
matured tea leaves show corrosion inhibition effect on corrosion of copper in aerated HCl
solutions. The results obtained shows that methanol extract has high corrosion
inhibition potential in solutions of low acidic concentrations (below 0.05 mol dm-3).22
Inhibition of Brass Corrosion in Acid Medium Using Thiazoles , Benzothiazole and
substituted benzothiazoles offer inhibition by adsorption. They adsorb on the electrode
surface obeying Freundlich adsorption isotherm. The distortion in the double layer
structure due to this adsorption was found to be greater for MBTH > PhBTH >
ABTH > MeBTH > BTH. The inhibitors chemisorbed on surface through coordinate
type of bond between lone pair of electrons on heteroatoms.
Benzothiazoles anchor to the surface through the “N” and “S” at either side of the
thiazole ring and the π-overlap of the benzene ring is favoured. With the introduction of CH-, -NH2, C6H5- and –SH groups the molecule increased and the extent of adsorption
increased. MBTH formed thin polymeric film and offer inhibition. The result obtained
experimentally in this study agree exactly with the theoretical quantum mechanical
calculations done for these compounds. 23
21
K.F. Khaled; Corrosion Science 52 (2010) 3225–3234
Rathiga Senthooran;Namal Priyantha; Annual Research Journal of SLSAJ (2012),Vo l . 12, pp. 01-10
23
K. K. Taha, M. E. Mohamed, S. A. Khalil, S. A. Talab; International Letters of Chemistry, Physics and Astronomy 9(2) (2013)
87-102
22
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13. The corrosion inhibition of copper-nickel alloy by Ethylenediamine (EDA) and
Diethylenetriamine (DETA) in 1.5M HCl, The corrosion rate of Cu-Ni alloy in 1.5 M HCl
acid solution, increased with increase in temperature, and decreased with increase in
inhibitors concentration, Results showed that the N4 in both molecules (EDA and DETA)
involved in the chemical reactivity of these molecules with the metal surface. 24
Also in acidic medium we can use Pyrimidine and its Derivatives as corrosion inhibitor of
some copper alloys , inhibiting corrosion of two copper alloys (4.47% Fe, alloy I, and
10.67% Al, 5.02% Fe, alloy II) in HCl .25
24
Anees A. Khadom, Aprael S. Yaro, Ahmed Y. Musa, Abu Bakar Mohamad, Abdul Amir H. Kadhum; Journal of the Korean
Chemical Society; 2012,Vol. 56 ;pp 406-415
25
S. S. Mahmoud, M. M. Ahmed, R. A. El-Kasaby; Advances in Materials and Corrosion; Vol 2, No 1 (2013)
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14. Conclusion :
1- numerous compounds can be used as copper corrosion inhibitors and the possibility of their
application depends on a few factors.
2- Media that inhibitor is used in is very important for selection. The presence of
aggressive ions and pH are among the most important parametres.
3- Action mechanisms are different. Inorganic compounds act through oxide films
formation.
4- Organic compounds mostly act via adsorption on metal surface and complex formation. That is
the basis of the adverse effect of high temperature on the efficiency of organic compounds.
5- Higher inhibitor concentration and longer exposure of copper in inhibitor solution lead to
inhibition efficiency increase.
6- Molecular structure of inhibitor is the main factor determining its characteristics. Presence of
heteroatoms (S,N,O) with free electron pairs, aromatic rings with delocalized electrons, high
molecular weight alkyl chains, substituent groups in general improves inhibition efficiency. The effect
of electron-donor groups is particularly favourable. Group position is also important, 2- and 5positions are shown to be more convinient.
7- It is noticed that higher inhibition efficiency is achieved by application of organic compounds
related to inorganic. Thiazoles, benzotriazole, triazoles give good protection except in strongly
acidic media, where tetrazoles and imidazoles are revealed to be good.
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