Sci. & Cult. 78 (11-12) 574-576 (2012)
Making the Glitter Last - Development
bonds with copper resulting in chemisorptions of these
organic molecules forming a protective layer.1,2 Use of these
of A Novel Lacquer for Copper
organic inhibitors is a success to prevent corrosion in
Based Alloys
solution medium but very few of them provide efficient
inhibition for long duration when used as a coating as
ABSTRACT : A novel polymeric corrosion inhibitor based
required for preservation of outdoor and indoor metal
lacquer was developed at CSIR-NML that can be used as a
architectural work. In the present work, a novel polymeric
coating to prevent tarnishing of copper and its alloys for long
durations. The tarnishing inhibition efficiency of the lacquer
corrosion inhibitor based lacquer was developed at CSIR-
was evaluated using electrochemical, salt spray and outdoor
NML that can be used as a coating to prevent tarnishing
exposure techniques. Results obtained from these studies
of copper and its alloys for long durations.
suggest that the developed lacquer efficiently protects the
copper and brass surfaces from tarnishing for very long
Materials and Methods
: The copolymer was
durations.
synthesized following a procedure described elsewhere3.
Keywords : Corrosion inhibitor, Lacquer, Copper, Brass
The copolymer contains two kinds of functional groups.
One functional group is responsible for the corrosion
inhibition properties whereas the other functional group
he metal architectural work and handicrafts made from
imparts hydrophobicity to the copolymer. The lacquer was
T
copper and its alloys (brass, bronze) tarnish (surface
prepared by dissolving the copolymer in a suitable organic
becomes black) when exposed to humid environments
solvent. Corrosion tests were performed on brass of the
resulting in loss of aesthetic appeal. This has led to a
following composition: 65.8% Cu, 34.1% Zn, 0.05% Pb
decrease in sale of Indian made brass/bronze handicrafts
and 0.03% Fe. Pretreatment of the surface of the specimens
in the international and domestic market threatening the
were carried out by polishing with P400 emery paper,
livelihood of the brass artisans of India and the survival
rinsing with distilled water, degreasing with acetone and
of the age old profession of brass artifacts production.
drying at room temperature before use. Electrochemical
Lacquers can be used to prevent tarnishing of the brass,
measurement was performed using a Princeton VersaSTAT3
bronze or copper handicrafts for long durations. IncralacTM,
Potentiostat/Galvanostat. Salt spray test was carried out
developed by International Copper Research Association,
following the procedure of ASTM B 117 using a salt spray
is such a lacquer available in the international market.
chamber manufactured by Ascott Analytical, UK. The
Unfortunately, very few such lacquers are available in
flower of sulfur test was carried out following ASTM B
Indian markets and those available lacquers have poor
809 procedure.
efficiency compared to Incralac. The cost of Incralac (~Rs.
3000/liter) compels the brass artisans of India not to use
Results and Discussion : A new approach was
it on their products. The Chinese products on the other
adopted to prepare a lacquer with efficiency better than
hand are coated with efficient lacquers which protect them
the lacquers available in the market. Instead of utilizing
from tarnishing for long durations and hence are becoming
the existing practice of simply mixing the corrosion
more popular worldwide. So there is a strong need to
inhibitors with a polymer, a new polymeric corrosion
develop a cheap but efficient anti tarnishing lacquer for
inhibitor
(copolymer) was designed and synthesized in
the brass artisans of India.
which the functional groups responsible for corrosion
inhibition are chemically bonded to the polymer chain.3
Lacquers are generally formulated by mixing polymers
We believe that this will result in strong binding of the
with one or more corrosion inhibitors, levelers and
copolymer on the metal surface through chemisorptions
antioxidants in a suitable organic solvent. Many corrosion
instead of simple physical adsorption resulting in better
inhibitors for copper and its alloys are reported so far in
corrosion inhibition efficiency. The copolymer was then
the literature. Few of them are inorganic inhibitors
used to prepare a lacquer by dissolving in suitable organic
(chromate, molybdate, tetraborate) but majority of them
solvent. The lacquer can be applied on the metallic surface
are organic compounds (azoles, amines, amino acids).1 The
by dipping, brushing or spraying. The efficiency of the
widely accepted inhibition mechanism of organic inhibitors
lacquer to prevent tarnishing was than evaluated.
is that the hetero atoms (N, S, and P) form coordinative
574
SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2012
developed lacquer remain untarnished even after 20 days
of the test. The brass panel coated with the Saboo lacquer
got partially tarnished after 10 days (Figure 2A). This
indicates that the lacquer developed at CSIR-NML is more
efficient than the Saboo lacquer available in the market
and can provide efficient protection from tarnishing of brass
for long durations. ASTM B 809 test, also known as
“flower of sulfur test” is widely used to evaluate the
efficiency of the polymeric coatings to prevent tarnishing
of copper, copper alloys, and silver in humid sulfur vapor
atmosphere. A brass artifact (horse) collected from the
Moradabad market was partially coated with the lacquer
and was put to “flower of sulfur” test. The blank portion
of the brass artifact got tarnished within 30 minutes where
as the coated part remain unchanged even after 10 days
(Figure 2B). This test further confirmed that the developed
lacquer can provide protection for long durations.
Figure 1. Photographs of brass panels coated with the lacquer and
exposed to outdoor atmosphere for 10 months (A) and indoor atmosphere
Potentiostatic Polarization Studies : Electrochemical
for 65 days (B).
studies were carried out to gain insight into the mechanism
of corrosion inhibition of the lacquer. Figure
3 shows
Exposure Tests : The efficiency of the lacquer to
polarization curves for brass in 1 N H2SO4 with and without
prevent tarnishing of brass was evaluated by exposure tests.
the lacquer coating. The corrosion potential of the coated
A brass panel of 18" x 4" x 0.1" size was partially coated
sample shifts towards noble side by 117 mV and corrosion
with the lacquer using a brush and was exposed to the
outdoor atmosphere on the roof top of CSIR-NML building.
The uncoated portion of the panel got tarnished within 10
days of the exposure where as the coated part remain
unchanged even after 10 months of exposure (Figure 1A).
Indoor exposure tests were also performed in which brass
panels fitted to the doors of CSIR-NML building was
coated with the lacquer. These brass panels were repeatedly
touched by human hands throughout the day while opening
and closing of the doors. It was observed that the bare
panel got tarnished quickly and finger prints started
appearing on the panels within 2-3 days whereas the coated
panel remained tarnish free for more than 7 months (Figure
1B). The result of these studies confirmed that the lacquer
can be used to preserve the brass architectural works
exposed to indoor and outdoor atmospheres for long
durations.
Accelerated Corrosion Tests : Accelerated corrosion
tests (ASTM B117 and ASTM B809) were performed to
evaluate long term anti-tarnishing efficiency of the
developed lacquer. The salt spray test (ASTM B117) was
performed on the brass panels dip coated with the
developed lacquer. One uncoated brass panel (blank) and
another brass panel dip coated with the acrylic lacquer
made by Saboo Coatings Ltd. (collected from Moradabad,
Uttar Pradesh market) was included in the test for
comparison purpose. The blank brass panel got tarnished
Figure 2. Photographs of brass items after 20 days of salt spray test
within 24 hours where as the brass panel coated with the
(A) and 10 days of flower of sulfur test (B).
VOL. 78, NOS. 11-12
575
current density is reduced 3 times (10.6 x 10-6 against 32.4
alloys for long durations. Outdoor and indoor exposure
x 10-6 A cm-2) indicating the effectiveness of the coating.
tests, accelerated tarnishing tests, and electrochemical tests
Further, on the coated sample, the current increases linearly
revealed that the developed lacquer can protect the copper
up to ~ 0.2 VSCE and become passive thereafter showing
based alloy surfaces from tarnishing both in indoor and
the barrier protection of the substrate.
outdoor atmospheres. The lacquer has a huge market
potential and CSIR-NML with National Innovation Council
of India
(NInC) are jointly working to provide the
developed lacquer to the brass artisans of Moradabad, Utter
Pradesh. The objective is to enable the artisans to make
better quality brass artifacts that can compete with the
Chinese products in international market. This will help
them to earn more and to live a better life.
ASHOK MOHANTY1,
S. K. TIWARI, TRILOCHAN MISHRA,
AND SANCHITA CHAKRAVARTY
CSIR-National Metallurgical Laboratory,
Jamshedpur - 831 007, Jharkhand, India
1 Corresponding author, Email: akm@nmlindia.org
Received : 16 July, 2012
Figure 3. Potentiodynamic polarization curves for bare and lacquer
coated brass in 1 N sulfuric acid.
1.
M. M. Antonijevic, M. B. Petrovic, Int. J. Electrochem. Sci., 3,
1 - 28 (2008) and references therein.
Conclusions : In summary, a new polymeric corrosion
2.
Kokalj, A; Peljhan, S; Finsgar, M; Milosev, I; J. Am. Chem. Soc.,
inhibitor was synthesized and a lacquer was formulated
132, 16657-16668, (2010).
using the polymer to prevent tarnishing of copper based
3.
A. Mohanty, S. K. Tiwari, T. Mishra, S. Chakravarty, Indian
Patent IN0059NF2012.
576
SCIENCE AND CULTURE, NOVEMBER-DECEMBER, 2012