Paper No.
17038
17th APCCC
CORROSION OF PHOSPHORUS BRONZE IN DIFFERENT
BIODIESEL BLENDS AND ITS REMEDIAL MEASURES
M. A. Fazal1*, B. Rathinee2, H. H. Masjuki3
1-3
Department of Mechanical Engineering, University of Malaya,
50603 Kuala Lumpur, Malaysia
* email : fazal@um.edu.my
Abstract: Biodiesel, as an alternative renewable fuel has some technical advantages over conventional
petroleum diesel. However, it is more corrosive for automotive materials. The corrosion behaviour of
phosphor bronze was studied through immersion test in B0 (diesel), B20 (20% biodiesel and 80%
diesel), B50 (50% biodiesel and 50% diesel) and B100 (biodiesel) for 1440 hours. Similar test was
carried out with the addition of additive Tert-butylamine and Benzotriazole in B20 and B100. The
coupons were weighed before and after the immersion test to determine the weight loss and corrosion
rate. The metal surface was characterized by Scanning Electron Microscopy and Energy Dispersive
X-Ray (SEM/EDX), while fuels were analysed by measuring the Total Acid Number (TAN) and
density. The results show that corrosiveness of biodiesel blend for phosphorous bronze increases with
the increase of biodiesel concentration. The presence of additive Tert-butylamine and Benzotriazole
retards the corrosion attack and protects the phosphorous bronze from deterioration. However,
Benzotriazole was found to be more efficient and effective corrosion inhibitor for phosphor bronze in
biodiesel.
Keywords: Corrosion, leaded bronze, additives and palm biodiesel
1. Introduction
Biodiesel is produced from different renewable sources such as animal fats and vegetable oils.
However, vegetable oil is extensively used as biodiesel feedstock as it can easily be obtained through
continuous plantation [1,2]. The most commonly used vegetable oils are coconut, rapeseed,
sunflower, palm, peanut, cotton seed and soybean oil. Biodiesel has very close properties to those of
diesel and therefore it can be potentially used to replace diesel completely or partially [3]. It has also
some technical advantages over diesel. However, biodiesel fuel is generally unstable, whereby its
properties and composition can be degraded over time under different operating conditions [3,4].
Research has shown that there are certain deficiencies in the properties of biodiesel such as low
volatility, high viscosity and its cold flow properties that can lead to reduced atomization of fuel,
partial combustion with heavy smoke discharge, carbon deposition, and injector choking within the
combustion-ignition (CI) engine etc. [5-6]. The factors that can affect the stability and performance of
biodiesel include auto-oxidation, thermal decomposition, presence of oxygenated moieties as well as
unsaturated molecules [4,7]. Palm and coconut biodiesel exhibits the least amount of unsaturated
fatty acid, thus making them much more stable when compared to other biodiesel feedstock such as
peanuts, rapeseed, soybean and sunflower [4].
The physical and chemical properties of biodiesel fuel depends on the type of used biodiesel feedstock
and its composition [8,9]. The variation feedstock gives both advantages and disadvantages to the
overall use of biodiesel. Biodiesel in its pure and unblended form is indicated as B100. B100 is hardly
used as fuel because of its higher viscosity and incompatibility with engine components. Additionally,
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
pure biodiesel is more corrosive than conventional petroleum diesel for automotive engine
components. The poor corrosion resistance of automotive components in contact with biodiesel fuel
has a major impact to the commercial use of biodiesel fuel in CI engines. Upon exposure in biodiesel,
materials such as copper, brass and bronze tend to accelerate biodiesel degradation, leading to weight
loss and formation of pitting on the metal surfaces [7]. Therefore, in most cases, biodiesel is usually
used by blending with petroleum diesel. Biodiesel blends are primarily formulated in order to improve
the chemical and physical properties as well as to reduce the materials incompatibility, thus making it
suitable for automotive application. The most commonly used biodiesel blend is B20 consisting of
20% biodiesel and 80 % diesel [10]. Haseeb et al., [11] conducted an immersion test by immersing
copper and leaded bonze in diesel, biodiesel and their blend B50 (50% biodiesel in diesel). They
observed increased corrosion rate of metals with the increase of biodiesel concentration. Therefore
fuel blend with lower percentage of biodiesel could be one of the ways to reduce corrosion for
automotive components. In addition, different additives such as Tert-butylamine (TBA),
Benzotriazole (BTA) can reduce the corrosiveness of biodiesel [12,13]. The present study aims to
analyse the corrosion behaviour of phosphor bronze in contact with petroleum diesel (B0), biodiesel
fuel (B100) and different diesel-biodiesel fuel blends (e.g. B20, B50) in the absence and presence of
different additives.
2. Experimental
Petroleum diesel and palm biodiesel used in this study were supplied by Petron Malaysia and
Weschem technology Sdn Bhd, Malaysia respectively. The phosphor bronze coupons (29 mm
diameter X 2 mm thickness) were machined and ground with 800, 1000 and 1200-grit silicon carbide
papers. A hole of 2 mm diameter was drilled near the edge of each coupon to enable hanging of the
specimen in biodiesel. The ground coupons were dipped into alcohol for several minutes, followed
by degreasing with acetone. The dried coupons were then used for immersion test. The fuel/ blends
selected were B0 (diesel), B20 (20% biodiesel in diesel), B50, B100 (biodiesel), B20/TBA (500ppm
TBA doped B20), B100/TBA, B20/BTA (500 ppm BTA doped B20), B100/BTA. After the
immersion for 1440 h, the samples were washed in a stream of tap water. Before and after exposing
the test coupon into different test fuels, weight of each coupon was measured upto four decimal
points. For each coupon, the weight loss was calculated by subtracting the final weight (after
exposure) from its initial weight (before exposure). The weight loss was then converted into corrosion
rate (mm/y) by using equation 1. Efficiency of the inhibitors used was measured by equation 2.
8.76 10 6 w
(1)
Corrosion rate (CR) 
Dt A
 CR
 CRInhibited 
 %
Inhibitor Efficiency  100   unhibited
CR
unhibited


(2)
where corrosion rate (CR) is in millimetre per year (mm/y), ‘w’ is the weight loss (kg), ‘D’ is the
density (kg/m3), ‘A’ is the exposed surface area (m2) and ‘t’ is the exposure time (h).
The characterization study of phosphor bronze coupons and fuels was carried out after completion of
the immersion test. The tested coupons were characterized using a scanning electron microscopy
(SEM) to study the changes in surface morphology. Energy Dispersive X-Ray (EDX) analysis was
conducted to study the elemental and compositional analysis of the corrosion products. The used fuel
was analysed for the measurement of its Total acid Number (TAN) and density.
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
3. Results and Discussion
Fig.1 shows the physical appearances of phosphor bronze before and after exposure in Biodiesel
blended fuels for 1440 hours. It is seen that the colour of the corrosion compounds formed on the
coupons upon exposure in biodiesel or its blends is green. The appearance of the coupons exposed to
neat diesel fuel was not significantly changed. Fig.1 also shows that a much darker greenish corrosion
products form on the coupons with the increase of biodiesel concentration into the blends.
a) PB / As-received
c) PB / B20
b) PB/ B0
d) PB / B50
e) PB / B100
Figure 1: Appearance of phosphor bronze (PB) coupons (a) before and (b-e) after exposure in
(b) B0, (c) B20, (d) B50 and (e) B100 fuels for 1440 hours
Fig.2 shows the effect of additives on the appearance of phosphor bronze immersed in B20 and B100
blends. It is seen that the addition of TBA and BTA in the fuels caused the reduction of the greenish
corrosion products. This demonstrates that additives are effective in reducing the corrosion of
phosphor bronze. Coupons immersed in BTA doped fuels did not show any discolouration on the
exposed surface. Therefore, BTA seems to be more effective than TBA in inhibiting corrosion attack
phosphor bronze in both B20 and B100.
a) PB / B20
b) PB / B20 / TBA
c) PB / B20 / BTA
d) PB / B100
e) PB / B100 / TBA
f) PB / B100 / BTA
Figure 2: Effect of additives, TBA and BTA on the appearance of phosphor bronze (PB) upon
exposure in B20 and B100
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
The weight loss measurement of the respective phosphor bronze coupons was recorded and applied to
calculate the corrosion rates. Fig.3 shows the corrosion rate of phosphor bronze coupons in different
fuels. The result shows that with the increasing biodiesel content in the blend, corrosion rate of
phosphor bronze increases. However, it does not indicate a significant change in corrosion rate for the
coupons exposed in biodiesel (B100) and B50 diesel-biodiesel blend. The average corrosion rates of
phosphor bronze in neat diesel and biodiesel are seen to be 0.000160 and 0.000257 mm/y
respectively. This finding proves that biodiesel fuel is much more corrosive than neat diesel fuel.
Figure 3: Corrosion rate of phosphor bronze in different fuels
Table 1 shows the corrosion rate of phosphor bronze in the absence and presence of additives, TBA
and BTA. The results prove that the addition of corrosion inhibitor retards the corrosion rate and
provides better corrosion protection to the test samples. It is also seen that BTA is more effective in
retarding corrosion activity as compared to the TBA. The efficiency of TBA additive is much lesser in
both B20 and B100 fuels when compared to the efficiency of BTA additive. Although a significant
change is not recorded in terms of corrosion rate and corrosion inhibitor efficiency, the trend still
proves that the addition of corrosion inhibitors improves the corrosion resistance of phosphor bronze,
whereby, BTA additive is seen to show a much better performance in terms of corrosion inhibition.
Table 1: Corrosion rate of B20 and B100 fuels in the presence and absence of additives
Fuel Without
Additive
(mm/y)
Fuel with TBA
additive
(mm/y)
Efficiency of
TBA additive
(%)
Fuel with
BTA additive
(mm/y)
Efficiency of
BTA additive
(%)
B20
0.000232
0.000205
11.64
0.000202
12.93
B100
0.000257
0.000240
6.61
0.000234
8.95
Corrosion
Rate
Fig.4 shows the SEM micrographs of the coupon different fuel exposed copper surfaces. Corrosion
attack on biodiesel exposed copper surface is comparatively more than that in diesel exposed copper
alloy surface. The as-received sample shows a clean and scratch free appearance. Sample B0 shows
the least corrosion attack when compared to sample B100.Copper and brass tends to exhibit a higher
corrosion attack in the biodiesel environment [15]. Research has shown that increasing biodiesel
volume in the immersion solution tends to increase the corrosion rate of the sample [15]. It is also
seen that BTA addition is more effective in corrosion inhibition of copper and copper based alloys.
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
Sample immersed in BTA doped fuels (Fig.5g and Fig.5h) shows the least corrosion attack where the
initial polishing / grinding lines are still clearly visible. BTA forms a protective barrier film when in
contact with copper and copper alloys. BTA is more effective at higher pH values, leading to the
formation of Cu(I)BTA surface complex that is responsible for corrosion protection [16].
It is also reported that thickness of the Cu(I)BTA layer is dependent on the transport of Cu(I) ions
from the copper metal to the surface layer, whereby the transferred cuprous ions will then react with
the physisorbed BTA molecules and form Cu(I)BTA protective layer. Also, it is reported that
increasing thickness of Cu(I)BTA layer, tends to increase the inhibitory effectiveness of the layer.
However, the actual theory on the corrosion inhibition mechanism of BTA on copper and its alloys is
still not well defined [16]. Based on these findings, BTA is seen to be the most efficient and effective
corrosion inhibitor for phosphor bronze in biodiesel environment.
Figure 4: SEM micrographs of as-received phosphor bronze (PB) (a) and PB immersed in
different fuels in the absence of additive (b-d) and presence of TBA and BTA additive (e-h)
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
The elemental analysis in Figure 5 shows that there is a variation in the composition of the corrosion
products of different fuels mainly C, O and Cu.
Figure 5: EDX analysis of as-received phosphor bronze (PB) (a) and PB immersed in different
fuels in the absence of additive (b-d) and presence of TBA and BTA additive (e-h)
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
The coupon immersed in neat diesel (B0) contains the least amount of oxygen, that is 6.90 wt% while
sample immersed in pure biodiesel contains the most amount of oxygen content, that is 20.07 wt%.
There is also an increase in the carbon content when comparing between B0, B20 and B100. Research
has shown that the higher concentration of oxygen drives to increase the reaction between metal and
metal compounds [15] Similar findings were reported earlier stating that the higher concentration of
oxygen drives to increase the reaction between metal and metal compounds [15]. The increasing metal
oxidation is also due to the hygroscopic nature of biodiesel, which causes water retention. Water is
available through condensation or dissolution in the air. Excessive water retention can also promote
microbial growth and contamination within the biodiesel fuel.
The standard limit of TAN value in biodiesel blend stocks is 0.5mg KOH/g, as per ASTM D6751.
This represents the content of fatty acid within the solution. The increasing TAN value is due to the
increasing level of biodiesel oxidation to form free fatty acids in the fuel. The presence of corrosive
acids in the fuel can also lead to the increase in TAN value [15]. The presence of additives in the fuels
as shown in Fig.6 is seen to improve the TAN value, whereby fuels doped with BTA show the least
increment in TAN value when compared to the as-received fuels. Similar findings were seen in the
density of fuelblends in the absence and presence of TBA and BTA additives as shown in Fig.7.
Increasing biodiesel content in the blend increases the density of the fuels. The increase in density of
biodiesel could be due to the increase in higher molecular weight compounds in the solution [9, 18]. It
is seen that BTA doped fuels tend to be more effective in reducing the density increment of the fuel
when compared to the addition of TBA. This finding is supported by the similar decreasing trend seen
through TAN analysis, thus proving that corrosion inhibitor, particularly BTA is a practical solution
for corrosion prevention of phosphor bonze in the biodiesel.
Figure 6: Comparison of change in TAN of B20 and B100 in the absence and presence of TBA
and BTA additive
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The 17th Asian Pacific Corrosion Control Conference, January 27-30, 2016, IIT Bombay, Mumbai, India
Figure 7: Comparison of density of fuels in the absence and presence of TBA and BTA additive
4. Conclusions
The following conclusions could be drawn from the present study:
i.
The lowest corrosion rate was recorded in the B0 while the highest corrosion rate was
recorded in the B100 bio diesel. The presence of corrosion inhibitors was seen to reduce the
corrosion rate of phosphor bronze. Addition of BTA shows a higher efficiency in inhibiting
corrosion as compared to TBA. This is supported by the SEM studies of the exposed coupon
surfaces as well.
ii.
There is an increase in the oxygen and carbon content on phosphor bronze coupons with
increasing biodiesel in the fuel. This indicates that there is an increase in the corrosion
compound formed on the sample surface. The increasing biodiesel content leads to the
dissolution and oxidation of biodiesel to form free fatty acids, thus resulting in the instability
of biodiesel.
iii.
The addition of corrosion inhibitors is capable of improving the corrosion resistance of
phosphor bronze to bio diesel blends. BTA additive serves as a better and more efficient
corrosion inhibitor in reducing the corrosion of phosphor bronze in bio diesel blends.
5. Acknowledgement
The authors would like to acknowledge the financial support provided by the Research Grant of
University Malaya (UMRG), Grant No RPO13A-13AET and REG137-12AET.
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