Arid Zone Journal of Engineering, Technology and Environment, December, 2018; Vol. 14(4): 533-539.
ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng

533

EFFECT OF INOCULANT ON THE DEGRADATION BEHAVIOUR OF MULTI LAYERED
MILD STEEL/Al-Cr PLATE IN PSIDIUM GUAJAVA LEAF EXTRACT

M. A. Bawa1,M. Abdulwahab2, O. B. Umaru1, S. M. Adams3, L. M. Sani4 and N. Agidani2

(1Department of Mechanical/Production Engineering, Abubakar Tafawa Balewa University, Bauchi, Nigeria
2 Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria
3Department of Metallurgical and Materials Engineering, University of Nigeria, Nsukka, Nigeria

4National Airspace Management Authority, Kano, Nigeria)
*Corresponding author’s email: buokatengwu@atbu.edu.ng

Abstract
The effect of an inoculant, [triethylamine (TEA)] on the corrosion behavior of multilayered mild steel/Al-Cr
plates in guava leaf extract was investigated in 0.5M HCl solution using gravimetric based mass-loss test and
potentiodynamic polarization techniques. The mild steel plates were sectioned into coupons of 4 � ��� and
then pickled, after which they were coated at 750� with an Al-Cr alloy. The gravimetric-based mass loss test
was carried out at room temperature for different concentrations and time intervals of 2.0, 4.0, 6.0, 8.0%v/v and
24, 48, 72, 96 hours respectively. The result showed that triethylamine (TEA) decreased the corrosion rate at the
various concentrations indicating protection efficiency up to 59.02% in the gravimetric-based-mass-loss
technique. Equally the potentiodynamic polarization technique indicates higher corrosion resistance of 98.49%.
The two methods used for the evaluation of the degradation of multilayered mild steel/Al-Cr plates in 0.5M
HCl/guava leaf extract medium were in agreement.

Keyword: Corrosion rate, linear polarization, Corrosion coupons, Inoculant molecules, Microstructure, Metals

1. Introduction
Carbon steel, the most widely used material accounts for approximately 85% of the annual steel
production worldwide. Despite its relatively limited corrosion resistance, carbon steel is used in large
tonnages in maritime application, nuclear and fossil fuel power plants, chemical processing, petroleum
production and refining, pipelines, mining, construction and metal processing equipment (Atama, 2005;
Abostra et al., 2009; Idu et al., 2015). Today, there are various engineering materials which have
different areas of application. These materials are subject to environmental degradation. A class of
these engineering materials is Metals. Metals have a wide range of application in modern engineering
due to their superior mechanical properties. Metals are subject to degradation which may also be called
corrosion ( Abostra et al., 2009; Abdulwahab et al., 2015; Amitha and Bharathi, 2011). Corrosion is
due to the reactivity of metallic elements with their environment and oxygen. Corrosion shortens the
service life of metals and this poses a big problem to engineering designs and installations (Peabody,
2001; WanNik et al., 2010). This has led to investigations and studies on the control of this
degradation so as to tackle this problem.

A significant amount of energy is put into a metal when it is extracted from its ores, placing it in a
high-energy state. These ores are typically oxides of the metal such as hematite (�u��� ) for steel or
bauxite (�R������� ) for aluminum (Umaru et al., 2016). One principle of thermodynamics is that a
material always seeks the lowest energy state. In other words, most metals are thermodynamically
unstable and will tend to seek a lower energy state, which is an oxide or some other compound. The
process by which metals convert to the lower-energy oxides is called corrosion (Abdulwahab et al.,
2015). Corrosion of most common engineering materials at near-ambient temperatures occurs in
aqueous (water-containing) environments and is electrochemical in nature. The aqueous environment
is also referred to as the electrolyte and, in the case of underground corrosion, is moist soil (Peabody,
2001).

mailto:buokatengwu@atbu.edu.ng
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Bawa et al.: Effect of Inoculant on the Degradation Behaviour of Multi Layered Mild Steel/Al-Cr Plate in
Psidium Guajava Leaf Extract. AZOJETE, 14(4):433-439. ISSN 1596-2490; e-ISSN 2545-5818,
www.azojete.com.ng

534

Various research has demonstrated ways of controlling corrosion but due to the ever evolving
technology, more research is needed to develop more effective and suitable corrosion control means so
as to reduce the cost implication of corrosion and also increase the service life and maintainability of
engineering equipment and structures. This work is there for focused on improving the corrosion
resistance of a coated metal even in the presence of an inhibitor.

2. Experimental
2.1 Materials and equipment
The materials used in this research include; flat mild steel plates (low carbon steel), distilled water,
Methanol, 192g of Al-92% Cr-8%, pure HCl, 0.5M HCl solution, guava leaf (psidium guajava)
extracts and triethylamine solution. While some of the equipment used include; Potentiometer, digital
weighing balance, desiccator, beakers, series of grit papers, measuring cylinder which were sourced
from the Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria.

2.2 Sample preparation
The sample preparation involved cutting a 1mm thick mild steel plate into 10 small coupons of 4× 2 ×
1 mm each. The coupons were polished using grit paper of size 600 and then pickled.

Table 1: Nominal chemical composition of low carbon steel, (Hassan, 2006)
Steel grade %Carbon %Silicon %Manganese %Phosphorus %Sulphur Copper
Nst 0.12-0.17 0.18-0.28 0.40-0.60 0.04-Max 0.04-Max 0.25

2.3 Pickling
This was carried out to remove the rust (oxide layer), grease and dirt from the surface of the steel. The
samples were dipped in pure HCl of 16cm� for one minute each, washed under a running tap water and
then transferred into warm water to remove any salt layer present. After which it was again dipped in
cold water and swapped with a cotton wool immediately (Abdulwahab et al., 2015).

2.4 Hot dipping
In this step, the 8%-Cr and 92%-Al were charged into a crucible furnace and heated to about 750℃.
The melt was stirred then the mild steel coupons were hot-dipped for 5seconds each at the same
temperature and then left to normalize in the atmosphere (Mohammed and Dong, 2016).

2.5 Guava leaf extracts preparation
This was done using the soxhlet extractor. The soxhlet extractor is a piece of laboratory apparatus
designed for the extraction of a lipid from a solid material. Typically, a soxhlet extractor is used when
the desired compound has a limited solubility in a solvent. The solvent, methanol was heated to reflux.
The solvent vapor then travels into a distillation arm and floods a chamber housing the thimble of
powdered guava leaves. The condenser ensures that the solvent vapor cools and drips back the
chamber housing the solid material. After this, the liquid obtained was then dried using an evaporating
dish (Udom et al., 2017; Omoruwou et al., 2017).

2.6 Corrosion tests
2.6.1 Gravimetric-based mass loss test
At this stage, the 10 coupons were divided into two parts of 5 coupons each. 5 of the coupons were
taken to the corrosion lab and a sample of 0.5M HCl was prepared from the acid medium. The 0.5M
HCl solution was then divided into 5 beakers of 50 ml each. Thereafter 2g of powdered guava leaf

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Arid Zone Journal of Engineering, Technology and Environment, December, 2018; Vol. 14(4): 533-539.
ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng

535

extract was weighed and poured into each beaker. Varying concentration of 0.0, 2.0, 4.0, 6.0 and
8.0%v/v of the inoculant triethylamine was then added into the various beakers and the solution was
stirred using a rubber spoon. The initial weight of each coupon was measured and recorded prior to
immersion in the solution. The coupons were then kept for 24hrs, 48hrs, 72hrs and 96hrs time intervals
after which they were washed with distilled water and consequently weighed (Umaru et al., 2013).

2.6.2 Potentiodynamic polarization test
The potentiodynamic polarization and linear polarization resistance was used to characterize the
corrosion rate of the multilayered mild steel/Al-Cr plates in 0.5M HCl (200ml) solution containing 2g
of guava leaf extract and inoculant of concentrations; 0.0, 2.0, 4.0, 6.0 and 8.0%v/v. A potentiostat
coupled to a computer system, a glass corrosion cell kit with a platinum counter electrode, a saturated
Ag/Ag reference electrode and multilayered mild steel/Al-Cr plates as working electrode were used.
The working electrode specimens were positioned at the glass corrosion cell kit, leaving 1��� surface
in contact with the solution. Polarization test was carried out in the 0.5M HCl/guava leaf extract with
variation in concentration of inoculant at room temperature using the potentiostat. The polarization
curves were determined by stepping the potential at a scan rate of 0.001V/sec. The polarization curves
were plotted using Autolab data acquisition system and both the corrosion rate and potential were
estimated by the Tafel extrapolation method. The data obtained was used to calculate the protection
efficiency (IE) for the inoculant using equation 4 and corrosion rates were calculated using equation 1
respectively (Adams, 2014; Umaru et al., 2017).

2.7 Measurement of corrosion rates
There are three main methods used to express corrosion rates (Umaru et al., 2017)
a. Thickness reduction of the material per unit time.
b. Weight loss per unit area and unit time.
c. Corrosion current density.

ADT
KWR  (1)

Where:
R= Corrosion rate
K= Corrosion constant
A= Surface area in ���

W=Weight loss in grams
D= Density of material
T= Time of exposure in hours

For this case, corrosion rate is taken in 2/ /g cm hr (2)
The coupons used are cuboids in cross section, their surface area was calculated using;

Surface area 2 2 2lw lh hw   (3)
Where l is length, w is width and h is thickness.

Protection efficiency is given by;

P.E = �t���t
�t�

(4)

Where �t� polarization resistance in presence of inoculant/corrosion rate at certain inoculant
concentration

PR is polarization resistance without inoculant/corrosion rate in absence of inoculant

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Bawa et al.: Effect of Inoculant on the Degradation Behaviour of Multi Layered Mild Steel/Al-Cr Plate in
Psidium Guajava Leaf Extract. AZOJETE, 14(4):433-439. ISSN 1596-2490; e-ISSN 2545-5818,
www.azojete.com.ng

536

3. Results and Discussion
3.1 Gravimetric measurement result showing Variation of corrosion rate with inoculant
The Figure 1 below shows the variation of corrosion rates with immersion time at room temperature
for different concentrations of inoculant in 0.5M of HCl/guava leaf extract medium. It shows that the
corrosion rates decrease as the concentration of the inoculant increases (Adams et al., 2014).

Figure 1: Variation of corrosion rates with time for different inoculant concentration.

The sample in 8.0%v/v concentration of inoculant showed excellent corrosion resistance. Similar trend
was observed for samples in 6.0, 4.0 and 2.0%v/v concentration of inoculant. For example, the
corrosion rate decreased from 0.01260mm/yr. to 0.00990mm/yr. in immersion time of 72hrs. The
significant decrease in corrosion rate at increased inoculant concentration can be attributed to the
adsorption of inoculant molecules on multilayered mild steel/Al-Cr alloy surface which act as physical
barrier to restrict the diffusion of ions to and from the alloy surface and prevent the alloy atoms (ions)
from precipitating in further anodic or cathodic reactions, hence resulting in a decrease in corrosion
rate (Abdulwahab et al., 2013).

3.2 Potentiodynamic polarization Result
In the potentiodynamic polarization for multilayered mild steel/Al-Cr plates in 0.5M HCl/guava leaf
extract environment (Table 3), different measurements consisting of potentiodynamic polarization
corrosion rate, potentiodynamic polarization corrosion density (PP-Jcorr), and linear polarization
resistance (LPR) were used as a criteria for evaluation of corrosion resistance of multilayered Al-
Cr/mild steel plates in the environment.
Generally, the studies showed a decrease in corrosion rates with the addition of triethylamine as an
inoculant. The corrosion potential and polarization decreased except at 4.0%v/v concentration
indicating that triethylamine affects the cathodic reaction. The increase in Rp and corresponding
decrease in jcorr generally suggested an improvement in corrosion resistance of the alloy in the
presence of inoculant. This shows that the alloy was protected within the immersion time considered
(Adams et al., 2014).

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Arid Zone Journal of Engineering, Technology and Environment, December, 2018; Vol. 14(4): 533-539.
ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng

537

Figure 2: Potentiodynamic Polarization curves for multilayered mild steel/Al-Cr plates in 0.5M HCl
solution and guava leaf extracts in absence and presence of different concentrations of triethylamine
(TEA) as inoculant.

The inoculant showed high protection efficiency values of up to 98.49% at 4.0%v/v concentration. In
the absence of the inoculant, i.e. the control medium at 24hrs the corrosion rate was 0.1145mm/yr.
while at the same immersion time in 4.0%v/v of inoculant, the corrosion rate decreased to
0.01500mm/yr.

3.3 Protection efficiency
The results from the histogram showed that triethylamine had its highest protection efficiencies in both
gravimetric and potentiodynamic polarization methods at inoculant concentration of 4%v/v in the
0.5M HCl/guava leaf medium.

Figure 3: Variation of protection efficiency with inoculant concentration for gravimetric based mass
loss test and potentiodynamic polarization test.

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Bawa et al.: Effect of Inoculant on the Degradation Behaviour of Multi Layered Mild Steel/Al-Cr Plate in
Psidium Guajava Leaf Extract. AZOJETE, 14(4):433-439. ISSN 1596-2490; e-ISSN 2545-5818,
www.azojete.com.ng

538

In potentiodynamic polarization studies, triethylamine showed up to 98.49% efficiency at
concentration of 4%v/v while in gravimetric methods, triethylamine showed up to 59.02% protection
efficiency at 4%v/v inoculant concentration.

4. Conclusion
The result showed that the inoculant, triethylamine (TEA) decreased the corrosion rate at the various
concentrations indicating protection efficiency up to 59.02% in the gravimetric based mass loss
technique. The potentiodynamic polarization technique indicates higher corrosion resistance of 98.49%.
Finally, the two methods used for the evaluation of the degradation of multilayered mild steel/Al-Cr
plates in 0.5M HCl/guava leaf extract medium were in agreement.

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