analysis and evaluation of the inhibitive action of … · 2017-08-05 · inhibitors such as...

ELK ASIA PACIFIC JOURNAL OF MECHANICAL ENGINEERING RRESEARCH

ISSN 2394-9368 (Online); EAPJMER/issn. 2394-9368/2016; Volume 2 Issue 2 (2016)

www.elkjournals.com

………………………………………………………………………………………………

ANALYSIS AND EVALUATION OF THE INHIBITIVE ACTION OF BANANA

PEDUNCLE EXTRACT ON THE CORROSION OF MILD STEEL IN ACIDIC

MEDIUM

Ejiroghene Kelly Orhorhoro

Department of Mechanical Engineering,

Faculty of Engineering, Delta State Polytechnic,

Otefe-Oghara, Nigeria,

[email protected]

Oghoghorie Oghenekevwe

Department of Mechanical Engineering,

Faculty of Engineering, University of Benin,

Nigeria,

[email protected]

Oghenero Wilson Orhorhoro

Department of Electrical Electronic Engineering,

Faculty of Engineering,

Delta State Polytechnic, Otefe-Oghara,

Nigeria

ABSTRACT

The use of inhibitors is one of the most practical methods for protecting metal against corrosion, especially in acidic

media. This research work focused on the analysis and evaluation of the inhibitive action of banana peduncle extract

on the corrosion of mild steel in acidic medium (0.5M HCl solution). The mild steel bars were cut into coupons and

suspended in solution of 0.5M HCl to which varying concentrations of the inhibitor (0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0,

3.5% v/v) were added and allowed to stay in these media for a periods of days. The corrosion rate decreased with

increasing concentration of inhibitor to maximum level of 2.0v/v%. While the protective (inhibition) efficiency

increased with increasing concentration of inhibitor. The adsorption of the inhibitor to the mild steel was accredited

to the pairs of electron present in the functional groups which is the rich tannin and saponnin content. This work

has established that the abundant banana peduncle can be used for the corrosion inhibition of mild steel.

Keywords: Corrosion, Mild Steel, Banana Peduncle, Acidic Medium, inhibitive action.

INTRODUCTION

Mild steel is an important construction

material in the industrial. Most industrial

applications such as refining crude oil, acid

pickling, industrial cleaning, acid descaling,

oil–well acid in oil recovery and

petrochemical processes use mild steel as

their material. However, to prevent the

material from corroding has become a great

challenge for corrosion engineers or

http://dx.doi.org/10.16962/EAPJSS/issn.2394-9392/2014

http://www.elkjournals.com/

mailto:[email protected]



………………………………………………………………………………………………

scientists. Corrosion is an electrochemical

process by which metallic surfaces react with

their environment causing the metal to lose

its material properties due to surface

deterioration [1]. Corrosion process is a

natural process that results in considerable

waste of industrial investment. This

phenomenon is noticed in various types of

surfaces, thus, causing a major economic loss

in the industrial sector. Corrosion control

involves different aspects such as

environmental, economical and technical.

The use of inhibitors is one of the most

practical methods for protecting metal

against corrosion, especially in acidic media

[2]. As acidic media, hydrochloric acid (HCl)

and sulphuric acid (H2SO4) are often used as

industrial acid cleaners and pickling. Acid

solutions are used in the most important

industrial applications in etching and acid

cleaning [3]. Because of the general

aggressiveness of acid solutions, the practice

of inhibition is commonly used to reduce the

corrosive attack on metallic materials.

Corrosion inhibitors are common for

protecting steel structures and their alloys in

industry [4]. Hence, there is a growing

demand for environmentally appropriate

inhibitors such as vegetal inhibitors [5].

Several research works had been carry out

on the corrosion of carbon steel in acidic

solutions [6, 7]. The results showed that

large numbers of organic compounds such

as nitrogen, sulphur, and oxygen containing

organic compounds act as promising

inhibitors. However, these compounds are

not only expensive, but also toxic to living

man, thus not recommended if the

environment in which this compounds to be

use are to be considered [8]. Irrespective of

the fact that many synthetic compounds

showed good anticorrosive activity, most of

them are highly toxic to both human beings

and environment. The use of chemical

inhibitors has been limited because of the

environmental threat, and recently, due to

environmental regulations. These

inhibitors, namely, hydrazine, nitrites,

dichromates and chromates etc. may cause

reversible (temporary) or irreversible

(permanent) damage to organ system,

namely, kidneys or liver, or disturbing a

biochemical process or disturbing an

enzyme system at some site in the body. In

order words, they are carcinogenic [9]. The

toxicity may come to play either during the

synthesis of the compound or during its

applications. Considering safety, the

development of non-toxic and effective




………………………………………………………………………………………………

inhibitors is considered more important and

desirable, nowadays, which are also called

eco-friendly or green corrosion inhibitors.

These toxic effects have led to the use of

natural products as anticorrosion agents

which are eco-friendly and harmless.

Recently, many alternative eco-friendly

corrosion inhibitors have been studied and

developed, they range from rare earth

elements to organic compounds. These

known hazardous effects of most synthetic

corrosion inhibitors are the motivation for

the use of some natural products as

corrosion inhibitors [10]. Natural products

such as extracts of easily available plants

and trees have been used as eco- friendly

corrosion inhibitors. Plant extract contains

several organic compounds which have

corrosion inhibition abilities. The extracts

from different parts of many plants have

been reported as corrosion inhibitors in

acidic media [4,11]. There is lots of waste

banana peduncle around major market in

Otefe-Oghara, Delta-State Nigeria. The

waste constitute nuisance to the

environment. The technology for

harnessing the waste into useful materials is

least understood now, however the right

technology to convert the waste banana

peduncle into engineering materials has

remained a daunting challenge to

mechanical and materials engineers. This

problem sharpens the focus of this research

work, since it has been proved that most of

the plant extracts contains tannins which

make them to inhibit corrosion. The aim of

this research work is to explore the potential

of developing environmentally friendly

inhibitor using banana peduncle extracts

that will serve as substitute for synthetic

inhibitors.

METHODS AND MATERIALS

MATERIALS

The Banana peduncle was collected from

the market environment as waste in Otefe-

Oghara, Delta-State Nigeria (Refer Fig.1).

The mild steel sample with composition

shown in Table 1 was used for the purpose

of this research. (Refer Table 1) Beakers,

Hydrochloric acid (HCl) acid, measuring

cylinder, conical flask, ethanol acid,

brushes, polishing and grinding papers with

different sizes, sodium benzoate, triple

stand, Ultrasonic machines were used.

METHODS

BANANA PEDUNCLE EXTRACTION

A Retsch Planetary Ball Mill PM 400 (Fig.

2) was used for the pulverizing of the banana




………………………………………………………………………………………………

peduncle. The grinding jars are arranged

eccentrically on the sun wheel of the

planetary ball mill. The direction of

movement of the sun wheel is opposite to

that of the grinding jars in the ratio 1:2. The

difference in speeds between the balls and

grinding jars produces an interaction

between frictional and impact forces, which

releases high dynamic energies. The

interplay between these forces produces the

high and very effective degree of size

reduction of the planetary ball mill. After the

pulverizing, 350g of the pulverized banana

peduncle was taken in 1000ml round bottom

flask and enough quantity of ethanol was

added as a solvent for extraction. The round

bottom flask was covered with a stopper and

left for 48hrs. Decantation method was then

used to separate the banana peduncle from

the extract. From this 0.5-3.5v/v

concentration was made. Figure 3 shows the

banana peduncle extract produced. (Refer

Fig. 2, 3)

CHARACTERIZATION OF THE

EXTRACT DETERMINATION OF

TANNIN, SAPONIN, CARDIAC

GLYCOSIDES, TERPENOID AND

FLAVONOID

Tannin was determined following the

method of Makkar, et al. [12]. The process of

determining saponin content by Brunner [13]

was used. Cardiac glycosides and terpenoid

were obtained from the banana peduncle

plant extract following the order of while

flavonoid content of the extract of banana

peduncle plant was determined using

colorimeter assay.

INFRA- RED MEASUREMENT

The extract from the banana peduncle was

prepared for Infrared-Red measurement. FT-

IR spectrum was recorded for both the

extract. These spectra were recorded in a

Perkin-Elmer-1600 spectrophotometer. IR

spectra of the banana peduncle extracts were

recorded using Perkin Elmer spectrum 100

FT – IR spectrometer in the frequency range

4000 – 400cm-1, operating in ATR

(attenuated total reflectance) mode.

MICROSTRUCTURAL ANALYSIS OF

THE MILD STEEL

The scanning electron microscope (SEM)

JEOL JSM-6480LV and complemented by

energy dispersive spectrometer (EDS) was

used to identify the surface morphology of

the mild steel. The surface of the mild steel

was examined directly by the scanning




………………………………………………………………………………………………

Electron Microscope. The sample was

cleaned thoroughly, air-dried and observed

SEM at 20 kV.

SAMPLE PREPARATION

The mild steel samples of 20 x 20 x 3 mm

were used as coupons for the corrosion

study, while samples of 30cm length and

diameter 20mm was used for the ultrasonic

analysis. Initially, the coupons were

mechanically polished with emery papers

from 600 down to 1000 grit. The samples

were degreased in ethanol, dried, weighed

and stored in a desiccator. The initial weight

of each sample was taken and recorded.

GRAVIMETRIC MEASUREMENT

(GM)

Hydrochloric acid of 0.5M concentration

was poured into beakers at a constant volume

of 200ml. The banana peduncle extract was

added to the beakers at 0.5%, 1%, 1.5%, 2%,

2.5%, 3.0% and 3.5% respectively (Refer

Fig. 4). The experiment was carried out

using constant temperature of 30oC and time

range of 2, 4, 6, 8and 10days. At each time,

the samples were washed in distilled water,

dried and weighed. The weight loss, rate of

corrosion, inhibition efficiency and degree of

surface coverage were calculated. Also NDT

test was determined thereafter. The standard

expression for measurement of corrosion rate

in mills per year (mpy) was used which is

given as:

Corrosion rate (mm/day) = 87.6𝑊

𝐴𝑇𝜋𝑟2 (1)

Where w is the corrosion weight loss of mild

steel (mg), A is the area of the coupon (cm2),

t is the exposure time (h) and D is the density

of mild steel (g/cm3).

Inhibition efficiency was computed from

equation 2.2:

I. E (%) =W0−W

W0× 100 (2)

Where W and Wo are the corrosion rates with

and without inhibitor respectively. The

degree of surface coverage was computed

from equation 2.3

Degree of surface coverage (Ѳ) =1

%𝐼𝐸 (3)

ELECTROCHEMICAL METHOD

The specimen potential is scanned slowly in

the positive going direction and therefore

acts as an anode such that it corrodes or

forms an oxide coating. These measurements




………………………………………………………………………………………………

are used to determine corrosion

characteristics of metal specimens in

aqueous environments. Electrochemical

measurements were carried out using an

Autolab Potentiostat with the general

purpose electrochemical software package

version 4.9 (Fig. 5). A potentiostat coupled

to a computer system, a glass corrosion cell

kit with graphite rods as counter electrodes

and a saturated Ag/Ag reference electrode

were used. The working electrodes were the

mild steel samples. The inhibitor of varying

concentrations of 0.5-3.5%V/V was then

added in 0.5MHCl respectively. The system

was connected to a potentiostat and to a

computer with the required electrochemical

software (NOVA 30) for reading the results.

(Refer Fig.5)

ULTRASONIC TESTING

The ultrasonic testing was used for the

Lamination Check/ Thickness Check. The

machine was used to scan the specimen by

moving the probe horizontally through the

specimen. The cathode ray tube (CRT)

screen was observe for any change in

readings. If none, it means the specimen

thickness is uniform, if there is, then there is

a change in thickness in the area indicating

the reading. Mark area with different reading

and take its reading.

ATOMIC ABSORPTION

SPECTROSCOPY (AAS) ANALYSIS

Atomic absorption analysis was conducted

by using Atomic Adsorption Spectrometer

Model Bulk 200. This was carried out to

determine the concentration of iron (II) in

0.5M HCl acid after immersion time of

samples in the presence and absence of acid

extract of banana peduncle. The calibration

curve of iron (II) was drawn before analyzing

the electrolyte solution.

RESULTS AND DISCUSSION

PHYTOCHEMCIAL CONSTITUENTS

OF THE BANANA PEDUNCLE

EXTRACT

The result of the phytochemical analysis of

the banana peduncle extract is shown in

Table 2. From Table 2 it was observed that

the extract contains high amount of Tannin

(43.18%), Saponins (18.13%) and

flavonoids (15.39%). With the presence of

the high amount of these organic

compounds, this simply means that the

extract can be used as corrosion inhibitor.

(Refer Table 2)




………………………………………………………………………………………………

INFRA- RED (FTIR) RESULT OF THE

BANANA PEDUNCLE EXTRACT

Table 3 shows the FTIR result of the banana

peduncle extract. The FTIR results of the

banana peduncle extract confirmed the

presence of COOH (carboxylic acid), C-H

(Alkanes), C-I (Alkyls Halides), C=C

(Alkenes) and R-CH2-OH (Alcohols), which

are the functional groups readily available in

organic tannins. The extract shows major

peaks of 3035.33↔ strong COOH

carboxylic acid, 2909.26↔ strong C-H

alkane, 2093.80↔ medium C=C Alkene,

1342.80 medium C-H Alkanes, 1080.88↔

OH Alchohols, 455.11↔ Alkyl halides.

There was no absorbance in between 2220-

2800 which indicates the absence of

cyanides which are generally toxic to the

biological system. This agree with the work

of Makkar, et al. [13]. This result indicated

that the banana peduncle extract is nontoxic

and contain a rich tannin and saponnin

content. (Refer Table 3)

SCANNING ELECTRONIC

MICROSCOPE ANALYSIS OF THE

MILD STEEL

Figure 6 showed the scanning electronic

microscope/energy dispersive spectrometer

(SEM/EDS) analysis of the mild steel used

for the corrosion experiment. The SEM

morphology clearly shown pearlite (dark)

phase in ferrite matrix (white). The ferrite

phase region is large in the SEM than the

pearlite phase. These phase also supported

the analysis in Table 3. The energy

dispersive spectrometer analysis revealed

major peaks of Fe and C with some minor

peaks Mn, Si and Cr. The high peaks of Fe

and C confirmed that the steel used is a plain

carbon steel. (Refer Fig. 6)

GRAVIMETRIC RESULTS

Figure 7 and Table 4 shows the gravimetric

results. From Fig. 7 and Table 4 it can be

observed that the corrosion rate (CR) of the

mild steel decreased with addition of banana

peduncle plant extract and exposure time.

Increases in time of exposure from 2 to

10days reduced the corrosion rate. (Refer

Table 4 or Fig 7)

ULTRASONIC SOUND CORROSION

TEST

The samples used for the ultrasonic sound

test is shown in fig.8 and the results is shows

in Table 5. (Refer Fig. 8)

From Table 5, it was observed that the

thickness reduction of the control sample is




………………………………………………………………………………………………

higher than all that other samples. The

sample with 2.0%v/v inhibitor has the lower

attack; this ultrasonic sound result is in line

with the weight loss and electrochemical

corrosion results discussed above. Localised

corrosion attack was also observed at the

control sample and 0.5%v/v inhibitor

sample. (Refer Table 5)

ANALYSIS OF THE EFFECT OF

BANANA PEDUNCLE EXTRACTS

CONCENTRATION ON THE IRON

The result of the analysis of the effect of

banana peduncle extract concentration on the

iron (II) dissolution into the electrolyte is

shows in fig. 9. It can be observed in fig. 9,

the amount of Fe2+ in electrolyte decreases

with increased in the concentration of the

extract. According to Shah and Chin [14],

corrosion process at the interface can be

divided into two steps: The oxidation of the

metal (charge transfer process) and the

diffusion of the metal ions from the metal

surface into the electrolyte solution (mass

transport process). The diffusion of the metal

ions into the electrolytic solution was

retarded by the addition of the banana

peduncle extract. This confirmed that the

banana peduncle extract inhibits the metal

dissolution process. (Refer Fig. 9)

CONCLUSION

From the discussion on the potential of using

banana peduncle extract on the corrosion

inhibition of mild steel. Banana plant extract

inhibit the corrosion of mild steel in 0.5M

HCl solution. The banana peduncle extract

inhibitor contains organic compounds (like

tannins, pigments, alkaloids). The inhibition

efficiency increases with increasing

concentration of the inhibitor to maximum

level of 2.0v/v% and start to decrease. The

mechanism of physical adsorption, where

adsorbed inhibitors lie on the metals surface

thereby blocking the active sites could have

been responsible for these inhibition actions.

The use of the banana peduncle extract as

local inhibitor is a promising one and can be

use in pickling of steel and storage of low

concentration of acid.

REFERENCES

KM Saeid and A Bambang, Mechanisms

of Microbiologically Influenced

Corrosion: A Review World. Applied

Sciences Journal, 2012, 17 (4): 524-531

[2] EE Ebenso, UJ Ekpe, S Umoren, J

Ekrete, OK Abiola, NC Oforka and S

Martinez, Corrosion inhibition studies of

some plant extracts on aluminium in




………………………………………………………………………………………………

acidic medium, J. Cor. Sc. and Tech.,

2004, 1.1, pp. 96-101

[3] IH Farooqi, MA Quraishi, PA Saini,

Corrosion prevention of mild steel in 3%

NaCl water by some naturally-occurring

substances, Corrosion Prevention and

Control, 1999, Vol. 46, no. 4, pp. 93–96

[4] MA Faisal, RB Abbas, RS John, LO

David and M Brajendra, Characterization

of Microbiologically Influenced

Corrosion on Line Pipe Steel Exposed to

Facultative Anaerobic Desulfovibrio sp,

Int. J. Electrochem. Sci., 2013,8: pp859 –

871

[5] O Mouden, A Id El, R Anejjar, S

Salghi1, O Jodeh, I Hamed, MZ Warad

and RS Dassanayake, Inhibitive Action

of Capparis Spinosa Extract on the

Corrosion of Carbon Steel in an Aqueous

Medium of Hydrochloric Acid Journal of

Mineral Metal and Material Engineering,

2015, 1, 1-7

[6] SK Hasan and S Pinky, Paniala

(Flacourtia Jangomas) Plant Extract

Aseco Friendly Inhibitor On the

Corrosion of Mild Steel in Acidic Media,

Rasayan. J.chem, 2011, vol.4, No.3, 548-

553

[7] JT Nwabanne and NO Vincent,

Adsorption and Thermodynamics Study

of the Inhibition of Corrosion of Mild

Steel in H2SO4 Medium Using Vernonia

amygdalina, Journal of Minerals and

Materials Characterization and

Engineering, 2012, 11, 885-890

[8] IM Iloamaeke, TU Onuegbu, UC

Umeobika and NL Umedum, Green

Approach to Corrosion Inhibition of Mild

Steel Using Emilia Sonchifolia and Vitex

Doniana in 2.5M HCl Medium,

International Journal of Science and

Modern Engineering (IJISME), ISSN:

2319-6386, Volume-1, Issue-3, February

2013, 48-52

[9] A Minhaj, PA Saini, MA Quraishi and

IH Farooqi, A study of natural

compounds as corrosion inhibitors for

industrial cooling systems, Corrosion

Prevention and Control, 1999, vol. 46, no.

2, pp. 32–38

[10] M Sangeetha, S Rajendran, J

Sathiyabama and P Prabhakar P, Eco

friendly extract of Banana peel as

corrosion inhibitor for carbon steel in sea

water, J. Nat. Prod. Plant Resour., 2012,

2 (5):601-610

[11] S Leelavathi and R Rajalakshmi,

Dodonaea viscosa (L.) leaves extract as

acid corrosion inhibitor for mild Steel – A




………………………………………………………………………………………………

Green approach, J. Mater. Environ. Sci.,

2013, 4(5), 625-638

[12] HP Makkar, M Blummel, NK

Borowy and K Becker, Gravimetric

determination of tannins and their

correlations with chemical and protein

precipitation methods, J. Sci. Food

Agric., 1993, 61: pp161-165

[13] JH Brunner, Direct spectrophometry

dertermination of saponin, Animal

Chemistry, 1994, 34, pp.1314- 1326

[14] DA Shah and I chin l, Inhibition of

Stainless Steel Pitting Corrosion in

Acidic Medium by 2-

Mercaptobenzoxazole, Appl. Surface

Sci., 2013, 236, pp175-181.




………………………………………………………………………………………………

LIST OF FIGURES:

Fig. 1 Banana peduncle

Fig. 2 Retsch Planetary Ball Mill used for the pulverizing of the banana peduncle

Fig. 3 Banana peduncle extract

Fig. 4 Corrosion Test




………………………………………………………………………………………………

Fig. 5 Autolab Potentiostat used for the electrochemical test

Fig. 6 SEM/EDS morphology of the mild steel




………………………………………………………………………………………………

Fig. 7 Variation of Corrosion rate with inhibitor concentration

Fig. 8 Photograph of samples used for Ultrasonic sound test

Fig. 9 Concentration of Fe2+ dissolution with %v/v banana peduncle extract




………………………………………………………………………………………………

LIST OF TABLES:

Table-1 Chemical composition of steel

%C %Si %S %P %Mn %Cr %Ni %A1 %Fe

0.1762 0.1232 0.032 0.050 0.0853 0.0128 0.01532 0.0771 balance

Table-2. Result of Chemical Analysis of Extract

Component (%) Extract

Moisture content 7.5

Phenolic 5.67

Flavonoids 15.39

Saponins 18.13

Tannin 43.18

Alkaloids 10.13

Tables-3. Frequencies and peaks of infrared absorption bands of functional groups in banana

peduncle extract

S/N Frequency (Cm-1) Intensity (%) Assignment Class of compound

1

2

3

4

5

6

7

8

9

3035.34

2909.26

2093.80

1606.30

1342.80

1156.67

1086.26

1160.88

455.11

25.495

35.751

50.488

30.866

38.252

32.130

42.493

32.131

19.065

O-H sstretch

OH stretch

OH stretch

C=C stretch

C-H bend

C-O stretch

C-O stretch

C-O stretch

C-I stretch

Carboxylic acid/Phenols

Phenols

phenols

Alkynes

Alkanes/ Alkynes

Alchohol

Alchohol

Alchohol

Alkyl halides

Table-4. Corrosion rate (CR), Inhibition efficiency and surface coverage (θ) for mild steel in

0.5M%HCl

Exposure

time (days)

Concentration of

inhibitor (g/v)

CR 0.5M HCl

(mm/day)

Surface coverage

(θ) for 0.5MHCl

Inhibition

Efficiency (%) for 0.5MHCl

2 0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1.0378

0.5010

0.2757

0.1299

0.0988

0.1151

0.1147

0.1098

------

0.5172

0.7343

0.8748

0.9048

0.8890

0.8880

0.8750

-------

51.72

73.43

87.48

90.48

88.90

88.80

87.50

4

0

0.5

1.0

1.5

2.0

1.0316

0.4980

0.2561

0.1001

0.0667

------

0.5173

0.7517

0.9030

0.9353

------

51.73

75.17

90.30

93.53




………………………………………………………………………………………………

2.5

3.0

3.5

0.0843

0.0821

0.0803

0.9183

0.9150

0.9122

91.83

91.50

91.22

6 0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1.0219

0.4412

0.0908

0.0561

0.0185

0.0346

0.0325

0.0324

-------

0.5682

0.9111

0.9451

0.9717

0.9551

0.9543

0.9432

-------

56.82

91.11

94.51

97.17

95.51

95.43

94.32

8 0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5565

0.1719

0.0303

0.0176

0.0952

0.0303

0.0302

0.0300

-------

0.5981

0.9291

0.9675

0.9734

0.9291

0.9286

0.9156

-------

59.81

95.75

96.75

97.34

92.91

92.86

91.56

10 0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.3220

0.1010

0.0185

0.0165

0.0067

0.0120

0.0110

0.0105

-------

0.6864

0.9025

0.9352

0.9757

0.9624

0.9603

0.9567

--------

68.64

90.25

93.52

97.57

96.24

96.03

95.67

Table-5. Ultrasonic sound results

Inhibitor con

%v/v

Initial Thickness Final Thickness Difference Pits noted Remark

0.0 11.50 9.0 2.5 yes Localized

0.5 10.81 10.5 0.31 yes Localized

1.0 11.50 11.3 0.2 No Uniform

1.5 10.43 10.3 0.13 No Uniform

2.0 10.12 10.1 0.02 No Little or no attack 2.5 10.43 10.2 0.23 No Uniform

3.0 10.13 10.0 0.13 No Uniform

3.5 10.32 10.1 0.22 No Uniform


analysis and evaluation of the inhibitive action of … · 2017-08-05 · inhibitors such as...

Documents