dermaj, a. et al. atmospheric corrosion inhibition of historical steel. 2007

8/7/2019 Dermaj, A. Et Al. Atmospheric Corrosion Inhibition of Historical Steel. 2007

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1. INTRODUCTION

The corrosion of a metal is often considered as an in-

convenience because it implies a change of the objects in

the course of time. The exhibition of an old object is ac-

companied by a change depending on the environmental

conditions, which can sometimes accelerate objectsdegradation.

The knowledge of the corrosion system, its initiation

as well as its evolution, depends on the choice of the con-

servation techniques and different methods used to pro-

tect the objects against corrosive agents [1].

For protection against the corrosion, many ways are

accessible [2]: manufacture new metals resistant to corro-

sion, establish physical barrier to isolate the metal using

organic coatings as example, or apply an electrolyte using

corrosion inhibitors.

The use of the inhibitors is an adapted and convenient

method to protect metals in the most situations.

The state of conservation of an archaeological object

essentially depends on the nature of the alloy from which

it has been manufactured, as well as the environment ag-

gressiveness [3].

In this study, we are interested in protection of the fer-

rous objects. At first, we have studied the electro-chemi-

cal behaviour of iron in different environments (marine,

acidic, alkaline…) [4-7].

Then, we have tested the effect of a formulation in-

hibitor containing a synthetic compound (PTS), on the

corroded iron coupons in the presence and absence of 3

wt% NaCl solution.

The obtained results with two applied methods, brush

and immersion show that after one month, the inhibition

effect is very important. The EDX surface analysis con-

firms these results.

2. EXPERIMENTAL CONDITIONS

2.1 Material: corroded ironAll the coupons are iron based metal measuring 7cm

length, 5cm width and of 2mm thick. These coupons were

corroded artificially to simulate the behaviour of historical

and archaeological metal artefacts. Analytical work on the

samples was carried via atomic emission arc induced spec-

troscopy. Analyses were carried out on three different

spots on the metal surface. Each spot was analyzed in tripli-

cate and an average value in % for each element was ob-

tained. This composition weight %(wt%) is 0.157 wt % C,

0.201 wt % Si, 0.519 wt % Mn, 0.007 wt % P, 0.009 % S

>99 wt% Fe, total remaining elements < 0.2%.

2.2 SEM-EDX

The micrographic negatives have been taken out us-

ing SEM (HV 16 Kv), equipped by EDX analysis (ZAF

quantification standard less).

2.3 Inhibitor

The products used as organic corrosion inhibitors is as

follow: Formulation FPTS of 3-phenyl-1, 2,4-triazole-5-

thione (PTS), synthesized in our laboratory.

2.4 Studying methods: Atmospheric corrosion

Before beginning experiments, iron samples were

cleaned with a brush, and then degreased with ethanol.

143

Atmospheric Corrosion inhibition of historical steel by FPTS

formulation based of triazole-thioneAhmed Dermaj1, Driss Chebabe1, Hind Hammouch1, Mohamed Goursa1,

Najat Hajjaji1 and Abdellah Srhiri2

1Laboratory of Electrochemistry, Corrosion and Environment, Faculty of sciences2SERVICHIM Sarl society corrosion inhibitors production, Morocco

Kenitra city 14000,BP 133 [email protected]

Several techniques have been used to conserve archaeological metal objects: mechanical cleaning, elec-trolytic treatment and even oil immersion. In this work, we have tested the inhibiting effect against corro-

sion of formulation, which is based on a synthetic compound (PTS). We have examined the inhibition effi-ciency on corroded iron either in the presence and the absence of 3% NaCl solution. The results obtainedusing different application methods (brush and immersion) after one month of exposure have shown thatthe inhibiting effect was very important in the event of atmospheric corrosion. The surface analyses bySEM/ EDX confirm these results.

Keyword: inhibitor, corrosion, archaeological iron, atmospheric corrosion

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A. Dermaj et al.

The inhibitor formulation, was used either by immersion of coupons into ethanol solution of FPTS for an hour, or bybrushing FPTS formulation directly on the iron surface.

3. RESULTS AND DISCUSSION

3.1 Iron samples

After the preparation of iron coupons, visual inspec-tion was carried out, and the condition of iron samplesduring this study was documented using digital pho-tographs. Figure 1 represents the condition of couponbefore application of the inhibitor.

ence with 3% NaCl solution treatment that showed acorrosion accelerated on the whole surface which seemsto cover with corrosion products. The general view of this case coupon is dark.

3.2 SEM and EDX analysis

The obtained results after a month of exposure tothe atmospheric corrosion, with and without inhibitorare illustrated below.

3.3 Reference sample exposed to atmospheric corrosion:

To examine the effect of chloride solution on theiron coupons behaviour, we have compared two cases:coupons with 3% NaCl solution sprayed on the surfaceand coupons without 3% NaCl.3.3.1 Without 3% NaCl solution

The state of the reference sample in the absence of 3% NaCl solution is illustrated by the SEM photo shownin Figure 3.

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Face 1 Face 2

Figure 1 - Iron sample before FPTS application

In general, these coupons present two different zones:— White zone, characterised by its brightness and ab-

sence of corrosion pits.— Black zone corresponds to corrosion pits dispersed

in the whole surface indicating the development of artificial corrosion.After the mechanical cleaning of these metal coupons,

we have chosen a group of five samples A, B, C, D and E.After the application of the inhibitor on these

coupons by immersion or brush in the presence and theabsence of 3% NaCl solution, they were exposed to am-bient temperature 25oC and controlled relative humiditybetween 63% to 68%) (Figure 2).

A : Inhibitor by immersion without 3% NaCl solution

B: Inhibitor by brush in the presence of 3% NaCl solutionC: Inhibitor by brush without 3% NaCl solution

D: Reference with 3% NaCl solution

E: Reference without 3% NaCl solution

Figure 2 - state of surface samples after 10 days of exposure

In spite of the bad quality of the photos, all couponsdon’t undergo any visual modifications except the refer-

A B C D E

White site(B)

100Ìm

Black site(A)

Figure 3 - SEM photo of a reference samplein the absence of 3% NaCl

This photo shows the existence of black and whitearea. So as to understand the difference between the twoobserved sites on samples areas, EDX analysis coupledto SEM observations was carried out. The correspond-ing spectrum is shown in Figure 4.

Figure 4 - EDX spectra of a reference samplein the absence of 3% NaCl after a month of exposure

Black site (A)

White site (B)




Atmospheric Corrosion inhibition of historical steel by FPTS formulation based on triazole-thione

The examination of this Figure indicates that analysisat the black site shows an important quantity of oxygen,and less weight percentage of iron. Other chemical ele-ments were detected as shown in Tables 1A and 1B.

Table 1 A - EDX analysis of black site (A)

Figure 6 - EDX spectra of reference sample in presence

of 3% NaCl after one month of exposure

The Table 3 shows the % of three elements present in

corrosion products.

Table 3 - EDX analysis of a reference sample

in the presence of 3% NaCl

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Table 1B - EDX analysis of white site (B)

In the event of white site, the peak attributed to oxygenis nonexistent. The corresponding analyses show the pres-ence of iron peaks with high intensity.

The white zone which is resistant to corrosion containsthe basic metal elements.

The black zone contains in addition to the basic ele-ments, a great percentage of the oxygen and the carbonwhich may indicates corrosion at the level of this zone.3.3.2 In the presence of 3% NaCl solution

Our visual assessment shows a big difference with thesample without sodium chloride. The metal coupon is

completely corroded as shown in Figure 5.

Figure 5 - SEM photo of a reference samplein the presence of 3% NaCl

The corrosion products layer is heterogeneous and fis-sured. The observed heterogeneity may be attributed tooxide and chloride corrosion products formed on thecoupon, which was confirmed by EDX analysis showingoxygen, chloride and iron peaks in Figure 6.

50Ìm

We note the following:— The existence of only one zone in the whole area

formed by a layer of the corrosion products.— Appearance of rust layer which is fissuring and cover-

ing all sample surfaces.— A presence of higher wt% of oxygen and Cl- in the cor-

rosion products layer. This may lead to propose a for-mation of oxychloride iron as corrosion product, cover-ing the sample area.

— So the effect of the chloride ions is marked well.

3.4 Application of the inhibitor (FPTS) by brush method

3.4.1 SEM observations and EDX analysis in the absence

of 3% NaCl

The results obtained with FPTS on iron coupons in theabsence of 3%NaCl are given in Figures 7 and 8.

The microscopic observations in Figure 7 show thepresence of white zones corresponding to a basic iron met-al uncorroded, and also the presence of corrosion pits richon iron oxides. More information about the presence of in-hibitor film on the surface are carried out by EDX analysesas given in Figure.8.




A. Dermaj et al.

B 100Ìm A 20Ìm Table 5 - EDX analysis of black site for iron couponProtected with FPTS in the absence of 3%NaCl

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Figure 7 - SEM photo of iron coupon coated by FPTSin absence of 3%NaCl after one month of exposure.

Figure 8 - EDX spectra of iron coupon protected by FPTSin the absence of 3%NaCl after one month of exposure

There are differences on elemental composition be-tween the distinguished zones. The white zone composi-tion is represented in Table 4.

Table 4 - EDX analysis of white site for ironcoupon protected by FTPS in the absence of 3%NaCl

Black site (A)

White site (B)

Compared to a reference composition of the white site,we note the apparition of new elements when the FPTS ispresent on the coupon surface like S, C, and K and whichcome only from inhibitor formulation. EDX analysis of black zone is represented on Table .5

From Table 5, the presence of C, S and K attributed tothe inhibitor film, and also it appears that the oxygen per-centage in this zone compared to the reference one, de-creases from 50% to 27%, which may be due to the pro-tecting character of the FPTS formulation.

3.4.2 SEM observations and EDX analysis in the pres-

ence of 3% NaCl

SEM observations of iron coupon presented in Figure9 show the existence of two zones which correspond to the

EDX spectra represented in Figure 10. The EDX analysispermits to note only one zone. This leads us to concludethat the inhibitor forms thick corrosion products on themetal area as shown in Figures 9 and 10.

200Ìm 500Ìm

Figure 9 - SEM photo of iron coupon with FPTSin presence of 3%NaCl after one month of exposure

A remarkable difference is seen in samples surface be-tween photographs obtained in the presence and the ab-sence of inhibitor with of 3 % NaCl as a corrosive solution.This difference may be explained by a decrease of chloridefrom 5% to 0.12% as shown in Table 6, and oxygen from57.64% to 22% when the inhibitor was added, also thepresence of Nitrogen, Carbon and Sulphur was noted .

Figure 10 - EDX spectra of iron coupon contains FPTS inpresence of 3%NaCl solution after one month of exposure




Atmospheric Corrosion inhibition of historical steel by FPTS formulation based on triazole-thione

Table 6 - EDX analysis of iron coupon with FPTSin the presence of 3%NaCl

Table 7 - EDX analysis of iron coupon with FPTS appliedby immersion

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3.5 Inhibitor applying by immersion

The inhibitor FPTS was also tested by immersion of theiron coupon in solution of 20ml of ethanol containing 15mg of inhibitor in the absence of 3% NaCl during 1 hour.

The choice of percentage of the inhibitor is based onthe concentration effect of PTS(3-phenyl-1, 2,4-triazole-5-thione) [10].

The visual observation shows a remarkable differenceof the surface state compared to the reference. The pro-tected iron coupon presents a good resistance to atmos-pheric corrosion; corresponding SEM photo reported inFigure 11.

Figure 11 - SEM photo of iron coupon with FPTS in theabsence of 3% NaCl solution after one month of exhibition

EDX spectra and elemental composition are reportedin Figure 12 and Table 7 respectively

Figure 12 - EDX analysis of metal coupon (A) containsFPTS in the absence of 3% NaCl solution

after one month of exposure

The obtained results show the existence of sulphur, ni-trogen and an increase of carbon percentage due to the in-hibitor presence on the surface coupon.

Comparison with reference system in the presence andthe absence of 3% NaCl indicates a decrease of oxygenpercentage, justifying the inhibiting effect of the FPTS ap-plied by immersion method.

After three months of exposure, the state of iron sur-faces is represented in Figure 13:

100Ìm

A B C

D E

Figure 13 - The state of surface iron coupon(A, B, C, D and E) after three months of exposure

A : reference without inhibitor and 3%NaCl solution

B: inhibitor by immersion without 3% NaCl solutionC: inhibitor by brush without 3% NaCl solution

D: reference without inhibitor but with 3% NaCl solution

E: inhibitor by brush in the presence of 3%NaCl solution

A general observation of the iron surface after 3months shows the presence of pits on the whole surface forthe reference coupon. For coupon treated by immersion of FPTS manifests a development of corrosion in the level of

pits.— The system brush is more resistant against atmospheric

corrosion (not evolution of the corrosion both in thelevel of pits and white site) In the presence of 3% NaClsolution, all coupon surfaces were severely corroded.

— For the system brush with NaCl, the development of active corrosion on the black site of iron coupon wasseen.

4. CONCLUSION

This study has been realized by visual inspection, spectro-scopic methods (SEM and EDX) techniques to study ar-




A. Dermaj et al.

chaeological iron. From all these techniques we haveproved the inhibiting effect of FPTS against atmosphericcorrosion. The effect of FPTS leads to strong reduction of oxygen percentage and ions chloride.

ACKNOWLEDGEMENTS

This work was realized in the framework of “PROMET”project. The authors gratefully acknowledge the financialsupport. Also they would thank CNRST Morocco for itscollaboration (PICS).

REFERENCES

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[2] Bommersbach, P.: “Evolution some proprieties of thecorrosion inhibitor film under effect of temperatureand hydrodynamic condition”, thesis, Institut des Sci-ences appliqués Lyon, France (2005).

[3] Chase, T.: ”Chinese bronzes: casting, finishing, pati-nation and corrosion”, In: Scott,.D.A.,,Podany, J. andCosidine, B.B (eds.): “Metallurgy of the Heritage andsurface Science”, The Getty Conservation Institute,pp. 85-117.(1994).

[4] Chebabe, D., Ait Chikh, Z.A., Dermaj, A., Rhattas,K., Jazouli, T. , Hajjaji, N., El Mdari, F., Srhiri, A.:“Synthesis of bolaamphiphile surfactants and their in-hibitive effect on carbon steel corrosion in hydrochlo-

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[6] Chebabe, D., Dermaj, A., Aitchikh, Z.A., Hajjaji, N.,Srhiri, A.: “Corrosion inhibition of carbon steel (E24)in 1M HCl solution by monopolar surfactants of 1.2.4- triazole-5- thione”, Physical. Chemical. News19, pp. 120-126 (2004).

[7] Dermaj, A., Chebabe, D., Hajjaji, N., Joiret, S., Rah-mouni, K., Srhiri , A.,Takenouti, H., Vivier, V.:“Etude de la corrosion du bronze Cu-8%Sn et l’effetinhibiteur de 3-phenyl-1.2.4- triazole -5-thione“, In:Gabrielli, C. (ed.): “Act of the 17th Forum on theElectro-chemical Impedances”, Paris p257-268(2005).

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dermaj, a. et al. atmospheric corrosion inhibition of historical steel. 2007

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