The efficiency of electrochemical methods for the removal of chloride ions from iron marine archaeological objects: A comparative study

Materials and Corrosion 2012, 63, No. 9999 DOI: 10.1002/maco.201206584 1

The efficiency of electrochemical methods for the removalof chloride ions from iron marine archaeological objects:

A comparative study

J. C. Coelho*, C M. Oliveira, M. D. Carvalho and I. T. E. Fonseca*

The conservation of archaeological marine iron artefacts requires chloride ions

removal. In this study, the removal of chloride ions was undertaken by two

electrochemical methods: the electrolytic and the galvanic reduction in alkaline

media. The results were compared with those obtained by the washing and the

sulphite reduction methods, under identical conditions. The experiments

were performed on samples coming from an 18th century cast iron cannon-ball,

found in the archaeological context of a shipwreck, l’Ocean, which sank near the

southern Portuguese coast, in 1759. The extraction of chloride ions was

monitored by ionic chromatography (IC). The results allow to conclude that the

sulphite reduction experiments using the mixture 0.5M NaOH/0.5M Na2SO3

presents the higher efficiency in the first week, being further overcome by both

electrochemical methods. After 40 days of treatment, the electrolytic reduction

is the most efficient method.

1 Introduction the environment in which the object was kept. Depending on

Archaeological objects frommarine environments are necessarily

subjected to degradation processes. The phenomenon is

particularly relevant when the objects are removed from a wet

medium with low contents of oxygen to a dry and oxygenated

atmosphere [1–7].

Concerning to the conservation of iron marine archaeological

objects, the removal of chloride ions is an important step to prevent

or at least to reduce the rate of further corrosion, since chloride

ions have been reported as one of the major factors which leads to

localized corrosion, due to local acidification [3–10].

The first experiments for the treatment and conservation of

archaeological iron artefacts, conducted by electrochemical

techniques, are dated from the 19th century [11] and have been

accurate during the last two decades [12–17].

The corrosion products on the surface of an archaeological

artefact depend on different factors, particularly on the

conjugation between its composition and the characteristics of

J. C. Coelho, C M. Oliveira, M. D. Carvalho, I. T. E. Fonseca

Centro de Ciencias Moleculares e Materiais (CCMM), Departamento de

Quımica e Bioquımica da Universidade de Lisboa, Campo Grande, C8,

1749-016 Lisboa (Portugal)

E-mail: [email protected]

J. C. Coelho

Divisao de Arqueologia Nautica e Subaquatica, Instituto de Gestao do

Patrimonio Arquitectonico e Arqueologico IP, MARL – Pavilhao CC1,

2660-421 S. Juliao do Tojal (Portugal)

E-mail: [email protected]

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factors like the aeration, pH, temperature and time, different

corrosion products can be formed (see North and MacLeod [2],

Selwyn [3], North [18], Argo [19], among others).

Techniques addressed to the stabilization of metallic marine

artefacts, such as the simply immersion in alkaline aqueous

solutions and the so-called alkaline sulphite reduction method have

been intensively tested and data reported in the literature [7, 20–28].

Electrochemical techniques, like cyclic and linear sweep

voltammetry, have been recognized as powerful tools for the

characterization of archaeological metallic objects [12–17].

This study deals with samples coming from an iron cannon-

ball, belonging to the archaeological context of a shipwreck from

1759 [29–31], taken from a profundity of 4/5m of the sea, at the

South of Portugal (Lagos, Algarve). The ball was covered with a

concretion with a thickness of 0.9 cm. The aim of the work

consisted in the comparison of the efficiency of two classical

techniques (simple immersion in non de-oxygenated alkaline

medium and reduction in alkaline sulphite solution at 50 8C) andtwo electrochemical techniques [electrolytic reduction (ER) and

galvanic reduction (GR) in alkaline medium], for the extraction of

chloride ions from samples of the iron cannon-ball (genuine

archaeological iron). The amount of chloride ions removed by the

different methods was monitored by ionic chromatography,

which is a less time consuming methodology when compared

with the classical methods of titration [6, 21].

Samples from the iron cannon-ball have been characterized

by cyclic voltammetry (CV), X-ray powder diffraction (XRD) and

scanning electron microscopy coupled to X-ray microanalysis

(SEM/EDS). It was concluded that the iron used for the

fabrication of the cannon-ball was cast iron which is in agreement

� 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2 Coelho, Oliveira, Carvalho, and Fonseca Materials and Corrosion 2012, 63, No. 9999

with the literature concerning to the production and applications

of iron in the 18th century [32, 33].

The efficiency of each method, measured by the amount of

chloride ions extracted per unit area in a certain period of time,

was studied for different reduction methods: electrochemical

techniques (ER and GR) and the sulphite reduction method (SR1

and SR2). These studies were performed using small samples of

archaeological iron and have been compared with the data

obtained from simple immersion (IM) in alkaline solution.

The extraction rates, Vextr, measured over the six weeks of each

treatment, have been analysed and compared.

2 Experimental

This work was conducted on small samples carefully cut from the

cannon-ball. Samples included a portion from the nucleus and

another from the surface of the ball.

For the electrochemical tests, the samples have been

mounted using epoxy resin (Araldite1 standard – CEYS1) and

a metallic connection (insulated copper wire soldered with tin

solder, Sn60), which were used as working electrodes. An image

of such a sample is given in Fig. 1.

After being constructed, these electrodes were carefully kept

under wet conditions in seawater taken from the archaeological

site. The surface of all the electrodes was photographed in a plan

parallel to the objective of the camera, and further vectorized

using the CorelDraw 12 software. The superficial areas were

calculated using the ‘Get Area’ (IsoCalc.com) tool. Values between

2.0 and 3.6 cm2 were obtained. All results were normalized using

the area of the corresponding working electrode.

The aqueous solutions were prepared with pure KOH

from Pronalab ([Cl�]< 0.01%); NaOH, QP, from Panreac

([Cl�]< 0.01%) and Na2SO3 PA, from Riedel-de Haen

([Cl�]< 0.005%). Salts were dissolved in ultrapure water from

Millipore1 Milli-Q and all the experiments (with the exception of

the alkaline sulphite methods) were performed in non-

deoxygenated solutions, at room temperature.

The open circuit potential (EOCP) measurements were

performed using a digital multimeter, HP 34401A, with

automatic acquisition, through Microsoft1 Excel, using the

Figure 1. Photograph of the working electrode


tool ‘Excel IntuiLink for Multimeters Toolbar Addin’ (Agilent

Technologies). All pH measurements have been performed with

an HANNA1 HI 1131 electrode coupled to a pHmeter also from

HANNA1, model HI 3222.

The electrochemical experiments for the removal of chloride

ions were conducted in polyethylene bottles covered with its caps

in which holes for the passage of the contacts of each electrode

have been drilled.

The reference electrode used was a Ag/AgCl, KCl 3M

electrode with double junction from Metrohm1 (E0¼þ0.210Vvs. SHE). Before each experiment the electrode was maintained

during 24 h in a KOH 1% aqueous solution and its potential

checked against another Ag/AgCl (KCl 3M) commercial

electrode from Metrohm1.

The simple immersion method, also known as washing

method, was performed by the introduction of the iron sample in

the alkaline solution (KOH 1%). The evolution of the process was

followed by measuring the OCP (EOCP) of the working electrode

against a reference electrode.

The removal of chloride by the alkaline sulphite reduction

method has been performed in two different solutions with the

following compositions: (SR1) 0.1M NaOHþ 0.05M Na2SO3,

pH 13.3, and (SR2) 0.5MNaOHþ 0.5MNa2SO3, pH 13.8. In this

case, the experiments were carried out with the iron samples

placed in bottles filled with 50mL of the corresponding solution,

sealed in order to avoid contact between the solution and the air

and placed in an oven (Lenton WF 30) at 50 8C.The removal of chloride ions by the ER method was

performed by a three electrode cell, with Pt acting as counter

electrode. A potentiostat AUTOLAB1 PGSTAT10 (Eco Chemie

B.V.) controlled the potential of �0.950V against the reference

electrode. The evolution of the chloride ions removal was

followed by recording the current passing between the working

and the secondary electrode during six successive weeks.

According to the literature [13–15] the potential value of

�0.950V versus Ag/AgCl is the correct value for the chloride

extraction from archaeological iron, avoiding the evolution of

hydrogen, which could provoke damage in the graphitized layer,

where is usually the information of archaeological interest.

For the extraction of chloride ions by the GR method a three

electrode cell (a working electrode made with the iron sample and

a zinc coupon of 8.8 cm2 (E0(Zn2þ/Zn)¼þ0.763V vs. SHE)

acting as sacrificial anode giving cathodic protection to the iron

(E0(Fe2þ/Fe)¼þ0.440V vs. SHE) was used. The cell was filled

with 50mL of KOH 1% non-deoxygenated solution and the

evolution of the process was followed by recording the potential of

the working electrode against the reference electrode. For all the

methods tested, at least two replicas have been performed and

very good reproducibility was obtained.

The quantification of chloride ions removed in each experiment

was performed by ionic chromatography with a chromatograph

Dionex1 DX-500 equipped with an isocratic pump Dionex1 IP20

and columns IonPac AG9-HC and IonPac AS9-HC, a suppressor of

ions Dionex1 ASRS-ULTRA II plus, and a conductivity detector

Dionex1 CD20. The data acquisition was performed by the

Peaknet1 software. The eluent used was a solution of Na2CO3

3.5mMþNaHCO3 1mM. Due to the sensitivity of the column, the

solutions have been diluted (1:100) using ultrapure water.

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Materials and Corrosion 2012, 63, No. 9999 Removal of chloride ions from iron marine archaeological objects 3

SEM/EDS studies have been performed on samples from the

nucleus of the ball and from the corrosion products taken from

the surface (in powder form). This study was undertaken using a

scanning electronic microscope (JEOL JSM 35C) coupled to a

spectrometer (Noran Voyager).

3 Results and discussion

3.1 The archaeological site and the cannon-ball

At 24 of August 2009 a cannon-ball was recovered from the

archaeological site of the shipwreck of l0Ocean (Salema beach,

Lagos, Portugal). The ball (Fig. 2) was raised from a profundity of

about 5m at a spot where the seabed is covered with similar

cannon-balls. The artefact had a weight of 8.171 kg and a diameter

of 13.2 cm. Measurements of the properties of the seawater

collected at the archaeological site have given the following values:

pH¼ 7.8 and dissolved O2¼ 64.9%. The photograph of the ball

shows a concretion including a zone of orange colour corrosion

products observed on the left side. Grey and black corrosion

products are also visible all over the ball surface. According to

Argo [19], the orange products are most probably iron (II)

hydroxide-oxide, namely, lepidocrocite (g-FeOOH). The grey

black and black colours may be attributed to FeO and Fe3O4,

respectively (Selwyn [3] and Argo [19]), while, the white colour may

be related with the formation of iron (II) chloride (FeCl2) (Selwyn[3], Turgoose [34], Askey et al. [35], among others). However, none

of such phases could be identified by XRD.

3.2 Nucleus and surface (cannon-ball) characterization

Figure 3 gives a representative cyclic voltammogram (CV) of a

sample obtained from the core of the cannon-ball, in a KOH 1%

aqueous solution, polarized between þ0.65 and �1.5 V versusAg/AgCl.

Figure 2. The ball after being retrieved from the archaeological site

(photo by Jose Paulo Ruas)

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The cyclic voltammogram shows during the cathodic scan

and before the H2 evolution, a cathodic peak, A0, at �1.08V(�0.87V vs. SHE). Then, during the anodic scan a peak A is

observed at �0.72V (�0.51V vs. SHE), followed by a decay in the

current leading to a passive region between �0.25 and 0.50V. At

þ0.50V (þ0.71V vs. SHE) the oxidation of Fe(II) or even the

Fe(III) compounds and/or the evolution of O2 may take place

leading to the abrupt increase in the anodic current of the order of

45mA/cm2, about ten times higher than the passivation current.

According to the Pourbaix diagram of the Fe-Cl-H2O, at 25 8C[36, 37], the potential of peak A and the pH value of 13 define a

point located in the passive region. The passivity can be attributed

to the Fe3O4 oxide species. However, as under anodic polarization

kinetics should also be considered, peak A could be related

with the oxidation of the Fe(II) into Fe(III) species and peak

A0 (�0.87V vs. SHE) probably due to the reduction of Fe (III)

oxide/hydroxide to Fe (II) [38, 39].

Concerning to the analysis of the cannon-ball (core) Fig. 4

presents the EDS spectrum corresponding to the global analysis.

From the analysis of the EDS spectrum it was concluded that the

main constituent elements of the nucleus are Fe, C, P and Si.

Apart from the global analysis, local regions have also been

analysed by SEM/EDS, some micrographs being presented in

Fig. 5. The zones where the EDS analysis has been performed are

indicated (Z1 to Z5). The micro-constituents of the grey colour

zone (Z1) were predominantly iron and carbon in amounts

corresponding to cementite; in zone Z2, of white grey colour, a

mixture a-ferrite and cementite could be identified; zone Z3

contains clearly a phosphorousmixture and zone Z4 inclusions of

MgS. Finally, in zone Z5, the inclusions of black colour have been

assigned to lamellar graphite.

The relatively high percentages of carbon (6–7% w) and Si

(0.5–0.6% w), as well as the white grey colour have allowed to

conclude that the nucleus was made of cast iron, must probably

white cast iron. According to Mentovich et al. [33] the

concentration of Si is the principal factor allowing to distinguish

between white and grey cast iron. The relevant literature [3, 32, 33]

reports also that the white cast iron consisting of a mixture of

a-ferrite and cementite, is very hard and presents high resistance

against cutting. These properties were effectively verified during

Figure 3. Cyclic voltammogram of a sample of the cannon-ball in KOH

1%. n¼0.10 V/s; Ei¼þ0.65 V; Elc¼�1.5 V versus Ag/AgCl



Figure 4. EDS spectrum of a sample from the nucleus of the

cannon-ball

Figure 5. Micrographs of a sample from the nucleus (zones Z1 to Z5)

Table 1. EDS results (at%) of the corrosion products on the surface of

the cannon-ball

Analysis Al Si P S Cl Ca Fe Na Mg

Global – 6.3 4.6 0.9 0.9 – 87.3 – –

Point 1 – 6.0 3.2 3.5 1.7 0.3 78.9 4.7 1.7

Point 2 – 6.0 2.0 0.5 0.9 – 88.4 2.2 –

Point 3 – 11.0 12.2 0.6 1.6 – 70.1 3.9 0.7

Point 4 – 6.5 4.3 29.2 2.8 – 53.6 3.6 –

Point 5 0.6 8.9 9.9 1.3 1.2 – 72.9 4.2 1.1

the cutting of the various small samples representative of the

cannon-ball. In addition, as stated by Scott [32], this type of alloy

presents a structure including inclusions of lamellar graphite, as

observed in zone Z5 of the studied samples.

Concerning the corrosion products on the surface of the

cannon-ball, many factors may lead to transformations in the

corrosion products even during its analysis (see Selwyn [3]). In

the present work, the EDS analysis performed on powders

removed from one sample of the cannon-ball allowed the

identification of several elements as resumed in Table 1, where

besides a global analysis, the results of the analysis performed in

different points were also included (1–5). For a better comparison

of the relative amount of these elements, C and O, presented in all

cases, were excluded. Besides the elements previously identified in

the nucleus, Cl and Na were also identified, as expected.

3.3 Removal of chloride ions

3.3.1 Simple immersion in alkaline solutions

The simple immersion of iron samples in alkaline solutions such

as of KOH 1%, allow the removal of chloride ions of the iron

artefacts by exchange of Cl� with hydroxide ions (OH�) [3–10].

The experiment was followed by the OCP (EOCP) evolutionand by the determination of the amount of chloride ions removed

after each period during the six successive weeks of the washing

process. These results are depicted in Fig. 6.

During the first instants of immersion, the EOCP is displacedin the negative direction reaching the value of�0.60V, but in few

hours an inversion is observed and the potential is displaced in

the anodic direction reaching a value of about�0.45V, after about12 days, and then decreases abruptly reaching the minimum of

�0.475V followed by another increase till a value of �0.37 V. Atthe end of the chemical treatment the EOCP presents a value of

�0.42V. According to the Pourbaix diagram for the system Fe-Cl-

H2O [36] the observed behaviour may be related with the

formation of a passive film of an oxide/hydroxide, Fe3O4 species,

due to the contact of the iron sample with a high concentration of

hydroxyl ions in solution. The initial decrease of EOCP can be

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Figure 6. Evolution of the EOCP and total amount of chloride ions

removed by simple immersion in KOH, during 6 successive weeks

Figure 7. EOCP evolution and total amount of chloride ions removed

from an iron sample immersed in the following alkaline sulphite

solutions: 0.1 M NaOHþ0.05 M Na2SO3 (SR1), pH¼ 13.3; 0.5 M

NaOHþ0.5 M Na2SO3 (SR2), pH¼ 13.8

Figure 8. Current transients and total amount of chloride ions

removed from the iron sample polarized at �0.950 V, in KOH 1%

attributed to the reaction between the corrosion layer and the

hydroxyl ions in solution [14].

The total amount of chloride ions removed during the

40 days of treatment was 4.8mg cm�2 (97 ppm/cm2 of the

superficial area).

3.3.2 Reduction by the alkaline sulphite method

The removal of chloride ions by the alkaline sulphite solution is

promoted by the conjugation between the decrease of O2 due to

the action of sulphite ions and by the ion-exchange action of

the alkaline solution [20–22, 24–26]. In the present work, these

experiments were carried out under 50 -C, and the temperature

certainly influences the kinetic’s of the removal process. In this

case and taking into account previous works [20–23] two different

alkaline solutions have been used: 0.1MNaOHR 0.05MNa2SO3

(SR1) and 0.5M NaOHR 0.5M Na2SO3 (SR2). The experiments

were also conducted over six successive weeks and the

solutions changed every week. The results were followed by

the determination of the EOCP, when the sample was taken out

from the oven (weekly). The amount of chloride ions was

determined in each solution (see data in Fig. 7).

The OCP of the sample immersed in the solution with

lower concentration of OH� and SO2�3 ions (SR1) has gradually

changed from�0.70 to�0.95V versus Ag/AgCl after approximately

3 weeks, being almost constant after that. In the case of SR2

experiment, the value of approximately �0.95V was attained at the

thirdweek, and slightly changed until a value close to�0.85V�0.92in the last week. The maintenance of the open circuit voltage after a

certain time can be explained considering that chemical reactions

occur especially at the beginning of the experiment, and that after

some time the chemical composition of the electrode is almost

unchanged. Such behaviour has also been observed by other authors

[3, 13, 26, 27]. The evolution of the open circuit voltage observed on

SR1 and SR2 experiments are in accordance with the evolution of

chloride ions extraction, as, an almost constant value is observed

after 3 weeks in the case of SR1, while the value determined for SR2

abruptly increased after �20 days, and, although slowly, continued

to increase until the end of the experiment (6 weeks).

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The total amount of chloride ions removed during the six

successive weeks was �5mg/cm2 (101 ppm/cm2) for the weaker

solution (SR1) and 15.6 (309 ppm/cm2) for the stronger alkaline

solution (SR2).

3.3.3 Electrolytic reduction

The ER was performed in KOH 1%, at a constant potential of

�0.950V versus Ag/AgCl. In this case, the experiment was

followed by recording the current transients and by the

determination of the chloride ions removed. The results obtained

along the experiment are presented in Fig. 8.

The i versus t curve shows an abrupt decrease of the reduction

current value during the first seven days of treatment. Then, a

slight increase is observed, with oscillations ranging from �125to 75mA (62.5 and 37.5mA/cm2). It should be emphasized that

those oscillations in the negative direction are observed at the

beginning of each period, just after immersing the electrode in

the new fresh solution. Such behaviour may be explained by the



Figure 10. Evolution of the total amount of chloride removed by the

different methods

fact that during the transference of the electrode from the old to

the new solution, the reduction of the corrosion products (such as

Fe(III) to Fe(II) compounds) may occur simultaneously with the

removal of chloride ions. Effectively, a colour change from red-

brown to black was observed on the sample during the ER.

At the end of the experiment (39 days) the total amount of

chloride removed was 22.4mg/cm2 (439 ppm/cm2). The reduc-

tion potential of �0.95V versus Ag/AgCl (�0.74V vs. SHE)

applied to the sample (working electrode) certainly promotes the

reduction of Fe(III) to Fe(II) species. North and Pearson [23] and

Selwyn [3] stated that the ER promotes the reduction of the Fe(III)

oxide/hydroxide leading to magnetite, a less dense compound,

thus a more porous film on the surface of the iron sample.

3.3.4 Galvanic reduction

The potential between the sample from the iron cannon-ball

(acting as cathode) and the zinc electrode (acting as anode), both

in the same solution of KOH 1%, over the period of treatment is

presented in Fig. 9. From the analysis of this figure, a decay in the

potential in the cathodic direction can be observed during the first

5 days, being further maintained at an almost constant value of

about �1.0 V. Considering the pH value of the solution, this

potential leads to a point in the passivity region of the Pourbaixdiagram of the Fe-Cl-H2O system at 25 -C [36]. Similarly to what

has been observed in the ER method, a big displacement of

the potential in the negative direction from �0.58 to �1.0V is

observed during the first week, and then, this value is kept as an

average value. Slight decays at the beginning of the renewal of the

solution, just when the sample is introduced in the new fresh

solution, are visible. This behaviour may be associated with

modifications in the corrosion layer and/or to changes in the

chloride ions gradient since at the beginning of each treatment, the

concentration of chloride ions in the fresh solution is almost zero.

After the end of the GR treatment (39 days), the total amount

of chloride removed was 17.5mg/cm2 (352 ppm/cm2).

3.3.4 Comparison of the efficiency of the various methods

Figure 10 presents the curves of the total amount of chloride ions

removed during the different treatments, namely the two classical

Figure 9. Potential values (E) and total amount of chloride removed

from the iron sample subjected to GR


ones and the two electrochemical methods, after successive

6 weeks of immersion. Under identical conditions (�40 days,

50mL of alkaline aqueous solution, samples with areas ranging

between 2.0 and 3.6 cm2) the efficiency of the four methods

tested followed the order: ER 22.4mg/cm2 (439 ppm/cm2) >GR

17.5mg/cm2 (352 ppm/cm2) > reduction by the alkaline

sulphite method, with the equimolar solution (SR2) 0.5M

NaOHR 0.5M Na2SO3, 15.6 g/cm2 (309 ppm/cm2) > reduction

by the alkaline sulphite solution (SR1) 0.1M NaOHR 0.05M

Na2SO3, 5.1mg/cm2 (101 ppm/cm2) > simple immersion in

KOH 1% 4.8mg/cm2 (97 ppm/cm2). When the simple immer-

sion (IM) and the alkaline sulphite reduction (SR1) treatments

were used, the total amounts of extracted chloride ions are

significantly lower.

Figure 11. Extraction rates (Vextr) of chloride ions removal for all the

methods during the six successive periods. SR1: sulphide reduction

(0.1 M NaOHþ 0.05 M Na2SO3); SR2: sulphide reduction (0.5 Mþ0.5 M

Na2SO3); IM: immersion in KOH; ER: electrolytic reduction; GR: galvanic

reduction

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Figure 11 represents the evolution of the rate of the chloride

ions extraction (measured as mg per area and per day) for each

week, for all the methods. Significant differences are observed on

the extraction rates profiles (Vextr per week): while the sulphite

reduction method defines a curve which indicates a diffusive

model (higher values of rate extraction for the first week), both

electrochemical methods ER and GR define a peak shaped curve

with maximums at the third week of treatment. The simple

immersion method in 1% KOH (IM) presents almost constant

and quite low rates all over the 6 weeks.

4 Conclusions

In this work, different methods were used to remove chloride

ions from iron samples obtained from a cannon-ball, which was

identified as being cast iron, as expected.

Under identical conditions (�40 days, samples with areas

ranging between 2.0 and 3.6 cm2) the efficiency of the tested

methods followed the order: ER>GR> reduction by the alkaline

sulphite method (SR2)> reduction by the alkaline sulphite

method (SR1)� simple immersion in KOH 1% (IM).

The higher efficiency of the reduction methods (ER, GR and

SR2) for the removal of chloride ions frommarine iron archaeological

objects, during a 40 days period, when compared to the simple

washing in alkaline solution (IM) and the less concentrated sulphite

(SR1) has been well demonstrated in this study.

Both the simple immersion (IM) and the SR1 methods

present very low efficiencies and very low rates of chloride

ions extraction. It is also noteworthy that the extraction

rate profiles (Vextr vs. time) for the sulphide reduction methods

(both SR1 and SR2) define a curve which indicates processes

most probably controlled by diffusion, while the electrochemical

methods ER and GR both define a peak shaped curve with

maximums extraction rates after the third week.

Acknowledgements: The authors acknowledge the financial

support from FCT (Fundacao para a Ciencia e Tecnologia) to

CCMM (Centro de Ciencias Moleculares e Materiais). The

authors thank also to IGESPAR (Instituto de Gestao do

Patrimonio Arquitectonico e Arqueologico, IP) for providing

the samples of the cannon-ball and to SUBNAUTA, S.A. for the

logistic support during the recovery of the ball.

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(Received: March 10, 2012)

(Accepted: April 1, 2012)

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Documents

The efficiency of electrochemical methods for the removal of chloride ions from iron marine archaeological objects: A comparative study