Degrigny, C. Stabilisation CH Artefacts. 2010

8/7/2019 Degrigny, C. Stabilisation CH Artefacts. 2010

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Leiden, 11-15 January 2010

Stabilisation of CH artefactsAn overview

Christian Degrigny


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A bit of history, choice of solution

The same as for the

cleaning overview could besaid here


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Why a stabilisation treatment?

Iron ingots from the1st centuryBC Mediterranean

Sea DRASSM site

Part of the cargoleft to dry outdoor

Ingots left to dry

in storage areaDRASSM

ArcAntique ArcAntique


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Rupture of the equilibrium

HR and O2

- Drying of corrosion products and

- Crystallisation of salts

- Oxidation of some salts- If the artefact contains chlorides:

development of active corrosion

- Formation of akaganeite (-FeOOH ):mechanical effecton the corrosion layer, unstable,- Weeping phenomenon, droplets

Droplets (Fe2+,Fe3+, Cl-)

Exposure to the atmosphere


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Stabilisation without polarisation

Storage in KOH solution

Uncleaned Cleaned

ArcAntique


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Passivation observed

On clean iron-based alloys

V


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Ecorr

time

Transformationof the oxide layer

corroded

bare

Passivation

On corroded iron-based alloys


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confirmation in practice

Max. extraction

= solution reach M

ArcAntique

Artificial steel coupon


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Marine wrought iron

stock

shackle

shank

flukearm

EVTEK

Active or not?Finnish, 19th c.


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Fe

Fe O3 4

FeOOH Cl- ?

Humid chamber

EVTEK

EVTEK

EVTEK

EVTEK


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Set-up of theelectrical contact

Checking of the goodelectrical contact

Immersion ofthe anchor

EVTEK

EVTEK

EVTEK


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- 3 5 0

- 3 0 0

- 2 5 0

- 2 0 0

- 1 5 0

- 1 0 0

- 5 0

00 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1

E(mV/Ag-Ag-Cl)

T im e ( h o u r s )

E c o r r m e a s u r e m e n t a n c h o r w i t h s t o c ki n 1 % ( w / v ) K O H

Transformation of

the corrosion layer

Passivation

And no extraction of chloride: stable artefact

Quick diffusion of KOHthrough thin corrosion layers

Monitoring Ecorr vs time


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Metals with thick corrosion layers?

Corroded Fe in KOH solution

thin corrosion layers

thick corrosion layers

KOH

KOH

KOH

KOH

KOH

Remainingmetal

CL

CL

CL

CL

CL

KOH


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Weeping on the surface of ingots

ArcAntique

ArcAntique

High reactivity of the insideof one ingot in the atmosphere

ArcAntique ArcAntique

Iron ingots (Mediterranean sea)


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Questions

slow re-increase ofEcorr after III step?

-Cl-

compete withOH-?- KOH still diffuseswithin the cracks ofthe ingot and cannotpassivate the wholemetal surface?

Slow diffusion of KOH

Quick diffusionof chlorides

Stabilisation in KOH


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How chlorides interfere with the behaviourof iron in KOH solutions?

E (V)

t (time)

Passivation of Fe in KOH solution

Interference with Cl-

Further perturbations


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Ecorr

CCl-

pH

Full monitoring of the stabilisation


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Cathodic polarisation

speed up of stabilisationprocesses


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Use of pulsed currents

17,0=total

Cl

Q

Q

Ec=-0.75V/SHE

29,0=total

Cl

Q

Q

-preventing hydrogen bubbling-accelerating the stabilisationprocess by favouring rapid

processes


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Application

EVTEK

EVTEK

Mass treatment: 23 iron bulletsfrom a grape shot

EVTEK


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Cathodic polarisation in 1% KOH at 0.95V/Ag-AgCl

EVTEKEVTEK


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St bili ti f b d


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Pitting corrosion of copper

Pitting corrosion: autocatalytic corrosion process- metal dissolved inside the pit : excess of positivecopper ions.

- chlorides migrate from the environment or the metalbulk inside the pit to maintain electroneutrality, andnantokite (CuCl) is formed.- Inside the pit, the metal is hydrolysed, resulting in low

pH inside the pit.- Low pH and high concentration of chlorides:acceleration of corrosion

CuCl, nantokite

Cu2(OH)

3Cl, atacamite

Cu

Cl-

Stabilisation of copper-basedalloys

EDF-Valectra


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Bell - Ecorr and Cl- with time in sodium sesquicarbonate 1%

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

0 100 200 300 400 500 600 700

time (h)

0

10

20

30

40

50

60

70

0

1

2

3

4

5

Ecorr

Ecorr

CCl-

CCl-

In sodium sesquicarbonate

EVTEK

Stabilisation of aluminium-


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Stabilisation of aluminium-based alloys

Pitting corrosion sensitivityaccording to the alloys

[NaCl]=10-3M

AWM


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Risk of pitting corrosion

pH=5.4, [NaCl]=10-3M

C th di i l i i ll i


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Cathodic corrosion on aluminium alloys inNaCl solutions

Al

e-

2H2O + 2e- H2 + 2OH

- pH

Al2O3 is dissolved preferably aboveactive sites (Al3Fe and Al2Cu)

Al2O3 + 2OH- AlO2

- + H2O

H2

pH : Al is dissolvedUnder the H2 bubble


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Optical monitoring


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Modification of the Pourbaix diagram

Field ofstability6082 alloy with the

fields of pitting

corrosion andcathodic corrosion

in neutral pHadded.

[NaCl]=10-3M


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Marine composite objects


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Impregnation of the wood iIn PEG 400 andPEG 4000

EVTEK

Cleaning of the wood:soaking in 1% EDTAdisodique followed by

electrophoresis in tapwater(2 times): appearance ofthe wood more natural

Porthole, Finnishwreck, 19th c.

Marine composite objects

L th / d l


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Leather/wooden clog

Day Solution Iron conc.

(mg/L)

Iron Content

(mg)

1 1 % Na2EDTA 0.2 1.7

2 61 529

3 200 1736

3 1 % triammonium

citrate

1.2 10

4 11 95

5 23 200

5 18 Stored in tap water and treated with electrophoresis

19 - 25 1 % Na2EDTA

EVTEK


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0

50

100

150

200

250

0 10 20 30 40 50 60

time (hours)

Current(mA

)

0

2

4

6

8

10

12

14

16

Voltage current

voltage

1st side 2nd side

In tap water

EVTEK

with metal left


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stabilisation of the barrelsin un-buffered KNO3 (+ addition

of HNO3 to keep the pH neutral)

XX X

XX

X XX

X

X

X

XX

XX

X XX

+-

Cl-

with metal left

Rifles, 17th c.

ArcAntique


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B tt it i f th th di t ti l


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Better monitoring of the cathodic potential

Stabilisation in a neutralunbuffered solution(1% (w/v) NaNO3)

Stabilility of the pH?

Glass

rubber

Dry porthole, 19th c.,

Finnish waters

EVTEK

EVTEK

EVTEK

Preparation of the artefact


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Preliminary mechanicalcleaning

Electrical contact

Preparation of the artefact

EVTEK

EVTEK

Simulating the treatment in NaNO3


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Bare nail

Slightlypolished nails

Corrodednails

Simulating the treatment in NaNO3

EVTEK

Bare iron nails


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Bare iron nails

Potentialcorrespondingto the highest

extractionof chlorides

The following reaction is favoured:2 H2O+ O2d + 4 e- 4 OH-

Slightly polished iron nails


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Slightly polished iron nails

The following reaction is favoured:2 H2O+ O2d + 4 e

- 4 OH-

x FeO(OH) + x e-

x Fe + x OH-

Corroded iron nails


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Corroded iron nails

Opposite behaviour than before:with corrosion layers and an increase of the

cathodic potential,

the pH tends to decrease

Application on the porthole


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Application on the porthole

pH

Cathodicpotential

Anodicpotential

Monitoring of all electrochemical parameters


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Decreaseof pH

Addition of NaOH

(day)

Night

Low!


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Conditions modified

During the 5 first days.Same conditions

Afterwards: anodic

Control andEa=1.1V/Ag-AgCl and

Ec=-0.5V/Ag-AgCl

Stabilisation of corroded Pbf


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ArcAntique

ArcAntique

artefacts

Jacquardlooms

(Musedes Arts

etMtiers,

Paris)

-1.3V

Pb2+

Pb

E (V/HSE)

I (mA)ArcAntique

Cathodic polarisation of a lead couponcarbonated artificially in Na2SO4 0.5M

(objective: treatment of composite artefacts),vb= 1mV/s

Chronoamperometric curve at 1.3V/HSE in Na2SO40 5M Counter electrode: Pb


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0.5M. Counter-electrode: Pb

ArcAntique

Application


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ArcAntique

ArcAntique

ArcAntique

Originalsurface lost

Conservation of corroded lead seals stillattached to parchments with silk threads


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Simulation of the treatmentof real composite artefacts:-lead: fragments from lead

seals-silk threads: naturally diedsilk coupons

- counter-electrode: leadplates

Dissolution of the dieswithout any protectionArcAntique

Protection of the textile threads


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ArcAntique

ArcAntique

ArcAntique

Paper impregnated with paraffine

Cathodic reduction

Loss ofadherence

Simulation of a treatment on artificialmaterials


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materials

ArcAntiqueArcAntique

ArcAntique

Enveloppe +CDDafter

immersion

test

Immersiontest

Preparation of a simulated composite


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ArcAntique

ArcAntique

ArcAntique

Absorbing paper

Leadhemp

silk


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Design of a special support for the artefactonce protected


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ArcAntique

ArcAntique

ArcAntique

ArcAntique

p


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ArcAntique

ArcAntique


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ArcAntique

ArcAntique

Optimisation: use ofPerspex rods to give

a better strength


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Parchment from the

French National Archives

ArcAntique

ArcAntique

Reinforcing of the protectedcomposite with Perspex rods

ArcAntique

Packing the organic materials in PE

envelops sealed with cyclododecane

Documents

Degrigny, C. Stabilisation CH Artefacts. 2010