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