synergistic effects of additives to benzotriazole solutions applied as corrosion inhibitors to ...

596 Pages·2013·45.38 MB·English

SYNERGISTIC EFFECTS OF ADDITIVES
TO BENZOTRIAZOLE SOLUTIONS APPLIED AS CORROSION
INHIBITORS TO ARCHAEOLOGICAL COPPER AND COPPER
ALLOY ARTEFACTS
Vol. I - TEXT
Stavroula Golfomitsou
A thesis presented to the University of London in fulfilment of the requirements for
the degree of Doctor of Philosophy
University College London
Institute of Archaeology
July 2006
1
UMI Number: U5920B0
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
Dissertation Publishing
UMI U592030
Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author.
Microform Edition © ProQuest LLC.
All rights reserved. This work is protected against
unauthorized copying under Title 17, United States Code.
ProQuest LLC
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, Ml 48106-1346
To my father for his faith in me and
my mother and sister for their love and
support
2
Synergistic effects of additives to benzotriazole solutions applied as corrosion inhibitors to
archaeological copper and copper alloy artefacts
Stavroula Golfomitsou
Abstract
Benzotriazole (BTA) is a corrosion inhibitor extensively used for the stabilisation of active
corrosion of archaeological copper and copper alloys. However, BTA often fails to
effectively retard corrosion when applied on heavily corroded artefacts. Although there are
numerous studies about its mode of action on clean copper, there is no comprehensive
understanding about the way it is bonded to corroded copper. This thesis aimed to
understand and compare BTA and its mode of action on clean and corroded copper by
examining possible factors that could affect efficiency including concentration, solvent,
period of immersion and pH. BTA efficiency could be improved by making use not only of
these results but also of the synergism that is observed between BTA and other inhibitive
compounds. The combination of inhibitors and the use of the synergistic effect between
compounds is common in industry but has never been tested before for use in conservation.
The synergistic effect could be beneficial for use on corroded copper alloys suffering with
active corrosion. The six compounds selected were 5-Amino-2-Mercapto-l, 3, 4-
Thiadiazole (AMT), Benzylamine (BZA), Ethanolamine (ET), l-Phenyl-5-Mercapto-
Tetrazole (PMT), Potassium Ethyl Xanthate (KEX) and Potassium Iodide (KJ). These were
tested on their own and in combination with BTA. Accelerated corrosion tests were carried
out on artificially corroded copper coupons. Analysis using SEM-EDS, XPS, and FT-IR
allowed a better understanding of the way different factors affect the formation of the
copper-BTA complex formed and subsequently the BTA efficiency. The addition of other
compounds into the BTA solutions significantly affected the complex formed and the film
properties. Copper(I)-inhibitor complexes were proven to be more protective than
copper(II) complexes. The results also showed that there is a synergistic effect between
BTA and AMT which results in improved inhibitive efficiency of both inhibitors. The
composition of the film formed was mainly dependent on the concentration of the solution,
however, it was found to be effective in very low concentrations as well as aqueous
solutions. Finally, field trials of some of the more effective solutions of compounds were
performed on archaeological objects from Turkey and Greece and these results confirmed
those of the laboratory experiments. All of the experiments and fields trials were designed
and analysed statistically.
3
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF GRAPHS
ACKNOWLEDGMENTS
CHAPTER 11NTRODUCTION______________________________________ 19
CHAPTER 2
2.1 Introduction............................................................................................................................34
2.2 Corrosion Fundamentals....................................................................................................35
2.2.1 Thermodynamics of Corrosion............................................................................................35
2.2.2 Nemst Equation....................................................................................................................40
2.2.3 Corrosion potential...............................................................................................................40
2.2.4 Potential-pH..........................................................................................................................41
2.2.5 Electric Double layer...........................................................................................................44
2.3 Kinetics of Corrosion.......................................................................................................46
2.3.1 Corrosion in different environments..........................................................................51
2.3.2 Corrosion forms...........................................................................................................52
2.3.3 Corrosion Products of Copper....................................................................................53
CHAPTER 3:CORROSION INHIBITION OF METALS______________________________________59
3.1 Corrosion Inhibition Mechanisms....................................................................................59
3.2 Definition of Corrosion inhibition...................................................................................60
3.3 Corrosion inhibition mechanism........................................................................................61
3.4 Primary and Secondary Inhibition..................................................................................63
3.5 Factors that affect the effectiveness of inhibitors..................................................64
3.6 Factors affecting the function of inhibitors...............................................................65
3.7 Classification of corrosion inhibitors..........................................................................68
3.7.1 Anodic inhibitors...................................................................................................................69
3.7.2 Cathodic inhibitors...............................................................................................................70
3.7.3 Organic and Inorganic inhibitors.......................................................................................72
3.7.4 Interface and Interphase inhibitors.....................................................................................74
3.7.5 Vapour-phase.........................................................................................................................75
3.7 Hard, Soft and Borderline Inhibitors.................................................................................76
.6
3.8 SynergisticE ffect......................................................................................................77
3.9 Inhibitors: A Review of Archaeological Applications.............................................78
3.9.1 Introduction............................................................................................................................78
3.9.2 Benzotriazole..........................................................................................................................79
3.9.3 2-Amino-5-Mercapto-l, 3, 4- Thiadiazole (AMT)............................................................87
3.9.4 Mercaptobenzothiadazole (MBT)........................................................................................91
3.9.5 Health and safety considerations........................................................................................93
3.10 Selected inhibitive compounds..........................................................................................94
3.10.1 Benzylamine (CH N)...........................................................................................................95
7 9
3.10.2 Ethanolamine (C H NO)......................................................................................................97
2 7
3.10.3 Potassium Ethyl Xanthate (KCtH^S^O).............................................................................98
3.10.4 Potassium Iodine (KI).........................................................................................................100
3.10.5 I-Phenyl-5 Mercapto-Tetrazole (C^H^N^S).....................................................................102
CHAPTER 4 METHODOLOGY AND EXPERIMENTAL DESIGN________________ 105
4
4.1 Introduction.........................................................................................................................................105
4.2 Copper coupons.....................................................................................................................................108
4.3 Coupon Preparation............................................................................................................................110
4.4 Corrosion Testing...............................................................................................................................112
4.5 Accelerated corrosion testing......................................................................................................112
4.5.1 Monitoring.............................................................................................................................................................117
4.6 Experimental method.........................................................................................................................117
4.6.1 Experimental design...........................................................................................................................................121
4.6.2 Statistical analysis..............................................................................................................................................122
4.7 Testing on archaeological artefacts.........................................................................................124
4.8 Restrictions and Limitations...........................................................................................................127
4.9 Analysis of copper-inhibitor complexes......................................................................................128
4.9.1 SEM-EDS..............................................................................................................................................................128
4.9.2 Fourier Transform Infrared Spectroscopy (FTIR)..................................................................................130
4.9.2.1 Aims of Ac analysis.....................................................................................................................132
4.9.2.2 Methods........................................................................................................................................133
4.9.2.2.1 Transmittance (KBr pellets)....................................................................................................133
4.9.2.2.2 Analysis of inhibitor solutions.................................................................................................133
4.9.2.2.3 Reflectance..............................................................................................................................134
4.9.3 X-Ray Photoelectron Spectroscopy (XPS)..................................................................................................134
4.9.4 pH measurements...............................................................................................................................................139
4.9.5 Colorimetric study..............................................................................................................................................139
CHAPTERS: BENZOTRIAZOLE________________________________________________________143
5.1 Introduction........................................................................................................................................143
5.2 Accelerated Corrosion Tests.........................................................................................................144
5.3 Artificially Corroded copper........................................................................................................147
5.3.1 Experiment BTA 1..............................................................................................................................................147
5.3.1.1 Colour changes of BTA 1.............................................................................................................148
5.3.1.2 Results of BTA 1..........................................................................................................................149
5.3.1.3 Statistical analysis of BTA 1.........................................................................................................150
5.3.2 Experiment BTA 2..............................................................................................................................................151
5.3.2.1 Colour changes of BTA 2.............................................................................................................152
5.3.2.2 Results of BTA 2..........................................................................................................................152
5.3.2.3 Statistical analysis of BTA 2.........................................................................................................153
5.3.3. Experiment BTA 3..................................................................................................................................154
5.3.2.4 Colour changes of BTA 3.............................................................................................................155
5.3.2.5 Results of BTA 3..........................................................................................................................155
5.3.2.6 Statistical analysis of BTA 3........................................................................................................157
5.3.3 Experiment BTA 4..............................................................................................................................................158
5.3.3.1 Results of BTA 4..........................................................................................................................159
5.3.4 Re-use of BTA solutions..................................................................................................................................161
5.3.5 Experiments BTA 5 and BTA 6......................................................................................................................162
5.3.5.1 Colour changes of BTA 5 and BTA 6..........................................................................................163
5.3.5.2 Results of BTA 5..........................................................................................................................164
5.3.5.3 Results of BTA 6..........................................................................................................................165
5.3.6 Experiments BTA 7 and BTA 8......................................................................................................................166
5.3.6.1 Colour changes of BTA 7 and BTA 8...........................................................................................166
5.3.6.2 Results of BTA 7..........................................................................................................................167
5.3.6.3 Results of BTA 8..........................................................................................................................167
5.3.7 Weight changes of coupons after BTA treatments....................................................................................170
5.3.8 Discussion of results of artificially corroded copper.............................................................................171
5.3.9 pH of BTA solutions..........................................................................................................................................172
5.4 U NCORRODED COPPER COUPONS............................................................................................................174
5.4.1 Colour changes of clean copper treated with BTA..................................................................................175
5.4.1.1 0.1M BTA/H20............................................................................................................................176
5.4.1.2 O.IMBTA/EtOH.........................................................................................................................176
5
5.4.1.3 0.25M BTA /EtOH......................................................................................................................176
5.4.1.4 Comments....................................................................................................................................177
5.5 Colour measurements.......................................................................................................................177
5.6 SEM imaging..........................................................................................................................................179
5.6.1 SEM observations of corroded copper coupons.......................................................................................181
5.6.2 SEM-EDS semi-quant linescans.....................................................................................................................185
5.6.2.1 Comments on SEM linescans.......................................................................................................185
5.7 Analysis of Cu-BTA film...................................................................................................................186
5.7.1 FTIR analysis of BTA......................................................................................................................................187
5.7.1.1 BTA 0.1 Min deionised HzO........................................................................................................194
5.7.1.2 BTA in ethanol.............................................................................................................................195
5.7.1.3 Analysis of non-aqueous BTA solutions.......................................................................................198
5.7.2 XPS..........................................................................................................................................................................201
5.7.2.1 Clean and corroded copper..........................................................................................................203
5.7.2.2 BTA0.1M/H2O...........................................................................................................................206
5.7.2.3 BTA 0.25M..................................................................................................................................208
5.7.2.4 Elemental quantification..............................................................................................................209
5.7.2.5 Conclusion on XPS analyis..........................................................................................................211
5.7.2.6 Oxidation/reduction reactions during XPS analysis......................................................................211
5.7.2.7 Angle-resolved measurements.....................................................................................................212
5.7.2.8 Comparison of samples before and after exposure to high RH.....................................................213
5.8 Discussion..............................................................................................................................................214
CHAPTER 6: SYNERGISTIC EFFECT___________________________________________________ 221
6.1 Introduction.........................................................................................................................................221
6.2 Accelerated corrosion testing of BTA solutions with additives.....................................224
6.3 BTAandAMT(C2H3N3S2)...................................................................................................................226
6.3.1 Experiment BTA +AMT1.................................................................................................................................227
6.3.1.1 Results BTA + AMT 1................................................................................................................228
6.3.1.2 pH of solution..............................................................................................................................229
6.3.2 Experiment BTA + AMT 2...............................................................................................................................229
6.3.2.1 Colour alterations BTA + AMT 2................................................................................................230
6.3.2.2 Results of BTA + AMT 2............................................................................................................231
6.3.3 Experiment BTA + AMT 3...............................................................................................................................233
6.3.3.1 Results of BTA + AMT 3............................................................................................................234
6.4 Benzotriazole and Benzylamine (C7H9N)....................................................................................236
6.4.1 Experiment BTA + BZA 1................................................................................................................................237
6.4.1.1 Colour changes BTA + BZA 1....................................................................................................238
6.4.1.2 pH................................................................................................................................................238
6.4.1.3 Results of BTA + BZA I.............................................................................................................238
6.4.2 Experiment BTA + BZA 2................................................................................................................................240
6.4.2.1 Colour changes............................................................................................................................241
6.4.2.2 Results of BTA + BZA 2.............................................................................................................242
6.5 BTA AND ETH (C2H7NO)......................................................................................................................244
6.5.1.1 pH................................................................................................................................................245
6.5.1.2 Results BTA + ETH 1..................................................................................................................246
6.5.2 Experiment BTA + ETH 2...............................................................................................................................247
6.5.2.1 Colour changes............................................................................................................................248
6.5.2.2 Results BTA + ETH 2..................................................................................................................250
6.6 BTA AND KEX (KC3H5S20)..................................................................................................................251
6.6.1 Experiment BTA + KEX 1...............................................................................................................................251
6.6.1.1 pH................................................................................................................................................252
6.6.1.2 Results of BTA + KEX 1.............................................................................................................252
6.6.2 Experiment BTA + KEX 2...............................................................................................................................254
6.6.2.1 Colour changes............................................................................................................................254
6.6.2.2 Results BTA + KEX 2.................................................................................................................256
6.7 BTA AND KI.............................................................................................................................................258
6.7.1 Experiment BTA + Kl 1....................................................................................................................................258
6
6.7.1.1 pH................................................................................................................................................259
6.7.1.2 Colour changes BTA + KJ...........................................................................................................259
6.7.1.3 Results BTA + KJ 1....................................................................................................................260
6.7.2 Experiment BTA +KI2.......................................................................................................................262
6.7.2.1 Colour changes BTA + KI 2........................................................................................................262
6.1.2.2 Results of BTA + KI 2..................................................................................................................263
6.7.3 Experiment BTA + KJ 3.....................................................................................................................264
6.7.3.1 Results of BTA + KI 3..................................................................................................................265
6.8 BTA AND PMT (CtH ^S )......................................................................................................................268
6.8.1 Experiment BTA + PMT 1.................................................................................................................268
6.8.1.1 Colour alterations BTA + PMT 1................................................................................................269
6.8.1.2 Results BTA + PMT 1................................................................................................................269
6.8.2 Experiment BTA + PMT2.................................................................................................................271
6.8.2.1 Colour alterations BTA + PMT 2.................................................................................................271
6.8.2.2 Results of BTA + PMT 2..............................................................................................................272
6.8.3 Comparative study offactors affecting combinations of inhibitors..............................................274
6.8.4 pH of solutions...................................................................................................................................275
6.8.5 Weight change of coupons after treatment......................................................................................277
6.8.6 Behaviour of treated corroded coupons to high RH.....................................................................278
6.8.7 Observations on weight changes of treated clean copper coupons............................................281
6.8.8 Comparative colour changes on clean coupons............................................................................282
6.9 Colour measurements of treated coupons................................................................................282
6.10 SEM-EDS.................................................................................................................................................284
6.10.1 SEM imaging of BTA + AMT.....................................................................................................285
6.10.2 SEM imaging of BTA + BZA......................................................................................................286
6.10.3 SEM imaging of BTA + ETH......................................................................................................287
6.10.4 SEM imaging of BTA + KEX......................................................................................................288
6.10.5 SEM imaging of BTA + KJ.........................................................................................................290
6.10.6 SEM imaging of BTA + PMT.....................................................................................................292
6.11 FT1R ANALYSIS OF COMBINATIONS.......................................................................................................293
6.11.1 BTA + AMT 294
6.11.1.1 Corroded copper..........................................................................................................................295
6.11.1.2 0.01M BTA + 0.01M AMT..........................................................................................................297
6.11.1.3 0.1M BTA + 0.01 M AMT............................................................................................................299
6.11.2 BTA + BZA.....................................................................................................................................301
6.11.3 BTA + ETH.....................................................................................................................................302
6.11.4 BTA + KEX.....................................................................................................................................304
6.11.5 BTA + KJ........................................................................................................................................306
6.11.6 BTA + PMT....................................................................................................................................309
6.12 X-Ray Photoelectron Spectroscopy (XPS) of combinations.................................................313
6.12.1 XPS of BTA + AMT......................................................................................................................314
6.12.1.1 AMT............................................................................................................................................314
6.12.1.2 BTA+AMT..................................................................................................................................315
6.12.2 XPS of BTA + BZA........................................................................................................................317
6.12.2.1 BZA 0.1M clean and corroded copper..........................................................................................317
6.12.2.2 BTA + BZA..................................................................................................................................318
6.12.3 XPS of BTA +ETH.........................................................................................................................319
6.12.3.1 ETH.............................................................................................................................................319
6.12.3.2 BTA + ETH.................................................................................................................................319
6.12.4 XPS of BTA + KEX........................................................................................................................321
6.12.4.1 KEX.............................................................................................................................................321
6.12.4.2 BTA + KEX..................................................................................................................................322
6.12.5 XPS of BTA + KI...........................................................................................................................323
6.12.5.1 KI.................................................................................................................................................323
6.12.5.2 BTA + Kl.....................................................................................................................................324
6.12.6 XPS of BTA + PMT......................................................................................................................325
6.12.6.1 PMT.............................................................................................................................................325
6.12.6.2 BTA + PMT.................................................................................................................................326
7
6.12.7 Elemental ratios............................................................................................................................................327
6.12.8 Discussion on XPS results........................................................................................................................328
6.13 Discussion of results.....................................................................................................................333
CHAPTER 7: TESTING OF SELECTED TREATMENTS ON EXCAVATED COPPER ALLOY
ARTEFACTS__________________________________________________ 337
7.1 Introduction........................................................................................................................................337
7.2 Objects used for field tests.............................................................................................................339
7.2.1 Kaman Kalehoyiik..............................................................................................................................................339
7.2.1.1 Methodology................................................................................................................................341
7.2.1.2 Treatment selection.....................................................................................................................344
7.2.1.3 Evaluation of treatments.............................................................................................................344
7.2.1.4 Colour changes............................................................................................................................346
7.2.1.5 Results........................................................................................................................................348
7.2.1.5.1 Results of test set 1 (2000)....................................................................................................348
7.2.1.5.2 Results of field test 2 (2001)..................................................................................................350
7.2.1.5.3 BTA treatments.....................................................................................................................351
7.2.1.5.4 BTA + AMT treatments........................................................................................................354
7.2.1.5.5 BTA + PMT treatments.........................................................................................................355
7.2.1.6 Comparative study of treatments using CARS scale.....................................................................356
7.2.1.7 Surveying the objects....................................................................................................................358
7.2.2 Application of BTA + AMT treatments on Mochlos objects................................................................358
7.3 Discussion/Conclusions...................................................................................................................363
CHAPTER 8: DISCUSSION_______________________________________________ 366
8.1 Accelerated corrosion testing.....................................................................................................367
8.2 Suitability of tested solutions fro use on archaeological objects................................377
8.3 Colour changes..................................................................................................................................380
8.4 pH effect on corrosion inhibition..................................................................................................382
8.5 Archaeological testing...................................................................................................................384
CHAPTER 9: CONCLUSION____________________________________________________________387
9.1 Benzotriazole......................................................................................................................................387
9.2 Synergistic effect..............................................................................................................................387
9.3 Factors affecting inhibition process...........................................................................................390
9.3.1 Surface condition................................................................................................................................................390
9.3.2 Concentration......................................................................................................................................................391
9.3.3 Time of Immersion..............................................................................................................................................391
9.3.4 Solvent....................................................................................................................................................................391
9.4 Colour alterations...........................................................................................................................392
9.5 Further research...............................................................................................................................394
LIST OF REFERENCES 400
Appendices (Volume II)
Appendix 1 -Experimental Data 423
Appendix 2-Photos of Clean and Corroded Copper coupons treated with inhibitors 515
Appendix 3-Table of colour measurements 521
Appendix 4-SEM images of coupons treated with different inhibitor solutions 523
Appendix 5-FTIR spectra 534
Appendix 6-XPS spectra and tables with atomic concentrations 552
Appendix 7-Testing on Archaeological objects: selected pictures of objects 648
8
LIST OF TABLES
Table 2.1. Electromotive Force Potential Series (EMF) (after Craig, 1991: 6)....................38
Table 2.2. Galvanic Series in Seawater (after Jones, 1996: 14)............................................39
Table 2.3. Selected copper corrosion products (Scott, 2002: 418-421).................................54
Table 4.1. Classification of artificially corroded copper coupons based on consistent weight
gain...............................................................................................................................110
Table 4.2 Guidelines for statistically designed experiments (after Montgomery, 1997: 14)
........................................................................................................................................119
Table 4.3. Scale used for the assessment of the treatments on archaeological objects from
Mochlos and Kaman. 126
Table 5.1. Factors and levels examined in experiment BTA 1............................................147
•y
Table 5.2. Full 2 factorial design with five replicates used of experiment BTA 1 showing
the standard order, the run order, the factors examined and the weight change for 24
hours. This is just an example of the experimental designs used.................................148
Table 5.3. Colour changes of the corroded coupons treated with BTA solutions...............149
Table 5.4. Average values of Inhibitive Efficiency % after 24, 48, 168, 504 and 840 hours
of exposure to 95% RH and 25 °C................................................................................150
Table 5.5. The two factors examined in experiment BTA 2 were the immersion and the
solvent............................................................................................................................152
Table 5.6. Average values of efficiency of 0.1 M BTA in ethanol and deionised water
applied on corroded coupons for 1 and 24 hours of immersion...................................153
Table 5.7. The factors examined in Experiment BTA 3 were concentration and solvent. 155
Table 5.8. Average values of efficiency % of 0.1M and 0.01M BTA in ethanol and water.
The range of values was very high in some of these treatments..................................156
Table 5.9. BTA 4 examined 3 factors, concentration, time of immersion and RH.............159
Table 5.10. Average values of inhibitive efficiency of experiment 4..................................160
Table 5.11. The same factors and levels were used for experiments 5 and 6, for 1 and 24
hours of immersion respectively...................................................................................163
Table 5.12. Average inhibitive efficiency values of treatments with re-used BTA solutions,
experiments 5 and 6.......................................................................................................164
Table 5.13. Factors examined at BTA 7 and BTA 8 experiment. In BTA 7 the immersion
time was 1 hour and in BTA 8, 24 hours......................................................................166
Table 5.14. Average inhibitive efficiency values of treatments with re-used BTA solutions
examined in BTA 7 and BTA 8.....................................................................................167
Table 5.15. pH values of aqueous BTA solutions................................................................173
Table 5.16. Table showing the effect treatments had on the metallic appearance of clean
coupons..........................................................................................................................177
Table 5.17. DL*, Da*, Db* and calculated DE values of corroded copper coupons treated
with different BTA solutions.........................................................................................178
Table 5.18. SEM observation of copper treated with BTA solutions..................................182
Table 5.19. Comparable table with BTA treatments on clean and corroded copper and
assignment of peaks. The strongest peaks of each group are marked in red...............193
Table 5.20. Main copper and oxygen XPS binding energies of clean and corroded copper
coupons used as reference.............................................................................................204
9