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Radiation induced corrosion of copper for spent nuclear fuel storage
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-8341-094X
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-9453-1333
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2013 (English)In: Radiation Physics and Chemistry, ISSN 0969-806X, E-ISSN 1879-0895, Vol. 92, 80-86 p.Article in journal (Refereed) Published
Abstract [en]

The long term safety of repositories for radioactive waste is one of the main concerns for countries utilizing nuclear power. The integrity of engineered and natural barriers in such repositories must be carefully evaluated in order to minimize the release of radionuclides to the biosphere. One of the most developed concepts of long term storage of spent nuclear fuel is the Swedish KBS-3 method. According to this method, the spent fuel will be sealed inside copper canisters surrounded by bentonite clay and placed 500 m down in stable bedrock. Despite the importance of the process of radiation induced corrosion of copper, relatively few studies have been reported. In this work the effect of the total gamma dose on radiation induced corrosion of copper in anoxic pure water has been studied experimentally. Copper samples submerged in water were exposed to a series of total doses using three different dose rates. Unirradiated samples were used as reference samples throughout. The copper surfaces were examined qualitatively using IRAS and XPS and quantitatively using cathodic reduction. The concentration of copper in solution after irradiation was measured using ICP-AES. The influence of aqueous radiation chemistry on the corrosion process was evaluated based on numerical simulations. The experiments show that the dissolution as well as the oxide layer thickness increase upon radiation. Interestingly, the evaluation using numerical simulations indicates that aqueous radiation chemistry is not the only process driving the corrosion of copper in these systems.

Place, publisher, year, edition, pages
2013. Vol. 92, 80-86 p.
Keyword [en]
Corrosion, Copper, Gamma irradiation, Dose, Oxidation
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-131704DOI: 10.1016/j.radphyschem.2013.06.033ISI: 000324609900015Scopus ID: 2-s2.0-84883052341OAI: oai:DiVA.org:kth-131704DiVA: diva2:657240
Note

QC 20131018

Available from: 2013-10-18 Created: 2013-10-17 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Molecular studies of initial atmospheric corrosion of copper: Exploration of ultra-sensitive techniques for the inhibiting effect of self assembled monolayers, and the effect of gamma radiation
Open this publication in new window or tab >>Molecular studies of initial atmospheric corrosion of copper: Exploration of ultra-sensitive techniques for the inhibiting effect of self assembled monolayers, and the effect of gamma radiation
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atmospheric corrosion indoors is of great practical importance for the degradation of metals, for example in electronics, military equipment, and cultural heritage items. It involves a wide range of chemical, electrochemical, and physical processes occurring in gas, liquid, and solid phases, and at the interfaces between them. Hence, a molecular understanding of the fundamental interactions during atmospheric corrosion is of utmost importance.

Copper is one of the most used metals in electrical contacts, power generators, heat exchangers, etc. and is prone to indoor atmospheric corrosion. Although corrosion and oxidation of copper in the presence of corrosion stimulators is thermodynamically inevitable, there are ways to reduce the kinetics of corrosion and oxidation reactions.

Self assembled monolayers (SAMs) of organic molecules, when adsorbed on copper surfaces, have proven to be efficient barriers against copper corrosion. However, understanding at the molecular level of the initial stages of corrosion of SAM covered copper in atmospheric corrosion conditions is lacking. The main reason is the inability of the conventional analytical methods to detect and characterize very thin corrosion products formed during the initial stages (from seconds to days) of atmospheric corrosion of SAM covered copper. To overcome this situation a highly surface sensitive technique, vibrational sum frequency spectroscopy (VSFS), has been utilized in situ and ex situ in this thesis to detect and follow the oxidation of alkanethiol SAM covered copper in dry air as well as to assess the conformational changes of SAM molecules during oxidation.  A very sensitive gravimetric method, quartz crystal microbalance with dissipation monitoring (QCM-D), and a highly sensitive and versatile optical technique, nanoplasmonic sensing (NPS), were combined in situ with VSFS to quantify this very slow oxidation process. This combination allowed the heterogeneity of the oxidation process as well as the mass and the rigidity of the corrosion products to be detected simultaneously.

To address indoor atmospheric corrosion conditions where carboxylic acids play an important role we next studied the interaction between SAM covered copper and humidified air, to which formic acid was added. The in situ identification of the corrosion products and their formation kinetics was done using near surface sensitive infrared reflection/absorption spectroscopy (IRAS), and the effect of hydrocarbon chain length in alkanethiol SAMs on their corrosion protection efficiency was investigated. The effect of the anchoring group in the SAMs on their corrosion protection efficiency was studied for hexaneselenol using -SeH as the anchoring group, and the results were compared with its thiol counterpart, hexanethiol, with -SH as the anchoring group. Complementary in situ and ex situ VSFS measurements were performed to assess the quality of the SAMs before, during, and after exposure.

It was shown that the SAMs of alkanethiols greatly inhibited the formation of copper (I) oxide and slowed down the formation of other corrosion products, i.e. copper formate and copper hydroxid. This was due to a selective hindrance of the corrosion stimulators, oxygen, water, and formic acid molecules reaching the copper-SAM interface. The corrosion inhibiting effect increased with the hydrocarbon chain length. The SAMs of hexaneselenols, on the other hand, exhibited an accelerated formation of copper (I) oxide, copper formate and copper hydroxide compared to an unprotected surface as a result of the partial removal of hexaneselenol molecules from the copper surface during prolonged exposure.

The experience gained in characterizing and quantifying thin copper oxides was further used to explore the influence of gamma (γ) radiation on copper corrosion in anoxic water. This multi-analytical approach included IRAS, cathodic reduction, confocal Raman microscope, atomic force microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, and inductively coupled plasma - atomic emission spectroscopy. The results clearly showed that copper dissolution as well as the oxide layer thickness increase with gamma radiation under the exposure conditions.

Abstract [sv]

Atmosfärisk korrosion under inomhusförhållanden är av stor praktisk betydelse på grund av dess inverkan på exempelvis vårt kulturarv i museimiljöer, tillförlitligheten hos elektronik i olika industriella sammanhang, eller militär utrustning förvarad i olika förråd. Den atmosfäriska korrosionen styrs av ett brett spektrum av kemiska, elektrokemiska och fysikaliska processer som äger rum i tre faser: atmosfären, den tunna fuktfilmen på objektytan och den fasta fasen, samt i de bägge fasgränserna mellan de tre faserna. För att kunna hitta motmedel mot korrosionen är det av yttersta vikt att öka den molekylära förståelsen för dessa processer.

Koppar är en mycket använd metall i elektriska eller elektroniska komponenter, i värmeväxlare eller VVS-sammanhang, som beslag och i en rad olika dekorer. Metallen korroderar eller oxiderar spontant i många korrosiva miljöer, men det finns ett brett spektrum av metoder för att minska korrosions- eller oxidationshastigheten. Monoskikt av tätpackade självassocierande organiska molekyler (engelska: self assembled monolayers, förkortat SAM) adsorberade på kopparytan har visat sig vara effektiva barriärer för kopparkorrosion. Den molekylära insikten i dessa monoskikts funktionssätt för att minska den atmosfäriska korrosionen är dock ännu rätt så begränsad. Den främsta orsaken är oförmågan hos mer etablerade analytiska metoder att kunna karakterisera de ytterst små mängder av korrosionsprodukter som bildas under den atmosfäriska korrosionens inledande skeenden upp till några dagars exponering.

Den extremt ytkänsliga och i korrosionssammanhang fortfarande relativt oprövade analysmetoden summafrekvensspektroskopi (engelska: vibrational sum frequency spectroscopy, förkortat VSFS) har därför använts för att under pågående exponering följa det mycket långsamma oxidationsförlopp som uppstår när koppar, skyddat av något organiskt monoskikt, exponeras för torr luft. VSFS har även kunnat användas för att under pågående oxidation följa strukturella förändringar hos monoskiktet. För att kvantifiera en så långsam oxidationsprocess har även en annan extremt masskänslig metod kunnat kombineras med VSFS, en kvartskristallmikrovåg med s.k. dissipationsövervakning, förkortat QCM-D. Ytterligare en i korrosionssammanhang oprövad men lika masskänslig teknik har kunnat kombineras med VSFS. Den metoden besitter än så länge bara ett engelskt namn, nanoplasmonic sensing (NPS). Kombinationen VSFS–QCM-D–NPS har utnyttjats i en serie unika försök, där inte bara de ytterst långsamma oxidationshastigheterna kunnat mätas upp, utan även andra viktiga faktorer såsom graden av heterogenitet i den bakomliggande oxidationsprocessen.

För att närma sig en miljö som kan efterlikna korrosiva inomhusförhållanden har atmosfären i nästa steg befuktats och dessutom har låga halter av myrsyra tillsats. Just tillsatsen av karboxylsyror har visat sig generera korrosionsprodukter med en sammansättning som på koppar och vissa andra metaller efterliknar de som bildas under atmosfärisk korrosion inomhus. Identifiering av korrosionsprodukter och deras tillväxthastighet på koppar, skyddat av olika långa tätpackade kolkedjor med en tiolgrupp i ena ändan som binder till kopparsubstratet, har kunnat ske med infraröd reflektions-absorptionsspektroskopi (IRAS) under in situ-förhållanden. Ju längre kolvätekedjor desto större korrosionsinhibieringsförmåga kunde påvisas. När den på koppar förankrade tiolgruppen ersattes med en selenolgrupp blev korrosionsinhibieringsförmågan sämre. Kompletterande mätningar in situ och ex situ  utfördes med hjälp av VSFS för att undersöka kvaliteten på de tätpackade kolvätekedjorna, varvid kunde påvisas att graden av tätpackning hos kolkedjorna försämrades med ökad exponeringstid.

Förutom den allmänna nedbromsningen av korrosionshastigheten på koppar blev sammansättningen av bildade korrosionsprodukter på oskyddat koppar en annan än på  koppar skyddat av tioler. I det förra fallet detekterades korrosionsprodukterna koppar(I)oxid, koppar(II)format och koppar(II)hydroxid, under det att ingen koppar(I)oxid påvisades på skyddat koppar, endast små mängder koppar(II)format och koppar(II)hydroxid kunde detekteras. De adsorberade kolkedjorna tycks hindra de korrosionsstimulerande molekylerna vatten, myrsyra och syrgas från att nå kopparytan lika effektivt. När de tiolförankrade kolvätekedjorna ersattes med selenolförankrade kolvätekedjor desorberades en del kolvätekedjor från kopparsubstratet vid längre exponeringstider. Resultatet blev att mängden korrosionsprodukter nu blev signifikant större än på oskyddat koppar, sannolikt på grund av galvanisk korrosion.

Erfarenheterna från detta doktorsarbete vad gäller kvantifiering av små mängder kopparoxider har även utnyttjats för att undersöka inverkan av g-strålning på kopparkorrosion i rent vatten. Härvid användes ett multianalytiskt angreppssätt bestående av IRAS, katodisk reduktion, konfokal Ramanmikroskopi, atomkraftsmikroskopi, svepelektronmikroskopi, fotoelektronspektroskopi, samt analys av utlöst mängd koppar i vattenlösningen med induktivt kopplad plasmaatomemissionsspektroskopi. Resultaten visar tydligt att utlösningen av koppar, liksom det bildade oxidskiktets tjocklek, ökar med g-strålningen under rådande exponeringsförhållanden.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xvii, 85 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:50
Keyword
Corrosion, copper, self assembled monolayer, sum frequency spectroscopy, qcm, gamma radiation
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-136267 (URN)978-91-7501-950-5 (ISBN)
Public defence
2013-12-20, Kollegiesallen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131206

Available from: 2013-12-06 Created: 2013-12-04 Last updated: 2013-12-06Bibliographically approved
2. Radiation induced corrosion of copper
Open this publication in new window or tab >>Radiation induced corrosion of copper
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The process of radiation induced corrosion of copper is not well understood. The most obvious situation where the knowledge of this process is crucial is in a deep repository for high level spent nuclear fuel where the fuel will be sealed inside copper canisters. The radiation will penetrate the canisters and be absorbed by the surrounding environment. In this study gamma irradiations of polished and pre-oxidized copper cubes in anoxic pure water, air of 60-100 % RH and in humid argon were performed. The copper surfaces were examined using IRAS, XPS, cathodic reduction, SEM, AFM, and Raman spectroscopy. The concentration of copper in the reaction solutions was measured using ICP-OES.  Also the formation of oxidative species caused by radiation absorption of water was studied by numerical simulations using MAKSIMA software. The corrosion of copper during gamma irradiation vastly exceeds what is expected. The production of oxidative species caused by radiation absorption of water is hundreds of times too low to explain the amount of oxidized copper. A possible explanation for this mismatch is an enhanced radiation chemical yield of HO· on the copper surface. Another one is an increased surface area due to oxidation of copper. One speculation is that HO· interacting with the copper oxide can cause oxidation of the metal. If the thermodynamic driving force is large enough then electrons can be conducted from the metal through the oxide to the oxidant. A dramatic increase in surface area together with an increased interfacial yield of HO· might explain the radiation enhanced corrosion process.   

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. vii, 77 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:57
Keyword
Corrosion, oxidation, copper, copper oxide, gamma radiation, radiolysis, hydrogen peroxide, hydroxyl radical
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-175739 (URN)978-91-7595-710-4 (ISBN)
Public defence
2015-11-18, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20151022

Available from: 2015-10-22 Created: 2015-10-20 Last updated: 2015-10-22Bibliographically approved

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