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Bioaccessibility of Stainless Steels: Importance of Bulk and Surface Features
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.ORCID iD: 0000-0002-2123-2201
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

With increasing environmental awareness, the desire to protect human beings and the environment from adverse effects induced by dispersed metals has become an issue of great concern and interest. New policies, such as REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) within the European Community, have been implemented to reduce hazards posed by the use of chemicals on producers and downstream users. The generation of exposure assessment data and relevant test procedures able to simulate realistic scenarios are essential in such legislative actions.

This doctoral study was initiated to fill knowledge gaps related to the metal release process of stainless steels. A wide range of stainless steel grades, fourteen in total, were investigated. They cover a very broad range of applications, and the focus in the thesis was to simulate a few selected exposure scenarios: precipitation, the human body and food intake. Comparisons were made between metal release from stainless steel alloys and the pure metals that constitute each stainless steel in order to explore the differences between alloys and pure metals, and to provide quantitative data on metal release rates of different alloy constituents. Because of similar surface properties between stainless steel and pure chromium, this metal exhibits similar release rates, whereas iron and nickel exhibit significantly lower release rates as alloy components than as pure metals. Detailed studies were also performed to elucidate possible relations between metal release and steel surface properties. Key parameters turned out to be chromium enrichment of the self-passivating surface film, surface roughness, the electrochemically active surface area and the microstructure of the steel substrate. The degree of metal release increased with decreasing chromium content in the surface oxide, increasing surface roughness, and increasing presence of inhomogeneities in the bulk matrix.

More detailed studies were initiated to possibly correlate the nucleation of metastable pits and the extent of metal release. Evidence was given that metastable pits exist even when the stainless steel is passive, and may cause extremely short-lived bursts of released metal before the surface film repassivates again.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , 73 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:39
Keyword [en]
Stainless steel, iron, chromium, nickel, corrosion, metal release, artificial rain, synthetic body fluids, acetic acid, surface oxide, surface finish
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4773ISBN: 978-91-7178-977-8 (print)OAI: oai:DiVA.org:kth-4773DiVA: diva2:13879
Public defence
2008-06-03, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100810Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-08-10Bibliographically approved
List of papers
1. A comparison of release rates of Cr, Ni and Fe from stainless steel alloys and the pure metals exposed to simulated rain events
Open this publication in new window or tab >>A comparison of release rates of Cr, Ni and Fe from stainless steel alloys and the pure metals exposed to simulated rain events
2005 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 1, B23-B29 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study is to demonstrate differences in metal release rates of Cr, Ni, and Fe from pure metals and stainless steels alloys (grades 304 and 316) exposed to identical simulated rain events. Panels were exposed to two 8 h continuous rain periods, separated by a 40 day dry period, in a specially designed rain chamber which permits artificial rain of known composition to be introduced at a given intensity. The study is intended to provide further knowledge of the behavior of stainless steels exposed to atmospheric corrosion and to show the discrepancy between estimated release rates based on nominal alloy composition and actual, measured release rates. Release rates of Fe and Ni were found to be substantially higher from the pure metals than from the stainless steels due to the presence of a chromium-rich surface film. The release rate of Cr was similar for stainless steel alloys and pure chromium. X-ray photoelectron spectroscopy investigations after single-rain events showed chromium to be enriched in the surface film upon rain exposure resulting in decreasing release rates of Cr, Ni, and Fe. Comparison between actual release rates of alloy constituents and calculated rates based on the pure metals and the nominal alloy composition, showed calculated data to substantially overestimate release rates of Ni and Fe.

Keyword
Composition; Corrosion; Electrolytic analysis; Iron; Nickel; Rain; Stainless steel; X ray photoelectron spectroscopy; Alloy composition; Pure metals; Rain events; Stainless steel alloys
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-8524 (URN)10.1149/1.1834901 (DOI)000225864900043 ()2-s2.0-12744274675 (Scopus ID)
Note
QC 20100810Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
2. Metal release from various grades of stainless steel exposed to synthetic body fluids
Open this publication in new window or tab >>Metal release from various grades of stainless steel exposed to synthetic body fluids
2007 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 49, no 1, 103-111 p.Article in journal (Refereed) Published
Abstract [en]

Release rates of individual alloy constituents have been determined from seven grades of stainless steels exposed to two synthetic body fluids, used as surrogates for different areas of potential exposure in the lung: "Gamble's solution", (pH 7.4) that represents the interstitial fluid of the deep lung, and artificial lysosomal fluid (ALF) that represents the more acidic (pH 4.5-5) milieu of particles following their phagocytosis by macrophages. Total metal release rates from all grades of stainless steel investigated were low (< 5 mu g cm(-2) week(-1)). The more acidic environment of ALF resulted in significantly higher total metal release rates (0.3-4.6 mu g cm(-2) week(-1)) compared to Gamble's solution (< 0.1 mu g cm(-2) week(-1)).

Keyword
stainless steel; XPS; passive film
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8525 (URN)10.1016/j.corsci.2006.05.008 (DOI)000243680400012 ()2-s2.0-33751326121 (Scopus ID)
Note
Conference: International Symposium on Progress in Corrosion Research. Hokkaide Univ, Sapporo, JAPAN. SEP 14-16, 2005 Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
3. Factors that influence the release of metals from stainless steels exposed to physiological media
Open this publication in new window or tab >>Factors that influence the release of metals from stainless steels exposed to physiological media
2006 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, no 8, 2120-2132 p.Article in journal (Refereed) Published
Abstract [en]

Release rates of chromium, nickel and iron from grade 304 stainless steel with three different surface finishes, BA, 2B and 2D, have been determined after exposure to artificial lysosomal fluid. Metal release rates are discussed in relation to corrosion resistance, compositional changes of the outermost surface film of the stainless steel and to measurements of the effective surface area and roughness. The total metal release decreased in the following sequence: 2D > 2B approximate to BA, and was primarily related to the electrochemically active surface area. No direct correlation was observed between corrosion resistance and metal release rates.

Keyword
stainless steel; EIS; XPS; passive film
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8526 (URN)10.1016/j.corsci.2005.08.006 (DOI)000240055200017 ()2-s2.0-33746266425 (Scopus ID)
Note
QC 20100810Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
4. Corrosion-induced release of chromium and iron from ferritic stainless steel grade AISI 430 in simulated food contact
Open this publication in new window or tab >>Corrosion-induced release of chromium and iron from ferritic stainless steel grade AISI 430 in simulated food contact
2008 (English)In: Journal of Food Engineering, ISSN 0260-8774, E-ISSN 1873-5770, Vol. 87, no 2, 291-300 p.Article in journal (Refereed) Published
Abstract [en]

Ferritic stainless steel grade AISI 430 with three different surface finishes, glossy, line and abraded has been evaluated regarding changes in metal release rates and corresponding changes in surface composition when immersed in 3 vol% acetic acid at two different temperatures, 40 degrees C for ten days and 100 degrees C during three consecutive immersions of 30 min each. Test parameter intervals were set by one of the very few regulatory texts for metal release in food applications, the Italian law text D.M. 21-03-1973, Art. 37. The metal release process was found to be strongly dependent on surface area to solution volume ratio where a specific surface finish would be within the allowed limit, 0.1 mg Cr L-1 for the lowest ratio, 0.5 cm, but exceeded for the highest ratio, 2 cm(-1). The amount of released metal increased with increasing temperature and increasing surface roughness (surface finish).

Generated data show the regulatory text insufficient and to provide large degrees of freedom, specifically in terms of defining the surface area to solution volume ratio and the acidic cleaning of test vessels, essential parameters to enable reproducible and relevant migration data.

Keyword
metal release; acetic acid; ferritic stainless steel; iron; chromium; cuttlery
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8527 (URN)10.1016/j.jfoodeng.2007.12.006 (DOI)000254722500016 ()2-s2.0-39749135591 (Scopus ID)
Note
QC 20100810Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
5. Metal release rate from AISI 316L stainless steel and pure Fe, Cr and Ni into a synthetic biological medium: a comparison
Open this publication in new window or tab >>Metal release rate from AISI 316L stainless steel and pure Fe, Cr and Ni into a synthetic biological medium: a comparison
2008 (English)In: Journal of Environmental Monitoring, ISSN 1464-0325, E-ISSN 1464-0333, Vol. 10, no 9, 1092-1098 p.Article in journal (Refereed) Published
Abstract [en]

Metal release rates from stainless steel grade 316L were investigated in artificial lysosomal fluid (ALF), simulating a human inflammatory cell response. The main focus was placed on release rates of main alloying elements using graphite furnace atomic absorption spectroscopy, and changes in surface oxide composition by means of X-ray photoelectron spectroscopy. To emphasise that alloys and pure metals possess totally different intrinsic properties, comparative studies were performed on the pure alloying constituents: iron, nickel and chromium. Significant differences in release rates were observed due to the presence of a passive surface film on stainless steel. Iron and nickel were released at rates more than 300 times lower from the 316L alloy compared with the pure metals whereas the release rate of chromium was similar. Iron was preferentially released compared with nickel and chromium. Immersion in ALF resulted in the gradual enrichment of chromium in the surface film, a small increase of nickel, and the reduction of oxidized iron with decreasing release rates of alloy constituents as a result. As expected, released metals from stainless steel grade 316L were neither in proportion to the bulk alloy composition nor to the surface film composition.

Keyword
CORROSION PITS; NICKEL RELEASE; IN-VITRO; CHROMIUM; IRON; CONTACT; ALLOYS; URBAN
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-17781 (URN)10.1039/b805075a (DOI)000258737700011 ()2-s2.0-50849097045 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
6. Corrosion-induced release of the main alloying constituents of manganese-chromium stainless steels in different media
Open this publication in new window or tab >>Corrosion-induced release of the main alloying constituents of manganese-chromium stainless steels in different media
2008 (English)In: Journal of Environmental Monitoring, ISSN 1464-0325, E-ISSN 1464-0333, Vol. 10, no 9, 1084-1091 p.Article in journal (Refereed) Published
Abstract [en]

The main focus of this paper is the assessment of release rates of chromium, nickel, iron and manganese from manganese-chromium stainless steel grades of low nickel content. The manganese content varied between 9.7 and 1.5 wt% and the corresponding nickel content between 1 and 5 wt%. All grades were exposed to artificial rain and two were immersed in a synthetic body fluid of similar pH but of different composition and exposure conditions. Surface compositional studies were performed using X-ray photoelectron spectroscopy (XPS) in parallel to correlate the metal release process with changes in surface oxide properties.

All grades, independent of media, revealed a time-dependent metal release process with a preferential low release of iron and manganese compared to nickel and chromium while the chromium content of the surface oxide increased slightly. Manganese was detected in the surface oxide of all grades, except the grade of the lowest manganese bulk content. No nickel was observed in the outermost surface oxide. Stainless steel grades of the lowest chromium content (approximate to 16 wt%) and highest manganese content (approximate to 7-9 wt%), released the highest quantity of alloy constituents in total, and vice versa. No correlation was observed between the release rate of manganese and the alloy composition. Released main alloy constituents were neither proportional to the bulk alloy composition nor to the surface oxide composition.

Keyword
NICKEL; METALS; PITS
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-8529 (URN)10.1039/b805058a (DOI)000258737700010 ()2-s2.0-50949108910 (Scopus ID)
Note
QC 20100810. Uppdaterad från submitted till published (20100810).Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
7. Multi-analytical investigation of stainless steel grade AISI 420 in simulated food contact
Open this publication in new window or tab >>Multi-analytical investigation of stainless steel grade AISI 420 in simulated food contact
2009 (English)In: Journal of Food Engineering, ISSN 0260-8774, E-ISSN 1873-5770, Vol. 93, no 1, 23-31 p.Article in journal (Refereed) Published
Abstract [en]

Martensitic stainless steel grade AN 420 intended for cutlery knives and scissor blades has been investigated in all attempt to correlate microstructure and surface finish (polishing procedure) to metal release rates of the main alloy constituents, iron and chromium. Metallographic investigations proved the knife steel and, in particular the scissor steel to have very inhomogeneous microstructures. The knife steel contained bands of ferrite in the martensitic structure while the scissor steel revealed large amounts of tempered martensite and inclusions of manganese sulphides and silicon oxides. Samples of different surface finish were immersed in 3 vol% acetic acid at 40 degrees C from 1 to 10 days for metal release testing. simulating food contact. The largely inhomogeneous microstructure of the scissor steel results in high and greatly varying metal release rates. despite a fairly high chromium content Of the Surface oxide. Areas of inclusions seem to act as initiation points for accelerated metal release and the forming of a surface oxide depleted in chromium, but rich in copper. The generation Of high Surface temperatures during polishing was found beneficial from a metal release perspective as a result Of the formation of a surface oxide of improved passivating properties.

Keyword
Metal release; Martensitic stainless steel; Acetic acid; Surface finish
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-8530 (URN)10.1016/j.jfoodeng.2008.12.019 (DOI)000265133700004 ()2-s2.0-61849172424 (Scopus ID)
Note

QC 20100810. Uppdaterad från submitted till published (20100810). Tidigare titel: Multianalytical investigation of stainless steel grade AISI 420 in simulated food contact

QC 20150731

Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved

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