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Stainless Steel in Biological Environments – Relation between Material Characteristics, Surface Chemistry and Toxicity
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0003-2145-3650
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Triggered by the regulatory need of the industry to demonstrate safe use of their alloy products from an environmental and health perspective, and by the significant lack of metal release data and its correlation to material and surface characteristics for iron- and chromium-based alloys, a highly interdisciplinary in-depth research effort was undertaken to assess the relation between material/surface characteristics and toxicity with main emphasis on stainless steel alloys. This thesis focuses predominantly on studies made on AISI 316L both as massive sheet and as powder particles, but includes also results for other stainless steel grades and reference metals and metal oxides.

 

The work comprises multi-analytical bulk and surface characterizations combined with particle characterizations and corrosion investigations, all correlated with in-depth kinetic metal release (bioaccessibility) studies as a function of route of manufacture, powder particle characteristics, surface finish, stainless steel grade, solution composition, pH, acidity and complexation capacity, as well as the presence of proteins. Speciation (chemical form) measurements were in addition conducted of released chromium, and of metal species in the surface oxide. Protein interactions were investigated in terms of adsorption, protein-metal complexation both at the surface and in solution, and the relative strength of protein-stainless steel surface interaction was addressed. In vitro and in vivo toxicological studies were conducted for the same inert-gas-atomized 316L powder sized < 4µm.

 

Bulk and surface oxide properties, such as phase, structure, morphology, chemical and electrochemical stability, protein-surface interactions, bioavailability of released metals, were all clearly evident to largely influence the metal release process and any induced toxicity. The route of manufacture was shown to strongly influence the bulk and surface oxide characteristics of stainless steel powders, hence also their electrochemical and catalytic properties, as well as the release/dissolution of metals from the powders (Papers VIII, XIII, XIV-XVII). The release of metals from both stainless steel sheets and powders was in general low compared to pure iron or nickel metal, and highly dependent on bulk and surface characteristics, the composition, complexation capacity and buffering capacity (and pH) of the solution, as well as on many experimental factors including time and sonication (Papers VI, VIII, XI, and XVII).

 

Surface-protein interactions strongly enhanced the release of alloy constituents (Papers IX, XI, and XVII). Iron was preferentially released (manganese in the case of inert-gas-atomized stainless steel powders) (Papers VIII, XI, and XVII). Protein-stainless steel surface interactions were most probably governed by chemisorption at given experimental conditions (Papers XI-XII). A strong protein-adsorption was evident for all stainless steel surfaces investigated, independent of protein charge, size or structure (Paper IX). Protein-metal complexes were formed both at the surface and in solution (Papers X-XII). Differences in protein charge and type resulted in varying degrees of interaction with differences in the extent of enhanced metal release as a consequence (Papers XI-XII). The inert-gas-atomized stainless steel powder sized <4 µm induced neither any significant increase of lysis of erythrocytes (rupture of red blood cells) nor any cytotoxicity, but resulted in a slight DNA damage in in vitro toxicity measurements (Paper VI). No adverse effects were however observed in an in vivo 28-day repeated-dose inhalation study on rats using the same powder (Paper VII).

 

The most important bulk, surface, particle, and experimental factors governing the bioaccessibility properties of stainless steel were identified and mechanistically elucidated. Detailed knowledge of all factors is essential for accurate hazard or risk assessment of metal alloys and enables read-across possibilities with materials of the same or similar characteristics. However, in cases where data is different from known systems for one factor or more, bioaccessibility data should be generated before any risk assessment is made.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , XIV, 38 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:57
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-105521ISBN: 978-91-7501-521-7 (print)OAI: oai:DiVA.org:kth-105521DiVA: diva2:571308
Public defence
2012-12-14, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121126

Available from: 2012-11-26 Created: 2012-11-22 Last updated: 2012-11-26Bibliographically approved
List of papers
1. Bioaccessibility, bioavailability and toxicity of commercially relevant iron- and chromium-based particles: in vitro studies with an inhalation perspective
Open this publication in new window or tab >>Bioaccessibility, bioavailability and toxicity of commercially relevant iron- and chromium-based particles: in vitro studies with an inhalation perspective
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2010 (English)In: Particle and Fibre Toxicology, ISSN 1743-8977, E-ISSN 1743-8977, Vol. 7, no 23Article in journal (Refereed) Published
Abstract [en]

Background

Production of ferrochromium alloys (FeCr), master alloys for stainless steel manufacture, involves casting and crushing processes where particles inevitably become airborne and potentially inhaled. The aim of this study was to assess potential health hazards induced by inhalation of different well-characterized iron- and chromium-based particles, i.e. ferrochromium (FeCr), ferrosiliconchromium (FeSiCr), stainless steel (316L), iron (Fe), chromium (Cr), and chromium(III)oxide (Cr2O3), in different size fractions using in vitro methods. This was done by assessing the extent and speciation of released metals in synthetic biological medium and by analyzing particle reactivity and toxicity towards cultured human lung cells (A549).

Results

The amount of released metals normalized to the particle surface area increased with decreasing particle size for all alloy particles, whereas the opposite situation was valid for particles of the pure metals. These effects were evident in artificial lysosomal fluid (ALF) of pH 4.5 containing complexing agents, but not in neutral or weakly alkaline biological media. Chromium, iron and nickel were released to very low extent from all alloy particles, and from particles of Cr due to the presence of a Cr(III)-rich protective surface oxide. Released elements were neither proportional to the bulk nor to the surface composition after the investigated 168 hours of exposure. Due to a surface oxide with less protective properties, significantly more iron was released from pure iron particles compared with the alloys. Cr was predominantly released as Cr(III) from all particles investigated and was strongly complexed by organic species of ALF. Cr2O3 particles showed hemolytic activity, but none of the alloy particles did. Fine-sized particles of stainless steel caused however DNA damage, measured with the comet assay after 4 h exposure. None of the particles revealed any significant cytotoxicity in terms of cell death after 24 h exposure.

Conclusion

It is evident that particle and alloy characteristics such as particle size and surface composition are important aspects to consider when assessing particle toxicity and metal release from alloy particles compared to pure metal particles. Generated results clearly elucidate that neither the low released concentrations of metals primarily as a result of protective and poorly soluble surface oxides, nor non-bioavailable chromium complexes, nor the particles themselves of occupational relevance induced significant acute toxic response, with exception of DNA damage from stainless steel.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24699 (URN)10.1186/1743-8977-7-23 (DOI)000282502100001 ()2-s2.0-77956491106 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

QC 20101006

Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
2. Inhalation toxicity of 316L stainless steel powder in relation to bioaccessibility
Open this publication in new window or tab >>Inhalation toxicity of 316L stainless steel powder in relation to bioaccessibility
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2013 (English)In: Human and Experimental Toxicology, ISSN 0960-3271, E-ISSN 1477-0903, Vol. 32, no 11, 1137-1154 p.Article in journal (Refereed) Published
Abstract [en]

The Globally Harmonized System for Classification and Labelling of Chemicals (GHS) considers metallic alloys, such as nickel (Ni)-containing stainless steel (SS), as mixtures of substances, without considering that alloys behave differently compared to their constituent metals. This study presents an approach using metal release, explained by surface compositional data, for the prediction of inhalation toxicity of SS AISI 316L. The release of Ni into synthetic biological fluids is >1000-fold lower from the SS powder than from Ni metal, due to the chromium(III)-rich surface oxide of SS. Thus, it was hypothesized that the inhalation toxicity of SS is significantly lower than what could be predicted based on Ni metal content. A 28-day inhalation study with rats exposed to SS 316L powder (<4 mu m, mass median aerodynamic diameter 2.5-3.0 mu m) at concentrations up to 1.0mg/L showed accumulation of metal particles in the lung lobes, but no signs of inflammation, although Ni metal caused lung toxicity in a similar published study at significantly lower concentrations. It was concluded that the bioaccessible (released) fraction, rather than the elemental nominal composition, predicts the toxicity of SS powder. The study provides a basis for an approach for future validation, standardization and risk assessment of metal alloys.

Keyword
stainless steel, inhalation, rat, toxicity, metal release, bioaccessibility
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-105511 (URN)10.1177/0960327112472354 (DOI)000327377400003 ()2-s2.0-84889062341 (Scopus ID)
Note

QC 20131220. Updated from accepted to published.

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
3. Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure
Open this publication in new window or tab >>Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure
2011 (English)In: Biometals, ISSN 0966-0844, E-ISSN 1572-8773, Vol. 24, no 6, 1099-1114 p.Article in journal (Refereed) Published
Abstract [en]

Iron, chromium, nickel, and manganese released from gas-atomized AISI 316L stainless steel powders (sized < 45 and < 4 mu m) were investigated in artificial lysosomal fluid (ALF, pH 4.5) and in solutions of its individual inorganic and organic components to determine its most aggressive component, elucidate synergistic effects, and assess release mechanisms, in dependence of surface changes using atomic absorption spectroscopy, Raman, XPS, and voltammetry. Complexation is the main reason for metal release from 316L particles immersed in ALF. Iron was mainly released, while manganese was preferentially released as a consequence of the reduction of manganese oxide on the surface. These processes resulted in highly complexing media in a partial oxidation of trivalent chromium to hexavalent chromium on the surface. The extent of metal release was partially controlled by surface properties (e.g., availability of elements on the surface and structure of the outermost surface) and partially by the complexation capacity of the different metals with the complexing agents of the different media. In general, compared to the coarse powder (< 45 mu m), the fine (< 4 mu m) powder displayed significantly higher released amounts of metals per surface area, increased with increased solution complexation capacity, while less amounts of metals were released into non-complexing solutions. Due to the ferritic structure of lower solubility for nickel of the fine powder, more nickel was released into all solutions compared with the coarser powder.

Keyword
Stainless steel, Powder, Complexation, Metal release, Dissolution, Inhalation
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-52543 (URN)10.1007/s10534-011-9469-7 (DOI)000297117100012 ()2-s2.0-83555165202 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20111220

Available from: 2011-12-20 Created: 2011-12-19 Last updated: 2017-12-08Bibliographically approved
4. Adsorption and protein-induced metal release from chromium metal and stainless steel
Open this publication in new window or tab >>Adsorption and protein-induced metal release from chromium metal and stainless steel
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2012 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 366, no 1, 155-164 p.Article in journal (Refereed) Published
Abstract [en]

A research effort is undertaken to understand the mechanism of metal release from, e.g., inhaled metal particles or metal implants in the presence of proteins. The effect of protein adsorption on the metal release process from oxidized chromium metal surfaces and stainless steel surfaces was therefore examined by quartz crystal microbalance with energy dissipation monitoring (QCM-D) and graphite furnace atomic absorption spectroscopy (GFAAS). Differently charged and sized proteins, relevant for the inhalation and dermal exposure route were chosen including human and bovine serum albumin (HSA, BSA), mucin (BSM), and lysozyme (LYS). The results show that all proteins have high affinities for chromium and stainless steel (AISI 316) when deposited from solutions at pH 4 and at pH 7.4 where the protein adsorbed amount was very similar. Adsorption of albumin and mucin was substantially higher at pH 4 compared to pH 7.4 with approximately monolayer coverage at pH 7.4, whereas lysozyme adsorbed in multilayers at both investigated pH. The protein-surface interaction was strong since proteins were irreversibly adsorbed with respect to rinsing. Due to the passive nature of chromium and stainless steel (AISI 316) surfaces, very low metal release concentrations from the QCM metal surfaces in the presence of proteins were obtained on the time scale of the adsorption experiment. Therefore, metal release studies from massive metal sheets in contact with protein solutions were carried out in parallel. The presence of proteins increased the extent of metals released for chromium metal and stainless steel grades of different microstructure and alloy content, all with passive chromium(III)-rich surface oxides, such as QCM (AISI 316), ferritic (AISI 430), austentic (AISI 304, 316L), and duplex (LDX 2205).

Keyword
Chromium, Protein adsorption, Metal release, Stainless steel, Lysozyme, Albumin, Mucin
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-53387 (URN)10.1016/j.jcis.2011.09.068 (DOI)000297385900023 ()2-s2.0-80655124456 (Scopus ID)
Note

QC 20111229

Available from: 2011-12-29 Created: 2011-12-28 Last updated: 2017-12-08Bibliographically approved
5. Chromium-protein complexation studies by adsorptive cathodic stripping voltammetry and MALDI-TOF-MS
Open this publication in new window or tab >>Chromium-protein complexation studies by adsorptive cathodic stripping voltammetry and MALDI-TOF-MS
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2012 (English)In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 42, no 5, 349-358 p.Article in journal (Refereed) Published
Abstract [en]

A methodology using stripping voltammetry has been elaborated to enable sensitive and reliable protein-chromium complexation measurements. Disturbing effects caused by adsorption of proteins on the mercury electrode were addressed. At low concentrations of proteins (< 60-85 nM), chromium-protein complexation measurements were possible. Chromium(VI) complexation was quantitatively determined using differently sized, charged, and structured proteins: serum albumin (human and bovine), lysozyme, and mucin. Generated results showed a strong relation between complexation and protein size, concentration, and the number of amino acids per protein mass. Complexation increased nonlinearly with increasing protein concentrations. The nature of this complexation was based on weak interactions judged from combined results with MALDI-TOF-MS and adsorptive cathodic stripping voltammetry.

Keyword
Chromium, Complexation, Lysozyme, Serum albumin, Mucin, Stripping voltammetry
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-93903 (URN)10.1007/s10800-012-0404-6 (DOI)000302410900009 ()
Funder
Swedish Research Council
Note
QC 20120504Available from: 2012-05-04 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
6. Surface-protein interactions on different stainless steel grades: effects of protein adsorption, surface changes and metal release
Open this publication in new window or tab >>Surface-protein interactions on different stainless steel grades: effects of protein adsorption, surface changes and metal release
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2013 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 24, no 4, 1015-1033 p.Article in journal (Refereed) Published
Abstract [en]

Implantation using stainless steels (SS) is an example where an understanding of protein-induced metal release from SS is important when assessing potential toxicological risks. Here, the protein-induced metal release was investigated for austenitic (AISI 304, 310, and 316L), ferritic (AISI 430), and duplex (AISI 2205) grades in a phosphate buffered saline (PBS, pH 7.4) solution containing either bovine serum albumin (BSA) or lysozyme (LSZ). The results show that both BSA and LSZ induce a significant enrichment of chromium in the surface oxide of all stainless steel grades. Both proteins induced an enhanced extent of released iron, chromium, nickel and manganese, very significant in the case of BSA (up to 40-fold increase), whereas both proteins reduced the corrosion resistance of SS, with the reverse situation for iron metal (reduced corrosion rates and reduced metal release in the presence of proteins). A full monolayer coverage is necessary to induce the effects observed.

Keyword
stainless steel, protein, metal release, surface, corrosion resistance
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-105512 (URN)10.1007/s10856-013-4859-8 (DOI)000318509100017 ()2-s2.0-84876288008 (Scopus ID)
Funder
Swedish Research CouncilFormasKnut and Alice Wallenberg Foundation
Note

QC 20130614. Updated from submitted to published.

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
7. Interaction of bovine serum albumin and lysozyme with stainless steel studied by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy
Open this publication in new window or tab >>Interaction of bovine serum albumin and lysozyme with stainless steel studied by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy
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2012 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 47, 16306-16317 p.Article in journal (Refereed) Published
Abstract [en]

An in-depth mechanistic understanding of the interaction between stainless steel surfaces and proteins is essential from a corrosion and protein-induced metal release perspective when stainless steel is used in surgical implants and in food applications. The interaction between lysozyme (LSZ) from chicken egg white and bovine serum albumin (BSA) and AISI 316L stainless steel surfaces was studied ex situ by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) after different adsorption time periods (0.5, 24, and 168 h). The effect of XPS measurements, storage (aging), sodium dodecyl sulfate (SDS), and elevated temperature (up to 200 °C) on the protein layers, as well as changes in surface oxide composition, were investigated. Both BSA and LSZ adsorption induced an enrichment of chromium in the oxide layer. BSA induced significant changes to the entire oxide, while LSZ only induced a depletion of iron at the utmost layer. SDS was not able to remove preadsorbed proteins completely, despite its high concentration and relatively long treatment time (up to 36.5 h), but induced partial denaturation of the protein coatings. High-temperature treatment (200 °C) and XPS exposure (X-ray irradiation and/or photoelectron emission) induced significant denaturation of both proteins. The heating treatment up to 200 °C removed some proteins, far from all. Amino acid fragment intensities determined from ToF-SIMS are discussed in terms of significant differences with adsorption time, between the proteins, and between freshly adsorbed and aged samples. Stainless steel–protein interactions were shown to be strong and protein-dependent. The findings assist in the understanding of previous studies of metal release and surface changes upon exposure to similar protein solutions.

Keyword
Adsorption time, AISI316L stainless steel, Amino acid fragments, Bovine serum albumins, Chicken egg white, Elevated temperature, Ex situ, Food applications, Heating treatments, High concentration, High-temperature treatment, Metal release, Oxide layer, Partial denaturation, Photo-electron emission, Protein coating, Protein layers, Protein solution, Sodium dodecyl sulfate, Stainless steel surface, Surface changes, Surface oxide, Time of flight secondary ion mass spectrometry, ToF SIMS, Treatment time, X ray irradiation, XPS measurements
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-105513 (URN)10.1021/la3039279 (DOI)000312515200010 ()2-s2.0-84870209570 (Scopus ID)
Note

QC 20121219

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
8. Ultrafine 316 L stainless steel particles with frozen-in magnetic structures characterized by means of electron backscattered diffraction
Open this publication in new window or tab >>Ultrafine 316 L stainless steel particles with frozen-in magnetic structures characterized by means of electron backscattered diffraction
2011 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 65, no 14, 2089-2092 p.Article in journal (Refereed) Published
Abstract [en]

Electron Backscatter Diffraction (EBSD) studies clearly revealed a different crystallographic structure of the smallest particle size fraction of gas-atomized AISI 316 L stainless steel powder (<4 mu m) compared with larger sized fractions of the same powder (<45 mu m). Despite similar chemical compositions, the predominating structure of the smallest particle size fraction was ferritic (i.e., has ferromagnetic properties) whereas the larger sized particle fractions and massive 316 L revealed an expected austenitic and non-magnetic structure. From these findings, it follows that direct magnetic separation can be applied to separate very fine sized particles. These structural differences explain previously observed dissimilarities from corrosion and metal release perspectives.

Keyword
Electron backscattered diffraction, Particles, Stainless steel, Phase transformation, Metals and alloys, Crystal structure
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-37149 (URN)10.1016/j.matlet.2011.04.019 (DOI)000292444200001 ()2-s2.0-79955892970 (Scopus ID)
Available from: 2011-08-03 Created: 2011-08-02 Last updated: 2017-12-08Bibliographically approved
9. Surface characterisation of fine inert-gas- and water-atomised stainless steel 316L powders - formation of thermodynamically unstable surface oxide phases
Open this publication in new window or tab >>Surface characterisation of fine inert-gas- and water-atomised stainless steel 316L powders - formation of thermodynamically unstable surface oxide phases
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2013 (English)In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 56, no 2, 158-163 p.Article in journal (Refereed) Published
Abstract [en]

New insights are presented on the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 mu m) and water atomised (WA, <45 mu m) stainless steel AISI 316L powders. X-ray photoelectron and Auger electron spectroscopy, scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidised manganese was strongly enriched in the outermost surface oxide of the GA powders (13 and 47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enriched in oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powder surface. Tri-or tetravalent manganese oxides were observed on the GA particles in addition to alpha-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of a silicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr, which was confirmed not present as chromate.

Keyword
Stainless steel, Powder, Gas atomisation, Water atomisation, Surface characterisation, Oxide
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-105515 (URN)10.1179/1743290112Y.0000000041 (DOI)000318021100025 ()2-s2.0-84877910584 (Scopus ID)
Funder
Swedish Research CouncilFormas
Note

QC 20130604

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
10. Influence of Surface Oxide Characteristics and Speciation on Corrosion, Electrochemical Properties and Metal Release of Atomized 316L Stainless Steel Powders
Open this publication in new window or tab >>Influence of Surface Oxide Characteristics and Speciation on Corrosion, Electrochemical Properties and Metal Release of Atomized 316L Stainless Steel Powders
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2012 (English)In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 7, no 12, 11655-11677 p.Article in journal (Refereed) Published
Abstract [en]

Surface oxide characteristics of powder particles are important to consider for any toxicological risk assessment based on in-vitro or in-vivo tests. This study focuses on a multi-analytical approach (X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning- and transmission electron microscopy, and different electrochemical techniques) for in-depth characterization of surface oxides of inert-gas-atomized (GA) AISI 316L stainless steel powder, compared with massive sheet and a water-atomized (WA) 316L powder. Implications of differences in surface oxide phases and their surface distribution on corrosion, electrochemical properties and metal release are systematically discussed. Cr was enriched in an inner surface layer for both GA powders, with Mn and S enriched in the outermost surface oxide. The surface oxide was 2-5 nm thick for both GA powder size fractions, amorphous for the GA powder sized <4 μm and partially crystalline for the powder sized <45 μm. A strong ennoblement, i.e. positive shift in open circuit potential, of up to 800 mV, depending on solution, was observed for the GA powders. This ennoblement was induced by catalytic oxygen reduction properties of tri- or tetravalent Mn-oxides, not present on the massive sheet or WA powder. In contrast to the predominant presence of a trivalent Cr-oxide in the surface oxide of the GA powder particles, the WA<45μm powder revealed oxidized Cr, most probably present in its hexavalent state (not chromate), within a silicate-rich surface oxide. This study clearly shows that the surface oxide composition and speciation of differently sized GA and WA powders are unique (strongly connected to the atomization process) and of large importance for their pitting corrosion and metal release properties. For the GA<45μm powder, Mn-rich oxide nanoparticles were proposed to account for its higher pitting corrosion susceptibility, a more stable surface ennoblement, and a shift of the MnO2 oxidation/reduction peaks in the cyclic voltammogram, compared with the GA particles sized <4μm. The thermodynamically unstable ferritic structure of the small sized particle fraction (GA <4μm), despite an austenitic composition, revealed a higher pitting corrosion susceptibility and higher nickel release compared with the austenitic particle fraction of the GA <45 μm powder.

Keyword
surface oxide, speciation, characterization, manganese dioxide, oxide nanoparticles
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-105517 (URN)000312936700002 ()2-s2.0-84871125613 (Scopus ID)
Funder
Swedish Research CouncilFormas
Note

QC 20130201

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
11. Micro-Capillary Electrochemical and Microscopic Investigations of Massive and Individual Micrometer-Sized Powder Particles of Stainless Steel 316L
Open this publication in new window or tab >>Micro-Capillary Electrochemical and Microscopic Investigations of Massive and Individual Micrometer-Sized Powder Particles of Stainless Steel 316L
2012 (English)In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 7, no 12, 11678-11695 p.Article in journal (Refereed) Published
Abstract [en]

Material properties, corrosion, and metal release from stainless steel powders are important factors to assess any occupational health hazards. This paper elucidates the corrosion behavior of stainless steel particles (inert-gas-atomized AISI 316L powders sized < 45μm, polished and non-polished) compared with corresponding massive low-sulfur bulk sheet material. Electrochemical measurements using a microcapillary technique are compared with ex-situ optical and scanning electron microscopy imaging and electron dispersive X-ray spectroscopy elemental analysis on the same area of individual particles. Non-polished 316L particles were significantly more passive compared to polished massive sheet and polished particles that in general showed a similar corrosion behavior. Corrosion was not induced by bulk compositional differences but could be attributed to surface inhomogeneities. The results are in agreement with the high passivity of non-polished particles in macroscopic studies, an effect caused by an unique surface oxide, characterized in part I of this paper series.

Keyword
stainless steel, surface oxide, powder, pitting corrosion, passive films
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-105519 (URN)000312936700003 ()2-s2.0-84871115971 (Scopus ID)
Funder
Swedish Research CouncilFormas
Note

QC 20130124

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
12. Metal release from stainless steel powders and massive sheets - comparison and implication for risk assessment of alloys
Open this publication in new window or tab >>Metal release from stainless steel powders and massive sheets - comparison and implication for risk assessment of alloys
2013 (English)In: Environmental Sciences: Processes and Impacts, ISSN 2050-7887, Vol. 15, no 2, 381-392 p.Article in journal (Refereed) Published
Abstract [en]

Industries that place metal and alloy products on the market are required to demonstrate them being safe for all intended uses, and that any risks to humans, animals or the environment are adequately controlled. This requires reliable and robust in-vitro test procedures. The aim of this study is to compare the release of alloy constituents from stainless steel powders of different grades (focus on AISI 316L) and production routes into synthetic body fluids with the release of the same metals from massive sheet in relation to material and surface characteristics. The comparison is justified by the fact that the difference between massive surfaces and powders from a metal release/dissolution and surface perspective is not clearly elucidated within current legislations. Powders and abraded and aged (24 h) massive sheets were exposed to synthetic solutions of relevance for biological settings and human exposure routes, for periods up to one week. Concentrations of released iron, chromium, nickel, and manganese in solution were measured, and the effect of solution pH, acidity, complexation capacity, and proteins elucidated in relation to surface oxide composition and its properties. Implications for risk assessments based on in-vitro metal release data from alloys are elucidated.

Keyword
Patch Test Reactivity, Particles In-Vitro, Ion Release, Nickel Release, Pure Metals, Orthodontic Appliances, Ferrochromium Alloy, Contact-Dermatitis, Oxygen Reduction, Aisi 316l
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-105520 (URN)10.1039/C2EM30818E (DOI)000315397700008 ()2-s2.0-84874439615 (Scopus ID)
Note

QC 20130213

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2016-08-30Bibliographically approved

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