Knowledge on metal release processes from stainless steel powder, which can be potentially inhaled at occupational settings, is essential within the framework of human health and environmental risk assessments. An in-depth knowledge concerning powder history, physical properties of particles (e.g. size, morphology, and active surface area) combined with their chemical properties (such as the chemical composition of the particles and their metal release behavior) is needed for better understanding of the interaction mechanisms between metal powders and humans. So far, limited in vitro and in vivo studies exist that assess the correlation between stainless steel surface properties, protein adsorption effects, and metal release processes. The aim of this study is to add information to fill this knowledge gap through in vitro investigations of protein-induced metal release (iron, nickel, chromium, and manganese) and induced surface changes of five differently sized and/or produced (water-atomized (WA) and gas-atomized (GA)) stainless steel powder particles (three austenitic: AISI 316L, 310B, and 304B; one martensitic: AISI 410L; and one ferritic: AISI 430L) after exposure up to one week into a phosphate buffer saline (PBS) solution of pH 7.2-7.4 containing either lysozyme (LYS) or bovine serum albumin (BSA). The results show that the outmost surface oxide composition of the powders strongly depends on the production method and particle size. Gas-atomized 316L powder particles (with spherical shapes) indicated a high relative manganese content in their surface oxide (more significant in the case of 316L particles sized <4µm), while no manganese compounds were detectable in the surface oxide of water-atomized powders (of irregular particle shapes). Although austenitic stainless steels should present non-magnetic properties, the investigation of magnetic properties indicated that differently sized gas-atomized 316L particles and water-atomized 304B were to some extent ferromagnetic suggesting the presence of ferrite. BSA induced a significant enrichment of chromium in the surface oxide of all investigated powders (especially for ferritic WA430L and austenitic WA316L), except in the case of 316L powders (<4µm) showing no significant change. Metal release studies illustrated that both proteins enhanced the amount of released metal, with a preferential iron release from water-atomized particles and manganese release from gas-atomized powders. BSA-containing medium induced the highest extent of metal release in comparison with other tested biological media (up to 35-fold increase in the case of ferritic 430L particles produced by water atomization). Comparison between the metal release behavior of particulate and massive stainless steel indicated a significantly higher extent of metal released from abraded stainless steel sheets compared with particles, which is most probably an effect of freshly abraded surfaces of the massive metal sheets, not true for the particles with aged surface oxides, along with the presence of higher relative chromium content in the surface oxide.

Numerous metal release data have been published by the Div. Surface and Corrosion Science and the AISI 316L stainless steel particles’ behavior in artificial lysosomal fluid (ALF). This study aims to evaluate the effect of chemical components in ALF on metal release from stainless steel particles with a bottom-up methodology. Two sizes of 316L stainless steel particles were used to assess the particle size influence on the metal release in detail. The results show that organic complexing agents e.g. lactate, tartrate and citrate are responsible for the high metal release rate in ALF. Correlations between the metal release rate and the number of carboxyl groups of the organic ligand were observed. Moreover, metal release data in this study indicates no synergistic effects in ALF solution, and continued research is on-going to study the synergistic effects further. No quantitative rules of iron, chromium and nickel release from the same stainless particles could be found which may indicate that these metals are released through different pathways e.g. diffusion or chemical dissolution. In different solutions with different chemical components, one or more metal release mechanisms dominate over others and make the metal release rate unpredictable.

Knowledge on metal release processes from stainless steel powder, which can be potentially inhaled at occupational settings, is essential within the framework of human health and environmental risk assessments. An in-depth knowledge concerning powder history, physical properties of particles (e.g. size, morphology, and active surface area) combined with their chemical properties (such as the chemical composition of the particles and their metal release behavior) is needed for better understanding of the interaction mechanisms between metal powders and humans. So far, limited in vitro and in vivo studies exist that assess the correlation between stainless steel surface properties, protein adsorption effects, and metal release processes. The aim of this study is to add information to fill this knowledge gap through in vitro investigations of protein-induced metal release (iron, nickel, chromium, and manganese) and induced surface changes of five differently sized and/or produced (water-atomized (WA) and gas-atomized (GA)) stainless steel powder particles (three austenitic: AISI 316L, 310B, and 304B; one martensitic: AISI 410L; and one ferritic: AISI 430L) after exposure up to one week into a phosphate buffer saline (PBS) solution of pH 7.2-7.4 containing either lysozyme (LYS) or bovine serum albumin (BSA). The results show that the outmost surface oxide composition of the powders strongly depends on the production method and particle size. Gas-atomized 316L powder particles (with spherical shapes) indicated a high relative manganese content in their surface oxide (more significant in the case of 316L particles sized <4µm), while no manganese compounds were detectable in the surface oxide of water-atomized powders (of irregular particle shapes). Although austenitic stainless steels should present non-magnetic properties, the investigation of magnetic properties indicated that differently sized gas-atomized 316L particles and water-atomized 304B were to some extent ferromagnetic suggesting the presence of ferrite. BSA induced a significant enrichment of chromium in the surface oxide of all investigated powders (especially for ferritic WA430L and austenitic WA316L), except in the case of 316L powders (<4µm) showing no significant change. Metal release studies illustrated that both proteins enhanced the amount of released metal, with a preferential iron release from water-atomized particles and manganese release from gas-atomized powders. BSA-containing medium induced the highest extent of metal release in comparison with other tested biological media (up to 35-fold increase in the case of ferritic 430L particles produced by water atomization). Comparison between the metal release behavior of particulate and massive stainless steel indicated a significantly higher extent of metal released from abraded stainless steel sheets compared with particles, which is most probably an effect of freshly abraded surfaces of the massive metal sheets, not true for the particles with aged surface oxides, along with the presence of higher relative chromium content in the surface oxide.

Highly corrosion-resistant alloys are used in sensitive environments such as the human body and food environments. However, even tiny amounts of released metals from these surfaces could potentially cause adverse effects. It is hence important to study the biointerface between corrosion-resistant alloys and protein-rich environments. This licentiate thesis focused on the metal release processes for stainless steels and cobalt-chromium-molybdenum (CoCrMo) alloys in different protein-rich environments. It aimed at investigating the effect of protein displacement (Vroman effect), gamma irradiation, and friction on the metal release processes. Trace metal analysis was the main tool, combined with other solution analytical tools, electrochemical methods, and surface sensitive techniques. The effect of gamma irradiation, of relevance for cancer radiotherapy, on metal release from CoCrMo and stainless steel 316L was investigated in Paper I. The effect was minor, however the released amount of metals increased after irradiation causing an enhanced surface passivation effect. Whether the displacement of surface proteins (Vroman effect) was playing a role on the metal release and corrosion processes of stainless steels 316L and 303, and of CoCrMo, was investigated in Papers II and III. A Vroman effect influencing the metal release could be observed for stainless steel 316L, but not for CoCrMo and stainless steel grade 303. However, the displacement of the smaller protein bovine serum albumin (BSA) from the surface by the larger protein fibrinogen (Fbn) was observed for both stainless steel grades. The Vroman effect also caused a higher corrosion susceptibility of stainless steel 303, probably due to a thicker layer or patches of adsorbed Fbn. Most probably, protein aggregation and precipitation caused an underestimation of the extent of metal release, especially in the case of CoCrMo. Protein aggregation and precipitation were significantly observed in all studies, especially for solutions with high protein concentrations (Papers II-IV). The effect of friction, by using different setups (stirring with physical contact and sliding in a pin-on-disk machine), on metal release from stainless steel 316L and CoCrMo was investigated in Papers II and IV. Friction induced an increased extent of metal release, increased protein aggregation and precipitation, and enhanced metal precipitation. A combined friction and complexation effect was observed for stainless steel 316L, resulting in an etching effect and relatively high amounts of released metals. Due to enhanced precipitation effects and the experimental setup, it is recommended to strongly consider protein aggregation and metal precipitation events in systems where this could be expected and where friction is present. Otherwise, there is a risk to strongly underestimate the extent of metal release in these protein-rich environments. / <p>QC 2020-09-28</p>

Corrosion and metal release mechanisms of CoCrMo alloys are at human biological conditions not fully understood. The main objective of this master thesis was to investigate whether the Vroman effect influences the extent of metal release from CoCrMo alloy in mixed protein solutions. The project focuses on the corrosion properties and release of cobalt (Co), chromium (Cr) and molybdenum (Mo) from a CoCrMo alloy into simulated physiological solutions of pH 7.2-7.4 in the presence of proteins. The metal release study was performed in phosphate buffered saline (PBS) for 4 and 24 h at 37 °C with and without different concentration of proteins (bovine serum albumin-BSA and fibrinogen-Fbn from bovine plasma). In order to investigate whether any Vroman effect could affect the extent of released metals in solutions, sequential tests were performed by sampling after 1, 4, 6 and 24 h in solutions that were partially replenished after 5 h. Significant metal-induced protein aggregation and precipitation were observed in solutions of physiologically-relevant protein concentrations (40 g/L BSA and 2.67 g/L Fbn). Cr was strongly enriched in the surface oxide of CoCrMo after exposure in all solutions. This was for all solutions accompanied by metal release processes dominated by Co. Based on electrochemical investigations, the electrochemical activity did not increase, but rather decreased, in protein-containing solutions as compared to PBS alone. This could possibly be explained by blocking of cathodic areas as a result of protein adsorption.

<p>This study has been triggered by the fact that stainless steel is being increasingly used in new applications, where possible environmental effects may be a matter of concern. When stainless steel is exposed to a given environment, a key issue is the release of small amounts of the main alloying elements iron, chromium, nickel and molybdenum. Published release rate data of these elements turned out to be sparse. Furthermore, only little was known about the role of different parameters that may affect the release rate, such as degree of alloying, exposure time and surface finish. Hence, the aim of this study was to develop methodological means and to provide accurate metal release rates of alloying constituents from different grades of stainless steels- austenitic, ferritic and duplex- when exposed to selected environments: artificial rain and synthetic body fluids. The results and discussion have been summarised in this thesis by formulating and answering ten questions, all believed to be crucial for the understanding of possible environmental effects of stainless steels.</p><p>Some common conclusions could be drawn, independent of stainless steel grade and exposure condition. Iron was always preferentially released, and the release rates of chromium, nickel and molybdenum (when measured) were significantly lower than of iron, also when considering the bulk proportion of these elements. The release rate of all elements was initially high and decreased with exposure time, mainly because of an observed enrichment of chromium in the passive film formed.</p><p>The release rates of iron (2 μgcm^-2week^-1) and nickel (0.08 μgcm-²week-¹) from stainless steel from grades 304 and 316 exposed to artificial rain were much lower than corresponding rates for the pure metals (750 μgcm-²week^-1 released Fe and 15 μgcm^-2week^-1 released Ni), whereas chromium exhibited similar release rates from stainless steel and the pure metal (0.1 μgcm^-2week^-1). This implies that the common procedure to calculate release rates, based on the pure metals and the nominal steel composition, significantly overestimates release rates of iron and nickel from stainless steel, but not of chromium.</p><p>Total release rates from seven stainless steel grades in synthetic body fluid were found to decrease with increasing alloy content in the following release rate order: grade 409 >> grade 430 > grades 316L ≈ 201 ≈ 2205 ≈ 304 > grade 310. The release rate was highly sensitive to pH of the synthetic body fluid but only slightly sensitive to stainless steel surface finish.</p>

<p>At present the automotive industry is due to an EU directive, replacing hexavalent chrome on vehicles. This is an extensive job as hexavalent chrome is used all over the vehicle and to large extent on fasteners (screws, nuts, rivets etc.). Chrome (VI) is used as a passivating layer on mainly zinc-iron. When replacing the hexavalent chrome with a chrome (VI) free product, the passivating properties are reduced. One of the alternatives is to replace the zinc-iron coating with a zinc-nickel coating. This coating shows great promise from the corrosion resistance point of view. Zinc-nickel is a cathodically protecting coating, and will in principle dissolve to protect the substrate from corrosion. It is therefore important to understand how, and at what rates nickel is released from zinc-nickel coatings when exposed to a chloride-rich automotive environment. The potential environmental impact of nickel needs to be evaluated before Scania can introduce this alternative as corrosion protection. Tests by Scania have previously shown that contact allergy is not an issue for zinc-nickel coatings with Cr (III) passivation.</p><p>Nickel release rates corresponding to 0,12 mg m^-2yr^-1 for zinc-15 % nickel coatings at a pH of 4,2 were determined from an accelerated corrosion test. Based on these values, less than 1 kg of nickel per year would be released from the Scania rolling stock if Scania were to introduce zinc-nickel coatings preferably on fasteners. This value is low compared to other sources of nickel release. In order to evaluate the toxicity of the released nickel, information about the chemical speciation, i.e. chemical forms, is needed.</p><p>Total or dissolved metal are not good predictors of ecotoxicity of metals. Chemical speciation and bioavailability must be incorporated in toxicity testing. Total or dissolved metal may be used as a worst case approximation.</p>

<p>Humans are exposed to metals and metal-containing materials daily, either conscious, e.g. using metal tools or objects, or unconscious, e.g. during exposure to airborne metal-, and metal-containing particles. The diffuse dispersion of metals from different sources in the society, and the concern related to its potential risk for adverse effects on humans have gained an increased public and governmental attention both on a national and international level. In this context, the knowledge on metal release from metallic objects or metal-containing particles is essential for health risk assessment.</p><p>This thesis focuses on the study of metal release from powder particles of stainless steel and Cu-based materials exposed to synthetic body fluids mainly for simulating lung-like environments. The study comprises: i) development of a suitable experimental method for metal release studies of micron sized particles, ii) metal release data of individual alloy constituents from stainless steel powder particles of different particle sizes, and iii) Cu release from different Cu-based powder particles. In addition, the influence of chemical and physical properties of metallic particles and the test media are investigated. Selected results from Ni powder particles exposed to artificial sweat are presented for comparison. The outcome of this research is summarized through ten questions that are formulated to improve the general understanding of corrosion-induced metal release from metallic particles from a health risk perspective.</p><p>A robust, reproducible, fairly simple, and straightforward experimental procedure was elaborated for metal release studies on particles of micron or submicron size. Results in terms of metal release rates show, for stainless steel powder particles, generally very low metal release rates due to a protective surface oxide film, and Fe preferentially released compared to Cr and Ni. Metal release rates are time-dependent for both stainless steel powder particles and the different Cu-containing powders investigated. The release of Cu from the Cu-containing particles depends on the chemical and compositional properties of the Cu-based material, being either corrosion-induced or chemically dissolved. Moreover, the test medium also influences the metal release process. The metal release rate increases generally with decreasing pH of the test media. However, even at a comparable pH, the release rate may be different due to differences in the interaction between the particle surface and specific media.</p><p>The nature of particles is essentially different compared to massive sheet in terms of physical shape, surface composition and morphology. The surface area, and even the surface composition of metallic particles, depend on the particle size. The specific surface area of particles, area per mass, is intimately related to the particle size and has a large effect on the metal release process. Release rates increase with decreasing particle size due to a larger active surface area that takes part in the corrosion/dissolution process. The surface area that actually is active in the corrosion and metal release process (the effective area) governs the metal release process for both particles and massive sheet of metals or alloys. For particles, the effective surface area depends also on agglomeration conditions of particles during exposure.</p>

This study has been triggered by the fact that stainless steel is being increasingly used in new applications, where possible environmental effects may be a matter of concern. When stainless steel is exposed to a given environment, a key issue is the release of small amounts of the main alloying elements iron, chromium, nickel and molybdenum. Published release rate data of these elements turned out to be sparse. Furthermore, only little was known about the role of different parameters that may affect the release rate, such as degree of alloying, exposure time and surface finish. Hence, the aim of this study was to develop methodological means and to provide accurate metal release rates of alloying constituents from different grades of stainless steels- austenitic, ferritic and duplex- when exposed to selected environments: artificial rain and synthetic body fluids. The results and discussion have been summarised in this thesis by formulating and answering ten questions, all believed to be crucial for the understanding of possible environmental effects of stainless steels. Some common conclusions could be drawn, independent of stainless steel grade and exposure condition. Iron was always preferentially released, and the release rates of chromium, nickel and molybdenum (when measured) were significantly lower than of iron, also when considering the bulk proportion of these elements. The release rate of all elements was initially high and decreased with exposure time, mainly because of an observed enrichment of chromium in the passive film formed. The release rates of iron (2 μgcm-2week-1) and nickel (0.08 μgcm-2week-1) from stainless steel from grades 304 and 316 exposed to artificial rain were much lower than corresponding rates for the pure metals (750 μgcm-2week-1 released Fe and 15 μgcm-2week-1 released Ni), whereas chromium exhibited similar release rates from stainless steel and the pure metal (0.1 μgcm-2week-1). This implies that the common procedure to calculate release rates, based on the pure metals and the nominal steel composition, significantly overestimates release rates of iron and nickel from stainless steel, but not of chromium. Total release rates from seven stainless steel grades in synthetic body fluid were found to decrease with increasing alloy content in the following release rate order: grade 409 &gt;&gt; grade 430 &gt; grades 316L ≈ 201 ≈ 2205 ≈ 304 &gt; grade 310. The release rate was highly sensitive to pH of the synthetic body fluid but only slightly sensitive to stainless steel surface finish. / QC 20120217

Humans are exposed to metals and metal-containing materials daily, either conscious, e.g. using metal tools or objects, or unconscious, e.g. during exposure to airborne metal-, and metal-containing particles. The diffuse dispersion of metals from different sources in the society, and the concern related to its potential risk for adverse effects on humans have gained an increased public and governmental attention both on a national and international level. In this context, the knowledge on metal release from metallic objects or metal-containing particles is essential for health risk assessment. This thesis focuses on the study of metal release from powder particles of stainless steel and Cu-based materials exposed to synthetic body fluids mainly for simulating lung-like environments. The study comprises: i) development of a suitable experimental method for metal release studies of micron sized particles, ii) metal release data of individual alloy constituents from stainless steel powder particles of different particle sizes, and iii) Cu release from different Cu-based powder particles. In addition, the influence of chemical and physical properties of metallic particles and the test media are investigated. Selected results from Ni powder particles exposed to artificial sweat are presented for comparison. The outcome of this research is summarized through ten questions that are formulated to improve the general understanding of corrosion-induced metal release from metallic particles from a health risk perspective. A robust, reproducible, fairly simple, and straightforward experimental procedure was elaborated for metal release studies on particles of micron or submicron size. Results in terms of metal release rates show, for stainless steel powder particles, generally very low metal release rates due to a protective surface oxide film, and Fe preferentially released compared to Cr and Ni. Metal release rates are time-dependent for both stainless steel powder particles and the different Cu-containing powders investigated. The release of Cu from the Cu-containing particles depends on the chemical and compositional properties of the Cu-based material, being either corrosion-induced or chemically dissolved. Moreover, the test medium also influences the metal release process. The metal release rate increases generally with decreasing pH of the test media. However, even at a comparable pH, the release rate may be different due to differences in the interaction between the particle surface and specific media. The nature of particles is essentially different compared to massive sheet in terms of physical shape, surface composition and morphology. The surface area, and even the surface composition of metallic particles, depend on the particle size. The specific surface area of particles, area per mass, is intimately related to the particle size and has a large effect on the metal release process. Release rates increase with decreasing particle size due to a larger active surface area that takes part in the corrosion/dissolution process. The surface area that actually is active in the corrosion and metal release process (the effective area) governs the metal release process for both particles and massive sheet of metals or alloys. For particles, the effective surface area depends also on agglomeration conditions of particles during exposure. / QC 20101119