Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure

Abstract

Iron, chromium, nickel, and manganese released from gas-atomized AISI 316L stainless steel powders (sized <45 and <4 μm) 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 μm), the fine (<4 μm) 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.

Influence of Citric Acid on the Metal Release of Stainless Steels

“…1, Fe was predominantly released from both grades followed by the release of Ni, Cr, and Mn. This is in agreement with previous investigations of metal release from these grades in citric acid and other aqueous acidic or neutral solutions [11][12][13][14][15][16][17][18][19] . The release pattern is related to the passive mixed surface oxide of Cr 2 O 3 and Fe 2 O 3 with metallic nickel present in the alloy surface layer beneath the surface oxide 11,20) .…”

“…The release of Cr was among the investigated alloying constituents most dependent on the pH. Cr released from stainless steel is in its trivalent form at these conditions 13,27) and complexed to citrate 13) . This has been confirmed for as-received 304 exposed for 10 days to 5 g/L citric acid (pH 2.4), measured by stripping voltammetry as in 13) (data not shown).…”

“…Cr released from stainless steel is in its trivalent form at these conditions 13,27) and complexed to citrate 13) . This has been confirmed for as-received 304 exposed for 10 days to 5 g/L citric acid (pH 2.4), measured by stripping voltammetry as in 13) (data not shown). Generally, trivalent Cr shows a slower surface and/or solution complexation compared with the bivalent or trivalent metal ions of Fe, Ni, and Mn 28) .…”

Chemical Stability of Chromium Carbide and Chromium Nitride Powders Compared with Chromium Metal in Synthetic Biological Solutions

“…However, this may be explained by a higher dissolution of Cr 2 N in this solution compared with CrN according to the findings of Lyutaya and Kulik [13] combined with a partial dissolution of chromium(III) oxides observed on the surface of the Cr-N powder by means of XPS. Another reason may be related to the presence of organic complexing agents such as citric acid in ALF, previously shown to enhance the release of metals including chromium from stainless steel [7,41,42].…”

“…Elaborate studies have been performed generating data on release, dissolution, and solubility aspects of chromium and chromium-containing alloys such as stainless steels and ferrochromium alloys [1][2][3][4][5][6][7][8][9], data that has been utilised within the framework of the European chemicals legislation (REACH) implemented in 2007. Bioaccessibility and environmental impact aspects of chromium have been discussed by, for example, [9][10][11].…”