Influence of Proteins and Building Direction on the Corrosion and Tribocorrosion of CoCrMo Fabricated by Laser Powder Bed Fusion.

Cobalt-chromium-molybdenum (CoCrMo) alloys are common wear-exposed biomedical alloys and are manufactured in multiple ways, increasingly using additive manufacturing processes such as laser powder bed fusion (LPBF). Here, we investigate the effect of proteins and the manufacturing process (wrought vs LPBF) and building orientation (LPBF-XY and XZ) on the corrosion, metal release, tribocorrosion, and surface oxide composition by means of electrochemical, mechanical, microscopic, diffractive, and spectroscopic methods. The study was conducted at pH 7.3 in 5 g/L NaCl and 5 mM 2-(N-morpholino) ethanesulfonic acid (MES) buffer, which was found to be necessary to avoid metal phosphate and metal-protein aggregate precipitation. The effect of 10 g/L bovine serum albumin (BSA) and 2.5 g/L fibrinogen (Fbn) was studied. BSA and Fbn strongly enhanced the release of Co, Cr, and Mo and slightly enhanced the corrosion (still in the passive domain) for all CoCrMo alloys and most for LPBF-XZ, followed by LPBF-XY and the wrought CoCrMo. BSA and Fbn, most pronounced when combined, significantly decreased the coefficient of friction due to lubrication, the wear track width and severity of the wear mechanism, and the tribocorrosion for all alloys, with no clear effect of the manufacturing type. The wear track area was significantly more oxidized than the area outside of the wear track. In the reference solution without proteins, a strong Mo oxidation in the wear track surface oxide was indicative of a pH decrease and cell separation of the anodic and cathodic areas. This effect was absent in the presence of the proteins.

The ability of sweat and buffer solutions to reduce hexavalent chromium of relevance for leather extraction.

The European Union restricted the amount of hexavalent chromium (Cr(VI)) in leather in 2015, but skin allergy cases due to Cr-tanned leather are not declining. Standardized extraction methods have been criticized to both over- and underestimate the expected amount of bioavailable Cr(VI) in leather. This study aims to evaluate the ability of four extraction solutions to reduce or preserve Cr(VI): artificial sweat solutions (ASWs) of pH 4.7, 6.5, and 8.0, and phosphate buffer (PB) of pH 8.0. This was investigated by incubating each solution with added Cr(VI) as a function of time, and then measuring the recovered Cr(VI). All solutions, especially PB, preserved Cr(VI) for 24 h. These solutions were also pre-exposed to Cr-free vegetable-tanned leather (VTL) before incubation with Cr(VI). Released vegetable tannin species strongly reduced Cr(VI), with up to 4000 µg/L added Cr(VI) reduced in all solutions after 24 h. However, after 1 h, Cr(VI) was still detectable in extraction solutions at pH 6.5 and above. The reduction of Cr(VI) in relevant extraction solutions is hence a process dependent on time, pH, and the presence of co-released leather species. All extraction solutions, but least PB, have the potential to underestimate any Cr(VI) present on the surface of leather.

Genotoxicity and inflammatory potential of stainless steel welding fume particles: an in vitro study on standard vs Cr(VI)-reduced flux-cored wires and the role of released metals.

Welders are daily exposed to various levels of welding fumes containing several metals. This exposure can lead to an increased risk for different health effects which serves as a driving force to develop new methods that generate less toxic fumes. The aim of this study was to explore the role of released metals for welding particle-induced toxicity and to test the hypothesis that a reduction of Cr(VI) in welding fumes results in less toxicity by comparing the welding fume particles of optimized Cr(VI)-reduced flux-cored wires (FCWs) to standard FCWs. The welding particles were thoroughly characterized, and toxicity (cell viability, DNA damage and inflammation) was assessed following exposure to welding particles as well as their released metal fraction using cultured human bronchial epithelial cells (HBEC-3kt, 5-100 µg/mL) and human monocyte-derived macrophages (THP-1, 10-50 µg/mL). The results showed that all Cr was released as Cr(VI) for welding particles generated using standard FCWs whereas only minor levels (< 3% of total Cr) were released from the newly developed FCWs. Furthermore, the new FCWs were considerably less cytotoxic and did not cause any DNA damage in the doses tested. For the standard FCWs, the Cr(VI) released in cell media seemed to explain a large part of the cytotoxicity and DNA damage. In contrast, all particles caused rather similar inflammatory effects suggesting different underlying mechanisms. Taken together, this study suggests a potential benefit of substituting standard FCWs with Cr(VI)-reduced wires to achieve less toxic welding fumes and thus reduced risks for welders.

Analytical survey of tattoo inks-A chemical and legal perspective with focus on sensitizing substances.

BACKGROUND: Tattoo inks have been reported to elicit allergic contact dermatitis. OBJECTIVES: To investigate the labels and the contents of metals and pigments in tattoo inks, considering restrictions within the European Union. METHODS: Seventy-three tattoo inks currently available on the market, either bought or donated (already used), were investigated for trace metals and pigments by inductively coupled plasma mass spectrometry and by matrix-assisted laser desorption/ionization time of flight tandem mass spectrometry. RESULTS: Ninety-three percent of the bought tattoo inks violated European, legal requirements on labeling. Fifty percent of the tattoo inks declared at least one pigment ingredient incorrectly. Sixty-one percent of the inks contained pigments of concern, especially red inks. Iron, aluminium, titanium, and copper (most in green/blue inks) were the main metals detected in the inks. The level of metal impurities exceeded current restriction limits in only a few cases. Total chromium (0.35-139 µg/g) and nickel (0.1-41 µg/g) were found in almost all samples. The levels of iron, chromium, manganese, cobalt, nickel, zinc, lead, and arsenic were found to covary significantly. CONCLUSIONS: To prevent contact allergy and toxic reactions among users it is important for tattoo ink manufacturers to follow the regulations and decrease nickel and chromium impurities.

Using chemical speciation modelling to discuss variations in patch test reactions to different aluminium and chromium salts.

BACKGROUND: Allergic contact dermatitis to metals is diagnosed by applying a metal salt in a patch test. The bioavailability of the metal salt might depend on the choice of metal salt, the concentration, sweat composition, and pH. OBJECTIVES: The main purpose of this study was to apply chemical speciation modelling, which is based on experimentally derived input data and calculates the concentrations of chemical forms (species) in solutions, to reproduce and discuss clinical patch test results of aluminium and chromium. METHODS: Joint Expert Speciation System (JESS), Hydra/Medusa, and Visual MINTEQ were employed to study the bioavailable fraction and chemical form of clinically applied aluminium and chromium salts as a function of salt type, applied concentration, sweat composition, and pH. RESULTS: Investigated aluminium and chromium salts can have a very low bioavailability with a large dependency on sweat composition, pH, metal salt, and concentration. Both aluminium and chromium ions could shift the pH towards acidic or basic values based on their chemical form. CONCLUSIONS: Reported seasonal and interpatient variability in positive reactions to aluminium is likely related to sweat pH and composition. Potassium dichromate increases the pH, whereas aluminium and trivalent chromium chloride strongly decrease the pH, possibly increasing skin diffusion.

Detection of gold cysteine thiolate complexes on gold nanoparticles with time-of-flight secondary ion mass spectrometry.

Gold (Au) nanoparticles (NPs) are widely used in nanomedical applications as a carrier for molecules designed for different functionalities. Previous findings suggested that biological molecules, including amino acids, could contribute to the dissolution of Au NPs in physiological environments and that this phenomenon was size-dependent. We, therefore, investigated the interactions of L-cysteine with 5-nm Au NPs by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). This was achieved by loading Au NPs on a clean aluminum (Al) foil and immersing it in an aqueous solution containing L-cysteine. Upon rinsing off the excessive cysteine molecules, ToF-SIMS confirmed the formation of gold cysteine thiolate via the detection of not only the Au-S bond but also the hydrogenated gold cysteine thiolate molecular ion. The presence of NaCl or a 2-(N-morpholino)ethanesulfonic acid buffer disabled the detection of Au NPs on the Al foil. The detection of larger (50-nm) Au NPs was possible but resulted in weaker cysteine and gold signals, and no detected gold cysteine thiolate signals. Nano-gold specific adsorption of L-cysteine was also demonstrated by cyclic voltammetry using paraffine-impregnated graphite electrodes with deposited Au NPs. We demonstrate that the superior chemical selectivity and surface sensitivity of ToF-SIMS, via detection of elemental and molecular species, provide a unique ability to identify the adsorption of cysteine and formation of gold-cysteine bonds on Au NPs.

Quantification of aluminium release from Finn chambers under different in vitro test conditions of relevance for patch testing.

BACKGROUND: Contact allergy to aluminium (Al) might pose a risk of false-positive readings of patch-test results when testing with Finn chambers. OBJECTIVES: To quantify the release of Al from empty Al Finn chambers, covered Finn Aqua chambers, and Al Finn chambers containing different baseline patch-test substances. METHODS: Al Finn chambers of different conditions and with different patch-test substances were tested in artificial sweat and their Al release was analyzed by atomic absorption spectroscopy and inductively coupled plasma sector field mass spectrometry. RESULTS: The amount of Al released from empty Finn chambers corresponded to a skin dose of 0.03%-0.5% Al chloride hexahydrate applied in plastic chambers. Although most patch-test substances reduced the release of Al from the Finn chambers due to covering the surface, some substances significantly increased the release of Al from the Finn chambers, most notable for Caine mix II 10% pet., Myroxylon pereirae 25% pet., and sodium tetrachloropalladate hydrate 3.0% pet. CONCLUSIONS: The release of Al from Finn chambers corresponds in some cases to clinically relevant concentrations of Al for Al-sensitized individuals.

Metals in used and unused metalworking fluids: X-ray fluorescence spectrometry as a screening test.

BACKGROUND: Exposure to metalworking fluids (MWFs) is a well-known cause of occupational contact dermatitis. OBJECTIVES: We aimed to (1) determine the amount of nickel, chromium, and cobalt in large samples of used and unused MWFs collected from metalworking plants in Denmark, and (2) evaluate a handheld x-ray fluorescence (XRF) device as a screening instrument for metals in MWFs. METHODS: A handheld XRF device was used to screen for metals in MWFs. All samples were also analyzed for concentrations of nickel, chromium, and cobalt using graphite furnace atomic absorption spectroscopy (GFAAS). RESULTS: GFAAS analysis showed that 13 of 80 samples (16.3%) contained >1 mg/kg (ppm) nickel (range: 6.4-17.7 mg/kg), 3 of 80 (3.8%) contained >1 (range: 1.4-3.1) mg/kg chromium, and 1 of 80 (1.3%) contained 1.3 mg/kg cobalt. XRF-screening detected nickel in eight samples (range: 2.5-15.5 mg/kg), but only one sample with 3.0 (±0.5) mg/kg was found subsequently to contain 9.9 (0.02) mg/kg nickel by GFAAS. Although no chromium was found by XRF analysis, cobalt was found in two samples with 6 (±1.5) mg/kg and 5 (±1.5) mg/kg, subsequently found to contain 0.1 (±0.01) mg/kg and 0.08 (±0.01) mg/kg by GFAAS. Similar concentrations of nickel were found in used (N = 6, range: 6.4-17.7 mg/kg) and unused MWFs (N = 7, range: 9.1-17.3 mg/kg). CONCLUSION: Considerable levels of nickel, chromium, and cobalt were found in some used and unused MWFs indicating that these might represent a source of metal allergy. The XRF device is a poor screening test for these metals in MWFs.

Release of hexavalent chromium from cement collected in Honduras and Sweden.

Hexavalent chromium in cement 5-8 mg/kg hexavalent chromium (Cr(VI)) was found in Honduran cement samples, which was slightly higher than in Swedish samples. Variable amounts of Cr(VI) (0.4 and 4.7 mg/kg) found in Swedish cement samples that were older than 1 year. There are still many countries that do not have a compulsory reduction of Cr(VI) in cement. Several measures can be employed to reduce risks related to Cr(VI) in cement.

Macrophage-Assisted Dissolution of Gold Nanoparticles.

Gold nanoparticles (AuNPs) are readily functionalized and considered biocompatible making them useful in a wide range of applications. Upon human exposure, AuNPs will to a high extent reside in macrophages, cells that are designed to digest foreign materials. To better understand the fate of AuNPs in the human body, their possible dissolution needs to be explored. In this study, we tested the hypothesis that macrophages, and especially stimulated macrophages, can impact the dissolution of AuNPs in a size-dependent manner. We developed an in vitro method to compare the dissolution of citrate coated 5 and 50 nm-sized AuNPs, in terms of released gold ions as measured by inductive coupled mass spectrometry (ICP-MS), in (i) cell medium (alone) (ii) in medium with macrophages present and (iii) in medium with lipopolysaccharide (LPS) triggered macrophages (simulating inflammatory conditions). We found an evident, time-dependent dissolution of AuNPs in cell medium, corresponding to 3% and 0.6% of the added amounts of 5 and 50 nm AuNPs, respectively, after 1 week (168 h) of incubation. The dissolution of 5 nm AuNPs was further increased to 4% in the presence of macrophages and, most strikingly, 14% was dissolved in case of LPS-triggering. In contrast, only a minor increase was observed for 50 nm AuNPs after 1 week in the presence of LPS-triggered macrophages compared to medium alone. Dissolution experiments in the absence of cells highlighted the importance of biomolecules. Our findings thus show dissolution of citrate coated AuNPs that is dependent on size, presence of macrophages, and their inflammatory state. These findings have implications for understanding the transformation/dissolution and fate of AuNPs.

Mechanistic insight on the combined effect of albumin and hydrogen peroxide on surface oxide composition and extent of metal release from Ti6Al4V.

The titanium-aluminium (6 wt%)-vanadium (4 wt%) (Ti6Al4V) alloy is widely used as an orthopedic and dental implant material due to its high corrosion resistance in such environments. The corrosion resistance is usually determined by means of electrochemical methods, which may not be able to detect other chemical surface reactions. Literature findings report a synergistic effect of the combination of the abundant protein albumin and hydrogen peroxide (H2 O2 ) on the extent of metal release and corrosion of Ti6Al4V. The objectives of this study were to gain further mechanistic insight on the interplay of H2 O2 and albumin on the metal release process of Ti6Al4V with special focus on (1) kinetics and (2) H2 O2 and albumin concentrations. This was accomplished mainly by metal release and surface oxide composition investigations, which confirmed the combined effect of H2 O2 and albumin on the metal release process, although not detectable by electrochemical open circuit potential measurements. A concentration of 30 mM H2 O2 induced substantial changes in the surface oxide characteristics, an oxide which became thicker and enriched in aluminum. Bovine serum albumin (BSA) seemed to be able to deplete this aluminum content from the outermost surface or at least to delay its surface enrichment. This effect increased with increased BSA concentration, and for time periods longer than 24 h. This study hence suggests that short-term (accelerated) corrosion resistance measurements are not sufficient to predict potential health effects of Ti6Al4V alloys since also chemical dissolution mechanisms play a large role for metal release, possibly in a synergistic way. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 855-867, 2019.

Chromium(III), chromium(VI) and cobalt release from leathers produced in Nicaragua.

BACKGROUND: Leather exposure has been associated with chromium (Cr) and cobalt (Co) contact dermatitis. Cr(VI) in leather is now restricted to <3 mg/kg in the EU. Cr(III) is not restricted. OBJECTIVES: To analyse 29 differently coloured Cr-tanned leather samples from two Nicaraguan tanneries, and to compare their release of Cr, Cr(VI) and Co with that of leathers produced in Europe. METHODS: Cr, Cr(VI) and Co were extracted in phosphate buffer for 3 hours at 25°C according to EN ISO 17075. Atomic absorption spectroscopy and spectrophotometry were used for detection of the metals in phosphate buffer. RESULTS: There was no difference in total Cr or Cr(VI) release between European and Nicaraguan leathers. There was no association between Cr(VI) and total Cr release. Co was released primarily from leathers of one tannery. Cr(III) was released in significantly higher amounts than Cr(VI). CONCLUSIONS: Future investigations and regulations should focus on Cr(III) and Co as well as on Cr(VI).

Synergistic effects of metal-induced aggregation of human serum albumin.

Exposure to cobalt (Co), chromium (Cr), and nickel (Ni) occurs often via skin contact and from different dental and orthopedic implants. The metal ions bind to proteins, which may induce structural changes and aggregation, with different medical consequences. We investigated human serum albumin (HSA) aggregation in the presence of CoII, CrIII, and/or NiII ions and/or their nanoparticle precipitates by using scattering, spectroscopic, and imaging techniques, at simulated physiological conditions (phosphate buffered saline - PBS, pH 7.3) using metal salts that did not affect the pH, and at HSA:metal molar ratios of up to 1:8. Co ions formed some solid nanoparticles in PBS at the investigated conditions, as determined by nanoparticle tracking analysis, but the CrIII anions and NiII ions remained fully soluble. It was found that all metal ions induced HSA aggregation, and this effect was significantly enhanced when a mixture of all three metal ions was present instead of any single type of ion. Thus, the metal ions induce aggregation synergistically. HSA aggregates formed linear structures on a mica surface in the presence of CrIII ions. A clear tendency of aggregation and linearly aligned aggregates was seen in the presence of all three metal ions. Spectroscopic investigations indicated that the majority of the HSA molecules maintained their alpha helical secondary structure and conformation. This study highlights the importance of synergistic effects of metal ions and/or their precipitates on protein aggregation, which are highly relevant for implant materials and common exposures to metals.

Non-oxidative hair dye products on the European market: What do they contain?

BACKGROUND: Hair dyeing is very common and may cause allergic contact dermatitis. Oxidative (often termed permanent or semi-permanent) hair dye products have constituted the focus of market surveys and toxicological risk assessments, while non-oxidative (semi-permanent, temporary or direct) products have not been assessed. OBJECTIVES: To identify the hair dye substances presently used in non-oxidative hair dye products in Europe. METHODS: Ingredient label data on eligible products in 5 European countries were collected, and 289 different non-oxidative hair dye products were included in this study. RESULTS: Up to 9 hair dye substances were present in each product. Sixty-eight individual hair dye substances were identified on the 289 product labels, and their occurrence ranged from 0.3% to 34%. There were differences concerning substances used and their number per product between products of different consistency and colour. CONCLUSIONS: The hair dye substances in non-oxidative hair dye products are different from those in oxidative hair dye products, and are currently not covered by patch test series. The toxicological and skin-sensitizing profile of the substances in non-oxidative hair dye products, as well as their concentrations, should be further investigated.

Size-dependent genotoxicity of silver, gold and platinum nanoparticles studied using the mini-gel comet assay and micronucleus scoring with flow cytometry.

Metallic nanoparticles (NPs) are promising nanomaterials used in different technological solutions as well as in consumer products. Silver (Ag), gold (Au) and platinum (Pt) represent three metallic NPs with current or suggested use in different applications. Pt is also used as vehicle exhaust catalyst leading to a possible exposure via inhalation. Despite their use, there is limited data on their genotoxic potential and possible size-dependent effects, particularly for Pt NPs. The aim of this study was to explore size-dependent genotoxicity of these NPs (5 and 50 nm) following exposure of human bronchial epithelial cells. We characterised the NPs and assessed the viability (Alamar blue assay), formation of DNA strand breaks (mini-gel comet assay) and induction of micronucleus (MN) analysed using flow cytometry (in vitro microflow kit). The results confirmed the primary size (5 and 50 nm) but showed agglomeration of all NPs in the serum free medium used. Slight reduced cell viability (tested up to 50 µg/ml) was observed following exposure to the Ag NPs of both particle sizes as well as to the smallest (5 nm) Au NPs. Similarly, at non-cytotoxic concentrations, both 5 and 50 nm-sized Ag NPs, as well as 5 nm-sized Au NPs, increased DNA strand breaks whereas for Pt NPs only the 50 nm size caused a slight increase in DNA damage. No clear induction of MN was observed in any of the doses tested (up to 20 µg/ml). Taken together, by using the comet assay our study shows DNA strand breaks induced by Ag NPs, without any obvious differences in size, whereas effects from Au and Pt NPs were size-dependent in the sense that the 5 nm-sized Au NPs and 50 nm-sized Pt NPs particles were active. No clear induction of MN was observed for the NPs.

Chromium(III) release from chromium-tanned leather elicits allergic contact dermatitis: a use test study.

BACKGROUND: Chromium (Cr) is a common skin sensitizer. The use of Cr(VI) in leather is restricted in the EU, but that of Cr(III) is not. OBJECTIVES: To assess whether prolonged exposure to Cr-tanned leather with mainly Cr(III) release may elicit allergic contact dermatitis in Cr-allergic individuals. METHOD: Ten Cr-allergic subjects and 22 controls were patch tested with serial dilutions of Cr(III) and Cr(VI), and with leather samples. They then conducted a use test with a Cr-tanned and a Cr-free leather bracelet over a period of 3 weeks, for 12 h per day. Cr deposited on the skin from the bracelets was measured in the controls, and the diphenylcarbazide test for Cr(VI) and extraction tests for Cr(III) and Cr(VI) were conducted for the different leathers. RESULTS: Four of 10 Cr-allergic subjects developed positive reactions to the Cr-tanned bracelet within 7-21 days, whereas only 1 of 10 had a positive patch test reaction to this leather. Cr released from the Cr-tanned leather was most probably entirely Cr(III), with a quantifiable amount being deposited on the skin. CONCLUSIONS: This study strongly suggests that prolonged and repeated exposure to Cr-tanned leather with mainly Cr(III) release is capable of eliciting allergic contact dermatitis in Cr-allergic individuals.

Nanoparticles of WC-Co, WC, Co and Cu of relevance for traffic wear particles - Particle stability and reactivity in synthetic surface water and influence of humic matter.

Studded tyres made of tungsten carbide cobalt (WC-Co) are in the Northern countries commonly used during the winter time. Tungsten (W)-containing nano- and micron-sized particles have been detected close to busy roads in several European countries. Other typical traffic wear particles consist of copper (Cu). The aims of this study were to investigate particle stability and transformation/dissolution properties of nanoparticles (NPs) of WC-Co compared with NPs of tungsten carbide (WC), cobalt (Co), and Cu. Their physicochemical characteristics (primarily surface oxide and charge) are compared with their extent of sedimentation and metal release in synthetic surface water (SW) with and without two different model organic molecules, 2,3- and 3,4-dihydroxybenzoic acid (DHBA) mimicking certain sorption sites of humic substances, for time periods up to 22 days. The WC-Co NPs possessed a higher electrochemical and chemical reactivity in SW with and without DHBA molecules as compared with NPs of WC, Co, and Cu. Co was completely released from the WC-Co NPs within a few hours of exposure, although it remained adsorbed/bonded to the particle surface and enabled the adsorption of negatively charged DHBA molecules, in contrast with the WC NPs (no adsorption of DHBA). The DHBA molecules were found to rapidly adsorb on the Co and Cu NPs. The sedimentation of the WC and WC-Co NPs was not influenced by the presence of the 2,3- or 3,4-DHBA molecules. A slight influence (slower sedimentation) was observed for the Co NPs, and a strong influence (slower sedimentation) was observed for the Cu NPs in SW with 2,3-DHBA compared with SW alone. The extent of metal release increased in the order: WC < Cu < Co < WC-Co NPs. All NPs released more than 1 wt-% of their metal total mass. The release from the Cu NPs was most influenced by the presence of DHBA molecules.

Surface passivity largely governs the bioaccessibility of nickel-based powder particles at human exposure conditions.

The European chemical framework REACH requires that hazards and risks posed by chemicals, including alloys and metals, are identified and proven safe for humans and the environment. Therefore, differences in bioaccessibility in terms of released metals in synthetic biological fluids (different pH (1.5-7.4) and composition) that are relevant for different human exposure routes (inhalation, ingestion, and dermal contact) have been assessed for powder particles of an alloy containing high levels of nickel (Inconel 718, 57 wt% nickel). This powder is compared with the bioaccessibility of two nickel-containing stainless steel powders (AISI 316L, 10-12% nickel) and with powders representing their main pure alloy constituents: two nickel metal powders (100% nickel), two iron metal powders and two chromium metal powders. X-ray photoelectron spectroscopy, microscopy, light scattering, and nitrogen absorption were employed for the particle and surface oxide characterization. Atomic absorption spectroscopy was used to quantify released amounts of metals in solution. Cytotoxicity (Alamar blue assay) and DNA damage (comet assay) of the Inconel powder were assessed following exposure of the human lung cell line A549, as well as its ability to generate reactive oxygen species (DCFH-DA assay). Despite its high nickel content, the Inconel alloy powder did not release any significant amounts of metals and did not induce any toxic response. It is concluded, that this is related to the high surface passivity of the Inconel powder governed by its chromium-rich surface oxide. Read-across from the pure metal constituents is hence not recommended either for this or any other passive alloy.