Proportion Of Cu Research Articles

Assessment of Post-eutectic Reactions in Multicomponent Al-Si Foundry Alloys Containing Cu, Mg, and Fe

Post-eutectic reactions occurring in Al-Si hypoeutectic alloys containing different proportions of Cu, Mg, and Fe were thoroughly investigated in the current study. As-cast microstructures were initially studied by optical and electron microscopy to investigate the microconstituents of each alloy. Differential scanning calorimetry (DSC) was then used to examine the phase transformations occurring during the heating and cooling processes. Thermodynamic calculations were carried out to assess the phase formation under equilibrium and in nonequilibrium conditions. The Q-Al5Cu2Mg8Si6 phase was predicted to precipitate from the liquid phase, either at the same temperature or earlier than the θ-Al2Cu phase depending on the Cu content of the alloy. The AlCuFe-intermetallic, which was hardly observed in the as-cast microstructure, significantly increased after the solution heat treatment in the alloys containing high Cu and Fe contents following a solid-state transformation of the β-Al5FeSi phase. After the solution heat treatment, the AlCuFe-intermetallics were mostly identified with the stoichiometry of the Al7Cu2Fe phase. Thermodynamic calculations and microstructure analysis helped in determining the DSC peak corresponding to the melting temperature of the N-Al7Cu2Fe phase. The effect of Cu content on the formation temperature of π-Al8Mg3FeSi6 is also discussed.

Accumulation and effects of metal mixtures in two seaweed species

Metal pollution, due to various anthropogenic sources, may pose a threat to marine ecosystems. Metals can be introduced into food chains via bioaccumulation in primary producers, and may potentially lead to toxic effects. Macroalgae are used as food by a wide variety of organisms, and are therefore extremely important in aquatic systems. This study investigated the accumulation and effects of metals in two macroalgae species. The green seaweed, Ulva lactuca and the red seaweed, Agardhiella subulata were each concurrently exposed to five metals (Cu, Ni, Pb, Cd, and Zn) and U. lactuca was also exposed to each metal individually for 48h. Metal accumulation in the seaweed was measured, and various photosynthetic parameters were assessed, using imaging pulse amplitude modulated (PAM) fluorometry. Increased metal accumulation occurred in both seaweed species after 48h exposure to metal mixtures and each metal individually. The distribution of metals in both seaweed species changed with increasing metal exposure concentrations, resulting in higher proportions of Cu and Zn in the metal-exposed groups, as compared to respective controls. Further, U. lactuca accumulated higher concentrations of metals when exposed to each metal individually rather than in metal mixtures, suggesting interactions among metals for uptake and/or bioaccumulation. Significant impairment of photosynthetic parameters in U. lactuca was observed after exposure to 100 and 1000μg/L metal mixtures, as well as 100μg/L of either Cd or Cu. These results demonstrate metal bioaccumulation and toxic effects in important primary producers, and may have implications for higher trophic levels.

Effects of Different Doping Ratio of Cu Doped CdS on QDSCs Performance

We use the successive ionic layer adsorption and reaction (SILAR) method for the preparation of quantum dot sensitized solar cells, to improve the performance of solar cells by doping quantum dots. We tested the UV‐Vis absorption spectrum of undoped CdS QDSCs and Cu doped CdS QDSCs with different doping ratios. The doping ratios of copper were 1 : 100, 1 : 500, and 1 : 1000, respectively. The experimental results show that, under the same SILAR cycle number, Cu doped CdS quantum dot sensitized solar cells have higher open circuit voltage, short circuit current density photoelectric conversion efficiency than undoped CdS quantum dots sensitized solar cells. Refinement of Cu doping ratio are 1 : 10, 1 : 100, 1 : 200, 1 : 500, and 1 : 1000. When the proportion of Cu and CdS is 1 : 10, all the parameters of the QDSCs reach the minimum value, and, with the decrease of the proportion, the short circuit current density, open circuit voltage, and the photoelectric conversion efficiency are all increased. When proportion is 1 : 500, all parameters reach the maximum values. While with further reduction of the doping ratio of Cu, the parameters of QDSCs have a decline tendency. The results showed that, in a certain range, the lower the doping ratio of Cu, the better the performance of quantum dot sensitized solar cell.

Construction of Cu/ZrO2/Al2O3 composites for ethanol synthesis: Synergies of ternary sites for cascade reaction

The hydrogenation of dimethyl oxalate (DMO) to ethanol involves the stepwise hydrogenation of CO bonds and hydrogenolysis of CO bonds. In the present work, the assembly of ternary active sites (Cu, ZrO2, Al2O3 sites) for this reaction was investigated. The calcination temperature was demonstrated to have profound influences on the catalytic performance, evolutions of texture and structure properties and functionality of active phases of the ternary catalysts with similar compositions. The Cu/ZrO2/Al2O3 catalyst calcined at a high temperature of 750°C exhibited an ethanol yield up to 97.4% and stable performance (>200h). Key to success is the concurrence of the stable metallic Cu sites with more proportions of Cu+ sites, active crystalline ZrO2 phases and sufficient acid sites which were generated upon high temperature calcination. The high-temperature calcination annealed Cu particles into large ones, facilitating the high stability. Another factor for the good stability is the formation of CuAl2O4 spinel and the resulted strong interactions between Cu and Al2O3 after reduction. Overall, the design of efficient multifunctional catalysts for hydrogenation/hydrogenolysis of CO/CO bonds lies in the adequate assembly and modulation of textural, structural and surface properties of catalysts. The structure-performance relationships were well elucidated by the analysis of structural and surface properties of active phases and catalytic performance, which provide more rational choices for making high-performance catalysts for CO hydrogenation and CO hydrogenolysis reactions.

On the control of copper colloidal distribution by humic substances in the Penzé estuary

In this study, we investigated the variations of colloidal Cu in a temperate macrotidal estuarine system (Penzé, NW France). The originality of this work resides on examining seven colloidal/dissolved fractions at seven different periods of the year whereas previous studies on estuaries generally considered two or three fractions and were focused on a unique survey. A high proportion of Cu (∼90%) was generally found as colloids (5kDa–0.45μm) throughout the salinity gradient with divergent size distributions being observed over the seasonal cycle. This consisted essentially in two contrasted periods, i.e. winter-spring with a greater association of Cu with high molecular weight (HMW) compounds (50kDa–0.45μm) and summer-autumn with Cu being found mainly as low molecular weight (LMW) forms (5–50kDa). The comparison of Cu with humic substances (HS) data allowed to us to highlight the importance of the pedogenic refractory organic matter in controlling the concentrations and the size distribution of Cu in the estuary. In the mixing zone, Cu behaved conservative in autumn and winter but important additions of HMW compounds were observed in spring in the lower estuary as the result of particulate organic matter degradation in the sediment. Although HS appears to be the background chelators of Cu in the systems, the strong benthic inputs occurring in spring may be of different (biotic) origin and may be in part responsible for the higher association of Cu with HMW compounds.

Effect of Compost on the Distribution of Copper in Heavy Metal Contaminated Soil

Pot experiments were carried out to study the effect of compost application amount on the distribution of copper in heavy metal contaminated soil. The results showed that the total Cu content reduced 11.54%, 11.60%, 22.02%, 25.27%, 7.08% and 3.65% after the amendment of 0, 20, 40, 60, 80, 100 g/kg compost to soil with Brassica juncea, respectively. The amount of water-soluble fraction had no correlation with the compost application amount. However, compost amendment decreased the proportion of Cu in the exchangeable and residual fractions, and increased the percentage of Cu in the carbonate bound, Fe-Mn oxide bound and organic-bound Cu. Furthermore, though the mobility factor of Cu decreased slightly only from 16.64% to 16.27-16.52% due to the addition of compost, the addition of compost to soil can immobilize the heavy metal through bound to organic matter and therefore, lowered their mobility and their phytotoxicity.

Recovery of phosphorus from sewage sludge in combination with the supercritical water process.

In this paper, the fraction transformation and recovering of phosphorus (P) from sewage sludge (SS) residues, derived from supercritical water process, was investigated by extraction and precipitation processes. In addition, the form of heavy metals existing during the recovery process is also discussed. First, P in the solid residues was recovered by acid leaching with HCl, and then the derived P was adsorbed by activated alumina (Al(2)O(3)). Finally, the Al2O3 was desorbed with low concentration of NaOH. Results showed that 80% organic P was converted into HCl-P. The total P (the chief ingredient of HCl-P) in solid residue increased from 86.1 to 95.6% as temperature increased from 350 to 400 °C. The amount of P in the solid residue that was dissolved by 1 M HCl was 97.8%, and over 95% of P in the leaching solution (15 mg/L for P concentration) was adsorbed after 5.0 g of Al(2)O(3) powder was added. The amount of P desorbed from Al(2)O(3) with 0.1 M NaOH was 98.7%. Ultimately, over 85% of TP in SS was recovered. Moreover, the proportion of Cu, Zn and Pb in the extracted P products was lower than 5%.

Pigment changes during processing of green table olive specialities treated with alkali and without fermentation

Green table olive preparations including an alkaline treatment, but not preservation by natural fermentation, such as Castelvetrano-style, are gaining importance in international trade. One of the main highly valued characteristics for this product is a bright green colour, as similar as possible to the fresh fruit. Large proportions of Cu–chlorophyll complexes have been quantified in commercial products of Castelvetrano-style table olives thus in the present work the changes in the chlorophyll and carotenoid composition of olive fruits during this processing style were investigated. The high alkaline pH of the process was the most important feature governing the subsequent transformation of the chlorophyll pigments initially present in the fresh fruit. During processing, the main transformations of pigments were due to allomerization and solvolysis reactions of chlorophylls a and b, which affected the isocyclic ring of the chlorophyll structure but not the Mg atom that remained, and did not change substantially the pigment colour and, consequently, the fruit colour. No Cu–chlorophyll derivatives were detected. Then, even though the intense alkali treatment of the olives may cause such damage in the fruit cells that enables contact between the chlorophyll derivatives and the endogenous Cu of the fruit, the absence of acidic conditions during the olive processing did not lead to the previous reaction of Mg replacement by 2H, which is necessary for the following insertion of Cu. With respect to the carotenoid fraction, any noticeable change took place.

New copper binding components of blood plasma (992.1)

It has been assumed for some time that the main Cu‐containing proteins in blood plasma are ceruloplasmin (Cp), albumin and transcuprein/a2‐macroglobulin, Cp being the main ferroxidase (Fx) implicated in mediating efflux of iron from certain cells. Recent studies in our laboratory suggest the picture is much more complex, and that other known and unknown factors containing Cu are still to be identified. We had previously shown in mice that knocking out Cp only knocked down plasma Fx activity by half. We now have evidence that knocking out hephaestin (Hp) a membrane‐tethered Cp‐homologue reduces plasma Fx activity and a peak in the Cu profile obtained by size exclusion chromatography (SEC), indicating that solubilized Hp may be entering the circulation. Also, a patient with twice normal level of plasma Cu but Cp protein in the normal range had twice normal levels of Fx activity, suggesting that ratios of holo to apo‐Cp were elevated or that another Fx increased in response to the contraceptives. Use of the anticoagulant, EDTA, to collect plasma had a dramatic effect on SEC Cu profiles, moving a large proportion of Cu in larger components (but not Cp) to one of low molecular weight normally present in trace amounts, which is not Cu‐EDTA or metallothionein. We conclude that the proportions of plasma Cu associated with Cp and Fxs can vary widely and speculate that a copper peptide normally attached to other proteins is dislodged by EDTA.Grant Funding Source: HHMI 52007532

Insight into the Tunable CuY Catalyst for Diethyl Carbonate by Oxycarbonylation: Preparation Methods and Precursors

Three different methods were used to prepare CuY catalysts, which play an important role in Cu loading and ion-exchange level during the oxidative carbonylation of ethanol to synthesize diethyl carbonate. Of the prepared CuY catalysts, those synthesized by the ammonia evaporation method exhibited a significantly enhanced activity compared to those obtained by the other two methods. In addition, under optimized conditions, four different copper precursors were applied to adjust the textural properties and chemical states of the CuY catalysts. To obtain a deep understanding of their structure–performance relationship, XRD, XPS, CO adsorption, DRIFTS, and NH3 TPD were conducted to characterize the CuY catalysts. The experimental results indicated that the catalytic performances were in line with the proportions of Cu+ in CuY catalysts, which can be regulated by cupric precursors. In addition, the textural structures of the catalysts and the acidity and type of Cu+ species influenced by the precursors were al...

An Experimental Investigation on the Solubility of Zr in Cu-Sn Alloys

An experimental investigation on the solubility of Zr in Cu-Sn alloy was conducted in a resistance furnace. The solubility of Zr in Cu-Sn alloy was determined by investigating the influence of different conditions such as the ratio of Cu-Sn alloy and temperature. The solubility of Zr in Cu-Sn alloy changes with the proportion of Cu and Sn, and it increases with the increasing of Cu content. The experimental temperature has a significant effect on the solubility of Zr in Cu-Sn alloy. The maximum solubility of Zr in Cu-Sn alloy is 6.2 mass % at 900 °C with the mass ratio of Cu : Sn = 8:2.

Preferential CO oxidation on Pt–Cu/Al2O3 catalysts with low Pt loadings

This work demonstrates that a small loading of Pt (0.2–0.5 wt.%) selectively located at the top of the Cu/Al2O3 solid is enough to obtain active catalysts for the COPrOx reaction. The characterizations of the catalysts prepared in this work using different Pt:Cu ratios show that the phases formed strongly depend on the Cu and Pt loadings. For the samples with 4 wt.% of Cu, the formation of defective CuAl2O4-like species is predominant, with Cu2+ occupying distorted sites in the alumina surface. For the samples with 8 wt.% of Cu, CuO and metallic Cu in the form of small crystals are observed besides Cu2+. For both 0.2 and 0.5 wt.% of Pt, some proportion of Cu–Pt alloy is found which increased with the Cu content. Metallic Pt particles are only observed by EXAFS for the samples with a higher loading of the noble metal.The higher CO conversions at low temperatures were obtained for the Pt0.5Cu8/Al2O3 sample, probably due to the simultaneous formation of small Pt crystals in close contact with CuO. The XPS results show that a strong surface enrichment in Pt takes place in all the samples. Thus, a small loading of the noble metal is enough to obtain effective catalysts. The surface Pt enrichment observed is most probably due to the impregnation of the Pt salt onto the Cu/Al2O3 solid, with a relatively low calcination temperature (300 °C) that prevents the formation of bulky CuAl2O4 spinel crystals.

Evidence of sulfur-bound reduced copper in bamboo exposed to high silicon and copper concentrations

We examined copper (Cu) absorption, distribution and toxicity and the role of a silicon (Si) supplementation in the bamboo Phyllostachys fastuosa. Bamboos were maintained in hydroponics for 4 months and submitted to two different Cu (1.5 and 100 μm Cu2+) and Si (0 and 1.1 mM) concentrations. Cu and Si partitioning and Cu speciation were investigated by chemical analysis, microscopic and spectroscopic techniques. Copper was present as Cu(I) and Cu(II) depending on plant parts. Bamboo mainly coped with high Cu exposure by: (i) high Cu sequestration in the root (ii) Cu(II) binding to amino and carboxyl ligands in roots, and (iii) Cu(I) complexation with both organic and inorganic sulfur ligands in stems and leaves. Silicon supplementation decreased the visible damage induced by high Cu exposure and modified Cu speciation in the leaves where a higher proportion of Cu was present as inorganic Cu(I)S compounds, which may be less toxic.

Dependence of the properties of copper zinc tin sulfide thin films prepared by electrochemical deposition on sulfurization temperature

Copper zinc tin sulfide (CZTS, Cu2ZnSnS4) is a low band gap semiconductor that is attractive for use in solar cells. We investigated the dependence of the structure and properties of CZTS thin films on the temperature used to sulfurize precursor thin films composed of copper, zinc and tin fabricated by electrochemical deposition. The precursor films were sulfurized in a furnace with three zones, which allowed fine control of the sulfurization temperature between 250 and 400 °C. X-ray diffraction and Raman spectroscopic measurements confirmed that the films were composed of CZTS following sulfurization. The grain size and crystallinity of the films increased with sulfurization temperature. The composition of CZTS also varied with sulfurization temperature. The proportions of Cu and Zn increased while that of Sn decreased with increasing sulfurization temperature. Absorption and reflectance spectra revealed that the absorption coefficients and band gaps of the CZTS films varied with sulfurization temperature between 3–4.1 × 104 cm−1 and 1.4–1.53 eV, respectively. Solar cells containing CZTS sulfurized at 400 °C showed a maximum efficiency of 2.04 %, which was attributed to the higher crystallinity and larger grain size of CTZS compared with thin films sulfurized at lower temperatures. Our results show that control of sulfurization temperature is an important factor in optimizing the performance of CZTS thin films in solar cells.

Highly efficient catalyst PdCl2–CuCl2–KOAc/AC@Al2O3 for gas-phase oxidative carbonylation of methanol to dimethyl carbonate: Preparation and reaction mechanism

The supported Wacker catalysts previously used for the synthesis of dimethyl carbonate (DMC) by gas-phase oxidative carbonylation of methanol have the drawbacks of low selectivity and poor catalytic stability. To solve these problems, PdCl2–CuCl2–KOAc/AC was treated by both Al2O3 and dilute hydrochloric acid to obtain PdCl2–CuCl2–KOAc/AC@Al2O3 in this work. The treatment brought about not only the higher activity but also the better stability and selectivity: 98% of DMC selectivity to methanol, 70% of DMC selectivity to CO, and space–time yield of DMC ranging from 600 to 700gL-cat−1h−1 for the runtime of 40h. PdCl2–CuCl2–KOAc/AC@Al2O3 was characterized and the results showed that it possessed enlarged specific surface area (BET), enriched active components on the surface (SEM), increased proportion of Cu+/Cu2+ and new Cu2O crystalline phase formed (XPS), as compared with PdCl2–CuCl2–KOAc/AC. The new formed Cu2O can be used not only as a catalyst for the synthesis of DMC but also as an inhibitor for the loss of Cl− by the reaction of Cu2O with Cl− to CuCl, resulting in the promotion of the catalytic stability. The characterization of the recovered catalyst further identified that the inhibition of KCl crystal formation and the increase in Cu+/Cu2+ proportion could improve the catalytic stability and selectivity. In addition, the higher ratio of Cu+/Cu2+ can reduce Pd2+ concentration and prohibited side-reaction of CO oxidation, so DMC selectivity to CO is increased. On the basis of activity evaluation and characterization, the catalytic reaction mechanism is proposed.

Diet composition as a cause of different contaminant exposure in two sympatric passerines in the Middle Urals, Russia

Contaminant exposure can vary between species but primary causes of it are often unclear. In order to estimate heavy metal intake of two sympatric passerines – Ficedula hypoleuca Pall. and Parus ater L. – we studied nestling diet and metal concentrations in prey invertebrates, near the Middle Ural copper smelter and in an unpolluted area. Diet of P. ater contained more Cu, Cd and Zn compared to F. hypoleuca and the same amount of Pb. Contribution of different prey taxa to bird metal intake was not equal to their dietary proportion. Proportion of Cu, Zn, Pb and Cd provided to birds by spiders and molluscs, as well as Cd and Pb provided by ants and imagoes Diptera, exceeded their dietary fraction by several times. In contrast, the contribution of Lepidoptera and sawfly larvae to bird metal intake was less than their dietary proportion. Pollution-related changes in the diet modified bird contaminant exposure along with pollutant concentrations in preys.

Zn(II) Ions Substantially Perturb Cu(II) Ion Coordination in Amyloid-β at Physiological pH

The interaction of Cu(II) and Zn(II) ions with amyloid-β (Aβ) plays an important role in the etiology of Alzheimer's disease. We describe the use of electron spin resonance (ESR) to measure metal-binding competition between Cu(II) and Zn(II) in amyloid-β at physiological pH. Continuous wave ESR measurements show that the affinity of Cu(II) toward Aβ(1-16) is significantly higher than that of Zn(II) at physiological pH. Importantly, of the two known Cu(II) coordination modes in Aβ, component I and component II, Zn(II) displaces Cu(II) only from component I. Our results indicate that at excess amounts of Zn(II) component II becomes the most dominant coordination mode. This observation is important as Aβ aggregates in the brain contain a high Zn(II) ion concentration. In order to determine details of the metal ion competition, electron spin echo envelope modulation experiments were carried out on Aβ variants that were systematically (15)N labeled. In the presence of Zn(II), most peptides use His 14 as an equatorial ligand to bind Cu(II) ions. Interestingly, Zn(II) ions completely substitute Cu(II) ions that are simultaneously coordinated to His 6 and His 13. Furthermore, in the presence of Zn(II), the proportion of Cu(II) ions that are simultaneously coordinated to His 13 and His 14 is increased. On the basis of our results we suggest that His 13 plays a critical role in modulating the morphology of Aβ aggregates.

Dielectric and Spectroscopic properties of CuO doped multi-component Li2O[sbnd]PbO[sbnd]B2O3[sbnd]SiO2[sbnd]Bi2O3[sbnd]Al2O3 glass system

Multi-component silicate glasses of the chemical composition 19.4Li2O20PbO20B2O330SiO2 (10−x) Bi2O30.6 CuO: x Al2O3 with x ranging from 0 to 5mol% have been synthesized.A variety of spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties (over a range of frequency and temperature) of these glasses have been investigated as a function of Al2O3 concentration. The results of optical absorption and ESR spectral studies have indicated that a part of copper ions do exist in Cu+ state in addition to Cu2+ state especially in the samples containing low concentration of Al2O3. The IR and Raman spectral studies have revealed that there is a decreasing degree of disorder in the glass network with increase in the concentration of Al2O3 upto 3.0mol%. The values of dielectric parameters viz., dielectric constant, loss and ac conductivity at any frequency and temperature are observed to decrease as the concentration of Al2O3 is increased up to 3.0mol%. Such changes have been attributed to increase of redox ratio or increasing proportions of Cu+ ions that take part in the glass network with CuO4 structural units The quantitative analysis of the results of ac conductivity and dielectric properties have indicated a decrease in the insulating character of the glasses when the concentration of Al2O3 is raised beyond 3.0mol% in the glass network. This has been attributed to adaption of aluminium ions from tetrahedral co-ordination to octahedral co-ordination and also due to declustering influence of copper ions by aluminium ions in the glass network.

H2S splitting on Cu(110): Insight from combined periodic density functional theory calculations and microkinetic simulation

Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H2S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H2S → H2S* → SH* → S* and (2) 2H2S → 2H2S* → 2SH* → S* + H2S* → S* + H2S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H2S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H2S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H2S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc.

Spatial distribution and speciation of copper in root tips of cucumber revealed by μ-XRF and μ-XANES

The localization, biotransformation, and chemical speciation of copper in root tips of cucumber (Cucumis sativus) were investigated using synchrotron-based micro X-ray fluorescence (μ-XRF) and micro X-ray absorption near edge structure (μ-XANES). The highest content of Cu was found in root cap and meristematic zone whereas low Cu content in elongation and maturation zone. There was a dramatic increase of Cu content in root cap and meristematic zone after treatment with 100 μM CuSO4 for 72 h. The μ-XANES analysis revealed that most of Cu in root tip was bound with alginate, citrate, and cysteine-like ligands whereas rarely deposited in form of CuO. From root cap to maturation zone, the proportion of Cu bound with alginate-like ligands increased whereas that bound with citrate-like ligands decreased. The proportion of Cu bound with cysteine-like ligands increased from root cap to elongation zone but sharply declined in maturation zone. The results suggested that Cu was chelated by S ligands in the cell walls which protect protoplasm against possible damage caused by Cu excess.