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Item type:Publication, Effect of the concentration and the type of dispersant on the synthesis of copper oxide nanoparticles and their potential antimicrobial applications(American Chemical Society, 2021-07-27)High Resolution Image Download MS PowerPoint Slide The bactericidal properties of copper oxide nanoparticles have growing interest due to potential application in the medical area. The present research investigates the influence of sodium dodecyl sulfate (SDS) and poly(vinylpyrrolidone) (PVP) on the production of copper oxide nanoparticles prepared from copper sulfate (CuSO 4 ) and sodium borohydride (NaBH 4 ) solutions. Different analytical techniques were used to determine the crystal nature, mean size diameter, and surface morphology of the copper oxide nanoparticles. The X-ray diffraction (XRD) patterns showed formation of nanoparticles of cuprite (Cu 2 O) and tenorite (CuO) when PVP and SDS were added at the beginning of the reaction. In fact, when the Cu/PVP ratio was 1.62, Cu 2 O nanoparticles were obtained. In addition, nanoparticles of CuO were synthesized when the Cu/PVP ratios were 0.54 and 0.81. On the other hand, a mixture of copper oxides (CuO and Cu 2 O) and cuprite (Cu 2 O) was obtained when PVP (Cu/PVP = 0.81 and 1.62) and SDS (Cu/SDS = 0.90) were added 30 min after the beginning of the reaction. Transmission electron microscopy (TEM) images show agglomerated nanoparticles with a size distribution ranging from 2 to 60 nm, while individual particles have sizes between 4.1 ± 1.9 and 41.6 ± 12.8 nm. The Kirby–Bauer method for the determination of antibacterial activity shows that small CuO (4.1 ± 1.9 nm) and Cu 2 O (8.5 ± 5.3 nm) nanoparticles inhibit the growth of Escherichia coli, Staphylococcus aureus MRSA, S. aureus and Pseudomonas aeruginosa bacteria. The antibacterial test of cotton fabric impregnated with nanoparticles shows positive results. The determination of the optimal ratio of copper oxide nanoparticles per cm 2 of fabric that are able to exhibit a good antibacterial activity is ongoing.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Copper Tannate (CuTn) based coating on 3D printed face masks(Trans Tech Publications Ltd, 2022-01-01)The impact of COVID-19 crisis on global supply chains caused a critical shortage of essential goods like medical devices. Additionally, massive consumption increased mask contamination and waste. 3D printing has become a fast and versatile manufacturing alternative that prevents a single use of masks. However, SARS-CoV-2 virus can persist on plastic surfaces for days. This study proposes the optimization of 3D printed masks, by applying a coating rich in hydrolyzable tannins and copper, in order to diminish the virus presence. Different paints were formulated with copper tannate and applied on thermoplastic polyurethane 3D panels to test bacterial stability. Results showed a significant reduction of colony-forming units on coated polymeric surfaces. Paints pigmented with copper tannates could improve the protection provided by printed masks, even against the COVID-19 virus. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Genesis of the exotic chrysocolla — “copper pitch/wad” — atacamite/brochantite ore at the Exótica (Mina Sur) deposit, Chuquicamata, Chile(Springer Science+Business Media, 2022-11-09)Detailed mineralogical and textural studies, combined with sequential X-ray diffraction and geochemical modeling, helped to solve the “copper pitch/wad” enigma in the Exótica deposit located downstream of the Chuquicamata porphyry copper deposit. Copper pitch and copper wad are essentially chrysocolla with co-precipitated Mn oxides, mainly birnessite, as well as pseudo-amorphous Mn oxide/oxyhydroxides. Linking the mineralogical, geochemical, and textural evidences with the geological, tectonic, and climatic evolution of the Chuquicamata–Calama area, a four-step genetic model for the evolution of the Exótica deposit is presented: (A) formation of a mature supergene enrichment profile at Chuquicamata (~ 30–25 Ma to ~ 15 Ma) during an erosion-dominated regime (∼900 m of erosion) which was accompanied by acidic (pH ∼2–4) Cu-Mn-Si-dominated rock drainage (ARD) with fluid flow southwards through the Exótica valley towards the Calama Basin, resulting in a strongly kaolinized and chrysocolla/copper wad-impregnated bedrock of the Exótica deposit; (B) deposition of the Fortuna gravels in the Exótica valley (starting ∼19 Ma) intercepted the Cu-Mn-Si-dominated ARD, triggering the main chrysocolla, copper pitch/wad mineralization as syn-sedimentary mineralization by chiefly surficial flow in strongly altered gravels; (C) tectonic freezing and onset of hyper-aridity (∼15–11 Ma) exposed the enriched chalcocite blanket of Chuquicamata to oxidation, resulting in acidic (pH ~ 2–4) and Cu-Si-dominated solutions with less Mn. These solutions percolated in a slightly more reducing groundwater flow path and mineralized relatively unaltered gravels with pure chrysocolla; and (D) ingression of confined chloride-rich groundwater in the upper oxidation zone of Chuquicamata, most likely between 6 and 3 Ma, is responsible for the atacamite/brochantite mineralization (pH ~ 5.5–7) of mainly unaltered gravels in the northern and central part of the Exótica deposit. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Neoformation of exotic copper minerals from gel-like precursors at the Exótica deposit, Chuquicamata, Chile(Springer Science+Business Media, 2022-11-16)At the Exótica deposit, south of the giant porphyry copper deposit of Chuquicamata (Atacama Desert, Chile), Cu-rich groundwater seeped out at several locations in the Exótica open pit (Mina Sur) during sampling in 2009–2011. At their outflows, these solutions formed blueish and greenish copper-bearing gel-like precipitates. These gels contained atacamite and copper sulfate hydroxides such as devilline, spangolite, posnjakite, schulenbergite, and brochantite, which were identified by XRD, SEM, ESEM, and FTIR. The formation of the gel materials was studied under humid and dry conditions during and after maturation and water evaporation. Atacamite was found associated to outflowing saline solutions with pH 5.7, SO4/Cl weight ratios of 0.42–0.48, SO4/NO3 ratios of 0.48–0.50. These solutions are seen as an expression of the the lower aquifer of the Calama basin. Most copper sulfate hydroxides (spangolite, posnjakite, schulenbergite) were associated with slightly acidic freshwaters (pH 6.0 to 6.5, SO4/Cl ratios of 3.08–4.99, SO4/NO3 ratios of 2.52–3.13). In contrast, devilline formed in gels with near neutral to slightly alkaline water (pH 7.2 to 7.8, SO4/Cl ratio of 8.34, and SO4/NO3 ratio of 6.05). Non-copper-bearing precipitates formed by evaporation of the supernatant solutions from the gel. Gypsum precipitated first, then blödite (sodium-magnesium sulfate), and finally halite. Slightly negative sulfur isotope values suggest that the sulfur source in the neoformed gels is primarily the oxidation of sulfides rather than sulfate of sedimentary origin. The studied copper-gel seeps suggest that they might represent a modern precursor of the latest atacamite-brochantite-gypsum mineralization event at Exótica. These data support that the atacamite-brochantite-gypsum mineralization at Exótica is linked to the inflow of Cl-SO4-dominated groundwater from the lower saline aquifer of the Calama basin into the Chuquicamata-Exótica-Radomiro Tomic complex. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, How Does China Economic Policy Uncertainty (EPU) Impact Copper-Firms’ Stock Returns and Copper Prices Returns?(Emerald Publishing, 2023-06-29)This study focuses on how China EPU may impact copper-firms stock returns and also how China EPU mediates between stock returns and copper prices returns. Design/methodology/approach: The sample consists of 44 copper firms from January 2011 to March 2022. The study also considers a subsample of 29 net-exporters countries. Panel data methodology is used, allowing to control for unobservable heterogeneity and endogeneity problems. The equations are estimated through a dynamic panel using the generalized methods of moments (GMM). Findings: China EPU has a negative and statistically significant relationship with stock returns. Copper price returns are positively associated with stock returns. This research also considers two scenarios: high and low levels of China EPU. For high levels of China EPU states it is reported a negative relationship between stock returns and China EPU and copper price returns show a positive relationship with stock returns. Research limitations/implications: There is need to explore other metals for what China exhibits a high demand and observe if China EPU and Global EPU have similar impacts on stock returns. It will be useful to identify main firm's consumers of copper and these other metals to explore the relationship between EPU and stock returns. Originality/value: To the best of the authors’ knowledge, this is the first paper that analyzes China EPU index and its impact on both copper-firms stocks returns and on changes in copper prices. This is done using all public copper firms worldwide. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, How Does Economic Policy Uncertainty (EPU) Impact Copper-Firms’ Stock Returns? International Evidence(Elsevier Ltd, 2023-03-01)Using monthly data, we study 43 copper firms between January 2011 and March 2022. We analyze how copper-firms stock returns depend on copper-spot prices returns. Nevertheless, the main contribution of this article is to study how changes in Global EPU (GEPU) and Local EPU may impact on copper-firms stock returns and how both of them may influence the sensitivity of stock returns to copper prices returns. We find that both GEPU and Local EPU have a statistically significant and negative impact on stock returns. We also study regimes of high and low levels of EPU (Global and Local). For high levels of GEPU we find a negative relationship between stock returns and GEPU and for low levels of GEPU we detect a positive relationship. We also consider how high levels and low levels of Local EPU impact the relationship between copper spot returns and stock returns. When there are high levels of GEPU the sensitivity of stock returns to copper spot returns increases and the opposite is verified when there are low levels of GEPU. Using Local EPU we do not find significant changes in the sensitivity of stock returns to copper spot returns. As robustness test, we consider firms from other four industries (Gold, Oil, Electric Distribution and Gas Distribution). Most of the results show different behavior in each industry regarding the association between EPU and stock returns. We also run the main equations considering a six-factor model for returns (five factors from Fama and French) and the momentum factor. Finally, we do the analysis for copper future returns (90 days and 15 months), reporting similar results. We do not find significant changes in the results after doing all the robustness checking. - Some of the metrics are blocked by yourconsent settings
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Item type:Publication, Authoritarian Practices Between ‘Para-Coloniality’ and ‘Cheap Security’: When Chinese State Capital Meets Neoliberal Copper Mining (and Protests) in Las Bambas, Peru(Taylor & Francis, 2023-03-05)How does Chinese state capital operate in the neoliberal setting of Peruvian mining? The article tackles this question by focusing on Las Bambas, a large mine in the Andean highlands of Apurimac. We argue that China’s quest for Peruvian copper entwines state capital with neoliberal and authoritarian practices of state violence in a case of ‘para-coloniality.’ This concept explains how Chinese mining operations build on and reproduce the legacies of European colonialism and authoritarian rule under Fujimorismo to extract natural resources from formerly colonized territories. A corollary element in this relationship is that of ‘cheap security’, i.e. the Peruvian state’s practice of legally selling its policing services to mining companies who use them to discipline dissidents. The article draws on Critical Geopolitics, Legal Sociology and Political Ecology and highlights the shifting hierarchies of power that shape conflicts around copper extraction in the Andean highlands of Peru. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, A Diachronic Archaeometallurgy Study of Metal Fishhooks in Huanchaco: Alloys and Manufacturing Techniques(John Wiley and Sons, 2025)Archaeological excavations at three sites in Huanchaco, Moche Valley, North Coast of Peru, have yielded metal fishhooks in domestic and funerary context occupations from 150/50 bc to ad 1530. The marine‐oriented nature of the Huanchaco occupations points to the necessity of using metal fishhooks in their daily subsistence activities. However, metal fishhooks seem to have been of more exclusive usage rather than of common availability. This article focuses on the results obtained through optic microscopy, X‐ray fluorescence and scanning electron microscopy with disperse spectrometry energy and digital radiographic imagery done on the metal of these artefacts. We conclude that copper was the preferred metal during all periods. However, there are slight differences in the alloys employed within and between societies and time periods, while the manufacturing technique seems to have been the same (plastic deformation and annealing) with a few variances over time.1