High Concentrations Of Cr Research Articles

An innovative ionic liquid-aqueous biphasic system for simultaneously highly efficient dechroming and collagen recovery from chrome-tanned leather shavings at room temperature

Chrome-tanned leather shavings (CTLS) with abundant collagen of 70–90 wt% but high Cr content of 2–4 wt% are considered as hazardous wastes. Due to the stable covalent bond between Cr and collagen, current processes for collagen recovery from CTLS face challenges including low dechroming efficiency, collagen disruption, high energy and chemical consumption and secondary pollution. In this paper, an innovative IL-targeted homogeneous isolation (IL-THI) process based on the reusable ionic liquid-aqueous biphasic system (IL-ABS) was established for the simultaneous resource recovery and complete dechroming of CTLS at room temperature, with the recovery rate of collagen reached 72.4 % while Cr content in collagen is reduced from 35.65 × 103 mg/kg to 1.78 mg/kg. This IL-ABS enriched TBAH in the upper phase and potassium tartrate in the lower phase. Moreover, TBAH demonstrated excellent reproducibility across five cycles, achieving consistently low Cr content of 2.65 mg/kg in collagen, far below the 50 mg/kg limit in national standards. The triple helix conformation and the molecular weight of the collagen product were confirmed via Fourier-transform infrared spectroscopy, X-ray diffraction analyses, circular dichroism spectra analysis and SDS-PAGE. Moreover, economic calculations demonstrated the suitability of this novel process for sustainable CTLS recovery. The superior dechroming ability of IL-ABS is attributed to the formation of Cr(III)-Tartrate complexes, which preferentially migrate to the lower phase due to the solvophobic effect, while dissolved collagen is recovered from the upper phase, as disclosed by UV–Vis spectra, ICP-OES, and all-atom molecular dynamics simulations. Additionally, IL-THI process demonstrates considerable potential for the isolation of Cr(III) and collagen in solid waste, with low energy consumption, improved separation efficiency, and increased design flexibility.

Assessment of macro, trace and toxic element intake from rice: differences between cultivars, pigmented and non-pigmented rice

Pigmented and non-pigmented rice varieties (grown in different areas) were collected in China, Yunnan, to investigate the content of macro-, trace elements and potentially toxic elements (PTEs), and to assess the health risk associated with dietary intake. The order of elemental concentrations in rice was Mn > Zn > Fe > Cu > Se for trace elements, P > K > Mg > Ca > Na for macro elements, and Cr > As > Cd for PTEs. Rice with a high concentration of essential elements also associated with a high content of PTEs. In addition, higher content of Cr, Mn and Na were found in pigmented rice. The health risk assessment showed that the daily intake of all elements was below the tolerable limit (UL). Moreover the intake of Fe, Zn and Se was far from sufficient for the nutrient requirement. The PTEs in rice dominated the health risk. Of concern is that this rice consumption is likely to contribute to carcinogenic risks in the long term and that adults are at higher health risk from pigmented rice compared to non-pigmented rice. This study confirms that the lack of essential micronutrients in rice and the health risk associated with rice diets should remain a concern.

Risk assessment of trace elements in vegetables grown in river Yamuna floodplain in Delhi.

Urban agriculture is common in fertile river floodplains of many developing countries. However, there is a risk of contamination in highly polluted regions. This study quantifies health risks associated with the consumption of vegetables grown in the floodplain of the urban river 'Yamuna' in the highly polluted yet data-scarce megacity Delhi, India. Six trace elements are analyzed in five kinds of vegetable samples. Soil samples from the cultivation area are also analyzed for elemental contamination. Ni, Mn, and Co are observed to be higher in leafy vegetables than others. Fruit and inflorescence vegetables are found to have higher concentrations of Cr, Pb, and Zn as compared to root vegetables. Transfer Factor indicates that Cr and Co have the highest and least mobility, respectively. Vegetable Pollution Index indicates that contamination levels follow as Cr > Ni > Pb > Zn. Higher Metal Pollution Index of leafy and inflorescence vegetables than root and fruit vegetables indicate that atmospheric deposition is the predominant source. Principal Component Analysis indicates that Pb and Cr have similar sources and patterns in accumulation. Among the analyzed vegetables, radish may pose a non-carcinogenic risk to the age group of 1-5year. Carcinogenic risk is found to be potentially high due to Ni and Cr accumulation. Consumption of leafy vegetables was found to have relatively less risk than other vegetables due to lower Cr accumulation. Remediation of Cr and Ni in floodplain soil and regular monitoring of elemental contamination is a priority.

Spatial separation of photocarriers and selective adsorption on flower-like core-shell heterojunction of Cr(VI) imprinted polymer@BiOI for boosted photocatalytic Cr(VI) reduction

BackgroundConstructing heterojunction photocatalyst is a well-established strategy for enhancing photocatalytic Cr(VI) reduction due to the heightened separation and transfer of photocarriers. Whereas, aimless and random transfer of photocarriers and low photocarrier utilization rate deriving from the weak interface interaction between heterojunction and Cr(VI) are still limited the photocatalytic reduction performance of Cr(VI). MethodsHerein, a flower-like core-shell heterojunction photocatalyst was designed by wrapping a pyridine-based Cr(VI) imprinted polymer (PCIP) onto flower-like BiOI to achieve spatial separation of photocarriers and selective adsorption of Cr(VI), resulting in an outstanding photocatalytic reduction performance of Cr(VI). Significant findingsIn the core-shell heterojunction, photocarriers could be spatially separated, and then brought about high-efficient photocatalytic Cr(VI) reduction close to the selective adsorption sites of Cr(VI). After measurement, the optimal PCIP@BiOI core-shell heterojunction, polymerized for ≈30 min, exhibited a robust photocatalytic reduction performance of Cr(VI), without adding any free radical sacrifice agents. Within 1 h, the aqueous solution containing 100 mg/L of Cr(VI) could be completely removed, and the photocatalytic reduction rate constant of Cr(VI) was ≈20 times superior to BiOI. This study presents a methodology for designing core-shell heterojunction photocatalysts on the basis of inorganic/organic conjunction for environmental remediation of high concentrations of Cr(VI).

Neoproterozoic (ca. 830 Ma) carbonatite dykes from Qianlishan in the western North China Craton: Petrogenesis and metallogenic implications

Carbonatite and the associated alkaline intrusive complexes are the primary sources of light rare earth element (REEs). Our field investigations in the western margin of the North China Craton (NCC) have firstly identified over 20 carbonatite dykes and minor coeval carbonate-rich lamprophyre dykes intruding the Paleoproterozoic Qianlishan Group in the southern Qianlishan area. Zircon LA-ICP-MS U-Pb dating on six carbonatite samples yielded crystallization ages ranging from 835.2 ± 3.7 Ma to 828.9 ± 3.8 Ma, indicating emplacement of the carbonatite dykes at ca. 830 Ma during the Neoproterozoic. Geochemical data show that most of the carbonatite dykes are rich in light REEs with total light REEs > 600 ppm to 4932 ppm, and the carbonate-rich lamprophyre dykes are characterized by high Cr (1219–1267 ppm) and Ni concentrations (857–1076 ppm). Petrological and scanning electron microprobe (SEM) analytical results show that the dominant REE-bearing minerals in the carbonatites are monazite, and other REE-bearing minerals are parisite and bastnäsite. Geochemical and carbon–oxygen isotopic results indicate that the ca. 830 Ma carbonatite dykes were produced by low-degree partial melting of a previously metasomatised subcontinental lithospheric mantle with assimilation of crustal material. Emplacement of the ca. 830 Ma carbonatite and carbonate-rich lamprophyre dykes in the southern Qianlishan area and the previously reported ca. 810 Ma mafic dykes in the middle Qianlishan area occurred in a continental rift environment. Simultaneous development of the Neoproterozoic (830 − 810 Ma) continental rifting events in the western margin of the NCC and the eastern margin of the Alxa Block as previously suggested may indicate a connection between the eastern Alxa Block and the western NCC during and before the middle Neoproterozoic.

Biomonitoring potentially toxic elements in atmospheric particulate matter of greater Dhaka region using leaves ofhigher plants.

In this study, four different plant species, namely Artocarpus heterophyllus, Mangifera indica, Psidium guajava, and Swietenia mahagoni, were selected from seven different locations to assess the feasibility of using them as a cost-effective alternative for biomonitoring air quality. Atmospheric coarse particulate matter (PM10), soil samples, and leaf samples were collected from residential, industrial, and traffic-congested sites located in the greater Dhaka region. The heavy metal concentrations (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in the leaves of the different species, PM10, and soil samples were analyzed. The highest Pb (718ng/m3) and Zn (15,956ng/m3) concentrations were found in PM10 of Kodomtoli which is an industrial area. On the other hand, the highest Fe (6,152ng/m3) and Ni (61.1ng/m3) concentrations were recorded in the PM10 of Gabtoli, a heavy-traffic area. A significant positive correlation (r = 0.74; p < 0.01) between Pb content in plant leaves and PM fraction was found which indicated that atmospheric PM-bound Pb may contribute to the uptake of Pb by plant leaves. The analysis of the enrichmentfactor (EF)revealed that soils were contaminated with Cd, Ni, Pb, and Zn. The abaxial leaf surfaces of Psidium guajava growing at the polluted site exhibited up to a 40% decrease in stomatal pores compared to the control site. Saet's summary index (Zc) demonstrated that Mangifera indica had the highest bioaccumulation capacity. The metal accumulation index (MAI) was also evaluated to assess the overall metal accumulation capacity of the selectedplants. Of the four species, Swietenia mahagoni (3.05) exhibited the highest MAI value followed by Mangifera indica (2.97). Mangifera indica and Swietenia mahagoni were also found to accumulate high concentrations of Pb and Cr in their leaves and are deemed to be good candidates to biomonitor Pb and Cr contents in ambient air.

Effect of Cr content on thermally activated deformation in single-crystal micropillars of Fe–Cr binary alloys

This study identifies the role of solute Cr in the thermal activation process in the plastic deformation of α-(Fe, Cr) ferrite (BCC solid solutions) using micropillar compression tests for micron-sized single-crystals fabricated on various Fe–Cr binary alloys that were solution-treated at 1573 K. Fe–18%Cr single-crystal micropillars with a mean diameter d of ∼2 μm exhibited a relatively higher strain rate sensitivity (m) of 0.12 for the stress required for slip initiation. Larger Fe–18%Cr micropillars (d = 5 μm) exhibited a lower m value of 0.04. The corresponding activation volume of 50 b3 was equivalent to the millimeter-sized pure Fe and Fe–18%Cr alloy specimens (60–70 b3), indicating the prevalence of a general mechanism involving dislocation motion (kink-pair nucleation of screw dislocations). This mechanism controls the thermal activation process of plastic deformation in the Fe–18%Cr alloy, which has sufficient sources for dislocation multiplication. In the Fe–25%Cr and Fe–40%Cr single crystal micropillars, a less pronounced size-dependent m value (0.01–0.03) was determined, almost independent of specimen size. The corresponding activation volumes of large micropillars (74–77 b3) were similar to those of millimeter-sized specimens, which indicates a mild effect of solute Cr atoms on the thermal activation process of dislocation motion in Fe–Cr binary alloys at ambient temperature. Initial dislocations, rather than Cr content in Fe–Cr binary alloys, led to the low changes in size-dependent activation volume of Fe–Cr alloys with higher Cr content. Planar faults (Cr-enriched regions) were observed in Fe–40%Cr alloys, which may become sufficient sources for dislocation nucleation. However, the influence of Cr-enriched regions on dislocation motion remains unclear.

Leachability of hexavalent chromium from fly ash-marl mixtures in Sarigiol basin, Western Macedonia, Greece: environmental hazard and potential human health risk

Hexavalent chromium (Cr (VI)) is an environmental contaminant brining high concerns due to its higher toxicity and mobility in comparison with trivalent chromium Cr(III). Cr (VI) has been linked with several adverse health effects, including respiratory diseases, lung cancer, and skin irritation. The primary sources of it in the environment are industrial activities.Most of the time, fly ash made of lignite can release Cr(VI) when it comes into contact with water in an aquatic environment. The objective of this study is the investigation of Cr (VI) concentration in leachates of fly ash and marl mixtures and the determination of its solubility under different pH conditions. Samples of fly ash were collected from the Power Plant of Agios Dimitrios. Additionally, samples of marl were collected from the mine of South Field, and both samples were mixed and prepared in in different proportions (% w.t.). The leaching experiments were carried out according to the EN-12457/1-4 (2003) standard under different pH conditions and chemical analysis of the leachates were performed by spectrophotometry with diphenylcarbazide (DPC). The environmental footprint of Cr (VI) in the study area was significant, especially in mixtures containing higher concentrations of fly ash. A critical pH range between 6 to 12 is observed. At acidic pH values, a high release of Cr (VI) was observed, while at the mentioned critical values (pH 10–12), a gradual decrease in its leachability was noticed. The high concentrations of Cr (VI) in the industrial area studied require immediate actions in terms of managing and limiting the potential hazardous impacts on the environment and by extension on the public health by developing appropriate prevention strategies.Graphical abstract

Effect of pool temperature on microstructure and corrosion resistance of PTAW Ni layer

In plasma transferred arc welding (PTAW), the weld pool temperature often fluctuates. The spray weld layer is prone to overheating, leading to adverse effect on its performance. This study investigated the influence of spray welding current on the weld pool temperature and in turn on the microstructure, microhardness and corrosion resistance of the PTAW-Ni layer on a steel substrate. Weld pool temperature increased with increasing spray welding current and varied along the welding gun path before reaching the steady state. With increasing pool temperature, more Fe diffused from the substrate into the spray weld layer, leading to a widened fusion zone, an increased dilution rate and a decreased microhardness. The spray weld layer has a dendritic microstructure. The dendrites have a higher Cr content, while the interdendritic regions have a higher Ni content. Increasing weld pool temperature increased diffusion, resulting in reduced enrichment of the Cr and Ni elements. The increase of Fe and decrease of Cr in the spray weld layer caused the decreasing corrosion resistance.

Effects of alloying elements on the microstructure of precipitation strengthened Co-based superalloys

The alloying effects on the microstructure, especially precipitation of harmful phases and solvus temperature of L12-structured γʹ phase, etc., are essential for alloy design and development of precipitation strengthened Co-based superalloys. Based on the newly reported Co30Ni9Al5Mo10Cr2Ta0.03B alloy, alloying elements Mo, Cr, Al, Ta and Ni are systematically changed and alloys are fabricated to investigate their microstructures in two heat treatment statuses, namely homogenization and aging, respectively. Results show that Mo and Cr are γ forming elements and have limited effect on γʹ solvus temperature, but high concentration of Mo and Cr facilitates the formation of harmful μ phase. Al, Ta, and Ni are all γʹ stabilizers and can effectively increase γʹ solvus temperature, but roles of Al, Ta and Ni are different. Increasing Al and Ta would result in other harmful phases, such as the μ phase in the 6Ta and 4Ta alloys, and μ + B2 phases in the 13Al and 11.5Al alloys. However, Ni addition significantly increases solvus temperature and area fraction of γʹ phase without occurrence of harmful phases. The current findings might provide guidelines for design and development of precipitation strengthened Co-based alloys.

Hydrothermal Corrosion of Latest Generation of FeCrAl Alloys for Nuclear Fuel Cladding.

After the Fukushima nuclear disaster, the nuclear materials community has been vastly investing in accident tolerant fuel (ATF) concepts to modify/replace Zircaloy cladding material. Iron-chromium-aluminum (FeCrAl) alloys are one of the leading contenders in this race. In this study, we investigated FA-SMT (or APMT-2), PM-C26M, and Fe17Cr5.5Al over a time period of 6 months in simulated BWR environments and compared their performance with standard Zirc-2 and SS316 materials. Our results implied that water chemistry along with alloy chemistry has a profound effect on the corrosion rate of FeCrAl alloys. Apart from SS316 and Zirc-2 tube specimens, all FeCrAl alloys showed a mass loss in hydrogen water chemistry (HWC). FA-SMT displayed minimal mass loss compared to PM-C26M and Fe17Cr5.5Al because of its higher Cr content. The mass gain of FeCrAl alloys in normal water chemistry (NWC) is significantly less when compared to Zirc-2.

Effects of exogenous riboflavin or cytochrome addition on the cathodic reduction of Cr(VI) in microbial fuel cell with Shewanella putrefaciens.

Bioreduction of Cr(VI) is recognized as a cost-effective and environmentally friendly method, attracting widespread interest. However, the slow rate of Cr(VI) bioreduction remains a practical challenge. Additionally, the direct removal efficiency of microbes for high concentrations of Cr(VI) is not ideal due to the toxicity. Therefore, this study investigated the effects of exogenous riboflavin or cytochrome on the cathodic reduction of Cr(VI) in microbial fuel cells. The results demonstrated that the exogenous riboflavin or cytochrome effectively improved the voltage output of the cells, with riboflavin increasing the voltage by 52.08%. Within the first 24h, the Cr(VI) removal ratio in the normal, cytochrome, and riboflavin groups was 14.3%, 29.3%, and 53.8%, respectively. And the final removal ratio was 55.1%, 69.1%, and 98.0%, respectively. These results showed different enhancement effects of riboflavin and cytochrome on Cr(VI) removal. The analysis of riboflavin and cytochrome contents revealed that the additions did not have a significant impact on the autocrine riboflavin of S. putrefaciens, but affected the autocrine cytochrome. SEM, XPS, and FTIR results confirmed the presence of reduced Cr(III) on the cathode, which formed precipitate and adhered to the cathode surface. The EDS analysis showed that the amount of Cr on the cathode in normal, cytochrome, and riboflavin groups was 4.71%, 6.37%, 7.56%, respectively, which was consistent with the voltage and Cr(VI) removal data. These findings demonstrated the significant enhancement of exogenous riboflavin or cytochrome on Cr(VI) reduction, thereby providing data reference for the future bio-assisted remediation of Cr(VI) pollution.

Effect of Alloying Elements in Steels on the Interfacial Structure and Mechanical Properties of Mg to Steel by Laser-GTAW Hybrid Direct Lap Welding.

Mg alloy AZ31B was directly bonded to SK7 with a low alloy content, DP980 with a high Mn content, 316L with a high Cr and high Ni content by laser-gas tungsten arc welding (GTAW) and hybrid direct lap welding. The results showed that the tensile loads of AZ31B/SK7 and AZ31B/DP980 joints were 283 N/mm and 285 N/mm respectively, while the tensile load of AZ31B/316L joint was only 115 N/mm. The fracture and interface microstructures were observed using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and identified through X-ray diffractometry (XRD). For AZ31B/SK7 and AZ31B/DP980, the interface of the front reaction area and the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase. However, for AZ31B/316L, the interface of the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase, but a multi-layer composite structure consisting of the Mg17Al12 compound layer and eutectic layer was formed in the front reaction area, which led to a deterioration in the joint property. The influencing mechanism of Mn, Cr and Ni elements in steel on the properties and interface structure of the laser-GTAW lap joint between the Mg alloy and the steel was systematically analyzed.

Effect of high-energy shot peening on the corrosion behavior and chloride threshold concentration of AISI 316L stainless steel rebar in simulated concrete pore solution

The corrosion behavior and chloride threshold concentration of AISI 316L stainless steel reinforcement bar (rebar), subjected to high-energy shot peening (HESPed), are compared with its solution-annealed (SAed) counterpart in simulated concrete pore solution (CPS). X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that HESP significantly reduces the surface grain size to the ultrafine/nanometric range and increases the density of various dislocation structures, including dislocation walls and cells. This augmented presence of grain boundaries and dislocations, acting as high diffusivity paths, contributed to the formation of a thicker surface film with higher Cr content and lower donor/acceptor density in the HESPed sample compared to the SAed. Moreover, corrosion behavior analyses in CPSs with NaCl concentrations ranging from 0.0 to 2.0 M demonstrated that HESPed samples exhibit broader passivation ranges, more positive corrosion potentials, and higher polarization resistance under equivalent chloride concentrations. Additionally, threshold chloride concentrations obtained from the potentiodynamic polarization tests show values between 0.5 and 1.0 M for the SAed and between 1.0 and 1.5 M for the HESPed samples. Based on diffusion equations, a physical model is proposed to elucidate the improved behavior resulting from the HESP treatment.

Assessment of medicinal plants colonizing abundantly on metal-enriched fly ash deposits: phytoremediation prospective

Heavy metal-enriched fly ash (FA) deposits are recognized as hazardous contaminated sites on the earth, which pollute our ecosystems. Consequently, the present investigation was carried out to explore the phytoremediation potential of naturally growing medicinal plants in the FA dumpsite. This present study chose two native medicinal plants i.e., Bacopa monnieri and Acmella oleracea found to be naturally colonizing abundantly on FA dumpsite to assess heavy metal accumulation. FA sample of B. monnieri thriving sites found to have metal content in order Mn (216.6)> Cr (39.27)> Zn (20.8)> Ni (16.1)> Cu (15.03)> Co (6.7)> Pb (5.43) whereas for A. oleracea FA dumpsites, the order of metal availability was Mn (750.3)> B (54.5)>Cr (37.2)>Zn (31.33)> Cu (18.7)> Ni (16.93)> Co (7.7)>Pb (4.23). In B. monnieri, higher concentrations of Cr and Mn were observed in the shoot in comparison to the root, indicative of its potential as a hyperaccumulator plant. Conversely, in A. oleracea, greater amounts of Pb were detected in the shoot relative to the root. Hence, it is recommended that B. monnieri and A. oleracea grow on such heavy metal-enriched substrates should be avoided for medicinal purposes; however, these plants can be used for phytoremediation purposes.

Monitoring of the Fluctuation of the Pollutant Load of Leachate Rejected in Environment. Study in the Northeast of Algeria

In order to model the environmental impact of leachate produced at the engineered landfill center (ELC) of Bouguerguer, Guelma located in the north east of Algeria. A physico-chemical characterization during 2020, was carried out in order to estimate this impact. For this purpose fourteen parameters have been studied which are, In vivo: pH, conductivity, Salinity. In vitro: Organic element contents (BOD5, COD); Heavy metal contents (Fe, Zn, Pb, Cd and Cr); The contents of nutrient elements (Nitrate, Nitrite, Ammonium and Suspended matter). The results obtained show that the leachates studied, have the following characteristics: A basic pH of 8,85 , Suspended matter a fairly large load with 5397,92 mg/L. The organic load interpreted by a COD that reaches an average 1603, 75 mg O2/L and a BOD5 that reaches an average of 778,54 mg O2/L, which strongly justifies the presence of organic pollution. The mineral pollution is also present, translated by a high electrical conductivity which reaches an average value of 33,38 mS/cm, Nitrates and nitrites average 15,68 and 17,93 mg/l respectively. The leachates are also characterized by a high content of Fr, Zn, Pb, Cd and Cr with an average of (42,70 ; 10,44 ; 8,27 ; 4,37 and 5,97 mg/l) respectively. Noting that the results obtained constitute the first characterization of leachates in this landfill and thus provide a database for future research.

Performance and properties evolution of near-term accident tolerant fuel: Cr-doped UO2

Chromium-doped UO2 fuel has received significant interest due to the ability for chromium to produce pellets with large average grain size (>30 μm), which has shown to increase fission gas retention during operation. Sintering of chromium-doped UO2 pellets was pursued with oxygen potential and sintering atmosphere controlled to tailor the final microstructure of the material. Chromium additions in this study ranged from 750 to 7800 ppm. Cr concentrations were studied pre and post sintering using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Effects of chromium content on lattice parameter and microstructure were examined with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Contraction of the UO2 lattice parameter was observed, as well as enlargement of grain size with increasing chromium content up to 4900 ppm Cr2O3. SEM indicated Cr incorporation within the matrix and the formation of chromium oxide precipitates throughout the microstructure at high Cr concentrations. Evaluation of thermophysical properties of Cr-doped UO2 pellets were conducted up to 1200 °C to illustrate their evolution with increased dopant concentration and microstructural changes. The results show that grain size is maximized at 52 μm with Cr2O3 concentration equal to 4900 ppm; however, grain size decreases at higher Cr2O3 concentrations. No significant changes were observed in specific heat capacity, linear thermal expansion, and coefficient of thermal expansion compared to undoped UO2. The thermal conductivity also decreased through the incorporation of Cr2O3 dopants above 750 ppm and is shown to be ∼15 % lower than reported UO2 values.

An investigation on the effect of heat input to wear behavior and corrosion-cavitation erosion mechanism of Hastelloy C-276 coating by cold metal transfer

Cold metal transfer (CMT) technology based on wire-arc manufacturing has attracted wide attention because of its advantages of high manufacturing efficiency, low heat input (HI) and near-net-shape. In this study, a CMT-Hastelloy C-276 superalloy surface modification coating by optimizing HI is used to solve the problem of premature failure of key over-flow components of stainless steel in marine engineering. When the HI is increased from 269 J/mm to 358 J/mm, the serious cavitation erosion (CE) damage caused by pore defects and excessive residual tensile stress due to excessive low HI of Hastelloy C-276 coating can be avoid, which is attributed to the effective Orowan strengthening and high proportion of low angle grain bounds (LAGBs: 70.2%). In addition, high contents of Cr, Mo and W elements can promote it's passivation film to maintain excellent self-healing ability during CE to provide continuous and stable protection effect (Rct = 75.68 kΩ·cm2) in the 3.5 wt% NaCl artificial seawater. Therefore, even after 10 h-CE, it still maintains the highest corrosion resistance from both of the thermodynamic (Ecorr = −193.5 ± 3.6 mV) and kinetic perspective (Icorr = 69.3 ± 3.1 μA·cm−2) and has the lowest mean depth erosion rates (MDER, 0.94 ± 0.07 μm/h). However, further increase of HI will cause coarsing of grains (89.6 ± 2.7 μm → 342.8 ± 9.7 μm), excessive precipitation of brittle Mo-rich p phase and excessive dilution of elements from the substrate, resulting in changes in the wear mechanism and deterioration of strength and corrosion resistance. Moreover, the potential of zero charge (PZC) measurements and Mott-Schottky (M-S) test confirmed the decreasing trend of the repulsive ability to Cl ions (ΔE = 0.58 V) and the increased ion doping concentration (ND = 5.94 ± 0.02 × 1022 cm−3) of the weakened n-type passivation films. The optimal combination of wear resistance, corrosion resistance and CE resistance of Hastelloy C-276 coating is obtained by regulating HI, which can lay a theoretical foundation for the related production and application of marine engineering.

Pollution Status of Groundwater Resource by Some Heavy Metals Using Index Approach in Some Part of Nasarawa Area, Kano State, Nigeria

Groundwater is the world's most significant natural resource providing water for different purposes, including drinking, domestic, industrial and irrigational. However, polluted groundwater may endanger human survival. This research evaluated the status of groundwater resource pollution caused by some heavy metals in some parts of the Nasarawa local government area of Kano State. 15 groundwater samples were collected from functional boreholes in the area. Heavy metals concentrations evaluated include Zn, Mn, Cr, Mg, Cd, Fe, Cu, and Pb and were compared with the World Health Organization and Nigerian Standard for Drinking Water Quality to establish their suitability for human consumption. Descriptive statistics was employed to summarize the analyzed data. Metal index was used to determine the pollution status of the groundwater. The result revealed that Zn, Fe, Cu, and Mn with the mean value of (0.090, 0.160, 0.191 and 0.11) were found within the stipulated limit set by WHO (3.0, 0.3, 2.0 and 0.5) and NSDWQ (3.0, 0.5-50, 1.0 and 0.2), while Pb, Cd, Cr, and Mg (0.105, 0.127, 0.206 and 0.82) exceeded the permissible limits recommended by WHO (0.01, 0.003, 0.05 and 0.5). A high concentration of Pb, Cd, Cr, and Mg may be attributed to anthropogenic influences possibly deriving from improper municipal and Bampai industrial waste disposal. The values of the metal index (MI) revealed that the water is seriously affected by Pb, Cd and Cr, which can pose serious health damage to consumers. It is recommended that constant and continuous monitoring of Pb, Cd and Cr in groundwater be made in the study area due to its proximity to Bampai and Sharadda industrial sites.

Enhancing Mechanical Properties of a Lightweight TiAlCrNbVZr Medium-Entropy Alloy: Fine-Tuning Alloy Composition and Thermomechanical Treatment

Enhancing Mechanical Properties of a Lightweight TiAlCrNbVZr Medium-Entropy Alloy: Fine-Tuning Alloy Composition and Thermomechanical Treatment