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1.
Sci Rep ; 14(1): 10152, 2024 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-38698028

RESUMO

Aluminum matrix composites (AMCs), incorporating Zirconium Nitride (ZrN) as reinforcing additives, demonstrate immense promise for applications in aerospace, automotive, and power generation due to their unique combination of low density, superior mechanical properties, and excellent thermal/electrical conductivity. This study explores the influence of ZrN reinforcement on the microstructure and mechanical properties of AlSi10Mg metal-matrix composites. Utilizing high-energy ball milling (HEBM) and spark-plasma sintering (SPS), ZrN/AlSi10Mg composites were synthesized, achieving nearly full density with uniform ZrN distribution, while phase and chemical transformations were not observed in the bulk composites. The addition of ZrN resulted in a notable increase in hardness of 237% (182 ± 8 HV2), elastic modulus of 56% (114 ± 3 GPa), compressive and tensile strength of 183% (565 ± 15 GPa), and 125% (387 ± 9 GPa), respectively, for composites containing 30% ZrN, compared to the non-reinforced alloy. Experimentally determined coefficients of thermal expansion (CTEs) for composites with 10%, 20%, and 30% ZrN content were 19.8 × 10-6 °C-1, 19.1 × 10-6 °C-1, and 18 × 10-6 °C-1, respectively, which well relates to Schapery's model. These findings contribute to understanding the synthesis, mechanical behavior, and thermal properties of ZrN/AlSi10Mg composites, demonstrating their potential for diverse engineering applications.

2.
Heliyon ; 10(7): e26464, 2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38689948

RESUMO

A novel concept of developing multi-principal elements, or compositional complex alloys is referred as high-entropy alloys (HEAs). This review addresses the role of entropy in alloying additions along with the effect of various elements listed in the periodic table in forming the HEAs. Phase formation rules and the associated parameters along with their significance are discussed. The physical metallurgy technique is elaborated with reference to the high-entropy effect, severe lattice distortion effect, sluggish diffusion effect, and cocktail effects. Various types of HEAs such as light weight HEAs, nanoprecipitate HEAs, ultrafine-grained HEAs, dual-phase HEAS and TRIP/TWIN HEAs are discussed. Further, the effects of mechanical alloying in HEAs are presented. Finally, the microstructural effects and mechanical properties of HEAs are addressed with reference to the published literature.

3.
Spectrochim Acta A Mol Biomol Spectrosc ; 316: 124289, 2024 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-38692101

RESUMO

Biphasic calcium phosphate (BCP), consisting of bioceramics such as HAp + ß-TCP and Ca10(PO4)6(OH)2 + Ca3(PO4)2, is a popular choice for optimizing performance due to its superior biological reabsorption and osseointegration. In this study, BCP was produced by calcining the bones of tilapia fish (Oreochromis niloticus) reared in net cages and slaughtered at an age ranging from 15 to 420 days. The bones were cleaned and dried, calcined at 900 °C for 8 h, and then subjected to high-energy grinding for 3 h to produce BCP powders. After the calcination process, the crystalline phase's hydroxyapatite (HAp) and/or beta-tricalcium phosphate (ß-TCP) were present in the composition of the bioceramic. The age-dependent variation in phase composition was confirmed by complementary vibrational spectroscopy techniques, revealing characteristic peaks and bands of the bioceramic. This variation was marked by an increase in HAp phase and a decrease in ß-TCP phase. Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) from 25 to 1400 °C showed the characteristic mass losses of the material, with a greater loss observed for younger fish, indicating the complete removal of organic components at temperatures above 600 °C. Comparison of the results obtained by X-Ray Diffraction (XRD) and Rietveld refinement with Raman spectroscopy showed excellent agreement. These results showed that with temperature and environment control and adequate fish feeding, it is possible to achieve the desired amounts of each phase by choosing the ideal age of the fish. This bioceramic enables precise measurement of HAp and ß-TCP concentrations and Ca/P molar ratio, suitable for medical orthopedics and dentistry.


Assuntos
Osso e Ossos , Cerâmica , Análise Espectral Raman , Animais , Cerâmica/química , Osso e Ossos/química , Tilápia/metabolismo , Difração de Raios X , Hidroxiapatitas/química , Espectroscopia de Infravermelho com Transformada de Fourier , Fosfatos de Cálcio/química , Termogravimetria
4.
Ann Sci ; : 1-21, 2024 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-38666321

RESUMO

Paracelsus was a transmutational alchemist: For most of his career, he believed that one metal could be turned into another. In an alchemical text, the De renovatione et restauratione, he explored the theoretical foundations of transmutation and hinted at recipes for bringing it about. He proposed that from plants, gems, metals, and minerals might be prepared a class of marvelous medicaments, which he called prima entia (first entities). Each primum ens had particular uses, but the entia were all supposed to be able to revitalize the human body and cleanse it of disease. Certain entia could also transmute metals. The De renovatione et restauratione affirmed the metaphysical centrality, in goldmaking and medicine alike, not just of purification or alteration but of renewal and transformation. It expressed the author's eschatological excitement at God's works of wonder, whether within or above nature.

5.
Materials (Basel) ; 17(8)2024 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-38673079

RESUMO

Recently, researchers have focused on improving motor performance and efficiency. To manufacture motors with performance and efficiency higher than those of motors manufactured through the additive process, compressibility verification through the parameter control of soft magnetic composites (SMCs) is essential. To this end, this study aims to select suitable powders for manufacturing high-performance, high-efficiency motors by exploring powder mixing ratios and milling times. Through physical property tests, the optimal mixing ratio is predicted using the Multi-Particle Finite Element Method (MPFEM) and powder compression molding analysis, and compressibility is predicted in view of the influence of a change in particle size as a function of the powder mixing ratio and milling time. In addition, based on the result of a comparative analysis of density through experiments and an analysis of internal defects through SEM, a 50:50 mixing ratio of hybrid atomizing and gas atomizing powders milled for 3 h provided the best compressibility. Therefore, the use of SMC cores fabricated using powder compression molding is expected to improve motor performance and efficiency.

6.
Materials (Basel) ; 17(3)2024 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-38591537

RESUMO

The material undergoes high temperature and high strain rate deformation process during the cutting process, which may induce the dynamic recrystallization behavior and result in the evolution of dynamic mechanical properties of the material to be machined. In this paper, the modified Johnson-Cook (J-C) model for nickel-based powder metallurgy superalloy considering dynamic recrystallization behavior in high strain rate and temperature is proposed. The dynamic mechanical properties of the material under different strain rates and temperature conditions are obtained by quasi-static compression test and split Hopkinson pressure bar (SHPB) test. The coefficients of the modified J-C model are obtained by the linear regression method. The modified model is verified by comparison with experimental and model prediction results. The results show that the modified J-C model proposed in this paper can accurately describe the mechanical properties of nickel-based powder metallurgy superalloys at high temperatures and high strain rates. This provides help for studying the cutting mechanism and finite element simulation of nickel-based powder metallurgy superalloy.

7.
Materials (Basel) ; 17(3)2024 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-38591589

RESUMO

Various foaming agents can be used to achieve foaming of the precursors obtained by using the powder metallurgy method. However, the thermal behavior of pure aluminum precursors with different foaming agents has been studied very little in recent times. For the production of aluminum foams with closed cells, 1 wt.% of calcium carbonate (CaCO3), titanium hydride (TiH2), heat-treated TiH2 and zirconium hydride (ZrH2) were used. The foaming capability of the compacted precursors was investigated at temperatures 700, 720 and 750 °C. CaCO3 and TiH2 showed the best foamability at all considered temperatures, while ZrH2 achieved relatively good foaming only at the highest temperature, 750 °C. Due to their low onset temperature of the decomposition compared to the melting point of the unalloyed aluminum, in hydride-based foaming agents the drainage occurred at the bottom part of the foam samples. Among the investigated foaming agents, precursors with heat-treated TiH2 had the worst foaming properties, while CaCO3 showed the best foamability without the occurrence of drainage.

8.
Materials (Basel) ; 17(3)2024 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-38591591

RESUMO

To investigate the effect of the sintering temperature on the microstructure characteristics of porous NiTi alloys, two types of porous NiTi alloys with equal atomic ratios were fabricated via elemental powder sintering at 950 °C and 1000 °C. Afterwards, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were collectively applied to investigate the pore characteristics and microstructure of the fabricated porous NiTi alloy. The results show that when the sintering temperature increases from 950 °C to 1000 °C, the average pore size increases from 36.00 µm to 181.65 µm, owing to the integration of these newly formed small pores into these pre-existing large-sized pores. The measured density increases from 2.556 g/cm3 to 3.030 g/cm3, while the porosity decreases from 60.4% to 51.8%. This is due to the occurrence of shrinkage after the sufficient diffusion of atoms. Furthermore, the characterization results confirm that a change in the sintering temperature would not change the phase types within a porous NiTi alloy; namely, the matrix consists primarily of B2 NiTi, with a significant amount of Ni4Ti3 precipitates and a small amount of Ni3Ti precipitates and Ti2Ni precipitates. However, as the sintering temperature increases, the number of Ni4Ti3 precipitates decreases significantly. The formation of a Ni4Ti3 phase in the present study is closely related to the enrichment of Ni content in the matrix owing to the diffusion rate difference between Ni atoms and Ti atoms and the absence of a transient liquid phase (TLP) during the sintering process owing to the relatively low sintering temperature (lower than the eutectic temperature). Moreover, the increasing sintering temperature speeds up the atom diffusion, which contributes to a reduction in the enrichment of Ni as well as the number of formed Ni4Ti3 precipitates.

9.
Ultrason Sonochem ; 104: 106838, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38432150

RESUMO

Ultrasonic transducers (UTs) are the main components for generating sonic waves. These types of transducers are nonlinear loads, and they are adversely affected by changes in mechanical load or temperature. UTs are operated in the region close to the resonant frequency. An ultrasonic transducer needs to be driven by a high-frequency inverter. In this paper, a Class D resonant inverter circuit is implemented for ultrasonic mixer application. The proposed circuit operates at 34306 Hz at 140 V and has low cost and size. The simulation results of Class D inverter verified with the prototype experimental circuit. Al (Aluminum) alloy with ethanol and graphene is mixed in order to show the mixing performance of the resonant inverter fed transducer with probe. The system achieved the fine particles and homogen mixture according to the SEM images and EDX analysis.

10.
Materials (Basel) ; 17(5)2024 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-38473463

RESUMO

In this work, a new use of mixed Ti-6Al-4V powder, consisting of the retained powder after screening for additive manufacturing and the recycled powder after multiple printing, has been exploited. The powder mixture has been hot-isostatically-pressed (HIPed) at 930 °C/120 MPa for 3 h to reach full density. The hot deformation behavior of the as-HIPed powder compacts were investigated through isothermal compression tests, kinetic analyses, and hot processing maps. Finally, the optimized hot working parameters were validated using upsetting tests. The results show that the as-HIPed Ti-6Al-4V alloy has a fine and homogeneous microstructure. The activation energies were calculated to be 359 kJ/mol in the α + ß phase regime and 463 kJ/mol in the ß phase regime, respectively. The optimal hot working parameters are a deformation temperature above 950 °C and strain rate higher than 0.1 s-1. The hot workability of as-HIPed powder compacts is better than the as-cast billets. The deformed microstructure can be finer than that of as-HIPed state, and the mechanical performance can be further improved by the optimal thermo-mechanical processing treatment.

11.
Biomed Mater ; 19(2)2024 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-38387058

RESUMO

In this study, porous magnesium (Mg) scaffolds were investigated with varying strontium (Sr) and constant zinc (Zn) concentrations through the powder metallurgy process. All samples were examined at room temperature to evaluate their microstructure, mechanical andin-vitrodegradation behaviour and biological properties. Results indicated that adding Sr was associated with fine average grain size, increased mechanical strength, and a decreased corrosion rate. All samples show tiny isolated and open interconnected pores (porosities: 18%-30%, pores: 127-279 µm) with a suitable surface roughness of less than 0.5 µm. All the provided samples possess mechanical and hemocompatible properties that closely resemble natural bone. Mg-4Zn-2Sr has the highest hardness (102.61 ± 15.1 HV) and compressive strength (24.80 MPa) than Mg-4Zn-0.5Sr (85 ± 8.5 HV, 22.14 MPa) and Mg-4Zn-1Sr (97.71 ± 11.2 HV, 18.06 MPa). Immersion results revealed that samples in phosphate-buffered saline solutions have excellent degradability properties, which makes them a promising biodegradable material for orthopaedic applications. The scaffold with the highest Sr concentration shows the best optimised mechanical and degradation behaviour out of the three porous scaffolds, with a 2.7% hemolysis rate.


Assuntos
Magnésio , Ortopedia , Porosidade , Próteses e Implantes , Morte Celular , Estrôncio
12.
Sci Total Environ ; 921: 171130, 2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38401729

RESUMO

Electroplating sludge is extensively produced in chemical precipitation-based treatment of electroplating wastewater. It poses a huge threat to environmental safety if not properly disposed, ascribed to its high contents of heavy metals. An innovative metallurgical approach was proposed a to recycle Cu, Cr, and Ni from it. Ammonia leaching was firstly performed to selectively leach Cu from Cr, in which the Cu oxide and sulfide were leached into the leachate while the Cr oxide and Ni carbide (NiCx) retained in the residue. (NH4)2SO4 increased the Cu leaching rate via increasing the dissolved oxygen amount in the ammonia leachate and converting CuS to Cu2+. Under the optimal conditions, the leaching efficiency of Cu achieved 96.5 % while that of Cr was only 0.1 %. In the followed aluminothermic reduction, C in the leaching residue could be effectively removed via a thermal oxidation, which in turn decreased the formation of a C-containing compound of high melting point and benefited the Cr and Ni recovery. Cr and Ni from the residue were reduced and recovered in a Cr-Ni alloy, and the reductant of Al first changed to a refractory Al2O3 and then transformed to a low melting point 12CaO·7Al2O3 with the additive of CaO. This transformation increased the molten slag fluidity and promoted the separation of Cr-Ni alloy from slag. Moreover, the excessive Al increased the Cr and Ni yields and concentrated all of them to be together. Partial Al was used as reductant, and the other Al transferred into Cr-Ni alloy to decrease its melting point. Cr and Ni contents in the smelting slag could be decreased to 0.11 wt% and 0.12 wt% respectively, showing an efficient recovery. This work provided a high efficiency method to recover Cu, Cr, and Ni from waste electroplating sludge.

13.
Materials (Basel) ; 17(4)2024 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-38399210

RESUMO

Numerical methods are crucial to supporting the development of new technology in different industries, especially steelmaking, where many phenomena cannot be directly measured or observed under industrial conditions. As a result, further designing and optimizing steelmaking equipment and technology are not easy tasks. At the same time, numerical approaches enable modeling of various phenomena controlling material behavior and, thus, understanding the physics behind the processes occurring in different metallurgical devices. With this, it is possible to design and develop new technological solutions that improve the quality of steel products and minimize the negative impact on the environment. However, the usage of numerical approaches without proper validation can lead to misleading results and conclusions. Therefore, in this paper, the authors focus on the development of the CFD-based (computational fluid dynamics) approach to investigate the liquid steel flow inside one metallurgical device, namely a ladle furnace combined with an EMS (electromagnetic stirring) system. First, a numerical simulation of electromagnetic stirring in a scaled mercury model of a ladle furnace was carried out. The numerical results, such as stirring speed and turbulent kinetic energy, were compared with measurements in the mercury model. It was found that the results of the transient multiphase CFD model achieve good agreement with the measurements, but a free surface should be included in the CFD model to simulate the instability of the flow pattern in the mercury model. Based on the developed model, a full-scale industrial ladle furnace with electromagnetic stirring was also simulated and presented. This research confirms that such a coupled model can be used to design new types of EMS devices that improve molten steel flow in metallurgical equipment.

14.
J Environ Sci (China) ; 140: 46-58, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38331514

RESUMO

Reducing CO2 emissions of the iron and steel industry, a typical heavy CO2-emitting sector, is the only way that must be passed to achieve the 'dual-carbon' goal, especially in China. In previous studies, however, it is still unknown what is the difference between blast furnace-basic oxygen furnace (BF-BOF), scrap-electric furnace (scrap-EF) and hydrogen metallurgy process. The quantitative research on the key factors affecting CO2 emissions is insufficient. There is also a lack of research on the prediction of CO2 emissions by adjusting industrial structure. Based on material flow analysis, this study establishes carbon flow diagrams of three processes, and then analyze the key factors affecting CO2 emissions. CO2 emissions of the iron and steel industry in the future is predicted by adjusting industrial structure. The results show that: (1) The CO2 emissions of BF-BOF, scrap-EF and hydrogen metallurgy process in a site are 1417.26, 542.93 and 1166.52 kg, respectively. (2) By increasing pellet ratio in blast furnace, scrap ratio in electric furnace, etc., can effectively reduce CO2 emissions. (3) Reducing the crude steel output is the most effective CO2 reduction measure. There is still 5.15 × 108-6.17 × 108 tons of CO2 that needs to be reduced by additional measures.


Assuntos
Poluentes Atmosféricos , Ferro , Poluentes Atmosféricos/análise , Dióxido de Carbono/análise , Aço , Carbono , Metalurgia , Hidrogênio
15.
Angew Chem Int Ed Engl ; 63(10): e202318149, 2024 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-38169516

RESUMO

Aqueous Zn-based batteries have emerged as compelling candidates for grid-scale energy storage, owing to their intrinsic safety, remarkable theoretical energy density and cost-effectiveness. Nonetheless, the dendrite formation, side reactions, and corrosion on anode have overshadowed their practical applications. Herein, we present an in situ grown carbon network reinforcing Zn matrix anode prepared by powder metallurgy. This carbon network provides an uninterrupted internal electron transport pathway and optimize the surface electric field distribution, thereby enabling highly reversible Zn deposition. Consequently, symmetrical cells demonstrate impressive stability, running for over 880 h with a low voltage hysteresis (≈32 mV). Furthermore, this Zn matrix composite anode exhibits enhanced performance in both the aqueous Zn-ion and the Zn-air batteries. Notably, Zn//MnO2 cells display superior rate capabilities, while Zn-air batteries deliver high power density and impressive Zn utilization rate (84.9 %). This work provides a new idea of powder metallurgy method for modified Zn anodes, showcasing potential for large-scale production.

16.
J Occup Med Toxicol ; 19(1): 3, 2024 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-38297383

RESUMO

OBJECTIVE: To describe the proportions of subjects exposed to crystalline silica and the sectors of activity concerned between 1965 and 2010 in a sample of the general French population. METHODS: We included 2942 participants aged 40 to 65 years, recruited at random from electoral rolls, from the French general population in the cross-sectional ELISABET study between 2011 and 2013. The proportions of subjects exposed to crystalline silica and their sectors of activity were determined on the basis of their career history and the use of the Matgéné job-exposure matrix. RESULTS: In the total sample, occupational exposure to crystalline silica was found for 291 subjects (9.9%) between 1965 and 2010, with a predominance of men (20.2% of exposed subjects among men (282 out of 1394) versus 0.6% among women (9 out of 1548)). The highest proportion of participants exposed to crystalline silica was reached in 1980 with 6.1% and then decreases to 4.4% in 2010. Among men, the most frequently exposed sectors of activity were manufacture of basic metals (41.5% of exposed men (117 out of 282)), specialised construction activities (23.1% of exposed men (65 out of 282)) and construction of buildings (14.2% of exposed men (40 out of 282)). CONCLUSIONS: Although the proportion of workers exposed to crystalline silica has been decreasing since the 1980s, it is still significant at least until 2010, particularly in the construction sector, and further research is needed to improve the monitoring of workers who are or have been exposed to crystalline silica.

17.
Materials (Basel) ; 17(2)2024 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-38255472

RESUMO

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al-Ti-Cu-Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 µm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al-Ti-Cu-Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8-5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

18.
J Biomed Mater Res B Appl Biomater ; 112(1): e35338, 2024 01.
Artigo em Inglês | MEDLINE | ID: mdl-37846459

RESUMO

Titanium and its alloys are used to make dental implants because of its low density, high strength, and corrosion resistance. This paper describes the development of a potential biomaterial Ti-10Nb by powder metallurgy utilizing four different compaction pressures and analyses its microstructural, physical, mechanical, electrochemical, biological, and tribological behavior under various situations. The alloys were fabricated using four different compaction pressures, that is, 600, 650, 700, and 750 MPa, and sintered in a vacuum atmosphere at 1000°C for 1.5 h. The density of the samples was measured using Archimedes principle. X-ray diffraction and scanning electron microscopy equipped with energy dispersive spectroscopy were used to investigate the phase composition and microstructure, and a profilometer was used to examine the surface roughness of various samples. Vickers hardness tester was used to evaluate hardness, and a universal testing machine was used for compression testing. Corrosion and wear behavior were examined using a potentiostat and a Bio-Tribometer, respectively. This Ti-10Nb alloys consist of α + ß phase, and have 16% highest porosity in sample compacted at 600 MPa. The samples compacted at 750 MPa achieved highest hardness, yield strength, compressive strength, and elastic modulus of 450 ± 29.72 HV, 718.22 ± 16.37 MPa, 1543.59 ± 24.37 MPa, and 41.27 ± 3.29 GPa, respectively. In addition, it also possesses highest corrosion and wear resistance with lowest icorr of 0.3954 ± 0.008 µA/cm2 and wear volume of (31.25 ± 0.206) × 10-3 mm3 . These results indicate that the developed alloys have a variety of desirable properties, including high hardness, adequate compressive strength, good corrosion and wear resistance, apatite-forming capability, and a low elastic modulus, which is advantageous for avoiding stress shielding. Therefore, it may be recommended to use it as a dental implant material.


Assuntos
Ligas , Titânio , Ligas/química , Titânio/química , Pós , Materiais Biocompatíveis , Corrosão , Metalurgia , Teste de Materiais
19.
Sci Total Environ ; 912: 169431, 2024 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-38142989

RESUMO

Records from polar and alpine ice reflect past changes in background and industrial toxic heavy metal emissions. While Northern Hemisphere records have been used to evaluate environmental effects and linkages to historical events such as foreign conquests, plagues, economic downturns, and technological developments during the past three millennia, little is known about the magnitude and environmental effects of such emissions in the Southern Hemisphere or their historical linkages, especially prior to late 19th century industrialization. Here we used detailed measurements of the toxic heavy metals lead, cadmium, and thallium, as well as non-toxic bismuth, cerium, and sulfur in an array of five East Antarctic ice cores to investigate hemispheric-scale pollution during the Common Era. While thallium showed no anthropogenic increases, the other three metals increased by orders of magnitude in recent centuries after accounting for crustal and volcanic components. These first detailed records indicate that East Antarctic lead pollution started in the 13th century coincident with Late Intermediate Period metallurgy in the Andes and was pervasive during the Spanish Colonial period in parallel with large-scale exploitation of Andean silver and other ore deposits. Lead isotopic variations suggest that 19th-century increases in lead, cadmium, and bismuth resulted from Australian lead and Bolivian tin mining emissions, with 20th century pollution largely the result of the latter. As in the Northern Hemisphere, variations in heavy metal pollution coincided with plagues, cultural and technological developments, as well as global economic and political events including the Great Depression and the World Wars. Estimated atmospheric heavy metal emissions from Spanish Colonial-era mining and smelting during the late 16th and early 17th century were comparable to estimated European emissions during the 1st-century apex of the Roman Empire, with atmospheric model simulations suggesting hemispheric-scale toxic heavy metal pollution during the past five centuries as a result.

20.
Materials (Basel) ; 16(23)2023 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-38068012

RESUMO

Original compositions based on iron micro-powders and an organic binder mixture were developed for the fabrication of sintered metallic elements with micro-powder injection molding (µPIM) and material extrusion additive manufacturing of metal powders (MEX). The binder formulation was thoroughly adjusted to exhibit rheological and thermal properties suitable for µPIM and MEX. The focus was set on adapting the proper binder composition to meet the requirements for injection/extrusion and, at the same time, to have comparable thermogravimetric characteristics for the thermal debinding and sintering process. A basic analysis of the forming process indicates that the pressure has a low influence on clogging, while the temperature of the material and mold/nozzle impacts the viscosity of the composition significantly. The influence of the Fe micro-powder content in the range of 45-60 vol.% was evaluated against the injection/extrusion process parameters and properties of sintered elements. Different debinding and sintering processes (chemical and thermal) were evaluated for the optimal properties of the final samples. The obtained sintered elements were of high quality and showed minor signs of binder-related flaws, with shrinkage in the range of 10-15% for both the injection-molded and 3D printed parts. These results suggest that, with minor modifications, compositions tailored for the PIM technique can be adapted for the additive manufacturing of metal parts, achieving comparable characteristics of the parts obtained for both forming methods.

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