Search Results (32)

A variety of variables, such as organic matter input, redox conditions, depositional rates, and terrigenous input, affect the deposition of black shale. Furthermore, because of the significant regional variations in paleodepositional environments, these factors have a complex role in organic matter enrichment. Global geological events influenced sedimentary conditions, organic enrichment, and the development of organic-enriched shales during the Late Ordovician to Early Silurian. The Wufeng–Longmaxi Formation black shales in Southeastern Chongqing were analyzed for X-ray diffraction (XRD), major and trace element geochemistry, and total organic carbon (TOC) data; this led to further analysis of the relationship between the depositional environment and organic matter aggregation and rock type evolution. The primary minerals found in the Wufeng–Longmaxi shale are quartz, feldspar, carbonatite (calcite and dolomite), and clay. The high index of compositional variability (ICV) values (>1) and the comparatively low chemical index of alteration (CIA) values (52.6–72.8) suggest that the sediment source rocks are juvenile and are probably experiencing weak to moderate chemical weathering. The selected samples all show negative Eu anomalies, flat heavy rare earth elements, and mildly enriched light rare earth elements. The ratios of La/Th, La/Sc, Th/Sc, ΣREE-La/Yb, TiO₂-Ni, and La/Th-Hf suggest that acidic igneous rocks were the main source of sediment, with minor inputs from ancient sedimentary rocks. The correlations of paleoclimate proxies (Sr/Cu, CIA), redox proxies (V/Cr, V/Ni, V/(V + Ni), Ni/Co, U/Th), paleoproductivity proxies (Ba_xs, Cu_EF, Ni_EF), and water mass restriction proxies (Mo/TOC, U_EF, Mo_EF) suggest a humid–semiarid, anoxic, moderate–high paleoproductivity, and moderate–strongly restricted environment. On the basis of the aforementioned interpretations, the paleoenvironment of the Wufeng–Longmaxi Formations was established, with paleoredox conditions and restricted water masses likely being the primary factors contributing to organic matter enrichment. Full article

The powder bed fusion of metals using a laser beam (PBF-LB/M) is an additive manufacturing process for the direct production of metal parts using powder as a starting material. The PBF-LB/M process consists of two main steps: the application of a new powder layer and the melting of the cross-sections of the parts in each layer. Laser exposure usually takes up a lot of time during a build process; however, the application of powder layers, also taking up a considerable amount of time, offers potential to shorten production times. In this work, a powder test rig that mimics the real flow conditions of a PBF-LB/M system is used to measure the quality of X3NiCoMoTi18-9-5 powder layers applied at different recoater speeds by determining the powder surface roughness. The same recoating settings are then used on a real PBF-LB/M system to produce samples and investigate their densities as a function of recoater speed. The results show that the recoater speed influences the surface of the applied powder bed and has an effect on the density of the manufactured samples. However, this influence decreases if only samples with a high relative density are considered. Full article

To extend the safety service life of aviation TC4 alloy, the composite coatings of TC4 + Ni-MoS₂ + WC + xY₂O₃ (x = 0, 1, 2, 3, 4 wt.%) were prepared on TC4 by coaxial powder feeding laser cladding technology. The results showed that all the coatings had the same generated phases which mainly consisted of TiC, Ti₂Ni, Ti₂S, matrix β-Ti, and unfused residual WC. Y₂O₃ formed co-dependent growth relationships with TiC, Ti₂S, and Ti₂Ni. Meanwhile, TiC-Ti₂S, TiC-Ti₂Ni, and Ti₂S-Ti₂Ni coherent composite structure phases were effectively synthesized in all the coatings. With the increase in the Y₂O₃ content, the exposed area of the matrix increased and other phases refined progressively. When the Y₂O₃ content in the coatings were 3 and 4 wt.%, the degree of phase refinement in the coatings was consistent and the phases grew along grain boundaries, but microstructure segregated in the 4 wt.% Y₂O₃ coating. The microhardness of all the coatings was higher than that of TC4 and decreased with the increase in the Y₂O₃ content. Higher friction coefficients and lower wear rates both appeared in all the coatings than in the substrate, and they presented a trend of decreased first and then increased with the addition of Y₂O₃, in which the 3 wt.% Y₂O₃ coating had the lowest friction coefficient and optimal wear resistance. The research found that the Y₂O₃ could not change the types of phases in the coatings and could serve as a heterogeneous nucleation center for the refinement of the TiC-Ti₂S-Ti₂Ni coherent structure phase. Meanwhile, except for the matrix phase, Y₂O₃ could attract other phases to pinning on the grain boundaries of the coatings. The content of Y₂O₃ was negatively correlated with the hardness and wear resistance of the coating and it had the optimal tribological properties with the moderate amount of Y₂O₃. The wear mechanism of all coatings was abrasive wear. Full article

The CoCrFeNi₂Mo_x (x = 0, 0.4, 0.5, 1.0, x values in atomic ratio) high-entropy alloy coatings were designed and prepared on the Ti-6Al-4V substrate by laser cladding technology, their microstructures, and dry sliding wear resistance were studied in detail. When x < 0.4, the coatings were mainly composed of BCC solid solution phase, (Ni, Co)Ti₂ phase, and α-Ti phase. When x ≥ 0.4, the new σ phase appeared in the coatings. As the Mo content increases from 0 to 1.0, the hardness showed a trend of first increasing and then decreasing, especially when x = 0.5, the coating hardness reached its maximum (882 HV), which was 2.65 times the hardness of the Ti-6Al-4V substrate. The CoCrFeNi₂Mo_x high-entropy alloy coatings significantly improved the wear resistance of Ti-6Al-4V substrate, and with the increase in Mo content, the friction coefficient, widths/depths of worn tracks and wear rates of the coatings showed a trend of first decreasing and then increasing. In particular, when x = 0.5, the CoCrFeNi₂Mo_0.5 high-entropy alloy coating has the lowest friction coefficient (0.63), widths/depths of worn tracks (width: 803.690 μm; depth: 20.630 μm) and wear rate (5.136 × 10⁻⁵ mm³/(N·m)), which is one order of magnitude smaller than that of the substrate (3.694 × 10⁻⁴ mm³/(N·m)), demonstrating the best wear resistance. This is mainly because the appropriate proportion of hard α-Ti and σ phases effectively played a supporting role in resisting wear, while the relatively soft and dispersed BCC and (Ni, Co)Ti₂ phases could effectively prevent the occurrence of brittle fracture during wear test process. Full article

The assessment of soil contamination in the vicinity of integrated siderurgical plants is of outmost importance for agroecosystems and human health, and sensitive techniques should be employed for accurate assessment of chemical elements (metals, potential toxic elements, rare earths, radioelements) in soil and further evaluation of potential ecological and safety risk. In this paper a total of 45 major, minor and trace elements (Al, As, Au, Ba, Br, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Eu, Fe, Hf, Hg, I, K, La, Mg, Mn, Mo, Na, Nd, Ni, Pb, Rb, Sb, Sc, Sm, Sn, Sr, Ta, Tb, Th, Ti, Tm, U, V, W, Y, Yb, Zn and Zr) were quantified in soils located around a large siderurgical works (Galati, SE Romania) using instrumental neutron activation analysis (INAA) in combination with X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP–MS). The statistical analysis results and vertical distribution patterns for three depths (0–5 cm, 5–20 cm, 20–30 cm) indicate inputs of toxic elements in the sites close to the ironmaking and steelmaking facilities and industrial wastes dumping site. For selected elements, a comparison with historical, legislated and world reported concentration values in soil was performed and depth migration, contamination and toxic risk indices were assessed. The distribution of major, rock forming elements was closer to the Upper Continental Crust (UCC), and to the Dobrogea loess, a finding confirmed by the ternary diagram of the incompatible trace elements Sc, La and Th, as well as by the La to Th rate. At the same time, the La/Th vs. Sc and Th/Sc vs. Zr/Sc bi-plots suggested a felsic origin and a weak recycling of soils’ mineral components. Full article

The use of metal-coated ceramic powders not only effectively enhances the wettability of the metal–ceramic interface but also promotes a more uniform microstructure in Ti(C,N)-based cermets, which is advantageous for improving their mechanical properties. In this study, ultrafine Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders were synthesized via the spray-drying-in-situ carbothermal reduction method. Subsequently, Ti(C,N)-based cermets were effectively fabricated using the as-prepared ultrafine Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders. The impact of reaction temperature, heating rate, and isothermal time on the phase and microstructure of prepared powders was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the microstructure of the as-sintered cermets was experimentally investigated. The findings reveal that the complete reduction of Co and Ni metal salts, pre-coated on the surface of (Ti,W,Mo,Ta)(C,N) particles, can be achieved through rapid heating (10 °C/min) in a specific temperature range (600–1000 °C) with an isothermal time of 3 h at a lower reduction temperature (1000 °C). The synthesized powders have only two phases: the (Ti,W,Mo,Ta)(C,N) phase and Co/Ni phase, and no other heterogeneous phases were observed with an oxygen content of 0.261 wt.%. Notably, the conventional core–rim structure was not dominant in the cermets obtained from the prepared Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders. Moreover, the heterogeneous segregation effect of the Co/Ni coating on the ultrafine powder particles resulted in a finer microstructure than the traditional cermets with the same composition. However, the grain size is mainly in the range of 0.5–0.8 μm. The weaker residual stresses at the core and rim interfaces and the finer particle distributions could theoretically enhance the toughness of Ti(C,N)-based cermets, simultaneously. Full article

The Upper Silesian Coal Basin (USCB), located in southern Poland, is the major coal basin in Poland, and all technological types of hard coal, including coking coal, are exploited. It is also an area of high potential for coal-bed methane (CBM). Despite the increasing availability of alternative energy sources globally, it is a fact that the use of fossil fuels will remain necessary for the next few decades. Therefore, research on coal-bearing formations using modern research methods is still very important. The application of geochemistry and chemostratigraphy in reservoir characterization has become increasingly common in recent years. This paper presents the possibility of applying chemostratigraphic techniques to the study of the Carboniferous coal-bearing succession of the Upper Silesian Coal Basin. The material studied comes from 121 core samples (depth 481–1298 m), representing the Mudstone Series (Westphalian A, B). Major oxide concentrations of Al₂O₃, SiO₂, Fe₂O₃, P₂O₅, K₂O, MgO, CaO, Na₂O, K₂O, MnO, TiO₂, and Cr₂O₃ were obtained using X-ray fluorescence (XRF) spectrometry. Trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP/MS). The geochemical record from the Mudstone Series shows changes in the concentration of major elements and selected trace elements, leading to the identification of four chemostratigraphic units. These units differ primarily in the content of Fe, Ca, Mg, Mn, and P as well as the concentration of Zr, Hf, Nb, Ta, and Ti. The study also discusses quartz origin (based on SiO₂ and TiO₂), sediment provenance and source-area rock compositions (based on Al₂O₃/ TiO₂, TiO₂/Zr, and La/Th), and paleoredox conditions (based on V/Cr, Ni/Co, U/Th, (Cu+Mo)/Zn, and Sr/Ba) for the chemostratigraphic units. Chemostratigraphy was used for the first time in the study of the Carboniferous coal-bearing series of the USCB, concluding that it can be used as an effective stratigraphic tool and provide new information on the possibility of correlating barren sequences of the coal-bearing succession. Full article

Boron presents an important role in chemistry, biology, and materials science. Diatomic transition-metal borides (MBs) are the building blocks of many complexes and materials, and they present unique electronic structures with interesting and peculiar properties and a variety of bonding schemes which are analyzed here. In the first part of this paper, we present a review on the available experimental and theoretical studies on the first-row-transition-metal borides, i.e., ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, CuB, and ZnB; the second-row-transition-metal borides, i.e., YB, ZrB, NbB, MoB, TcB, RuB, RhB, PdB, AgB, and CdB; and the third-row-transition-metal borides, i.e., LaB, HfB, TaB, WB, ReB, OsB, IrB, PtB, AuB, and HgB. Consequently, in the second part, the second- and third-row MBs are studied via DFT calculations using the B3LYP, TPSSh, and MN15 functionals and, in some cases, via multi-reference methods, MRCISD+Q, in conjunction with the aug-cc-pVQZ-PP_M/aug-cc-pVQZ_B basis sets. Specifically, bond distances, dissociation energies, frequencies, dipole moments, and natural NPA charges are reported. Comparisons between MB molecules along the three rows are presented, and their differences and similarities are analyzed. The bonding of the diatomic borides is also described; it is found that, apart from RhB(X¹Σ⁺), which was just recently found to form quadruple bonds, RuB(X²Δ) and TcB(X³Σ⁻) also form quadruple σ²σ²π²π² bonds in their X states. Moreover, to fill the gap existing in the current literature, here, we calculate the TcB molecule. Full article

The qualitative X-ray phase analysis of natural and artificial food sweeteners was applied to trace the authenticity of such food additives. The mineral composition of different sweeteners commonly added to foods was studied to estimate their mineral profiles and assess the risk related to the toxic elements intake caused by sweetener consumption. The concentration of twenty elements (Ag, Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr, Ti, V, and Zn) was measured using the inductively coupled plasma–optical emission spectroscopy (ICP-OES) method after the representative samples were wet-digested with a concentrated nitric acid and hydrogen peroxide mixture in a closed-vessel microwave-assisted system. Differences between the mineral compositions of the examined sweeteners were statistically evaluated and discussed. The relationships between the concentrations of the elements determined in the analyzed sweeteners were also investigated. The successful application of the X-ray powder diffraction method proved the identity of all investigated sweeteners; all the analyzed products contained the expected sweetening agent. The results of the quantification of all the elements in the examined sweeteners indicated that these products cannot be considered nutritionally dense. Hence, the presence of toxic elements like Cd, Cr, Ni, and Pb distinctly indicates the need to test such products to guarantee their quality and ensure consumer safety. Full article

Due to the excellent properties of Ti (C,N)-based ceramics, such as high hardness, excellent wear resistance, exceptional thermal deformation resistance, and sound chemical stability, they have been widely used in cutting tools or molds. Thus, revealing their tribological behavior against hard materials is of great significance. Some studies have reported the tribological behavior of Ti(C,N)-based cermets and hard cermets, but so far, the effects of Mo₂C additions on the frictional properties of Ti(C,N)-based cermets are still unclear. In this study, Ti(C,N)-10WC-1Cr₃C₂-5Co-10Ni-x Mo₂C cermets (x = 4, 6, 8, 10 and 12 wt.%) were sintered using a vacuum hot-pressing furnace. Furthermore, the core–rim morphologies of the sintered samples were observed in SEM images. Then, the wear resistance of the cermets was studied against a Si₃N₄ ball at a 50 N load using the fretting wear test. Finally, the wear mechanism was characterized using a combination of SEM, EDS and XPS. The experimental results indicated that the wear mechanisms of the cermets were mainly abrasive wear, adhesive wear, and the formation of an oxide film. As the content of Mo₂C increased from 4 wt.% to 12 wt.%, the friction coefficient and wear volume had a variation law of first decreasing and then decreasing, and reached minimum values at 6 wt.% and 12 wt.%, and the lowest friction coefficient and wear rate were 0.49 and 0.9 × 10⁻⁶ mm³/Nm, respectively. The 6 wt.% Mo₂C greatly improved the hardness and fracture toughness of the cermet, while the 12 wt.% Mo₂C promoted the formation of an oxide film and protected the friction surface. The cermet with 6 wt.% Mo₂C is recommended because it has comprehensive advantages in terms of its mechanical properties, tribological properties, and cost. Full article

Al_xCoCrFeNiTi (x = 0.1, 0.3, 0.6, 1) powders were prepared via mechanical alloying and were used as binders for SPS-produced Ti(C,N)-based cermets. The effects of AlxCoCrFeNiTi binder on phase composition, morphology, room-temperature mechanical properties, and oxidation resistance of cermets were studied. The research showed that cermets with Al_xCoCrFeNiTi binders exhibited a more homogeneous core–rim structure than cermets with cobalt binders. The Vickers hardness and fracture toughness of cermets with Al_xCoCrFeNiTi binders increased with the aluminum molar ratio due to the grain refinement and solid solution strengthening effect of carbonitrides. After static oxidation at 1000 °C, the mass gain of the cermets with Al_xCoCrFeNiTi binders changed according to a quasi-parabolic law, and the lowest mass gain was obtained in the cermet with Al_0.6CoCrFeNiTi binder. The oxidation kinetics curve of the benchmark cermet with cobalt followed a linear law. The oxidation product of Ti(C,N)-based cermet with cobalt was rich in TiO₂, and the Ti(C,N)-based cermets with Al_xCoCrFeNiTi binders were transformed into complex oxides, such as NiMoO₄, NiWO₄, FeMoO₄, Fe₃Ti₃O₉, and Ni₃TiO₇. The oxide layer on the cermet with Al_0.6CoCrFeNiTi appeared to be dense and protective, which inhibited the diffusion of oxygen into the cermet and improved the oxidation resistance of the final product. Full article

The method of improving the microstructure and thus the properties of alloys by adjusting their composition has been widely used in the study of high entropy alloys (HEAs). However, most studies have focused on improving the properties of HEAs with face-centered cubic (FCC) or body-centered cubic (BCC) structures by adjusting the contents of elements such as Ni, Al, Ti, Cr, Mn and Mo. The doping of B, Mg and Zr also has a certain effect on the mechanical properties of HEAs. In this paper, the phase structure, microstructure, and mechanical properties of Ni_45.5Co₂₂Fe₂₂Al₅Ti₅ HEA doped with B, Mg, and Zr were investigated. The results demonstrated that the three-phase structures of FCC matrix, L1₂ precipitate, and BCC phase were present in all the as-cast HEAs of Ni_45.5Co₂₂Fe₂₂Al₅Ti_5×0.5 (X = B, Mg, and Zr). The microstructures of the as-cast alloys showed typical dendritic and inter-dendritic architecture. The maximum hardness was found in the alloy doped with B element, with a value of 433 HV. During the compressive test at room temperature, neither the Mg0.5 HEA nor the Zr0.5 HEA cracked until the load limit, but the B0.5 HEA cracked at a compressive strain of about 12%. B0.5 HEA had the highest compressive yield strength of the three alloys, followed by Zr0.5 HEA, while Mg0.5 HEA had the lowest, with values of 1030 MPa, 754 MPa, and 628 MPa, respectively. The work is expected to provide a boost for the research on the optimization of the properties of new HEAs reinforced by precipitation of L1₂ phase by providing a simple solution-microalloying method. Full article

High-entropy alloys (HEAs) contain more than five alloying elements in a composition range of 5–35% and with slight atomic size variation. Recent narrative studies on HEA thin films and their synthesis through deposition techniques such as sputtering have highlighted the need for determining the corrosion behaviors of such alloys used as biomaterials, for example, in implants. Coatings composed of biocompatible elements such as titanium, cobalt, chrome, nickel, and molybdenum at the nominal composition of Co₃₀Cr₂₀Ni₂₀Mo₂₀Ti₁₀ were synthesized by means of high-vacuum radiofrequency magnetron (HVRF) sputtering. In scanning electron microscopy (SEM) analysis, the coating samples deposited with higher ion densities were thicker than those deposited with lower ion densities (thin films). The X-ray diffraction (XRD) results of the thin films heat treated at higher temperatures, i.e., 600 and 800 °C, revealed a low degree of crystallinity. In thicker coatings and samples without heat treatment, the XRD peaks were amorphous. The samples coated at lower ion densities, i.e., 20 µAcm⁻², and not subjected to heat treatment yielded superior results in terms of corrosion and biocompatibility among all the samples. Heat treatment at higher temperatures led to alloy oxidation, thus compromising the corrosion property of the deposited coatings. Full article

(1) This work answers the question of whether and to what extent there is a significant difference in mechanical properties when different additive manufacturing processes are applied to the material 1.2709. The Laser-Powder-Bed-Fusion (L-PBF) and Laser-Metal-Deposition (LMD) processes are considered, as they differ fundamentally in the way a part is manufactured. (2) Known process parameters for low-porosity parts were used to fabricate tensile strength specimens. Half of the specimens were heat-treated, and all specimens were tested for mechanical properties in a quasi-static tensile test. In addition, the material hardness was determined. (3) It was found that, firstly, heat treatment resulted in a sharp increase in mechanical properties such as hardness, elastic modulus, yield strength and ultimate strength. In addition to the increase in these properties, the elongation at break also decreases significantly after heat treatment. The choice of process, on the other hand, does not give either process a clear advantage in terms of mechanical properties but shows that it is necessary to consider the essential mechanical properties for a desired application. Full article

NiMo sulfide catalysts were prepared by the impregnation of high surface area supports with an aqueous solution made of NiCO₃·2Ni(OH)₂, MoO₃ and citric acid, followed by freeze drying and sulfidation in H₂S/H₂ mixture. N₂ physisorption and X-ray diffraction were selected to investigate the amphoteric oxides Al₂O₃ and TiO₂, acidic SiO₂-Al₂O₃ and activated carbon supports, fresh prepared sulfide NiMo catalysts and spent catalysts after model parallel reaction of octanoic acid deoxygenation and 1-benzothiophene hydrodesulfurization. The studied mesoporous amphoteric oxides Al₂O₃ and TiO₂ did not lead to highly active NiMo catalysts due to the low hydrothermal stability of these supports during the preparation of the active sulfide phase and deoxygenation reaction. The most active catalyst based on oxidic support was the NiMo sulfide supported on acidic mesoporous SiO₂-Al₂O₃, which was explained by the increased stability of this support to the water and CO/CO₂ mixture during the activation of the sulfidic phase and deoxygenation reaction. The extraordinarily high stability of the activated carbon support led to outstanding activities of the sulfidic NiMo/C catalyst. Full article