Substrate For Nucleation Research Articles

Effect of ultra-fine grain zone on mechanical properties of CuCrZr-Hastelloy X bimetallic structure manufactured by laser-directed energy deposition

In this study, CuCrZr-Hastelloy X bimetallic structure featuring an ultra-fine grain zone (UFGZ) near the interface were fabricated by laser-directed energy deposition (L-DED). Samples with UFGZ were obtained with 300 °C preheating, whereas samples without preheating did not contain UFGZ. The microstructures and mechanical properties of samples with and without UFGZ were compared. The formation of UFGZ was attributed to the presence of a spherical phase near the interface, which was identified as Ni (Fe, Cr, Mo). Due to the higher melting point of Hastelloy X compared to CuCrZr, Ni elements mixed into CuCrZr with the flow of the molten pool, solidified first, and served as substrates for the heterogeneous nucleation, ultimately promoting the formation of UFGZ. With 300 °C preheating, the hardness of CuCrZr near the interface increased from 115.07 HV to 148.51 HV due to the presence of UFGZ. And the hardness gap near the interface decreased from 172.58 HV to 147.19 HV, which improved the uniformity of mechanical properties. Moreover, the nanoindentation tests results that UFGZ increased the hardness of the zone near the interface from 1.42 GPa to 1.72 GPa. Tensile test results indicated that the UFGZ altered the fracture mode from brittle to ductile. Samples with UFGZ exhibited ductile fracture, while those without UFGZ exhibited brittle fracture. At room temperature, the tensile strength of samples with UFGZ increased from 298.44 MPa to 347.05 MPa. For tests conducted at 400 °C, the tensile strength increased from 165.12 MPa to 229.53 MPa. This enhancement indicated that UFGZ could improve the strength and toughness of the interface, thereby enhancing the interfacial bonding strength. This study is of great significance for improving the interfacial bonding strength of CuCrZr-Hastelloy X bimetallic structures.

Pre-planting amorphous carbon films based on Ir composite substrates for diamond nucleation

A tunable locally ordered amorphous carbon layer was pre-implanted on the iridium (Ir) composite substrate using a multi-excitation source plasma coating system. The nucleation interface was mainly studied by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that by designing and modulating the content and ordering of sp2/sp3 hybridized carbon bonds in the amorphous carbon on the surface of Ir thin films, an overall ordered diamond nucleation layer was obtained. When the pulse frequency of the carbon source was regulated to 9 Hz, the (100) diamond grains were uniformly aligned without the appearance of twins after 4 h of growth, and the nucleation density was 7.5 × 109 cm−2, which was subsequently expected to obtain single-crystal diamond by grain boundary annihilation. Based on the Ir-amorphous carbon pre-growth layer, it can accelerate the dissolution-precipitation process of carbon ions into the Ir film to form a supersaturated solid solution during the bias nucleation, and increase the nucleation sites, which is of great significance for improving the nucleation density of large-size single-crystal diamond heterogeneous epitaxy.

Enhanced nucleation at Al(111)/Ti3AlC2(0001) interfaces: The role of doping in adhesion and interfacial stability

This study investigates the structure of the Al(111)/Ti3AlC2(0001) interface and elucidates the mechanism of heterogeneous nucleation of Ti3AlC2 particles within aluminum-based composite materials. A comprehensive examination of adhesion work, interfacial energy, and electronic structure is conducted for pristine and doped Al(111)/Ti3AlC2(0001) interfaces. The findings reveal that the C(TiC)-terminated hexagonal close-packed (HCP) stacking configuration at the Al(111)/Ti3AlC2(0001) interface exhibits the highest adhesion work and the lowest interfacial energy. This is attributed to the prominent covalent bonding between Al-3p and C-2p orbitals, indicating robust interfacial bonding strength and stability. Consequently, the results substantiate the potential of Ti3AlC2 particles as suitable substrates for heterogeneous nucleation of α-Al grains, effectively enhancing the strength and ductility of aluminum-based composites. Notably, doping the interface layer with specific elements significantly influences the adhesion work and interfacial energy. Introducing Ti and Mn at the interface substantially enhances adhesion work and concurrently reduces the interfacial energy of the C(TiC)-terminated HCP stacking Al(111)/Ti3AlC2(0001) interface, actively promoting nucleation of the aluminum matrix. However, incorporating Mg, Cu, and Zn at the interface decreases the adhesion work, unfavorable for the nucleation of Ti3AlC2 on the aluminum matrix. The binding energy at the doped Al(111)/Ti3AlC2(0001) interface follows the hierarchy: Mn > Ti > Mg > Cu > Zn. These findings provide valuable insights into the distinctive characteristics of Al(111)/Ti3AlC2(0001) interfaces and the underlying nucleation processes, holding substantial promise for the development of advanced aluminum-based composites.

Sedimentary dolomite in Western Australia and the dolomite problem: Genesis of channel and playa uranium deposits

ABSTRACTQuaternary to Recent sedimentary dolomite in groundwater calcrete and saltmarsh sediments of Lake Way and Lake Maitland, Western Australia, provide new information about the formation of low‐temperature dolomite. Dolomite can form through numerous pathways depending on the depositional and diagenetic environment. Many pathways involve microbial processes and/or the presence of a nucleation substrate which help overcome kinetic barriers preventing precipitation in the laboratory. Petrographic, mineralogical, hydrogeochemical and stable isotopic data in this study reveal the importance of Mg‐clays as nucleation sites for dolomite precipitation in a range of aquifer environments. There is also a close association between authigenic Mg‐clays, dolomite and the potassium–uranyl–vanadate ore mineral carnotite in channel and playa uranium deposits. It is interpreted that evaporation‐driven precipitation of dolomite establishes a positive feedback loop promoting the dissociation of aqueous uranyl–carbonate complexes and concomitant increase in carnotite saturation. Critical to this model is the presence of authigenic Mg‐clays because they facilitate dolomite precipitation and promote carnotite nucleation by concentrating potassium ions on clay surfaces via adsorption. This Mg‐clay–dolomite–carnotite relationship is widespread throughout Western Australian channel and playa uranium deposits and has been observed in similar deposits in Namibia and Botswana. In addition to this economic implication, Mg‐clay mediated nucleation of dolomite potentially has global relevance as a precipitation mechanism for low temperature dolomite in sedimentary deposits where detrital and/or authigenic Mg‐clays are present. Maturation of sedimentary dolomite from disordered high‐calcian dolomite to ordered low‐calcian dolomite occurs very early in the meteoric realm making it resistant to alteration during burial diagenesis. Diagenetic resistance may be further increased by early meteoric silicification related to the degradation of associated Mg‐clays. These findings indicate that Mg‐clay associated sedimentary dolomite has potential to retain a primary isotopic signature indicative of its origin, making it a useful recorder of palaeoenvironmental conditions.

Composition templating for heterogeneous nucleation of intermetallic compounds.

Refinement of intermetallic compounds (IMCs) through enhancing heterogeneous nucleation during casting process is an important approach to improve the properties of aluminium alloys, which greatly increases the economy value of recycled Al-alloys. However, heterogeneous nucleation of IMCs is inherently more difficult than that of a pure metal or a solid solution. It requires not only creation of a crystal structure but also the positioning of 2 or more different types of atoms in the lattice with specific composition close to that of the nucleated IMCs. Previous understanding on heterogeneous nucleation is based on structural templating, usually considering the small lattice misfit at the interface between the nucleating solid and substrate. In this work, we proposed a hypothesis and demonstrated that composition templating plays a critical role in heterogeneous nucleation of IMCs. The experimental results revealed that segregation of Fe atoms on the AlB2 surface, i.e., the Fe modified AlB2 particle, provides the required composition templating and hence enhances heterogeneous nucleation of α-Al15(Fe, Mn)3Si2, resulting in a significant refinement of the α-Al15(Fe, Mn)3Si2 particles in an Al-5Mg-2Si-1.0Mn-1.2Fe alloy.

A critique of using epitaxial criterion to discriminate between protogenetic and syngenetic mineral inclusions in diamond

Distinguishing syngenetic from protogenetic inclusions in natural diamonds is one of the most debated issues in diamond research. Were the minerals that now reside in inclusions in diamonds born before the diamond that hosts them (protogenesis)? Or did they grow simultaneously and by the same reaction (syngenesis)? Once previously published data on periclase [(Mg,Fe)O] and magnesiochromite (MgCr2O4) inclusions in diamond have been re-analysed, we show that the main arguments reported so far to support syngenesis between diamond and its mineral inclusions, definitely failed. Hence: (a) the epitaxial relationships between diamond and its mineral inclusion should no longer be used to support syngenesis, because only detecting an epitaxy does not tell us which was the nucleation substrate (there are evidences that in case of epitaxy, the inclusion acts as a nucleation substrate); (b) the morphology of the inclusion should no longer be used as well, as inclusions could be protogenetic regardless their shapes. Finally, we advance the hypothesis that the majority of inclusions in diamonds are protogenetic, e.g., they are constituent of rocks in which diamonds were formed and not products of reactions during diamond growth.

Evaluating the Role of Titanomagnetite in Bubble Nucleation: Novel Applications of Low Temperature Magnetic Analysis and Textural Characterization of Rhyolite Pumice and Obsidian From Glass Mountain, California

AbstractNucleation of H2O vapor bubbles in magma requires surpassing a chemical supersaturation threshold via decompression. The threshold is minimized in the presence of a nucleation substrate (heterogeneous nucleation, <50 MPa), and maximized when no nucleation substrate is present (homogeneous nucleation, >100 MPa). The existence of explosively erupted aphyric rhyolite magma staged from shallow (<100 MPa) depths represents an apparent paradox that hints at the presence of a cryptic nucleation substrate. In a pair of studies focusing on Glass Mountain eruptive units from Medicine Lake, California, we characterize titanomagnetite nanolites and ultrananolites in pumice, obsidian, and vesicular obsidian (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336), calculate titanomagnetite crystal number densities, and compare titanomagnetite abundance with the physical properties of pumice to evaluate hypotheses on the timing of titanomagnetite crystallization. Titanomagnetite crystals with grain sizes of approximately 3–33 nm are identified in pumice samples from the thermal unblocking of low‐temperature thermoremanent magnetization. The titanomagnetite number densities for pumice are 1018 to 1020 m−3, comparable to number densities in pumice and obsidian obtained from room temperature methods (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336). This range exceeds reported bubble number densities (BND) within the pumice from the same eruptive units (average BND ∼4 × 1014 m−3). The similar abundances of nm‐scale titanomagnetite crystals in the effusive and explosive products of the same eruption, together with the lack of correlation between pumice permeability and titanomagnetite content, are consistent with titanomagnetite formation having preceded the bubble formation. Results suggest sub‐micron titanomagnetite crystals are responsible for heterogeneous bubble nucleation in this nominally aphyric rhyolite magma.

Grain refinement of Mg-Ca alloys by native MgO particles

In Mg-Ca alloys the grain refining mechanism, in particular regarding the role of nucleant substrates, remains the object of debates. Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys, the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet. Herein, we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO, which are then comprehensively studied by advanced electron microscopy. The results show that grain refinement is enhanced as the particle number density of MgO increases. The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface. Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy, we reveal the nature of these Ca/N interfacial layers at the atomic scale. Irrespective of the crystallographic termination of MgO, Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites, respectively, forming an interfacial structure of a few atomic layers. The interfacial structure is slightly expanded, less ordered and defective compared to the MgO matrix due to compositional deviations, whereby the MgO substrate is altered as a poorer template to nucleate Mg solid. Upon solidification in a TP-1 mould, the impotent MgO particles account for the grain refining mechanism, where they are suggested to participate into nucleation and grain initiation processes in an explosive manner. This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.

Evolution of static recrystallization microstructure caused by residual strain of an Al-richen Ni-based single crystal superalloy

Recrystallization has a devastating effect on the service process of single crystal superalloys (SX). This study mainly investigated the static recrystallization (SRX) behavior of an as-cast high Al content nickel-based SX under local or global deformation at room temperature, as well as heat treatment at various temperatures. The microstructural evolution was observed under different conditions using electron back scatter diffraction (EBSD), which was employed to determine the SRX threshold. The results indicated that the critical SRX temperature exceeds 1260 °C, and the critical plastic strain is greater than 5 %. In particular, the characteristic of the higher SRX tendency in the interdendritic region (IDR) of the as-cast SX was discovered, which was attributed to the phenomenon that the IDR with lower deformation resistance was prone to significant plastic accumulation and the bulk γ' could be the nucleation substrate of the SRX. Furthermore, with the increase in heat treatment temperature, there are certain changes in the morphology characteristics of re-precipitated γ' in the vicinity of the SRX grain boundary with a higher migration rate. This is mainly attributed to the decrease in the internal subcooling of the bulk γ' phase and the increase in the concentration of γ' forming elements at the grain boundary front.

Nature of Oxides in Al–Mg Alloys

Acting as substrates for heterogeneous nucleation, native oxides in Al–Mg alloys have shown their potential for grain refinement. However, the limited knowledge about the nature of the oxides in Al–Mg alloys impedes the widespread application as native grain refiners. The aim of this work is to comprehensively investigate the native oxides in Al–Mg alloys through electron microscopy. Our results show that the predominant inclusions in Al–Mg alloys are oxides in three types of oxide films at the micrometer scales: young films, old films and oxide skins. All oxide films consist of discrete oxide particles of three types in nanometer scale depending on the Mg contents: γAl2O3 (< 0.4 wt.%), MgAl2O4 (0.08–3.5 wt.%) and MgO (> 2 wt.%). Specifically, MgAl2O4 particles have sizes ranging from a few tens to a few hundreds nanometer and possess an elementary shape of octahedron faceted by {111} planes. In Al–Mg alloys, the native oxides have a lognormal size distribution, with the average mean size fluctuating in accordance with the oxide configurations as Mg content varies. The agglomerating feature causes inhomogeneous sampling, and dual-peak lognormal curves are found for low-Mg-content alloys (0.08/0.4%), which could be eliminated by increasing the Mg content (2.0/3.5%) or by using the high-shear melt conditioning (HSMC) technology. Understanding the native oxides in Al–Mg alloys shall provide instructions on their application in grain refinement.

Effect of self‐seed crystal structure on growth of polymorphs in poly(butylene 2,6‐naphthalate): A cross‐nucleation study

AbstractCross‐nucleation between different crystal polymorphs is a particular, self‐seed assisted type of heterogeneous nucleation, where a fast‐growing polymorph nucleates at a pre‐existing crystal surface of another polymorph. Here, we present a study on cross‐nucleation between different crystalline phases of poly(butylene 2,6‐naphthalate) (PBN), employing hotstage polarized‐light optical microscopy and temperature‐resolved wide‐angle X‐ray scattering as analysis tools. PBN forms α‐crystals at relatively low temperature and β′‐crystals at rather high temperature, with cross‐nucleation experiments designed such to first obtain few α‐ or β′‐seed crystals (mother phase) which then are transferred to higher or lower temperature, respectively, to monitor the continuation of the crystallization process and possible growth of the other polymorph. In case of cooling β′‐crystals to lower temperature where typically α‐crystals form in the non‐seeded isotropic melt, β′‐crystals nucleate growth of α‐crystals, following many examples of cross‐nucleation in the literature. In contrast, if low‐temperature‐generated α‐crystals are heated to a temperature where β′‐crystals form in a non‐seeded melt, the cross‐nucleation efficacy is reduced as, beside growth of cross‐nucleated β′‐crystals, also growth of the mother phase is observed. This unexpected result demonstrates the importance of the structure of the nucleating substrate and the interplay between kinetic and thermodynamic aspects of crystal growth.

Comparative study of alternating dry and wet corrosion behavior of Q345qDNH steel and Q420qENH steel in industrial atmospheric media containing PM2.5

AbstractThe corrosion behavior of Q345qDNH steel and Q420qENH steel under the industrial atmosphere containing PM2.5, as well as the effect of PM2.5 on the rust layer were studied by dry–wet alternating accelerated corrosion experiment. The results show that the corrosion rate of Q345qDNH is always less than that of Q420qENH, the Cr content of rust layer is higher than that of Q420qENH steel. After 30 days of corrosion, compared with Q420qENH steel, the self‐corrosion potential of Q345qDNH is larger, the self‐corrosion current density is smaller, and the rust resistance is 1.49 times of Q420qENH steel, the Iα‐FeOOH/Iγ‐FeOOH ratio is 1.29 times of Q420qENH, indicating that the protection of the rust layer of Q345qDNH is better than that of Q420qENH. This is due to the effect of microstructure factors in the early stage of corrosion and alloying elements in the late stage of corrosion. PM2.5 with SiO2 as the main component is easy to deposit at cracks and holes, which becomes the nucleation substrate for corrosion products, promotes the nonuniform nucleation of corrosion products, making the rust layer develop unevenly, leading to an increase in holes in the outer rust layer.

Effect of trace rare earth La on microstructure and properties of Al-7%Si-0.6%Fe alloy

&lt;sec&gt;Al-Si alloys have been widely used in electronic information, communication, and other fields because of their high specific strength, excellent castability and good thermal conductivity. In recent years, with the rapid development of 5G communication technology, electronic communication equipment is gradually developing towards high integration and lightweight. The power of related equipment is higher and higher, which puts forward higher requirements for thermal conductivity and mechanical properties of materials.&lt;/sec&gt;&lt;sec&gt;Si can improve the fluidity and strength of the Al-Si alloy, but a large amount of Si will aggravate the lattice distortion and increases amount of eutectic Si. This will reduce the plasticity of the alloy, increase the electron scattering and reduce the thermal conductivity. In order to improve the mechanical properties and thermal conductivity of Al-Si alloys, chemical inoculation is generally used. Sr is usually used as modifier and Al-B serves as grain refiner. However, the simultaneous addition of Sr and B into Al-Si alloy results in “poisoning” phenomenon, it becomes impossible to refine &lt;i&gt;α&lt;/i&gt;-Al grains and modify eutectic Si simultaneously.&lt;/sec&gt;&lt;sec&gt;In recent years, rare earth La has attracted more and more attention in improving the properties of aluminum alloys. However, previous studies mainly focused on the effects of La addition, consequently, the research on the effects of combined addition of La, Sr, B on the microstructure and properties of Al-7%Si-0.6%Fe alloy is lacking. In this work, solidification experiments are performed to investigate the effects of combined addition of La, Sr, B on the microstructure and properties of Al-7%Si-0.6%Fe alloy. The results show that the addition of trace rare earth La can effectively eliminate the poisoning effect of Sr and B, and enhance the modification effect of eutectic Si. Besides, the addition of La can promote the formation of &lt;i&gt;α&lt;/i&gt;-Al heterogeneous nucleation substrate LaB&lt;sub&gt;6&lt;/sub&gt; and La can be used as a surfactant to reduce the undercooling of &lt;i&gt;α&lt;/i&gt;-Al nucleation, thus it refines &lt;i&gt;α&lt;/i&gt;-Al grains. The thermal conductivity of the alloy is significantly improved when the addition of La ranges from 0.02% to 0.06%; with the further increase of La addition, LaAlSi intermetallic compounds are formed in the alloy, leading the thermal conductivity of the alloy to decrease.&lt;/sec&gt;

A capillary-induced negative pressure is able to initiate heterogeneous cavitation.

A capillarity-induced negative pressure is of general importance for understanding the phase behaviors of liquids in small pores and cracks. A unique example is the embolism in the xylem of plants and the cavitation at the limiting negative pressure generated by evaporation of water from nanocapillaries in the cell walls of leaves. In this work, by combining the effect of a capillary and cavitation together, we demonstrate with molecular dynamics (MD) simulations that capillarity is able to induce spontaneous cavitation in the presence of hydrophobic heterogeneities. Our simulation results reveal separately how the capillary generates a negative pressure and how the generated negative pressure affects the onset of cavitation. We then interpret the cavitation mechanism and determine the occurrence of cavitation as a function of the hydrophobicity of the nucleating substrates where the cavitation initiates and as a function of the hydrophilicity of the capillary tube from which the negative pressure generates. Our results reveal that the capillary-induced cavitation can be described well with a heterogeneous nucleation mechanism, within the framework of classical nucleation theory.

First-principles investigation on the tensile strength, interfacial stability and electronic structure of the heterogeneous nucleation Al/VB2 interfaces

First principles calculations based on the density functional theory were performed on the interfacial properties of Al(111)/VB2(001) and Al(100)/VB2(100) interfaces including interfacial stability, bonding features and tensile strength. Fourteen different interfaces with different VB2 terminations (V-terminated and B-terminated) were studied. The convergence test shows that 7-layered Al(111) and 9-layered Al(001), 9-layered VB2(001) and 13-layered VB2 (100) are thick enough to build Al/VB2 interface. The (001)-V-hcp and (100)-V-cen site interface have the largest work of adhesion (Wad) among the Al(111)/VB2(001) and Al(100)/VB2(100) interfaces. And under V-rich condition, there interfacial energies are − 0.44 J/m2 and − 0.45 J/m2 which are much lower than 0.15 J/m2, indicating it is an effective heterogeneous nucleation substrate for α-Al. The main bonding characteristics is metallic for the (001)-V-hcp interface, while it is covalent with metallic for the (100)-V-cen interface, making it has the largest Wad. The calculated tensile strength of (001)-V-hcp site interface is about 7.36Gpa when the strain is 12 %. While it is 6.27Gpa for the (100)-V-cen site interface at 10 %. Finally, the VB2 particles are proved to be an effective heterogeneous nucleation substrate for α-Al as observed from experiment.

Influence of cerium and yttrium addition on strength and electrical conductivity of pure aluminum alloys

To develop pure aluminum alloys with high conductivity and strength, Al-0.2Ce and Al-0.2Ce-0.1Y alloys were prepared by rolling and annealing processes in this study. The effects of trace rare earth elements on the strength and electrical conductivity of the pure aluminum alloys were investigated. It is revealed that the addition of Ce and Y to pure aluminum can effectively enhance the strength and electrical conductivity of the alloys. In Al-0.2Ce, the addition of Ce can effectively refine the grain size of α-Al, with an average grain size of 90.68 μm in the as-cast state. The grain size of the alloy is further reduced to 87.55 μm by the simultaneous addition of Y. The synergistic addition of Ce and Y changes the properties of the alloy. The addition of Ce and Y also produces the Al11Ce3 and Al3Y second phases, which have coherent relationship with α-Al. The two-dimensional mismatch degree was calculated to be only 4.43% and 0.85%, respectively, which can provide a certain amount of nucleation substrate for α-Al in the incubation stage. The interfacial match between the L12 structure of Al3Y and α-Al was calculated using first-principles simulations. The results indicate that Al3Y has a strong bonding effect with α-Al. Nanoscale second phases at grain boundaries can be effective in reducing resistivity due to dislocation motion. Nanoscale second phases with better matching interfaces to the substrate have no positive effect on the scattering motion of electrons.

Sonosynthesis of manganese ferrite nanoparticles on the cellulosic fabric and production of colored nanocomposite with magnetic and photocatalytic properties via statistically optimized method

Cellulosic fibers provide a favorable substrate for nucleation and growth of the nanoparticles. Manganese ferrite nanoparticles can serve as catalysts for various purposes. Here, sonosynthesis of manganese ferrite nanoparticles on cotton fabric was carried out through sonochemical processing by using iron chloride and manganese chloride salts at different temperatures and times in alkaline media. Also, the central composite design based on the response surface methodology was used to optimize the production conditions such as temperature and time. The formation of synthesized nanoparticles on cotton was evaluated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and elemental mapping tests. FESEM images confirmed the spherical manganese ferrite nanoparticles with an average size of 48 nm on cotton fabric. The photocatalytic activities, washing and lightfastness, and magnetic, mechanical, and colorimetric properties of the modified fabrics were investigated. The nanocomposites boosted methylene blue photodegradation under sunlight. In addition, the vibrating sample magnetometer (VSM) test indicated the paramagnetic nature of the manganese ferrite nanoparticles with a magnetic saturation of 1.32 emu/g. The treated fabrics with the proper magnetic properties are suitable for use in diverse applications such as supercapacitors.

No biological effect on magnesium isotope fractionation during stromatolite growth

The growth and morphology of stromatolites have been previously linked to diverse microbial activities. However, the role of microbial metabolisms on carbonate formation during stromatolite growth remains controversial. Magnesium isotopes have been proposed to serve as a tracer of microbial carbonate formation, implying a potential biological isotope fractionation. To further elucidate whether Mg isotope fractionation is modified during microbial carbonate formation, this study reports Mg isotope compositions of Holocene stromatolites and pore waters from Lagoa Salgada, a coastal ephemeral lake in Brazil. The stromatolitic carbonates are composed of high-Mg calcites characterized by extremely positive inorganic δ13C values, up to +20‰, and variable δ26Mg values, ranging from −2.98‰ to −0.68‰. Multiple pieces of evidence consistently demonstrate changes in microbial metabolism resulting from ecosystem fluid chemistry evolution. However, the direction of Mg isotope fractionation associated with carbonate precipitation remained invariable despite the changes in microbial activity. Mineralogical features indicate that the stromatolitic carbonates formed via 2-D nucleation. An isotopic mass balance calculation based on the observed variations in δ26Mg values and Mg concentrations of associated pore waters argues for an Mg isotopic equilibrium fractionation factor of −2.60‰ associating with the carbonate formation at Lagoa Salgada, well-matching experimental values for abiotic calcite precipitation. Thus, the observed δ26Mg variability of stromatolitic carbonates is primarily controlled by the changes of physicochemical conditions in the ambient fluid. We infer that during the formation of stromatolites, a consortium of different microbial communities produces extracellular polymeric substances, which serve as a substrate for carbonate nucleation from ambient fluid without significantly affecting the fractionation of Mg-isotopes. Our findings shed light on the effects of microbial processes on carbonate formation during stromatolite growth and improve the current understanding of the Mg isotope record in microbial carbonates.

Segregation of Yttrium at the Mg/MgO interface in an Mg-0.5Y Alloy

Interfacial segregation of selected elements can be exploited to manipulate the potency of solid substrates for heterogeneous nucleation, thus controlling the solidification process. As the native inclusions in Mg alloys, MgO acts as the nucleating substrate, but it has rarely been studied in terms of its interactions with alloying elements. In this work, investigations of yttrium (Y) segregation at interfaces between native MgO particles and Mg in an Mg-0.5Y alloy were carried out by state-of-the-art aberration-corrected scanning transmission electron microscopy (STEM) and associated spectroscopy. Experimental results show that native MgO particles in Mg-0.5Y possess two typical morphologies: truncated octahedron primarily faceted by {111}MgO and minorly by {100}MgO, and cubic shape with unique {100}MgO facets. Y atoms are found to segregate at both Mg/{111}MgO and Mg/{100}MgO interfaces, leading to the formation of two different 2-dimensional compounds (2DCs). The 2DC at the Mg/{111}MgO interface is identified as two atomic layers of a face-centered cubic Y2O3 phase in terms of crystal structure and chemistry, whilst it is an Mg(Y)-O monolayer at the Mg/{100}MgO interface, coherently matching with the terminating {100}MgO plane. Discussion is focused on the mechanisms underlying the formation of the 2DCs, their effects on the nucleation potency of MgO particles, and grain refinement. This work sheds light on how heterogeneous nucleation can be manipulated by altering the nucleation potency of a substrate through deliberately promoting elemental segregation of carefully chosen element(s).

Hierarchical construction of MoSe2 nanoparticles anchored on N-doped porous carbon nanocages with Mo-C bonding for enhanced potassium-ion storage

Molybdenum selenide (MoSe2) is considered as a promising anode material for potassium ion batteries (PIBs) due to its high theoretical capacity and large interlayer spacing. However, the low intrinsic conductivity and large volume expansion impede its practical application. Herein, hierarchical nanostructure of MoSe2 nanoparticles tightly anchored on hollow porous nitrogen-doped carbon nanocages (MoSe2/NCC) is constructed as an anode material for PIBs. Nitrogen-doped carbon nanocages not only improve the conductivity, provide more active sites, and alleviate the volume expansion during K+ insertion and desertion, but also serve as a nucleation substrate for suppressing the agglomeration of MoSe2 nanoparticles. Importantly, the structural stability and electron/ion transfer kinetics are significantly enhanced by strong interfacial coupling between MoSe2 and carbon via the formation of Mo-C bonding. Consequently, MoSe2/NCC electrode exhibits a reversible capacity of 321 mA h g−1 at 0.1 A g−1, excellent cycling stability with a retention of 323 mA h g−1 after 80 cycles, and rate capability of 173 mA h g−1 at 5 A g−1. In addition, the storage mechanism and transfer kinetics of potassium ions during the charging and discharging process are investigated. This work paves the ideas for the design of novel anode materials for high-rate and stable PIBs.