Lower Gibbs Free Energy Research Articles

Effects of the proportions of carbon on the microstructure and properties of NbC-reinforced Ni-WC composite coatings by laser cladding in-situ synthesis

Laser cladding was utilized to prepare NbC carbide-enhanced Ni-WC composite coatings in the work. First-principle calculations and tests were conducted to study the effects of different proportions of carbon on the characteristics and organization of in-situ synthesized NbC-enhanced coatings. Firstly, differences in coating phases and microstructures were analyzed under different proportions of carbon according to the experiment. NbC with lower Gibbs free energy was the first to precipitate, and other compounds were non-uniformly nucleated around NbC in terms of thermodynamic calculation results. The higher the proportion of carbon, the finer the grain structure. The tests of hardness and friction wear showed that the higher the proportion of carbon, the better the hardness and wear resistance of the coating. The difference in grain morphology was the main reason for the difference in coating performance. Secondly, the first-principles calculation was used to model NbCx. The elastic modulus, mechanical properties, anisotropy, and electronic properties of carbides were calculated to explore the effects of carbon vacancies on the properties of NbC. The mechanical properties of carbides decreased with increased carbon vacancies, accompanied by increased anisotropy and weakened covalence. The results provide a theoretical foundation for understanding the effects of the proportions of carbon on nickel-based composite coatings prepared by laser cladding.

Adsorption and removal of polystyrene nanoplastics from water by green-engineered clays

Human exposure to micro- and nanoplastics (MNPs) commonly occurs through the consumption of contaminated drinking water. Among these, polystyrene (PS) is well-characterized and is one of the most abundant MNPs, accounting for 10 % of total plastics. Previous studies have focused on carbonaceous materials to remove MNPs by filtration, but most of the work has involved microplastics since nanoplastics (NPs) are smaller in size and more difficult to measure and remove. To address this need, green-engineered chlorophyll-amended sodium and calcium montmorillonites (SMCH and CMCH) were tested for their ability to bind and detoxify parent and fluorescently labeled PSNP using in vitro, in silico, and in vivo assays. In vitro dosimetry, isothermal analyses, thermodynamics, and adsorption/desorption kinetic models demonstrated 1) high binding capacities (173–190 g/kg), 2) high affinities (103), and 3) chemisorption as suggested by low desorption (≤42 %) and high Gibbs free energy and enthalpy (>|−20| kJ/mol) in the Langmuir and pseudo-second-order models. Computational dynamics simulations for 30 and 40 monomeric units of PSNP depicted that chlorophyll amendments increased the binding percentage and contributed to the sustained binding. Also, 64 % of PSNP bind to both the head and tail of chlorophyll aggregates, rather than the head or tail only. Fluorescent PSNP at 100 nm and 30 nm that were exposed to Hydra vulgaris showed concentration-dependent toxicity at 20–100 µg/mL. Importantly, the inclusion of 0.05–0.3 % CMCH and SMCH significantly (p ≤ 0.01) and dose-dependently reduced PSNP toxicity in morphological changes and feeding rate. The bioassay validated the in vitro and in silico predictions about adsorption efficacy and mechanisms and suggested that CMCH and SMCH are efficacious binders for PSNP in water.

Controllable Electrocatalytic to Photocatalytic Conversion in Ferroelectric Heterostructures.

Photocatalytic and electrocatalytic reactions to produce value-added chemicals offer promising solutions for addressing the energy crisis and environmental pollution. Photocatalysis is driven by light excitation and charge separation and relies on semiconducting catalysts, while electrocatalysis is driven by external electric current and is mostly based on metallic catalysts with high electrical conductivity. Due to the distinct reaction mechanism, the conversion between the two catalytic types has remained largely unexplored. Herein, by means of density functional theory (DFT) simulations, we demonstrated that the ferroelectric heterostructures Mo-BN@In2Se3 and WSe2@In2Se3 can exhibit semiconducting or metallic features depending on the polarization direction as a result of the built-in field and electron transfer. Using the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) as examples, the metallic heterostructures act as excellent electrocatalysts for these reactions, while the semiconducting heterostructures serve as the corresponding photocatalysts with improved optical absorption, enhanced charge separation, and low Gibbs free energy change. The findings not only bridge physical phenomena of the electronic phase transition with chemical reactions but also offer a new and feasible approach to significantly improve the catalytic efficiency.

Unveiling the inhibition of chlortetracycline photodegradation and the increase of toxicity when coexisting with silver nanoparticles

Silver nanoparticles (AgNPs) and antibiotics inevitably co-exist in water environment. Nonetheless, little is known regarding the interactions between AgNPs and antibiotics or the effects of AgNPs on environmental behavior of antibiotics, particularly on sunlight-driven transformation. In the present work, we found that AgNPs obviously inhibit the photochemical decay of chlortetracycline (CTC), and CTC boosts the dissolution of AgNPs. With the help of electron paramagnetic resonance (EPR) and quenching experiment, we ascertained that these results originated from the competition between AgNPs against CTC for capturing 1O2 generated from CTC photosensitization. 1O2 reacting with CTC contributed mostly to CTC photodegradation, while 1O2 as well reacting with AgNPs leads to release of Ag+. When compared to reaction of 1O2 with CTC, 1O2 is prone to react with AgNPs, based on lower Gibbs free energy of AgNPs reacting with 1O2. Therefore, upon CTC co-existing with AgNPs, the release of Ag+ was accelerated and the photodegradation of CTC was inhibited obviously. Furthermore, the accelerated release of Ag+ significantly increased their toxicity toward E. coli cells under simulate sunlight irradiation. Overall, the findings demonstrate how AgNPs interact with CTC and how these interactions affect the environmental behaviors of CTC or AgNPs, allowing more accurate assessments of the risk to ecosystems posed by AgNPs coexisting with antibiotics.

Tailoring the Hydrophobic Interface of Core-Shell HKUST-1@Cu2O Nanocomposites for Efficiently Selective CO2 Electroreduction.

The electrochemical reduction of carbon dioxide (CO2) to ethylene creates a carbon-neutral approach to converting carbon dioxide into intermittent renewable electricity. Exploring efficient electrocatalysts with potentially high ethylene selectivity is extremely desirable, but still challenging. In this report, a laboratory-designed catalyst HKUST-1@Cu2O/PTFE-1 is prepared, in which the high specific surface area of the composites with improved CO2 adsorption and the abundance of active sites contribute to the increased electrocatalytic activity. Furthermore, the hydrophobic interface constructed by the hydrophobic material polytetrafluoroethylene (PTFE) effectively inhibits the occurrence of hydrogen evolution reactions, providing a significant improvement in the efficiency of CO2 electroreduction. The distinctive structures result in the remarkable hydrocarbon fuels generation with high Faraday efficiency (FE) of 67.41%, particularly for ethylene with FE of 46.08% (-1.0V vs RHE). The superior performance of the catalyst is verified by DFT calculation with lower Gibbs free energy of the intermediate interactions with improved proton migration and selectivity to emerge the polycarbon（C2+） product. In this work, a promising and effective strategy is presented to configure MOF-based materials with tailored hydrophobic interface, high adsorption selectivity and more exposed active sites for enhancing the efficiency of the electroreduction of CO2 to C2+ products with high added value.

Integrating CaIn2S4 nanosheets with Co3O4 nanoparticles possessing semiconducting and electrocatalytic properties for efficient photocatalytic H2 production

A well-designed photocatalytic system needs to have broad light absorption, efficient charge separation and transfer kinetics, and excellent photostability. However, achieving these characteristics with a single photocatalyst is challenging. In this study, we propose coupling CaIn2S4 nanosheets with narrow band gap Co3O4 nanoparticles, which possess semiconducting and electrocatalytic properties, to form a Type II heterojunction with strong built-in electric field and high surface catalytic activity. We employs a two-step hydrothermal reaction to obtain the Co3O4/CaIn2S4 composite. The composite material displays an average rate of H2 evolution of 457.0 μmol g−1·h−1, which is 32.2 times higher than the rate achieved using pure CaIn2S4. Additionally, the composite photocatalyst demonstrates minimal decline in H2 production in five consecutive cycles. Our mechanism investigation reveals that Co3O4 can act as a semiconductor, forming a Type II heterojunction with CaIn2S4 producing an efficient photoelectron transfer channel from the conduction band of CaIn2S4 to Co3O4. Simultaneously, Co3O4 effectively transfers the separated electrons into the aqueous solution, functioning as a promising cocatalyst with low H-adsorption Gibbs free energy, thus enhancing the H2 production performance. This study highlights the importance of properly aligning energy levels and surface catalysis acceleration in the rational design of novel photocatalytic composites.

Enhanced Solar Fuel Production over In2 O3 @Co2 VO4 Hierarchical Nanofibers with S-Scheme Charge Separation Mechanism.

The conversion of CO2 into valuable solar fuels via photocatalysis is a promising strategy for addressing energy shortages and environmental crises. Here, novel In2 O3 @Co2 VO4 hierarchical heterostructures are fabricated by in situ growing Co2 VO4 nanorods onto In2 O3 nanofibers. First-principle calculations and X-ray photoelectron spectroscopy (XPS) measurements reveal the electron transfer between In2 O3 and Co2 VO4 driven by the difference in work functions, thus creating an interfacial electric field and bending the bands at the interfaces. In this case, the photogenerated electrons in In2 O3 transport to Co2 VO4 and recombine with its holes, indicating the formation of In2 O3 @Co2 VO4 S-scheme heterojunctions and resulting in effective separation of charge carriers, as confirmed by in situ irradiation XPS. The unique S-scheme mechanism, along with the enhanced optical absorption and the lower Gibbs free energy change for the production of * CHO, significantly contributes to the efficient CO2 photoreduction into CO and CH4 in the absence of any molecule cocatalyst or scavenger. Density functional theory simulation and in situ diffuse reflectance infrared Fourier transform spectroscopy are employed to elucidate the reaction mechanism in detail.

A Reversible Six-Electron Transfer Cathode for Advanced Aqueous Zinc Batteries.

The electrochemical reactions for the storage of Zn2+ while embracing more electron transfer is a foundation of the future high-energy aqueous zinc batteries (AZBs). Herein, we report a six-electron transfer electrochemistry of nano-sized TeO2/C (n-TeO2/C) cathode by facilitating the reversible conversion of TeO2↔Te and Te↔ZnTe. Benefitting from the integrated conductive nanostructure and the proton-rich environment in providing optimized electrochemical kinetics (facilitated Zn2+ uptake and high electronic conductivity) and feasible thermodynamic process (low Gibbs free energy), the as-prepared n-TeO2/C with stable cycling performance exhibits a superior reversible capacity of over 800mAh g-1 at 0.1 A g-1. A precise understanding of the reaction mechanism via ex-situ and in-situ characterizations presents that the reversible six-electron transfer reaction is proton-dependent, and a proton generating and consuming mechanism of three-phase conversion n-TeO2/C in the acidic electrolyte is thoroughly revealed.

A Reversible Six‐Electron Transfer Cathode for Advanced Aqueous Zinc Batteries

AbstractThe electrochemical reactions for the storage of Zn2+ while embracing more electron transfer is a foundation of the future high‐energy aqueous zinc batteries. Herein, we report a six‐electron transfer electrochemistry of nano‐sized TeO2/C (n‐TeO2/C) cathode by facilitating the reversible conversion of TeO2↔Te and Te↔ZnTe. Benefitting from the integrated conductive nanostructure and the proton‐rich environment in providing optimized electrochemical kinetics (facilitated Zn2+ uptake and high electronic conductivity) and feasible thermodynamic process (low Gibbs free energy change), the as‐prepared n‐TeO2/C with stable cycling performance exhibits a superior reversible capacity of over 800 mAh g−1 at 0.1 A g−1. A precise understanding of the reaction mechanism via ex situ and in situ characterizations presents that the reversible six‐electron transfer reaction is proton‐dependent, and a proton generating and consuming mechanism of three‐phase conversion n‐TeO2/C in the weakly acidic electrolyte is thoroughly revealed.

Extremely high selective Si1−xGex-film wet etchant generating highly dissolved oxygen via peracetic acid oxidant for lateral gate-all-around FETs with a logic node of less than 3-nm

For lateral gate-all-around (LGAA) field-effect transistors (FETs) having design rules of logic devices below 3-nm and 3D-DRAM below 10-nm, multi-stacked Si1−xGex/Si-films should be epitaxially grown on the Si surfaces, and a highly selective wet etching of Si1−xGex-film is essentially followed for forming nanoscale-thick (5–7 nm) Si channel multi-sheets. A high selective etchant has required a lateral Si1−xGex etch rate of >30 nm⋅min-1 and etch rate selectivity between Si1−xGex- and Si-films of >200:1 at patterned multi-stacked Si1−xGex/Si-films. The selective Si1−xGex-film etchant using an etching agent (HF), a selectivity enhancing agent (CH3COOH), and a strong oxidant peracetic acid (PAA; CH3COOOH) unlike a conventional oxidant (H2O2 or HNO3) presented an extremely high Si0.5Ge0.5-film etch rate (82 nm⋅min-1@5 wt% of PAA) and etch rate selectivity between the Si0.5Ge0.5- and Si-films (265:1). Thus, it performed sufficient lateral Si1−xGex-film etching in the 3 multi-stacked Si0.5Ge0.5/Si-films line pattern and satisfied the requirement for a selective etching of Si1−xGex-film for LGAA having a logic-node of less than 2.1-nm. The excellent Si1−xGex-film etch rate using PAA was driven by a lower decomposition energy, lower Gibbs free energy, and higher standard reduction potential compared to the oxidant H2O2. Therefore, the amount of diffused dissolved oxygen using 5 wt% PAA was ∼1.48 times higher than that of H2O2; hence, the chemical oxidation degree (GeOx, and SiOx-bonds on the Si0.5Ge0.5-film surface) for 5 wt% PAA was ∼1.1 times higher than that of H2O2. Furthermore, the etch rate of the Si0.5Ge0.5-film using 5 wt% PAA was ∼5.4 times higher than that of H2O2; thus, we provide a cost effective Si1−xGex-film etching process for LGAA.

Mo2C nanocrystalline coupling with Ni encapsulated in N-doped fibrous carbon network as bifunctional catalysts towards advanced anion exchange membrane electrolyzers

Anion exchange membrane water electrolysis (AEMWE) has been considered to be the promising approach for cost-effective hydrogen production. However, the noble metal catalysts of AEM enable it still under the early stage of development. Herein, Mo2C nanocrystalline coupling with Ni have been successfully encapsulated into robust carbonaceous network (Mo2C/NC@0.5Ni) as inexpensive transition metal catalysts for AEM electrolyzers. The Mo2C nanocrystals are uniformly confined in N doped porous carbon network which is derived from the decomposition of PVP and urea during carbonation process. Importantly, rational designed Ni layers are also coated on the surface of the network structure. When utilized as bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the Mo2C/NC@ 0.5Ni can achieve desirable overpotentials of 103 mV and 307 mV at a current density of 10 mA cm−2 in 1 M KOH, respectively. Furthermore, the Mo2C/NC@ 0.5Ni‖Mo2C/NC@ 0.5Ni AEM electrolyzers requires only a voltage of 1.9 V to reach a current density of 110.5 mA cm−2 with remarkable durability over 50 h. Numerous interconnected porous structure and defects caused by N doping can provide abundant active sites, facilitate electrons transportations and suppress the aggregation of inner Mo2C. Particularly, the conductive Ni layers could effectively improve the structural strength and induce the synergistic effect with Mo2C component, thereby, improving the catalytic activity and stability. In addition, the DFT calculation results indicate that the Mo2C/NC@ 0.5Ni catalyst has a lower Gibbs free energy of hydrogen adsorption (ΔGH*=−0.21 eV), which is beneficial to its HER catalytic activity. This work provides an insight in developing advanced AEMWE for high efficient and green hydrogen production.

Theoretical Analysis of Metals Supported on Tungsten Oxide Nanowires (W18O49) for Water Dissociation Reaction

AbstractPt is the cause of the high total cost of fuel cells and electrolyzers, leading to difficult commercialization. Here, various types of metal atoms, i.e., Pt, Pd, Ni, Ir, Ag, and Rh, suitable for catalysts are used and supported by W18O49 nanowires for oxygen evolution reaction (OER) by the density functional theory (DFT) method. Four adsorbate molecules involved in OER were tested on adsorption energy: OH, O, OOH, and OO. Although the adsorption energy of these adsorbate molecules indicates that W18O49 has low adsorption energy, the Gibbs free energy diagram demonstrates that W18O49 has high OER reaction energy. Pt, Pd, Ni, and Rh have the lowest Gibbs energy to initiate the reaction and reasonable Gibbs free energy for other OER reactions. Bimetallic or trimetallic active sites can be developed along with selecting other metals with Pt, Pd, Rh, and Ni to reduce the Gibbs free energy difference for the decomposition of OH to O and OOH to H2O. Ag metal can also be applied as a second or third metal because Ag exhibits a relatively low Gibbs free energy difference in the O to OOH step. A selectivity study of each step on bimetallic and trimetallic active sites needs to be performed.

Effect of wire diameter on structure and electrical properties of (Al + Al2O3)-sheathed MgB2 with Nb barrier

Effect of wire diameter and annealing on the properties of internal magnesium diffusion (IMD)-processed MgB2 composite wires is studied by establishing a correlation with the characteristics of the interfacial reaction zones developed at Mg − B and barrier (Nb) – sheath (Al + Al2O3) interfaces. The MgB2 superconductor phase grows at the Mg − B interface along with the B-rich MgB4 phase. Formation of MgB2 prior to MgB4 is anticipated owing to a relatively lower Gibbs free energy at annealing temperatures studied. An intermetallic NbAl3 phase has developed at the barrier – sheath interface whose thickness decreases with an increase in the wire diameter. Development of NbAl3 further provides mechanical reinforcement and aids at yielding a dense superconductor phase. Resistivity – voltage characteristics of wire indicates the formation of MgB2 through a huge drop in resistivity values across the core of the wire. An annealing temperature of 645 °C near the melting point of pure Mg (650 °C) and annealing time of 120 min results in highest critical current of the MgB2 wire. Annealing time beyond 120 min has shown an impediment to the flow current due to crack propagation possibly because of accumulation of stresses within the developed superconductor phase due to grain growth. A significantly greater resistance for the wire with the smallest diameter is attributed to the formation of a thicker NbAl3 phase. However, highest engineering current density has also been attained by the wire with the smallest diameter annealed at 645 °C for 60 min.

1T-WS2/NCN photocatalyst with unique trion behavior and cyano-defects: Photocatalytic hydrogen evolution and mechanistic insights

The interfacial catalytic reaction rate determines the hydrogen production performance of the photocatalyst. In this work, high specific surface area and cyano-defects g-C3N4 with 1T-WS2 as a co-catalyst was prepared to construct 1T-WS2/NCN photocatalytic system. The two-electron interfacial catalytic reaction pattern formed due to the unique trions behaviour of 1T-WS2 greatly enhanced the interfacial catalytic reaction rate. Under 180 min of light, the hydrogen production of the photocatalytic system could reach 5769.3 μmol/g, which was 91.6 times that of the pristine g-C3N4. It was found that the excellent electrical conductivity of 1T-WS2 with metallic nature and the low Gibbs free energy of its active edge facilitated the hydrogen production and release. Meanwhile, the unique trions behaviour of the two-electron catalytic reaction formed in 1T-WS2 is a significant factor in increasing the rate of photocatalytic hydrogen production. And the cyano-defects in g-C3N4 acts as an electron trap, which drives charge space separation and provides sufficient electrons for trions formation, facilitating two-electron catalytic hydrogen production. This study provides a new idea for the development of electron-hole separation to improve the photocatalytic hydrogen production activity, which has important theoretical significance and application value.

Doped MoS2 Polymorph for an Improved Hydrogen Evolution Reaction.

Green hydrogen produced from solar energy could be one of the solutions to the growing energy shortage as non-renewable energy sources are phased out. However, the current catalyst materials used for photocatalytic water splitting (PWS) cannot compete with other renewable technologies when it comes to efficiency and production cost. Transition-metal dichalcogenides, such as molybdenum disulfides (MoS2), have previously proven to have electronic and optical properties that could tackle these challenges. In this work, optical properties, the d-band center, and Gibbs free energy are calculated for seven MoS2 polymorphs using first-principles calculations and density functional theory (DFT) to show that they could be suitable as photocatalysts for PWS. Out of the seven, the two polymorphs 3Ha and 2R1 were shown to have d-band center values closest to the optimal value, while the Gibbs free energy for all seven polymorphs was within 5% of each other. In a previous study, we found that 3Hb had the highest electron mobility among all seven polymorphs and an optimal bandgap for photocatalytic reactions. The 3Hb polymorphs were therefore selected for further study. An in-depth analysis of the enhancement of the electronic properties and the Gibbs free energy through substitutional doping with Al, Co, N, and Ni was carried out. For the very first time, substitutional doping of MoS2 was attempted. We found that replacing one Mo atom with Al, Co, I, N, and Ni lowered the Gibbs free energy by a factor of 10, which would increase the hydrogen evolution reaction of the catalyst. Our study further shows that 3Hb with one S atom replaced with Al, Co, I, N, or Ni is dynamically and mechanically stable, while for 3Hb, replacing one Mo atom with Al and Ni makes the structure stable. Based on the low Gibbs free energy, stability, and electronic bandgap 3Hb, MoS2 doped with Al for one Mo atom emerges as a promising candidate for photocatalytic water splitting.

Exploring Regio- and Stereoselectivity in [3+2] Cycloaddition: Molecular Electron Density Theory Approach for Novel Spirooxindole-Based Benzimidazole with Pyridine Spacer

A new ethylene derivative was synthesized as a precursor for the [3+2] cycloaddition (32CA) reaction to access a novel spirooxindole embodied with benzimidazole with a pyridine spacer. The chalcone derivatives 3a–j is obtained with condensation of the acetyl derivative with aryl aldehydes. The one-pot multi-component reaction of the ethylene derivative, 5-Cl-isatin, and octahydroindole-2-carboxylic acid enables the construction of a highly functionalized quaternary center spirooxindole scaffold in a high chemical yield. A study using the Molecular Electron Density Theory (MEDT) explains the complete regio- and stereoselectivity of the reaction, resulting in the exclusive formation of the ortho/endo-cycloadduct under kinetic control. The low activation Gibbs free energy is the result of the supernucleophilic character of the in situ-generated azomethine ylide and the strong electrophilic character of the ethylene derivatives.

Vacancy-induced spontaneous H2 evolution by overall water splitting on MoTe2/Ti2CO2: A two-dimensional direct Z scheme heterostructure

Photocatalysts with direct Z-scheme heterostructures hold great potential for hydrogen production by solar-driven overall water splitting. However, building highly efficient direct Z-scheme heterostructures is still a challenge. This work develops a novel MoTe2/Ti2CO2 heterostructure as a potential direct Z-scheme photocatalyst for overall water splitting. First-principles computations utilizing density functional theory (DFT) have been used in this study to carefully study several aspects of the heterostructure, including vdW binding energy, formation of the internal electric field, electronic structure, optical properties, and thermodynamic feasibility of water splitting. According to these calculations, the superior interlayer interaction in MoTe2/Ti2CO2 results in a substantial built-in electric field suitable for carrier separation. These findings indicate that the suggested vdW heterostructure is a direct Z-scheme water-splitting photocatalyst with suitable band alignments and a broad light absorption range. This enhanced interaction resulted in a significant increase of photocurrent compared to both the monolayers. Additionally, it is envisaged that the heterojunction will serve as photocatalyst for the oxygen evolution process (OER) and the hydrogen evolution process (HER). The results demonstrate that MoTe2/Ti2CO2 heterostructure with Te vacancy has a low Gibbs free energy of the HER, favoring spontaneous hydrogen evolution in both acidic and neutral conditions. The suggested heterostructure exhibits a commendable solar-to-hydrogen efficiency of 15.25%, making it a viable option for commercial implementation. This research offers a theoretical foundation for designing novel, two-dimensional overall water-splitting photocatalysts in an effort to produce clean energy.

Phase, chemical constitution and effective depth of oxide overgrowth and its influence on SmPrCo5 magnetic properties

Ternary Sm-Pr-Co magnets with CaCu5-type hexagonal structure exhibit superior magnetic properties and investigating their oxidation behavior is crucial for assessing their stability under the service conditions. In this regard, here thermal oxidation of sintered SmPrCo5 magnet is carried out by varying the oxidation temperature from 373 to 973 K for 5 hr under atmospheric pressure. Owing to their lower negative Gibbs free energy, rare earth oxides of Sm2O3 and Pr2O3 are found to initially form, making cobalt free from SmPrCo5 lattice. Cobalt is then observed to migrate to the oxide surface, because of the difference in chemical potential between the surface and inner layers, leading to Co3O4 formation. Moreover, here a comprehensive discussion on the occurrences of different oxide phases and their depth distributions in the oxide layer are being made. Finally, a correlation between these oxide phases and the alterations in their magnetic properties is discussed.

Cu aggregation behavior on interfacial reaction of Sn-3.0Ag-0.5Cu/ENIG solder joints

Cu aggregation of Sn-3.0Ag-0.5Cu /electroless nickel-immersion gold (ENIG) solder joints generally affect the formation of intermetallic compounds (IMCs) at the interfacial region. Herein, the interfacial microstructure of Sn-3.0Ag-0.5Cu/ENIG solder joint is compared with the joints obtained with Cu-free solder or substrate to reveal the Cu contributor and its metallurgical behavior. Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) were used to observe the IMCs and elemental distribution, respectively. The Gibbs free energy of the Sn-Ni-Cu system was calculated by JMatPro software. The results showed that Cu had significant aggregation in the interface. The solder is the major contributor to Cu aggregation in the interface, while the ENIG substrate also makes a minor contribution. The Cu6Sn5 is then formed at the interface because of its lowest Gibbs free energy in the system. These results are of significance for subsequently controlling the interfacial microstructure and performance of joints.

Laser welding of SiCp/2024Al composites with novel TiB2/2024Al composite filler

The effect of TiB2/2024Al filler on the microstructure and mechanical properties of SiCp/2024Al joint was investigated in this paper. The results indicated that needle-like Al4C3 phase with a content of 18.9% was the dominant precipitate in the weld zone (WZ) of direct welded (DWed) joint, which weakened the tensile strength (109.3 MPa) of DWed joint. The introduction of TiB2/2024Al filler changed the microstructure of WZ. In the molten pool, TiC precipitate was precipitated preferentially due to the higher chemical affinity of Ti and C atoms and lower Gibbs free energy of TiC formation. The dispersed TiC blocks presented strong fine grain strengthening and precipitation strengthening effects. Compared with DWed joint, the strength of SiCp/2024Al joint with TiB2/2024Al filler increased to 268 MPa, approximately 72.9% of that of base metal (BM).