Dense Metal Research Articles

Designing of highly-efficient OER and ORR transition metal-nitrogen active centers with the aid of the revised d electron density

It is quite important to suggest a suitable modification method for the design of highly-efficient catalysts with the aid of the local atomic structures of active center. In this work, the d electron density (D’d) of transition metal (TM) ions was revised to correlate the local atomic structures and catalytic activity of TM1N4 active centers by introducing the dynamic radius of TM and N ions. Meanwhile, the “volcano” relationship between the OER/ORR potentials and D’d values was acquired to suggest the modification methods. The pressure (tensile) stress would be applied to increase (weaken) the d-p orbital hybrid strength of Fe1-N (Co1-N and Ni1-N) bonds and increase (reduce) the D’d values of Fe1N4 (Co1N4 and Ni1N4) active centers. Based on the theoretical prediction, the Fe1-pyrrolee N4 (0 %) and Fe1-pyrrolee N4 (−2%) active centers respectively exhibited the lowest overpotentials of 213 mV for OER and 189 mV for ORR in this work. Hence, the revised d electron density could be applied for the method of external stress field, and this strategy would be adopted to design more highly-efficient catalysts.

An autotransferable alloy overlayer toward stable sodium metal anodes

Sodium (Na) metal anodes receive significant attention due to their high theoretical specific energy and cost-effectiveness. However, the high reactivity of Na foil anodes and the irregular surfaces have posed challenges to the operability and reliability of Na metals in battery applications. In the absence of inert environmental protection conditions, constructing a uniform, dense, and sodiophilic Na metal anode surface is crucial for homogenizing Na deposition, but remains less-explored. Herein, we fabricated a Tin (Sn) nanoparticle-assembled film conforming to separator pores, which provided ample space for accommodating volumetric expansion during the Na alloying process. Subsequently, a seamless Na-Sn alloy overlayer was formed and transferred onto the Na foil during Na plating through a separator-assisted technique, thereby overcoming conventional operational limitations of metallic Na. As compared to traditional volumetrically expanded cracked ones, the present autotransferable, highly sodiophilic, ion-conductive, and seamless Na-Sn alloy overlayer serves as uniform nucleation sites, thereby reducing nucleation and diffusion barriers and facilitating the compact deposition of metallic Na. Consequently, the autotransferable alloy layer enables a high average Coulombic efficiency of 99.9 % at 3.0 mA cm−2 and 3.0 mAh cm−2 in the half cells as well as minimal polarization overpotentials in symmetric cells, both during prolonged cycling 1200 h. Furthermore, the assembled Na||Sn-1.0h-PP||Na3V2(PO4)3@C@CNTs full cell delivers high capacity retention of 97.5 % after 200 cycles at a high cathodic mass loading.

Covalent organic frameworks derived Single-Atom cobalt catalysts for boosting oxygen reduction reaction in rechargeable Zn-Air batteries

The design and development of high-performance and long-life Pt-free catalysts for the oxygen reduction reaction (ORR) is of great important with respect to metal-air batteries and fuel cells. Herein, a new low-cost covalent organic frameworks (COFs)-derived CoNC single-atoms catalyst (SAC) is fabricated and compared with the engineered nanoparticle (NP) counterpart for ORR activity. The ORR performance of the SAC catalyst (CoSA@NC) surpasses the NP counterpart (CoNP-NC) under the same operation condition. CoSA@NC also achieves improved long-term durability and better methanol tolerance compared with the Pt/C. The zinc-air battery assembled by the CoSA@NC cathode delivers a higher power density and energy density than that of commercial Pt/C catalyst. Molecular dynamics (MD) is performed to explain the spontaneous evolution from clusters to single-atom metal configuration and density functional theory (DFT) calculations find that CoSA@NC possesses lower d-band center, resulting in weaker interaction between the surface and the O-containing intermediates. Consequently, the reductive desorption of OH*, the rate-determine step, is further accelerated.

Demonstration of low-mode shape control in indirect-drive double shell implosions at the NIF

Double shell inertial confinement fusion is a concept for achieving robust thermonuclear burn that uses dense metal shells to compress deuterium-tritium (DT) fuel to fusion conditions. Double shell implosions are typically indirectly driven and involve a target that consists of a low-Z ablator, a foam layer, and a high-Z pusher surrounding the DT fuel. The goal of the campaign is to achieve a volumetric burn as radiation losses from the DT fuel are trapped by the opaque high-Z shell. The overall performance of double shell implosions relies on the efficient collisional transfer of kinetic energy between layers. The efficiency of this transfer (and therefore the overall performance of a given implosion) is degraded by the presence of low-mode asymmetries. P2 asymmetries are often observed in spatially resolved 2D radiographs of nominal double shell implosions. This work discusses three such experiments: one with an oblate P2 asymmetry, one with a prolate P2 asymmetry, and one with an approximate spherical symmetry. After performing a shape analysis of the oblate and prolate implosions to quantify asymmetries, these experimental results were compared with the results of hydrodynamic simulations for the two experiments. Differences between the experiment and simulation were then used to design an approximately spherical implosion by altering the incident laser cone fraction. Radiographs from the experiment that implemented the modified cone fraction show evidence of an implosion that is approximately spherical until bang time. This design is intended to serve as a point design for future studies that will seek to optimize various aspects of the double shell target.

Enhanced Pool Boiling Heat Transfer with Porous Ti-6Al-4V-Coatings Produced by Cold Spray Metal Additive Manufacturing

In advancing industrial heat transfer mechanisms, surface coatings offer significant potential. This research elucidates the efficacy of the metal additive manufacturing Cold Spray deposition technique for producing enhanced boiling surfaces, specifically focusing on Ti-6Al-4V (Ti64) coatings on Aluminium substrates. This offers a rapid and low-cost fabrication method for producing lightweight enhanced boiling surfaces. The Cold Spray method is typically used to create dense metal deposits. Here, the process has been specially tuned to create highly inhomogeneous honeycomb-type porous Ti64 coatings. Critical Cold Spray deposition parameters, such as particle velocity, preheat temperature, and deposition rate have been identified to create repeatable porous coatings, with thicknesses of up to 3.0 mm achievable. Following deposition, several samples were subjected to systematic boiling heat transfer tests in a purpose-built pool boiling apparatus. Boiling curves were generated for the augmented Cold Spray surfaces as well as a bare surface, with the latter acting as a baseline to which enhancement levels were assessed. Initial data analysis shows that some of the tested surfaces exhibit a notable increase in boiling heat transfer coefficient and Critical Heat Flux (CHF). This enhancement is potentially attributed to increased surface area, increased nucleation site density, capillary wicking, and mitigation of lateral bubble coalescence, though excessive coating thickness may degrade heat transfer. In summary, the novel Ti64 surface structures developed using the Cold Spray deposition technique exhibits high potential for industries necessitating superior boiling heat transfer performance. Importantly, the manufacturing process is industrially scalable, offering the capacity to rapidly coat large areas at low cost compared with subtractive manufacturing other metal additive manufacturing methods.

Hybrid additive manufacturing of aluminum matrix composites with improved mechanical properties compared to extruded counterparts

Great difficulties existed in fabricating large components of SiC particles reinforced aluminum matrix composites with excellent mechanical properties using existing manufacturing procedures. This study demonstrated that the challenges can be addressed by developing a hybrid solid-state additive manufacturing method. The influence of the deposition procedures and the post-processing heat treatment on the microstructure and mechanical properties of the SiC particles reinforced 2009 aluminum ally matrix composites (SiCp/2009Al composites) was systematically investigated using advanced technologies such as spherical aberration corrected transmission electron microscope, atom probe tomography, etc. The results showed that the SiCp/2009Al composites produced by the hybrid solid-state additive manufacturing exhibited enhanced tensile properties and improved isotropy in mechanical properties compared to the extruded feedstock of SiCp/2009Al composites. This was attributed to the formation of dense metal with uniformly distributed SiC particles, high-density of Cu–Mg co-clusters, refined grains and SiC particles, low deformation texture, tightly bonded SiCp/2009Al interface, and sound interfacial bonding between deposited layers.

Enhancing X-ray radiation protection with novel liquid silicone rubber composites: A promising alternative to lead aprons

This study introduces a lead-free alternative for enhanced radiation protection. While lead aprons effectively attenuate ionizing radiation, concerns regarding flexibility, weight, and environmental hazards persist. In response, the present research is focused on producing an innovative sheet shielding comprised of carefully selected dense metal oxide microparticles (DMOs-MPs) and liquid silicone rubber (LSR). To evaluate the efficacy of the LSR samples, the current study uses rigorous testing procedures, such as microstructure characterization using EDX and FESEM. Furthermore, the study investigated key attenuation parameters within the LSR samples. Radiation protection was greatly and effectively supplied using DMOs-MPs filler (Bi-1 to Bi-7) in LSR samples; this protection reached 99.9% in the X-ray energy range. Due to the unique characteristics of the Bi-7, the results demonstrated that the samples’ shielding efficiency improved with the addition of high atomic number and high-density fillers. It had the greatest attenuation coefficient and density. At 60 keV, Bi-7’s density was 2.980 gcm−3, and its LAC and MAC were 19.2621 cm−1 and 6.4638 cm2/g, respectively. It also had the lowest half-value layer values in the energy range of 60–120 keV. The LSR samples showed effective radiation absorption for different energy levels, indicating that LSR can enhance the flexibility and comfort of the apron while providing adequate radiation protection. The incorporation of the DMOs-MPs with LSR represents an effective contribution and a noteworthy stride to enhance the safety and well-being of medical professionals routinely exposed to ionizing radiation.

THE EFFECT OF MODIFICATION WITH HIGHLY DISPERSED SILICON CARBIDE ON THE MECHANICAL PROPERTIES AND DENSITY OF THE SECONDARY ALUMINUM ALLOY OF THE AL-SI SYSTEM

The effect of modification on the mechanical properties of the secondary aluminum casting alloy (wt.%: 0,528 Mg, 1,124 Cu, 11,539 Si, 84,969 Al, 0,905 Fe, 0,692 Zn, 0,242 Mn) without heat treatment was determined by the introduction of silicon carbide with a particle size of 1-3 μm in the amount of 0.1, 0.2, 0.3 wt. %. Castings were made in steel molds. It is established that the strength of unmodified alloy (σв) is 110 - 120 MPa. When the content of SiC in the alloy from 0.1% to 0.2%, the indicators of σв increase from 130-145 MPa to 155-166 MPa, respectively. Increasing the SiC content to 0.3% leads to a decrease in σв values in the range of 117 - 127 MPa. Hardness indices (HВ): unmodified alloy - 42 - 43, alloy with a content of 0.1% SiC - 43 - 44, with a content of 0.2% SiC - 46 - 47, with a content of 0.3% SiC - 43 - 44. Determination of the density of cast metal obtained in a steel mold and in a sandy-clay form was carried out by the method of hydrostatic weighing of samples in СCl4. It has been established that the density of the alloy of castings with a silicon carbide content of 0.1% is 2761 kg/m3, and that of the unmodified alloy is 2715 kg/m3. With an increase in the silicon carbide content to 0.2%, the density of the metal is 2735 kg/m3. With a SiC content of 0.3 wt.%, the density of the alloy is 2752 kg/m3. The density of the metal of the castings obtained in the sandy-clay form with the modification of 0.1% SiC is 2673 kg/m3, with 0.3% SiC - 2676 kg/m3.

Self-sustaining alkaline seawater electrolysis via forward osmosis membranes

Seawater electrolysis for hydrogen production faces inherent challenges, including side reactions, corrosion, and scaling, stemming from the intricate composition of seawater. In response, researchers have turned to continuous water splitting using forward osmosis (FO)-driven seawater desalination. However, the necessity of a neutral electrolyte hampers this strategy due to the limited current density and scarcity of precious metals. Herein, this study applies alkali-durable FO membranes to enable self-sustaining seawater splitting, which can selective withdraw water molecules, from seawater, via concentration gradient. The membranes demonstrated outstanding perm-selectivity of water/ions (∼5830 mol mol−1) during month-long alkaline resistance tests, preventing electrolyte leaching (>97% OH− retention) while maintaining ∼95% water balance (VFO = Velectrolysis) via preserved concentration gradient for consistent forward-osmosis influx of water molecules. With the consistent electrolyte environment protected by the polyamide FO membranes, the NiFe-Ar-P catalyst exhibits promising performance: a sustain current density of 360 mA cm−2 maintained at the cell voltage of 2.10 V and 2.15 V for 360 h in the offshore seawater, preventing Cl/Br corrosion (98% rejection) and Mg/Ca passivation (99.6% rejection). This research marks a significant advancement towards efficient and durable seawater-based hydrogen production.

Zinc‐Coordinated Imidazole‐Based Ionic Liquid as Liquid Salt for All‐Temperature Aqueous Zinc‐Ion Batteries

AbstractOwing to the intrinsically high safety, low cost, natural abundance, and high energy density of Zn metal, aqueous Zn ion batteries (AZIBs) have become a promising candidate for large‐scale energy conversion and storage. However, the practical application of AZIBs is hampered by the severe Zn dendrites growth and the poor low‐temperature performance due to the elevated freezing point of aqueous electrolyte. Herein, the study proposes a new kind of room‐temperature liquid Zn salt, which is called Zn coordinated ionic liquid (i.e., (EMIM)5Zn(OTF)7), for all‐temperature AZIBs. The aqueous electrolyte containing 0.261 mol kg−1 (EMIM)5Zn(OTF)7 in Ethylene Glycol (EG) / H2O (6:4) exhibits ultralow freezing point below −100 °C. The liquid Zn salt and EG molecules not only modulate the solvation structure of Zn2+ ion, reducing the coordinated H2O in the first solvation sheath, but also suppresses the parasitic side reaction. As a proof of concept, Zn || Zn symmetric cells and Zn || PANI full cells with the designed electrolyte achieve improved cycling stability and can operate under wide temperature (from −40 to 60 °C). Even with high Zn utilization ratio of 40%, long cycle life over 70 times with capacity retention of 80% is achieved.

Effect of post-weld heat treatment on corrosion resistance of X90 pipeline steel joints

Abstract In order to improve the corrosion resistance of welded joints, X90 pipeline steel joints were subjected to post-weld heat treatment at 610 °C, 640 °C, and 670 °C (holding time was 1 h). Through electrochemical corrosion and full immersion corrosion experiments, the corrosion resistance of welded joints under various conditions was tested, and the surface morphology and corrosion products of the corroded samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. The experimental results show that the corrosion products of X90 pipeline steel welded joints in simulated soil solution mainly include Fe(OH)3, γ-FeOOH, α-Fe2O3, γ-Fe2O3, and a small amount of Fe3O4, FeCl3 and Fe. After heat treatment at 610 °C, the corrosion current density of the parent metal, heat-affected zone, and weld metal of the joint changes from 1.081, 2.889, 2.079 (×10−5 A cm−2) to 0.977, 2.211, 1.810 (×10−5 A cm−2), respectively, the corrosion resistance is improved.

Europa’s structural conditions for the existence of subsurface ocean and the absence of metallic core-driven magnetic field

During the Galileo spacecraft’s flyby of Europa, magnetic field measurements detected an inductive signal due to the response of Europa’s interior conductors to temporal fluctuations in the Jovian magnetic field. In contrast, no signatures of intrinsic magnetic field originating from the dynamo motion in the metallic core were acquired. These measurements suggest that a global sub-surface ocean containing electrolytes exists beneath the solid ice shell and that the metallic core lacks convection. Europa’s interior is expected to be divided into the metallic core, rocky mantle and hydrosphere based on the moment of inertia factor estimated from gravity field measurements. Specifically, the thickness of the outermost water layer is 120–170 km, and the radius of the metallic core is 0.12–0.43 times the surface radius. No systematic investigation of Europa’s internal evolution has been conducted to estimate the current state of the subsurface ocean and to explain the absence of a core dynamo field within such uncertainty for internal structure and material properties (especially ice properties). Herein, I performed a numerical simulation of the long-term thermal evolution of Europa’s interior and investigated the temporal changes in the ocean thickness as well as the temperature and heat flow of the metallic core. If the ice reference viscosity is greater than 5 × 1014 Pas, the sub-surface ocean can persist even in the absence of tidal heating. In the case of a tidal heating of 10 mW/m2 and 20 mW/m2, the ice shell thickness is ≤90 km if the ice reference viscosity is ≥1 × 1015 and 1 × 1014 Pas, respectively. Regardless of the ice reference viscosity, if the tidal heating is ≥50 mW/m2, the shell thickness will be ≤40 km. The thermal history of the metallic core is determined by the hydrosphere thickness and the metallic core density, and is unaffected by variations in the ice shell (ocean) thickness. Preferred conditions for the absence of the core dynamo include CI chondritic abundance for the long-lived radioactive isotopes, lower initial core–mantle boundary (CMB) temperature and thicker hydrosphere. The core may be molten without convection if the composition is near the eutectic in a Fe–FeS alloy, or not molten (without convection) if the composition is near the Fe or FeS endmember. Specifically, if the rocky mantle has a CI chondritic radioisotope abundance, any core composition and hydrosphere thickness allow the absence of the core dynamo if the initial temperature at the CMB is lower than 1,250 K. If the rocky mantle has the ordinary chondritic radioisotope abundance, or a higher initial temperature (∼1,500 K) at the CMB, the core density lower than 6,000 kg/m3 is preferred for the absence of the core dynamo. In the case of the core composition near the eutectic one, a hydrosphere thicker than 150 km is required for the lacking core dynamo. The lower pressure of Europa’s rocky mantle due to its thinner hydrosphere compared with that of Ganymede may facilitate heat transfer in the mantle, lowering its temperature and making dynamo motion more challenging.

A novel magnetic field assisted powder arc additive manufacturing for Ti60 titanium alloy: Method, microstructure and mechanical properties

Due to the rapid heating-cooling process and unstable keyhole, pore defects are easily formed during the high energy beam-powder additive manufacturing (AM) process, posing great challenges to the high-performance manufacturing of aerospace components. Using an arc with lower energy density as a heat source can effectively avoid these defects, but its matching raw materials are limited to wire. In this paper, a novel magnetic field assisted powder arc additive manufacturing (MFA-PAAM) method has been proposed, which combines arc heat source and powder raw material to achieve dense metal parts. A transverse magnetic field (TMF) was introduced to solve the powder spattering problem which impacts the stability of the PAAM process, by regulating the direction of the arc plasma flow and the arc pressure. The unique melting behavior of the powder under arc heating was captured by a high-speed camera, which can be summarized into two steps: balling and adsorption by the molten pool. And the well-formed and fully dense Ti60 high-temperature titanium alloy wall components were successfully manufactured using the self-developed equipment. The microstructure of the thin-wall component is dominated by basket-weave distributed α laths and few β sheets remaining at their boundaries. A layered periodic distribution along the building direction was observed, which is mainly distinguished from the content and morphology of the β phase. The average ultimate tensile strength (UTS) and elongation to failure in the travelling direction are 1003.2 MPa and 15.1%, while the average UTS and elongation along the building direction are 1009.3 MPa and 16.6%, respectively. The fracture morphologies in both directions are characterized by ductile fracture. The MFA-PAAM technique shows great potential for fabricating materials that are difficult to be drawn into wires with high efficiency and performance.

Neutronic performance of 208Pb-Bi eutectic-cooled fast reactor with uranium nitride fuel (enriched 15N)

Fast reactors (FRs) require more uranium enrichment than LWRs and fuel reprocessing. The solution proposed to address these issues is to use the modified CANDLE burnup scheme on the reactor core. The use of uranium nitride (UN) as fuel was proposed because the UN fuel has several advantages, such as high melting point, high heavy metal density, and large thermal conductivity. However, using UN as a fuel can produce the radioactive isotope 14C via the reaction 14N (n, p)14C. Therefore, in this study, a neutronic analysis was performed in a modified CANDLE fast reactor employing UN and UN (enriched 15N) as fuel using SRAC. The modified CANDLE fast reactor fuelled with UN (99% 15N) has a higher keff than the UN-fuelled reactor with similar parameters. Similarly, the atomic density of fissile nuclides and power density are higher because the 15N isotope has a smaller neutron capture cross-section than the 14N isotope.

Relationship between Shape Retention and X-ray Absorption Value of the Tip of Microcatheters in Neuroendovascular Treatment.

Objective We noticed that the X-ray absorption value of the tip of each microcatheter used for aneurysm treatment varied from product to product. We hypothesized that the differences were caused by variations in the metal's density braid, which could be related to the ability of the tip to retain its shape. Methods The X-ray absorption value of each microcatheter tip was measured. Next, heat forming was performed using a shaping mandrel at 6 mm and 90 degrees to determine whether there was a correlation between the X-ray absorption value and the forming angle. Next, the optimal mandrel angle for forming each microcatheter at 90 degrees was investigated. We also examined the shape retention after 20 times wire insertions into each microcatheter. Conclusion It was found that the higher the X-ray absorption value, the harder it was for the microcatheter to be formed. The mandrel angle required to form 90 degrees was determined by the X-ray absorption value. The higher the X-ray absorption value, the higher the shape retention of the tip shape. The heat formation and shape-retention conditions of the microcatheter tip were correlated with the X-ray absorption value of the metal braid. Even for unknown microcatheters, the optimum shaping conditions can be inferred from the X-ray absorption value.

Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf

Dynamically active planetary systems orbit a significant fraction of white dwarf stars. These stars often exhibit surface metals accreted from debris disks, which are detected through infrared excess or transiting structures. However, the full journey of a planetesimal from star-grazing orbit to final dissolution in the host star is poorly understood. Here, we report the discovery that the cool metal-polluted star WD 0816–310 has cannibalized heavy elements from a planetary body similar in size to Vesta, and where accretion and horizontal mixing processes have clearly been controlled by the stellar magnetic field. Our observations unveil periodic and synchronized variations in metal line strength and magnetic field intensity, implying a correlation between the local surface density of metals and the magnetic field structure. Specifically, the data point to a likely persistent concentration of metals near a magnetic pole. These findings demonstrate that magnetic fields may play a fundamental role in the final stages of exoplanetary bodies that are recycled into their white dwarf hosts.

Novel hybrid-CMOS inverter utilizing phase transition material for enhancing digital logic performance at lower operating voltages

This research paper introduces a novel design for a hybrid-CMOS inverter using vanadium dioxide (VO2), a phase transition material. The proposed inverter exhibits a remarkably steep transition for falling logic at the output(1–0). By leveraging the insulating to metallic current density (IC-IMT) of VO2, the depth and gain of this transition can be finely tuned. Notably, a higher IC-IMT value yields a greater gain in the transition slope. In comparison to a traditional CMOS inverter, the designed inverter demonstrates several advantages. It achieves higher values of lower noise margin (NML) and significantly reduces static power dissipation by 97.7%. These promising outcomes present an exciting opportunity for designing inverters at lower drain voltages, especially in devices operating at lower technology nodes. Furthermore, the hybrid-CMOS inverter is designed to excel in the sub-threshold region of operation, resulting in elevated values of lower noise margin and reduced leakage current values.

Suppressing the Growth of Dendrites On Ultrathin Lithium Metal Anodes by an Amide Electrolyte Additive

The practical applications of high energy density lithium (Li) metal rechargeable batteries are hindered by the formation of lithium dendrites. Besides, using the thick Li anodes (typically 50 μm to 750 μm) provide more Li inventory than is needed in the cell as well as disappears the advantage of high energy density of Li metal over Li-ion batteries.Therefore, in this study, N-N-diallyl-2,2,2-trifluoroacetamide (NDT) is proposed as an electrolyte additive to inhibit the growth of dendrites on the ultrathin Li anode (20 μm). By virtue of its preferential reduction as well as its participation in the primary Li+ solvation shell, NDT contributes to the formation of a Li3N-contained uniform SEI layer on the Li metal, leading to a low polarization in LillLi cells. Be benefited, the LillLFP cell, utilizing a carbonate-based electrolyte containing 2 wt% NDT, exhibits a prolonged life-span, an enhanced reversibility, along with a retention capacity of 72% after 75 cycles, while the cell using baseline electrolyte shows a retention capacity of 68% after 50 cycles at 0.3 C. Additionally, NDT improves the ionic conductivity, and wettability of the electrolyte to the separator. These significant findings provide valuable insights for designing electrolyte additives to stabilize ultrathin Li metal anodes.

High-pressure study of a 3d-4f heterometallic CuEu-organic skeleton.

We prepared a 3d-4f heterobimetallic CuEu-organic framework NBU-8 with a density of 1921 kg m-3 belonging to the family of dense packing materials (dense metal-organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu2+ and Eu3+ as the metal centres; the molecular formula is Cu3Eu2(PBA)6(NO3)6·H2O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10-2) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch-Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu-BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol-1. The present work will provide fresh ideas for the study of mechanical energy in other materials.

In-situ synthesis and wear mechanism of Ni- based self-lubricating composite coating with a dense continuous metal sulfide layer prepared by laser cladding

The friction and wear of bearing cages, sealing rings and other transmission components working in harsh environments such as high vacuum and heavy load directly affect the operational stability and safety reliability of the equipment. Therefore, it is vitally important to improve the tribological properties of machine components. In this paper, NiCrBSi alloy coating, NiCrBSi-30 wt% WS2 coating and double-layer NiCrBSi-30 wt% WS2 coating were prepared on 38CrMoAl steel by laser cladding. The results show that a metal sulfide layer is formed on the double-layer NiCrBSi-30 wt% WS2 coating compared to NiCrBSi-30 wt% WS2 coating. The NiCrBSi-30 wt% WS2 coating consists of γ-(Ni,Fe) solid solution, (Fe,Ni)9S8, Cr7S8 and M7C3 phases. The metal sulfide layer consists of γ-(Ni, Fe) solid solutions, Fe3S4, CrxSy and M7C3 phases. The double-layer NiCrBSi-30 wt% WS2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS2 coating. The average microhardness values of NiCrBSi coating, NiCrBSi-WS2 coating and double-layer NiCrBSi-WS2 coating are 412.6 ± 15.2HV0.3, 383.9 ± 14.5HV0.3, and 368.6 ± 13.3HV0.3, respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS2 coating is 1.51 × 10−5 mm3/(N·m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 × 10−5 mm3/(N·m)) and NiCrBSi-30 wt% WS2 coating (2.32 × 10−5 mm3/(N·m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS2 coating has the best wear resistance and friction reduction performance at room temperature. A more continuous lubricating film was formed on the surface of the double-layer NiCrBSi-30 wt% WS2 coating, which explains its lowest coefficient of friction and wear rate.