Controllable preparation of boron nitride microspheres and their epoxy-based thermoconductive composites

How to prepare spherical boron nitride (BN) particle with different size is an extremely challenging work. In this paper, the controllable preparation of spherical BN particle from nanospheres to microsphere was realized by changing the synthesis temperature of trimethyl borate (B(OMe)₃) and ammonia. The spherical precursor (SP) with high oxygen content was obtained first, and then it was heated under flowing ammonia atmosphere to form stable boron nitride microspheres (BNMS). The BNMS exhibits onion-like cavitation structure with a diameter of 0.8–3.4 μm. The effects of the lower reaction temperature (700–825 °C) and gas flow rate on the spherical precursor are discussed. A possible mechanism is proposed to explain the formation of precursors and the appearance of onion-like structure. It is believed that the formation of microsphere is due to the deposition and growth of BO species during the flow process of nanosphere. In addition, the effect of the addition of BNMS on the thermal conductivity of epoxy resin (EP) composites was investigated.     

Dehydrogenation of formic acid mediated by a Phosphorus–Nitrogen PN3P-manganese pincer complex: Catalytic performance and mechanistic insights

The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN³P)(CO)₂]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy.     

Microstructural characteristics and hydrogen storage properties of the Mg–Ni–TiS2 nanocomposite prepared by a solution-based method

Magnesium hydride is considered as a promising solid-state hydrogen storage material due to its high hydrogen capacity. How to improve hydrogen desorption kinetics of MgH₂ is one of key issues for its practical applications. In this study, we synthesize a Mg–Ni–TiS₂ composite through a solution-based synthetic strategy. In the as-prepared composite, the co-precipitated Mg and Ni nanoparticles are highly dispersed on TiS₂ nanosheets. As a result, the activation energy for hydrogen desorption decreases to 79.4 kJ mol⁻¹. Meanwhile, the capacity retention rate is kept at the level of 98% and only slight kinetic deterioration is caused after fifty hydrogenation-dehydrogenation cycles. Further investigation indicates that the superior hydrogen desorption kinetics is attributed to the synergistically catalytic effect of the in situ formed Mg₂NiH₄ and TiH₂, and the remained TiS₂. The excellent cycle stability is related not only to the inhibition effect of the secondary phases on powder agglomeration and crystallite growth of Mg and MgH₂ but also to the prevention effect of MgS and TiS₂ on redistribution of catalytic Mg₂NiH₄ and TiH₂ nanoparticles during cycling. This work introduces a feasible approach to develop Mg-based hydrogen storage materials.     

Pressureless-sintered boron nitride nanosheets/glass composite ceramics for excellent mechanical,dielectric and thermo-conductive performances

Because they have a high application potential in the thermal management of insulation environments, high-quality hexagonal boron nitride (h-BN)-based multiphase ceramics have been highly desired. However, so far, their synthesis is still full of challenges. Here, a kind of boron nitride nanosheets (BNNSs)/glass (GS) composite ceramics was prepared by a pressureless sintering method at a lower temperature of 900 °C. Due to a tightly bonded interaction between BNNSs and GS, the formed BNNSs/GS ceramics exhibit excellent multifunction performance. They have an outstanding compressive strength in the range of 19 ∼ 64 MPa and Vickers hardness ranging from 50 to 179 HV. For the BNNSs/GS ceramics with BNNS’s filling fraction of 90 wt%, their maximum side-surface TC values are 12.01 ± 0.18 W m⁻¹ K⁻¹ at 25 °C and 13.64 ± 0.37 W m⁻¹ K⁻¹ at 300 °C, respectively. In the ultra-high frequency range of 26.5 ∼ 40 GHz, the dielectric constant values of the BNNSs/GS ceramics are primarily between 2 and 3, and the corresponding loss tangent values are < 0.3. In addition, based on the remarkable integrity of their structure, these BNNSs/GS ceramics exhibit outstanding thermal-shock stability and prominent thermal management capacity during lots of heating/cooling-testing cycles. Therefore, we believe this kind of BNNSs/GS ceramic system will have great application potential in the new-generation thermal management and/or insulation packaging fields.     

Controlling the Intermediate Phase to Improve the Crystallinity and Orientation of Cs3Sb2ClxI9-x Films for Efficient Solar Cells

Lead-free 2D antimony-based halide perovskites with excellent optoelectronic properties, low toxicity, and good intrinsic stability are promising for photovoltaic devices. However, the power conversion efficiency (PCE) of antimony-based perovskite solar cells (PSCs) is still lower than 3% due to the poor crystallinity and random orientation. Herein, it is found that the Cs₃Sb₂Cl_xI_9-x films prepared by adding methylamine chloride as an additive to the precursor solution can form a mixed intermediate phase with 0D dimer phase and 2D layered phase after low pressure treatment. During the annealing process, the 0D dimer phase will completely transition to 2D layered phase due to the partial replacement of I by Cl. Compared to adding SbCl₃ directly, this method considerably increases the crystallinity of Cs₃Sb₂I_xCl_9-x films. The obtained films have a preferential orientation along the (201) direction, which is beneficial for charge carrier transportation. Consequently, the champion device shows a PCE of 3.2%, which is one of the highest efficiencies achieved for inorganic Sb-based PSCs with the n-i-p architecture to date.     

High-Entropy Microdomain Interlocking Polymer Electrolytes for Advanced All-Solid-State Battery Chemistries

All-solid-state polymer electrolytes (ASPEs) with excellent processivity are considered one of the most forward-looking materials for large-scale industrialization. However, the contradiction between improving the mechanical strength and accelerating the ionic migration of ASPEs has always been difficult to reconcile. Herein, a rational concept is raised of high-entropy microdomain interlocking ASPEs (HEMI-ASPEs), inspired by entropic elasticity well-known in polymer and biochemical sciences, by introducing newly designed multifunctional ABC miktoarm star terpolymers into polyethylene oxide for the first time. The tailor-made HEMI-ASPEs possess multifunctional polymer chains, which induce themselves to assemble into micro- and nanoscale dynamic interlocking networks with high topological structure entropy. HEMI-ASPEs achieve excellent toughness, considerable ionic conductivity, an appreciable lithium transference number (0.63), and desirable thermal stability (T_d > 400 °C) for all-solid-state lithium metal batteries. The Li|HEMI-ASPE-Li|Li symmetrical cell shows a stable Li plating/stripping performance over 4000 h, and a LiFePO₄|HEMI-ASPE-Li|Li full cell exhibits a high capacity retention (≈96%) after 300 cycles. This work contributes an innovative design concept introducing high-entropy supramolecular dynamic networks for ASPEs.     

Structure,microstructure and disorder in low temperature chemical vapor deposited SiC coatings

Chemical vapor deposited SiC coatings were investigated at different scales by X-Ray diffraction, Raman microspectroscopy and transmission electron microscopy. They were prepared under specific conditions explaining the various (micro)structures obtained. The deposits all have a columnar morphology with a preferential orientation and a faulted cubic structure. They differ in how disorder is incorporated in the structure. Fine XRD analyses and stacking fault density assessment by TEM revealed the one-dimensionally-disordered (ODD) polytype in the < 111 > textured coatings. The frequency and spatial distribution of stacking faults vary and sometimes locally generate periodic alpha sequences. A specific type of disorder was also identified where {111} planes are arranged parallel to the growth direction within the columns. These disorders, more energetic than stacking faults, induce multiple and particularly large Raman modes. Crystal distortions, such as dislocations, are localized at the ODD domain boundaries, which are frequently interrupted as they extend during the growth.     

Recycling Polyethylene into High-Value Porous Carbon Composites for Microwave Absorption

The recycling of solid plastic waste has been a major challenge to the sustainable development of today's society. Herein, one of the commonly wasted plastic raw materials, linear low-density polyethylene (LLDPE), is used as the carbon source to explore high-value porous carbon composites for microwave absorption applications. The carbon composites are simply obtained through the delicate carbonization of LLDPE, followed by in situ introducing Ni nanoparticles (NPs) into the carbon monolith. The porous carbon composites show a minimum reflection loss (RL_min) value of −52.2 dB at 1.65 mm, which demonstrates excellent microwave absorption properties of the wasted plastic-derived carbon materials. In addition, the anticorrosion performance of the carbon composites is evaluated by electrochemical technique. Above all, the current study provides a new idea and simple strategy for processing wasted plastics to high-value porous carbon materials.     

Electron microscopy studies of the “Premartensitic” transformations in an aged Ti-51 at%Ni shape memory alloy

“Premartensitic” transformations in an aged Ti-51at%Ni shape memory alloy have been studied by means of electrical resistance measurements, and electron diffraction and microscopy. On aging at 500°C or below following solution treatment, premartensitic transitions appear in Ti-51at%Ni. The appearance of the premartensitic transitions is attributable to the formation of Ti₃Ni₄ precipitates. Crystallographic and morphological aspects of the premartensitic transitions in specimens aged under several conditions are described in detail. The premartensitic behavior of the present aged specimens is essentially the same as that of the ternary TiNiFe [8–10] and TiNiAl alloys [16].