Search Results (218)

In this study, a multiphysics finite-element model was developed for the deposition of W–C–B coatings in a hot-wall tubular CVD reactor from a gas mixture of tungsten hexafluoride (WF₆), hydrogen (H₂), and trimethylamine borane ((CH₃)₃N:BH₃) at 550 °C and 5 Torr. The aim of this work is to deepen the understanding of reactant transport mechanisms and to optimize the process parameters for obtaining targeted tungsten carbide or boride phases. The simulations were performed in COMSOL Multiphysics (ver. 6.1) using a 2D axisymmetric formulation that couples laminar flow, heat transfer, and multicomponent diffusion, accounting for heterogeneous chemical reactions at the reactor walls. The obtained spatial distributions of reactant concentrations demonstrate precursor depletion along the reactor length. A comparison of the calculated B/W and C/W stoichiometric ratios for 13 operating conditions with experimental data confirms a transition from W and W–B phases at low trimethylamine borane (TMAB) flow rates to tungsten carbide-based coatings at higher flow rates. Furthermore, a parametric sweep was utilized to determine the optimal parameter range for the synthesis of tungsten borides. Full article

The generation of high-purity hydrogen via chemical reaction from hydrogen-rich materials is one of the ways in the alternative energy industry. In this approach, the utilization of catalytic materials that possess the capacity to initiate the decomposition of the starting material and the subsequent release of hydrogen is of paramount importance. In this study, nickel/cobalt-plated copper catalysts (NiCo/Cu) are presented, comprising from 4 to 90 wt.% of cobalt as catalytic materials for hydrogen generation via sodium borohydride (NaBH₄) hydrolysis reaction. The NiCo/Cu catalysts were synthesized via electroless deposition from glycine-based baths, utilizing Ni²⁺ and Co²⁺ ions as metal sources and morpholine borane (MB) as the reducing compound. The catalytic performance in alkaline NaBH₄ hydrolysis was found to correlate with the cobalt loading in the coating. The maximum rate of hydrogen production, which was determined to be 14.22 L min⁻¹ gcat⁻¹, was achieved at 343 K for a catalyst composed of 90 wt.% Co. The reaction proceeded with the activation energy of 52.5 kJ mol⁻¹, while the catalyst exhibited high durability, preserving nearly 88% of its initial activity after five successive reaction cycles. The combination of nickel and cobalt, along with their synergistic effect and high efficiency in the borohydride hydrolysis reaction, makes them promising catalysts. Full article

The present article is the product of ongoing research by the present authors into pre-reform meditation traditions in Siam. Historical and textual circumstances indicate that the Phra Lakkhaṇa Dhamma (lit., the honorable characteristics of Dhamma) the meditation manuscript under our study here, was copied during the reign of King Taksin (r.1767–1782), the founder of Thonburi, post-Ayutthaya Siam. The manuscript has, until now, been kept unstudied at Wat Hongrattanaram, one of the most important temples during Taksin’s reign, located adjacent to this palace in Thonburi city. The authors, while engaged in researching manuscript collections in Thonburi, were shown this important manuscript. Its contents clearly show this to have been aligned with what some contemporary authors have designated the boran kammatthan (“old-” or “traditional meditation”) or yogāvacara (“meditation practitioner”) tradition that flourished in pre-modern Siam and has been the subject of recent research by the present authors and others. In this article, the manuscript is described, summarily translated, and contextualised, and its meditational contents are analysed. Full article

This study aimed to develop an industrially scalable coating route for enhancing the oxidation resistance of carbon fiber fabrics, a critical requirement for next-generation aerospace and high-temperature composite structures. To achieve this goal, synthesis of hexagonal boron nitride (h-BN) layers was achieved via a single wet step in which the fabric was impregnated with an ammonia–borane/THF solution and subsequently nitrided for 2 h at 1000–1500 °C in flowing nitrogen. Thermogravimetric analysis coupled with X-ray diffraction revealed that amorphous BN formed below ≈1200 °C and crystallized completely into (002)-textured h-BN (with lattice parameters a ≈ 2.50 Å and c ≈ 6.7 Å) once the dwell temperature reached ≥1300 °C. Complementary XPS, FTIR and Raman spectroscopy confirmed a near-stoichiometric B:N ≈ 1:1 composition and the elimination of O–H/N–H residues as crystallinity improved. Low-magnification SEM (100×) confirmed the uniform and large-area coverage of the BN layer on the carbon fiber tows, while high-magnification SEM revealed a progressive densification of the coating from discrete nanospheres to a continuous nanosheet barrier on the fibers. Oxidation tests in flowing air shifted the onset of mass loss from 685 °C for uncoated fibers to 828 °C for the coating produced at 1400 °C; concurrently, the peak oxidation rate moved ≈200 °C higher and declined by ~40%. Treatment at 1500 °C conferred no additional benefit, indicating that 1400 °C provides the optimal balance between full crystallinity and limited grain coarsening. The resulting dense h-BN film, aided by an in situ self-healing B₂O₃ glaze above ~800 °C, delayed carbon fiber oxidation by ≈140 °C. Overall, the process offers a cost-effective, large-area alternative to vapor-phase deposition techniques, positioning BN-coated carbon fiber fabrics for robust service in extreme oxidative environments. Full article

Ammonia borane (AB) is recognized as a highly promising material for hydrogen storage owing to its exceptional safety and high hydrogen density, enabling controllable hydrogen release at room temperature through catalytic hydrolysis. The development of efficient catalysts to accelerate this process remains a critical research challenge. In this work, carbon nanotube (CNT)-supported Co-MoO₃ nanoparticles were synthesized through reduction with sodium borohydride. The catalyst with a Co/MoO₃ molar ratio of 1.0:0.1 (denoted as Co₁Mo_0.1/CNTs) showed optimal performance in AB hydrolysis, with a turnover frequency (TOF) of 19.15 mol_H2 mol_cat⁻¹ min⁻¹ and an activation energy (E_a) of 26.41 kJ mol⁻¹. The superior performance of the Co₁Mo_0.1/CNTs catalyst can be ascribed to the efficient proton-transfer promotion by carboxylated carbon nanotubes and the synergistic catalytic effect between Co and Mo in the system. This study offers a viable pathway for constructing high-efficiency noble metal-free catalysts for hydrogen production from AB hydrolysis. Full article

Ammonia borane is a promising hydrogen storage material due to its high hydrogen content, but its use as hydrogen carrier under thermal stimuli involves the production of several byproducts, such as borazine, reducing hydrogen purity and the overall efficiency. This work is focused on the use of high-boiling-point amines to modulate ammonia borane decomposition, aiming to enhance hydrogen release and suppress volatile N_xB_y species. Kissinger’s equation kinetics revealed that amines significantly influence the decomposition mechanism, and TGA-IR investigation showed a maximum of 2.4 wt.% of pure hydrogen release in the presence of triphenyl amine. Furthermore, the experimental data herein discussed, together with a computational study of activation energies, allowed us to derive a detailed mechanism that leads to a foundation for further advancement in the exploitation of ammonia borane as a hydrogen carrier, suggesting that the formation of linear species is anchored to amine over the release of borazine and production of poly borazine-like species. Full article

Cobalt–boron (Co–B) coatings containing different amounts of boron were electrolessly deposited using morpholine borane as the reducing agent. Diethylenetriamine (dien) was applied to obtain a controllable amount of boron in the coatings. Depending on the concentration of diethylenetriamine in the solution, the deposited coatings contained between 0 and 12 at% of boron. It was shown that diethylenetriamine suppresses the incorporation of boron into Co–B alloys. The same tendency was observed when the solution pH increased. Higher temperatures promote the incorporation of boron into cobalt films. The kinetic data on the electroless deposition process of Co–B alloys under different conditions are presented and discussed. The coatings obtained were characterized by means of XRD, SEM, and AFM methods. Since the use of diethylenetriamine hinders boron incorporation into coatings, pure cobalt films can be obtained. Full article

The mechanism of the electrophilic addition between phenylacetylene and N-heterocyclic carbene borane (NHC–borane), initiated by di-tert-butyl peroxide (DTBP), was elucidated at the M06-2X-D3/ma-def2-TZVP level to yield the Z-configured product. The computational results show that DTBP undergoes homolysis to generate two t-BuO· radicals; subsequently, it undergoes an H-shift reaction with N-heterocyclic carbene borane to form the N-heterocyclic carbene boron radical. Then, it is added to phenylacetylene to obtain the product radical intermediate. Finally, the product is yielded via an H-shift reaction. Meanwhile, this paper also explores the formation pathways of relevant byproducts. Structural analysis of the reaction reveals that weak interactions have a significant impact on the selectivity of the Z-configuration of the product. In addition, electron spin density contour maps are used to explain the electron distribution and reaction sites during the reaction process. This paper will provide relevant theoretical support for this type of addition reaction. Full article

This paper outlines the implementation and core results of a combined archaeological, historical, and ethnographic study of the histories of well construction and water management among Boran, Gabra, and Rendille pastoralists in arid and semi-arid areas of Northern Kenya and Southern Ethiopia. Co-developed with representatives from different local communities from the outset, this project sought to document the spatial distribution of different types of hand-dug wells found across the study areas, their associated oral histories and, if possible, establish through archaeological means their likely date of initial construction. Concurrent with addressing these academic objectives, this project aimed to train a cohort of local heritage stewards in archaeological, historical, and ethnographic data collection and interpretation, equipping them with the necessary skills to monitor sites of heritage value and further record additional elements of the tangible and intangible heritage of the study areas. This paper discusses the archaeological work that the community trainees participated in, the strategies developed with them to create wider awareness of this heritage, and its implications for identifying ways to ”weather” climate change in the future. Full article

This study aimed to develop a reliable method for profiling reducing sugars in honey using capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). Reducing sugars were derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) in the presence of 2-picoline borane, a safer alternative to sodium cyanoborohydride. Key parameters influencing the derivatization efficiency—temperature, pH, incubation time, and reagent concentrations—were systematically optimized. The highest labeling efficiency for glucose, mannose, and maltose was achieved at 50 °C in 0.5 M citric acid with 0.1 M APTS, while fructose showed low reactivity due to its ketose structure. To reduce the background signal from excess reagents, three cleanup strategies were evaluated. Liquid–liquid extraction with ethyl acetate effectively removed unreacted APTS without significant analyte loss, whereas solid-phase extraction and microextraction caused substantial losses of hydrophilic sugars. The method showed good linearity (0.5–10 mM, R² > 0.994), precision (RSD 0.81–13.73%), and accuracy (recoveries 93.47–119.75%). Stability studies indicated that sugar standards should be stored at –20 °C. The method was successfully applied to the analysis of four nectar honeys—rapeseed, acacia, phacelia, and dandelion—revealing differences in glucose and fructose content related to botanical origin. The results confirm the suitability of CZE-LIF for sensitive and selective carbohydrate analyses in complex food matrices. Full article

Phosphine–boranes have garnered growing interest for their potential in catalysis and as building blocks for inorganic polymers. While various synthetic methods exist, flexibility to introduce diverse substituents on the P centers remains limited. Our group reported routes to monoalkylated phosphanylboranes starting from primary phosphanylboranes or sodium phosphide. In this work, we extend these strategies to enable the synthesis of dialkylated phosphanylboranes bearing either identical or different substituents on the P atoms. This expanded methodology provides access to a broader scope of diverse P centers, a key factor influencing the reactivity and applications of phosphine–borane derivatives. Full article

Ammonia borane (AB), with a theoretical hydrogen content of 19.6 wt%, is constrained by its low crystalline density (0.758 g/cm³) and poor thermal stability (decomposing at 100 °C). In this study, AB/ammonium perchlorate (AP) composites were synthesized via freeze-drying at a 1:1 molar ratio. The integration of AP introduced intermolecular interactions that suppressed AB decomposition, increasing the onset temperature by 80 °C. Subsequent vacuum calcination at 100 °C for 2 h formed oxygen/fuel-integrated ammonium perchlorate borane (APB), which achieved decomposition temperatures exceeding 350 °C. The proposed mechanism involved AB decomposing into borazine and BN polymers at 100 °C, which then NH₃BH₂⁺/ClO₄⁻ combined to form APB. At 350 °C, APB underwent the following redox reactions: 4NH₃BH₂ClO₄ → N₂↑ + 4HCl↑ + 2B₂O₃ + N₂O↑ + O₂↑ + 7H₂O↑ + H₂↑, while residual AP decomposed. The composite exhibited improved density (1.66 g/cm³) and generated H₂, N₂, O_2, and HCl, demonstrating potential for hydrogen storage. Additionally, safety was enhanced by the suppression of AB’s exothermic decomposition (100–200 °C). APB, with its high energy density and thermal stability, was identified as a promising high-energy additive for high-burning-rate propellants. Full article

Ionic liquids (ILs) have been explored as a way of improving the performance of ZnO-based optoelectronic devices; however, there are few fundamental studies of the IL/ZnO interface. Here, the adsorption of the IL 1-octyl-3-methylimidazolium tetrafluoroborate [C₈C₁Im][BF₄] on ZnO (0001) and ZnO ($10\overline{1}0$) has been studied using synchrotron-based soft X-ray photoelectron spectroscopy. The results indicate that [C₈C₁Im][BF₄] is deposited intact on the ZnO (0001) surface; however, there is some dissociation of [BF₄]⁻ anions, resulting in boron atoms attaching to the oxygen atoms in the ZnO surface and forming B₂O₃. In contrast, the deposition of [C₈C₁Im][BF₄] on the ZnO ($10\overline{1}0$) surface at −150 °C results in the appearance of more chemical environments in the spectra. We propose that the high temperature of the IL evaporator causes some conversion of [C₈C₁Im][BF₄] to a carbene–borane adduct, resulting in the deposition of both the IL and adduct onto the ZnO surface. The adsorption and desorption of the analogous IL 1-butyl-3-methylimidazolium tetrafluoroborate [C₄C₁Im][BF₄] was investigated on ZnO (0001) using synchrotron-based soft X-ray photoelectron spectroscopy. The results indicate that [C₄C₁Im][BF₄] is deposited largely intact at −150 °C and forms islands when heated to room temperature. When heated to over 80 °C, it begins to react with the ZnO surface and decomposes. This is a much lower temperature than the long-term thermal stability of the pure IL, quoted in the literature as ~400 °C, and of IL on powdered ZnO, quoted in the literature as ~300 °C. This indicates that the ZnO surface may catalyse the thermal decomposition of [C₄C₁Im][BF₄] at lower temperatures. This is likely to have a negative impact on the potential use of ILs in ZnO-based photovoltaic applications, where operating temperatures can routinely reach 80 °C. Full article

Ammonia borane (AB) has attracted much attention in the field of solid-state hydrogen storage due to its high hydrogen storage capacity. Nanoconfinement in UiO-66 can reduce the hydrogen release temperature. In particular, terephthalic acid was used as a linker to further improve the dehydrogenation properties through the modification of -NH₂, -OH, -NO₂, -Br, and -F groups. The hydrogen release content of 0.5AB/UiO-66 was 1.98 wt.%, whereas the hydrogen release content of UiO-66-2OH modified by -OH groups increased to 3.85 wt.%. The non-covalent interaction results show that -NH₂ and -OH preferred adsorption with -BH₃, and the H in -NH₂ and -OH were able to interact directly with the H in AB to modify the dehydrogenation process of AB, whereas -NO₂, -Br, and -F indirectly affected the charge density of hydrogen atoms in AB to alter the dehydrogenation property of AB. The modification of functional groups provides a theoretical basis for the design of high-performance MOF nanoconfinement AB composite hydrogen storage materials. Full article

Ammonia borane (NH₃BH₃, AB) is recognized as a promising hydrogen carrier due to its high hydrogen storage density (146 gL⁻¹, mass fraction 19.6%), safety, non-toxicity, and high chemical stability. The hydrolysis of AB has also become a research hotspot in recent years and offers a viable route for hydrogen production. However, the practical application of AB hydrolysis encounters substantial challenges, including undefined catalytic mechanisms, suboptimal catalytic performance, and intricate issues in AB regeneration. Thus, elucidating catalytic mechanisms, developing highly efficient catalysts, and exploring effective regeneration methods for NH₃BH₃ are critical and urgent. This paper delves into the catalytic hydrolysis process of AB, detailing the mechanisms involved, and simplifies the steps that affect AB hydrolysis activity into the adsorption, activation, dissociation of reactants, and the formation and desorption of H₂. It discusses the structural characteristics of metal catalysts used in recent studies, assessing their performance through metrics such as turnover frequency (TOF), activation energy (E_a), and reusability. On this basis, this paper conducts a relatively comprehensive analysis and summary of the strategies for optimizing the performance of AB hydrolysis catalysts, including three aspects, focusing on optimizing the number and dispersion of active centers, enhancing reactant adsorption and activation, and facilitating hydrogen desorption. In addition, it also addresses strategies for controlled hydrogen release during AB hydrolysis and methods for regenerating AB from spent solutions. Finally, corresponding conclusions and prospects are proposed, to provide a certain reference for the subsequent development of safe and efficient catalysts and research on the catalytic mechanism of AB hydrolysis. Full article