B NMR of boron-doped graphite as the negative electrode of a lithium secondary battery

Boron-doped graphite used as a negative electrode for a lithium rechargeable battery is known to have higher discharge capacity than undoped graphite. Herein, the graphites were mixed with 1, 2.5, 5, and 7 wt.% of boron carbide during the graphitizing process. The structural states of boron in those boron-doped graphites were successfully identified by solid-state ¹¹B NMR spectroscopy. For 1 wt.% sample, all boron atoms were at substitutional sites, as evident by the second-order quadrupole broadened ¹¹B NMR line having a quadrupole coupling constant, Q_CC=3.36(2) MHz. The NMR results show evidence of excess boron atoms recrystallizing as boron carbide during the graphitizing process which is in agreement with XRD data. Agreement of experimental results with computer simulated data indicate that the substitutional sites in boron-doped graphites were observed for the first time.     

萘系沥青树脂的制备和性质

以对苯二甲醇（PXG）为交联剂,萘为芳烃原料,在对甲苯磺酸的催化作用下,合成了沥青树脂。研究中考察了沥青树脂的多种性能参数。结果表明：沥青树脂是萘与对苯二甲醇结合而成的低聚体混合物,固化后具有良好的热稳定性,是一种新型的耐热树脂。     

Para-xylene adsorption separation process using nano-zeolite Ba-X

The liquid phase adsorption process was studied on nano-zeolite Ba-X for separating para-xylene from a feed mixture containing all C₈ aromatics. Nano-zeolite Ba-X with different ratios of SiO₂/Al₂O₃ was synthesized through hydrothermal process and ion-exchanged with barium. The product was characterized by X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption and in situ Fourier transform infrared (FTIR) spectroscopy. The adsorption process was carried out in a breakthrough system at temperature range of 120–160 °C under 4–7 atm pressure. The influence of nano-zeolite water content on the separation process was studied. The optimization of adsorption process was also investigated by changing the operation conditions. The adsorption isotherm for all C₈ aromatic isomers and also desorbents indicated the typical Langmuir type. The selectivity factor of adsorbent for para-xylene and the adsorption capacity at saturation of the different adsorbate samples with each component from C₈ aromatic mixture were determined. It was observed that the selectivity of para-xylene increased by barium ion-exchange of cationic sites in nano-zeolite X and the adsorbent selectivity for para-xylene relative to each of meta-xylene, ortho-xylene and ethyl-benzene under the optimum conditions was found to be 7.191, 2.819 and 3.745, in the order given. It was also studied the influence of desorbent type on its selectivity for para-xylene compared to each isomer from the C₈ aromatic mixture.     

Thermal conductivity and microstructure of Ti-doped graphite

Ti doped and Si-Ti doped graphites have been developed. The influence of the dopants on the properties and microstructure of doped graphites was analyzed. Test results reveal that Ti doped graphite has excellent bending strength and high thermal conductivity, with highest values reaching 50.2 MPa and 424 W m⁻¹ K⁻¹ for a Ti concentration of 15 wt% in the raw materials. Si added simultaneously with Ti promotes the growth of graphite crystals resulting in an increased thermal conductivity. A kind of Si-Ti doped graphite has been developed with thermal conductivity as high as 494 W m⁻¹ K⁻¹ by optimizing the compositions. Correlation between the content of dopant and the properties and microstructure of doped graphites was studied, and catalytic graphitization mechanism of dopants is also discussed.     

Shape selective catalysis in methylation of toluene: Development,challenges and perspectives

Toluene methylation with methanol offers an alternative method to produce p-xylene by gathering methyl group directly from C1 chemical sources. It supplies a “molecular engineering” process to realize directional conversion of toluene/methanol molecules by selective catalysis in complicated methylation system. In this review, we introduce the synthesis method of p-xylene, the development history of methylation catalysts and reaction mechanism, and the effect of reaction condition in para-selective technical process. If constructing p-xylene as the single target product, the major challenge to develop para-selective toluene methylation is to improve the p-xylene selectivity without, or as little as possible, losing the fraction of methanol for methylation. To reach higher yield of p-xylene and more methanol usage in methylation, zeolite catalyst design should consider improving mass transfer and afterwards covering external acid sites by surface modification to get short “micro-tunnels” with shape selectivity. A solid understanding of mass transfer will benefit realizing the aim of converting more methanol feedstock into para-methyl group.

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A new method for solid-state diffusion of boron atoms into powders of a multicomponent carbide

Multicomponent boron-containing carbide (ie, Zr-Ti-C-B) composites show good ablation resistance. The present work is the first report to introduce the powder fabrication of Zr-Ti-C-B using a new method for solid-state diffusion of boron atoms. First, the nonstoichiometric carbide (ie, Zr_0.8Ti_0.2C_0.8) with carbon vacancies was fabricated by free-pressureless spark plasma sintering. Different boron sources such as B₂O₃, B, and B₄C were used to react with the nonstoichiometric carbide. The Zr_0.81Ti_0.19C_0.86B_0.14 can be finally generated through the solid-state diffusion of boron atoms using the B₂O₃ boron source at 1300°C followed by carbon thermal reduction using the phenolic resins at 1600°C.     

Characteristics of meso-carbon microbeads separated from pitch

Mesophase spherules separated by solvent fractionation from heat-treated coal-tar pitch and from heat-treated asphalt at 430°C are named “meso-carbon microbeads”. Characteristics of these mesophase microbeads were studied. The meso-carbon microbeads are classified into three types, type C, type M and type P, corresponding to the raw pitch materials. The chemical composition of type C and type M consists of high molecular weight aromatic hydrocarbons having short side chains of aliphatic hydrocarbons, and that of type P consists of small ring number aromatic hydrocarbons having long side chains of aliphatic hydrocarbons. The shapes of the meso-carbon microbeads are classified into lemon-like and spherical by their shape. The meso-carbon microbeads do not fuse or melt by heat-treatment. The graphitizability of heat-treated meso-carbon microbeads is not high. When the meso-carbon microbeads are heat-treated at 300–500°C in a medium of polynuclear aromatic hydrocarbons (anthracene, pyrene, chrysene and pitch) their behavior is similar to that of mesophase spherules in pitch. However, when the ratio of the meso-carbon microbeads to the polynuclear aromatic hydrocarbon was changed, the behavior of the microbeads was peculiar.     

Effects of boron-doping and heat-treatment on the electrical resistivity of carbon nanohorn-aggregates

Boron-doping of carbon nanohorn-aggregates was carried out by using arc-vaporization of a boron-containing composite carbon rod in a balanced gas of Ar with 5% of O₂. Transmission and scanning electron microscopy revealed that the obtained sample powder consisted of high purity nanohorn-aggregates. The temperature dependence of the electrical resistivity of a pellet formed from the sample indicated a feature based on the three-dimensional variable-range hopping (3D-VRH) conduction. From the analyses of 3D-VRH, it was found that the electronic density of states near the Fermi-level, N(0), was enhanced due to the boron-doping, reaching an enhancement factor of ∼1.7 × 10³ compared with the N(0) of the un-doped nanohorns. Moreover, the magnitude of the electrical resistivity decreased as the boron concentration increased. The electrical resistivity of the un-doped nanohorns also decreased with heat-treatment, but the N(0) value did not change significantly. These facts suggest that the change in N(0) should be associated with the boron atoms that are substitutionally doped in the sp²-bonded carbon network.     

Production of nanoTiC–graphite composites using Ti-doped self-sintering carbon mesophase powder

This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO₂ nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC.     

Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

It has been demonstrated that it is possible to produce p-xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p-xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p-xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p-xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p-xylene isomer, under optimised conditions.     

Molecular simulation of plasma polymerized polyaniline-iodine compounds

This work presents a molecular simulation study of plasma-polymerized polyaniline-iodine compounds. The simulation is focused on the ortho, meta and para substitutions of aniline benzene rings where the polymers can grow into the maximum and partially reduced and oxidized states of polyanilines. This simulation offers the possibility of visualizing the spatial conformation of polyanilines while interacting with iodine atoms with and without chemical bonds between them. Such cases are often found in plasma polymerization and doping processes.     

Aromatic Transformations Over Mesoporous ZSM-5: Advantages and Disadvantages

Catalytic behavior of mesoporous ZSM-5 was investigated in toluene disproportionation, toluene alkylation with isopropyl alcohol, and p-xylene alkylation with isopropyl alcohol to understand the effect of the presence of mesopores. Three ZSM-5 zeolites (conventional one and two mesoporous differing in the mesopore volume) having similar Si/Al ratio were synthesized and characterized as for their acidity (internal and external) as well as their micropore/mesopore volume. No substantial differences among three samples were observed as for the type and concentration of Brønsted and Lewis acid sites as well as their location in zeolite channels or on external surface of zeolite crystals. Conversions of toluene and p-xylene increased with increasing volume of mesopores in ZSM-5 zeolite while the selectivity to individual products depended on the type of reaction. In general, selectivity to sum of xylenes in toluene disproportionation, sum of isopropyltoluenes in toluene alkylation and to 1-isopropyl-2,5-dimethylbenzene in p-xylene alkylation increased due to a shorter contact time molecules spent in mesoporous ZSM-5 catalysts. In contrast, para-selectivity decreased as diffusion pathways were shorten due to the presence of mesopores.     

Preparation and characterization of α-cyclodextrin-containing membranes—application to the selective extraction of xylene isomers

Polymer membranes containing α-cyclodextrin (α-CD) were prepared by the casting method using cross-linking reaction with hexamethylenediisocyanate. The film synthesis conducted with and without dibutyltin dilaurate as catalyst, resulted in two series of materials in which α-CD host entities were chemically linked to polyvinyl alcohol and physically entrapped, respectively. The obtained membranes were successfully applied to the separation of o-/p- and o-/m-xylene isomer mixtures by pertraction from water. p- and m-xylenes were found to be the faster permeants compared to the o-isomer. The separation factor of p-xylene over o-xylene varied from 7.75 to 0.35 depending on the membrane α-CD content and the feed concentration ratio. Permeation rate and separation selectivity data were discussed in terms of molecular recognition by α-CD and of coupling transport effect. Both kinds of materials showed similar behaviour in their permeation performances indicating that inclusion interaction was not changed by the chemical grafting on PVA chains.     

Effects of boron content on the microwave-transparent property and high-temperature stability of continuous SiBN fibers

Owing to their high-temperature stability and microwave-transparent properties, SiBN fibers are promising reinforcement materials for microwave windows or radomes in harsh environments. This work investigates the high-temperature properties of continuous SiBN fibers with different boron contents. Compared with Si₃N₄ fibers, the SiBN fibers demonstrated superior high-temperature stability, retaining their original tensile strength up to 1600°C with a smooth surface and amorphous structure. The boron-containing microstructure improved the microwave-transparent properties of the SiBN fibers by decreasing their dielectric constant and loss. The values were stabilized at temperatures up to 1200°C. The high-temperature stability and microwave transparency of the SiBN fibers were likely contributed by the synergistic effect of the amorphous BN phase and the Si–N–B networks (the main existing state of the boron atoms).     

前驱体法制备Si-C-N-M基高性能陶瓷的研究进展

综述了聚合物前驱体热解转化法制备高性能Si-C-N-M基陶瓷的研究进展，着重介绍了3类Si-C-N-B基陶瓷前驱体（主链或侧基含有环硼氮烷或含硼杂环的聚硼硅氮烷、含硼聚硅氮烷和含硼聚硅基碳化二亚胺）及Si-C-N-Al基陶瓷前驱体。     

Effect of B2O3 on the structural and in vitro biological assessment of mesoporous bioactive glass nanospheres

In this paper, the boron-containing mesoporous bioactive glass (MBG) nanospheres have been successfully synthesized by modified sol-gel method assisted by surfactant, and the effect of boron substitution on structure and bioactivity was evaluated by combining experiments and ab initio molecular dynamics (AIMD) simulations. All of the samples exhibit regularly uniform mesoporous spherical microstructure with an average size of about 60 nm, and the boron-containing MBGs show higher specific surface area with the value up to 416.20 m²/g. The simulated body fluid (SBF) immersion test confirms that the deposited hydroxyapatite (HA) evidently increases with the increasing of boron content, indicating that the biological behavior has been significantly improved resulting from incorporation of boron. Additionally, our results also reveal that B₂O₃ substitution has positive impact on cell proliferation of human periodontal ligament cells (hPDLCs) at lower extracted concentration. Furthermore, AIMD simulation is employed to understand the relationship between structural changes and in vitro bioactivity in terms of structural information, especially the boron coordination number. The results illustrate that the boron-containing MBG nanospheres with excellent bioactivity are great potential for biomedical applications.     

A facile strategy for preparation of phosphorus modified HZSM-5 shape-selective catalysts and its performances in disproportionation of toluene

The phosphorous modified HZSM-5 catalysts were prepared by using phosphoric acid as the precursor with the addition of ethanol during the impregnation process and their shape-selective performances in the synthesis of p-xylene by disproportionation of toluene were investigated. An excellent para-selectivity along with a relatively high catalytic activity was achieved over the phosphorous modified HZSM-5 catalysts. The addition of ethanol during the impregnation process promotes the transition of phosphoric acid to phosphate, which accomplished the cover of the external acid sites and the reserve of the acid sites in the pores of HZSM-5 zeolite after phosphorous modification.     

Boron sources as sintering additives for alumina-based refractory castables

Sintering additives (SA) have great potential to be used in refractories to enhance their thermo-mechanical properties at intermediate temperatures (600–1200 °C). Boron-based compounds are pointed out as suitable options for this purpose as they undergo phase transformations (i.e., decomposition, oxidation, etc.) at relatively low temperatures, which may lead to boron-rich liquid phase generation and transient liquid phase sintering. Considering these aspects, the present study aims to evaluate the role of five different SA [boron oxide (B₂O₃), boric acid (H₃BO₃), sodium borosilicate (BS), magnesium borate (BM) and boron carbide (B₄C)] when 0.5, 1.0 and 2.0 wt% of these materials were added to alumina-based castable compositions bonded with hydratable alumina. Flowability, apparent porosity, XRD, hot elastic modulus, thermal shock resistance and mechanical tests were carried out in order to identify whether (i) transient liquid phase sintering would be favored in these refractories, and (ii) at which temperature range such compositions might be submitted during service and still present an improved performance when compared to an additive-free castable (reference). Based on the results, incorporating boron oxide into the alumina-based castables was not recommended as this hygroscopic material reduced the flowability of the compositions, preventing a suitable preparation of the samples. The other boron-containing compounds could be directly added to the high-alumina mixtures without resulting in major changes in their processing steps. Nevertheless, the paper highlights the importance of selecting a proper SA source and optimizing its content in the castable composition as these parameters may affect its overall rheology and thermo-mechanical properties. The formulations containing 0.5 wt% of H₃BO₃ or B₄C, 1 wt% of sodium borosilicate and 2 wt% of magnesium borate presented enhanced erosion and thermal shock resistances and hot mechanical strength at 1000 °C and 1200 °C, which makes them potential refractory castables to be used in petrochemical and aluminum industries.     

Synthesis and characterization of aryl boron-containing thermoplastic phenolic resin with high thermal decomposition temperature and char yield

Phenol, zinc acetate dihydrate and paraformaldehyde are firstly performed to synthesize thermoplastic phenolic resin (PR), then phenylboronic acid (PBA) and other two boron compounds (4-hydroxymethyl phenylboronic acid & boronic acid) are introduced to fabricate the boron-containing thermoplastic phenolic resins (BPRs). The corresponding molecular structure, softening points, thermal decomposition temperature and char yield ratio of the BPRs are characterized and investigated by FTIR, NMR, XPS and TGA. Compared to pure thermoplastic PR, all the BPRs present relatively higher softening points, more excellent thermal decomposition temperature and higher char yield values. BPR-a exhibits the optimal thermal decomposition temperature (T ₅ of 317.4 °C) and char yield ratio at 800 °C (69.6 %).     

Vapour liquid equilibrium with association in both phases: A model with the concentration-dependent liquid phase association constant applied to acetic acid—benzene, -toluene, -p- and -o-xylene

A model employing the correction factors of Marek and Standart, but using a concentration-dependent liquid phase association factor of Jenkins—Robinson, has been used to model vapour—liquid equilibrium data for mixtures of acetic acid with benzene, toluene, o-xylene and p-xylene. With the aim to use systems of acetic acid—benzene and acetic acid—toluene as the test mixtures for distillation columns, the examination of the systems of acetic acid—aromatic hydrocarbons was undertaken. The model promises to be useful in modelling isobaric and isothermal data of acetic acid—benzine, acetic acid—toluene, acetic acid-p-xylene and acetic acid-o-xylene systems. Deviation plots show that the isothermal and isobaric data are represented well.