Synthesis and characterization of nanoboron powders prepared with mechanochemical reaction between B<Subscript>2</Subscript>O<Subscript>3</Subscript> and Mg powders

Amorphous boron powders with small particle size, narrow size distribution and high purity are very important in the high-tech fields. Mechanochemical synthesis was used to prepare amorphous boron nanoparticles. Synthesis process stage was carried out using stoichiometric amounts of B₂O₃ and Mg powders (6.7 g). Milling was carried out under argon atmosphere in the high-energy planetary ball mill with a ball-to-powder weight ratio (32 : 1) for 10 h. The vial rotation speed was about 440 rpm. Milled products were leached by 28% hydrochloric acid (only one) to remove impurities. Boron powders were obtained after centrifuging, decanting, washing and drying operations. Sample was characterized by inductively coupled plasma (ICP), energy-dispersive spectroscopy, X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ICP results showed that boron powders with purity about 91 wt% can be prepared in the planetary ball mill. Also, the leached powders had an amorphous structure. According to the SEM observation, average particle size of boron powders was smaller than 32 nm and the yield of synthesized nanoboron was more than 74%.     

Characterization and antibacterial properties of nanoboron powders and nanoboron powder coated textiles

The antibacterial properties of boron-containing compounds are well known although there are limited studies available on the pure boron nanoparticles. In this paper, nanoboron particles are characterized in terms of their particle size, shape, stability and surface charge before and after their application onto textile surfaces to study their impact on bacterial activity. It was observed that the boron nanoparticles are effective in limiting the bacterial growth of both Gram-negative and positive species without requiring any stimulation to initiate the antibacterial action. In addition to the antibacterial functionality evaluation of the free boron nanoparticles, nanoboron coated textiles were also characterized and determined to change the wettability and surface charge of the textiles with a variable antimicrobial response to the different species. Consequently, we propose pure nanoboron as a new anti-bacterial agent that can function without external stimulation.     

Electroextraction of boron from boron carbide scrap

Studies were carried out to extract elemental boron from boron carbide scrap. The physicochemical nature of boron obtained through this process was examined by characterizing its chemical purity, specific surface area, size distribution of particles and X-ray crystallite size. The microstructural characteristics of the extracted boron powder were analyzed by using scanning electron microscopy and transmission electron microscopy. Raman spectroscopic examination of boron powder was also carried out to determine its crystalline form. Oxygen and carbon were found to be the major impurities in boron. Boron powder of purity ~ 92 wt. % could be produced by the electroextraction process developed in this study. Optimized method could be used for the recovery of enriched boron (¹⁰B > 20 at. %) from boron carbide scrap generated during the production of boron carbide.     

Preparation and characterization of nanoboron by cryo-milling

Cryo-milling of coarse micron grade elemental boron powder was investigated for possible generation of nanosized boron powder. Process parameters were optimized for the least contamination and least particle size. The as-milled powders were characterized by scanning and transmission electron microscopy (SEM/TEM) and x-ray diffraction (XRD) for powder morphology, average particle size, and phase analysis. The particle size and surface area were also estimated using dynamic laser scattering (DLS) and BET techniques to correlate with the performance of the material. Thermo-gravimetric and differential thermal analysis (TG-DTA) studies were performed to ascertain mass change and energy release in unmilled and milled powder. The average particle size of boron powder after 9 h of cryo-milling was<100 nm. The cryo-milled powder was made air-stable and dispersible in JP10 fuel by coating it with ligand through the mechanical milling method. The TOPO (tri-n-octyl phosphine oxide) coated nano boron powder exhibited dispersion stability for a week.     

Synthesis of LTA zeolite beads using alum sludge and silica rich wastes

This study successfully recycled alum sludge with either lithium slag or bottle glass to make high purity zeolite LTA beads. The basic synthesis approach was to fuse the waste material with sodium hydroxide then complete hydrothermal crystallization. Separate fusion of individual wastes promoted zeolite LTA formation compared to combined fusion. Preferred synthesis conditions were: 10 Na₂O:Al₂O₃:2.5 SiO₂:300 H₂O; hydrothermal temperature = 80 °C; time = 5 h. Zeolite LTA purity was between 80 and 85 wt% from the two waste combinations. Use of pseudoboehmite and carboxymethyl cellulose favoured granulation/extrusion/spheronization of zeolite LTA powder. However, the beading process decreased calcium exchange capacity (CEC) from 99.5 to 37 mg Ca²⁺/g for alum sludge + lithium slag and from 64.5 to 37 mg Ca²⁺/g for alum sludge + waste glass. Additionally, when using 20 wt% pseudo-boehmite as a binder the ion-exchange equilibrium time increased from 60 to 300 min. The importance of not only making zeolite powder from waste materials but also to extend studies to shaped forms was evident. It is recommended that future studies should also focus on making extrudates or beads as these are the forms used commercially.     

Controllable Fabrication of Highly Uniform Sub-10 nm Nanoparticles from Spontaneous Confined Nanoemulsification

Sub-10 nm nanoparticles are known to exhibit extraordinary size-dependent properties for wide applications. Many approaches have been developed for synthesizing sub-10 nm inorganic nanoparticles, but the fabrication of sub-10 nm polymeric nanoparticles is still challenging. Here, a scalable, spontaneous confined nanoemulsification strategy that produces uniform sub-10 nm nanodroplets for template synthesis of sub-10 nm polymeric nanoparticles is proposed. This strategy introduces a high-concentration interfacial reaction to create overpopulated surfactants that are insoluble at the droplet surface. These overpopulated surfactants act as barriers, resulting in highly accumulated surfactants inside the droplet via a confined reaction. These surfactants exhibit significantly changed packing geometry, solubility, and interfacial activity to enhance the molecular-level impact on interfacial instability for creating sub-10 nm nanoemulsions via self-burst nanoemulsification. Using the nanodroplets as templates, the fabrication of uniform sub-10 nm polymeric nanoparticles, as small as 3.5 nm, made from biocompatible polymers and capable of efficient drug encapsulation is demonstrated. This work opens up brand-new opportunities to easily create sub-10 nm nanoemulsions and advanced ultrasmall functional nanoparticles.     

Preparation of self-supporting boron targets

The procedure for the fabrication of self-supporting isotopically enriched ¹¹B targets for the application to nuclear scattering measurements using an electron-beam-excited plasma (EBEP) method was described. A boron target layer of thickness 100±10 μg/cm² was obtained. The thickness and uniformity of the prepared ¹¹B film were determined by measuring the energy loss of alpha particles across the target area. The purity of the target was examined, and it was found that the investigated boron film contained about 10% impurities.     

Thick c-BN coatings - Preparation, properties and application tests

Due to the outstanding properties of cubic boron nitride (c-BN) - c-BN is the second hardest of all known materials, has a high wear resistance and a high thermal stability - this material is very promising for a broad range of applications, especially for cutting tools, both as bulk and as a coating material. The state-of-the-art is the use of sintered cutting inserts with c-BN grains. Such c-BN grains are synthesized in an expensive high-pressure-high-temperature process.The requirements for cutting tools continuously increase in production engineering and this leads to a strong demand for new super hard tool coatings. Cubic boron nitride coatings could be an attractive solution. Unfortunately, the preparation of thick c-BN coatings, on the μm scale, is difficult, due to some serious drawbacks and has been successful only in the last years for a few research groups worldwide.PVD processes allow the preparation of c-BN films thicker than 2 μm on silicon and 1 μm c-BN top layers on pre-coated cemented carbide cutting inserts. Measurements of mechanical properties like hardness and Young's modulus reveal that the properties of the c-BN coatings, with hardness of about 60 GPa, are nearly identical to those of c-BN bulk material.Results of systematic turning and milling tests of different coatings in combination with a c-BN top-layer on cemented carbide cutting inserts will be presented in detail. The new results confirm the high potential of c-BN coatings on cutting tools.     

Progress in Ni-based anode materials for direct hydrocarbon solid oxide fuel cells

Ni-based anode materials of solid oxide fuel cells (SOFCs) are susceptible to carbon deposition and deactivation in direct hydrocarbon fuels, greatly limiting the commercialization. Extensive studies on finding new alternative anode materials have been developed; however, new problems such as low electrochemical performance and complex cell preparation process destroyed the further research passion of Ni-free anode materials. Considering the superior catalytic activity and mature technology of Ni-based anode materials, a large number of recent research results proved that it is still important and promising to solve the carbon coking of Ni-based anode materials. In this review, progress in four typically promising Ni-based anode materials free from carbon coking has been summarized, including the noble metals, ceria, Ba-containing oxides and titanium oxide. Correspondingly, the mechanisms that improve the carbon tolerance of Ni-based modified SOFCs anodes are clearly concluded, providing the materials and theoretical basis for the use of direct hydrocarbon SOFCs as early as possible.     

Comprehensive study on surfactant role on silver nanoparticles (NPs) prepared via modified Tollens process

Surfactants represent not only commonly used wetting agents but also substances that can be used as growth modifiers in the process of solid nanoparticle (NP) preparation. In this study we report influential character of different types of surfactants – i.e. ionic (SDS, CTAC) and non-ionic (Tween 80) – on fundamental characteristics of silver NPs, which were prepared by a modified Tollens process. The influential character of surfactants was evaluated throughout a reasonable improvement of the polydispersity (in the case of the tested non-ionic surfactants from 8.5% even down to 2.5%) and in the case of ionic surfactant, SDS and CTAC, also significant change of zeta potential (from −20 to −50 mV for the highest tested concentration of SDS). A slight influence of the tested surfactants was observed on the sizes of the prepared silver NPs. Therefore the obtained results from the performed surfactant-assisted syntheses revealed a possibility how to tailor silver NPs by means of their polydispersity and zeta potential according to the application demands.     

Atomic-scale study of the role of carbon on boron clustering

Boron (BF₂, 20 keV, 3.14/cm²) and carbon (13 keV, 10¹⁵/cm²) implanted silicon annealed at 800 °C during 30 min or at 1000 °C during 10 s has been investigated using a laser-assisted wide-angle tomographic atom probe (LaWaTAP) instrument. Boron-silicon clusters containing ~ 1.3 at.% of boron atoms have been observed in boron implanted silicon with a concentration exceeding the solubility limit. Often identified as BICs, they are interpreted as a metastable phase. Furthermore, addition of carbon clearly reduced the clustering of boron. This was interpreted as a diminution of boron diffusion or as an increase of the solubility limit of boron. Carbon-silicon clusters containing ~ 1.5 at.% of carbon atoms were observed, maybe the precursors of the SiC phase.     

Influence of coal tar pitch coating on the properties of micro and nano SiC incorporated carbon–ceramic composites

Carbon-micro or nano silicon carbide–boron carbide (C-micro or nanoSiC–B₄C) composites were prepared by heating the mixtures of green coke and carbon black as carbon source, boron carbide and silicon at temperature of 1,400 °C. Green coke reacts with silicon to give micron sized silicon carbide while the reaction between silicon and carbon black gives nano silicon carbide in the resulting carbon–ceramic composites. The green coke was coated with a suitable coal tar pitch material and used to develop carbon-(micro or nano) silicon carbide–boron carbide composites in a separate lot. The composites were characterized for various properties including oxidation resistance. It was observed that both types of composites made from uncoated as well as pitch-coated green coke exhibited good oxidation resistance at 800–1,200 °C. The density and bending strength of composites developed with pitch-coated green coke improved significantly due to the enhanced binding of the constituents by the pitch.     

Effect of boron waste and boric acid addition on the production of low energy belite cement

The effect of boron oxide addition on the production of low energy belite cements has been investigated. Three types of clinkers were prepared with 1.5 wt.% (BC_BA1.5) boric acid, and 1.0 wt.% (BC_BW1) and 6.5 wt.% (BC_BW6.5) boron waste addition. The design of the raw mixtures was based on modified Bogue equations. According to the free lime content and the evolution of the microstructure of the clinkers, firing was performed at 1330 °C, 1350 °C and 1310 °C for BC_BA1.5, BC_BW1 and BC_BW6.5, respectively. Boron addition favored the reduction of the clinkering temperature as well as the stabilization of upper belite polymorphs. According to the present results, late compressive strength development of belite cements depends mainly on the crystal type rather than on the content of belite in the clinker. The results indicate that controlled quantities of boron oxide can be beneficial in the production of belite cement.     

Mesoporous niobium oxides with tailored pore structures

Novel thermally stable and 2D mesoporous niobia phases were prepared by the evaporation induced self-assembly (EISA) with high surface areas (up to 211 m²/g). The pore size of these novel mesoporous niobium oxides was tuned in a wide range from 4.6 to 21 nm by increasing the aging temperature, aging time, and humidity of aging atmosphere. Mixtures of two nonionic surfactants, Pluronic P123 and Brij 35, were for the first time used to tune the pore structure of resultant mesoporous niobia phases which showed that the mesopore shape may be switched from cylindrical to ink-bottle. The niobia mesostructures obtained in this study were thermally stable up to 500 °C. These novel mesoporous niobium oxides with tunable pore sizes are highly promising as catalytic supports and a major component in the synthesis of porous Nb-containing mixed metal oxides, such as MoVTeNbO _x catalysts for selective (amm)oxidation of propane.     

Effect of surfactants on preparation of nanoscale α-Al2O3 powders by oil-in-water microemulsion

The nanoscale α-Al₂O₃ powders have been synthesized by the O/W microemulsion system using cyclohexane as the oil phase, ultrapure water as the water phase, OP-10 and alcohol as the surfactant and co-surfactant. It has been found that the nature of surfactants played an important role to regulate the size and morphologies of the α-Al₂O₃ nanoparticles. Three different nonionic surfactants (OP-10, Triton X-100 and Tween-80) have been used for the preparation of microemulsions. The microemulsions were characterized by Zeta Potential Analyzer. The results showed that the OP-10 system possesses wide and stable microemulsion phase regions. The synthesized α- Al₂O₃ powders have been comprehensively characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD). The powders calcined at 900–1150 °C showed the presence of alumina phase with crystal structure, The SEM images showed that the powders was an average diameter of 30–100 nm.     

Effects of organic additives on the microstructural,rheological and electrical properties of silver paste for LTCC applications

Silver powders were prepared by a chemical reduction method. Effects of different surfactants during this preparation process were examined. Using these silver powders, silver pastes were prepared for low temperature co-fired ceramics (LTCC) applications. Another batch of different surfactants were added into the silver paste and evaluated. Moreover, various organic thixotropic agents were used to modify the thixotropy behavior of the silver paste. It was found that the surfactants of PVP (Polyvinyl pyrrolidone, for preparation of the silver powder) and Span-85 (for the preparation of silver paste) exhibited the best performance, with an electrical resistivity of 0.11 mΩ mm. The silver paste with the thixotropic agent of hydrogenated castor oil shows the largest thixotropic index of 1.56. Using different organic additives, the microstructural, rheological and electrical properties of the silver paste can be considerably improved, and our results shed light on the optimization of the silver paste for LTCC applications.

     

Synthesis of nanocrystalline boron carbide from boric acid–sucrose gel precursor

A novel method, based on the combustion of boric acid–sucrose xerogel was developed to synthesize nanocrystalline boron carbide powder. This xerogel was pyrolyzed at 1273 K. Boron carbide was obtained by heating this precursor at 1823 K. The yield of boron carbide was improved by the use of a novel graphite crucible designed for this purpose. The xerogel and the precursor were characterized by using Fourier transform infrared spectroscopy. The constituent phases were identified by using X-ray diffraction while their elemental composition was established with the help of chemical assay. The microstructure of the final product was examined with the help of scanning electron microscopy and transmission electron microscopy. This study demonstrates that the yield of boron carbide would be enhanced to about 48% while the free carbon content in the final product could be reduced to about 6 wt%. These are significant improvements over similar studies reported so far on the gel-based preparation of boron carbide.     

Optimization and sensitivity study of biodiesel synthesis from Jojoba oil using mixed-integer programming

Jojoba oil-based biodiesel is promising alternative fuel due to its versatile properties. Renewable transportation fuels are considered as promising alternatives to conventional fuels. The physical and chemical properties of these fuels enabled them to be used in modern internal combustion engines; this makes them attractive for use as direct replacements or as additives of fossil fuels. Jojoba oil is extracted from Jojoba seeds, and it is an excellent feedstock for biodiesel after the transesterification process. The plant is highly adaptable to harsh weather including salty water, desert, and hot temperatures; thus, it can be grown in Saudi Arabia. This research work comprises a detailed optimization study of biodiesel production from Jojoba oil using mixed-integer programming. golden section search method was used for the optimization and sensitivity study was conducted for reaction time and temperature. The result shows that 54.1 minutes and 47.5 °C are the optimized reaction time and temperature to produce biodiesel which is considerably low as compared to previous studies.     

Effects of heat treatment on the microstructure of amorphous boron carbide coating deposited on graphite substrates by chemical vapor deposition

A two-layer boron carbide coating is deposited on a graphite substrate by chemical vapor deposition from a CH₄/BCl₃/H₂ precursor mixture at a low temperature of 950 °C and a reduced pressure of 10 KPa. Coated substrates are annealed at 1600 °C, 1700 °C, 1800 °C, 1900 °C and 2000 °C in high purity argon for 2 h, respectively. Structural evolution of the coatings is explored by electron microscopy and spectroscopy. Results demonstrate that the as-deposited coating is composed of pyrolytic carbon and amorphous boron carbide. A composition gradient of B and C is induced in each deposition. After annealing, B₄C crystallites precipitate out of the amorphous boron carbide and grow to several hundreds nanometers by receiving B and C from boron-doped pyrolytic carbon. Energy-dispersive spectroscopy proves that the crystallization is controlled by element diffusion activated by high temperature annealing, after that a larger concentration gradient of B and C is induced in the coating. Quantified Raman spectrum identifies a graphitization enhancement of pyrolytic carbon. Transmission electron microscopy exhibits an epitaxial growth of B₄C at layer/layer interface of the annealed coatings. Mechanism concerning the structural evolution on the basis of the experimental results is proposed.     

Microwave direct synthesis of MgB2 superconductor

Intermetallic compound superconductor MgB₂ was synthesized from spherical magnesium powder and lower purity amorphous boron powder by microwave direct heating. Powder X-ray diffraction (XRD) analysis indicates that the phases of the synthesis sample are MgB₂ (major phase) and a small amount of MgO. Scanning electron microscope (SEM) observation shows that the MgB₂ grain size is homogeneous and the particle size is about several hundreds of nanometers. The onset superconducting transition temperature of the MgB₂ sample measured by the temperature dependence of magnetization measurement is about 37.6 K. The critical current density J_c calculated according to the Bean model are about 2.0 × 10⁵ A/cm² at 20 K in self-field and 1.0 × 10⁵ A/cm² at 20 K in 1 T applied field.