Silicothermic synthesis of phase-pure HfB2 fine powder

Phase pure and nano-sized hafnium diboride (HfB₂) fine powder was prepared via a novel sustainable silicothermic route at 1100°C from inexpensive raw materials HfO₂, Na₂B₄O₇ and Si. By introducing sodium oxysalts as source of Na₂O into the batch mixtures, the SiO₂/ Na₂O modulus in the melt were reduced from 5:1 to 2:1, and the original water-insoluble byproduct SiO₂ was taken by the melt at test temperature and converted into water soluble sodium silicate (Na₂Si₂O₅) which was easily removed from the reacted mass via simple hot water washing. Consequently, the aqua sodium silicate could be readily recycled and used as a precursor for preparing many other valuable materials due to absence of foreign salts (eg halides, especially in the molten salt-assisted synthesis process) in the synthesis process, and the relevant environmental concerns could be alleviated. Using excessive amount of 20 wt% Si and 15 wt% Na₂B₄O₇ as compensation for the evaporation loss of silicon, in the form of SiO (g), and B₂O₃ in the reduction process, a high reaction extent was achieved and HfO₂ and Na₂B₄O₇ were completely converted into HfB₂ at 1100°C.     

High-temperature electrochemical synthesis of carbides, silicides and borides of VI-group metals in ionic melts

Possible systems and conditions have been determined for the electrosynthesis of carbides, silicides and borides of chromium, molybdenum and tungsten on the basis of thermodynamic analysis of chemical and electrochemical reactions involved in high temperature electrochemical synthesis. Electrosynthesis of powdered molybdenum and tungsten carbides has been carried out under thermodynamic conditions from halide–oxide, under excess CO₂ pressure, and tungstate–molybdate–carbonate melts. Electrosynthesis of powdered silicides and borides of chromium, molybdenum and tungsten has been realized under kinetic conditions. Oxide and halide–oxide electrolytes have been developed for the electrodeposition of molybdenum and tungsten carbide coat ings.     

Electrooxidation and dischargeability of transition-metal borides as possible anodic materials in neutral aqueous electrolytes

A number of transition-metal borides were studied as anodic materials for neutral aqueous batteries. These borides are shown to have considerably high electrochemical activities in neutral electrolytes. The discharge capacities for TiB₂ reach 1,350 mAh g⁻¹ at a constant current density of 50 mA g⁻¹, exceeding those for all the metal electrodes reported so far. Amorphous CoB_x can deliver a discharge capacity of >650 mAh g⁻¹, and even simply ball-milled FeB_x can also give a discharge capacity of >200 mAh g⁻¹. These results suggest the possible use of boride compounds as a large family of new anodic materials for constructing neutral aqueous batteries with high electrochemical capacity and rate capability.     

Preparation of tungsten borides by combustion synthesis involving borothermic reduction of WO3

An experimental study on the preparation of two tungsten borides, WB and W₂B₅, was conducted by self-propagating high-temperature synthesis (SHS), during which borothermic reduction of WO₃ and elemental interaction of W with boron proceeded concurrently. Powder mixtures with two series of molar proportions of WO₃:B:W = 1:5.5:x (with x = 1.16–2.5) and 1:7.5:y (with y = 0.5–1.33) were adopted to fabricate WB and W₂B₅, respectively. The starting stoichiometry of the reactant compact substantially affected the combustion behavior and the phase composition of the final product. The increase of metallic tungsten and boron reduced the overall reaction exothermicity, leading to a decrease in both combustion temperature and reaction front velocity. The initial composition of the reactant compact was optimized for the synthesis of WB and W₂B₅. In addition to small amounts of W₂B and W₂B₅, the powder compact of WO₃ + 5.5B + 2 W produced WB dominantly. Optimum formation of W₂B₅ was observed in the sample of WO₃ + 7.5B + 0.85W. Experimental evidence indicates that an excess amount of boron about 10–13% is favorable for the formation of WB and W₂B₅.     

Synthesis of osmium borides by mechanochemical method

Transition metal osmium borides were synthesized by mechanochemical method using high‐energy ball‐milling with Os (Osmium) and B (Boron) powders as raw materials. The formation process, reaction mechanism, and thermal stability of the mechochemically synthesized osmium borides were studied. Almost pure Os₂B₃ phase was obtained when the Os‐to‐B molar ratio was 1:2; while ReB₂‐type hexagonal OsB₂ with a small amount of RuB₂‐type orthorhombic OsB₂ was obtained when the Os‐to‐B molar ratio was 1:3. Stoichiometry OsB₂ was obtained from boron rich starting mixture powders due to the B loss during the high‐energy ball‐milling process. It was also found that WC and osmium oxide were present as contaminants after ball milling for 40 hours. Heat treatment results revealed that the as‐synthesized Os₂B₃ powders are thermally stable in flowing Ar up to 800°C, but a transformation from hexagonal to orthorhombic structure partially occurred for the OsB₂ powders as low as 600°C.     

A facile route for the synthesis of high-entropy transition carbides/borides at low temperatures

As the main candidates in the field of ultra-high temperature ceramics, high entropy carbides/borides (HECs/HEBs) have good oxidation resistance properties, high hardness, as well as excellent thermal and electrical conductivities, which are the focused points of research nowadays. In the current study, (Hf,Ta,Zr,Nb,Mo,Ti)C powders were successfully synthesized by a three-step process, including the mixing process of raw oxides and carbon black with spaying Fe(NO₃)₃ solution, carbothermal reduction and subsequent calcium posttreatment. For the preparation of (Hf,Ta,Zr,Nb,Mo,Ti)B₂ powders, during the calcium posttreatment process, equal stoichiometric ratio of B₄C was added for the purpose of boriding reaction. The relevant X-ray diffraction and SEM characterizations indicate the successful preparations of face-centered cubic HECs and hexagonal HEBs. However, slight Mo local segregation was found in the prepared (Hf,Ta,Zr,Nb,Mo,Ti)B₂ powders. The iron generated from Fe(NO₃)₃ promotes the solid solution process between monocarbides during the carbothermal reduction process via the dissolution-diffusion-precipitation mechanism. In the calcium posttreatment process, the liquid calcium ensures the boriding reaction take place at a low temperature. In addition, the residual carbon could be combined with calcium to generate CaC₂ which is easy to be removed by acid leaching, and meanwhile, the added Fe could also be finally eliminated to produce pure HEC/HEB powders. The current method does not require the long-time high energy ball milling of raw materials, but only simple and mild mixing is enough. Therefore, such a facile route has a great potential application prospect for industrially preparing high entropy phase powders in a large scale.     

Synthesis of molybdenum carbide nanoparticles using pulsed wire discharge in mixed atmosphere of kerosene and argon

Pulsed wire discharge was used to prepare nanoparticles of molybdenum and its carbides from Mo wires in a gas mixture of argon and kerosene at pressures of 100, 50, and 25 kPa. The different pressures affected the carburization process and particle formation. The most effective pressure was 25 kPa, where the volume fraction of MoC was identified by Rietveld refinement of X-ray diffraction data to be 98.4%. The particle size distribution was also obtained from transmission electron microscopy measurements, and the smallest geometric mean diameter was determined tobe 24.3 nm for the sample prepared at 25 kPa.     

Ultra high temperature high-entropy borides: Effect of graphite addition on oxides removal and densification behaviour

The introduction of 0.5–1.0 wt.% graphite to the powders prepared by Self-propagating High-temperature Synthesis (SHS) is found to be highly beneficial for the removal of oxide impurities (from 2.7-8.8 wt.% to 0.2–0.5 wt.%) during spark plasma sintering (1950°C/20 min, 20 MPa) of (Hf_0.2Mo_0.2Ta_0.2Nb_0.2Ti_0.2)B₂ and (Hf_0.2Mo_0.2Ta_0.2Zr_0.2Ti_0.2)B₂ ceramics. Concurrently, the consolidation level achieved is enhanced from about 92.5% and 88%, respectively, to values exceeding 97%. While a further increase of graphite slightly improves samples densification, final products become progressively richer of the unreacted carbon.It is assumed that graphite plays a double role during SPS, e.g. not only as a reactant during the carbothermal reduction of oxides contaminant, but also as lubricating agent for the powder particles. The latter phenomenon is likely the main responsible for the densification improvement when 3 wt.% or larger amounts of additive are used. Another positive effect is the crystallite size refinement of the high-entropy phases with the progressive abatement of oxides, to confirm that their presence promotes grain coarsening during the sintering process.     

In situ synthesis mechanism of ZrC-ZrB2/Cu composites prepared by SHS-casting method

The self-propogating high-temperature syntheis (SHS) experiments in the glove box indicated that the combustion temperature decreased and the ignition time increased with increasing B₄C size in Cu-Zr-B₄C system. Once B₄C size exceeded 28 μm, the full conversion of ZrC and ZrB₂ failed. In situ ZrC and ZrB₂ ceramic particle-reinforced Cu matrix composites were produced by the self-propagating high-temperature synthesis reaction of Cu-Zr-B₄C system in molten Cu. Moreover, the phase formation mechanism was investigated by the combustion wave quenching experiment of Cu-Zr-B₄C powder compact in Cu liquid. Results showed that ZrC and ZrB₂ were mainly formed by the dissolution-reaction-precipitation mechanism. A developed method arresting the combustion front of a reactant in molten metal was proposed.     

Phase control during synthesis of nanocrystalline ultrahigh temperature tantalum‐hafnium diboride powders

Ta_1?xHf_xB₂ material is attractive for various aerospace applications. In this study, 2 low‐cost approaches were adopted to synthesize nanocrystalline Ta_0.5Hf_0.5B₂ solid solution and related composite powders. The first was based on carbothermal reduction reaction (CTR) of intimately mixed tantalum‐hafnium‐boron oxide(s) and carbon obtained from aqueous solution processing of TaCl₅, HfCl₄, B₂O₃, and sucrose as precursors. It was found that when using this method, due to the low solubility of each other for Ta₂O₅ and HfO₂ and the difference in reactivity of those 2 oxides with carbon (as well as B₂O₃), individual TaB₂ (‐rich) and HfB₂ phases always form separately. Those borides tend to remain phase separated due to the slow inter‐diffusion between them. However, it was observed that addition of copper “catalyst” noticeably accelerates the inter‐diffusion and the solid solution formation. The second approach was based on alkali metal reduction reaction, in which TaCl₅ and HfCl₄ are directly reacted with sodium borohydride (NaBH₄). This method yields a single phase Ta_0.5Hf_0.5B₂ solid solution nanopowders in one step at much lower temperatures (e.g., 700°C) by avoiding the oxides formation and the associated phase separation of individual borides as observed in the CTR‐based process.     

Facile synthesis of nanocrystalline hexagonal tungsten trioxide from metallic tungsten powder and hydrogen peroxide

A hexagonal form of tungsten trioxide (h‐WO₃, particle size: 15.9‐57.1 nm) was found to be formed by a direct reaction between metallic tungsten powder (W, particle size: 0.45‐0.59 μm) and 15%‐30% hydrogen peroxide (H₂O₂) aq solution. Oxide film on the powder surface having the similar crystal structure as h‐WO₃ was essential for the formation, and the surface oxide film was formed by aging the powder in air at 45°C, a relative humidity of 100% (P_H2O 96 hPa) for 3‐28 days or in ambient atmosphere at room temperature for 12 years. The Rietveld analysis performed in the space group P6₃/mcm (Z = 6) indicated the crystal structures were the same as those of the reported h‐WO₃ and that the crystallographic characteristic was as follows: a = 0.74219 nm, c = 0.77198 nm for h‐WO₃ from the 28‐day aged powder, and a = 0.74538 nm, c = 0.77194 nm for h‐WO₃ from the 12‐year aged powder.     

非晶态硼化物Ni-Fe-Co-B的合成及电催化析氧性能

电解水制氢是绿色氢能源研究中的热点课题。其中，析氧半反应较高的过电位是导致电解水动力学缓慢的主要原因。为了提高电解水制氢的效率，本文主要通过简单的液相合成方法，以硼氢化钠和过渡金属Ni，Fe，Co盐为原料，制备了非晶态的过渡金属硼化物Ni-Fe-Co-B，将其作为析氧半反应催化剂。对Ni-Fe-Co-B进行了SEM、TEM、XRD、XPS和电化学表征。结果表明，非晶态催化材料Ni-Fe-Co-B被成功合成，当n(Ni)∶n(Fe)∶n(Co)=1∶1∶1，电流密度为20 mA/cm2时，Ni-Fe-Co-B的过电位仅为299 mV，Tafel斜率为101 mV/dec。在0.47 V的恒电压测试下，Ni-Fe-Co-B具有12h以上的稳定性。     

Silver Nanoparticle Synthesis via Photochemical Reduction with Sodium Citrate

The aim of this paper is to provide a simple and efficient photoassisted approach to synthesize silver nanoparticles, and to elucidate the role of the key factors (synthesis parameters, such as the concentration of TSC, irradiation time, and UV intensity) that play a major role in the photochemical synthesis of silver nanoparticles using TSC, both as a reducing and stabilizing agent. Concomitantly, we aim to provide an easy way to evaluate the particle size based on Mie theory. One of the key advantages of this method is that the synthesis can be “activated” whenever or wherever silver nanoparticles are needed, by premixing the reactants and irradiating the final solution with UV radiation. UV irradiance was determined by using Keitz’s theory. This argument has been verified by premixing the reagents and deposited them in an enclosed space (away from sunlight) at 25 °C, then checking them for three days. Nothing happened, unless the sample was directly irradiated by UV light. Further, obtained materials were monitored for 390 days and characterized using scanning electron microscopy, UV-VIS, and transmission electron microscopy.     

A Novel Ag@AgCl Nanoparticle Synthesized by Arctic Marine Bacterium: Characterization,Activity and Mechanism

An additive- and pollution-free method for the preparation of biogenic silver and silver chloride nanoparticles (Ag@AgCl NPs) was developed from the bacteria Shewanella sp. Arc9-LZ, which was isolated from the deep sea of the Arctic Ocean. The optimal synthesizing conditions were explored, including light, pH, Ag⁺ concentration and time. The nanoparticles were studied by means of ultraviolet-visible (UV-Vis) spectrophotometry, energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometers (ICP-OES). The transmission electron microscope (TEM) showed that the nanoparticles were spherical and well dispersed, with particle sizes less than 20.00 nm. With Ag@AgCl nanoparticles, the kinetic rate constants for congo red (CR) and rhodamine B (RhB) dye degradation were 2.74 × 10⁻¹ min⁻¹ and 7.78 × 10⁻¹ min⁻¹, respectively. The maximum decolourization efficiencies of CR and RhB were 93.36% and 99.52%, respectively. Ag@AgCl nanoparticles also showed high antibacterial activities against the Gram-positive and Gram-negative bacteria. The Fourier transform infrared spectroscopy (FTIR) spectrum indicated that the O-H, N-H and -COO- groups in the supernatant of Arc9-LZ might participate in the reduction, stabilization and capping of nanoparticles. We mapped the schematic diagram on possible mechanisms for synthesizing Ag@AgCl NPs.     

Size-controlled green synthesis of silver nanoparticles assisted by L-cysteine

A green and size-controlled synthesis of silver nanoparticles (Ag NPs) in aqueous solution with the assistance of L-cysteine is presented. The size of Ag NPs decreases with the increase of L-cysteine concentration, and thus can be controlled by adjusting L-cysteine concentration. TEM analysis shows that Ag NPs with an average size of 3 nm can be produced in the presence of 1.0 mmol/L L-cysteine, about one sixth of the size of Ag NPs obtained in the absence of L-cysteine (17 nm). The as-synthesized silver colloidal solution is stable and can be stored at room temperature for at least two months without any precipitation. This L-cysteine assisted method is simple, feasible and efficient, and would facilitate the production and application of Ag NPs.     

单针-板脉冲放电处理染料废水的实验研究

采用单针-板脉冲放电反应器进行了罗丹明B染料废水的脱色研究。考察了脉冲电压、脉冲频率、针板间距和鼓气量等对罗丹明B脱色效率的影响,并对脱色过程中溶液TOC的变化进行了测试,得出当脉冲电压为32.5 kV、脉冲频率为60 Hz、针板间距为15 mm、曝气量为12 L/h时,处理50 min后,罗丹明B脱色效率达99.68%,溶液中TOC由70 mg/L降到19.2 mg/L。在以上实验的基础上,用该反应器进行罗丹明B、亚甲基蓝和甲基橙3种染料混合溶液脱色,脱色效率分别是99.75%,98.64%和97%,表明高压脉冲放电等离子体可无选择的对各种染料废水进行脱色。     

Synthesis of Calcium Hexaboride Powder via the Reaction of Calcium Carbonate with Boron Carbide and Carbon

The synthesis of calcium hexaboride (CaB₆) powder via the reaction of calcium carbonate (CaCO₃) with boron carbide (B₄C) and carbon has been investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products have been studied using X-ray diffractometry, and the morphologies of CaB₆ obtained at various temperatures and holding times have been investigated via scanning electron microscopy. The interaction in the CaCO₃–B₄C–carbon system by which CaB₆ is formed is a solid-phase process that passes through the transition phases Ca₃B₂O₆ and CaB₂C₂. The optimal conditions for CaB₆ synthesis are a holding time of 2.5 h at a temperature of 1673 K, under vacuum (a pressure of 10⁻² Pa). CaB₆ powder has the same morphology as B₄C, and the properties and the shape of CaB₆ powders can be improved by choosing good-quality raw materials.     

Improving the synthesis of single-walled carbon nanotubes by pulsed arc discharge in air by preheating the catalysts

Single-walled carbon nanotubes (SWCNTs) were synthesized in reduced pressure air using pulsed arc discharge after preheating the catalyst. Our experimental results revealed that preheating the catalysts can assist the synthesis of SWCNTs in air under a pressure of 5-10 kPa. The SWCNTs have a diameter of 1.5-2 nm and length can reach several micrometers. The consumption rate of the anode and the production rate of CNTs and SWCNTs in air are lower than in helium atmosphere at the same pressure, respectively. Further experiment demonstrates that 600 °C is optimum temperature for preheating the catalysts to synthesize SWCNTs in air.     

高纯铝酸钙粉体的化学合成

选用Ca(OH) 2 饱和溶液和AlCl3溶液为初始原料 ,按Al3+ 与Ca2 + 的摩尔比为 2 .2配成混合溶液 ,在常温、高pH值下 ,先合成前驱体铝酸钙水化沉淀物 ,再经110 0℃煅烧制成高活性、高纯度的铝酸钙粉体。煅烧后粉体的XRD分析和SEM观察显示 :合成物于 10 0 0℃煅烧有大量铝酸钙矿物形成 ,110 0℃时可获得稳定的铝酸钙矿物 ,它是以CA为主晶相 ,并含有少量CA2的二元混合物 ,其中位径d50 约为 0 .6 6 μm ,比表面积为13m2 ·g- 1。     

Development of Core-Shell Nanoparticle Drug Delivery Systems Based on Biomimetic Mineralization

Among various drug-delivery systems, core-shell nanoparticles have many advantages. Inspired by nature, biomimetic synthesis has emerged as a new strategy for making core-shell nanoparticles in recent years. Biomimetic mineralization is the process by which living organisms produce minerals based on biomolecule templating that leads to the formation of hierarchically structured organic–inorganic materials. In this minireview, we mainly focus on the synthesis of core-shell nanoparticle drug-delivery systems by biomimetic mineralization. We review various biomimetic mineralization methods for fabricating core-shell nanoparticles including silica-based, calcium-based and other nanoparticles, and their applications in drug delivery. We also summarize strategies for drug loading in the biomolecule-mineralized core-shell NPs. Current challenges and future directions are also discussed.