Large-scale synthesis of silver nanowires via a solvothermal method

Silver nanostructures have been synthesized through a simple solvothermal method by reducing silver nitrate (AgNO₃) with ethylene glycol (EG) and using poly(vinylpyrrolidone) (PVP) as an adsorption agent. Different concentrations of ferric chloride (FeCl₃) are added into the solution. It is found that AgCl colloids formed in the initial stage greatly influence the final morphologies of the products. When a low-concentration FeCl₃ solution is used, there is a mixture of silver nanoparticles and nanowires. However, when a high-concentration FeCl₃ solution (100 μM) is used, large amounts of AgCl colloids appear, resulting in decreasing free Ag⁺ during initial formation of silver seeds and slowly releasing of Ag⁺ to the solution in the subsequent reaction. This leads to the formation of silver nanowires. Furthermore, an increase in the concentration of FeCl₃ from 100 to 300 μM results in the synthesis of silver nanowires with larger sizes. In addition, Fe(III) is reduced to Fe(II) form which in turn reacts with and removes adsorbed atomic oxygen from the surface of silver seeds. In this case, uniform silver nanowires can be obtained.     

Large-scale synthesis of defect-free silver nanowires by electrodeless deposition

We report a new method that generates high-density, long aspect ratio and large-area silver nanowire arrays within the pores of anodic aluminum oxide (AAO) membrane by reducing silver nitrate with ethylene glycol. The freestanding and defect-free silver nanowires can be obtained at high yields. In a typical procedure, the as-prepared silver nanowires have a mean diameter of ∼ 53 nm. It is found out that both temperature and reaction time are important factors in determining the morphology and aspect ratios of nanowires. Lower temperature and longer time are favorable to form polycrystalline silver nanowires with high uniformity and aspect ratios.     

Preparation of fluoride-substituted hydroxyapatite by a molten salt synthesis route

Fluoride-substituted hydroxyapatite (FHAp) with high thermal and morphologic stability was successfully prepared by a molten salt synthesis route. XRD patterns and FTIR spectra identified the synthesized powders as FHAp solid solution. The FHAp obtained with potassium sulfate as the flux showed the rod-like morphology without detectable decomposition up to 1300°C and the flux, sodium sulfate, led to the spheriodal FHAp. After investigating the effects of salt species on the FHAp morphologies, it was found that solubility was not the exclusive factor, which affected the morphological development of apatite powders, and the cations of molten salt species also played an important role.     

两步熔盐法合成片状SrTiO3

以SrCO3和TiO2为原料,采用两步熔盐法合成出片状SrTiO3.首先在助熔剂NaCl中,1300℃保温6h合成出片状中间体;然后以片状中间体为模板晶粒,在助熔剂KCl中,1200℃保温4h制备出片状SrTiO3.所得产物过筛后,采用X射线衍射(XRD)和扫描电镜(SEM)分析粉体的相组成和显微结构,结果表明:中间体是由各向异性的Sr3Ti2O7、Sr4 Ti3O10、Sr2TiO4和各向同性的SrTiO3晶粒组成,而且各向异性晶粒的(001)和(200)峰均增强,片状晶粒为长方形,边长为40～60μm.SrTiO3粉体的相组成为纯钙钛矿相,其它杂相组分未曾检出,而且＞5μm粉体的(200)峰增强,说明该粉体为片状晶粒,呈正方或长方形,边长约为50μm.     

Grain orientation studies in YBCO superconductors by molten salt synthesis

The molten salt or the flux method is utilized in this study to fabricate a grainoriented YBa₂Cu₃O_7−x superconductor. The formation of YBa₂Cu₃O_7−x in the presence of molten salts of Na, K, Li belonging to chloride and iodide systems does not appear feasible due to the instability of the superconducting phase in these salt systems. Studies using the “green phase,” Y₂BaCuO₅, as seed crystals suggest a two-stage approach in the formation of YBa₂Cu₃O_7−x . The process uses Y₂BaCuO₅ formed by molten salt synthesis which has been observed to be stable in water and against most of the salts. The 211 crystals can be mixed with oxides and converted to 123. Analysis of X-ray data and SEM micrographs indicates a certain degree of grain orientation, which can be further enhanced by tape-casting or not-forging.     

Large-scale synthesis and characterization of hexagonal prism-shaped SiC nanowires

Abundant hexagonal prism-shaped SiC nanowires were synthesized on graphite substrate via heating silicon in a graphite crucible. The products were characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The characterization first showed that the product was nanowires of beta-SiC with almost a perfect hexagonal cross section. The growth was determined along [111] direction. The six side surfaces look smooth under low magnification microscopy, but faceted at high magnification. Based on the characterization results, a formation mechanism combining vapor-solid (VS) growth mechanism and the lowest surface energy principle is proposed.     

Synthesis of ZnWO4 nano-particles by a molten salt method

ZnWO₄ nano-particles were successfully synthesized by a molten salt method at 300 °C. The as-prepared powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL), respectively. The size and morphology of ZnWO₄ nano-particles were affected by such conditions as the calcining time and the weight ratio of the salt to the ZnWO₄ precursor. The resultant sample is a pure phase of ZnWO₄ without any impurities. The PL spectra results showed that the optical property of ZnWO₄ crystallites obviously relied on their particle sizes.     

Low temperature atmospheric synthesis of WAlB and Mn2AlB2 MAB phases by modified molten salt shielded synthesis method

Nowadays, transition metal-based boride-like layered MAB phases are getting more attention due to their excellent combination of metal-ceramic properties, like good thermal and electrical conductivity, oxidation and thermal shock resistance, excellent wear resistance etc. So far, WAlB was synthesized at high temperature (1550 °C) with 24 hr soaking time by aluminium flux technique with nominal single-phase purity, which requires huge investment and production costs. However, Mn₂AlB₂ was recently synthesized using KBr salt via molten salt shielded synthesis (MS³) at a relatively low temperature 1000 °C for a longer soaking time (12 hr) which may enhance the chances of oxidation. Therefore, the motivation of this work is to synthesize WAlB and Mn₂AlB₂ MAB phase at lower temperatures with high purity via a newly developed simple, cost-effective, environmental-friendly method named modified molten salt shielded synthesis method. This paper synthesized both these phases with high yield at lower temperatures and much shorter soaking time than earlier reported literature.     

Bi2SiO5 nanosheets prepared by molten salt method

Bi₂SiO₅ nanosheets were successfully synthesized by the molten salt method in NaCl–Na₂SO₄ flux using Bi₂O₃ and SiO₂ as raw materials. XRD analysis and SEM observation show that the incorporation of salt medium can greatly lower the formation temperature of Bi₂SiO₅ phase, and promote their crystallization. The results also demonstrate that the mass ratio of salts to reactants, the reaction time, and the calcination temperature have significant effects on the phase formation and morphology of the Bi₂SiO₅ powders. The UV–vis spectra result shows that the absorption of the Bi₂SiO₅ powders located at 380 nm, and the corresponding band gap energy (Eg) calculated is 3.26 eV.     

微波熔盐法合成片状晶体SrTiO3

采用在熔盐法中引入微波场的人工晶体生长新技术，在低温下成功地合成出了片状晶体SrTiO3。首先在助熔剂NaCl-KCl中合成片状前驱体Sr3Ti2O7，然后在片状晶体Sr3Ti2O7上外延生长制备出片状晶体SrTiO3，采用XRD和SEM分析产物的结构。结果表明，利用微波熔盐法在750℃保温3h得到了尺寸为10μm的片状Sr3Ti2O7，将前驱体Sr3Ti2O7和TiO2在微波场中于700℃保温2h得到了10～20μm的片状晶体SrTiO3。和常规熔盐法相比，微波熔盐法降低了SrTiO3的合成温度，节省了晶化时间，大幅度地降低了能耗。     

熔盐法制备铌镁酸铅基Y5V电子瓷料的研究

采用NaCl-KCl熔盐法成功地制备了纯钙钛矿相的铌镁酸铅基Y5V电子瓷料,系统地研究了其制备工艺、煅烧温度以及陶瓷的烧结温度、微观结构和介电性能.结果表明熔盐法制备的Y5V电子瓷料粉体不仅颗粒均匀、形貌好、易分散,而且活性高,使得多层陶瓷电容器的烧结温度可以降低到900～920℃,其介电性能要优于传统的二步合成法制备的粉体,十分有利于采用全银内浆,大大降低MLCC的生产成本.     

Large-scale synthesis of single crystal silver nanowires by a sodium diphenylamine sulfonate reduction process

Silver nanowires with high aspect ratios of up to more than 60 were synthesized on a large scale by the redox reaction between silver nitrate and sodium diphenylamine sulfonate at room temperature and in the absence of surfactant and hard-template and seed. When the molar ratio of reductant sodium diphenylamine sulfonate and silver nitrate < or =1, most products were all the nanowires. When the molar ratio increases to 2:1, silver nanowires and nanobelts were concomitantly formed. The redox product N, N'-diphenylbenzidinedisulfonate and sodium diphenylamine sulfonate all play an important role in the formation of silver nanostructures. The structure, morphology, and composition of the silver nanowires were characterized by the X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray energy dispersive microanalysis (EDX), and UV-Vis spectroscopy respectively. High-resolution transmission microscopy (HRTEM) and selected area electron diffraction (SAED) reveal the single-crystal nature of the silver nanowires.     

The synthesis of high purity Ti3AlC2 MAX phase via molten salt method

Many methods have been used to synthesize the Ti₃AlC₂ MAX phase, but obtaining high-purity (>99.0 %) Ti₃AlC₂ is still a challenge. In this work, nano/submicro-sized Ti₃AlC₂ powder was prepared using Ti/Al/C elemental powders by the molten salt method in a vacuum quartz tube system. The effects of reaction temperature and dwell time, mechanical activation, the ratio of flux to reactants, and the ratio of Al on the synthesis of Ti₃AlC₂ were systematically investigated. The results show that Ti₃AlC₂ powder with a high purity of up to 99.0 % was prepared using ball milled 3Ti/1.1Al/2C mixture as the reaction material, and NaCl-KCl as the molten salt at 1150 °C for 2 h. The reaction mechanisms of Ti₃AlC₂ in molten salt have been discussed.     

熔盐法合成金属氯化物-石墨插层化合物的判据

研究了熔融盐状态下金属氯化物-石墨层间化合物的合成判据.根据插层反应热动力学及化学键理论,选取元素的电负性和离子势作为键参数,并设计键参数函数λ为客体材料的遴选判据.基于键参数函数图对金属氯化物发生插层反应的难易程度和产物稳定性进行理论预估.研究结果表明:键参数函数图中λ≤1.2区域内的金属氯化物在700℃以下即可发生插层反应,且所得产物较为稳定;在1.2≤λ≤1.8区域内相应的客体材料在低温下很难单独插入石墨层间,常与低熔点氯化物形成共熔体后一起插入石墨层间;在λ≥1.8区域内大多为碱金属氯化物和碱土金属氯化物,理论分析认为这类物质的插层反应不适宜采用熔盐法.     

Large-scale synthesis of single-crystal alpha manganese sesquioxide nanowires via solid-state reaction

Smooth single-crystal α-Mn₂O₃ nanowires have been fabricated using a one-step solid-state reaction method. X-ray diffraction patterns show that the nanowires have pure phase of α-Mn₂O₃. Transmission electron microscopy was employed to investigate the size and morphology of the products. The α-Mn₂O₃ nanowires exhibit mean diameter of 50 nm and length of 10 μm. Selected-area electron diffraction pattern demonstrates the single-crystal structure of the α-Mn₂O₃ nanowires, which are in good agreement with the X-ray diffraction results. The processes of the reactions and the phase transitions were also studied by using a simultaneous thermal gravimetric/differential thermal analyzer. It is found that the concentration of the precursor MnCO₃ is a crucial factor in the formation of the nanowires. This work provides the probability of the industrialization of fabricating smooth single-crystal α-Mn₂O₃ nanowires.     

Piezoelectric and dielectric properties of PZT–PZN–PMS ceramics prepared by molten salt synthesis method

Piezoelectric powders and ceramics with the composition of Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Mn_1/3Sb_2/3)O₃ (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: _r = 1773; tan δ = 0.0040; T_c = 280 °C; d₃₃ = 455 pC/N; k_p = 0.70; Q_m = 888; E_c = 10.3 kV/cm; and P_r = 28.2 μC/cm², at calcination of 800 °C and sintering of 1120 °C temperature.     

Large-scale synthesis of ultralong copper nanowires via a facile ethylenediamine-mediated process

Ultralong copper nanowires (NWs) with an average diameter of 70 nm and length up to 30 μm were synthesized at 70 °C via a facile solution-method. These NWs possess a unique tapered shape on the top end. Ethylenediamine was used as capping agent and was found to be important for controlling the aspect ratio of one-dimensional Cu nanostructures. XRD and EDX analysis indicated that the Cu NWs were free of any contamination, and HRTEM revealed such NWs had preferred [110] growth direction. The current synthetic strategy is low-cost, simple handle, large production, and may provide a promising method for growing Cu nanostructures with controlled shapes or using as solid precursors to synthesize other heterostructures.     

Morphology-controlled synthesis of CdWO4 nanorods and nanoparticles via a molten salt method

Cadmium tungstate (CdWO₄) nanoparticles and nanorods have been successfully synthesized by a molten salt method at 270 °C, and the morphology of the nanocrystals can be controlled by adjusting such reaction conditions as the calcined time and the weight ratio of the salt to the CdWO₄ precursor. The resultant sample is a pure phase of CdWO₄ without any other impurities.     

Preparation of β-FeSi2 substrates by molten salt method

Large-sized β-FeSi₂ substrates were successfully prepared for the first time from the silicide bulk crystal grown by the molten salt method. The structural, electrical and optical properties of the as-grown β-FeSi₂ bulk crystals were also investigated. The crystal is single phase β-FeSi₂, and polycrystalline with no preferable growth crystallographic orientations. It was also determined that the β-FeSi₂ shows a p-type conduction, and the hole concentration and the Hall mobility at room temperature were about 10¹⁷ cm^− 3 and 10 cm²/Vs, respectively. In addition, the PL emission around 0.8 eV was realized from the β-FeSi₂ bulk crystal. This simple vacuum-free growth technique of β-FeSi₂ and the large-sized substrate preparation procedure encourage us to develop future silicide-based electronics.