Synthesis of Ni nanoparticles by plasma-induced cathodic discharge electrolysis

Ni nanoparticles were synthesized by plasma-induced cathodic discharge electrolysis in LiCl–KCl–CsCl + NiCl₂ at 573 K under 1 atm of Ar atmosphere. Ni nanoparticles with diameters of around 100 nm were obtained from the melt. It was also confirmed that particles predominantly grow at the surface of the melt, especially the region just under the discharge. Taking into account the above results, a novel type plasma-induced electrolytic cell has been designed and constructed; it operated successfully, a rotating Ni metal disk anode being adopted in order for the formed particles to be quickly removed from the region just under the discharge and be continuously transferred to the inner wall of the cold container. By using this novel type plasma-induced electrolytic cell, Ni nanoparticles with diameters of around 50 nm could be obtained.     

Formation and size control of titanium particles by cathode discharge electrolysis of molten chloride

Cathode discharge electrolysis of LiCl–KCl–K₂TiF₆ has been conducted under 1 atm of Ar. Near spherical particles consisting of metallic or partially oxidized titanium in the core and TiO₂ in the surface layer were obtained. The Ti particles are originally formed in the melt by reduction of Ti ions, and a surface TiO₂ layer is formed when the Ti particles are exposed to air or water. The particle sizes were in the range 10–400 nm, and were strongly dependent on electrolytic conditions, such as quantity of electricity, K₂TiF₆ concentration, bath temperature and current per melt volume. The particle growth mechanism was also investigated, and it was confirmed that reduction of ions at particle surfaces is involved in particle growth.     

Synthesis and characterization of superabsorbent composite by using glow discharge electrolysis plasma

A convenient and effective technique for polymerization to produce the poly(acrylic acid-co-acrylamide)/montmorillonite superabsorbent composite in aqueous solution was developed, in which the reaction was initiated by the glow discharge electrolysis (GDE) plasma rather than chemical initiators. The resulted superabsorbent has higher water absorbency, for example, 1024 g g⁻¹ for distilled water and 56 g g⁻¹ for 0.9% NaCl solution. To optimize the synthesis conditions, the following parameters were examined in detail: the discharge voltage, discharge time, ratio of acrylic acid to acrylamide, neutralization of acrylic acid, amount of crosslinking agent and montmorillonite added. The superabsorbent composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Results indicated that montmorillonite was effectively bonded with polymer. Moreover, the water absorbency, water retention and thermal stability of the superabsorbent composite prepared by GDE were higher than those of the superabsorbent composite by conventional chemical method under the same polymerization conditions.     

Oxidation behavior and catalytic property of intermetallic compound AuCu

Catalytic activity of CO oxidation reaction in relation to oxidation for an ordered AuCu intermetallic compound is studied. Oxidation performed at temperatures above 400 °C on the AuCu intermetallic compound leads to the formation of a composite consisted of Au and CuO, accompanied by a large increase in the surface area and significant enhancement of the activity. The oxidation performed at 600 °C yields a unique composite structure where an Au layer is sandwiched by two porous CuO layers, revealing a maximum in the surface area and the activity. The porous CuO layer is found to be key factor dominating catalytic activity. We show in this study that the oxidation of the intermetallic compound AuCu is a novel and an effective way to prepare metal/oxide composite for catalyst.     

Calciothermic reduction of NiO by molten salt electrolysis of CaO in CaCl2 melt

Metallic nickel powders with low and uniform residual oxygen content were produced from NiO using the molten salt electrolysis of CaO in CaCl₂ melt. Suitable amount of CaO for the reduction was in the range of 0.5–3.0 mol% CaO.The electrical isolation of NiO from both electrodes could produce metallic Ni in CaCl₂ melt. Separating the metal oxides from the cathode confirmed the mechanism of calciothermic reduction that the electrolysis of dissolved CaO in CaCl₂ melt produces Ca, and that the dissolved Ca in molten CaCl₂ successfully reduces NiO to metallic Ni. An average of about 600 ppm oxygen in Ni sample was achieved directly from oxide, when NiO was detached from the cathode.     

Thermodynamic analysis on the direct preparation of metallic vanadium from NaVO3 by molten salt electrolysis☆

A novel and environmentally friendly route to directly prepare metallic vanadium from Na VO_3 by molten salt electrolysis is proposed.The feasibility about the direct electro-reduction of NaVO_3 to metallic vanadium is analyzed based on the thermodynamic calculations and experimental veri fications.The theoretical decomposition voltage of NaVO_3 to metallic vanadium is only 0.47 Vat 800°C and much lower than that of the alkali and alkali earth metal chloride salts.The value is slightly higher than that of low-valence vanadium oxides such as V_2O_3,V_3O_5 and VO.However,the low-valence vanadium oxides can be further electro-reduced to metallic vanadium thermodynamically.The thermodynamic analysis is veri fied by the experimental results.The direct preparation of metallic vanadium from NaVO_3 by molten salt electrolysis is feasible.     

The effect of electrolyte constituents on contact glow discharge electrolysis

Ordinary electrolysis developed spontaneously to contact glow discharge electrolysis (CGDE) at sufficiently high voltage, with glow discharge taking place around a thin platinum anode which was in contact with electrolyte solution. During this transition, the critical voltage (V_D) was an important parameter for the onset of CGDE. The results indicated that V_D decreased with the increasing conductivity and then maintained a certain value. The different dimension and material of cathode had little effect on V_D. When the electrolyte conductivity was 5.0 mS/cm, V_D was hardly affected by electrolyte composition. And the concentrations of H₂O₂ producing in the anolyte were close in different inert electrolyte. However, the concentrations of H₂O₂ in NaCl, NaAc, Na₂CO₃ and NaHCO₃ solution were lower than that in Na₂SO₄ solution. And the concentration of H₂O₂ in the anolyte was also decreased by adding a minute amount of CH₃OH.     

Facile preparation of Bi nanoparticles by novel cathodic dispersion of bulk bismuth electrodes

A novel electrochemical approach has been developed to prepare clean bismuth nanoparticles (NPs) with a bulk Bi electrode in a 0.5 mol dm⁻³ NaOH solution under highly cathodic polarization of −8 V versus a saturated mercurous sulfate electrode, requiring no any precursor ions and organic protective agents. The bulk Bi electrode can be facilely dispersed into Bi NPs at the condition of intensive hydrogen evolution. This cathodic dispersion of the bulk Bi electrode involves the formation and decomposition of unstable bismuth hydrides and the aggregation of atomic bismuth from the decomposition. Moreover, Bi₂O₃ NPs have also been achieved by heating the precursor Bi NPs. Field-emission scanning electron microscopy, transmission electron microscope and X-ray diffraction were used to characterize these NPs. The as-prepared Bi NPs mainly existed in rhombohedral phase.     

Preparation of novel Pt-based nanoparticles by double potential step electrolysis and their electrocatalytic activity for oxygen reduction reaction

We have developed a novel preparation method for Pt-based nanoparticles by means of double potential step electrolysis (DPSE), in which Pt-Ni alloy deposited at the first step and Ni dissolved at the following step. A cycle of the DPSE in a nickel plating bath containing PtCl₆²⁻ led to the formation of the Pt-Ni nanoparticles with size of about 5.4 ± 1.5 nm, which gradually grew up with repeating the DPSE process, and surface Ni content of the particles by XPS was controllable by changing some parameters of the DPSE. The Pt-Ni nanoparticles deposited by the DPSE were covered with a Pt skin layer, which influence the improvement of both catalytic activity for oxygen reduction reaction (ORR) and corrosion resistance. The Pt-Ni nanoparticles by the DPSE exhibit ca. two times higher electrocatalytic activity for ORR than Pt nanoparticles, and further, of which catalytic activity was maintained high even with more than 1000 cycles of potential cycling test in H₂SO₄ solution, showing good corrosion resistance.     

熔盐电解法制备硼粉的研究

对熔盐电解法制备硼粉的方法进行了论述,比较了各熔盐体系的优点和缺点,得出了氯化钾或氯化钾和氟化钾混合物的熔盐体系最适宜。用冷却曲线法对KF-KCl-KBF4体系熔盐体系的初晶温度进行了研究,研究表明:KF-KCl-KBF4体系的初晶温度为1 023—1 033 K,即750—760℃之间,当电解温度高于初晶温度20—30℃时,电解效率最高。这就为熔盐电解法制备元素硼提供了依据。     

电解法制备氢氧化锂的研究进展

简述了氢氧化锂的应用,详细阐述了电解法制备氢氧化锂的不同生产方法、原理,以及原料中各离子对电解的影响及要求。分析了各方法的优缺点,并结合中国锂盐的基本情况和发展现状,总结了目前存在的问题,对前景做了预测。指出了在简化方法、降低成本生产氢氧化锂的同时,兼顾资源综合利用和环境保护是今后研究开发的方向。     

Effect of milling variables on the synthesis of NiAl intermetallic compound by mechanical alloying

NiAl intermetallic compound was synthesized by mechanical alloying of elemental mixtures of Ni and Al powders in a Spex mill. The compound formation took place according to a mechanically induced self-propagating reaction (MSR), and the influence of milling variables on its ignition time was determined using a factorial design. Results indicated ignition time as a function of initial particle size of Ni, process control agent, and ball-to-powder ratio. Also, an interaction between ball-to-powder ratio, process control agent, and a set of balls was found to control the average particle size of as-milled powders.     

电解法制备硼粉过程电流效率的影响因素

电流效率是电解法制备单质硼的一个重要生产指标,它涉及到硼电解槽的产量和电耗。在电解槽型的设计过程中,如何提高熔盐电解的电流效率对于硼粉的单位时间产量、降低单位电耗等主要技术经济指标具有重要的意义。文中采用氟化钾-氯化钾-氟硼酸钾体系,进行了实验研究。在电解槽内测定了制备过程中电流效率随电解温度、电流密度、电极间距离、电解时间的变化关系。结果表明:当电解温度为760—790℃、电流密度在0.8—1.14 A/cm2、电解时间为2.5—3 h、极间距离为4 cm时,电解的电流效率最高。     

熔盐电解NiO制备Ni的机理探讨

通过固态NiO在CaCl_2-NaCl熔盐中直接电化学还原制备Ni的电解产物随时间变化分析,石墨阳极破损研究以及对NiO低于理论分解电压的槽电压分解现象的解释,探讨了熔盐电解NiO制备Ni的电解反应机理。认为电解反应基本服从氧离子化机理,且NiO阴极片在低于理论分解电压的槽电压下,电化学还原反应和热还原反应同时发生。     

LiF对Na3AlF6-Al2O3熔盐电解阴极过程的影响

电解铝工业中铝在阴极上析出,铝析出反应的机理对电解铝生产具有理论指导意义。在运用循环伏安法研究的基础上,通过理论计算,对Na₃AlF₆-Al₂O₃和Na₃AlF₆-Al₂O₃-LiF体系中金属铝在钨电极上的电化学沉积行为以及铝钨金属间化合物的形成机理进行了研究。结果表明：两体系中铝钨金属间化合物在50 mV·s^-1≤ν≤150 mV·s^-1扫描速率下的形成过程是受扩散控制的准可逆过程。在化合物形成的过程中,两体系中Al³⁺的扩散系数从4.54×10^-9 cm²·s^-1增长到5.71×10^-9 cm²·s^-1,Al³⁺反应的活化能分别为11.14 kJ·mol^-1和10.47 kJ·mol^-1。在Na₃AlF₆-Al₂O₃-LiF体系的还原过程中,Li并没有还原析出,而在氧化过程中Al在金属间化合物中的氧化电流增大;在恒电流电解时,Al-W金属间化合物并不溶于熔盐中,会附着在工作电极表面,LiF的加入会使电极表面的WAl₄量变小,取而代之的是Al₂O₃的增加,说明LiF的加入使电解更加稳定,抑制了电极表面WAl₄的生长。     

Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles

The TiO₂ nanofibers and nanoparticles are prepared by electrospinning and molten salt method, respectively. The materials are characterized by X-ray diffraction scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and a thermal analysis. The SEM and TEM studies showed that fibers were of average diameter ∼100 nm and composed of nanocrystallites of size 10-20 nm. Electrochemical properties of the materials are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Cyclic voltammetric studies show a hysteresis (ΔV) between the cathodic and the anodic peak potentials for TiO₂ nanofibers and nanoparticles (sizes ∼15-30 nm) are in the range, 0.23-0.30 V and a redox couple Ti^4+/3+ around ∼1.74/2.0 V. Electrochemical cycling results revealed that the TiO₂ nanofibers have lower capacity fading compared to that of the nanoparticles. The capacity fading for 2-50 cycles was ∼23% for nanofibers, which was nearly one-third of that of corresponding nanoparticles (∼63%). We discussed the effect of particle size on hysteresis and cycling performance of TiO₂ nanoparticles. Impedance analysis of TiO₂ nanofibers and nanoparticles during first discharge cycle is analyzed and interpreted.     

Effect of nanoparticles on heat capacity of nanofluids based on molten salts as PCM for thermal energy storage

In this study, different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (selected as phase change material) with nanoparticles using the direct-synthesis method. The thermal properties of the nanofluids obtained were investigated. These nanofluids can be used in concentrating solar plants with a reduction of storage material if an improvement in the specific heat is achieved. The base salt mixture was a NaNO₃-KNO₃ (60:40 ratio) binary salt. The nanoparticles used were silica (SiO₂), alumina (Al₂O₃), titania (TiO₂), and a mix of silica-alumina (SiO₂-Al₂O₃). Three weight fractions were evaluated: 0.5, 1.0, and 1.5 wt.%. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements on thermophysical properties were performed by differential scanning calorimetry analysis and the dispersion of the nanoparticles was analyzed by scanning electron microscopy (SEM). The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of 15% to 57% in the solid phase and of 1% to 22% in the liquid phase. In particular, this research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO₃-KNO₃ binary salt. These results deviated from the predictions of the theoretical model used. SEM suggests a greater interaction between these nanoparticles and the salt.     

TiO2-HNTs催化剂协同介质阻挡放电等离子体降解亚甲基蓝废水

为进一步提高介质阻挡放电等离子体（DBD）降解亚甲基蓝（MB）的效率,研究了采用介质阻挡放电等离子体和光催化剂协同技术。实验采用溶胶-凝胶法制备TiO₂-HNTs复合光催化材料,并利用XRD、FTIR、TGA方法对催化剂进行表征分析。考察了该材料的光催化性能,以及它与介质阻挡放电的联合降解过程中操作因素的影响,并对反应进行动力学研究。研究结果表明,TiO₂-HNTs复合光催化材料与介质阻挡放电产生协同作用,并能有效地提高MB的去除率,处理60min后,协同体系对MB的降解率为85.37%,MB的降解过程符合表观一级反应动力学方程。MB的去除率与MB的初始浓度,TiO₂-HNTs的投加量、煅烧温度、放电功率和通气量有关。当MB的初始浓度为100mg/L、TiO₂-HNTs的投加量为70mg/L、煅烧温度为300℃、放电功率为200W、通气量为200mL/min时,MB的去除效果较好。