Preparation and characterization of hydroxyl (–OH) functionalized multi-walled carbon nanotube (MWCNT)–Dowtherm A nanofluids

In the present work, the thermal conductivity and viscosity of hydroxyl (–OH) functionalized multi-walled carbon nanotubes (MWCNTs)–Dowtherm A (eutectic mixture of biphenyl (C₁₂H₁₀) and diphenyl oxide (C₁₂H₁₀O)) nanofluids are discussed. As-received hydroxyl (–OH) functionalized MWCNTs are characterized using x-ray diffraction (XRD), FT-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and thermogravimetry, differential thermogravimetry, and differential scanning calorimetry (TGA-DTG/DSC) analysis. Hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids are prepared in different concentrations (0.001–0.005?g) of MWCNT and characterized at various temperatures (303–323?K). The thermal conductivity of hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids increases with the concentration of carbon nanotubes as well as with temperature. The possible mechanism for the enhancement observed may be ascribed to the percolation of heat through the nanotubes to form a tri-dimensional network. Also, as the temperature increases, the viscosity of the nanofluid decreases, which results in an increase in Brownian motion of nanoparticles, this sets convection-like effects resulting in enhanced thermal conductivity.     

Phase Formation in the Systems α(δ)-FeOOH–M(OH)2–H2O (M = Mn, Co, Zn)

The sequence of chemical transformations induced in the systems ()-FeOOH–M(OH)₂–H₂O (M = Mn, Co, Zn) by heat treatment in the range 125–200°C is studied. The results demonstrate that the kinetics of M(II) ferrite formation, the chemical and phase compositions of the product, and its particle size distribution depend on the heat-treatment temperature, the pH of the suspension (or NaOH concentration), the FeOOH polymorph used as a starting reagent, and the starting-mixture composition.     

Mg(OH)_2、Al(OH)_3的阻燃机理与性能研究

氢氧化铝和氢氧化镁是两种常用的无机阻燃材料。本文通过对氢氧化铝和氢氧化镁的热分析,研究了这两种材料的阻燃特性及机理,为阻燃材料进一步改良提供了一定的理论依据。     

δ-FeO (OH) and its solutions

Decomposition products of -FeO(OH)-type Fe_1–x M _x O_1–x (OH)_1+x phases (M=Mg, Zn, Ca, Cd) have been studied by X-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. It has been shown that the M=Mg and Cd -phases decompose to -Fe₂O₃-based solid solutions which in turn undergo exsolution to form some MgO and CdO at a higher temperature. In the case of Fe_1–x Zn _x O_1–x (OH)_1+x , the decomposition proceeds over -Fe₂O₃ ss to an unstable spinel solid solution. All decomposition products are topotactically related to their precursors in the decomposition chain. In the electron microscope some -type phases undergo in situ decomposition under intense beam bombardment with somewhat different results than obtained for thermal decomposition products under ambient conditions. The plate-like morphology and crystal size is retained in the decomposition products; however, the products have a more pitted appearance after decomposition.     

Co(OH)2 nanosheet-decorated graphene–CNT composite for supercapacitors of high energy density

A composite of graphene and carbon nanotubes has been synthesized and characterized for application as supercapacitor electrodes. By coating the nanostructured active material of Co(OH)₂ onto one electrode, the asymmetric supercapacitor has exhibited a high specific capacitance of 310 F g⁻¹, energy density of 172 Wh kg⁻¹ and maximum power density of 198 kW kg⁻¹ in ionic liquid electrolyte EMI-TFSI.     

Dissolution Behavior of Undoped and Sn-Doped InAs in HNO3–HBr–CH3CH(OH)COOH

The dissolution of undoped and Sn-doped InAs in HNO₃–HBr–lactic acid solutions is studied. The results demonstrate that doping with Sn markedly reduces the dissolution rate of indium arsenide. Bromine-releasing solutions of the system studied can be used for various treatments of InAs and InAsSn.     

Mg(OH)2-Al(OH)3-微胶囊红磷/高抗冲聚苯乙烯无卤阻燃复合材料

以氢氧化镁(MH)、氢氧化铝(ATH)和微胶囊红磷(MRP)为无卤阻燃剂,高抗冲聚苯乙烯(HIPS)树脂为聚合物基体,通过熔融共混法制备了一系列不同组成的MH-ATH-MRP/HIPS复合材料.采用水平燃烧、垂直燃烧、氧指数、锥形量热分析、高温热分解实验等方法研究了复合材料的阻燃性能.结果表明,阻燃剂用量相同时,在HIPS基体中同时引入MH和ATH得到的复合材料比单独加入MH或ATH得到的复合材料具有更好的阻燃性能.当MH-ATH/HIPS的质量比为70∶30∶100时,复合材料的水平燃烧级别达到FH-1级,氧指数为25.2％,但垂直燃烧无级别.在上述体系中加入极少量的MRP(占复合材料的质量分数为2.9％)就可使复合材料的火灾性能指数(FPI)提高85％,燃烧过程中热量释放和质量损失更慢、成炭能力明显增强,垂直燃烧级别达到FV-0级.当MH-ATH-MRP/HIPS的质量比为21∶9∶12∶100时,复合材料的各项阻燃性能达到最佳,可以大幅度减少阻燃剂的用量.MH、ATH和MRP对HIPS具有非常显著的协同阻燃作用.同时加入MH和ATH时不仅可以在更宽的温度范围内抑制HIPS的升温和分解,而且能够在更宽的温度范围内相继释放出水蒸气稀释氧气和可燃气体的浓度,从而起到协同阻燃作用.加入MRP后复合材料的成炭能力大大增强,进一步改善了凝聚相阻燃的效果,因此阻燃性能显著提高.     

Facile synthesis of MnO2@C@Ni(OH)2 core–shell nanowires for high-performance supercapacitor

Journal of Materials Science: Materials in Electronics - One-dimensional MnO2@C@Ni(OH)2 core–shell nanowires were successfully synthesized by simple hydrothermal and chemical bath method. The...     

δ-FeO(OH) and its solid solutions

A transmission electron microscope imaging investigation was performed on small -FeO(OH) crystallites less than 50 Å thick and several hundred angstroms across. We have observed faceting, and a hexagonal plate-like morphology with topological features near atomic step heights. Because of the mutual magnetic attraction on these particles, they tend to align with their thin direction (c-axis) either parallel or perpendicular to the support film surface. It is therefore possible to view dislocations or buckling of lattice planes of these plates either edge-on or perpendicular to this direction by direct lattice imaging in both the bright-field and dark-field modes. A highly distorted lattice is apparent when viewing the particles edge-on, and it is possible to show lattice projections to a resolution of 2.1 Å.     

δ-FeO(OH) and its solid solutions

-FeO(OH)-type solid solutions have been synthesized with compositions Fe_1–x M _x O_1–x (OH)_1+x ranging up tox=0.10 for M=Ca,x=0.35 for M=Mg or Cd andx=0.40 for M=Zn. The phases are characterized by X-ray diffraction and transmission electron microscope studies. A structural model giving satisfactory intensity agreement is postulated for Fe_1–x Zn _x O_1–x (OH)_1+x . In this model, Zn²⁺ ions are situated in the 0 0 0 octahedral sites of space group D _3d ³ -P¯3ml while the Fe³⁺ ions are almost equally distributed among both octahedral sites (0 0 0 and 0 0 1/2).     

Self-growth of micro- and nano-structured Mg(OH)2 on electrochemically anodised Mg–Li alloy surface

Formation of Mg(OH)₂ nanowires and their assemblies with sphere-shaped, echinus-shaped and nest-like micro-structures on a Mg-Li alloy surface was successfully demonstrated. Mg(OH)₂ nanowires were formed on the alloy surface via a self-growth process, after the alloy was electrooxidised in NaCl solution and the oxidation products were removed. The nanowires were characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Infrared spectroscopy. The nanowires have hexagonal rod-like or brush-like morphology and are poorly crystallised. Pre-anodisation and the presence of Li in the alloy are key factors for the nanowire growth, which likely proceeds via a dissolution–precipitation mechanism. The roles of Li can be attributed to the prohibition of the formation of passivation film on the alloy surface and the acceleration of the formation of OH^? anions through hydrogen-evolution reaction.     

Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

浸渍α-Ni(OH)2稳定性的研究

通过X射线衍射 (XRD)分析证实含B添加剂的镍电极活性物质晶型结构为α型 ,差热 热重 (DTA TG)分析则表明α Ni(OH) 2 层间有结构水或化学吸附水存在。探讨了添加剂B分别与Na2 S、Ca(NO3) 2 共沉积的镍电极性能。通过XRD及 50多次大电流充放电循环表明 ,该电极仍具有α型结构 ,且大电流放电容量的衰减受到一定程度抑制。     

Ni(OH)2晶型构造控制研究

采用氨络合沉淀法制备了Ｎｉ（ＯＨ）２微粒。基于Ｎｉ（ＯＨ）２的结构特征，考察了阴离子、氨浓度、反应陈化时间对Ｎｉ（ＯＨ）２的结构控制规律，并用负离子配位多面体生长基元理论对此进行解释，认为通过改变反应休 理论化学条件来改变有关生长长基元及其维度、连接方式是控制粉体结构的有效途径。     

纳米Ni(OH)2的控制结晶法制备

纳米Ni(OH)₂可以有效地提升镍氢电池的性能. 本文以NiSO₄和NaOH为原料, 聚乙二醇为分散剂, 采用控制结晶法制备了纳米Ni(OH)₂的胶体溶液, 控制结晶的pH值和温度分别为11.0 和45℃. 然后用正丁醇进行共沸蒸馏处理. 制备了分散性良好的纳米Ni(OH)₂粉体, 粉体颗粒粒径20nm左右, 团聚体系数为1.07. 并用TEM和XRD对粉体进行了表征. 所制备的样品在 1C倍率放电时电容量达到258mAh·g^-1.     

Interfacial microstructure and hardness of nickel (Ni) nanoparticle-doped tin–silver–copper (Sn–Ag–Cu) solders on immersion silver (Ag)-plated copper (Cu) substrates

Sn–Ag–Cu composite solder has been prepared by adding Ni nanoparticles. Interfacial reactions, the morphology of the intermetallic compounds (IMC) that were formed, the hardness between the solder joints and the plain Cu/immersion Ag-plated Cu pads depending on the number of the reflow cycles and the aging time have all been investigated. A scallop-shaped Cu₆Sn₅ IMC layer that adhered to the substrate surface was formed at the interfaces of the plain Sn–Ag–Cu solder joints during the early reflow cycles. A very thin Cu₃Sn IMC layer was found between the Cu₆Sn₅ IMC layer and the substrates after a lengthy reflow cycle and solid-state aging process. However, after adding Ni nanoparticles, a scallop-shaped (Cu, Ni)–Sn IMC layer was clearly observed at both of the substrate surfaces, without any Cu₃Sn IMC layer formation. Needle-shaped Ag₃Sn and sphere-shaped Cu₆Sn₅ IMC particles were clearly observed in the β-Sn matrix in the solder-ball region of the plain Sn–Ag–Cu solder joints. Additional fine (Cu, Ni)-Sn IMC particles were found to be homogeneously distributed in the β-Sn matrix of the solder joints containing the Ni nanoparticles. The Sn–Ag–Cu–0.5Ni composite solder joints consistently displayed higher hardness values than the plain Sn–Ag–Cu solder joints for any specific number of reflow cycles–on both substrates–due to their well-controlled, fine network-type microstructures and the homogeneous distribution of fine (Cu, Ni)–Sn IMC particles, which acted as second-phase strengthening mechanisms. The hardness values of Sn–Ag–Cu and Sn–Ag–Cu–0.5Ni on the Cu substrates after one reflow cycle were about 15.1 and 16.6 Hv, respectively–and about 12.2 and 14.4 Hv after sixteen reflow cycles, respectively. However, the hardness values of the plain Sn–Ag–Cu solder joint and solder joint containing 0.5 wt% Ni nanoparticles after one reflow cycle on the immersion Ag plated Cu substrates were about 17.7 and 18.7 Hv, respectively, and about 13.2 and 15.3 Hv after sixteen reflow cycles, respectively.     

Effects of single electrodes of Ni(OH)2 and activated carbon on electrochemical performance of Ni(OH)2–activated carbon asymmetric supercapacitor

Nickel hydroxide consisting of loosely packed nanospheres was synthesized as positive electrode material for an asymmetric capacitor based on Ni(OH)₂ and activated carbon (AC). Two series of supercapacitors were fabricated to investigate the effects of the single electrodes of Ni(OH)₂ and AC on the electrochemical performance of asymmetric Ni(OH)₂–AC capacitor. Parameters including cell voltage window, specific capacitance and cyclic stability were assessed. In one series of supercapacitors, mass of Ni(OH)₂ was excessive while mass of AC was varied, the AC electrode thus constrained both the capacitance and the upper limit of cell voltage. Deficiency of AC resulted in lower specific capacitance and narrower cell voltage window but benefited to cyclic stability. In the other series of supercapacitors, the mass of AC was excessive whereas the mass of Ni(OH)₂ was changeable in each cell, Ni(OH)₂ electrode thus dominated both the capacitance and the lower limit of cell voltage. As a consequence, deficiency of Ni(OH)₂ led to higher specific capacity and wider cell voltage window as well as lower cyclic stability. These results can contribute to improving understanding of and optimizing performance of asymmetric Ni(OH)₂–AC capacitor.     

α-Ni(OH)2/SiO2核壳以及α-Ni(OH)2空心微球的制备及表征

采用以正硅酸乙酯(TEOS)水解为基础的硅溶胶种子生长法制备了粒径约为270nm的近单分散二氧化硅球型颗粒.采用一种新的溶液生长法,以氢氟酸作为溶液中镍离子配位剂,加入氨水调节溶液pH值的同时作为镍离子补充配位剂,60℃水浴条件下在已制得SiO2微球表面均匀包覆α-Ni(OH)₂得到Ni(OH)₂/SiO₂核壳结构,Ni(OH)₂壳层厚度约为35nm.结合多步包覆法提高Ni(OH)₂壳层厚度,三次包覆后壳层厚度达到约100nm,四次包覆后约为140nm.采用20wt％的强碱NaOH溶液对三次包覆后的Ni(OH)₂/SiO₂核壳结构进行处理,得到了壳层厚度约为95nm的α-Ni(OH)₂空心微球.空心微球具有较大的比表面积为141.06m²/g.