Low-temperature hydrothermal reduction of metal hydroxides to metal powders

Hydroxides of copper, cobalt, nickel, bismuth, silver, palladium and osmium could be reduced to the metal powder below 250°C under hydrothermal conditions in formic acid medium. Particles in the resulting metal powder have single crystal morphology. Such powders show faster shrinkage kinetics. Powders of zirconia dispersed cobalt and nickel could be directly obtained by this method.     

镀钴泡沫镍基板界面机理研究

研究了泡沫镍镀钴镍电极的初期化成行为,发现在电池端电压0.2V附近出现一个充电电压平台,1.0V附近出现第二个充电电压平台,而纯泡沫镍做基板的镍电极无此现象.循环伏安和XRD测试验证了两个电压平台对应的反应是Co氧化为Co(OH)2和Co(OH)2氧化为CoOOH反应.EPMA线扫描显示,镍电极化成后基板表面钴元素呈梯度分布.结果表明,泡沫镍表面的金属钴通过电化学溶解沉淀机理,在基板附近生成梯度分布的CoOOH.     

喷雾干燥YPSZ纳米结构热喷涂粉末材料制备及表征

YPSZ纳米结构粉末材料的研究是热喷涂制备YPSZ纳米结构涂层必须首先进行研究的问题。本文采用喷雾干燥方法制备适合于热等离子体喷涂的YPSZ纳米结构粉末原料,同时采用等离子体喷涂制备涂层。利用扫描电子显微镜分析晶粒大小、颗粒形貌,X射线衍射分析相组成,对喷雾干燥后粉末进行热重-差热分析,测定粉末的松装密度、振实密度及流动性。结果表明制备的YPSZ粉末材料具有实心、流动性好、松装密度高、振实密度高、球形度高、单斜相少等优点,采用热等离子体喷涂沉积制备YPSZ纳米结构涂层。     

纳米镍/炭复合材料的制备与磁性表征

以废弱酸型聚丙烯酸系阳离子交换树脂为炭前驱体,经过与镍离子交换后,再经热解制备纳米镍粒子均匀分散于炭基体的纳米镍/炭(Ni/C)复合材料.以XRD、TEM为主要分析手段研究了热解条件对纳米镍粒子在Ni/C复合材料中的形貌、大小的影响.结果表明:通过热解条件可以控制Ni/C复合材料中纳米镍粒子的平均粒径;热解温度的升高和热解保温时间的增加都可使Ni/C中纳米镍粒径增大.磁性能测试结果表明: Ni/C-500表现为超顺磁特性,而Ni/C-600、Ni/C-700为铁磁性;Ni/C-600、Ni/C-700的比剩磁化强度、矫顽力都要大于微米镍粉与块体镍,但其比饱和磁化强度要小于微米镍粉和块体镍.     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

Preparing of nanostructured Al2O3–TiO2–ZrO2 composite powders and plasma spraying nanostructured composite coating

Nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders for plasma spraying were prepared by spray drying granulation technology. The effects of processing parameters on the microstructure and properties of composite powders were investigated. The results show that with increasing the slurry solid content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the binder content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the spray drying temperature, the particle size of powders increases, and the bulk density and flowability of powders increases firstly and then decreases. The most appropriate spray drying parameters are the slurry solid content of 40 wt.%, the binder content of 2.0 wt.% and the spray drying temperature of 250 °C. The nanostructured composite coating was successfully prepared by using the as-prepared nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders as feedstocks. The nanostructured coating possessed higher hardness and toughness compared with the conventional microstructured one, which was attributed to the use of the nanostructured composite powders feedstocks.     

Enhancement of catalytic activity of Raney nickel by cobalt addition

The effects of cobalt as a promoter of the catalytic activity of Raney nickel for various manufacturing esses have been studied. The variation of particle size distribution, specific surface area and residual aluminium content can also affect the catalytic properties of Raney nickel. The characteristics of the catalyst are considerably influenced by the relative nickel and aluminium contents. When the catalysts are prepared from 60 wt.% nickel and 40 wt.% aluminium, the electrode performance shows the highest current density of 450 mA/cm². With the addition of cobalt, the particle size is diminished from 13.92 to 11.70 μm and the decrease of the particle size contributes to a slight enlargement of the specific surface area. The mass activity of a hydrogen electrode manufactured with cobalt Raney nickel in alkaline solution is increased from 3.74 to 4.03 A/g when 120 mg/cm² of catalyst are loaded in the electrode.     

碳化钨/钴热喷涂粉末和涂层的研究进展

热喷涂传统碳化钨/钴金属陶瓷作为耐磨涂层已得到广泛的应用。近几年来,纳米结构涂层的热喷涂研究成为新的发展趋势。本文总结了传统和纳米结构 WC/Co热喷涂粉末的制备方法及其性质对涂层性能的影响因素,分析了涂层的微观结构和脱碳机理,简述了热喷涂纳米结构及纳米结构 微米结构 WC/Co涂层的研究进展,并指出了其发展方向。     

Synthesis and characterization of nanostructured powders of Bi2O3, BiOCl and Bi

In the last years, synthesis and characterization of bismuth compounds have received a great attention due to their potential applications. In this work, nanostructured powders of Bi₂O₃, BiOCl and Bi were prepared by a simple aqueous precipitation method using elemental bismuth as starting material and varying some experimental conditions. The samples obtained were characterized using X-ray diffraction (XRD) and transmission electronic microscopy (TEM); fluorescence, infrared and UV-vis absorption spectroscopies were also used. The obtained powders present a particle size under 100 nm, irregular morphology and agglomeration. A quantum confinement effect can be observed in the optical properties of the samples prepared in this work making them an interesting option for industrial applications.     

超细镍粉的制备及还原生长机理研究

以联氨为还原剂,在硫酸镍水溶液中控制液相还原反应条件制备了超细镍粉,并讨论了超细镍粉的还原生长机理.通过实验分析了工艺参数对还原反应的影响,采用X射线衍射(XRD),扫描电镜(SEM),比表面积测定等分析手段对超细镍粉进行表征,结果表明:超细镍粉的形核和生长独立进行;温度、Ni2+浓度和pH值调控着溶液中镍离子的释放并...     

Chemical vapor processing and applications for nanostructured ceramic powders and whiskers

A new chemical synthetic process for producing non-agglomerated nanostructured ceramic (n-ceramic) powders from metalorganic precursors is described. The process combines rapid thermal decomposition of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1–50 mbar. A wide variety of metalorganic precursors is available commercially, all of which can be utilized in this process to produce n-ceramic powders, including single phase, multiphase and multicomponent systems. The process has been used to synthesize nonagglomerated n-SiC_xN_y and n-ZrO_xC_y powders, with controlled particle size in the range 2–20 nm. Heat treatment of the as-synthesized n-powders in various high purity gas streams causes compositional and structural modifications, including particle purification and crystallization, as well as transformation to a whisker-like morphology. Non-agglomerated n-ceramic powders form uniformly dense powder compacts by cold pressing, which can be sintered to theoretical density at temperatures as low as 0.5 T_m.     

Rapid synthesis and morphology control of nickel powders via a microwave-assisted chemical reduction method

Nickel powders with different morphologies, such as sphere, chain, and thorn-like nickel wire have been successfully synthesized by hydrazine reduction of NiCl₂ in the presence of polyvinyl pyrrolidone (PVP) by using microwave-assisted chemical reduction method. The obtained products were characterized by XRD, SEM, TEM, and SAED techniques. Characterization by TEM and SAED showed that as-produced nickel powders were formed by self-assembly and aggregation of nanometer-sized nickel crystallites. PVP served as the structure directing agents and plays a key role for the morphology transformation of the nickel powders. In addition, compared with conventional heating method, microwave irradiation heating was in favor of the formation of nickel wires. The resultant nickel wires showed excellent electrical properties in the nickel wires/epoxy composite.     

Microwave-assisted hydrothermal synthesis of coralloid nanostructured nickel hydroxide hydrate and thermal conversion to nickel oxide

Coralloid nanostructured nickel hydroxide hydrate has been successfully synthesized by a simple microwave-assisted hydrothermal process using nickel sulfate hexahydrate as precursor and urea as hydrolysis-controlling agent. A pure coralloid nanostructured nickel oxide can be obtained from the nickel hydroxide hydrate after calcination at 400 °C. The thermal property, structure and morphology of samples were characterized by thermogravimetry (TG), temperature-programmed reduction (TPR), X-ray (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).     

热喷涂用纳米结构Al_2O_3/TiO_2/SiO_2团聚体粉末的研究

对喷雾干燥和不同温度热处理后Al2O3/TiO2/SiO2纳米团聚体粉末的流动性、松装密度及振实密度进行了测试,对喷雾干燥后的粉末进行了热重-差热分析,通过扫描电镜观察了粉末颗粒形貌和大小,采用X射线衍射分析了不同温度热处理后粉末的相组成,并对粉末的综合性能进行了比较。实验结果表明:在1000～1450℃热处理后的Al2O3/TiO2/SiO2纳米团聚体粉末颗粒仍近似球形,粒径在10～100μm之间。随着热处理温度升高,纳米团聚体大颗粒表面发生塌陷,大颗粒之间发生连接,大颗粒内部纳米颗粒明显长大。低于1250℃热处理后的粉末流动性好,振实密度高,适于等离子体喷涂制备纳米结构涂层。     

超音速火焰喷涂制备纳米和微米结构WC-η涂层的耐熔锌腐蚀性能

以钨氧化物、钴氧化物和炭黑为原料, 通过原位还原碳化反应制备纳米WC-η(η为Co₃W₃C、Co₆W₆C等缺碳相)复合粉, 粉末平均粒径为155 nm。该复合粉经团聚造粒制备得到具有高致密性和良好流动性的热喷涂粉末。以此纳米结构和商业化的微米结构低碳WC-12Co粉末作为喂料, 通过超音速火焰喷涂制备硬质合金涂层。结果表明, 纳米结构涂层中生成了一定量等轴状的W₂C相, 裂纹主要沿晶界或相界面扩展, 而微米结构涂层中除W₂C外还含有较多的W相, 主要包裹在WC颗粒表面, 穿晶断裂比例较高, 裂纹扩展路径较平滑。由于纳米结构涂层组织致密、晶粒细小、界面积大, 因此比微米结构涂层具有更高的硬度和断裂韧性。两种涂层在熔融锌液中浸泡200 h后, 微米结构涂层中产生了较多的横向和纵向裂纹, 导致材料的大面积剥落和基材腐蚀; 纳米结构涂层中没有发生锌的浸蚀, 在局部产生了少量纵向裂纹, 裂纹间隙被钨钴氧化物所填充, 反而抑制了熔锌对涂层的腐蚀, 因此纳米结构涂层表现出更高的耐熔锌腐蚀性能。     

A low temperature route to prepare LaFeO3 and LaCoO3

A combination of digestion and further low temperature calcination to crystallize the product was employed to prepare LaFeO₃ (LF) and LaCoO₃ (LC) powders. Freshly co-precipitated lanthanum and ferric (or cobalt) hydroxide gels by sodium hydroxide were allowed to react at 100 °C under refluxing and stirring conditions for 4-6 h. These oven dried powders were heated at 450 °C to form crystalline LF (or LC) powders. The phase contents and lattice parameters were investigated by X-ray diffraction (XRD). Transmission electron microscope (TEM) investigations were carried out to examine the morphology and average particle size of these powders.     

Nanostructural and optical properties of cobalt and nickel–oxide/silica nanocomposites

Cobalt, nickel and mixed cobalt–nickel nanostructured oxides have been obtained by thermal treatments in oxygen of Co, Ni and Co₅₀Ni₅₀/silica nanocomposites produced by ion implantation technique. The thermal treatment produces the total or partial oxidation of the original metallic species, which diffuse towards the surface and in the depth of the substrate. This process gives rise to the growth of different oxides in both regions depending on the kind of metal. In the Co sample, mainly Co₃O₄ is formed; in the Ni sample, Ni and NiO nanoparticles are present, while in the Co–Ni sample Co₃O₄, Ni₂SiO₄ and mainly (Co_xNi_1−x)O nanostructures are formed. The optical features of cobalt and nickel samples are determined by the optical properties of the Co₃O₄ and NiO p-type semiconductor phases, respectively, with energy gaps littler than the corresponding bulk ones. The Co–Ni mixed nanostructured oxide is characterized by a direct absorption gap at 3.4 eV that is smaller than the band gaps of CoO and NiO oxides.     

Influence of grinding on the texture,microstructure and chemical reactivity of nickel powders

The influence of grinding on the morphology, texture and microstructure of nickel powders has been studied. A series of three samples, the as-received one (NiNG) and those comminuted for 3 min (NiG3) and 30 min (NiG30), have been used. SEM observations have shown that cold-welding, leading to a decrease of particle size, takes place during the comminution process. Analysis of the XRD profiles by means of the Willianson and Hall method seems to demonstrate that the broadening of XRD peaks is produced by the microstrains generated during the milling of nickel powders, rather than by the diminution of crystallite size (coherently diffracting domains). On the other hand, it has been reported that the recrystallization temperature of this material by annealing under vacuum protection decreases on increasing the grinding time. Moreover, the mean XRD peak widths of samples annealed at 300 °C decreases according to the following trend: NiG30相似文献   

催化剂对乙醇催化燃烧法制备碳纳米纤维的影响

分别以硝酸铁、硝酸钴、硝酸镍以及氯化铁、氯化钴、氯化镍作为催化剂先体，利用乙醇催化燃烧法制备了碳纳米纤维。利用扫描电子显微术、透射电子显微术和X射线能量分散谱术对样品进行了表征。讨论了不同种类的催化剂先体对产物形貌和生长机制的影响。     

碳化钨粉末对聚晶金刚石复合片钻头胎体组织与力学性能的影响

以铸造碳化钨粉末混合镍粉作为骨架粉末,采用无压浸渍工艺制备了聚晶金刚石复合片（PDC）钻头胎体材料。研究了碳化钨的粉末粒形、粒度及质量分数对PDC钻头胎体的微观组织和力学性能的影响。结果表明,碳化钨的粉末粒形、粒度及质量分数是影响胎体微观组织和力学性能的重要因素。与破碎碳化钨相比,粉末粒度适中的球形碳化钨作为骨架制备的胎体组织更均匀、更致密,胎体的力学性能明显提高。采用150~180 μm的球形碳化钨混合13wt%的镍粉作为骨架粉末制备的胎体力学性能优于石油天然气行业标准SY/T 5217—2000,其硬度、冲击韧性和抗弯强度分别为HRC 34、6.7 J/cm2和820 MPa。