Metal-coated colloidal particles

Procedures are described for coating of submicrometre ceramic powders with copper and nickel. The process required precoating of the core particles with a palladium catalyst. A precoating procedure was developed in which palladium chloride is reduced by sodium hypophosphite or stannous chloride on the powder surface in aqueous suspensions. Commercial electroless solutions were used to deposit copper and nickel on the catalysed powders. The effect of various experimental parameters on the effectiveness of the surface conditioning of the particles was also investigated.     

The effect of chelating agents on the cathodic polarization and the electrodeposition of iron powders

The electrodeposition of iron powders from different baths containing the same major chemical constitutents was studied. The baths were mainly based on aqueous dilute solutions of ferrous sulphate and additives such as oxalic and citric ions. The effect of these additives on the cathodic polarization curves, current efficiency and powder morphology of the electrodeposited iron powders was investigated. It was found that electrodeposition systems with chelating agents were more polarized than a non-chelated system and produced finer powders with no dendrites.     

超细铜粉的制备方法、存在问题及应用

超细铜粉由于其特殊的物理、化学方面的性质已经广泛应用于导电材料、催化、润滑油添加剂、纳米晶铜、医药等多个领域中。介绍了目前超细铜粉的制备方法，各自的优缺点及在各领域中的应用情况，并概述了存在的问题及目前的解决方法。     

Rapid additive manufacturing of functionally graded structures using simultaneous wire and powder laser deposition

Laser additive fabrication allows the manufacturing of functionally graded structures that are not possible using conventional subtractive manufacturing. Laser deposition of injected powders with varying compositions, layer-by-layer, is often used for the building up of functionally graded fully dense structures or materials. This approach, however, has some drawbacks: the un-used powders (normally 60–80%) cannot be recycled as they will be contaminated by the powder mixture. In addition, multiple passes are needed to develop functionally graded structures. This paper reports the feasibility and characteristics of using simultaneous powder and wire feeding laser deposition to produce functionally graded structures in a single step. This approach has been shown to eliminate the above problems associated with powder feed laser deposition. In this work, copper powder and nickel wire have been used to deposit functionally grated copper/nickel/iron structures on H13 tool steel. A 1.5-kW diode laser is used for the build-up process. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy are used to analyse the deposited materials in terms of morphology, composition distributions, microstructures and phases formed. Successful deposition of functionally graded Cu–Ni–Fe structures has been demonstrated. Comparisons are made with the dual powder feed deposition process, which shows the inclusion of un-melted Ni powders in the Cu layer as a result of melting temperature difference of the two materials.     

Rapid additive manufacturing of functionally graded structures using simultaneous wire and powder laser deposition

Laser additive fabrication allows the manufacturing of functionally graded structures that are not possible using conventional subtractive manufacturing. Laser deposition of injected powders with varying compositions, layer-by-layer, is often used for the building up of functionally graded fully dense structures or materials. This approach, however, has some drawbacks: the un-used powders (normally 60-80%) cannot be recycled as they will be contaminated by the powder mixture. In addition, multiple passes are needed to develop functionally graded structures. This paper reports the feasibility and characteristics of using simultaneous powder and wire feeding laser deposition to produce functionally graded structures in a single step. This approach has been shown to eliminate the above problems associated with powder feed laser deposition. In this work, copper powder and nickel wire have been used to deposit functionally grated copper/nickel/iron structures on H13 tool steel. A 1.5-kW diode laser is used for the build-up process. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy are used to analyse the deposited materials in terms of morphology, composition distributions, microstructures and phases formed. Successful deposition of functionally graded Cu-Ni-Fe structures has been demonstrated. Comparisons are made with the dual powder feed deposition process, which shows the inclusion of un-melted Ni powders in the Cu layer as a result of melting temperature difference of the two materials.     

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...     

Influence of carbon nanotubes and dispersions of SiC on the physical and mechanical properties of pure copper and copper‐nickel alloy

This paper investigates the physical and mechanical properties of copper‐nickel alloy (at 50 wt.%–50 wt.%) and pure copper, mixed with various types of reinforcement materials such as carbon nanotubes (0.5 wt.%–2 wt.%) as nanoparticles, silicon carbide (1 wt.%–4 wt.%) as microparticles. The acquired composite specimens characteristics were estimated such as microstructure, density, electrical and thermal conductivity, hardness, and compression stress properties to determine the suitable reinforcement percentage that has the best physical and mechanical properties with different main matrix material whether copper‐nickel mechanical alloying or pure copper powder. The micron‐sized silicon carbide and nanosized carbon nanotubes were added to improve the mechanical and physical properties of the composite. The electrical and thermal conductivity of pure copper alloy enhanced compared with the copper‐nickel alloy matrix material. The hardness and compression yield stress of both pure copper and copper‐nickel composites have enhancement values and for copper‐nickel base composites hardness and compression yield stress have enhanced with the most positive enhancement values to examined an optimum percentage of reinforcing material.     

化学还原法制备超细铜粉工艺及机理研究

为了提高超细铜粉分散性、均匀性及抗氧化性,采用几种化学还原法工艺分别制备了铜粉,通过反应现象探讨了温度、还原剂、添加剂及葡萄糖预还原对铜粉性能的影响,利用SEM、粒度仪对铜粉形貌、粒径进行观察,并进行相关机理分析,确定了化学还原法制备超细铜粉的最佳工艺,结果表明,在温度为70℃时,添加分散剂PVP和抗氧化剂BTA,以甲醛-水合肼为复合还原剂,结合葡萄糖预还原法制备的铜粉具有抗氧化性强、粒径分布区间窄、几乎无团聚等优点。此工艺不仅体现了葡萄糖预还原的有利影响,还明显克服了单一还原剂的缺陷,所制铜粉质量好,具有良好的应用前景。     

Preparation of ultra-fine copper powder and its lead-free conductive thick film

In this paper, non-agglomerated monodispersed ultra-fine copper metallic powders have been synthesized with chemical reduction method. Fine lead-free glass powders were also prepared by solid synthesis process. Thick film paste prepared by above-mentioned copper metallic powders and lead-free glass powders was applied as conductive paste of MLCC. Mixture of glass and zinc oxide give the thick film a high adhesion strength which is attributed to the rough interface from interfacial reaction between glass and chip, and a good densification. Diffusion of metal between copper thick film and nickel thick film is clear. Ni-Cu solid solution appears under high temperature firing.     

非均相沉淀法制备纳米α-Al2O3/金属复合粉体

利用非均相沉淀法制备了平均粒径小于50 nm的α-Al₂O₃/W(Ni)复合粉体,并研究对比了纳米钨和镍对α-Al₂O₃相转变温度的影响。结果表明:纳米钨和镍的存在均可降低过渡型氧化铝向α型氧化铝转变的相变温度,但降低程度有所不同,含钨氧化铝于1000℃完成相变,而含镍氧化铝于1150℃完成相变;并且纳米第二相体积比越大,对相变温度的影响也越大。     

水雾化铁基混合粉末的流动性及其烧结体的尺寸变化率

以水雾化铁基预舍金粉ATOMET4401为原料,研究了添加剂（胶体石墨、电解铜粉和羰基镍粉）对混合粉末流动性及其烧结体尺寸变化率的影响规律。研究表明,添加剂的加入均将延长混合粉体的流失时间,添加剂粉末尺寸越小对混合粉体的流动性影响越大。当碳含量从0.3wt％增加至0.9wt％时,流失时间延长了30％以上。随着铜含量的增加,混合粉体的流失时间呈先缓后快的增加趋势,并且当碳含量为0.9wt％时,增加的趋势更加显著,与未加铜者相比流失时间延长了9.2％。在碳含量为0.9wt％和羰基镍粉含量为4wt％时,混合粉末流失时间延长了25．7％。当碳含量从0．3wt％增加至0．9wt％时,尺寸变化率增加两倍以上。随碳含量增加,尺寸变化率随铜含量的变化趋势显著减小。当碳含量为0．9wt％时,铜含量对尺寸变化率的影响基本稳定。随着镍含量的增加,混合粉末烧结体的尺寸变化率逐渐由正变为负,并且随碳含量增加,这种变化趋势在高镍含量范围内变得更加明显。值得注意的是,在镍含量为-1wt％左右可以获得尺寸变化率接近零的烧结零件。     

Understanding Powder Caking as a Consequence of a Range of Mechanisms by Means of Powder Rheometry

Over 70% of materials in the food, chemical, and pharmaceutical industries (from raw materials, additives, and intermediates through to manufactured products) are supplied as relatively free-flowing powders, intended to be suitable for the manufacturing process or final application. For logistical reasons however these materials will often have to be stored for extended periods during which time some powders have the potential to gain strength due to prolonged and undisturbed particle/particle interactions. This is generally referred to as “caking” and can significantly limit the ability of a powder to pass through the process train without interruption as well as detrimentally impacting product quality.

This paper will present case studies that evaluate the flow properties of different powder systems that are affected by chemical-, moisture-, and temperature-based caking mechanisms. It will show how the propensity to cake can be effectively quantified with respect to the powders’ flow properties and how this can assist in understanding and adapting the processing environment to retain optimal processability.     

Polymorphism of ZrO<Subscript>2</Subscript> nanopowders and mechanochemical synthesis of Zr<Subscript>0.88</Subscript>Sc<Subscript>0.1</Subscript>Ce<Subscript>0.01</Subscript>Y<Subscript>0.01</Subscript>O<Subscript>1.955</Subscript>

The structure of ZrO₂ powders prepared by dehydration of zirconium hydroxide and milling (including techniques with the introduction of grinding additives, such as NaF, CaF₂, diamond, and Cu) was investigated using x-ray powder diffraction and Raman spectroscopy. Samples containing crystallites with the smallest size were synthesized in the presence of copper additives. Ceramic powders of the composition Zr_0.88Sc_0.1Ce_0.01Y_0.01O_1.955 with an improved quality for the use as solid electrolytes in fuel cells were prepared by the mechanochemical synthesis from nanoprecursors and then were characterized. An analysis of the X-ray powder diffraction patterns revealed that the symmetry of the structure of strongly aggregated nanopowders of metastable zirconia increases as a result of twinning, which is favored by a high concentration of vacancies.     

Large-scale and shape-controlled synthesis and characterization of nanorod-like nickel powders under microwave radiation

The nanorod-like nickel powders were fabricated via hydrothermal liquid phase reduction route under microwave irradiation with hydrazine hydrate as a reducing agent as well as polyvinyl alcohol as a dispersant and/or structure directing agent. The morphology and structure of as-prepared products could be easily tuned by adjusting process parameters such as pH value and microwave irradiation time. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscopy and selected-area electron diffraction (SAED). The results demonstrated that pure nickel powders with face-centered cubic (fcc) structure were prepared at relatively mild condition and no characteristic peaks of nickel oxide in the XRD pattern were found. The phenomenon of lattice expansion for Ni powders was explained in details according to the XRD theory. As-prepared Ni sample was of obvious shape anisotropy with length diameter ratio of 5. Magnetic measurements shown that the magnetic properties of nanorod-like (fcc) Ni powders were quite different from those of hexagonal closed-packed (hcp) Ni nanoparticles. Furthermore, it had more strong ferromagnetic properties than that of Ni powders both bulk and nanoparticles.     

Hydrogen reduction of bleed stream of an Indian copper industry to produce nickel powder

Investigation on the synthesis of nickel powder by hydrogen reduction from a highly acidic solution i.e. copper bleed stream (CBS), from ICC Ghatsila has been reported here. Synthetic CBS having the similar chemical composition as that of actual bleed stream was used to optimize the parameters for the maximum recovery of nickel powder on bench scale. These parameters were substantiated by performing a few large-scale experiments under these optimized conditions for the synthesis of Ni powder. The properties of nickel powder such as compaction, green density, flowability, particle size and purity, produced from large-scale experiments using actual CBS have been evaluated for P/M applications. SEM shows that the particles are spherical in nature.     

Investigation on the Fe-based PM materials reinforced by In Situ synthesized TiC particulates

Atomized iron powder, carbonyl nickel powder, molybdenum powder, electrolytic copper powder, titanium powder and graphite powder were used as experimental materials; the titanium and graphite powders were added by an atomic ratio of Ti/C = 1:1 (the addition of Ti was 0 ～ 4 wt%) to Fe-2Ni-0.5Mo-2Cu-0.3C powder, and the iron-based powder metallurgy materials reinforced by in situ-synthesized TiC particulates were prepared by a powder metallurgy technique. The results show that the microstructures of sintered samples are mainly pearlite, ferrite and bainite. The amount of pearlite increases with the increase of Ti content, whereas the ferrite and bainite decrease. TiC particles sized 0.3 µm distribute mainly near the grain boundary of pearlite. The apparent hardness of sintered samples increases, while the sintered density and flexural strength decrease with the increase of Ti content. The fracture morphology of the sintered materials is brittle type.     

Effect of small amounts of additives on the sintering of high-purity Y-TZP

Superfine Y-TZP powders of high purity were prepared by using clean-room facilities. The effects of several kinds of minute or small amounts of additives on the densification and microstructural development of the Y-TZP powder were investigated. It was found that ≤1 wt% ferric or calcium oxides did not affect the densification of the Y-TZP powder compacts, while the addition of sodium oxides retarded the densification and that of copper oxide accelerated it, and these effects are most obvious at an additive level of 1 wt%. The retardation of the densification by sodium oxide was found to result from the agglomeration effect of the powder, and the formation of the eutectic liquid phase between zirconia and copper oxides promoted the densification and grain growth during sintering of copper oxide-doped powder. In addition, sodium and copper oxides both destabilize the tetragonal Y-TZP and lead to the formation of monoclinic phase. This revised version was published online in November 2006 with corrections to the Cover Date.     

镍电极的固相掺杂及在非对称电容中的应用

应用CoO、Zn粉对镍电极进行固相掺杂,电极经若干次充放电循环,Co、Zn元 素在Ni(OH)₂颗粒表层以固溶体的形式富集,可优化活性物质表面的组成和结构,提高活性物 质表层的快速反应能力,从而使镍电极更适用于C／Ni(OH)₂非对称电容器体系.实验结果表 明:在高倍率充放电条件下,掺杂10％CoO的镍电极,其容量为未掺杂电极的2倍;用5％的 Zn粉替代部分导电剂Ni粉,镍电极大电流条件下的循环性能和容量性质将明显改善.     

溶胶-凝胶法制备钇掺杂氧化锆的工艺研究

论述了用溶胶-凝胶法制备钇掺杂的氧化锆前驱体的过程,系统地研究草酸溶液的浓度、pH值、加热温度以及添加方式对溶胶、凝胶的影响,得出制备氧化锆前驱体的最佳工艺条件:当氧氯化锆溶液与草酸溶液的浓度比为1.25～2,草酸溶液pH值为1～2,加热温度为40～80℃,制得的前驱体溶胶、凝胶均匀,透明.正加方式得到的溶胶淡蓝色透明,较反加方式下的溶胶的胶凝时间短.并对最佳工艺条件制备的粉体进行SEM分析,结果表明,很好地合成了钇掺杂的纳米氧化锆粉体.     

Aqueous dispersion stability of nickel powders prepared by a chemical reduction method

Spherical nickel powders with the very smooth surface and the uniform size of 300 nm have been manufactured by the chemical reduction and post-treatment technique. The adsorption isotherms of various water-soluble polymers on nickel powders were measured, and their effects on the dispersion stability were investigated. The adsorption amounts of polymers such as PVP (polyvinyl pyrrolidone), PMAA (polymethacrylic acid), and PAAm (polyacrylamide) on nickel powders could be successfully determined by the UV-absorbance analysis technique. Simultaneously, the dispersion stability of nickel powders in the polymer solution was evaluated in terms of the sedimentation behavior and relative coagulation rate. These results showed that the polymers such as PAAm and PVP (Mwt. 1,300,000) were found to be very effective for stabilizing the aqueous nickel dispersion system, and consequently, the coagulation rate of nickel powders in the PAAm solution was almost 100 times slower than that in pure water.