金属镍电沉积中枝晶的分形生长

分别采用点电极电沉积和平行板电极喷射电沉积制备二维的镍枝晶,研究外加电压、电解质浓度、温度等对金属镍枝晶二维电沉积生长行为特性的影响,并从分形维数的角度对其进行分析.结果表明,在点电极电沉积时,枝晶的分形维数随外加电压的变化而波动,随NiSO4浓度和试验温度的升高而增大;气泡的析出使上述试验条件对枝晶生长特性的影响变得不明显.在喷射电沉积时,增大NiSO4浓度使气泡析出量减少,枝晶簇的分形维数随之减小,说明在大电流密度下,气泡对枝晶簇生长形貌的影响起主导作用;试验温度从55 ℃升高到60 ℃时分形维数先增加后减小.     

点阳极电沉积枝晶的分形生长

利用分形几何的原理模拟点阳极电沉积中枝晶的分形生长,分别研究阳极大小、射流速度、NiSO_4浓度和温度等试验条件对点阳极射流电沉积中金属镍枝晶二维电沉积生长行为特性的影响,并从分形维数的角度对其进行分析.结果表明:点阳极射流电沉积中的枝晶也呈分形生长,其分形维数随着点阳极尺寸的增大而增加;射流速度的提高使枝晶簇根部的生长点明显增多,但在射流速度较低时,枝晶簇顶部的形貌较为致密;大量气泡的析出有利于产生分枝,此时气泡对枝晶生长的形貌起主导作用,使射流速度变化时的分形维数出现波折;电解质浓度的增大使枝晶簇的分形维数逐渐减小;且随着试验温度的提高,分形维数也随之增加.     

射流电沉积镍中晶体形态的可控生长

利用分形理论编程模拟了射流电沉积中沉积几率较小时粒子簇的生长形貌。基于模拟的原理,利用摆动射流电沉积改变了枝晶的树枝状分形生长特性,制备不同电流密度、摆动速度、NiSO4浓度和电解液温度时的二维多孔交织的金属镍枝晶簇。结果表明:随着电流密度的增大,枝晶簇开始由分形生长形态向多孔交织形态转变,分形维数也随之增大。随着摆动速度的减小,枝晶簇向致密、均匀的多孔交织形态转变明显,分形维数逐渐增大。NiSO4浓度较小时,枝晶簇的分枝较多,形貌较为致密;NiSO4浓度最大时,气泡的析出量大大减少,枝晶簇的分枝显著减少,难以形成多孔交织的组织;分形维数随NiSO4浓度的变化先增大后减小;电解液温度的升高使枝晶簇的形貌向致密型转变,分形维数逐渐增大。     

射流电沉积镍工艺研究

通过射流电沉积瓦特镍电解液研究了电压、电解液温度、射流速度、主盐浓度、阳极喷嘴口径对沉积电流、沉积速率、电流效率的影响.结果表明:在电压为45V,温度为50℃,阴阳极间距离为17mm,NiSO4·6H2O浓度为280g/L时,从沉积电流、沉积速率、电流效率来看,效果最好.电压的增大使得沉积电流、沉积速率、电流效率增大,当电压增大到45V后,电流效率不再增大,而是趋于平稳,到55V后,沉积层烧焦.试验还发现,电解液流速和阳极喷嘴口径越大,沉积速率、电流效率也越大.     

枝晶形态逐层引导控制技术

在采用摆动射流电沉积实现枝晶二维可控交织生长的基础上,利用扫描摆动射流电沉积,逐层引导枝晶在扫描方向上交织生长,在不同摆动次数和扫描步进步长时制备三维多孔的金属组织,并对其形态变化进行分析,同时建立枝晶逐层引导生长模型。结果表明:不同摆动次数和步进步长时,枝晶生长形态的变化验证了该枝晶逐层引导生长模型的正确性;摆动次数较小时,相邻枝晶难以对接、交织;摆动次数较大时,相邻枝晶水平交织处的分支较为粗大;随着步进步长的增大,多孔金属组织的孔隙逐渐增大。通过调节各种工艺参数和控制条件,可以方便地实现对多孔金属组织形态的控制。     

电沉积法制备纳米晶材料

电沉积法是制备完全致密的纳米晶体材料最有前途的方法之一。本文综述了电沉积法制备纳米晶镍及其合金的研究现状及制备方法对纳米晶材料性质的影响。     

射流电沉积快速成形控制系统的研究

介绍了射流电沉积快速成形的计算机控制系统，并对系统的软、硬件组成、结构和功能做了分析和研究，给出了基于Windows平台以NC嵌入PC模式的射流电沉积快速成形控制系统的实现方法。     

金属铜电沉积过程中分形研究

以环形金属铜片作为阳极，细铜丝作为阴极，研究了酸性电解液条件下金属铜电沉积过程中的二级枝晶生长现象，测定了沉积时间－电流关系曲线，对外加电压，电解液中硫酸铜浓度等对金属铜的电沉积产物形貌及其分维数的影响进行了观测，分析。研究发现，沉积过程中，电流随沉积时间的增加而变大，沉积产物的分维数随电解液中硫酸铜的增加而变大，随外加电压的变动而波动。     

超重力条件下电沉积金属镍的结构与性能

在超重力垂直于电极表面的情况下,研究超重力场对水溶液金属电沉积镍箔的组织结构和性能的影响,利用原子力显微镜(AFM)和x射线衍射仪(xRD)对沉积镍箔的表面形貌和晶体结构进行观察.结果表明:超重力场下的镍箔晶粒细化,表面更平整,当重力系数为354时,表面粗糙度由常重力下的20.9nnl降低到4.9rim;并且随着重力系数的增加,沉积镍箔的晶体结构从有择优取向结构转变为无特定的择优取向结构.力学性能测试表明,当重力系数为354时,沉积镍箔的硬度和抗拉强度分别达到HV 898和944 MPa,比常重力下分别提高了HV604和646MPa.     

镍基合金焊丝GTAW熔敷金属凝固偏析行为

采用OM,SEM,EDS,EPMA等分析手段对试制的镍基合金焊丝GTAW熔敷金属开展了凝固偏析行为研究.结果表明,熔敷金属中主要包括γ相、（Nb,Ti） C碳化物、Laves相等,金相组织主要为柱状晶,在枝晶间存在宽度约为5~10 μm的偏析区域;按照Scheil公式对EPMA分析结果进行了偏析系数计算,估算的Nb,Mo,Ni,Cr,Fe偏析系数分别为k_Nb=0.23,k_Mo=0.68,k_Ni=1.07,k_Cr=1.05,k_Fe=1.23,在结晶过程中Nb,Mo更倾向于分配在残余液相,Nb的偏析倾向最大,Mo次之,Fe更倾向于分配在固相中,Ni,Cr基本为固液平均分配.文中试验用镍基合金焊丝GTAW熔敷金属凝固结晶路径为L→L+γ→L+γ+MC→L+γ+MC+Laves相→γ+MC+Laves相.     

Mechanism of abnormal grain growth in ultrafine-grained nickel

During annealing of ultrafine nickel powder compacts, abnormal grain growth (AGG) occurred with the formation of cube-shaped grains. The observed AGG is similar to the late-stage abnormal grain growth (LS-AGG) that is commonly observed in electrodeposited (ED) Ni sheets. The cube shape of the abnormal grains with {1 0 0} facets was identical to that of late-stage abnormal grains in ED Ni. As the temperature increased, the time to the appearance of abnormal grains decreased. After impingement of abnormal grains, little further grain growth occurred, indicating stagnant grain growth behavior. The formation of abnormal grains in the present study, however, cannot be explained by the previously suggested AGG mechanisms, i.e. the S phase wetting mechanism and initial texture mechanism, because no amorphous phase containing S was present and no texture developed in our samples. In contrast, the observed grain growth behavior can be well explained in terms of the coupling effect of the maximum driving force for grain growth and the critical driving force for appreciable migration of faceted boundaries. It is concluded that the AGG in ultrafine-grained Ni occurs via mixed migration mechanisms, i.e. diffusion and interface reaction-controlled, of faceted boundaries with respect to the driving force.     

Surface oxidation of nickel metal as studied by X-Ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been used to study the oxidation of polycrystalline nickel metal. The results indicate that the oxidation process takes place in three stages; associative adsorption of molecular oxygen, followed by the combination of oxygen atoms with surface nickel atoms and, ultimately, the formation of bulk oxide. At room temperature only the first two stages can be detected. For exposures below 1 L the O 1s photoelectron spectrum is considered to be characteristic of an associatively adsorbed oxygen species, but for exposures above this value evidence for the formation of a monolayer of NiO is suggested by the development of an O 1s peak at 529.9 eV. Incorporation of oxygen into the nickel lattice is observed at temperatures >500°K. The activation energy for this place-exchange process was estimated at 1.80±0.06 eV.     

Regeneration and decontamination of a nickel citrate complex in spent electroless nickel plating solutions

The possibility of citrate precipitation by excess metal ions in alkaline solutions suggests the use of Ni(II) together with OH^? to precipitate a Ni(II)-citrate complex from spent electroless plating solutions. After treatment of the precipitate with acid, excess Ni(II) can be removed in the form of insoluble Ni(OH)₂. The solution of the Ni(II)-citrate complex can then be reused for electroless nickel plating. During this procedure the additive adipate is not regenerated. For decontamination of spent electroless nickel plating solutions Fe(III) can be used as Ni(II)-citrate complex precipitant.     

废镍催化剂回收制备纤维状氢氧化镍

研究从废旧镍催化剂中回收镍以制备氢氧化镍。采用酸浸法,在90℃下用1mol／L硫酸浸没废镍催化剂,从中提取镍。向净化后的含镍溶液中加入NaOH,分别采用3种不同的方法,即尿素水解、传统方法和水热方法制得3种不同的氢氧化镍,分别命名为Ni（OH）2-U,Ni（OH）2-C和Ni（OH）2-H。与传统方法相比,采用水热方法制得的氢氧化镍具有更好的结晶度。Ni（OH）2-C和Ni（OH）2·H都含有β-Ni（OH）2与a-Ni（OH）2·0．75H20的混合相,而Ni（OH）2．U只含有a-Ni（OH）2．0．75H20相。TEM观察显示Ni（OH）2-U样品具有棒状结构。在这3种样品中,Ni（OH）2-U表现出最好的电化学活性。     

Recently developed strategies to restrain dendrite growth of Li metal anodes for rechargeable batteries

Lithium metal has been regarded as one of the most promising anode materials for high-energy-density batteries due to its extremely high theoretical gravimetric capacity of 3860 mAh·g^-1 along with its low electrochemical potential of-3.04 V.Unfortunately,uncontrollable Li dendrite growth and repetitive destruction/formation of the solid electrolyte interphase layer lead to poor safety and low Coulombic efficiencies(CEs) for long-term utilization,which largely restricts the practical a...     

利用低冰镍制备铁酸镍前躯体

以低冰镍为原料,采用草酸盐共沉淀法合成颗粒细小的铁酸镍前躯体 NiFe2(C2O4)3·6H2O。NiCl2?FeCl2?(NH4)2C2O4?H2O体系的热力学研究表明：Ni2+和Fe2+的理论最佳共沉淀pH值为2,2?24C O 对Ni2+、Fe2+离子具有较强的络合作用。在理论研究的基础上,考察沉淀参数对沉淀率和前躯体粒度的影响。结果表明：最佳共沉淀条件为溶液pH=2,反应温度为45°C,(NH4)2C2O4加入量为理论值的1.2倍,PEG400加入量为3%。在此条件下,Ni2+和Fe2+的沉淀率达99.8%,所得前躯体的粒径为1~2 um。XRD和TG?DTA分析表明：所得前躯体为单相置换固溶体,反应过程中镍、铁原子相互取代。