【作者】 陈劲松；

【导师】 黄因慧；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 针对目前泡沫金属制备方法普遍存在的工艺复杂、成本较高的缺点,提出了一种直接制备泡沫金属的新方法─喷射电沉积法。该方法基本原理是:在喷射电沉积过程中,采用很高的电流密度,金属沉积层会形成疏松、多孔的泡沫组织;此外,在高电流密度下,析氢反应的发生将产生大量气泡也有助于形成多孔沉积层。同其它方法相比,喷射电沉积法生成的泡沫组织完全是自组织原位生长的,在加工过程中,没有其它辅助材料的介入,工艺简单、成本也相对低廉。本方法在常温、常压下进行,对外界环境和设备要求不高。该项研究对丰富泡沫金属的制造工艺具有重要的现实意义。本文主要做了以下工作:(1)、分析喷射电沉积过程中枝晶生长的基本规律,并采用扩散限制凝聚模型(DLA)对喷射电沉积过程的多孔泡沫组织的形状和生长过程进行了模拟研究,使用喷射电沉积设备对DLA模型获得的枝晶进行了验证性试验。研究表明:用DLA模型来说明枝晶生长规律是有效的,DLA模型中的粒子移动速度、粒子释放数、结合概率分别同喷射电沉积工艺中电压、电沉积时间、电解液温度存在着内在的对应联系;模拟生成的粒子沉积层具有明显的枝晶结构,金属粒子从远端沿着主运动方向向阴极移动,被阴极极板俘获,形成了多孔的金属沉积层形貌。(2)、研制了包括控制系统、喷嘴提升机构、机床机械本体、电解液喷射与循环系统、电解液温控装置、阳极腔、喷嘴等部件在内的泡沫金属直接制备试验系统。使用该装置进行了喷射电沉积试验研究,成功制备了一组具有简单形状和一定厚度的泡沫镍金属样品;讨论了泡沫镍的显微结构、孔隙率和相对密度。结果表明:①可采用很高的阴极电流密度进行喷射电沉积,其电流密度约为常规电沉积的100倍,甚至更高;②枝晶容易在高的电流密度下生长,泡沫镍具有比较典型的多孔枝状晶结构;③在高电流密度下,很容易发生析氢反应,释放大量气泡;金属离子在气泡之间的空隙被还原形成多孔的沉积层;④电沉积参数对泡沫镍的相对密度和孔隙率有着比较明显的影响。泡沫镍的孔隙率随着电流密度的提高而减小,随着电解液喷射速度和电解液喷射距离的增加而减小;随着Ni2+浓度增大而减小。泡沫镍样品的孔隙率在50~70%之间、相对密度在0.3~0.5之间、孔径在0.3mm以内。(3)、分析了泡沫镍样品的相关力学性能、电学性能、热传导性能。结果表明:泡沫金属的硬度明显低于实体金属,不同孔隙率的泡沫镍的硬度也相差较大;泡沫镍的静态压缩性能具有明显的三阶段特征,即线弹性变形段、塑性平台段和压实段。孔隙率越高,平台应力越小;泡沫金属的电阻率明显高于实体金属,且随着孔隙率的增加,泡沫镍电阻率也随着增加。喷射电沉积直接制备的泡沫镍具有良好的散热性能,能够作为散热元件在电子行业中应用。鉴于上述特性,泡沫镍有望在电池电极材料、催化剂载体等方面有所应用。更多还原

【Abstract】 Based on the all-pervading complicated technology and high cost on preparing the porous foam metal, jet electrodeposition, a new method to prepare porous foam metal directly was put forward. Its principle were listed as follows. Deposited Layers generated loose and porous vesicular tissue on the condition of high current density. What’s more, the hydrogen evolution reaction produced a lot of bubbles and porous deposition layers were easily formed owing to that metal could only depose among those bubbles’clearance. Compared to other methods, vesicular tissue formed by jet electrodeposition growed totally all by itself at original place, without any auxiliary materials added. Meanwhile, the process is rather simplied and the cost is low relatively. This process can be carried out at normal temperature and atmospheric pressure, having no high requirement of external environment and equipments. This research is meaningful to enrich processes for preparing porous foam metals. The major works were as follows:1. The principles about jet electrodeposition and preparation of porous metals were investigated. The shape and growth process of porous dendritic structure in jet electrodeposition were simulated by the Diffusion-Limited Aggregation(DLA) model. Then, experiments were carried out to verify the simulation products by jet electrodeposition equipments. The results show that the DLA model was rather usable to explain the growth of dendritic structure. Migration of particles, releasing number of particles, joint probability in the DLA model were corresponding to voltage, deposition time, and electrolyte temperature during jet electrodeposition inherently. The deposition layer in simulation had obvious dendritic structures. Some particles which were moving toward cathode along main migration direction were captured by cathode polar plate and deposited together, forming the dendritic structure. At last, morphology of metal deposited layer was generated with foam point’s growth and extension.2. The devices of the direct fabrication of porous metals were designed and developed all by ourselves, including computer control system, nozzle lifting mechanism, the mechanical body, electrolyte injection and circulatory system, equipment to constant temperature and circulation of electrolyte, anode cavity and nozzle. A group of foam nickel metal samples with simple shape and a certain thickness were prepared. Microstructure, porosity and relative density of foam nickel metal were investigated. The results show as follows. One, current density in Jet electrodeposition can be very high. It can be 100 times of conventional one or even higher. Two, dendritic structure tended to grow under a higher current density and foam nickel has a typical dendritic structure. Three, hydrogen evolution reaction occured easily under a high current density, releasing a lot of bubble. It was only in the vacuity among the bubbles that metal ions could be reduced to be porous deposition layers. Four, experimental parameters in jet electrodeposition had a apparent effect on relative density and porosity of nickel foam. With current density, concentration of Ni2+, jet speed and distance of electrolyte increasing, the porosity of nickel foam became lower. Generally speaking, the porosity of nickel foam samples range from 50~70%, relative density 0.3~0.5 and aperture was confined within 0.3mm.3. Relational mechanical properties, electrical properties and heat transfer properties were studied. The results show that: hardness of foam metal is much lower than entitative metal. There were also much difference among the nickel foams. Static compressive properties of nickel foam had three stages: linear elastic deformation, plateau region and compacted section. The higher porosity was , the smaller plateau stress was. And, foam metal’s resistivity was much higher than entitative metal. Opening nickel foam prepared by jet electrodeposition had excellent heat dissipation performance, capable to be used in electronic industry as heat radiation elements. Give its basic nature, nickel foam is potential to be applied in battery or catalyst carrier , et al.更多还原