【作者】 魏风波；

【导师】 朱亮；

【作者基本信息】 兰州理工大学 ， 材料学， 2007， 硕士

【摘要】 电爆法是在一定的气体介质环境下，预先储存的电能对金属导体(导体丝或箔)脉冲放电，脉冲大电流使得金属导体熔化、气化、膨胀，发生爆炸。电爆法可以用来制备金属、合金、金属氧化物及氮化物等超细粉，具有能量利用率高，工艺参数可调，可有效控制制备粉末的粒度，不污染环境，所制粉末粒度分布窄、纯度高、化学活性高、不易团聚等特点。一般的丝导体电爆装置一般都是将丝导体通过夹具固定在两个电极之间，或者丝一端固定、一端触碰电极进行电爆，电爆的丝导体长度通常不能调节，其直径也受到一定限制。这些电爆方式中的丝导体都与电极接触，这样很容易出现一些问题，如电爆过程能量释放不充分，可能损伤电极以及所制备粉末中出现较多大颗粒等。因此，本文提出了一种丝导体电爆制备超细粉的新方法，丝可以在高压电场中无需与电极直接接触而电爆。这样就很好地解决了夹持式电爆容易出现的问题。本文在课题先期研究的基础上研制了一种丝导体无接触电爆实验设备。该设备主要由丝导体整列送进装置、电爆炸装置、粉末收集系统和高电压电路及控制系统四部分组成。该设备结构合理，操作简便，最主要的特点就是丝导体在电爆中是自由的，不需要用夹具固定在两个电爆电极之间。这样一方面使得所能电爆的丝导体不再受到长度和直径的限制。另外还可省去夹具操作机构、高压间隙开关以及开关行程控制系统，从而大大降低了设备的复杂度，提高了运行稳定性；能连续电爆炸丝导体，目前实验电爆炸频率为10次／分钟。电爆的过程参数可调，对不同规格的丝导体其适应性较强。在不同过程参数下进行电爆铜丝实验，研究了丝导体无接触电爆的特点以及用于制备金属超细粉的可行性。影响整个丝导体电爆过程的因素概括起来有：1)电爆最初阶段出现的电弧放电和此时形成等离子决定着丝导体电爆炸的起始状态，直接影响丝导体从固态加热、熔化，变成液态金属达到汽化状态前的整个加热过程。可以通过调节一些过程参数来改变这个加热过程。2)能量密度，即金属单位体积内所沉积的能量。电流密度直接影响着能量密度。电流密度越大，加热速度就越大，金属就可以在更短的时间内沉积更多的能量，电爆炸起始点就倾向在高能区出现，当能量密度高于金属的比电流作用时表现为快爆炸。在无接触电爆丝导体制备金属超细粉时，通过调节过程参数以获得不同粒径的超细粉。对电爆过程参数进行优化匹配，可使爆炸时沉积到金属的能量达到最大，从而使得紧接着发生的爆炸达到极大特征，因而可得到粒度均匀细小的高质量超细粉。在高能量快速作用下，大部分金属直接气化形成极微细粒子，爆炸冲击波驱使粒子在介质中高速运动形成了细小而均匀的颗粒。而在较低能量作用下丝导体首先发生熔化，只有小部分被蒸发，剩余金属经过爆炸冲击波作用形成熔滴和碎片，得到的粉末部分颗粒粗大或成片状，形貌不规则。接下来进行电爆炸铜丝制备粉末，获得了铜和铜的氧化物超细粉，研究了电爆过程参数对粉末的粒度和形态的影响。利用扫描电镜和透射电镜观察粉末形貌，利用激光粒度测试仪和电镜测量法分析粉末的粒度分布。电镜观察到粉末颗粒的微观形态多数为球形，有一部分呈不规则多面体状。激光粒度测试的粉末二次颗粒成正态部分布；电镜分析了部分粉末颗粒，中位径都在60nm以下，粒径主要分布在0.02μm～0.3μm。更多还原

【Abstract】 When a pre-stored electrical energy loaded upon a thin conductor (including wires and foils)fleetly in some ambience, a pulsed current generated through the conductor and the energy will be transferred to heat energy in high speed, supervene the fast electrothermal effect. The conductor will be melted, evaporated and ionized, resulting in a plasma that expands into the medium. This process is commonly called Conductor Electrical Explosion, and it can be used to produce ultra-fine powders of pure metal, alloy, metal nitrides and metal oxides. This application is provided with many advantages, such as high efficiency of energy, governable process variables, applicability of different metals, environmental friendliness, and so on. And this technics have more significant points in preparing powders, the characteristics of powders as follows: high purity, reactive and well-dispersed with narrow distribution.The device of wire electrical explosion(WEE)is generally designed as: the wire conductor is fixed by the clamps collocated in each electrode, or one end of the conductor is nipped, and another is non-restraint. The wire length always restricted by the interspace between two electrodes, and the wire diameter cannot be too large or too small, additionally, there are several defective aspects of device such as energy unable released completely, the two electrodes would be possibly broken in the forceful blast, and some tinpot presents in the powders prepared by this method.A novel method of preparing ultra-fine powder by wire explosion was proposed in respect of above devices, the metal wires could be exploded electrically in the high voltage electric field without contacting with electrodes. The limitations citied above are smoothly resolved.The un-contacted equipment of WEE is advisedly developed in this paper, which can be called "UCE-WEE". This equipment consists up "arranging-feeding" parts of wire, the vessel of wire electrical exploding, the powders collecting system, high voltage circuit and its controlling system. The makeup becomes more simple, and the operation is relatively flexible. The primary feature is that wire is completely non-restraint, wire no longer be fixed by clamps, and therefore this device can adjust wires with different length and diameter. In addition, the clamps, the gap switch and its operating system are removed, so the configuration of the equipment become more compact, and the managing reliability is well improved. We can explode wire continually using this new method, with presently frequency reaches 10 times/min.We exploded sets of Cu wires with different diameters and different lengths, in order to research the electrical explosion of un-contacted wires, and attest the possibility of application in preparing ultra-fine powders.The crucial factors which markedly influence the whole explosion are concluded generally as follows:1) Arc discharge and preliminary formation of plasma in the initial heating stage. Discharge and plasma in the initial heating stage determine the starting state of electrical explosion, because the transformation above observably exert an influence on the whole heating action which from wire solid state, melting, melted to liquate state till gasification. Many research reveals the transformation is controllable, so we can shift this energy-cumulating process by changing some parameters.2) Energy density. Energy density is named as the energy deposited the volume unit of metal. The explosion of materials inclines to start in the high-density sections if energy density is increased obviously, in addition, the explosion behave as fastexplosion when energy density excesses over the integral action of specific current.We discover that powders show some susceptivity to the process parameters when applying this new method to preparing powders. The energy deposited in wire during explosion of wire in some conditions is controllable to reach a high-point, and the explosion up to the utmost. If the energy is high enough, the process seemed as fast explosion, most of the material vaporizes into the medium and forms superfine droplets, the droplets impelled by the blast and turns into small particles. But if the energy is quite low, there is a small part of material vaporizes into the medium, the rest forms some large droplets and fragments, the last products contains a lot of large particles which always have irregular shapes.People can explode the wires under well-matched process parameters to obtain conceivable powdersAnd next, exploding copper wire experiments with "UCE-WEE" were carried out with a variety of process parameters to prepare the ultra-fine powder which includes Cu and oxides. Particle size distributions measured by laser particle sizer, the results indicate that large number of quadratic particles present in powders. In SEM and TEM images of the powders, particles display as round and polygon shaped, with size reach nanosize. We measured a finite number of particles in these images, and analyzed the data with the "log-normal" function , the results show that the median diameters of some powders are lower than 60nm, and granularity have the range from 0.02 μm～0.3μm.更多还原