The Research On Preparation Of Metallic Ultra-fine Powders Using Wire Electrical Explosion Method

Wire electrical explosion (WEE) is that a pulsed current is fed into a metallic wire that located in an ambient gas, making wire be melted, evaporated and ionized, resulting in a plasma that expands into ambient gas and producing strong blast. This technique can be used to produce ultra-fine powders of pure metal, alloy, metal nitride and metal oxide. WEE has many advantages, such as, utilizing energy with high efficiency, controlling the process variables easily, being friendly to environment, producing highly pure, reactive and dispersed powders with narrow distribution.The experimental equipment of exploding wire continually to prepare ultra-fine powders has been designed and fabricated in this paper. The equipment is composed of feeding setup of wire, high-voltage circuit system, controlling circuit system, powder collecting setup and so on. The equipment keeps the wire straight to be fed automatically, working stably;process variables can be controlled easily, and high productivity can be realized;the equipment has simple and reasonable structure, being operated easily. Wires can be exploded continually, with exploding frequency reaching 20 times/min.Exploding copper wire experiments were carried out with a variety of process parameters to prepare the ultra-fine powder of Cu and CuO. The effects of process parameters of wire explosion on the size and shape of the powder were studied. The powder is composed of CuO, Cu₂O, Cu. Particle size distributions measured by laser particle sizer have the range from 0.2 μm to 0.8 μm and the average of 0.5μm. The SEM images of the powders are sphere-shaped and polygon-shaped, showing that the average particle size of some powders is 48 nm. The grain is very fine, with grain size reaching nanosize.The factors which determine explosion of wire include energy density and instantaneous power. These two factors are affected by following process parameters: initial charging voltage, capacitance, inductance of circuit and size of wire. In given conditions, energy density liberated in the wire and instantaneous power of wire explosion could be increased by raising charging voltage, increasing capacitance and reducing diameter of wire andinductance of discharging circuit, and finer powders could be obtained. Powders with different particle could be prepared by adjusting process parameters. The process parameters must be matched properly, so that energy density and instantaneous power could reach as high as possible, resulting in producing highest current peak and strongest blast, and uniform, fine powders with high quality could be obtained. When energy density liberated in wire is large enough, the wire is evaporated fully. Metallic atom and ion can get high speed by strong blast and is more difficult to combine, result in producing uniform and fine powders. If not, the wire isn't evaporated fully, producing large molten drop and fragment after explosion and making the powder particle big and flake shape or other irregular shapes.The physical mechanism of wire explosion is studied. The electric characteristics and physical mechanism of electrical explosion of wire have been investigated from changing process of voltage, current, resistance, release process of energy and changing of wire's modality in explosion.