Preparation Of Metallic Ultra-fine Powders Using Wire Electrical Explosion Method And Development Of The Apparatus

Ultra-fine powder has nowadays become one of the most important materials.Because of having most different and novel physical chemistry characteristics and potential applications, it has become the need of modern high technology developing.Wire electrical explosion is that a pulsed current is fed into a metallic wire that ambient gas,making wire be melted ,evaporated and ionized ,rusulting 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 and so on .WEE has many advantages, such as utilizing energy with high efficiency, controlling the process variables easily, approving the granularity, being friendly to environment, producing highly pure reactive with narrow distribution.An experimental apparatus of electrical explosion of metal wire, in which the wire isn't contacted with electrodes in the high voltage field, is developed in this paper.The wire erect drop into the high voltage field by gravitation and explode quickly. This apparatus is composed of the aligning and segmenting setup, explosion room, high-voltage charging and discharging circuit-system, controlling and assistant system, powder collecting setup and so on.Adopting direct current electromotor bring along wheels which deliver wire lineally and cut the wire by definite matching.The cutting wires explode quickly and continuously in the the high voltage field which is surrounding different ambiences. This setup has many advantages,such as , working stably, controlling process variables easily, charging and discharging energy quickly, being operated easily and high automatization.With variations of the distance between electrodes, length of the segmented metal wire, and voltage of electrical field, a series of experimental explosion of segmented metal wire is carried out in the high voltage field. It is observed that the breakdown between electrodes and tips of the segmented wire, provides the channels through which the current flow in the segmented wire for explosion to occur, so that ablation of the electrodes could be alleviated. It is evident that the end tips of the segmented metal wire, around the point of air breakdown which is known as the shunting arc, do not explode in the same way as the rest of the wire, the length of the non-exploded tip is about 0.5-2 mm.because of the electrical explosion process under the air condition, the gotten Ultra-fine powder is become oxidation . The powder is composed of CuO, Cu₂O,Cu and the color is black.The SEM images of the powders are sphere-shaped, showing that the average particle size of some powders grain size reaching nano-size.The condition of wire electrical explosion in the high voltage field is that the current flow must transfer to wire segment by electrode immediately. But in the wire electrical explosion experiments, the electrical contacts do not occur directly between wire and electrode. The breakdown between electrodes and tips of the segmented wire, provide the channels through which the current flow in the segmented wire for explosion to occur. The plasma arc occur between electrodes and tips of the segmented wire before the wire electrical explosion. Because of the high voltage, the plasma arc is clamberring among surface of wire and and is surrounding a spot of wire .when the explosion to occur, around the point of air breakdown which is known as the shunting arc, the tip of the wire do not explode in the same way as the rest of the wire .According to observing and studing the wire electrical explosion experiments, It is find that the suitable process condition of wire electrical explosion for powder preparation in the high voltage field is that, for the given field voltages of 6 kV, 7 kV and 8 kV, the corresponding ranges of difference between electrode span and wire length are 1.8-4 mm ,2.2-5.8 mm and 3.2-8 mm, respectively.In this paper, the explosion processing factors which determine characteristics of Ultra-fine powder include voltage,energy, diameterand length of wire,electrode span, inductance of circuitry, resistance of discharging circuitry.At given conditions,the voltage, diameterand length of wire ,electrode span will have an effect on the diameter of powder. When process parameters matched properly, energy density and instantaneous power could reach as high as possible, resulting in producing highest current peak and strongest blast, and uniformfine powders with high quality could be obtained.The physical mechanism of wire characteristics and physical mechanism explosion is studied.The electric of electrical explosion of wire have been investigated from changing process of current, release process of energy and characteristics of needle-plate asymmetry high voltage electric field.