利用大气压脉冲微放电剥蚀源对铝合金进行光谱分析。 该针板结构微放电装置具有价格低廉、 操作便捷、 分析快速等特点。 脉冲放电能瞬间注入极大的放电能量, 不致使样品融化, 进而保证放电的稳定性。 在几微秒的时间内, 对钨针电极施加近-4 000 V的高压, 电极间迅速形成放电通道, 针尖和样品之间形成高达20 A的电流, 造成对样品的剥蚀, 并对被剥蚀的粒子进行激发。 单次放电脉冲注入能量约为85 mJ, 能量以电流的形式传递于放电电极。 剥蚀形貌图表明放电微等离子体局域在电极间隙, 针尖轴向上的能量传递和电流密度远高于离轴区域。 为了深入研究剥蚀机制和物理性质, 对等离子体源的电学特性进行了讨论。 通过精确的时序拍摄技术观测了等离子体的演化过程, 从ICCD相机的快速成像结果可以看到等离子体源寿命与脉冲高压放电源的脉宽相当, 发光强度与放电电流变化趋势相吻合。 与光谱分析装置相连接, 脉冲微放电剥蚀源可有效激发合金样品中的铝、 镁、 锰、 铜等元素原子谱线。 对放电过程等离子体光谱特性进行考察, 利用玻尔兹曼斜线法和Stark展宽法计算等离子体电子温度和电子数密度, 分别得到过程中等离子体电子激发温度约6 700 K, 等离子体电子数密度约1017 cm-3量级, 并验证了放电处于局域热平衡状态。 探究其定量分析性能, 结果表明该脉冲微放电等离子体直接作为一种光谱分析源可实现对铝合金样品快速定量分析。

The pulsed micro-discharge ablation source was applied to the optical spectra analysis of the aluminum alloy at atmospheric pressure. This needle-plane micro-discharge device has the merits of low cost, easy operation and fast analysis. Pulsed discharge allows large instantaneous input power without melting the sample, which is vital to keep the stability of the discharge. In the duration of a few microseconds, high voltage of about -4 000 V was applied to the tungsten needle electrode, which quickly initiates a discharge channel between the electrode and electrode, and results in current of 20 A between the tungsten needle tip and the sample. Thus, the sample was ablated before ablated particles were excited. The deposition energy, whose value was approximately 85 mJ per discharge pulse, was transmitted between the two discharge electrodes by means of the electric current. The surface morphology of the ablation crater generated by this pulsed needle-plane discharge indicated that a local micro-plasma was formed in the electrode gap. In addition, the on-axial energy flux and current density were much higher than those of the off-axis region. In order to further investigate the ablation mechanisms and physical properties, the electrical characteristic of this plasma source was discussed. The time evolution process of the discharge plasma was studied through precise timing shooting technique. From the fast imaging results of the ICCD camera, it could be seen that the lifetime of the plasma source was comparable with the pulse width of the high-voltage discharge source, and what was more, the change of optical intensity of plasma source showed good agreement with the variation of discharge current. Combined with an optical spectrometer, the pulsed micro-discharge ablation source could well excite atomic lines of aluminum, magnesium, manganese, bronze, and more in the alloy sample. The spectral characteristics of the discharge plasma were studied further. The electron excitation temperature of the discharge plasma was determined as about 6 700 K and the electron number density was obtained in the order of 1017 cm-3 using the Boltzmann plot method and Stark broadening of line, respectively. Besides, it was verified that the discharge plasma generated in this experiment was in local thermal equilibrium state. A further attempt was made to demonstrate the ability of this technique in quantitative analysis. Our results showed that the pulse micro-discharge plasma employed as spectral analysis source was an effective method for the quantitative analysis of aluminum alloy sample.