电弧及辉光微等离子体大气压取样的发射光谱研究

在线化学分析需要实现开放环境下的样品取样和电离/激发。相比于激光切削或者激光诱导击穿，大气压微等离子体系统结构简单，更利于小型化。因而基于大气压微等离子体的在线化学分析技术引起行业的广泛关注。为了确定合适的微等离子体源进行样品的在线元素检测，需要进一步了解各放电模式及工作参数下微等离子体的自身特性以及取样效果。该工作主要研究了电弧及辉光放电微等离子体在大气压下对样品铁取样发射光谱的特性。实现了在开放环境下对高熔点金属样品的在线检测，并发现电弧放电微等离子体与光谱分析源联用具有更高的取样效率。高采样效率的电弧放电微等离子体源为实现金属及难解离样品的检测提供了一种新的方法。同时，相较于传统的取样装置，避免了复杂的样品制备、样品传输过程。实验装置采取简单的针对板放电结构，分别利用高压脉冲电源、直流电源获得电弧放电和辉光放电。实验的结果表明，在放电功率近似相等的条件下，电弧放电产生的微等离子体对样品铁取样的光学发射谱中，样品元素的特征谱线占据主导地位，同时伴随有空气中氮气的谱线，而且铁离子(FeⅡ)谱线的相对强度显著高于氮气分子谱线的相对强度。而在直流辉光放电中，样品铁原子(FeⅠ)谱线相对强度非常不明显。由此说明，电弧放电产生的微等离子体具有更高的采样效率。放电在样品表面留下的溅射坑也得出了相同的结论。增加辉光放电电流到25 mA，发现样品元素铁的谱线仍然没有明显的增强。同时，也研究了采样间距对两种采样模式的影响。实验结果表明，间距对两种模式的采样光谱没有显著的影响。采用主要成分为铝的合金铝箔进行了上述对比实验，得出相同的结论，即电弧放电微等离子体更适合作为光谱分析源来实现对金属样品的实时快速检测。

Comparison of the Optical Emission Spectra of Iron Sample in Pulsed Arc and Glow Micro-Discharge under Ambient Atmosphere

In-stu chemical analysis requires sampling and ionization/excitation of sample in an open environment. The atmospheric pressure micro-plasma system is in a simpler structure and more advantageous for miniaturization than laser cutting or laser induced breakdown. Therefore, in-stu chemical analysis technology based on atmospheric pressure micro-plasma has attracted widespread attention in the industry. The micro-plasma sources produced by different excitation supplies have different parameter characteristics and sampling characteristics. In order to determine the appropriate micro-plasma source for in-stu element detecting, it is necessary to further understand the sampling and characteristics of the micro-plasma under each discharge mode and operating parameters. This paper focuses on the optical emission spectra of direct current(DC) glow and pulsed arc plasmas acting on iron samples in ambient atmosphere. The on-line detection of high melting point metal samples in an open environment was realized, and we also found that the arc discharge micro-plasma combined with the spectral analysis source has higher sampling efficiency. The high sampling efficiency of the arc discharge microplasma source provides a new method for the detection of metals and difficult to dissociate samples. At the same time, complex sample preparation and sample transfer processes were avoided compared to conventional sampling devices. The experimental device adopts a typical needle-plate discharge structure, which has the advantages of low price, convenient operation and quick analysis. Arc discharge and glow discharge are realized by using a high voltage pulse power source and a DC power source respectively. The sampling results of the two ways indicate that at the input of similar discharge power, the optical emission spectrum of the sample iron stimulated by the arc discharge micro-plasma, sample element lines occupies dominant position in the spectrum, accompanied by the line of nitrogen in the air. And the relative intensity of the iron ion (FeⅡ) line is higher than the relative intensity of the nitrogen molecule line. In the DC glow discharge, the relative intensity of the sample iron atom (FeⅠ) line is very weak. This shows that the micro-plasma generated by the arc discharge has higher sampling efficiency. The sputtering crater left on the surface of the sample can draw the same conclusion. The glow discharge current was increased to 25 mA, the spectral line of the sample elemental iron was still not significantly enhanced. At the same time, the effect of sampling spacing on the two sampling modes was also studied. Experimental results show that the spacing has no significant effect on the both sampling spectra of the two modes. In this paper, the above-mentioned comparative experiment was also carried out using the alloy aluminum foil whose main component is aluminum, and the same conclusion was obtained. It is concluded that the arc discharge micro-plasma is more suitable as a source of spectral analysis to achieve real-time rapid detection of metal samples.