Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 61875055)
Received Date:30 November 2020
Accepted Date:23 December 2020
Available Online:13 May 2021
Published Online:20 May 2021
Abstract:Bismuth brass has very good mechanical properties and is friendly to environment. Therefore, it can be widely used in different fields. In order to realize the convenient, rapid and sensitive elemental analysis of trace elements in bismuth brass, fiber laser based high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) is developed. In the experiments, a compact fiber laser operated at 5 kHz pulse repetition rate is used to ablate the sample and produce plasma, and the spark discharge is used to further break down the ablated sample and enhance the plasma emission for sensitive elemental analysis. A compact fiber-optic spectrometer coupled with non-intensified charge-coupled device (CCD) is used to record the spectra. Bismuth, lead and tin in several bismuth brass standard samples are quantitatively analyzed. The plasma temperature is determined to be about 7962 ± 300 K by using the Boltzmann plots of copper, zinc and tin elements; the electron density is determined to be about 1.049 × 10–17 cm–3 based on the Stark broadening of Cu (I) 510.47 nm analytical line. The plasma is determined to be in local thermodynamic equilibrium (LTE) state according to McWhirter criterion as well as appended criteria for transient plasma. Under the present experimental condition, the calibration curves of bismuth, lead and tin in bismuth brass are built with fitting goodness of higher than 95%. The detection limits of bismuth, lead and tin are determined to be 25.5 ppm, 64.2 ppm and 316.5 ppm, respectively. The weak transition probability of tin atoms leads to worse detection limit of tin than the scenarios of bismuth and lead. The ways to further improve the analytical sensitivity and minimize system dimensions are discussed in this article. It is demonstrated that high repetition rate laser-ablation spark-induced breakdown spectrometer based on compact fiber laser as well as compact fiber-optic spectrometer can be used to realize the convenient, rapid and sensitive elemental analysis of trace elements in bismuth brass. This study is also helpful in analyzing the trace harmful elements, including bismuth, lead and tin in high temperature alloys with HRR LA-SIBS. In comparison with laser-induced breakdown spectroscopy (LIBS), the HRR LA-SIBS technique has several intrinsic advantages, such as fast spectral data collection speed, cost-effective system and low continuum background and so on. This technique is very useful in implementing the elemental analysis of different alloy samples and can be potentially used in metallurgical industry in the future. Keywords:laser-ablation/ spark-induced breakdown spectroscopy/ bismuth brass/ elemental analysis/ compact
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2.实 验本研究所采用的HRR LA-SIBS的实验装置如图1所示. 实验装置主要由激光剥离、火花放电和光谱记录三部分组成. 采用一台MOPA (main oscillator + power amplifier) 型的光纤激光器(深圳市创鑫激光股份有限公司, 型号: MFPT-70P)作为剥离激光光源. 该激光器的主机大小为35 cm×26 cm × 12 cm, 输出激光的中心波长为1064 nm, 最大输出单脉冲能量为1.0 mJ, 脉宽在50—350 ns范围内可调, 激光脉冲的重复频率在1—1000 kHz范围内可调, 光束的品质因子M2为1.2. 实验中选择脉冲重复频率为5 kHz, 脉冲宽度为100 ns. 激光束经过一个焦距f = 60 mm的球透镜L1垂直聚焦于样品表面剥离样品并产生激光等离子体, 采用火花放电进一步击穿被剥离的样品并增强等离子体的光学辐射. 图 1 基于光纤激光器的HRR LA-SIBS的实验装置示意图 Figure1. Schematic diagram of the experimental setup of fiber laser based HRR LA-SIBS.