高温合金痕量分析中激光剥蚀电感耦合等离子体质谱的分馏效应机理研究

Study on Fractionation Effects in Superalloy Trace Analysis by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

详细研究了高温合金样品剥蚀过程中激光脉冲能量及频率与高温合金痕量元素信号强度的变化及其稳定性、能量密度对信号稳定性的影响,实现了激光对样品表面的层层剥蚀,从而使高温合金中低沸点元素被稳定地蒸发,并初步建立了激光剥蚀过程中理想的样品激发动力学模型。研究表明,激光剥蚀的过程是一个在固-液-气的相变基础上进行的热蒸发过程,分馏效应是基于各元素不同的蒸发能而发生的低沸点元素的选择性蒸发;随着剥蚀的层层推进,热效应的累积导致样品表面气化层下方的固-液相变,低熔点元素出现局域富集从而使信号增强是分馏效应的另一原因。

Some investigations have been done on the ablated surface of superalloy sample, the intensity stability to laser energy density, and the intensity changing curve corresponding to the laser pulse voltage and frequency. Samples have been ablated layer by layer under the optimum laser condition, and the lower boiling point elements evaporated steadily. The ideal inspiring dynamics model for laser ablation has been established. Results show that the laser ablation is a thermal evaporation process based on phase transformation in the solid - liquid - gas three-phase system. Fractionation effects are mainly caused by selective evaporation of the elements with lower boiling point for the different evaporation energy. With the ablation proceeding, phase transformation from the solid to the liquid happened due to the heat accumulation under the gasified layer of sample surface. The local enrichment of lower melting point elements during phase transformation induced to the abrupt enhancement of their signal intensities. It is also one of the reasons for fractionation effects.