Metallurgical Consideration on the Calibration Curve for Binary Alloy Samples in Low-pressure Argon Laser-induced Plasma Spectrometry

The composition dependence of the emission intensities was investigated in Cu-Ni as well as Ni-Zn binary alloy samples when a low-pressure argon laser-induced plasma was employed as the excitation source. The calibration curve in the Cu-Ni alloy system gave a linear relationship, implying that the selective evaporation of Cu or Ni atoms was caused less in those alloys having several chemical compositions. The Cu-Ni binary alloy has a solid solution phase all over the chemical compositions (all-proportional solid solution): Cu and Ni atoms form no intermetallic compounds but can occupy any positions of a face-centered cubic lattice without any particular interaction. This metallurgical structure would enable Cu and Ni atoms to be released from the sample surface individually, which means that the amount of ablation corresponds to the chemical composition of the alloy sample. For a comparison, a Ni-Zn binary alloy system was also investigated to find calibration curves yielding a nonlinear relationship, differing from those of the Cu-Ni alloy. The reason for this is that the Ni-Zn binary alloy has several metallurgical phases comprising different intermetallic compounds which would each vary the evaporation behavior of Zn. It should be paid attention in LIPS that the ablated composition after laser irradiation is sometimes different from the chemical composition, depending on the kinds of samples and their metallurgical structures.