Thermally induced phase transition of troilite during micro-raman spectroscopy analysis

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2023-01, Vol.390, p.115299, Article 115299
• Main Authors: Li, Xiaoguang, Chen, Yi, Tang, Xu, Gu, Lixin, Yuan, Jiangyan, Su, Wen, Tian, Hengci, Luo, Huiqian, Cai, Shuhui, Komarneni, Sridhar
• Format: Article
• Language: English
• Subjects: Laser irradiation; Magnetite; Nanophase metallic iron; Raman spectroscopy; Troilite
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2022.115299

Troilite is one type of FeS polymorph formed under reducing environmental conditions. However, its phase transition by laser heating during Raman analysis has not been investigated in detail. This study focuses on identifying changes to Raman spectra of troilite resulted by laser heating during Raman analysis so as to determine optimized analytical conditions for characterizing iron sulfides. We comfirm that iron sulfides exposed in air are easily transformed to magnetite and hematite after a high-power laser (> 200 mW/μm2 for pyrite and > 14 mW/μm2 for troilite) irradiation. Troilite crystal structure is also broken easily by laser (>12 mW/μm2) under the vacuum conditions due to the volatilization of S and Fe, possibly inducing the formation of nanophase metallic iron. Therefore, iron sulfides are expected to be sensitive to laser heating. Here, we have confirmed the laser heating effect through a set of heating experiments from ambient temperature to 500 °C with various laser powers. Our results suggest that Raman analysis for troilite should be performed with a low laser power of