A portable thermo-Raman system for the in-situ analysis of macro-scale mineral samples

Abstract

A portable thermo-Raman system (PTRS) for the in-situ analysis of macro-scale materials is presented and evaluated. The system integrates a compact Raman spectrometer with a custom-built resistive heating stage and standoff optics, enabling measurements at working distances of 10-25 cm without the need for optical windows. This design allows for a spatially averaged analysis of heterogeneous bulk samples and facilitates measurements under conditions that are not accessible to conventional laboratory setups. The temperature calibration demonstrated linear heating behavior with deviations within +/- 6 K. The performance of the PTRS was assessed using reference materials (silicon carbide, potassium nitrate) and synthetic hydrated sulfates. The system reliably tracked phase evolution and dehydration processes, with results consistent with laboratory thermo-Raman measurements and literature data. Systematic shifts in the apparent transition temperatures (typically 5-20 degrees C) were observed and are attributed to differences in the heat transfer, sample geometry, and thermal equilibration. The results demonstrate that PTRS provides robust qualitative information on thermally induced phase transformations in bulk materials. Due to its portability and mechanical simplicity, the system represents a promising approach for field-based thermoanalytical investigations of metastable and environmentally sensitive mineral phases.