High-fidelity and high-resolution phase mapping of granites via confocal Raman imaging

Abstract

In physical sciences such as chemistry and earth sciences, specifically for characterization of minerals in a rock, automated, objective mapping methods based on elemental analysis have replaced traditional optical petrography. However, mineral phase maps obtained from these newer approaches rely on conversion of elemental compositions to mineralogical compositions and thus cannot distinguish mineral polymorphs. Secondly, these techniques often require laborious sample preparations such as sectioning, polishing, and coating which are time-consuming. Here, we develop a new Raman imaging protocol that is capable of mapping unpolished samples with an auto-focusing Z-mapping feature that allows direct fingerprinting of different polymorphs. Specifically, we report a new methodology for generating high fidelity phase maps by exploiting characteristic peak intensity ratios which can be extended to any multi-phase, heterogenous system. Collectively, these enhancements allow us to rapidly map an unpolished granite specimen (~ 2 × 2 mm) with an exceptionally high accuracy (> 97%) and an extremely fine spatial resolution (< 0.3–2 µm).

Tracking spatiotemporal evolution of cementitious carbonation via Raman imaging

“…The definitive Raman phase maps were generated using a methodology from the recently published work on granite. [ 25 ] In summary, the Raman peaks of calcium hydroxide and calcium carbonate as assigned as characteristic peaks. Principal component analysis (PCA) was performed in Project Five 5.2 WITec software to generate a contrast image.…”

“…Detailed methodology for generating phase maps from elemental maps was explained in a recent publication. [ 25 ]…”

“…More importantly, by obtaining large area, mm‐scale maps (1 × 1 mm), we are able to gain sufficient statistics to reliably determine the extent of carbonation. We have recently demonstrated that large‐area, high‐resolution maps are highly useful in phase quantification of heterogenous, static systems ranging from granites [ 25 ] to cement clinkers. [ 26 ] And so here, extending this large‐area, high‐resolution mapping approach to a dynamic phenomenon such as carbonation is the main objective of this study.…”

A Comprehensive Review on Raman Spectroscopy Applications

“…Polavaram et al [174] proposed an innovative protocol to create 2D maps of mineralogical samples. The method proposed in this work greatly reduce the analysis times as it is able to analyze non-polished samples with an auto-focusing Z-mapping feature that allows for identifying different polymorphs with great accuracy (<97%) and a high spatial resolution (<0.3-2 µm).…”

Impact of Na/Al Ratio on the Extent of Alkali-Activation Reaction: Non-linearity and Diminishing Returns

“…Raman spectroscopy and imaging were used in this study with the aim of recognizing the spectrum representing metakaolin and then mapping and quantifying the presence of this spectrum in the AAM scans. Recently, Raman imaging has been instrumental in understanding various complex, heterogeneous systems such as granites (Polavaram and Garg, 2021b), pure cement phases (Potgieter-Vermaak et al, 2006), phase quantification in anhydrous cements (Polavaram and Garg, 2021a), hydrating cements (Loh et al, 2021), calcium aluminate cements (Black et al, 2006;Torréns-Martín et al, 2013a), and sulfate-attacked cementitious materials (Yue et al, 2013). The purpose of applying Raman spectroscopy and imaging here was to estimate the (Zhang et al, 2000), and reference Analcime (Na(AlSi 2 O 6 )•H2O) (Presser et al, 2008;Tsai et al, 2021).…”