研究目的
To develop and validate a novel double quantification methodology using Raman imaging and Laser Induce Breakdown Spectroscopy (LIBS) for analyzing original and degradation materials in Cultural Heritage samples, particularly focusing on hydrated compounds like calcium oxalate layers on marble.
研究成果
The combination of Raman imaging and LIBS provides a reliable and comparable quantitative method for analyzing hydrated mineral phases in Cultural Heritage materials. Both techniques yield consistent results within uncertainties, with Raman offering lower uncertainties. The confocality of Raman spectroscopy allows nondestructive depth analysis, useful for assessing layer thicknesses. This methodology can be extended to other hydrated salts and applied in situ with portable instruments, enhancing field studies in heritage conservation.
研究不足
The methodology requires reference spectra for all compounds present, collected under identical experimental conditions. LIBS measurements are affected by atmospheric moisture, introducing variability. Raman imaging is not portable, limiting in-situ application for this aspect. The technique may not be suitable for samples with very complex or unknown compositions without prior knowledge.
1：Experimental Design and Method Selection:
The study employs a combination of Raman imaging and LIBS for quantitative analysis. Raman imaging provides molecular information with high representativeness, while LIBS offers elemental analysis, especially for light elements like hydrogen. The methodology is designed to be nondestructive and applicable in situ with portable instruments.
2：Sample Selection and Data Sources:
Nine calcitic and dolomitic marble samples with or without a calcium oxalate (whewellite) layer were used. Standard compounds (calcite, bassanite, whewellite, gypsum, epsomite, mirabilite) with known H2O content were employed for calibration.
3：List of Experimental Equipment and Materials:
Equipment includes a Raman InVia spectrometer (Renishaw) with StreamLine image tool, a handheld InnoRam spectrometer (BWTek Inc.), and a portable easyLIBS spectrometer (IVEA system, model Easy 2C). Materials include marble samples and standard compounds from Sigma-Aldrich.
4：Experimental Procedures and Operational Workflow:
Raman measurements were performed using a 532-nm laser with optimized power and spectral resolution. LIBS measurements used a Nd:YAG laser at 1064 nm. Data were collected from homogeneous areas of 200x200 μm for Raman and similar spots for LIBS. Pretreatment included baseline correction, cosmic ray removal, and noise filtering. Quantitative analysis used Direct Classical Least Squares (DCLS) algorithm for Raman and univariate calibration for LIBS based on hydrogen band area.
5：Data Analysis Methods:
Chemometric analysis was applied, including DCLS for Raman spectra decomposition and linear regression for LIBS calibration. Statistical analysis provided mean concentrations and uncertainties.
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