Semi-Quantitative Mineralogical Analysis of Ceramic Coatings and Their Raw Materials Using ATR-FTIR Spectroscopy

Fourier Transform Infrared Spectroscopy (FTIR) is increasingly used for the mineralogical characterization of complex materials such as ceramics, soils and clays. However, its quantitative application remains limited due to spectral overlapping and matrix effects in solid samples. In this study, a semi-quantitative mineralogical analysis method based on Attenuated Total Reflectance FTIR (ATR-FTIR) is proposed. The method uses the principal absorption band of calcite as a normalization reference in order to estimate relative molar absorptivity coefficients according to the Lambert–Beer law. Experimental spectra obtained from pure minerals and laboratory mineral mixtures were analyzed using derivative spectroscopy and numerical optimization. The correlation between experimental and calculated spectra was performed using the GAMS equation modeling environment and the nonlinear programming solver CONOPT. Mineral mixtures were used to determine the minimum detectable band intensity and detection limits. Bands with normalized intensities lower than 0.01 were discarded, corresponding to a detection limit of approximately 7 mol%. Application of the proposed methodology to ceramic coatings samples from Teruel and Castellón demonstrated that the FTIR spectra are dominated by aluminosilicate bands associated with quartz and clay minerals, together with carbonate features attributable to calcite. These results are consistent with the expected mineralogical composition of ceramic raw materials and confirm the suitability of the method for analyzing natural samples. However, the ATR-FTIR method presents several inherent limitations that may affect both the accuracy and reproducibility of spectral data.