Determination of the Degree of Structural Heterogeneity of Kaolinites by the Decomposition of Their IR Spectra in the OH-Stretching Vibration Region

A new approach is proposed to assess the degree of defect density of kaolinite minerals using their IR spectra in the OH-stretching vibration region. Three linear equations were obtained that relate the ratios of spectroscopic parameters to each other: \(\frac{{A\left( {{{\nu }_{3}}} \right)}}{{A\left( {{{\nu }_{3}}} \right) + A\left( {{{\nu }_{2}}} \right)}} = - {\kern 1pt} 0.2177\frac{{FWHM\left( {{{\nu }_{1}}} \right)}}{{FWHM\left( {{{\nu }_{4}}} \right)}}\) + 1.247; \(\frac{{FWHM\left( {{{\nu }_{3}}} \right)}}{{FWHM\left( {{{\nu }_{2}}} \right)}} = - 0.5804\frac{{FWHM\left( {{{\nu }_{1}}} \right)}}{{FWHM\left( {{{\nu }_{4}}} \right)}}\) + 2.8696; \(\frac{{FWHM\left( {{{\nu }_{3}}} \right)}}{{FWHM\left( {{{\nu }_{2}}} \right)}} = 2.636\frac{{A\left( {{{\nu }_{3}}} \right)}}{{A\left( {{{\nu }_{3}}} \right) + A\left( {{{\nu }_{2}}} \right)}} - 0.4437\), where: FWHM(ν_i) is a full width at half maximum and A(ν_i) is the integral intensity of Lorentzian absorption bands at ν₁ ~ 3697 cm^–1, ν₂ ~ 3670 cm^–1, ν₃ ~ 3652 cm^–1 and ν₄ ~ 3620 cm^–1, respectively. These equations made it possible to establish criteria for decomposing the IR spectra into individual bands (ν_i) and determining the optimal values for the FWHM(ν_i) and A(ν_i) parameters used for calculating the contents of high-ordered kaolinite (HOK) and low-ordered kaolinite (LOK) phases in natural samples with an accuracy of ~5%.