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(νi) is a full width at half maximum and A(νi) 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 (νi) and determining the optimal values for the FWHM(νi) and A(νi) 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%.