Determination of structural disorder degree using an XRD profile fitting procedure. Application to Czech kaolins

Diffractions of (02, 11) band are very sensitive to the structural defects in kaolinite structure. Therefore, the empirical relation based on weighting peak intensity ratio of 0 2 0, 1 1̄ 0, and 1 1 1̄ (1 1̄ 1̄) reflections was used to estimate the degree of disorder in kaolinite samples collected from different Czech Republic kaolin deposits. X-ray diffraction (XRD) profiles taken from <5 μm fraction of kaolinite samples were used for determination of peak intensities I(1 1̄ 0), I(1 1 1̄), I(1 1̄ 1̄), I (0 2 0) and full width at half maximum (FWHM) values using profile fitting and decomposition procedure. The weighting intensity ratio index (WIRI) WIRI =1− exp {−[w 1 I(1 1 ̄ 0)+w 2 I(1 1 1 ̄ )+w 3 I(1 1 ̄ 1 ̄ )]/[w 4 I(0 2 0)]} was calculated. The w ₁, w ₂, w ₃, and w ₄ weight values are the reciprocal values of FWHM for 1 1̄ 0, 1 1 1̄, 1 1̄ 1̄, and 0 2 0 reflections, respectively. According the WIRI values (theoretically ranging from 0 to 1), three groups of kaolinite samples can be recognized: (I) one sample with high degree of structural order (0.70<WIRI<1.00), (II) two samples with medium degree of structural order (0.40<WIRI≤0.70), and (III) five samples with low degree of structural order (0.00<WIRI≤0.40). The WIRI values obtained were compared with Hinckley (HI) and Aparicio–Galán–Ferrell (AGFI) indices and very good relations were found between them.