Spectroscopic Methods in the Study of Kaolin Minerals and Their Modifications by Jacob (Theo) Kloprogge

Spectroscopic Methods in the Study of Kaolin Minerals and Their Modifications by Jacob (Theo) Kloprogge

Author:Jacob (Theo) Kloprogge
Language: eng
Format: epub, pdf
ISBN: 9783030023737
Publisher: Springer International Publishing


In soils, kaolinite is formed at pressure-temperature conditions of the Earth’s surface (i.e., 25–30 °C and atmospheric pressure). However, kaolinite also persists until late diagenesis at temperatures lower than 200 °C, and lithostatic pressure lower than 100 MPa or hydrostatic pressure of 30–40 MPa; furthermore, it can result from hydrothermal alteration , at 100–200 °C and 0.1–10 MPa. Friedrich and Weidler (2010) reported on the effects of contact pressure using diamond and germanium ATR infrared spectroscopy on kaolinite vibrational bands. The bands in the OH-stretching region of kaolinite are displayed in Fig. 5.40a. The strong vibration ν5 of the inner OH group occurred in all spectra at its expected position (3619 cm−1). Also, the weak out-of-phase vibrations ν2 and ν3 of the inner-surface hydroxyl s were observed at nearly the same positions in all spectra, ν3 at 3652 cm−1 (transmission, TR), 3650 cm−1 (ATR from suspension, no pressure, SUS), and 3651 cm−1 (ATR with pressure, ATR) and ν2 at 3668 cm−1 (TR), 3665 cm−1 (SUS), and 3669 cm−1 (ATR), but their intensities decreased with increasing pressure. Furthermore, in the SUS and ATR spectra an additional weak shoulder around 3640 cm−1 was observed. The strongest differences were visible in the region around the strong in-phase symmetric stretch ν1. The band component analyses revealed one band at the expected position (3694 cm−1) in all spectra, but in the SUS and ATR spectra an additional band occurred at 3684 cm−1 (ν4), whose intensity increased with increasing pressure. All bands that were affected by the anvil pressure exhibited a shift in their positions to lower wavenumbers with increasing pressure. The Si-O in-plane vibration shifted from 1028 cm−1 at 8.7 MPa to 1022 cm−1 at 104.9 MPa, while the shift of the second Si-O in-plane vibration was even stronger (1004–994 cm−1). However, the position of the inner-surface OH-deformation band at 939 cm−1 did not shift. Yet, the deformation band of the inner OH-group shifted from 910 cm−1, a position close to that measured with the other methods, to 904 cm−1. Similarly, the two Si-O deformation bands shifted from 530 and 461 cm−1 to 523 and 453 cm−1, respectively. The spectral differences between ATR and TR spectra were restricted mainly to basal Si-O vibrations and to some vibrations of the inner-surface OH group s (Fig. 5.40b). The vibrations related to the octahedral sheet exhibited hardly any effects. This is somehow surprising, because a number of publications have reported complex deformation processes, especially in the octahedral sheet and phase transitions in kaolin group minerals, when exposed to hydrostatic pressure s (Holtz et al. 1993; Johnston et al. 2002; Dera et al. 2003; Butler and Frost 2006). However, these spectral changes appeared at much higher pressures (1–4 GPa) than those applied in the ATR cell (Johnston et al. 2002; Dera et al. 2003; Butler and Frost 2006). Moreover, most of the bands in the region between 1240 and 440 cm−1 shifted to higher wavenumbers, reflecting the multiaxial compression of the clay mineral structure (Butler and Frost 2006). These



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