Fourier transform infrared spectroscopic characterization of clay minerals from rocks of Lalibela churches, Ethiopia

Abstract

This study demonstrates the Fourier transform infrared (FTIR), Raman spectroscopy and scanning electron microscope -energy dispersive X-ray spectrometer (SEM-EDS) techniques which has been applied to characterize decay products and processes occurring at the surface of rock-hewn churches at the UNESCO's World Heritage site of Lalibela, Northern Ethiopia. Spectroscopic analyses comparing the observed frequencies with the available literature, minerals were identified. A special emphasis is devoted to the presence of whewellite/weddellite and kaolinite minerals, never pointed out before this study in the rock hewn churches of Lalibela, and their possible roles on rock decay. The identification of montmorillonite as a weathering product up to 20 mm from the rock/atmosphere interface beyond the level at which kaolinite, whewellite and gypsum are found, suggests that montmorillonite may penetrate even deeper into the rock substrate causing major rock decay. Results indicate that biological attack by green algae and lichens is currently responsible for severe stone surface, physical and chemical weathering leading to considerable weakening of the churches walls. A prompt and careful removal of the biological and other deposits with the non-destructive method (laser cleaning) treatment is therefore recommended.

Fourier transform infrared spectroscopy and thermal analyses of kaolinitic clays from South Africa and Cameroon

“…Low frequency peaks at 3620 cm -1 and 3619 cm -1 were prominent in all the samples. Single broad bands at 3650/3651 cm -1 , were observed in samples ED 1 and 2, indicative of poor structural order (Saikia and Parthasarathy, 2010;Kiros et al, 2013;Djomgoue and Njopwouo, 2013). Muscovite + quartz interference was identified in all the samples whereas iron oxides were prominent in ZEB 2, DUT 1, DUT 2, MK 1 and MK 2 but absent in ED 1 and ED 2.…”

“…The OH bands in kaolin typically display four sharp stretching bands between 3600 and 3700 cm -1 namely; 3697, 3670, 3652/50 and 3620 cm -1 (Ekosse and Mulaba, 2008;Ekosse, 2008;Saikia and Parthasarathy, 2010;Kiros et al, 2013;Djomgoue and Njopwouo, 2013). The strong band at 3697 cm -1 arises from surface hydroxyls and produces an in-phase vibration perpendicular to the 1:1 layers (Ece et al, 2003).…”

Physicochemical Properties of Organophilic Clay Developed Using Hexadecyltrimethylammonium Chloride (HDTMAC) Modifier

“…The Fourier Transform Infra-Red spectrum and the vibrational band assignment for the HDTMAC-modified Ogwuta clay sample as presented in Fig. 7 and in Table 4 revealed that the peak at 671.25 cm -1 was due to Al-O-Si stretching while that at 771.55 cm-1 belongs to the Al-O-Fe bending in quartz [34]. The inner surface hydroxyl group (Al-OH-Al) deformation band was observed at 918.15 cm -1 and the bands associated with Si-O stretching, characteristic of kaolinite was 1010.75 cm -1…”