Clays and Clay Minerals, Vol. 49, No. 5, 410–432, 2001.
BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: INFRARED METHODS
´ JANA MADEJOVA AND
Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava, Slovakia
INTRODUCTION Infrared (IR) spectroscopy has a long and successful history as an analytical technique and is used extensively (McKelvy et al., 1996; Stuart, 1996). It is mainly a complementary method to X-ray diffraction (XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufﬁciently ...view middle of the document...
Dispersive IR spectrometers are slowly being replaced by quicker and more sensitive Fourier transform (FT) instruments (Rintoul et al., 1998). The greater sensitivity of the FTIR spectrometers is related to the continuous detection of the entire transmitted energy simultaneously, using interferometers, and rapid Fourier transformation of the interferogram into a spectrum (Koenig, 1992; Russell and Fraser, 1994). The increased sensitivity of FTIR spectrometers led to the development and recent broad application of reﬂectance techniques, such as ATR and DRIFT (Grifﬁths and de Haseth, 1986).
Copyright 2001, The Clay Minerals Society
Attenuated total reﬂectance (ATR) has been used as a sampling technique for IR spectroscopy since it was developed for dispersive instruments. However, only the increased sensitivity of FTIR spectrometers makes the ATR method a simple and routine technique (Rintoul et al., 1998). ATR has been used extensively to investigate adsorption of organic substances on minerals. The main advantage in clay-minerals research is that ATR allows the measurement of the spectra of dispersions, gels or pastes (Hunter and Bertsch, 1994; Shewring et al., 1995; Yan et al., 1996a,b). Diffuse reﬂectance infrared Fourier transform (DRIFT) is widely used in the analysis of solids and powders and generally requires little sample preparation. The DRIFT method is a rapid technique for analyzing samples without interference related to sample preparation. Its use is limited somewhat by interference effects created by particle size and incident IR wavelengths, which may appear toward the low-frequency region, normally below 1200 cm 1 for clays. To minimize such effects, the clay is mixed with KBr to obtain good DRIFT spectra in the 1200–400 cm 1 region. The DRIFT technique is most appropriate in the NIR region, where no dilution of the sample is necessary. Thus, DRIFT is suitable for studies of hydroxyl vibrations of clays in both MIR and NIR regions (Frost and Johansson, 1998). This paper summarizes data from FTIR spectra in the NIR and MIR regions (11,000–400 cm 1) of many of the Source Clay samples, using both transmission and reﬂectance techniques. METHODS The FTIR spectra were obtained using a Nicolet Magna 750 FTIR spectrometer, equipped with an IR source, KBr beam splitter, and DTGS KBr detector for MIR measurements, and a white light source, CaF2 beam splitter and PbSe detector for NIR measurements. For each sample, 128 scans in the 11,000–4000 cm 1 (NIR) and 4000–400 cm 1 (MIR) spectral ranges were recorded with a resolution of 4 cm 1. Fine fractions of the samples were prepared and described by Costanzo (2001), and these samples were analyzed as received. The KBr pressed-disc technique is most widely used for preparing a solid sample for routine scanning of the spectra in the MIR region. Samples of 2 and 0.5 mg were dispersed in 200 mg of KBr to record optimal
Vol. 49, No. 5, 2001
spectra in the...