Dehydroxylation induced structural transformations in montmorillonite: an isothermal FTIR study

Abstract

Abstract. Fourier transform infrared (FTIR) measurementson thermally shocked (290< T< 1100 K, t= 1 and 24 h) and thermally soaked (T= 803 K, 0< t < 25 h) Ca-montmorillonite from Texas show that the dehydroxylation temperature for this mineral is much lower than previously reported in the literature and depends upon the thermal soak time used. The effect of thermal shock temperature on vibrational frequencies, originating from the silicate sheet, and the intensity of A1-OH-A1 stretching mode suggest that Camontmorillonite dehydroxylates at 903<T<923 K and 773 < T< 823 K for 1 h and 24 h thermally shocked samples, respectively. Our similar measurements on the Mn and Fe exchanged-montmorillonite from Texas demonstrate that the dehydroxylation temperature range is also affected by the type of cations present in the interlayer. The thermal soak (T=803 K, 0<t<25h) measurement on Ca-montmorillonite indicates that the dehydroxylation of this montmorillonite proceeds via the development of intermediate structural phases. As noted by previous authors, the dehydroxylation of Mg 2+ and Fe 3 § octahedral sites does not affect the overall structure. However, if ~ 75 percent of the hydroxyls attached to A13 § are lost, then the lattice manifests an intermediate structural phase. In this intermediate phase, the structure of both octahedral and silicate layers is affected. On a further loss of hydroxyls (~ 90% of A13 + hydroxyls), the final montmorillonite dehydroxylate phase develops. The vibrational analysis of an isothermally treated sample suggests that the final phase is induced due to the rearrangement of the silicate oxygens, which leave the coordination around A1 to be 5. The dehydroxylation results of montmorillonite (Texas) have been discussed in terms of known mechanisms, and it appears that the dehydroxylation starts at the surface and proceeds via proton delocalization at trans hydroxyl positions, followed by the protons' migration across the vacant cation sites with the formation of H20 molecules below the hexagonal holes.

Ice nucleation of ammonia gas exposed montmorillonite mineral dust particles

“…3a. It shows the typical absorption bands of montmorillonite (Farmer, 1974), for example Al-OH-Al (Ogloza and Malhotra, 1989) stretching at 3625 cm −1 , OH (Ogloza and Malhotra, 1989;Russell, 1965) stretching of water at 3434 cm −1 and Si-O (Ogloza and Malhotra, 1989;Russell, 1965) bending at 1059 cm −1 . However, there is a broad peak at the band position of about 3220 cm −1 in Figs.…”

“…Ogloza and Malhotra, 1989) was conducted using a Bruker FT-IR spectrometer (Model Vector 22). About 1.0 mg mineral dust and 100 mg KBr were weighted and ground in an agate mortar prior to pellet making under a load of 1.0×10 4 kg of pressure for 2 min.…”

“…3a). Hydroxyl and amino groups show characteristic absorption bands (Coates, 2000;Ogloza and Malhotra, 1989) in the region from 3650 to 3200 cm −1 . Therefore the weak peak at 3220 cm −1 in the case of pure montmorillonite (Fig.…”

Review of experimental methods to determine spontaneous combustion susceptibility of coal – Indian context

“…Kok, 2008;Ledesma, Kalish, Nelson, Wornat, & Mackie, 2000;Liotta, Brons, & Isaacs, 1983;MacPhee, Giroux, Charland, Gransden, & Price, 2004;Mahidin, Usui, Ishikawa, & Hamdani, 2002;Ogloza & Malhotra, 1989;Painter, Snyder, Pearson, & Kwong, 1980;Rhoads, Senftle, Coleman, Davis, & Painter, 1983;Wu, Robbins, Winschel, & Burke, 1988). The changes of IR/FTIR spectra observed for a coal i.e.…”

Laboratory study of heterogeneous ice nucleation in deposition mode of montmorillonite mineral dust particles aged with ammonia, sulfur dioxide, and ozone at polluted atmospheric concentrations

“…They found that the presence of ammonia gas decreased the ice nucleation ability of silver iodide particles. The interactions of the trace gases with mineral dust particles have been studied (Russell 1965;Ogloza and Malhotra 1989;Umann et al 2005). However, the potential impact of trace gases on ice nucleation is still not well understood.…”