Rietveld Refinement of the Kaolinite Structure at 1.5 K

Abstract

Abstract--The crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (~ = 1.9102 A) and Rietveld refinement/ difference-Fourier methods to R,,,p = 1.78%, reduced x 2 = 3.32. Unit-cell parameters are: a = 5,1535 ( (5) ik ~. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 600-73 ~ with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.

2H NMR Study of Hydrogen Bonding in Deuterated Kaolinite

“…The refinement of the crystal structure also presented the presence of anisotropic positional disorders at 1.5 K (Bish 1993). The hydrogens in inner hydroxyls exhibit the largest amount of positional disorder perpendicular to the layers, whereas those of the inner-surface hydroxyl groups exhibits the largest amount of positional disorder within the plane of layers.…”

“…The crystal structure has recently been refined by Bish (1993). The R o~ values in the interlayer hydrogen bondings are 2.945, 2.980 and 3.087 A, which were related to infrared absorption bands at 3651, 3668 and 3696 c m -1, respectively.…”

“…Although the positions of non-hydrogen atoms have been well established, the positions of hydrogen atoms were in controversy until recently (Adams 1983;Young and Hewat 1988;Bish and Deele 1989). Recent neutron powder diffraction studies have concluded space group C1 (Bish 1993;Akiba et al 1994).…”

Laboratory investigation of the strength development of alkali-activated slag-stabilized chloride saline soil

“…The main diffraction peaks for Friedel's salt (Fs), calcium silicate hydrate (CSH), and NaCl are indicated in this figure. The relative amounts of constituents in the stabilized soil samples can be determined using the semi-quantitative procedure suggested by Bish (1993). Using this method, the generation mass percentage of Fs and the consumption mass percentage of NaCl in stabilized soil samples were calculated as shown in Fig.…”

Adsorption of an active molecule on the surface of halloysite for controlled release application: Interaction, orientation, consequences

“…Since accurate experimental geometry for halloysite nanotubes is not available, theoretical investigations were performed using the kaolinite clay mineral of similar structure as model system. The lattice parameters and atomic positions determined by low-temperature neutron powder diffraction by Bish [29] were used in the calculations. The Mercury [30] package was used for the construction of the crystal structures from the experimental parameters.…”