Basal reflection

M NaHC03 in the presence of cysteine (cysteine Fe = 1.1) at 70 °C for 60 hr. Addition of cysteine causes instantaneous darkening of the ferrihydrite and formation of a crystalline intermediate with an XRD pattern characterised by basal reflections at 1.04 and 0.504 nm. This intermediate transforms into a yellow precipitate of fairly monodispersed crystals (<100 nm across) ofgoethite (Cornell et al., 1991). 

Fig. 9. Typical temporal series of XRD patterns, for a polystyrene (1 =30,000)/C18FH mixture annealed in-situ at 160 °C in vacuum. Initially (time=0), the basal reflection of the or-gano-silicate were observed at 20=4.15° (d=2.13nm). During the annealing this reflection is progressively reduced in intensity, whereas a new basal reflection develops at 20=2.82° (d=3.13nm) that corresponds to the intercalated hybrid.

In our studies, the model substance (montmorillonite) was a calcium bentonite (Istenmezeje, Hungary), the characteristic features of which are given here. X-ray diffraction (intensity of the basal reflection) and thermoanalytical (weight loss upon heating) data show 91% montmorillonite content. The other constituents are 5% calcite, 3% kaolinite, 1% x-ray amorphous silicates, and a trace of quartz. The amorphous phase is silicate particles, which are not crystalline for... 

Layer thicknesses are similar to those of the AFm phases, and it would be difficult to distinguish the two groups of phases by XRD if only the basal reflections could be observed. Polytypism is common for example, sjogrenite, with a two-layer structure, has a three-layer polytype, called pyroaurite. Three-layer structures are the ones normally formed at room temperature. Meixnerite, which is a three-layer form, has a = 0.30463 nm, c = 2.293 (3 X 0.764)nm, space group R3m, Z = 3, D = 1950kgm (K30). Thermal dehydration (B86) and IR spectroscopic (FI35) studies on Mg-Al phases of this group have been reported. 

The only peaks clearly attributable to AFm phases are usually those at about 0.288 nm (11.0), 0.166 nm (30.0) and the first- and second-order basal reflections corresponding to one or, usually, more layer thicknesses. Taking... 

The black compound which is oxidized to goethite has large platy crystals (surface area ca. 10 m /g), shows two strong basal reflections at 1.04 and 0.504 nm, and has an Fe /Fe ratio of ca. 0.8-1. Thus, it appears to be a hitherto unknown layer compound akin to the well-known green rust phases (see chap. 13). 

Fig. 3 shows the XRD patterns after calcination of as prepared solids at 400 °C in Nz (M-4OO-N2). The disappearance of basal reflections at 20<1O deg suggests the lack of periodicity in the layer stacking. The products for M=Mn, Fe, and Zn exhibited diffraction peaks due to oxides of M, suggesting that part of intercalated metal acetates was precipitated as oxides. The Cu-400-Nz solely produced metallic precipitations in addition to anatase-type TiOz. FT-IR measurement confirmed the complete elimination of the organic components (vch 2840-2960 cm, Vco 1450. 1550 cm ) from these composites. As shown in Table 1, the BET surface areas of M-400-Nz were in the range of 23-100 m /g, compared to 11 m /g for pristine KzTi409 microcrystals. The largest surface area was attained by the Cr-400-Nz... 

It is evident that, in addition to smectitic interstratifications (the effect of which on illite crystallinity have been frequently el iminated by glycolation and/or deconvolution of the basal reflections), the various contents of interlayer K may considerably affect illite crystallinity. Recent issues prove that mo st probably, the amount of K should increase with increasing grade (temperature) (Hunziker et al. 1986 Livi et al. 1997). 

Stem WB, Mullis J, Ralm M, Frey M. (1991) Deconvolution of the first ilhte basal reflection. Schweiz mineral petrogr Mitt 71 453-462... 

Additionally, some layered silicates initially do not exhibit well-defined basal reflections. Thus, peak broadening and intensity decreases are very difficult to study systematically. Therefore, conclusions concerning the mechanism of nanocomposites formation and their structure based solely on WAXD patterns are only tentative. On the other hand, TEM allows a qualitative understanding of the internal structure, spatial distribution of the various phases, and views of the defect structure through direct visualization. 

Figure 10-2 displays the powder XRD spectra of the five samples, as synthesized, and Table 10-3 shows, the X-ray powder diffraction data for the layer silicate phases. These spectra exhibit the charact stic bands (hk) at 4.45-4.47A, at nearly 2.56A, and at 1.49A. The 1.49A band (060) indicates the dioctahedral nature of the layer silicates. Due to the basal reflection, there is also a peak in the low-angle region, the value of which varied with interlayer cation nature and relative humidity (Table 10-4, third and fourth columns). Some samples show other peaks that may be indexed as (001) reflections such as (002), (004) or (006). 

TABLE 10-4 Basal Reflections of the Various Samples at Different Relative Humidity (RH) and Glycerol Treated. ... 

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