Aluminosilicates spectra

On heating to > 980°C, the 30 ppm Al metakaolinite resonance which formed at the expense of the octahedral kaolinite resonance disappears abruptly, leaving the octahedral and tetrahedral peaks of a typical aluminosilicate spectrum (Rocha and Klinowski 1990, Temmujin et al. 1998a) (Figure 5.30). Al NMR offers little resolution of an ongoing debate over the nature of a cubic spinel phase which often forms at about 980°C, since, although the spectra of samples heated at this temperature have... 

Deuterium NMR has recently been used to study molecular motion of organic adsorbates on alumina (1.) and in framework aluminosilicates (2). The advantage of NMR is that the quadrupole interaction dominates the spectrum. This intramolecular interaction depends on the average ordering and dynamics of the individual molecules. In the present work we describe NMR measurements of deuterated benzene in (Na)X and (Cs,Na)X zeolite. 

The EDX spectrum (Fig. 11.8) shows the main surface scale impurity peaks of silica, aluminium, sodium, chloride and iron. If this EDX is compared to that of a new, clean membrane surface (Fig. 11.9), the clean surface shows sulphur, carbon and oxygen, which is typical of a porous polysulphone support. It was concluded that the scale is amorphous, composed of aluminosilicate and silicate. These compounds are normally found in trace amounts in brine solutions. Analysis showed that the surface could be cleaned with hydrochloric acid and analysis of the dissolved scale was similar to the EDX spectrum analysis. Review of the plant operation determined that the precipitation was the result of high pH in combination with high silica concentrations in the brine. 

The principal limitations of ESCA include the inability to detect elements present at trace concentrations within the analytical volume, and insufficient lateral resolution to characterize single micrometer-sized particles. The inability to characterize trace species is illustrated in Figure 10 for a sample of coal fly ash particles (11). The fly ash results from the noncombustible mineral components of the coal and consists largely of fused iron oxides and aluminosilicates (42). In addition, most elements are present in at least trace concentrations (22, 42), and many of these elements are highly enriched in the surface region of the particles (evidence for this will be discussed in the next section). However, the ESCA spectrum acquired over several hours of counting time indicates only the presence of detectable surface S and Ca in addition to the fly ash matrix constituents. 

Figure 4 shows the27 A1 NMR spectrum of a calcined sample. There are three peaks visible, a peak due to octahedrally coordinated aluminum (Oh), a peak due to tetrahedrally coordinated aluminum (Td) and a peak in between due to highly distorted tetrahedral sites. The tetrahedrally coordinated aluminum can be assumed to be incorporated into the aluminosilicate network while the octahedrally coordinated aluminum is occluded in the pores or exists as an amorphous by product. 

The O/Cs region (500 - 600 eV) of the numerically differentiated Auger spectrum of one of the cesium aluminosilicate crystals, found on the face of microcline exposed to 10 2 mol dm 3... 

The mid-infrared spectrum of the cesium aluminosilicate unequivocally identified it as pollucite. Moreover, the SAM results indicate that the material is uncontaminated by foreign alkali metal ions, such as K+ or Na+ from the feldspars, or the aqueous media. 

Figure 5. Effects of pulse length on wideline NMR spectra of aluminosilicate gels containing (a) 5% V, 7/ s pulse length, resulting in exclusive detection of bulk Vp05 (b) 3% V, 7/ s pulse length, resulting in exclusive detection of amorphous V Oj-and (c) 3% V, 1/xs pulse length, resulting in a spectrum representative of all V+D species present.

The high field aluminum-27 MAS NMR spectrum of the aluminosilicate gel under study contains resonances near 0 ppm 30 ppm and 58 ppm indicating the presence of aluminum in octahedral, pentahedral and tetrehedral coordination (16,17), see Fig. 1. Luminescence as... 

It was observed in synthetic Linde Type Na-Y, Ba-Y and Zn-Y zeolites (a crystalline aluminosilicate with the formula Nax(A102)x(Si02)y, etc.) that after the NO adsorption, only NO radicals could be detected at 77 K [99]. The use of 15NO gas confirmed the results with uNO. After UV irradiation at 77 K of the NO-treated Ba-Y, only N02 radical spectrum was observed. This photoinduced signal was stable at 77 K, decayed gradually at room temperature (Tj/2 = several hours) and disappeared completely when the sample was annealed at 50° for 30 min [99]. The role of NO, N02 and N2O3 species, photoelectron transfer between them and their reversible transformations have anready been discussed. 

Figure 7 27Al NMR spectra of potassium aluminosilicate solution 6e prepared by Method 2 of mixing. Acquisition time was 0.067s and the number of scans averaged 6000. All data was collected in 4K and transformed in 32K. Spectrum 1 = normal mixing as in Method 1,2 = 22% of excess alkali added to the silicate soltuion before mixing with aluminate, 3 = 44% of excess alkali, 4 = 66% of excess alkali and 5 = 88% of excess alkali.

Figure 8 27AI NMR spectra of potassium aluminosilicate solution 4b over time. Acquisition time was 0.067s and the number of scans 5000 for each spectrum. All data was collected in 4K and transformed in 32K.

The silicate species discussed in the preceding section can react with aluminate anions, Al(OH)4 to produce aluminosilicate anions. Si NMR spectra of solid silicates and aluminosilicates indicate that the replacement of Si by A1 in the second coordination sphere of a give Si causes a low-field shift of about 5 ppm. Since each Si atom can have up to four metal atoms in its second coordination spere, fifteen possible Qn(mAl) structural units can be envisioned. The estimated chemical shift ranges for these units are given in Table 3. It is apparent from this table that the 29si spectrum of an aluminosilicate solution in which A1 and Si atoms were statistically distributed would be much more complex than that of an analogous solution containing only silicate species. 

Fig. 8 (a) A 29 i NMR spectrum of a monomeric Na silicate solution of the composition 1.0 mol% SiC>2, R = 0.1 and an 27A1 spectrum of a monomeric Na aluminate solution of the composition 1 M NaAlC>2 (b)-(d) 29si and 27A1 spectra of aluminosilicate solutions with increasing AI concentration. 29si spectral frequencies are referenced to Si(OH)4 and Al spectral frequencies are referenced to the octahedral Al + ion in an aqueous solution of AICI3. 

The Mossbauer spectrum of the original sodium-bentonite shows the isomer shift and quadrupole splitting values as usual for montmorillonite (Stevens et al. 1983). The values 6 and d, exhibit Fe3+, while the values of S2 andd2reveal Fe2+ microenvironments. These values are typical for Fe3+ and Fe2+ ions that are in the central positions of octahedrons of aluminosilicates (Kuzmann et al. 1998 Stevens and Stevens 1978). The relative areas (A s) show that the Fe3+ species is dominant as usual for Na-bentonites (Stevens et al. 1983). The spectra at the temperature of liquid nitrogen show no magnetically split components. 

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