Mullite peaks

Fig. 2 X-ray powder diffraction patterns showing the crystallization of mullite from amorphous precursors as a function of temperature. M denotes mullite peaks, and Sp markers denote the intermediate y-Al203 spinel peaks. From [8]...

The significant amoimts of fluidized bed ashes are generated in 2000 the annual output was 723 thousand tones [ 131 ]. Some part is used in cement industry, as a raw material in Portland cement clinker production. They are also added to concrete on the base of technical approvals. They can be easily distinguished from the ash of pulverized-coal fired furnace, because they do not give the mullite peak on XRD pattern. 

She e/ alP have determined, using XRD, the major phases present in porous SiC ceramics sintered at different temperatures for 4 h. At 1400°C, porous SiC ceramics consist mainly of SiC, cristobalite and a- ALO3, but slight mullite peaks can be found. When the temperature increases to 1450°C, the mullite peaks are obvious. At 1500 and 1550°C, the amount of a- AljOj decreases abruptly and more extensive mullitization occurs. 

XRD patterns before and after the oxidation for 100 h are shown in Figure 4.11. For Zl, see Figure 4.11a, there are no visible changes for oxidation at 1000 "C compared with the as-sintered product. However, after 1200 "C oxidation, a visible silica (cristobalite) peak was detected and a very few muUite peaks were also detected. When the temperature reached to 1400 "C, the intensity of mullite peaks became stronger and more peaks were visible, and the peak of cristobalite was still... 

Figure 4 XRD scans of as-is untested bonded AZS (top spectra), and corroded bonded AZS (bottom spectra). Corroded sample does not show mullite peaks.

The thermal techniques are routinely used for quality control purposes. A typical TG/DTA analysis is shown in Fig. 13 for a Thessalian brick clay.t None of these clays contains kaolin and the characteristic mullite peak is absent. The endothermic peak between lOOand 160°Cisdue to the removal of adsorbed water, and its size is dependent on the surface area and crystallinity of the clay. The peak (400-700°C) is attributed to the dehydration of the combined water (dehydroxylation of the silicate lattice) and decomposition of the clay. The third peak (800°C) indicates decomposition of the carbonates and other salts present in the clays. 

Figure 4.29. Effect of grinding on the Si spectra of the alumina-silica system. A. Mixture of gibbsite, Al(OH)3 and silica gel, and B. Diphasic gel of mullite composition. Note in both systems the evidence of Si-O-Al bond formation (peak at about — 84 ppm). Adapted from Temuujin et al.

Figure 4.34. Si spectra of the stages in the oxidation of p-sialon. As the sialon peak at — 47 ppm decreases, the first oxidation product is amorphous Si02 (—113 ppm) followed by mullite (—86 ppm). From MacKenzie et al. (1997a), by permission of copyright owner.

Figure 5.10. MAS NMR spectra of a number of amorphous aluminosilicates of approximately mullite composition derived from various sources, showing the peak at ca.30 ppm attributed to Al (arrowed). From McManus et al. (2001), by permission of Elsevier Science.

The authors described the reaction mechanism as occurring by impregnation of the sample, bond reaction, and bond depletion. Immediately the alkali consumes the cristobalite and attacks the glass of the matrix bond. Next the fine crystalline mullite bridges associated with the bonding matrix react with the soda. The mullite x-ray peak intensity is quickly reduced. The extent of attack on the coarser crystalline mullite is intensified at higher temperatures or as the reaction proceeds. When equilibrium... 

XRD peaks occurred at the correct diffraction angles for mullite but were too weak to permit accurate intensity comparisons. 

When the nature of the material s crystalhne phases is known, the volume of each of the phases present can be determined. We saw in Chapter 1 that the integrated intensity of each peak in a given phase is directly proportional to the volume of the phase. Therefore, quantitative phase analysis is performed from the very precise measurement of these integrated intensities. Quantitative phase analysis should not be confused, of course, with the quantitative chemical analysis which is used to determine the amount of each element present in a sample. The first quantitative phase analysis by X-ray diffraction was conducted in 1925 on a ceramic material, in order to determine the amount of mullite in burned clays [NAV 25]. Despite the fact that this type of quantitative measurement has existed for 80 years, these analyses remain very difficult to conduct [BIS 89, TOR 99a, TOR 99b] and require experimental precautions which we will now discuss. However, we should point out that X-ray diffraction is virtually the only method available for quantitative phase analysis. ... 

Metallic silver is clearly evidenced by XRD beside mullite and corundum phases. The crystallite sizes are reported in Table 2 as well as the specific surface area. After the evaluation tests, we can observe a strong decrease of the intensity of the silver diffraction peaks disclosing a loss of the active phase during the hydrogen peroxide flow. In the case of sample Bl, an important weight loss is observed (- 8.1 %, Table 1), whereas for sample C, the weight loss is much lower (- 0.9 %) and a part of metallic silver transforms into silver oxide. 

Figure 3 shows a comparison between non fired D and fired F samples. The non-fired sample displays a high surface area due to the manganese oxide layer. The X-rays diffraction permits to identify the badly crystallized phase Na0.7MnO2.05 as the major phase which covers the substrate (the mullite difftaction peaks are very weak). After firing, an important weight loss is... 

Fig.8-a shows that the ciystallization of the t-Zi02(k-ss) reached the peak at I I50"C, then decreased significantly with the temperature increased to 1200 C and nSOX . From Fig.8-b, it could be seen that the intensity of m-Zr02 was linearly increased with the heat-treated temperature increase. Hence, the crystallization of Zr02 might be finished at 1150"C. Fig.8-c demonstrates the crystallization of mullite which began at HOOT , and reached to the maximum at IISOT, then... 

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