Probing the Environment of Al Atoms in Noncrystalline Solids: Al2O3SiO2 Gels, Soda Glass, and Mullite Precursors

Thomas, John Meurig; Klinowski, Jacek; Wright, Paul A.; Roy, Rustum

doi:10.1002/anie.198306141

Cited by 48 publications

(5 citation statements)

References 8 publications

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“…Samples with nominal Al/Si ratios between 1.5 and 4.7 display at 1000 °C the characteristic 27 Al NMR spectrum of mullites. ,,− In these samples, two tetrahedral components at 66 and 40 ppm were detected besides the octahedral component at ∼0 ppm. On the other hand, samples with Al/Si between 8 and 18 display specific features of transitional aluminas .…”

Section: Discussionmentioning

confidence: 99%

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

2007

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Thermal behavior of alumino-silicate gels prepared by spray pyrolysis, with Al/Si ratios between 1.5 and 18, has been analyzed by differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy, IR, and 29Si and 27Al magic angle spinning NMR techniques. In samples heated at 800 °C, tetra-, penta-, and octahedral aluminum were detected. In samples heated at 900 °C, Al-rich mullite (Al/Si = 4−6) or Si-spinel nuclei (Al/Si = 10−18) are formed after the partial segregation of SiO2 from alumino-silicate gels. The strong rearrangement of aluminum atoms, with formation of tetra- and octahedral Al at the expense of pentahedral Al, is responsible for the exothermic peak detected at ∼980 °C in DTA curves. Thermal treatments between 1000 and 1300 °C produce the progressive incorporation of SiO2 into newly formed mullite nuclei. In Al-rich samples, with nominal Al/Si ratios between 8 and 18, the formation of mullite nuclei is only detected above 1100 °C. In this case, spinel and mullite phases coexist in the temperature range 1100−1250 °C.

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Section: Discussionmentioning

confidence: 99%

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

2007

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“…Thomas et al, 9 Taulelle and Theveneau, 10 Figure 6 shows that AAS includes both Al(4) and Al (6) and the Al(4)͞[Al(4) 1 Al (6)] ratio was about 0.56. The ratio is similar to that in an ideal model of 3͞2-mullite.…”

Section: B Aas As a Mullite Precursormentioning

confidence: 94%

Mullite Precursor Part I. Characterization of Mullite Precursor Formed by a Reaction of Monosilicic Acid on Aluminum Hydroxide

et al. 1997

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By adsorption of monosilicic acid on aluminum hydroxide, an amorphous aluminosilicate (AAS) of Si͞Al ratio of 1͞3 was formed. When the AAS was heated to 1000 ± C, mullite (3Al 2 O 3 ? 2SiO 2 ) crystallized directly without the formation of a spinel phase. It was clearly evidenced that correct adjustment of three factors, the Si͞Al ratio, the proportion of 4-and 6-coordinated aluminums, and the single environment of a SiO 42 4 unit (no Si-O -Si bond), is important for the direct mullitization from AAS.

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“…This result is in agreement with Brown et al (1985). The former resonance is due to amorphous silica consisting of a three-dimensional network of SiO4 tetrahedra, and the latter resonance is ascribed to mullite (Thomas et al, 1983;Brown et al, 1985).…”

Section: Te Al L Y; ~ Alvlimentioning

confidence: 99%

²⁹Si- and²⁷Al-MAS/NMR study of the thermal transformations of kaolinite

et al. 1987

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Thermal transformations of kaolinite were studied by zgsi-and ZVA1-MAS/NMR and ESR techniques. In metakaolin, Si is still dominantly in the Q3 state (three Si atoms bonded to an Si-O4 tetrahedron) and A1 detectable by NMR is in both 4-coordination and 6-coordination. Coordination polyhedra around A1 or Fe replacing A1 are much distorted. Metakaolin crystallizes into y-alumina and mullite exothermically at ~ 980 ~ this crystallization being preceded by a faint endothermic reaction. The latter is due to segregation of SiO2 and A1203, which results in an increase of Si in the Q4 state and an increase of 6-coordinated A1203 .Kaolin minerals dehydroxylate at ~600~ this process corresponding to an intense endothermic peak on the DTA curve. The resultant anhydrous phase, called metakaolin or metakaolinite, is amorphous to X-rays. y-alumina plus mullite develop from the amorphous phase at ~ 980~ and this reaction is represented by a combination of a faint endotherm and a sharp and intense exotherm. The mechanism of this series of reactions has been studied from various standpoints, as reviewed by Brindley & Nakahira (1959), Tsuzuki (1971) andBrindley (1976). X-ray diffraction, electron microscopy, and X-ray fluorescence, IR absorption and M6ssbauer spectroscopy have all been used to study these reactions. Recent developments in high-resolution magic-angle-spinning MAS/NMR spectroscopy have allowed a new approach to this problem, Komarneni et al. (1985), MacKenzie et al. (1985b) and Brown et al. (1985) being forerunners in the application of this method to metakaolin and high-temperature phases of kaolinite. This paper gives the results of examination of a kaolinite heated to various temperatures, using 29Si-and 27A1-MAS/NMR and ESR techniques. Some new data are presented on the thermal transformation of kaolinite.

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Probing the Environment of Al Atoms in Noncrystalline Solids: Al₂O₃SiO₂ Gels, Soda Glass, and Mullite Precursors

Cited by 48 publications

References 8 publications

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

Mullite Precursor Part I. Characterization of Mullite Precursor Formed by a Reaction of Monosilicic Acid on Aluminum Hydroxide

²⁹Si- and²⁷Al-MAS/NMR study of the thermal transformations of kaolinite

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Probing the Environment of Al Atoms in Noncrystalline Solids: Al2O3SiO2 Gels, Soda Glass, and Mullite Precursors

Cited by 48 publications

References 8 publications

Formation of Mullite and Spinel Phases from SiO2−Al2O3 Gels Prepared by a Spray Pyrolysis Technique. A 29Si and 27Al MAS NMR Study

Formation of Mullite and Spinel Phases from SiO2−Al2O3 Gels Prepared by a Spray Pyrolysis Technique. A 29Si and 27Al MAS NMR Study

Mullite Precursor Part I. Characterization of Mullite Precursor Formed by a Reaction of Monosilicic Acid on Aluminum Hydroxide

29Si- and27Al-MAS/NMR study of the thermal transformations of kaolinite

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Probing the Environment of Al Atoms in Noncrystalline Solids: Al₂O₃SiO₂ Gels, Soda Glass, and Mullite Precursors

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

Formation of Mullite and Spinel Phases from SiO₂−Al₂O₃ Gels Prepared by a Spray Pyrolysis Technique. A ²⁹Si and ²⁷Al MAS NMR Study

²⁹Si- and²⁷Al-MAS/NMR study of the thermal transformations of kaolinite