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Structural and nano-composite features of TiO2–Al2O3 powders prepared by sol–gel method

“…The OH torsional mode observed at 750 cm −1 overlaps with Al-O stretching vibrations [42]. The band observed at 620 cm −1 is attributed to stretching mode of AlO 6 [42]. The broad band in the region of 500-750 cm −1 is assigned to ␣-AlO 6 , whereas the shoulder at 890 cm −1 is assigned to ␣-AlO 4 [42].…”

“…A small band at 1073 cm −1 and a shoulder at 1163 cm −1 are detected due to the symmetric and asymmetric bending modes of Al-O-Al bonds, respectively [42]. The OH torsional mode observed at 750 cm −1 overlaps with Al-O stretching vibrations [42].…”

“…The FTIR spectra of alumina show an intense band centered around 3447 cm −1 and a broad band at 1640 cm −1 , which are assigned to stretching and bending modes of adsorbed water [42]. A small band at 1073 cm −1 and a shoulder at 1163 cm −1 are detected due to the symmetric and asymmetric bending modes of Al-O-Al bonds, respectively [42].…”

Synthesis of submicron gibbsite platelets by organic-free hydrothermal crystallization process

“…As shown in Fig. 4, the spectrum of the amorphous solid prior to the hydrothermal treatment displayed one main resonance signal at d ¼ 3:6 ppm, and two satellite signal peaks at d ¼ 31:2 and 60.3 ppm, which were indicative of six-, five-and four-coordinate aluminum species, respectively [29][30][31]. In the gibbsite submicron platelets, only the six-coordinated Al species were observed, indicating that the four-and five-coordinated Al species were restructured to six-coordinated species during the hydrothermal crystallization at pH 5.0.…”

Efeito do íon Mn como aditivo na transição de fase <FONT FACE=Symbol>g ®a</FONT> da alumina

“…Estudos experimentais são contraditórios quanto ao assunto [5,20], no entanto, simulações considerando a presença de vacâncias apenas em sítios tetraédricos suportam esta possibilidade [21]. Assim, a estrutura pode ser derivada do espinélio normal AB 2 octaédricos e 0,67 ocupam sítios tetraédricos, o restante 0,33 de vacâncias catiônicas deve estar preferencialmente localizados em sítios tetraédricos [22].…”