27Al NMR spectroscopy at 104.2 MHz

Akitt, J. W.; Mann, Brian E.

doi:10.1016/0022-2364(81)90293-6

Cited by 37 publications

(26 citation statements)

References 3 publications

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“…Characterization of alumina and silica sols Figures 1 and 2 show the 27 Al Nuclear Magnetic Resonance spectra from the alumina sols, at pH ~6 and 1, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The distribution of particle sizes is related to the peptization of the larger alumina particles, giving rise to smaller ones or to Al 3+ ions, as a result of Al 3+ ion hydrolysis catalyzed by acid, indicated by the equilibrium shift of equation 2 to the left. 14,27,28 The Al 3+ ion hydrolysis is controlled by the pH and results in the aluminum cation being coordinated to aquo (H 2 O) and/or hydroxo (OH -) ligands, as a function of the degree of hydrolysis.…”

Section: Resultsmentioning

confidence: 99%

“…This tetrahedrally coordenated Al 3+ ions with octahedral coordination present in solution, besides small alumina particles, according to the 27 Al NMR and particle size data on the alumina sol. The majority of Al 3+ ions did not interact with the alumina particles as particle-particle interactions, being dispersed in the medium.…”

Section: Characterization Of Materialsmentioning

confidence: 99%

“…The alumina sols at pH 1 and 6 were characterized by 27 Al Nuclear Magnetic Resonance (NMR) spectroscopy using approximately 2 mL of the sol in NMR tubes with diameter of 10 mm. 27 Al NMR experiments were performed at room temperature with a Bruker AC 300/P spectrometer, operating at 78.2 MHz, with delay of 0.5 s between pulses.…”

Section: Characterization Of Materialsmentioning

confidence: 99%

“…27 Al NMR experiments were performed at room temperature with a Bruker AC 300/P spectrometer, operating at 78.2 MHz, with delay of 0.5 s between pulses. The chemical shifts were relative to a 1.0 mol/L aqueous solution of aluminum nitrate defined at 0 ppm.…”

Section: Characterization Of Materialsmentioning

confidence: 99%

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Mullite formation from mixtures of alumina and silica sols: mechanism and pH effect

Osawa¹,

Bertran²

2005

J. Braz. Chem. Soc.

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Este trabalho relata o efeito do pH no processo de formação de mulita a partir de misturas de sóis de alumina e sílica. O pH das misturas determina as cargas das superfícies das partículas e afeta suas interações e distribuições. A formação de mulita a partir de precursores amorfos na razão molar de 1:3, preparados pela mistura dos sóis, não foi afetada pelo pH. Neste caso, a concentração excessiva de sílica determinou sua distribuição ao redor da alumina, o que levou à formação de mulita tetragonal, conforme o mecanismo de Sundaresan e Aksay. Entretanto, para a formação de mulita a partir de precursores com Al:Si = 3:1, o pH desempenhou um papel muito importante nas interações entre partículas de alumina e de sílica, bem como nas espécies predominantes de alumínio. Em pH 1, íons Al 3+ octaedricamente coordenados predominaram no sol de alumina enquanto que íons Al 3+ tetraedricamente coordenados predominaram no sol a pH ~6. As interações entre as partículas de sílica e de alumina e suas distribuições nesses precursores determinaram a temperatura mínima de formação de mulita ortorrômbica.This work reports the effect of pH on the process of mullite formation from mixtures of alumina and silica sols. The pH of the mixtures determines the charges of particle surfaces and affects their interactions and distributions. Mullite formation from amorphous precursors with an Al:Si molar ratio of 1:3, prepared from the sols mixture, was not affected by pH. In this case, the higher concentration of silica determined its distribution around alumina, which led to tetragonal mullite formation, according to the Sundaresan and Aksay mechanism. However, for mullite formation from precursors with Al:Si = 3:1, the pH played an important role on the interactions between alumina and silica particles, as well as on the predominant aluminum species. At pH 1, octahedrically coordinated Al 3+ ions predominated in the alumina sol while tetrahedrically coordinated Al 3+ ions predominated in the sol at pH ~6. The interactions between silica and alumina particles and their distributions in these precursors determined the minimum temperature required for orthorhombic mullite formation.Keywords: pH effect, mullite formation, alumina sol, silica sol IntroductionMullite (3Al 2 O 3 . 2SiO 2 ) is a very important ceramic material, with high temperature applications, due to its excellent mechanical properties, such as high strength, low thermal expansion coefficient, low thermal conductivity, high thermal shock resistance and creep resistance. [1][2][3][4][5][6] Mullite is also an interesting model for the development of new procedures of ceramic material synthesis, due to the simplicity of its composition.7 This ceramic material is composed solely of silicon, aluminum and oxygen, and is the only crystalline phase of the Al 2 O 3 -SiO 2 system stable at atmospheric pressure. 1,[8][9][10] Studies of mullite formation from alumina and silica sols can be useful to evaluate the interactions of alumina and silica particles in an aqueous medium, as a funct...

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“…Characterization of alumina and silica sols Figures 1 and 2 show the 27 Al Nuclear Magnetic Resonance spectra from the alumina sols, at pH ~6 and 1, respectively.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Characterization Of Materialsmentioning

confidence: 99%

Section: Characterization Of Materialsmentioning

confidence: 99%

Section: Characterization Of Materialsmentioning

confidence: 99%

See 3 more Smart Citations

Mullite formation from mixtures of alumina and silica sols: mechanism and pH effect

Osawa¹,

Bertran²

2005

J. Braz. Chem. Soc.

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Multiscale and Multimodal Characterization of 2D Titanium Carbonitride MXene

Sun¹,

Wang

Vlček

et al. 2020

Adv Materials Inter

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A comprehensive study on the prototype solid solution phase carbonitride MXene Ti3CN is conducted using nuclear magnetic resonance, electron spin resonance, total and quasi‐elastic neutron scattering, combined with density functional theory‐based electronic structure and molecular dynamic calculations. The combination of experiment and theory lead toward rational atomic structural models of Ti3CN. The remnant Al ions from the etching process significantly tune the interlayer spacing, distinct from the more typical MXene, Ti3C2, prepared similarly. Neutron scattering indicates the surface terminations of Ti3CN display high oxygen and fluorine concentrations and rather low hydroxyl and hydrogen concentrations. Calculations show that the structure including both the residual Al ions and mixed surface terminations give the best agreement with the measurements. The water molecules in Ti3CN are highly immobile, in strong contrast to those in Ti3C2. The analysis of the electronic structure suggests that the nitride MXene displays higher conductivity than the carbides. The absence of hydroxyl groups in terminations, the solid‐solution in the anion sites, the remnants within layers, and immobile water altogether make the carbonitrides a unique series in the MXene family, implying a further exploration of their exotic properties and applications in energy storage.

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