Atomistic simulations on mullite Al2(Al2+2xSi2−2x)O10−x in a variable range of composition

Mazza, Daniele; Ronchetti, Silvia Maria; Costanzo, Alberto

doi:10.1016/j.jeurceramsoc.2007.03.003

Cited by 8 publications

(2 citation statements)

References 6 publications

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“…X denotes the number of lack oxygen atoms in unit cell and VI, IV stand for octahedral and tetrahedral coordination of Al atoms, respectively. The structure of mullite crystal is much more complicated, there are irregular tetrahedral double-stranded [XO 4 ] (X=Si,Al) existing in the structure, a number of oxygen vacancies exist in the structure and the position is not fixed, which can cause cationic displacement [4,5]. According to the theoretical model of anionic coordination polyhedron growth units [6,7], the single crystal cell is used to calculate as ideal crystal cell structure.…”

Section: VImentioning

confidence: 99%

CASTEP Calculation of Surface Property of Mullite Composites and Analysis of Crystal Growth Habit

Wang

Chen

et al. 2011

AMR

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According to the conditions of preparation of mullite composites by open-system hydrothermal crystallization method, surface energies of mullite crystal were calculated by the first principle plane pseudo-potential. Growth habit plane of mullite composites was also discussed and analyzed. The calculation results demonstrate that surface energies of (001), (010), (100), (210) and (120) of mullite crystal are 0.337KeV•nm-2, 0.029KeV•nm-2, 0.027KeV•nm-2, 0.032KeV•nm-2, 0.037KeV•nm-2, respectively. That is to say, the surface energies of mullite crystal follow the order of (001) >> (210) > (120) > (100) > (010). It is also found that E(001) is much larger than others. According to Curie-Wulff principle, growth rate of crystal face is directly proportional to its surface energy, which shows that growth rate of mullite crystal in (001) direction is the fastest and mullite crystal is favorable for one-dimensional growth to columnar.

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Section: VImentioning

confidence: 99%

CASTEP Calculation of Surface Property of Mullite Composites and Analysis of Crystal Growth Habit

Wang

Chen

et al. 2011

AMR

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“…The chemical formula of mullite is often given by Al 4+2x Si 2-2x O 10-x , where x=0, x=0.25 and x=0.4 correspond to sillimanite, 3:2 mullite and 2:1 mullite, respectively (Campos et al, 2012;Chakraborty, 2008;Cividanes et al, 2010a;Fischer et al, 1996). The amount of oxygen vacancies per unit cell is represented by x, which is related to the replacement of silicon ions (Si 4+ ) by aluminum ions (Al 3+ ) in the tetrahedral sites of the mullite structure (Mazza et al, 2008). With increasing alumina content, the cation Si 4+ is replaced by the cation Al 3+ and the anion (oxygen) and the oxygen vacancies are created to maintain charge neutrality (Campos et al, 2012;Cividanes et al, 2011;Okada, 2008).…”

Section: Introductionmentioning

confidence: 99%

Influence of Ethylene Glycol on the Mullite Crystallization Processes Analyzed by Rietveld Refinement

Fernandes

Campos

Cividanes

et al. 2013

J.Aerosp. Technol. Manag.

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Mullite is an excellent structural material due to its high temperature stability, high electrical insulation capabilities and creep resistance. This material has a number of technological applications, such as rocket nozzles used in the aerospace industry. In this work, mullite was obtained by sol-gel process, using silicic sol, aluminum nitrate and ethylene glycol, besides the following volume ratios of silica sol dispersion to ethylene glycol: 1/0; 1/1; 1/2; and 1/3. After drying, the samples were thermal treated at temperatures of 1,000; 1,100; 1,200 and 1,250°C. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and specific surface area (Bruner-Emmett-Teller-BET). SEM showed that mullite particles are fine and nearly equiaxed. The sample without ethylene glycol showed 3/2 mullite after heat treatment at 1,250°C. The sample with intermediate ethylene glycol concentration presented two crystallization processes: the first at 1,000°C forming mullite and spinel phases, and the second at 1,250°C forming only 3/2 mullite. However, the sample with the highest ethylene glycol concentration crystallized directly to mullite at 1,000°C with the highest yield. There is a strong dependence on the specific surface area with temperature. The Rietveld refinement showed that the a cell lattice of mullite and the Al/Si molar ratio in the mullite formula depend on the ethylene glycol presence and on the calcination temperature. The lattice parameters b and c are not dependent on the alumina content, but the parameter a increases with the increase in the alumina content. Samples prepared with higher ethylene glycol concentrations reached higher mullite yields at lower temperatures.

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Mullite crystallization using fully hydrolyzed silica sol: the gelation temperature influence

Campos

Cividanes

Machado

et al. 2014

J Sol-Gel Sci Technol

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Atomistic simulations on mullite Al2(Al2+2xSi2−2x)O10−x in a variable range of composition

Cited by 8 publications

References 6 publications

CASTEP Calculation of Surface Property of Mullite Composites and Analysis of Crystal Growth Habit

CASTEP Calculation of Surface Property of Mullite Composites and Analysis of Crystal Growth Habit

Influence of Ethylene Glycol on the Mullite Crystallization Processes Analyzed by Rietveld Refinement

Mullite crystallization using fully hydrolyzed silica sol: the gelation temperature influence

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