Mullite‐glass and mullite‐mullite interfaces: Analysis by molecular dynamics (MD) simulation and high‐resolution TEM

Abstract

The properties of mullite-glass and mullite-mullite interfaces have been investigated at 1800 K by molecular dynamics (MD) simulation and high-resolution TEM. The simulation showed that mullite-glass interfaces typically have much lower interfacial energies than mullite-mullite interfaces, which results from the structural flexibility of the glass and associated accommodation of interfacial mismatch. The (110)-glass interface has the lowest energy of all interfaces studied, which is consistent with the observed dominance of this interface in experimental mullite-glass samples examined by TEM. The simulation shows that the interfacial energies of the (100)-glass and (010)-glass interfaces are higher than that those of the (001) Thus, the mullite structure is similar to that of sillimanite, which consists of AlO 6 octahedra chains that are parallel to the c axis and linked by SiO 4 and AlO 4 tetrahedra. During this reaction, the substitution of Si by Al is charge compensated by the removal of O and consequent O vacancy formation, which results in the disordering of the tetrahedrally-coordinated cations. 3,4 Sintered mullite, which commonly is formed by heating aluminosilicates (e.g

Exploiting superspace to clarify vacancy and Al/Si ordering in mullite

“…DFT or molecular dynamics (MD) calculations are not possible with partially occupied atoms. Although the superspace symmetry of mullite allows the derivation of a simple vacancy-ordering distribution, recent MD studies use a random distribution of vacancies (Lacks et al, 2005;Chen et al, 2008;Zamani & Behdinan, 2017;Adabifiroozjaei et al, 2018), and DFT calculations use a vacancy distribution that is constrained by size considerations but not by superspace symmetry considerations (Chen et al, 2010;Aryal et al, 2012). The different studies partly avoid Si on the T* site, but Al/Si ordering on the T site is not considered.…”

Revealing Spatial Distribution of Al-Coordinated Species in a Phase-Separated Aluminosilicate Glass by STEM-EELS

“…Although no 5-fold Al site exists in crystalline mullite, it is often found in the magmatic aluminosilicate melt . With sufficient undercooling, such 5-fold Al species may be retained in the distorted network based on octahedra and tetrahedra units, which may be the reasons for finding abundant 5- and 6-fold Al in Al-rich phase …”

“…35 With sufficient undercooling, such 5-fold Al species may be retained in the distorted network based on octahedra and tetrahedra units, which may be the reasons for finding abundant 5-and 6-fold Al in Al-rich phase. 36 Figure 4 shows two structural models obtained from MD simulation. Simulation was performed with Al 2 O 3 composition ranging from 0 to 60 mol %.…”

Ultra‐low temperature preparation of mullite glass‐ceramics with high transparency sintered from EMT‐type zeolite

“…The grain growth of the prepared glass‐ceramics at a high temperature result in the reduction of transmittance, in consistent with the transmittance data. Mullite glass‐ceramic is usually fabricated from aluminosilicates via the high temperature sintering in the range of 1400°C−1600°C 35 through heating the single‐phase gel or the diphasic aerogels method 36 . Until now, the monophasic gel has been commonly thought to prepare mullite at 980°C, which is the lowest preparation temperature because the metakaolinite transformation would take place 37 .…”