Preparation of MgO-doped mullite by sol-gel method, powder characteristics and sintering

In situ formation of sintered cordierite–mullite nano–micro composites by utilizing of waste silica fume

“…Also, the mineral composition calculations agree with those qualitatively determined by X-ray analysis at 1400 8C. This indicates the addition of MgO and Al 2 O 3 to kaolin and silica fume is thermally mature at this corresponding temperature and the starting materials have completely reacted to form cordierite and mullite phases without any sign for the formation of Mg-A1 spinel [18]. Moreover, the presence of MgO lowered the surface free energy of the A1 2 O 3 -SiO 2 diphasic system and enhanced the reactivity.…”

Fabrication and properties of cordierite–mullite bonded porous SiC ceramics

“…As the mass fraction of MgO increased from 3.0 to 4.5 wt%, the flexural strength significantly increased from 58.09 to 78.71 MPa, and the open porosity decreased from 25.14% to 21.63%. This is because the addition of MgO favored the formation of mullite at a relatively lower temperature; i.e., the presence of MgO lowered the surface free energy of the Al 2 O 3 -SiO 2 biphasic system and enhanced the reactivity [24]. Furthermore, MgO accelerated the densification process in alumina and mullite by modifying the lattice diffusion coefficient [25].…”

Sintering of commercial mulite powder: Effect of MgO dopant

“…It has been reported (Ismail et al, 1990) that the addition of MgO above 0.5 wt.% has no effect in controlling mullite grain growth, and another study (Sivakumar et al, 2001) used only 0.25 wt.% in its analysis of the sintering of commercial mullite. On the other hand, most studies have used larger amounts of MgO, usually ranging from 1 to 5 wt.%.…”

“…The high density obtained with the 0.5% doped samples after sintering at 1600 • C, has only been observed in literature (Chandran et al, 1996;Jayaseelan et al, 2004;Montanaro et al, 1997;Viswabaskaran et al, 2003) with larger amounts of MgO (>2 wt.%). Some researchers have achieved high densities (≈99%) using small amounts of MgO (≤0.5%) (Ismail et al, 1990;Sivakumar et al, 2001), but they used pressure-assisted sintering procedure and non-commercial nanometer powders, which favor the densification. The high density attained here may be associated with the impurities in the mullite powder (ZrO 2 and TiO 2 ) and some synergistic effect of these impurities with the added MgO on the densification of the samples.…”