Reaction bonding of mullite (RBM) in presence of scandia Sc2O3

The presence of 3rd group transition metal oxides yttria and lanthana has a strong accelerating influence on the reaction bonding of mullite (RBM) from silicon and α-alumina, even at temperatures below 1350 °C. This is due to the formation of low-viscosity transient liquid phases enhancing Si-oxidation, alumina diffusion and mullite nucleation and growth. The presence of the 3rd group transition metal oxide scandia (Sc2O3) does not show a significant influence on the RBM process up to 1350 °C. Sc2O3 does not form low viscous Sc–Al–Si–O liquid phases which enhance reactivity. Instead, a direct formation of Sc-disilicate Sc2Si2O7 is observed. At temperatures between 1350 and 1550 °C, a slightly enhanced mullite formation due to accelerated solid state diffusion, and the formation of a ternary Sc-rich aluminosilicate is evident.