Nanosized alumina from boehmite additions in alumina porcelain: 1. Effect on reactivity and mullitisation

The influence of nanosized alumina additions and of grain size of alumina filler on the reaction-sintering of alumina porcelain is investigated. Phase and porosity evolution has been studied from room temperature up to 1400 °C. When vitrification occurs the presence of alumina nanoparticles leads to a new type of mullitisation which has two major consequences: a volume expansion resulting in a shrinkage inhibition and a decrease of the amount of liquid which causes densification problems at usual firing temperatures. This phenomenon is enhanced if the alumina filler is coarse but it is limited when fine and round alumina is used because in that last case vitrification kinetics is slowed down.