Control of the amorphous content in traditional ceramics by means of alternative fluxing agents

The role of KOH and NaOH as mineralisers in kaolinite-quartz (KQ) and kaolinite-quartz-feldspar (KQF) systems has been investigated, in order to determine how they affect the phase composition of ceramic bodies, and if they can replace traditional flux to boost formation of amorphous phases. Attention was paid to the effects induced by mineralisers on (i) the fundamental ceramic equilibrium reaction between crystal phases and amorphous phase, and (ii) on the morphology of the final ceramic product in terms of secondary mullite habit. NaOH and KOH turn out to be amorphous content boosters, but their efficiency to promote amorphous phases is related to quartz particle size, too. The amorphous component appears at the expenses of mullite and quartz, and an analysis of the formation Gibbs energy demonstrates that an increase in mineraliser content shifts the fundamental ceramic equilibrium reaction towards amorphous formation, though Na differs from K in affecting such transformation.