Effect of some additives on the development of spinel-based glass-ceramic glazes for floor-tiles

Abstract The feasibility of developing spinel-based glass-ceramic glazes from a glass with composition in the system ZnO–MgO–B 2 O 3 –Al 2 O 3 –SiO 2 was examined. To do it additional fluxes and/or nucleants were added to a parent glass before melting. Pressed pellets of powdered glasses were submitted to standard thermal treatments up to 1200 °C. The crystallization path and the microstructural development at several temperatures were followed by several experimental techniques. The results showed that additions of TiO 2 as nucleant or additional B 2 O 3 as flux to the chosen glass favored the crystallization of cordierite or mullite as main crystalline phase. Glasses which also contained minor amounts of Na 2 O and K 2 O, as additional fluxes, crystallized rapidly to spinel (Mg,Zn)Al 2 O 4 using a single relatively fast heating ramp without a previous nucleating heat treatment step. Microstructural examination revealed that a uniform, fine-scale phase separation preceded crystallization. Very small, well-shaped crystals of spinel with octahedral morphology were formed. Slips of these glasses on conventional tile supports thermally treated under single heating ramps developed similar microstructures that the ones raised from pellets. This feature allows to suggesting these spinel-based glass-ceramic glazes as good candidates to improve the mechanical properties of conventional glazes.