Induced crystallization porosity and properties of sintereds diopside and wollastonite glass-ceramics

A diopside (CaO·MgO·2SiO2) and wollastonite (CaO·SiO2) glass-ceramics, forming ∼60% crystal phase and ∼40% albite-like (Na2O·Al2O3·6SiO2) residual glass were studied. Two other diopside glass-ceramics with higher Na2O and Al2O3 content were also investigated.The phase formation was estimated by DTA, XRD and pycnometry, while the densification process was evaluated by porosity variations, dilatometry and SEM observations. The bending strength, Young modulus and coefficient of thermal expansion of the glass-ceramics were also measured and discussed.The compositions were characterized by a good sinter-ability and surface crystallization and, due to the different volume variation of diopside and wollastonite during the crystallization, diverse amounts of intragranular crystallization induced porosity, PCR, were formed in the glass-ceramics.Notwithstanding the higher porosity, the diopside glass-ceramics have better mechanical properties than wollastonite one. At the same time, despite of the different residual glass compositions and the diverse coefficients of thermal expansion, all diopside materials have comparable bending strength and Young modulus.The obtained diopside sintered glass-ceramics are characterized by significant porosity of 10–12 vol.%, high amount of residual glass (about 40%), large initial particles (<75 μm) and elevate crystal size (15–25 μm). Nevertheless high bending strength of 130 MPa and Young modulus of 100 GPa were obtained after only 1 min sinter-crystallization at 900 °C. The good mechanical properties were related to the PCR formation.