Residual Thermal Stress of Spinell Based-Ceramic Infiltrated with Glass Rich in Lanthanum

Ceramic composites developed for glass infiltration in ceramic substract has as main advantage the reduction of fabrication temperatures of ceramic parts compared to the solid state sintering. In this work, spinell based-ceramics infiltrated with glass rich in lanthanum, aiming applications in dental ceramics, were developed and studied. Pre-sintered spinell substrates with porosity of 10, 15 and 20% were infiltrated with glass at temperature 1120°C-120min, using heating and cooling rate of 10°C/min. The composites present relative density superior 98.6% in every investigated condition, and X-ray diffraction indicated the phase MgAl₂O₄, as unique crystalline phase detected. Hardness Vickers varying between 850-1000HV and fracture toughness varying between 3.0 to 4.5MPa.m^1/2 were obtained for composites with variation of intergranular phase quantity. The evaluation of residual thermal stress indicates that compressive thermal stress are generated in every composition varying from 70-90MPa, for compositions containing between 10 to 20% of infiltrated glass, respectively. Theoretical calculations indicate that the excellent quantity of inter-granular phase infiltrated must be 17%, for obtaining better resistance to crack propagation in this material.