چكيده به لاتين
In this project, a commercial dental lithium disilicate based glass-ceramic was studied (which has been added about 10% ZrO2 in it in order to increasing the fracture toughness and improvement of mechanical properties); then the optimized percent of P2O5 was determined.
First of all prepared batches were melted, casted and then annealed; after that each one was heat-treated in their crystallization peak temperatures –which has been determined by DSC- and finally 3 different glass-ceramics was obtained.
crystallization behaviors, micro-hardness, chemical resistance, flexural strength and fracture toughness of three lithium-disilicate glass compositions were determined; and by means of X-ray diffraction and scanning electron microscopy, it was discussed about the reason of improvement of properties.
According to the result of tests, it was defined that P2O5 encouraged the separation in melting and it created lithium phosphate (which is a suitable place for crystallization of both Li2SiO3 and Li2Si2O5 phases). Furthermore in more percent of P2O5, nucleacen agent’s density will be increased, so the viscosity of glass melt will be increased too, then the crystal growth will be caused in higher temperatures. Spatial limitation makes the final crystals in spherical shaped and it decrease the aspect ratio of crystals. This morphology changes will affect on mechanical properties. In fact the improvement of mechanical properties is because of both morphology changes and increasing of lithium disilicate crystalline phase in final heat-treated glass-ceramics.
Also it should be mentioned that P2O5 decreases the chemical resistance in the initial glasses (because of increasing P-rich zones in glass phase) but after all heat treatments and forming final glass-ceramics, it will increase the chemical resistance.
Keywords:
Glass-ceramic, Lithium-disilicate, Nucleacen agent, P2O5, Mechanical properties, Fracture toughness
