INFLUENCE OF COLORANTS ON CRYSTALLIZATION AND MECHANICAL-PROPERTIES OF LITHIA-BASED GLASS-CERAMICS

Objectives. The objective of the present study was to test the hypothesis that colorants such as AgNO3 and FeCl3 act as co-nucleating agents with P2O5 in the Li2O-Al2O3-CaO-SiO2 system and that the addition of either colorant and P2O5 produces a greater effect on crystallization and selected mechanical properties than the use of P2O5 alone. Methods. Microstructural effects were observed by SEM and optical microscopy. Mechanical properties were determined to monitor the effects of structural changes after crystallization. These include controlled-flaw flexure strength, fracture toughness (K-IC), and Vickers hardness (VHN). Results. Based on a glass composition of 27.84 mol% Li2O, 2.45 mol% Al2O3, 5.88 mol% CaO, and 63.84 mol% SiO2 (LACS), the mechanical properties of LACS glass-ceramics were influenced by P2O5, the colorant type, and the colorant concentration. The mean strength of the glass-ceramic disks without P2O5 increased with AgNO3 concentration to a peak value of 188 MPa at a concentration of 0.78 mmol%. The maximum value of controlled-flaw flexure strength increased from 120 MPa for one of the FeCl3 groups to 188 MPa for one of the AgNO3 groups. The maximum fracture toughness of glass-ceramic disks without P2O5 (2.45 MPa.m(1/2) was associated with a AgNO3 concentration of 0.58 mmol%. This value was significantly greater (p less than or equal to 0.05) than that of the corresponding group (1.90 MPa.m(1/2)) which also contained P2O5. There was no significant change in K-IC of glass-ceramic specimens containing P2O5 as the AgNO3 concentration increased. The increase in controlled-flaw flexure strength and fracture toughness of specimen groups containing 0.58 to 0.78 mmol% AgNO3 support its use as a colorant and as a nucleating agent in LACS glass-ceramics. Significance. The development of tougher, higher strength glass-ceramics can be controlled by the use of colorants that are also effective as nucleating agents. Although certain colorants are believed to act synergistically when used in combination with known nucleating agents to enhance the fracture toughness of glass-ceramics, this effect was not observed in this study for the combined use of AgNO3 and the classical nucleating agent, P2O5. In fact, the colorant used in this study (AgNO3) was more effective than P2O5 as a nucleating agent for lithia-based glass-ceramics.