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

Objectives. The objective of the present study was to test the hypothe sis 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 struc tural changes after crystallization. These include controlled-flaw fle xure strength, fracture toughness (K-IC), and Vickers hardness (VHN). Results. Based on a glass composition of 27.84 mol% Li2O, 2.45 mol% Al 2O3, 5.88 mol% CaO, and 63.84 mol% SiO2 (LACS), the mechanical propert ies of LACS glass-ceramics were influenced by P2O5, the colorant type, and the colorant concentration. The mean strength of the glass-cerami c disks without P2O5 increased with AgNO3 concentration to a peak valu e of 188 MPa at a concentration of 0.78 mmol%. The maximum value of co ntrolled-flaw flexure strength increased from 120 MPa for one of the F eCl3 groups to 188 MPa for one of the AgNO3 groups. The maximum fractu re 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 si gnificantly greater (p less than or equal to 0.05) than that of the co rresponding group (1.90 MPa.m(1/2)) which also contained P2O5. There w as 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 conta ining 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 u se of colorants that are also effective as nucleating agents. Although certain colorants are believed to act synergistically when used in co mbination with known nucleating agents to enhance the fracture toughne ss of glass-ceramics, this effect was not observed in this study for t he 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.