INFLUENCE OF P2O5, AGNO3, AND FECL3 ON COLOR AND TRANSLUCENCY OF LITHIA-BASED GLASS-CERAMICS

Objectives. The objective of this study was to characterize the influe nce of various metals, metal compounds, and P2O5 as a nucleating agent on the color and translucency of a Li2O-Al2O3-CaO-SiO2 glass-ceramic. Methods. Glass frits of Li2O-Al2O3-CaO-SiO2 (LACS), LACS with 1 mol% P2O5 (LACSP), and/or LACS with one of 16 colorants were melted, poured into a cylindrical graphite mold, cut into disks, annealed, nucleated , crystallized, and annealed again. Ten translucency measurements of e ach of five disks were made using a tristimulus colorimeter and a D65 standard CIE illuminant. The color of each disk was analyzed using the CIE La*b* color space system (1976) as a function of colorant, color ant concentration, and P2O5. Results. Mean L values of glass-ceramic disks ranged from 63.5 for LACS containing 6.2 mmol% FeCl3. (LACSP-6.2 Fe) to 84.1 for LACS. No significant difference (p>0.05) was found bet ween the mean L values for LACS, LACSP, and LACS with 0.19 mmol% AgNO 3 (LACS-0.19Ag). The mean contrast ratio of glass-ceramic specimens ra nged from 0.42 (LACS and LACS-1.0Fe) to 0.98 (LAGS-0.78Ag). Mean color difference values varied from 5.8 (LACSP-1.0Fe vs. LACS) to 36.3 (LAC SP-0.78Ag vs. LACSP). Significance. The results of this study indicate that, because certain colorants in glass-ceramics affect opacity as w ell as hue and chroma, the development of glass-ceramics should be sim plified by: 1) employing a nucleating agent that does not affect hue o r chroma significantly, 2) controlling fixed levels of translucency co nsistent with mechanical and physical property requirements, and 3) va rying the hue and chroma by means of colorants that do not affect the crystallization process. This implies that the volume fraction and mea n size of crystals must be controlled, since the translucency or opaci ty of glass-ceramics is associated with scattering of light at the int erfaces between adjacent crystals, and between crystals and the glass phase because of differences in refractive indices (McMillan, 1979a).