Effects of various nucleating agents on the crystallization and properties of lithium disilicate glass-ceramics

抄録

P₂O₅ is an efficacious nucleating agent for promoting the crystallization of lithium disilicate glass, with numerous studies attributing its effectiveness to the formation of Li₃PO₄ crystals, which serve as heterogeneous nucleation sites for Li₂Si₂O₅ precipitation. However, recent studies have not consistently observed Li₃PO₄ precipitation. To address this controversy, this study utilizes Li₃PO₄ as a nucleating agent to determine whether Li₃PO₄ crystallites induce the precipitation of Li₂Si₂O₅. Additionally, Na₃PO₄, an analogue of Li₃PO₄, is employed to evaluate its potential to promote nucleation, while P₂O₅ serves as a comparative reference under identical conditions. Upon heating, all three agents fully melt in the glass. Subsequent heat treatment results in the precipitation of Li₂SiO₃ crystals, followed by Li₂Si₂O₅ crystals. It remains unclear whether these phosphates precipitate prior to the Li₂SiO₃ crystals. Although all agents exhibit comparable effects, the Li₂Si₂O₅ grain size in the Na₃PO₄ group is finer, leading to decreased strength and increased transparency in the samples. This may be due to the mixed alkali effect, where Na⁺ ions inhibit the growth of Li₂Si₂O₅ crystals. Notably, the initially precipitated Li₂SiO₃ crystals exhibit a higher Li content than the original glass, indicating that the nucleating agents alter the local glass composition to resemble that of the Li₂SiO₃ crystals, thereby facilitating crystallization. Subsequently, Li₂SiO₃ crystals decompose to form Li₂Si₂O₅ crystals, resulting in a redistribution of Li⁺ ions from localized enrichment back to a uniform distribution consistent with the original glass.