Power ramp flash crystallization of a lithium silicate-based glass for dental applications: Structural insights and mechanical properties

This study presents a novel method for the ultrafast crystallization of bulk glasses, termed Power Ramp Flash (PRF) crystallization, which employs a controlled electric field and temperature modulation. We demonstrate the rapid monophase crystallization of a lithium silicate-based glass, relevant for dental applications. A non-stoichiometric, multicomponent glass-forming composition, similar to Ivoclar e.max (R) CAD, was melt-quenched into rectangular bar molds and then subjected to crystallization using flash crystallization and a conventional method for comparison. Our results highlight the importance of controlling the power surge during the flash event and the subsequent crystallization process to achieve glass-ceramics with the desired phases and volume fractions, enabled by precise temperature control. Additionally, distinct electrical signatures corresponding to the crystallization of lithium metasilicate and lithium disilicate were identified, demonstrating the potential for in-situ studies of crystallization processes. We validate our experimental results using finite element analysis to simulate the sample temperature during flash crystallization, accounting for Joule heating. Comprehensive structural characterization shows that our method crystallizes the disilicate phase within seconds at a furnace temperature of only 360 degrees C, significantly below the materials' glass transition temperature (T-g,T- onset = 470 degrees C). After optimizing the electrical parameters involved in flash crystallization, specimens were produced featuring mesoscale crystalline domains (similar to 50 nm), a Vickers hardness of approximately 6.80 GPa, and an indentation fracture toughness (K-C) of 1.54 MPa m(0.5). Overall, our findings demonstrate, for the first time, the capability of flash crystallization to rapidly crystallize these glass-ceramics in a controlled fashion without compromising their mechanical properties.