The glassy state

A modern definition of glass reads “glass is a non-equilibrium, non-crystalline condensed state of matter that exhibits a glass transition. The structure of glasses is similar to that of their parent supercooled liquids (SCL), and they spontaneously relax toward the SCL state. Their ultimate fate, in the limit of infinite time, is to crystallize.” We try to elucidate the glassy state of matter by researching on the fundamental concepts related to structure, relaxation, glass transition, and crystallization.

Schematics of how a first-order thermodynamic property, such as volume or enthalpy, varies with temperature for a glass-forming liquid.

Lithium disilicate crystals in a LS2 glass. Ellipsoids can be observed at two different views. Reproduced with permission from Elsevier.

The Nucleation

Crystal nucleation in supercooled liquids is of great relevance to chemists, physicists, and materials scientists dealing with the fundamentals of crystallization, and to engineers working in the development and application of inorganic oxide glasses, which are by far the most important family of commercial glasses. Theoretical, experimental and computer simulation research in this field are crucial for understanding the nature of the vitreous state and for the successful development of advanced materials, such as novel amorphous and polycrystalline substances. Despite the substantial knowledge accumulated since the derivation of the Classical Nucleation Theory (CNT) in the early 50s, there are still plenty of open issues regarding experimental results on nucleation in glass-forming substances and their correct theoretical interpretation within the framework of the CNT.

The Crystallization

The important natural processes, such as snow formation and crystallization of igneous rocks, such as obsidian (right image), as well as technological operations, for example, solidification of metallic alloys, and glass ceramization illustrate the utmost importance of crystallization. The structural rearrangements that are fostered by crystal nucleation and growth cause drastic changes in the macroscopic properties of glass-forming melts and magmas. We intend to study the most accepted models for the description of crystal nucleation, growth, and overall crystallization. We also dwell on the significant progress made in the understanding of crystallization over the past few decades through the combined use of theoretical models and experiments.

Partially devitrified obsidian volcanic glass showing crystobalite (snowflake) crystals of ~1cm.

Dental Glass-ceramics

Various stages of fabrication of lithium disilicate glass-ceramics by CAD/CAM. IPS e.max® CAD from Ivoclar Vivadent AG was selected as an example.

The global market for dental materials is predicted to exceed 10 billion dollars in 2020. The main drivers for this growth are easing the workflow of dentists and increasing the comfort of patients. Therefore, remarkable research projects have been conducted and are currently underway to develop improved or new dental materials with enhanced properties or that can be processed using advanced technologies, such as CAD/CAM or 3D printing. Among these materials, zirconia, glass or polymer-infiltrated ceramics, and glass-ceramics (GCs) are of great importance. Dental glass-ceramics are highly attractive because they are easy to process and have outstanding esthetics, translucency, low thermal conductivity, high strength, chemical durability, biocompatibility, wear resistance, and hardness similar to that of natural teeth, and, in certain cases, these materials are bioactive. They are divided into two groups: restorative and bioactive. Most restorative dental glass-ceramics are inert and biocompatible and are used in the restoration and reconstruction of teeth. Bioactive dental glass-ceramics display bone-bonding ability and stimulate positive biological reactions at the material/tissue interface. They are suggested for dentin hypersensitivity treatment, implant coating, bone regeneration, and periodontal therapy.

Bioactive Glass-ceramics

The interest around bioactive glass-ceramics has grown significantly over the last two decades due to their appropriate biochemical and mechanical properties. The intense research effort in this field has led to some new commercial products for biomedical applications. We work on the basic concepts of glass-ceramic processing and development via controlled heat treatments of monolithic pieces or sinter-crystallization of powdered glasses. We investigate processing, properties and applications of bioactive glass-ceramics and study several promising types of bioactive glass-ceramics.

Hydroxycarbonate apatite (HCA) formation on the SiO2–CaO–P2O5–ZrO2 glass-ceramic surface (partially sintered powder) after 24 h exposure to simulated body fluid (SBF).