Glass-ceramics

Glass-ceramics are innovative technological materials produced by the controlled crystallization of glass. They are composed of crystals dispersed in a glass matrix. This duality enables them to combine the advantages of glass (wide range of compositions, ease of synthesis and shaping, absence of porosity) with the specific properties of the crystalline phases formed during crystallization (notably a low coefficient of thermal expansion).

Since their chance discovery in the 1950s, a great deal of work has gone into understanding the mechanisms of crystallization in glass. This article begins with a description of the different nucleation and growth processes involved in crystallization. The theoretical aspects of homogeneous and heterogeneous nucleation are discussed, as well as the different growth modes. While classical nucleation theory offers a simplified approach to crystallization, new theories are now emerging that are both more effective and more complex, enabling the different information provided by increasingly high-performance characterization techniques to be reconciled.

Understanding nucleation/growth phenomena is an important step in the design and development of glass-ceramics. Indeed, while the macroscopic properties of a glass-ceramic are closely correlated with the composition of the initial glass, they are above all dependent on the nature and microstructure of the crystalline phases (size, morphology, quantity...). When designing a glass-ceramic with specific properties, it is therefore essential to master the crystallization process in order to determine the most suitable manufacturing process for producing the desired microstructure. Some of these processes are described in detail in this article, from the classic use of nucleating agents to promote high-volume crystallization, to modern laser irradiation crystallization for the design of glass-ceramics with complex 3D geometric structures.

As microstructure control is the key step in the design of glass-ceramics with special properties, it is essential to be able to characterize structural modifications during the crystallization process. The contribution of the many complementary techniques (thermal analysis, diffraction, electron microscopy, spectroscopy...) available to observe and characterize organization from the local order to the macroscopic scale is discussed and illustrated.

Finally, the wide choice of glass compositions, combined with the development of various microstructures, enables the production of glass-ceramics with a wide range of properties (thermal, mechanical, optical, electrical, medical, aesthetic, storage, energy, etc.). The most noteworthy applications and recent developments are detailed in this article, with a particular...