**2.3 Physical properties**

286 Sintering of Ceramics – New Emerging Techniques

The common treatment to obtain glass-ceramics is an appropriate thermal treatment from a base glass. The thermal treatment used in industry to get this material is a "two plateaus" treatment. It consists of heating the glassy matrix (base glass) at a temperature above the glass transition temperature, Tg in order to induce nuclei in the glass. The temperature is then increased to a second plateau to induce the growth of these nuclei. A second technique consists in a single plateau. The glass is heated at a temperature above Tg but below the crystallization temperature, Tc. This technique allows the nucleation phenomenon and

Oxide glass-ceramics are by far the most studied glass-ceramics. They have been widely investigated since 1950 and the research associated to this area is now slowing down. Today, research is more focused on the nucleation and growth phenomena to have a better understanding. However chalcogenide glass-ceramics still remain of great interest because of their transparency in the infrared range associated to better mechanical properties. As

Chalcogenide glass-ceramics transparent in the range 8-12 µm were first synthesized in 1973 by Mecholsky in the system 0.3 PbSe-0.7 Ge1.5As0.5Se3 with a 60% crystalline fraction. He showed that the glass-ceramic modulus of rupture was increased to as much as twice that of

Other researchers worked on systems such as As-Ge-Se-Sn (Cheng, 1982), Ga-Ge-Sb-Se (Ma et al., 2003) or Ge-Te-Se (Song et al., 1997) but the reproducibility of the glass-ceramics

First chalco-halide glass-ceramics, transparent in the far infrared (10 µm) was obtained in 2003 within the system GeS2-Sb2S3-CsCl in the "Glass and Ceramic" laboratory in Rennes (France) (Zhang et al., 2004) (Fig. 5). The simultaneous presence of ionic and covalent compounds prevent from the rapid and uncontrollable crystallization. Three years later, glass-ceramics transparent until 14µm, covering the second and third atmospheric windows

(a) (b)

(c) (d)

previously mentioned, potential applications are infrared lenses for thermal camera.

the base glass and the Vickers hardness increased by 30% (Mecholsky et al., 1976).

entirely, were synthesized in the system GeS2-Ga2Se3-CsCl (Calvez et al., 2007).

Fig. 5. Glass composition 62.5GeS2-12.5Sb2S3-25CsCl heated at 290°C for different

crystallization times (a) No thermal treatment (b) 7h (c) 73h and (d) 144h.

avoids excessive growth.

synthesis remained difficult.
