**2.2 Synthesis**

## **2.2.1 Glass**

### **2.2.1.1 Melt-quenching technique**

The chemical elements constituting the glass, weighed in predetermined quantities are introduced in the set-up as shown in Fig. 1. They are put under secondary vacuum during few hours then the reactional tube is obtained by sealing the silica tube (Fig. 1).

The reactional tube is then heated in a rocking furnace at the very low rate of 2°C/min (to avoid the rapid formation of vapor and therefore the explosion of the tube) until the homogenization temperature which depends on the glass composition. The glassy composition stays few hours at this temperature. The tube containing the melt is quenched into water or air. The glass rod is then annealed in an annealing furnace previously heated at a temperature Tannealing near the glass transition temperature Tg and then slowly cooled down to room temperature to release mechanical stress induced by the quenching. We therefore obtain a glass rod (Fig. 2). Usually to reach a high transmittance, raw elements such as sulphur or selenium are purified to avoid losses of transmission due to absorption bands (S-H, Se-H, O-H, etc)

Fig. 1. Experimental set-up.

282 Sintering of Ceramics – New Emerging Techniques

make IR glass-ceramics from glass powder with reduced time of crystallization in comparison with conventional technique, i.e, heating a glass bulk in a conventional furnace (Delaizir et al., 2010). Two different compositions have been tested: 62.5GeS2-12.5Sb2S3-

Finally, this chapter reports on an analysis of SPS consolidation of the latest chalcogenide glass composition little studied so far as well as the mechanisms of sintering and

Chalcogenide glasses are, by definition, glasses which contain at least one of the three elements: sulphur, selenium and tellurium and no oxygen. Depending on the application, other chemical elements such as arsenic, antimony, germanium, etc are added to improve mechanical and optical properties and also to increase the stability against devitrification. The most interesting property of these glasses is associated with their transparency in the

Glass-ceramics are defined as polycrystalline solids prepared by the controlled crystallization of glasses with an appropriate thermal treatment. They can also be seen as composite materials made of a glassy matrix containing crystals as fillers [Mc Millan, 1979]. These kinds of materials may have exceptional properties that can be optimized according to the targeted applications. In the literature, Stookey from Corning is the first who discovered accidentally this new material, called glass-ceramics, in the middle of the 1950s. Glass-ceramics are preferred to glasses because of their better mechanical properties and are usually preferred to ceramics because of the ease of processing. Indeed, moulding is easier, faster and cheaper than solid state sintering which is the common way to produce

The chemical elements constituting the glass, weighed in predetermined quantities are introduced in the set-up as shown in Fig. 1. They are put under secondary vacuum during

The reactional tube is then heated in a rocking furnace at the very low rate of 2°C/min (to avoid the rapid formation of vapor and therefore the explosion of the tube) until the homogenization temperature which depends on the glass composition. The glassy composition stays few hours at this temperature. The tube containing the melt is quenched into water or air. The glass rod is then annealed in an annealing furnace previously heated at a temperature Tannealing near the glass transition temperature Tg and then slowly cooled down to room temperature to release mechanical stress induced by the quenching. We therefore obtain a glass rod (Fig. 2). Usually to reach a high transmittance, raw elements

few hours then the reactional tube is obtained by sealing the silica tube (Fig. 1).

25CsCl (% mol) and 80GeSe2-20Ga2Se3 (% mol); the results are reported.

devitrification through the SPS technique.

**2.1 Background**

mid and far infrared (IR).

crystalline ceramics.

**2.2.1.1 Melt-quenching technique** 

**2.2 Synthesis 2.2.1 Glass** 

**2. Chalcogenide glasses and glass-ceramics** 

Fig. 2. Example of glass rod of the GeS2-Sb2S3-CsCl composition.
