**A Novel Approach to Develop Chalcogenide Glasses and Glass-Ceramics by Pulsed Current Electrical Sintering (PCES)**

Gaelle Delaizir1 and Laurent Calvez2

*1Groupe d'Etudes des Matériaux Hétérogènes (GEMH, ENSCI), Centre Européen de la Céramique, 12 rue Atlantis, Limoges, 2Equipe Verres et Céramiques, UMR CNRS Sciences Chimiques de Rennes, Université de Rennes 1, Rennes Cedex, France* 

#### **1. Introduction**

280 Sintering of Ceramics – New Emerging Techniques

Swab, J.J. (2009). *Advances in ceramic armor V: ceramic engineering and science proceedings.* I5, Vol.30, John Wiley and Sons, (2009), ISBN: 0470457554, 9780470457559 Ting, J. M. & Lin, R.Y. Effect of particle size distribution on sintering, *J. Mater. Sci.* 30, (1995)

Valenzuela, R., (2005). *Magnetic Ceramics*, Cambridge University Press, (2005) ISBN:

Yuan, Q..L.; Zhang, P.; Gao, L.; Peng, H.; Ren, X. & Zhang, D.(2010). MgO-Al2O3-SiO2 Glass-

Yu, Y., Wang, X., Cao, Y. & Hu, X., *Appl. Surf. Sci.,* 172, 3-4, (2001) 260-264, ISSN: 0169-4332 Wang. Y., (2008). *Introduction to ceramics,* McGraw-Hill Education (Asia), (2008), ISBN:

Wawrziniak,W. & Grunov, r. (1980). *Silikat technik,* 31, (1980) 238, ISSN: 0037-5233.

Ceramic Prepared by Sol-Gel Method, *Advan. Mater. Res.* 92, (2010) 131-137, ISSN:

2382-2389, ISSN 0022-2461

0521018439, 9780521018432

0071274979, 9780071274975

1022-6680

Chalcogenide glasses have been in the last decades, of paramount interest for night vision devices because of their remarkable transparency in the two atmospheric windows (3-5µm and 8-12µm). Chalcogenide glasses tend to replace, at least partially, the expensive monocrystalline Ge or polycrystalline ZnSe for infrared (IR) lenses (Zhang et al., 2003). The ease of processing due to their viscoplastic property and the lower cost of chalcogenide glasses compared to mono-crystalline Ge have made them one of the best candidates for lenses of optical thermal imaging cameras but are also very efficient for various fields of applications working in the second and third atmospheric windows. Thus, chalcogenide glasses are at the centre of active and passive applications such as night vision (Guillevic et al., 2009), generation of new infrared sources (Troles et al., 2010), electronic devices (Danto et al., 2010), chemical and biological sensors to detect CO2 or tumors respectively (Wilhelm et al., 2007), etc. They are also promising materials for energy applications, such as solid electrolyte (Hayashi et al., 2001) or thermoelectric materials (Goncalves et al., 2010). These glasses that contain no oxygen in their composition are usually synthesized in vacuumed silica ampoules using the so-called melt-quenching technique. The low thermal conductivity of silica limits the cooling rate during quenching. This usually leads to heterogeneous composition in the case of unstable glass composition (that tends to crystallize) and thus, reduces the glassy domain as well as the available diameters of these glasses. In this chapter, we describe a novel approach to synthesize chalcogenide glass bulks with large diameters including unstable compositions. This technique combines either the mechanical alloying to get amorphous powder or the grinding of glass obtained from previous small diameter melt-quenching technique and the Pulsed Current Electrical Sintering (PCES) also known as Spark Plasma Sintering (SPS) (Hubert et al., submitted). This new technique allows both the sintering of amorphous powder and its shaping in one step in few minutes. This paves the way for a new set of glasses previously impossible to synthesize, especially for crystallization concerns. Indeed, the fast heating rates reached by SPS (Joule effect heating) prevents the glass from undesirable crystallization. Also, the SPS technique is efficient to

A Novel Approach to Develop Chalcogenide Glasses and

Sealing

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

High energy ball milling process has been demonstrated to be a promising method for the preparation of amorphous powder with fine microstructure. The amorphization reaction during mechanical milling is usually attributed to microstructural breakdown followed by the interdiffusion of elements (Johnson, 1986) or mechanically driven atomic mixing (Lund et al., 2004 & Delogu et al., 2005) among previously formed nanocrystalline multilayers. In mechanical milling experiments, the kinetic process of the amorphization reactions usually proceeds slowly and therefore a glass forming composition is determined only after milling for an extended time (usually >100 h) (Eckert et al., 1997, Schurak et al., 1999 & Choi et al., 2006) (Fig. 3). The ability to synthesize a dense material from amorphous powders obtained by mechanical-alloying has recently been demonstrated for many systems regarding metallic glasses (Yan et al., 2008, Patil et al., 2005 & Kim et al., 2005). Also, amorphous powders in the systems Li2S-P2S5 or AgI-As2Se3 have been synthesized using the same method for solid electrolyte applications (Hayashi et al., 2001, Sekine et al., 2007 & Trevey et al., 2009). Few papers report the amorphization of metallic elements used in the manufacture of IR glasses; they are limited to the study of Ge-Se powder but none of these papers are relevant for the production of optical devices (Shirakawa et al., 2001 & Machado

bands (S-H, Se-H, O-H, etc)

Fig. 1. Experimental set-up.

Reactional tube

**2.2.1.2 Mechanical milling** 

et al., 2005).

Glass-Ceramics by Pulsed Current Electrical Sintering (PCES) 283

such as sulphur or selenium are purified to avoid losses of transmission due to absorption

Chemical Products

Vacuum

Dewar with liquid nitrogen

Trap

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

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 devitrification through the SPS technique.
