Formulation of glass and glass products

Pure silica, SiO ₂ , commonly exists in two different structures:

• quartz, a naturally occurring crystal with a trigonal structure;

• vitreous silica, whose disordered structure is that of an amorphous material or glass.

The exact nature of an amorphous structure is complex and continues to raise all kinds of questions. In its February 2005 issue, the CNRS journal ranks "the obscure nature of glass" among the ten great enigmas of physics! We'll only touch briefly on industrial glass manufacturing processes, which continue to evolve considerably, thanks in particular to advances in mathematical modelling. In this dossier, we focus mainly on industrial glass products and current trends in technological developments in this field.

Unlike silica, a pure material (SiO ₂ ), glass is a material with a complex composition. Often 8 to 10 different oxides ensure its properties: melting temperature and viscosity, mechanical properties, scratchability, chemical resistance, color, etc.

But what elements can be used to develop glass products? There are at least five, although the reality can often be more complex:

• glass composition;

• the structure of the glass matrix ;

• glass surface;

• the deposition of thin layers on the glass surface;

• finally, the production of complex glass products.

In this dossier, we'll just choose one or two examples from each of these categories.