Optical glass

Optical glasses can be produced with improved transparency in a designed range of wavelengths. This is the case for silica lenses and fibres used in optoelectronics technologies which have become widespread. These are used for transatlantic communication cables, telecoms and cable TV. In fact, silica-based fibres achieve extreme transparency over tens, or even hundreds of kilometers, as a window glazing over a few millimeters. The mechanical reliability of optical fibres is as important as their optical properties. These fibres can be formed with an internal core the refractive index of which is greater than that of the outside so that total reflection can be obtained at the interface. Another way to propagate an electromagnetic signal is to produce a continuously changing refractive index and light follows a path similar to the popular mirage effect at the proximity of a hot road during summer. The first type of fibre is produced by drawing a glass perform containing in its core the high- index glass. The second type of fibre can be produced by chemical diffusion.

These fibres can be protected from moisture and contact by hermetic coatings which a redeposited during the sizing step. As a matter of fact, fibres offer exceptional strength and optical performance that have yield such an impressive development in communications. One drawback of glass when considered for lenses is its density, and load gains are accomplished by controlling better glass distribution. It should be noted that nowadays spectacles are made of organic glasses. These allow load gains and comfort. Organic glasses are polymers formed by long organic chains. One single spectacle lens is composed of several layers, some of these being only protective because of the poor scratch resistance of polymers as compared to glass. This leads to application for night observations, detection of thermal loss in buildings and in situ medical observation. These glasses while showing “plastic” behavior remain very brittle at room temperature.

Optical fibre principle with discount sinuously changing index (n0>n1). The light beam follows Descartes’ law with reflection at the refractive index interface.

Glass fibres for insulation and reinforcement

The glazing, packaging and optical applications of glass are the most well known since they refer to glass transparency. Glass is also used for thermal and acoustic insulation or to reinforce plastics and concrete because of their low cost and high strength. In the latter case, compositions incorporating ZrO2 allow to resist concrete chemical attack. Polymers reinforced by glass fibres are fabricated as composites and used in transportation applications (automotive front ends, vehicle furniture, plane cockpits, etc.).

(a) Glass wool and

(b) fibre-reinforced composite used for the front end of an automobile.

Glass mats

Glass wool is produced for buildings and vehicles and forms an air–fibre composite. Notably, the glass composition is tailored accordingly for different applications. Wool fibres have been optimized to allow maximum recovery when unpacked and set. Also, their dissolution in vitro has been of utmost importance since the problems generated by asbestos. Biodegradable glass fibres have been developed accordingly.