Description
Glass which has the property of changing colour, in varying intensity, when it is exposed to different types of rays, belong to this group.
Photosensitive glass
This is silicate glass in which, after radiation of UV-rays and X-rays, through a perforated screen, followed by thermal treatment at a temperature between 400-600oC, a colouring can be developed in the radiated part. This sensitivity to radiation is irreversible and permanent and is due to a oxide-reduction mechanism with a transfer of electrons in the presence of activating ions, like cerium ions which provoke the rush of metallic particles (copper, gold, silver&). One of their applications, amongst others, is the construction of supports for printed circuits.
Photo-chromic glass
This is glass which has the property of darkening when exposed to UV and visible rays and behave in the opposite manner when the exposition is ceased.
The photosensitive process is based on the reversible decomposition of silver halide micro-crystals (coluri, bromuri, ioduri), which are present as a scattered phase in a lattice of a particular glass. One of its uses is the construction of lenses for sunglasses.
Intelligent glass
Glass sheets are a fundamental material for building construction; in the near future it will become the dynamic skin thanks to electro-chemical glass also known as intelligent glass. This glass already exists, but is too expensive at the moment to have wide-scale use; but it is only a question of time.
Simple glass is no longer enough to provide comfort for large buildings entirely covered in large structural windows. Sheets have therefore been produced with a coating of very thin films of metallic reflective material, using chemical and physical coating techniques. They allow better control of the light and energy from outside to inside the building and reduce the dispersal from inside to outside so as to reduce energy consumption and improve comfort. Due to their aesthetic characteristics (reflection, colour), they are a new architectural element, which have been exploited with incredible results, especially in the construction of skyscrapers.
But these sheets have static behaviour: the absorption of energy and the transmission of light are the same in the morning and at midday, in summer and winter.
With intelligent glass, a window or a transparent door can be transformed into an opaque surface or just a translucent one or transform it into a coloured material.
Electrical current is used to command miniscule crystals deposited on the surface of the sheet; when their direction changes with the current, the crystals modify the transmission of light. So, without human intervention, the windows change their behaviour to light to produce more comfortable light and temperature conditions inside the building, thereby reducing energy consumption to heat or cool the environment.
Protective glass
This is glass for nuclear applications, which contain a high barium oxide level and rare earths or in lead oxide (up to over 70% in PbO). This glass is used for screens and windows to observe rooms containing radioactive material.