All About Glass
Trasparency, compactness and structural uniformity, complete chemical and biological inertia, resistance to liquids, gases, vapors and micro-organisms, inalterable over the years, sterilizable and entirely eco-friendly, thanks to infinite recycling possibilities. These are just some of the exceptional intrinsic characteristics of glass, composed entirely of natural substances. Glass is a material obtained by the fusion of a mixture of raw materials at a high temperature.
When warm, it can be modelled into a variety of shapes, creating products with chemical and physical characteristics completely different from the raw materials of which it is composed. The basic raw materials used to make a vitreous mixture which, when fused and solidified becomes glass, are sand, sodium carbonate and calcium carbonate.
Sand is the “glazing” raw material that supplies silicon dioxide (SiO2) capable of forming the amorphous and unorderly lattice that characterizes a glass structure. It is present in different proportions according to the type of glass, usually about 70-74% in industrially produced glass containers. Sodium oxide (Na2O) is used as a “flux” or coadjutant substance for the fusion procedure, in variable proportions, from 12-13% in glass panes, 13-16% in glass containers and about 20% for artistic glass. It is introduced into the vitrifiable mixture through soda ash, industrial sodium carbonate.
The supply of sodium oxide is necessary to assure the fusion of the mixture and modification of properties, including the density, dilation, chemical resistance, workability interval. In fact, glass with a higher percentage of sodium oxide is more suitable for slow manual workmanship, while glass with a lower percentage of sodium oxide is suitable for high velocity industrial machinery. Glass does not possess only one temperature for solidification and molding of objects, as it takes place in a lapse of time called “workmanship”, during which a progressive increase in viscosity occurs.
Calcium carbonate is used to introduce a calcium oxide (CaO) stabilizer into the glass to make it less alterable, with respect to glass obtained from compositions containing only silica and sodium oxide. Calcium oxide stabilizes glass both chemically and mechanically, influencing the viscosity of the molten glass and reducing workmanship intervals. It usually accounts for not more than 12-13% of glass composition in weight. Sodium sulfate is also added to sand, soda ash and calcium carbonate. It acts as a refining substance facilitating the expulsion of gas bubbles from the mixture, generated by the decomposition of the components and improving uniformity.
The purity of the raw materials guarantees a transparent, colorless glass; the addition of small quantities of colored substances, for example iron oxide and chrome for green, sulphur compositions for yellow-brown, cobalt for blue, produces different colored glass in a variety of shades.
Today, glass is used in a vast range of applications, from industrial to domestic uses and is considered irreplaceable in many instances.There are common uses like jars and containers for food, beverages, cosmetics, medicines, window panes, artistic objects. Other uses include sophisticated technology like optical fibers, used in telecommunications, uninvasive micro surgery, visual image diagnostics and even special glass for space modules.