Brief discussion about Glass

         GLASS

           Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. Scientifically, the term "glass" is often defined in a broader sense, encompassing every solid that possesses a non-crystalline (that is, amorphous) structure at the atomic scale and that exhibits a glass transition when heated towards the liquid state.

TYPES OF GLASS, ITS STRUCTURE AND ITS ADVANTAGES:

               STRUCTURE OF GLASS

       The most familiar, and historically the oldest, types of glass are "silicate glasses" based on the chemical compound  silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO₂), sodium oxide (Na₂O) from sodium carbonate (Na₂CO₃), calcium oxide, also called lime (CaO), and several minor additives. A very clear and durable quartz glass can be made from pure silica, but the high melting point and very narrow glass transition of quartz make glassblowing and hot working difficult. In glasses like soda lime, the compounds added to quartz are used to lower the melting temperature and improve workability, at a cost in the toughness, thermal stability, and optical transmittance.

In the process of manufacture, silicate glass can be poured, formed, extruded and molded into forms ranging from flat sheets to highly intricate shapes. The finished product is brittle and will fracture, unless laminated or specially treated, but is extremely durable under most conditions. It erodes very slowly and can withstand the action of water. It is resilient to chemical attack and is an ideal material for the manufacture of containers for foodstuffs and most chemicals.

  A study seeking to decrease the brittleness of glasses was carried out. The brittleness, defined as the ratio of hardness to fracture toughness, was estimated from the ratio of median crack length to the diagonal length of a deformation impression. The brittleness of various kinds of glasses in the silicate as well as borosilicate systems was investigated as a function of glass properties. The brittleness of the glasses was correlated with densities, i.e., a variation of ∼1 to ∼9 μm^−1/2 in brittleness was observed as the density varied from ∼1.9 to ∼2.8 g/cm³. The brittleness of normal glasses decreased with decreasing density due to the ease of both plastic flow and densification. On the other hand, the brittleness of anomalous glasses increased with decreasing density due to the lack of plastic flow. In addition, the brittleness of normal glasses was less than that of the anomalous glasses with the same density. We also observed that a 50% decrease in brittleness resulted in an increase of crack initiation load by ∼15 times.

                    

   

                   

Above figures shows the fracture in glass.

APPLICATIONS:

Many applications of silicate glasses derive from their optical transparency, which gives rise to one of silicate glasses' primary uses as window panes. Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light. Glass can be colored by adding metallic salts, and can also be painted and printed with vitreous enamels. These qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or molded into any shape, and also because it is a sterile product, it has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also been used forpaperweights, marbles, and beads. When extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, and when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects historically were so commonly made of silicate glass that they are simply called by the name of the material, such as drinking glasses and reading glasses.

             In science, porcelains and many polymer thermoplastics familiar from everyday use are glasses too. These sorts of glasses can be made of quite different kinds of materials than silica: metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses (acrylic glass,polycarbonate or polyethylene terephthalate) are a lighter alternative than traditional glass.