Glass is an inorganic, non-metallic material that does not have a crystalline structure. Such materials are called amorphous and are practically solid liquids that are cooled so quickly that crystals cannot form. Typical glasses range from soda-lime silicate glass for glass bottles to extremely high-purity quartz glass for optical fibers. Glass is widely used for windows, bottles, drinking glasses, transfer lines and containers for highly corrosive liquids, optical glasses, windows for nuclear applications, etc. used. Historically, most products were made of blown glass. In recent times, most flat glass has been produced using the float process. Mass production of bottles and decorative products is carried out on an industrial scale using the blown glass process. The hand-blown glass items are made in art/craft centres across the UK.
Normal glass
The main component of glass is silicon dioxide (SiO 2). The most common form of silica used in glass production has always been sand.
The sand itself can be melted to make glass, but the temperature at which this can be achieved is around 1700o C. By adding other chemicals to the sand, the temperature of the melt can be significantly reduced. The addition of sodium carbonate (Na2CO3), known as soda ash, in an amount to make a molten mixture of 75% silica (SiO2) and 25% sodium oxide (Na2O) reduces the temperature of the melt to about 800o C. However, a glass of this composition is soluble in water and is called a water glass. To give stability to the glass, other chemicals such as calcium oxide (CaO) and magnesium oxide (MgO) are needed. The raw materials for the introduction of CaO and MgO are their carbonates, limestone (CaCO3) and dolomite (MgCO3), which emit carbon dioxide at high temperatures and leave the oxides in the glass.
Borosilicate glass:
Borosilicate glass is made from 70% - 80% silica (SiO2) and 7% - 13% boron oxide (B2O3) with small amounts of the alkali sodium oxide (soda) (Na2O) and aluminum oxide (AI2O3). Glassware is often used in laboratories where repeated contact with water vapor at high temperatures can leach alkali ions. Borosilicate glass has a relatively low alkali content and, as a result, high resistance to the attack of water. Borosilicate glass has exceptional thermal shock resistance, as it has a low coefficient of expansion (3.3 x 10 -6 K-1) and a high softening point. The maximum recommended working temperature (short-term) for borosilicate glass is 500oC Borosilicate glass has good optical properties with the ability to transmit light through the visible region of the spectrum and in the near ultraviolet range. It is therefore widely used in photochemistry. Due to its thermal and optical properties, it is widely used for high-intensity lighting applications. This glass is used in the manufacture of glass fibers for use in plastic and textile reinforcements - see below In the household, borosilicate glass is known in the form of stoveware and other heat-resistant household items such as Pyrex. These items are generally used at temperatures up to 250oC. Borosilicate glass has a very high resistance to the attack of water, acids, salt solutions, halogens and organic solvents. It also has moderate resistance to alkalis. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkalis cause significant corrosion of the glass. That is why this glass is widely used in chemical plants and for laboratory equipment.
General characteristics of glass
Mechanical strength
Glass has a great intrinsic strength. It is only weakened by surface defects, which give everyday glass its fragile reputation. A special surface treatment can minimize the effects of surface defects. The practical tensile strength of the glass is about 27MPa to 62MPa. However, glass can withstand extremely high compressive stresses. Therefore, most of the glass breakage is due to the failure of tensile strength. The reason for the weak tensile strength of glass is that it is usually covered by microscopic cracks that create local stress concentrations. Glass has no mechanisms to reduce the resulting high local stresses and is therefore subject to rapid brittle fracture. There are two methods to reduce/eliminate this problem: Thermal or chemical treatment of the glass so that the outer surfaces are under relatively high compressive stress, while the middle area between the surfaces is under tensile stress. The cracks are therefore "kept closed by the constant residual stress... It is toughened/toughened glass. The strength of the glass can be improved by up to a factor of 10 with this method. It ensures that the glass surfaces do not crack and that the glass does not come into mechanical contact with things during use that could scratch the surface. Glasses that are made without surface defects have a strength value
