What is glass and how is it produced?
Glass is a hard material normally fragile and transparent common in our daily life. It is composed mainly of sand (silicates, SiO2) and an alkali.
These materials at high temperature (i.e. molten viscous state) fuse together; then they are cooled rapidly forming a rigid structure, however not having enough time to form a crystalline regular structure.
Depending on the final use and application the composition of the glass and cooling rate will vary to achieve the adequate properties for the specific application. These are the common ingredients to obtain glass:
3. Limestone (calcium carbonate or CaCo3) or dolomite (MgCO3)
Other materials and oxides can be added to increase properties (tinting, durability, etc.), produce different effects, colors, etc.
Types of glass and market application
The main types of glass are described below:
- It has light transmission appropriate to be use in flat glass in windows;
- It has a smooth and nonporous surface that allows glass bottles and packaging glass to be easily cleaned;
- Soda-lime glass containers are virtually inert, resistant to chemical attack from aqueous solutions so they will not contaminate the contents inside or affect the taste.
Whereas pure glass SiO2 does not absorb UV light, soda-lime glass does not allow light at a wavelength of lower than 400 nm (UV light) to pass.
The disadvantages of soda-lime glass is that is not resistant to high temperatures and sudden thermal changes. For example, everybody has experienced a glass breaking down when pouring liquid at high temperature, for example to make tea.
Some of the use of soda-lime glass is primarily used for bottles, jars, everyday drinking glasses, and window glass.
Lead glass is composed of 54-65% SiO2, 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2), and various other oxides. When the content of PbO is less than 18% is known as crystal glass.
- In moderate amounts lead increases durability;
- In high amounts it lowers the melting point and decreases the hardness giving a soft surface;
- In addition it has a high refractive index giving high brilliance glass.
These two last properties make it appropriate for decorating purposes.
Glass with high lead oxide contents (i.e. 65%) may be used as radiation shielding glass because lead absorb gamma rays and other forms of harmful radiation, for example, for nuclear industry.
As with soda-lime glass, lead glass will not withstand high temperatures or sudden changes in temperature.
There are other special types of glass by adding different substances. For example:
Chemistry % by Weight of the most common types of glass
More information about other type of materials can be found through the following web-pages:
Information on the periodic elements can be reach at this webpage: