What is Glass?

 Reference :

 Writer :     E-mail :

 Writed Date : 07/17/2013   ( Last Edit : 1/9/2017 )


What is glass?

Glass is made in Egypt about 3000 BC. Ancient Egyptians were unique glass- blowers. Old glass didn’t pass light and because of its impurities were colored. Glass is a very cool liquid and it is also liquid in heat with its below freezing point. And generally, it is a clear thing which light passes through it very well and its behind is clearly visible. Glass is a material which has a solid shape because of its specific atomic- molecular structure. But unlike other solids it isn’t crystal. This state occurs when melt material becomes quickly cool before reaching to transition point glass.

Over view:

From molecular construction of glass in solid shape it has irregular molecular structure. In high temperature, glass is like any other liquids, but with decreasing temperature, its viscosity increases unmorally, and cause that molecular couldn’t gather in structure that is necessary for crystal. So, the molecular structure of glass is irregular like liquids, but this irregular structure isn’t movable. Glass has hard body which its hardship (difficulty) is 8 and it groove all except diamonds. The specific gravity of glass is 5/2 grams per cubic centimeter (cm 3) and it is very crisp and froglike.  Glass is resistant against all chemical materials, even strong acids and alkalis and it doesn’t affected by the corrosive, for this reason laboratory glassware are made of glass. Just HF affects it and it dissolves the glass

Compounds of Glass

Principal components of glass:

Three materials; Carbonate of soda, limestone, silica are the main materials of glass. Glass materials that approved by Institute of Industrial Research and Standard of Iran include: Silica, Boron dioxide, Oxide of phosphorus pentad.

Flux aids:

Sodium carbonate, potassium carbonate, glass-dust, sodium silicate and silica are flux aids which dissolved in water and gradually reduce the transparency of glass Because of this reason after a few years, most of used glasses are come opaque in green house and light cannot pass well through them.

for demonstrate the resistance of glass against the weather, we should add two-valence barium oxides, lead, calcium, magnesium and zinc to the mixture, that these elements are called stabilizers


Refined products:

The purifications’ reduce air bubbles in glass, and they are two kinds:

1. Physical: sodium sulfate and sodium chlorate with big bubbles (by creating big bubbles), absorb tiny bubbles and remove from the melt glass.

2. Chemical: salts of arsenic and antimony make compounds that destroy the tiny inside of glass:

1.Using of borax instead of oxide and sodium carbonate (flux aids) which hydrolyze in heat to sodium oxide and Broome oxide and actually it acts instead of both of those materials.

2 Using of sodium nitrate to eliminating the green color of glass that it is because of iron oxide that enters into furnace with other materials.

3.Using the manganese oxide which uses more resistance against atmospheric factors and more clear of glass.

4.Using of lead oxide instead if calcium oxide for making the crystals high quality glass that cause to blaze of glass.

5.Using of silver oxide to making high quality crystal.

6.Using of feldspar which cause to better resistance against the chemical materials.

7.Using phosphate for resistance of glass against fluoridric acid.

8.Using tiny glasses for increasing melt rate of materials

9.Use of metal oxide for making colored glass.

10.Sodium oxide is used to absorb in fared radiation and bore oxide for increasing thermal resistance.

Types of glass and their application:

Glass is used in various forms, and it has various uses. For instance; it is used in making decorative fixtures like flowers, panel, in laboratory glass ware or kitchen utensils like mug, bottle... And at the end, in making flat glass which are presented in two types: simple and wooded, it as many uses which the main usage of it, is for doors and window in construction works.


Colored glass:

Colored glass can b achieved in tow ways:

1.With adding and reducing some chemical in glass producing raw materials.

2.For coloring tow sides of glass, white glass is down into colored molten glass.

Fire-resistant glass (Pyrex): 

This kind of glass with raw materials has high resistance against heat, is used much amount of boric oxide and their amount of ceils are more than other ordinary glasses.

Flat glass:

 This kind of glass is made with adding metal mesh to glass, and it is used for entrance doors, workshops, powerhouses, elevators and anywhere that there is breaking danger and fall downing of glass.

Insulting glass (double):

This type of glass is made of two layers, simple and sometimes colored, which have been parallel to each other and their edges or gaps are airtight and the space between them filled up with drying materials like silica Zhen or in some cases is created vacuum between two layers. This kind of glass which is heat, cold, and sound insulation are used in many buildings like airport, hotels and hospitals.

Tempered glass:

In this case, again the glass is heated to 700c and then suddenly it is cooled under certain and monitored conditions. This increase the resistance of glass (about 3 to 5 times) against the impact and thermal shocks. When this kind of glass breaks, it is divided to fine and cubic-shaped particles, which aren’t harmful.

Safety glass:

These types of glasses include two or more layers of glass which are connected to each other by layers of clear nylon under heat and pressure.

Also some kinds of mica glass are used as sound insulation, heat absorber, reducing transparency and safety glass. When this glass breaks, the elastic properties of nylon, prevents of distribution and dispersion of particles.

Reflective glass: (Reflex)

In this type of glass, one surface of glass is covered with light and heat reflective coating and also with metal or metal oxide with this property.

These types of glass reflect sunlight and are effective in heat reduction and light luminosity.

Most famous glasses which are produced in industrial scale, are:

Soda lime glass, Borosilicate and crystal glass.

Soda lime glass:

More than %90 of total glass production in the world is Soda lime glass. Buildings door, windows, Auto glass, bottles and many other glass products are made of Soda lime glass. The main components of this glass are: Silicon oxide, Calcium oxide & Sodium oxide.

Borosilicate glass:

This glass has low to moderate thermal expansion coefficient, viscosity behavior, high temperature and low density. Many laboratories, industrial and domestic glassware are made of this glass. These glasses are known with brand names like: Pyrex, Symax , Treks, ....

Crystal glass:

Crystal glass or leaded glass is one of the silicate glasses which contain lead oxide in its composition. This kind of glass has a shiny appearance and it is like quartz crystals. It seems its name is because of this resemblance. This glass also has little stiff and there is the possibility of turning the glass. So decorative containers which known as crystal glass ware are made of this genus.

Other kinds of glass are: Photo chromic glass, Opal and Silica glass. Also there are different types of glass which aren’t produced in industrial scale.