report on glass

Report on glass

For my report I have chosen glass. In my report I will look into the history of glass, the chemical properties of glass, the optical properties, the uses of glass, how glass is made, different types of glass and the structural properties of glass.

Firstly I will look at the history of glass. Dictionary definition of glass, Glass 1. Any of a large class of materials with highly variable mechanical and optical properties that solidify from the molten state without crystallization, that are typically based on silicon dioxide, boric oxide, aluminium oxide, or phosphorus pentoxide, that are generally transparent or translucent, and that are regarded physically as super cooled liquids rather than true solids.

Natural glass

5000 BC

Glass was first made by volcanoes, lightening strikes and meteors this is called obsidian. Obsidian is a black, shiny, translucent material. It is formed when volcanic molten lava comes into contact with water and cools very quickly. This material obsidian is mainly made up of silicon dioxide SiO2 but with many impurities such as iron and magnesium. This form of glass was used as simple tools.

3500 BC

The earliest sign of man made glass were glass beads these were found in Egypt and Eastern Mesopotamia also in Mesopotamia they used glass to glaze pots and vases.

1500 BC

At this time Egyptian craftsmen are known to have started developing a method for making glass pots by dipping a core mould of compacted sand into molten glass and then turning the mould so that molten glass adhered to it. While still soft, the glass-covered mould could then be rolled on a slab of stone in order to smooth or decorate it.

27 BC-AD 14

The discovery of glassblowing happened some time between 27 BC and AD 14. The long thin metal tube used in the blowing process has changed very little since then. Then the ancient Romans In the last century BC began blowing glass inside moulds, this increased the variety of shapes possible for hollow glass items.

AD 100

The first people to use glass for an architectural purpose were the Romans. With the discovery of clear glass through the introduction of manganese oxide. Cast glass windows with poor optical qualities, then began to ...

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27 BC-AD 14

AD 100

11th century

At this time German glass craftsmen developed a technique for the production of glass sheets. By blowing a hollow glass sphere and swinging it vertically, gravity would pull the glass into a cylindrical pod measuring up to 3 metres long and with a width of up to 45 cm. While still hot the ends of the pod were cut off and the resulting cylinder cut lengthways and laid flat.

Other types of sheet glass were crown glass relatively common across Western Europe. With this technique, a glass ball was blown and then opened outwards on the opposite side to the pipe. Spinning the semi-molten ball then caused it to flatten and increase in size, but only up to a limited size. The panes would then be joined with lead strips and put together to create windows.

Glazing remained but it was a great luxury up to the late middle Ages with royal palaces and churches the most likely buildings to have glass windows. Stained glass windows reached their peak as the Middle Ages drew to a close with an increasing number of public buildings inns and the homes of the rich fitted with clear or coloured glass.

15th-16th centuries

In 15th century the craftsmen of Murano started producing particularly pure crystal using quartz sand and potash made from sea plants.

1674

The English glassmaker George Ravenscroft discovered lead crystal he then patented his new glass in 1674. He had been commissioned to find a substitute for the Venetian crystal produced in Murano and based on pure quartz sand and potash. By using higher proportions of lead oxide instead of potash, he succeeded in producing a brilliant glass with a high refractive index that was very well suited for deep cutting and engraving.

1688

In 1688 France invented a new way of producing glass sheets which would be used for mirrors. The molten glass was poured onto a special table and rolled out flat. After its cooled down the plate glass was ground on large round tables by rotating cast iron discs and increasingly fine abrasive sands, and then polished using felt disks. This then was coated on one side by a reflective low melting metal and this produced a high quality mirror.

19th century

The German scientist Otto Schott used scientific methods to study the effects of numerous chemical elements on the optical and thermal properties of glass. Schott teamed up with Ernst Abbe a professor at the University of Jena and joint owner of the Carl Zeiss firm to make substantial advances.

1900-1905

Michael Owens invented an automatic bottle-blowing machine. In 1923 with the development of the gob feeder, which ensured the rapid supply of more consistently sized gobs in bottle production

1905-1914

In 1905 a Belgian named Fourcault managed to vertically draw a continuous sheet of glass of a consistent width from the tank. Commercial production of sheet glass using the Fourcault process eventually got under way in 1914.

Also at the end of World War 1 Emil Bicheroux developed a process where the molten glass was poured from a pot through two rollers this made the glass a more even thickness and less time spent grinding and polishing.

1910

Edouard Benedictus invented laminated glass this was a form of safety glass and it was called triplex

1959

The Pilkington Brothers developed the float process after the Second World War. Molten glass, when poured across the surface of a bath of molten tin, spreads and flattens before being drawn horizontally in a continuous ribbon this left the glass with a brilliant finish of sheet glass with the optical qualities of plate glass.

Chemical properties of glass

Common glass is made from:

Sand or silica (SiO2)
Sodium carbonate (Na2CO3)
Limestone (CaCO3)
Magnesium carbonate (MgCO3)
Additives to improve the glass quality and to colour the glass.

Glass is much more resistant to corrosion to other materials this is why it is in use in all chemistry labs. However hydrofluoric acid, concentrated phosphoric acid when hot, or when it contains fluorides dissolves glass quickly. Water can also corrode glass but at very high temperatures especially if the water is alkaline water does corrode glass at a low temperature but this is very slowly. Acids and alkalis corrode glass in different ways. Alkalis corrode the silica directly while acids corrode the alkali in the glass. Glass is a good thermal conductor but it does not conduct electricity.

Optical

Glass does not transmit ultra-violet radiation which has short wavelengths this means that you cant get a tan behind a window. However it does transmit infrared radiation which has long wavelengths this means that it does let heat through which is why greenhouses are hot.

Structural properties

Glasses have three characteristics that make them resemble frozen liquids than rather than crystalline solids. First there is no order. Second, there are empty places. Finally glasses don't contain planes of atoms.

The simplest way to understand the difference between a glass and a crystalline solid is to look at the structure of glass at the atomic scale. By rapidly condensing metal atoms from the gas phase, or by rapidly quenching a molten metal, it is possible to produce glassy metals that have the structure shown in the figure below

The structure of a glassy metal on the atomic scale.

The amorphous structure of glass makes it brittle. Because glass doesn't contain planes of atoms that can slip past each other, there is no way to relieve stress. Excessive stress therefore forms a crack that starts at a point where there is a surface flaw. Particles on the surface of the crack become separated. The stress that formed the crack is now borne by particles that have fewer neighbors over which the stress can be distributed. As the crack grows, the intensity of the stress at its tip increases. This allows more bonds to break, and the crack widens until the glass breaks. Thus, if you want to cut a piece of glass, start by scoring the glass with a file to produce a scratch along which it will break when stressed.