RUSHIKESH M. RAVALRUSHIKESH M. RAVAL

GLASSES STRUCTURES, PROPERTIES AND

APPLICATIONS

DefinitionDefinition an inorganic product of fusion that has an inorganic product of fusion that has

cooled to a rigid condition without cooled to a rigid condition without crystallizing crystallizing

When glass is cooled from the hot molten When glass is cooled from the hot molten state, it gradually increases in viscosity state, it gradually increases in viscosity without crystallization over a wide without crystallization over a wide temperature range, until it assumes its temperature range, until it assumes its characteristic hard, brittle form. Cooling characteristic hard, brittle form. Cooling is controlled to prevent crystallization, or is controlled to prevent crystallization, or high strain.high strain.

Glass, chemically, is actually more Glass, chemically, is actually more like a liquid, but at room temperature like a liquid, but at room temperature it is so viscous or 'sticky' it looks and it is so viscous or 'sticky' it looks and feels like a solid. At higher feels like a solid. At higher temperatures glass gradually becomes temperatures glass gradually becomes softer and more like a liquid. It is this softer and more like a liquid. It is this latter property which allows glass to latter property which allows glass to be poured, blown, pressed and be poured, blown, pressed and moulded into such a variety of shapes.moulded into such a variety of shapes.

HistoryHistory Glass technology has evolved for 6,000 yearsGlass technology has evolved for 6,000 years A most important development in glass A most important development in glass

technology was the use of a blow pipe technology was the use of a blow pipe The first glass was coloured because of the The first glass was coloured because of the

presence of various impurities such as oxides presence of various impurities such as oxides of iron and chromium. Virtually colourless of iron and chromium. Virtually colourless glass was first made some 1,500 years ago.glass was first made some 1,500 years ago.

Today many products of glass are made in Today many products of glass are made in fully automatic processing lines fully automatic processing lines

Although glass is one of the oldest materials, Although glass is one of the oldest materials, its properties are unique and not yet fully its properties are unique and not yet fully understood.understood.

Glasses Glasses is one of three basic types of ceramics. Glass is an amorphous

(non-crystalline) solid material which is often transparent has widespread partical, technological, and decorative usage in things like window panes, tableware, and optoelectronics.

The most familiar, histrocially the oldest, types of glasses are based on the chemical compound silica (silicon dioxide), the primary constituent of sand, which is familiar from use as window glass and in glass bottles.

Actually glasses are extremely cooled liquid. Fusion of sand (SiO2), soda (Na2CO3) & lime (CaO) that produces a

transparent solid when cooled. A 3D network of atoms which lacks the repeated, orderly

arrangement typical of crystalline materials.

Raw Materials To Making Glass

Silica sandSilica sand Soda ashSoda ash Lime stoneLime stone DolomiteDolomite Feldspathic materials Feldspathic materials Lead oxideLead oxide Boric acidBoric acid Crushed glassCrushed glass

Raw Materials To Making Glass

1. Glass forming oxides: usually the dominant constituent SiO2, B2O3, P2O5, etc.

2. Fluxes: reduce melting temperatures Na2O, PbO, K2O, Li2O, etc.

3. Property modifiers: added to tailor chemical durability, expansion, viscosity, etc.

CaO, Al2O3, etc.4. Colorants: oxides with 3d, 4f electron structures; minor additives (<1 wt

%)5. Fining agents: minor additives (<1 wt%) to help promote bubble

removal As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates

Glasses Structure Structure : Network formers

Molecules that link up with each other to form long chains and networks. Hot glass cools, chains unable to organize into a pattern. Solidification has short-range order only.

Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+).

Impurities: interfere with formation of crystalline structure

CRYSTALLINE STRUCTURE OF GLASS

AMORPHOUS STRUCTURE OF GLASS

TYPES OF GLASSES Silica glass Borosilicate glass Lead glass Sodalime glass

Silica glass

It is mainly used where temperature resistance is required. They can be used at temperatures upto about 900 C. They have a very low co-efficient of thermal expansion and have a high resistance to thermal shock. Silica glass is also named as QUARTZ GLASS.

Borosilicate glass

It have some part of silica replaced by boron oxide. This provides some desirable properties. Borosilicate glass have not workability with high sterngth, high, high chemical stability, high electrical resistance and low thermal expansion. It is used in high tension insulators, kitchenware, telescope mirror, laboratory glass ware, industrial instrument glass. One type of trade name is PYREX.

Lead glass

lead glass also known as FLINT GLASSES. These glasses have low melting point, good hot workability, high electrical resistance and high refractive indices. It is used as optical glass, art and jewellery glass, thermometer tubing, fluorecent lamps, television tube, window and shields for protection from x-ray padition, table glass etc.

Sodalime glass It have good hot workability. It is

also melt at low temperature . These glasses are used as window glass, chemical apparatures, breakers, test tubes etc.

Some Other Types of Glasses

Coloured glass Recrystallised glass Fibre glass Glass wools Foam glass

Coloured glass

Various substanmces are added to get coloured glasses.

Recrystallised glass Various nucleating agents like sodium

fluoride, phosphorous pentoxide, titanium oxide or vanadium oxide are added to glass melt to get recrystallised glass. This glass also known as POLYCRYSTALLING GLASS. This glass process high hardness and impact strength and better thermal conductivity.

Fibre glass It is also known as glass fibre. The material

is in the form of fibres produced from glass. The fibres are produced from molten glass by drawing the material through dies giving fibre of 2 to 10 micron in diameter. The fibres are not brittle and have high tensile strength. They are non flammable, chemically inactive, poor conductor of sound and non- conductive to heat and electricity. Fibres are used to produce composite materials by mixing them with synthetic rasins.

Glass wools They are produced from molten

glass by forcing the material through some vents by centrifugal force. It gives short fibres at about 10 microns. This process is also known as CROWN PROCESS. Glass wools are used as heat insulation.

Foam glass It is produced by introducing

innumerable air cells in molten glass. It has low density and can float in water . It can be cut into suitable sizes and used for heat insulations.

Properties General properties of glasses

High hardness / Brittle Low density compared to high strength Low thermal expansion coefficient Low heat / electrical conductivity High melting point Good chemical resistance / Chemical inert Wide range of optical transmission

Transparent Translucent Opaque

Applications Solar cell Thin film transistors (TFT) Light sensors Optical memory devices Electro photographic application X-ray image sensors Eu-doped optical fiber DVD (digital video/versatile disc) Hard cover made from ta-C Windows, doors Specs Fabrication

References http:// www.designinsite.dk/gifs/pb1007.jpg www.cullenconsulting.com.au/ epsi/images/ www.scielo.br/.../ jbsmse/v26n1/a07fig03.gif www.turkcadcam.net www.esrf.fr/.../2002/ Materials/MAT3/fig081 www.mrf-furnaces.com/ images/4station.jpg met.iisc.ernet.in/ ~govind/Spray-forming.jpg