Types of Glass

Types of glass:

The glass may be broadly classified as:

1. Soda-Lime Glass (or) Crown Glass
2. Potash Lime Glass
3. Potash Lead Glass
4. Flint Glass
5. Pyrex (or) Heat resistant Glass
6. Common Glass and 
7. Special Glass

1. Soda Lime Glass: It is the cheapest quality of glass. It is mainly a mixture of sodium silicate and calcium silicate. It's composition, like that of most glass, is not rigidly fixed, but can be varied both as to the amount of ingredients and chemical compounds used. It is fusible at low temperature. In the fusion condition it can be Blown (or) Welded easily. It is colourless, clean and clear state. They are resistant to water not to the acids.

It is used as window panes and for the laboratory tubes and apparatus. 

2. Potash Lime Glass: It is mainly a mixture of potassium silicate and calcium silicate and potassium carbonate. It is also known as hard glass. It fuse at high temperature. It is used in the manufacture of glass articles which have to withstand high temperatures.

3. Potash Lead Glass: It is mainly a mixture of potassium silicate and lead silicate. It possesses bright lustre and great refractive power. It is used in the manufacture of artificial gems, electric bulbs, lenses, prisms etc.,

4. Flint Glass: Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). It contains varying proportion of lead oxide to make it suitable for varying purposes. Lead provides brilliance and high polish which makes the glass available for special purposes. Liquifies at lower temperature than Soda-lime glass and has better lustre.

5. Pyrex or Heat resistant glass: Both Soad-lime and Flint glass are unavailable to withstand sudden temperature changes, Because of their large coefficients of thermal expansion. The basic oxides that they contain make them susceptible to chemical attack by water and acids. Elimination of the basic oxides and inclusion of boron oxide produce a glass that is very resistant to thermal shock and to attack by water and acids.

6. Common Glass: It is mainly a mixture of sodium silicate, calcium silicate and iron silicate. It is brown, green or yellow in colour. It is mainly used in the manufacture of medicine bottles.

7. Special Glasses: Properties of glasses can be suitably altered by changing basic ingredients and adding few more ingredients. It has now emerged as versatile material to meet many special requirement in engineering. The following is the list of some of the special glasses:

  (a) Annealing glass

          To prevent glass articles becoming too brittle and falling into pieces at the slight shock they are annealed. Annealing is a process of slowly cooling hot glass to relieve internal stresses after it was formed. The process may be carried out in a temperature controlled Klin known as Lehr. The longer the annealing period, the better the quality of glass.

(b) Plate glass

          It is made by pouring white hot glass over an iron table and rolling it to a uniform thickness under heavy roller. It is stronger and more transparent to sheet glass. Plate glass includes transparent, transluscent, opacue and structural glasses. 

(c) Fluted glass

          When there are corrugation on one side of the plate glass then it is known as fluted glass. The other side is wavy but smooth. The light is admitted without glare of the sun.

(d) Fibre glass or wool glass

          Glass fiber (or glass fibre) is a material consisting of numerous extremely fine fibers of glass. The usual composition of Fibre glass is that of a soda-lime but it may be varied for different purposes. The glass fibre are made by letting the moltan glass drop through tiny orifices and blowing with air or steam to attenuate the fibres. They have high tensile strengths, upto about 2800 N/mm2.

          Glass wool is an insulating material made from fibres of glass arranged using a binder into a texture similar to wool. The process traps many small pockets of air between the glass, and these small air pockets results in high thermal insulation properties. Glass wool is produced in rolls or in slabs, with different thermal and mechanical properties. It may also be produced as a material that can be sprayed or applied in place, on the surface to be insulated. 

          The modern method of producing glass wool is the invention of Games Slayter.

(e) Foam glass

          Foam glass, is lightweight, opaque glass material having closed-cell structure.  It is prepared from powdered glass to which is added the desired quantity of carbon or any gas which makes the mass porous and light in weight. It is light enough to float in water and has been used as a substitute for cork, but it's main uses are for thermal and sound insulation. It is impervious to moisture, most fumes and vermin. This glass is water-proof also. It can be easily cut and worked with common masonry tools.

(f) Bullet proof glass

          Bullet proof glass (also known as ballistic glass, transparent armor, or bullet-resistant) is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck. This glass is made of several layers of plate glass and alternate layers consist of venyl-resign plastic. The outer layers of plate glass are made thinner than the inner layers. The thickness of this type of glass may vary from 15 mm to 75 mm. 

          Overall, bullet-proof glass is generally used to protect employees and objects of great value in banks, government buildings, convenience stores, liquor stores, jewelry stores, post offices, churches and schools. It has other uses, including protecting cars and transportation units.

(g) Structural glass

          Structural glass is the glass that is used as a building material. This type of glass is available in the form of glass-crete square blocks, or tiles in thickness varying from 5 to 30 mm. It is most typically used as transparent glazing material in the building envelope including windows in the external walls. Glass is also used for internal partitions and as an architectural feature. When used in buildings, glass is often of a safety type, which include reinforced, toughened and laminated glasses. 

(h) Glass blocks

          Glass block also known as glass brick, is an architectural element made from glass. These consist of two halves so fused together as to form a hollow inside. Glass bricks provide visual obstruction while admitting light. A recent innovation in the manufacture of glass blocks is the insulation of argon gas within the hollow centre of glass wall blocks. This advancement in production technique has resulted in a glass block which is able to offer significantly improved thermal insulation properties.

(i) Wired glass

          It is glass reinforced with wire netting or similar strengthening material embedded in it during manufacture. That is why it is called as reinforced glass. Wired glass has an impact resistance similar to that of normal glass, but in case of breakage, themesh retains the pieces of glass. This product is traditionally accepted as a low-cost fire-resistant glass.
Wired glass is produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling. A steel wire mesh is sandwiched between two separate ribbons of semi-molten glass, and then passed through a pair of metal rollers which squeeze the "sandwich of glass and wire" together. Wired glass may be further processed by grinding and polishing both surfaces, producing "polishing wired glass". 

(j) Ultraviolet ray glass

          Ultraviolet (UV) light is an electromagnetic radiation with a wavelength from 400 nm to 10 nm, Shorter than that of visible light but longer than X-Rays. These glasses transmit UV rays effectively even though it is not in the direction of the rays of sun. It is made from the raw mixture with minimum admixtures of iron, titanium and chrome.

(k) Perforated glass

    “There are two kinds of perforated glass : one having he perforations manufactured in the glass, the other having them afterwards cut. The later is the best, as the former break very readily". 

Uses of Glass

Uses of glass:

          Glass is an unlimited and innovative material that has plenty of applications. It is an essential component of numerous products that we use every day, most often without noticing it.

It is clear that modern life would not be possible without glass!

Glass is used in the following list of products:

• Glass is used to form a riffle barrel which is lighter and stronger than conventional type.
• Thousands of items in the body guided missile are made with glass.
• Glass is used for the roof, and often also for the walls, of green house. The glass in greenhouses functions as a selective transmitter of solar energy. The effect it has is to trap energy within the greenhouse, warming plants, air, soil, water and other things inside the greenhouse. As infrared frequencies are blocked by glass, this thermal energy  generated by plants is also conserved within the greenhouse, adding to the warming effect.
• Packaging (jars for food, bottles for drinks, flacon for cosmetics and pharmaceuticals)
• Tableware (drinking glasses, plate, cups, bowls)
• Housing and buildings (windows, facades, conservatory, insulation, reinforcement structures)
• Interior design and furnitures (mirrors, partitions, balustrades, tables, shelves, lighting), colour changing glass; a window with such a glass will be transparent during a day and it will be source of light at night.
• Appliances and Electronics ( Oven doors, cook top, TV, computer screens, smart-phones)
• Automotive and transport (windscreens, backlights, light weight but reinforced structural components of cars, aircrafts, ships, etc.)
• Optical glass is finding wide application for the development and advancement of sciences of Astronomy, Medical technology, Biotechnology, Life science Engineering.
• Radiation protection from X-Rays (radiology) and Gamma-rays (nuclear)
• The glass lining are applied on equipment likely to be affected by the chemical corrosion such as valves, pipes, pumps etc.,
• Fibre optic cables (phones, TV, computer: to carry information) 
• Renewable energy (solor-energy glass, wind turbines) 

All of this is made possible by the countless properties of the glass substance.

Advanced Ceramics

Advanced ceramics:

1. Glass ceramics:

          Glass-ceramics are polycrystalline materials of fine micro structure that are produced through controlled crystallisation (devitrification) of base glass. Glass ceramic materials share many properties with both glass and ceramics. These are special glass composition that are thermally treated prior to forming operations to devirtify or precipitate a crystalline phase from the material; this phase gives special properties such as zero thermal expansion for applications involving high thermal-shock applications.

         Numerous silicate based wastes, such as coal combustion ash, slag from steel production, fly ash and filter dusts from waste incinerators, mud from metal hydrometallurgy, different types of sludge as well as glass cullet or mixtures of them have been considered for the production of glass-ceramics.

          The composition in which nucleation and crystallisation have been commercially produced are : Li2O-Al2O3-SiO2,  MgO-CaO-SiO2, MgO-CaO-SiO2-P2O5

Charectirestics:

u Very low coefficient of thermal expansion.

u High thermal conductivity.

u High mechanical strength.

u Easily fabricated.

Properties and Uses of Some Glasses and Glass-Ceramics

Composition		Property		Use
		Glasses
Al2O3, MgO, CaO, SiO2		Translucent, chemically resistant		Window glass, bottles
PbO, SiO2		High refractive index		Lead crystal
B2O3, SiO2, Na2O		Acid resistant, low  expansion on heating		Pyrex
		Glass Ceramics
MgO, Al2O3, SiO2		Insulator with high  mechanical strength at  high temperatures		Spark plug insulators
CaSiO3, CaMgSi2O6, CaAl2Si2O8		Wear resistant		Building materials
Li2Si2O5		Resistant to thermal shock		Nose cones on  rockets, cookware

2. Dielectric ceramics:

          These ceramic material are used as both electrical insulators and as functional parts of an electric circuit such as capacitors, memories, sensors and actuators.

          An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (The operation of energy lost as heat), the more effective is a dielectric material.

          The electric insulators can be breakdown under high electrical voltages, the insulators are designed with lengthened surface paths to decrease the possibility of surface shorting. Since internal pores and cracks provide opportunity for additional surface failure, the insulator are glazed to make them non-absorbent.

          Non-linear dielectric ceramics are suitable in the miniaturising the electronic parts which have led to the development of increasingly sophisticated electrical circuitry.

Examples : Ferroelectrics such as BaTiO3 and PbTiO3 are used as sensors and actuators.

Lead zirconate titanate (Chemical formula Pb[ZrₓTi₁₋ₓ]O₃ ).

3. Cermets:

Cermets are composites in which ceramic material and metals join together (Ceramic plus metal = Ceramet), typically to give something with the high temperature performance or wear resistance of a ceramic and the toughness, flexibility or electrical conductivity of metal.

• Electrical components are one obvious application, Because they can get extremely hot, they need to behave like ceramics but, since they also need to conduct electricity, it helps if they work like metals. Cermets also make them useful for reducing friction in machine parts.
• These cermets are used in break shoes lining, oxidation resistant parts and inject engines.
• Machine tools are another increasingly common use for cermets, which offer greater toughness and wear resistance than more traditional materials. Cemented carbide such like composites are extensively used as cutting tools for hardened steels.

 

 

 

 

 

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Cermets meaning --https://youtu.be/KF6RvzXlXAE