Glass and Ceramic

 GLASS AND CERAMICS

Introduction

·         The raw materials for making glass and ceramics are obtained from the Earth’s crust.

·         The main component of both glass and ceramic is silica or silicon dioxide, SiO₂.

·         In silicon dioxide, every silicon atom is bonded covalently to 4 oxygen atoms in a tetrahedral shape. Every oxygen atom is also bonded to two silicon atoms to form a giant covalent molecule(Figure 1.0)

             

       

Figure 1.0 Structure of silicon oxide

Properties of Ceramic and Glass

Both glass and ceramic have the same properties as follows:

a)    Hard but brittle

b)    Inert to chemical

c)    Insulators or bad conductors of heat and electricity

d)    Withstand compression but not tension (stretching)

e)    Can be easily cleaned

a)    Both glass and ceramic are used widely in our daily life to replace metals because of the above advantages as well as their low cost of production. 

b)    The uses of glass and ceramic also depends on their differences. Table 1.0 below shows the differences between glass and ceramics

Table 1.0 Physical properties The differences in properties between glass and ceramic

Glass	Ceramic
Transparent	Opaque
Soften when heated	High melting point, hence retains shape on heating
Impermeable	Usually porous except when glazed

Ceramic 

a)    Ceramics encompass such a vast array of materials that a concise definition is almost impossible. However, one workable definition of ceramics is a refractory, inorganic, and nonmetallic material. Ceramics can be divided into two classes: traditional ceramics and advanced ceramics.

b)    Traditional ceramics include clay products, silicate glass and cement

         

                   

Figure 1.2 Example of traditional ceramic

c)    Advanced ceramics consist of carbides (SiC), pure oxides (Al2O3), nitrides (Si3N4), non-silicate glasses and many others

                        

    

                       

Figure 1.3 Example of advanced ceramic

d)    In general, advanced ceramics have the following inherent properties:

◦Hard (wear resistant)

◦Resistant to plastic deformation

◦Resistant to high temperatures

◦Good corrosion resistance

◦Low thermal conductivity

◦Low electrical conductivity

·         However, some ceramics exhibit high thermal conductivity and/or high electrical conductivity.

·         The combination of these properties means that ceramics can provide:

  

a)    High wear resistance with low density

b)    ◦Wear resistance in corrosive environments

c)    ◦Corrosion resistance at high temperatures

·         Ceramics offer many advantages compared to other materials. They are harder and stiffer than steel; more heat and corrosion resistant than metals or polymers; less dense than most metals and their alloys; and their raw materials are both plentiful and inexpensive. Ceramic materials display a wide range of properties which facilitate their use in many different product areas.

a)    ◦Aerospace: space shuttle tiles, thermal barriers, high temperature glass windows, fuel cells

b)    ◦Consumer Uses: glassware, windows, pottery, Corning¨ ware, magnets, dinnerware, ceramic tiles, lenses, home electronics, microwave transducers

c)    ◦Automotive: catalytic converters, ceramic filters, airbag sensors, ceramic rotors, valves, spark plugs, pressure sensors, thermistors, vibration sensors, oxygen sensors, safety glass windshields, piston rings

d)    ◦Medical (Bioceramics): orthopedic joint replacement, prosthesis, dental restoration, bone implants

e)    ◦Military: structural components for ground, air and naval vehicles, missiles, sensors

f)     ◦Computers: insulators, resistors, superconductors, capacitors, ferroelectric components, microelectronic packaging

g)    ◦Other Industries: bricks, cement, membranes and filters, lab equipment

h)    ◦Communications: fiber optic/laser communications, TV and radio  components, microphones

                      

Figure 1.4 space shuttle tiles         

                Figure 1.5 orthopedic joint replacement

           

Chemistry of Ceramic 

Materials

·         Different types of ceramics have different materials

·         Ceramic materials come in a variety of chemical forms:

a)    Silicates (silica, SiO₂ with metal oxide)

b)    Oxides (oxygen and metals)

c)    Carbides (carbon and metals)

d)    Nitrides (nitrogen and metals)

e)    Aluminates (alumina,Al₂O3 with metal oxides)

Composition of ceramic

·         Ceramic is manufactured substance made from clay that is dried and then baked in kiln at high temperature

·         The main constituent of clay is aluminosili-cate,(consist of aluminium oxide and silicon dioxide)with small quantities of sand and feldspar

·         Kaolinite is an example of high quality white clay that consist of hydrated aluminosilicate crystals,Al₂O3. 2SiO3. 2H₂O

·         Red clay contains iron(iii)oxide which gives the red colour

·         General properties of ceramics:

a)    Very hard and strong but brittle

b)    Inert to chemical

c)    Has a very  high melting point

d)    Good electrical and heat insulator

e)    Able to withstand compression.

Classification of Ceramic

·         The uses of ceramic in daily life are as shown in Table 1.0 below

Table 1.0 Summary properties, uses and chemical composition of Ceramic

Property of ceramic	Uses		Examples
Hard and strong	Building materials		Bricks, tile & cement
Attractive in appearance, long lasting & non corrosive	Materials for decorative items.		Porcelain & vases
Electrical insulators	To make insulating parts in electrical apparatus.		Insulators in toasters & irons, spark plug in car engines.
Chemically inert & non-corrosive	Household materials.		Plates, bowls, and cooking utensils.
Heat insulators	Heat insulating layers		Lining of furnace
Inert, hard & resist compression	In surgical and dental & dental apparatus		Artificial hands, legs & teeth.
Semiconductor types of ceramics	As microchips.		To make microchips in computers, radios & television

                       

  

           

Figure :  Some examples of Ceramic end products

Summary

·         The uses of glass in daily life are as shown in Table 1.1 below

Table 1.1 The uses of glass

Property of glass		Uses		Examples
Inert		Household materials		Lamp, bottles,glasses,plates,bowls & kitchen wares
Transparent		Building materials		Mirrors & window glass
Inert & easily cleaned		Scientific apparatus		Lens,burette,beakers,test tubes,conical flask,glass tubes & prism
Transparent		Industrial materials		Bulbs, glass tubes for radios,radar & television

                              

Figure :  Some examples of glass end products. (a) as a mirror in house (b) use as house decoration items.

Glass

Uses of glass

·         The physical and in particular the optical properties of glass make it suitable for technological applications such as windows, containers (bottles, jars, bowls), optics, optoelectronics and laboratory equipment. The ease of formability, and its aesthetic features, such as transparency and pigmentation, render glass a common art medium

Fused Glass

• ·         Fused glass is the simplest type of glass,which consist mainly of silica or silicon dioxide.(Occasional a little boron oxide is added)
• ·         Other types of  glass is mainly silicates.
• ·         Various types of glass can be produced by changing the composition of glass.Different types of glass have different properties and they are used for various specific purposes.The chemical composition,specific properties and uses of four types of glass are summarised in Table1.2.
• ·         Coloured glass is produced by adding traces of transition metal oxides to it.For example,addition of chromium oxide will give the glass a green colour ,cobalt oxide will gie a blue colour while man mangan manganesea purple colour of glass.   
  Manganese oxide will give a purple colour to the glass.

·          

Example of coloured glass.

                                       

       

Summary

Table 1.2 Summary of glass properties,composition & uses.

Name of glass		Properties		Chemical composition			Example of uses
Fused glass		·         Very high softening point(1700◦C),hence highly heat- resistant. ·         Transparent to ultra- violet and infrared light. ·         Difficult to be made into different shapes. ·         Does not crack when temperature changes (very low thermal expansion coefficient). ·         Very resistant to chemical attack		SiO₂(99%) B₂O3(1%)	Telescopr mirrors,lenses,optical fibres and laboratory glass wares
Soda-lime glass	·	·         Low softening point (700◦c),hence does not withstand heating. ·         Breaks easily ·         Craks easily with sudden temperature changes(high thermal coefficient of expansion). ·         Less resistant to chemical attack ·         Easy to make into different shapes.	Sio₂(70%) Na₂O(15%) CaO(10%) Others(5%)		Bottles, window-panes,light bulb,mirrors, flat glass, glass plates and bowls.(the most widely used type of glass)
Borosilicate glass	·	·         Quite high softening point,(800◦C)thus it is heat-resistant. ·         Does not crack easily with sudden change in temperature ·         Transparent to ultra-violet light ·         More resistant to chemical attack. ·         Does not break easily	SiO₂(80%)  B₂O3(15%)  Na₂O3(3%) Al₂O3(1%)		Laboratory apparatus, cooking utensils,electrical-tubes and glass pipelines
Lead glass	·	·         Low softening point(600 ◦C) ·         High density ·         High refractive index ·         Reflects light rays and appears shiny	SiO₂(55%) PbO(30%) K₂O(10%) Na₂O(3%) Al₂O3(2%)		Decorative items,crystal glass-wares,lens,prisms and chandeliers