PERPERTIES OF CERAMICS, USES OF CERAMICS, USES OF METALS, USE OF ALUMINUM AND ITS ALLOYS, CERAMICS, COMPOSITION OF CERAMICS, FINITE (Limited) RESOURCES OF MATERIALS AND THE IMPORTANCE OF RECYCLING

 VAPOUR PRESSURE:

             When a liquid is kept in a closed container some of the molecules evaporate and some vapours collide with the liquid and return back into liquid which is called condensation.

Initially the rate of evaporation is greater than the rate of condensation. As the number of molecules in the vapour phase increases the rate of condensation also increases. Ultimately at a given temperature a state will be reached where the rate of evaporation is equal to the rate of condensation. The system is then said to be at equilibrium. At this stage the pressure exerted by vapours on the walls of container is called vapour pressure. Since the number of molecules with higher energy increases with temperature hence, the rate of evaporation also increases. Thus vapour pressure increases with the increase in temperature.

 SOLIDS:

             In solids particles are closely packed. These particles may be atoms, molecules or ions. Most solids are crystalline i-e; the particles have regular three dimensional arrangement.

 IONIC CRYSTAL:

             Ionic crystals consisted of oppositely charged ions held by electrostatic forces of attraction. The ionic crystals have different patterns of arrangement depending upon the size of charged particles. The simple structure among ionic compounds is the cubic structure. Sodium chloride and magnesium oxide exist as face-centered cubic structure i.e; each face of cube has a particle at its centre. In this ionic crystal structure both +ve and –ve charged particles have six neighbor ions i.e; coordination of 6:6. Hence empirical ionic formula of sodium chloride and magnesium oxide are NaCL and Mgo respectively.

 SUBSTANCES:

             Covalent substances possessing this type of structure are composed of small discrete molecules.. The atoms are joined by covalent bonds. However, molecules are held by van der waals forces or hydrogen bonding as intermolecular forces. The physical properties of such molecules are determined by the strength of intermolecular forces. The example of such structure is crystalline iodine, which have face – centred cubic structure.

PHYSICAL PROPERTIES OF SIMPLEMOLECULES SUBSTANCES:

 (1)       The have low melting and boiling points or low heats of enthalpy.

(2)       Poor conductor of heat and electricity.

(3)       Dissolve better in non-aqueous solvents than in water.

 GAINT MOLECULAR COVALENTSUBSTANCES:

             A gaint molecular covalent substance contains atoms that are covalently bonded throughout the lattice to form an extended structure. The bonding may extend in three dimensions or in two dimensions.

 EXTENDED COVALENT BONDING INTHREE DIMENSION:

             In this case, the network of covalent bonding extends in all three dimensions e.g; Diamond, silicon dioxide (Quarts) and Boron nitride and silicon carbide.

Structure of diamond. In diamond each carbon is covalently bonded with four other carbon atoms. Each carbon has tetrahedral arrangement. Overall when different tetrahedron join three dimensionally, they form very compact hexagonal arrangement. Similar its for sid₂  and sic.

HYDROGEN BONDED LATTICES:

            Hydrogen bonding is a type of intermolecular forces which exist in compounds containing hydrogen covalently bonded with fluorine or oxygen or nitrogen. The common example of such crystal is ice.

Hydrogen bond are stronger than dipole – dipole forces but much weaker than covalent bonds.

METALLIC LATTICES:

           Metallic bonding is due to strong electrostatic forces between delocalized sea of electrons and positively charge ions of metal. In the metallic lattice metal ions are arranged in a compact crystal lattices. The common shapes of metallic lattice due to close packing of metal ions spheres are cubic or hexagonal. Metal ion use are arranged in layers and these layers due to close packing form cubic or hexagonal shape e.g; IN copper metal shape of metallic – crystal is cubic or more accurately its is called face – centred cubic lattice.

 CENTRED COVALENT BONDING IN TWO DIMENSIONS:

             In this case, bonding occurs two dimensions. In such macromolecules the lattice(crystal) consists of layers of atoms. All the atoms in a layer are bonded by covalent bonds. However, weak forces like van der waals forces hold the layers together in a crystal lattice. Due to weak forces layers can slide easily across one another e.g; in graphite, each carbon atom is bonded to three other carbon atoms and fourth electron is available as mobile electron this is way graphite is good conductor of electricity but only parallel to the plane not perpendicularly.

PROPERTIES OF DIAMOND ANDGRAPHITE :

 

	DIAMOND		GRAPHITE
1	It is very hard.	1	It is smooth and slippery.
2	It is very high melting point.	2	It is also has very high melting point.
3	It is electrical insulator because all four electrons are covalently bonded. No free  are available	3	It is good conductor only parallel to the plane because each carbon is bonded to three other carbon and fourth electron is available between the layers.

 

PERPERTIES OF CERAMICS:

 

(1)       They are good electrical insulators.

(2)       They are good thermal insulators.

(3)       They are hard and rigid.

(4)       They have very high melting point.

(5)       They are five resistant.

USES OF CERAMICS:

 (1)       Ceramics are used in furnace livings because they can with stand high temperature.

(2)       They are used in making electrical insulators which are used in over heated power lines.

(3)       They are used in making glasses for solar panels.

(4)       They are used in making crockery which could be used in micro wave over. The only disadvantage of being brittle.

(5)       Tiles containing high grade SiC2 are used in the U.S space shuttle as heat shields during re-entry to the Earth’s atmosphere.

 USES OF METALS:

             Now a day’s metals and their alloys are used widely in making different articles. The commonly used metals and their alloys are aluminum and copper.  The use of metals and their alloys depends upon their physical properties.

 USE OF ALUMINUM AND ITS ALLOYS:

Due to metallic bonding metal process the properties like malleability, ductility, combination of heat and electricity.

 CERAMICS:

             The group of substances generally known as ceramics containing compounds that have giant structures. A ceramic is a non-metallic, non-polymeric  solid that has been hardened by heating to high temperature i-e;. They are heat resistant substances. The strength of ceramics can be attributed to the pressure of a giant molecular structure.

COMPOSITION OF CERAMICS:

 

There are many types of ceramics which contains compounds like aluminum oxide, Al2O3; magnesium oxide, MgO; silicon carbide, SiC; silicon nitride, Si3H4 and silicon (III) oxide. All these compounds can withstand high temperature. Silicates or silica are ceramics which contain tetrahedral units of SiO4 joined together in a  three dimensional network. It has overall formula of SiO2.  Is used in making is used in making screws, hinges and other domestic objects.  (4)       Bronze is another alloy of copper with tin. It is stronger alloy which is used in making ships propellers and bearings of mechane.  (5)       Many countries use alloys of copper in their coins.

           

FINITE (Limited) RESOURCES OF MATERIALS AND THE IMPORTANCE OF RECYCLING:

 

            Raw materials extract from the Earth cannot last for wer. Some materials are more abundant then other but all materials have finite (limited) resources.  Somehow recycling of waste can meet the increasing demand of raw materials and it also considerably solve the growing problem of waste disposal. Recycling is important in a number of possible ways.

 (1)       It reduces the demand for new war materials.

(2)       It reduces the cost of waste disposal.

(3)       It may reduce the energy cost and may also reduce the cost of material.

(4)       It reduces the demand for sites to dump waste.

(5)       It may also reduce the environmental pollution.

(6)       It may also reduce the human labour making the body work of aeroplanes, trains and buses because it is low density metal. However in the pure form it is not very useful in construction work due to its softness. The aluminum used in aeroplane has been alloyed with other metals like magnesium. Its alloys are light and strong.

(7)       Aluminum and its alloyes are used in food packing and cooking utensils because it is quite resistant to corrosion. This is because aluminum metal is protected by very thin, hard but very stable oxide layer on its surface, which protects the metal from corrosion.

(8)       Aluminum is sued in making overhead electrical power lilnes and long distance transmission cables because it is good conductor of heat and electricity and is also low density metal.

 USES OF COPPER AND ITS ALLOYS INCLUDING BRASS:

 (1)       Pure copper metal is widely used in electrical wiring and central heating system because copper has high electrical and thermal conductivity.

(2)       It is used in making water pipes, kitchen utensils and roofing (roof tops) because it is resistant to corrosion, malleable and ductile.

(3)       Brass is an alloy of copper with zinc which is fairly soft and could easily be worked into shapes e.g; brass.