Cement as Synthetic materials with clay and lime stone For std 10 to 12 CBSE

CEMENT
Cement is an important synthetic material. It is the chief component of building materials. Chemically, cement is a mixture of calcium silicate and calcium aluminate, with small amout of gypsum salt.
The essential raw materials used in the manufacture of cement are clay and lime stone. Gypsum (calcium sulphate) is used to regulate setting rate.

Note
Cement resembles a type of lime stone available in port land. J. Aspadin gave the name port land cement in 1824.

Manufacture of cement : 

Manufacture of  Cement 

Finely powdered ground clay and limestone are mixed with water. This homogeneous mixture is called slurry. It is introduced into a rotary kiln (Fig). Hot air at Hot air at about 1873K is blown from the lower end of the rotary kiln. Due to high temperature the water present in the slurry evaporates. At this temperature clay and lime stone combine chemically to form cement balls.
1. Slurry tank
2. Vapourising zone
3. Rotary kiln
4. Combustion zone
5. Hot air
6. Clinker collector

The cement balls so formed are called clinkers. Clinkers. Clinkers are taken out of the kiln and cooled. Clinkers are then finely powdered by grinding and mixed with 3% gypsum. Gypsum slows down the rapid setting of cement. 

Setting and curing : Cement sets into a hard mass when mixed with water. Therefore it makes an excellent binding material in construction work. The mixture of sand and cement along with water undergoes many complex changes. The first stage of setting takes place within 24 hours after adding water to the cement. The second stage of setting requires about two weeks.

The subsequent setting of cement is achieved by adding water. The method of hardeing cement by treating it with water is known as curing. During curing cement absorbs water. Calcium silicate and aluminates of cement are converted into a colloidal gel. This process is exothermic and hence it requires continuous water treatment.

Cement concrete 
The mixture of cement, gravel and sand in the ratio of 1:2:4 or 1:3:6 is known as concrete. An iron skeleton inside concrete gives mechanical strength to the structure.

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Synthetic Materials

Synthetic materials like polymers polymerisation for std 10 to 12 CBSE

SYNTHETIC MATERIALS
Introduction – polymers – polymerization – types of polymers – uses – plastics – types of plastics uses – recycling of plastics – cement – manufacture of cement – setting and curing of cement – glass preparation – properties of glass – types of glass and uses – ceramics – porcelain – preparation and uses.

REVIEW
You have studied in your previous classes, about elements, compounds and how the compounds are formed. Let us recall some of them.
· Compounds contain elements, combined together in definite proportions.
· The type of chemical change in which two or more elements combine together to form a compound is called chemical combination.
· Simple compounds form compounds of higher molecular mass through chemical reactions.
· Glucose, starh, cellulose and proteins are some of the examples of naturally occurring compounds.
· Water, ammonia, carbondioxide, methane, ethane and benzene are some of the examples of simple molecules.
· Silica, limestone, washing soda, clay are some of the useful raw materials available in nature.

INTRODUCTION
From ancient times, man has been using many naturally available substances for various purposes. Cotton, silk and jute are some of the materials used to prepare fibres and clothes. Shikakai is used for cleaning. There is a long list of products like gum, resin, dyes, wood and many more which are very useful to us. In ancient days all needs of human beings were fulfilled by naturally available substances. Catering to the needs has become difficult due to increase in population, limited availability of natural materials and long duration required for their production. Hence there is a great demand for Alternatives to natural materials. Materials not available in nature but produced by using naturally available raw materials, are called synthetic materials. Nowadays we come across many synthetic materials such as plastics. Cement, glass, fibres, ceramics. 

POLYMERS
Polythene, nylon and terylene are some of the materials that are commonly used in our daily life. These synthetic materials are called polymers. (The words ‘poly’ means many are ‘meros’ means parts) they are prepared by using some naturally available materials. Do you know how polythene is made ? A number of ethane molecules chemically combine together to form a giant molecule. 

Polythene

Nylon

Terylene

Activity

Make a list of natural and synthetic materials that you come across in your daily life.

Compounds which are formed by the union of a very large number of molecules of a simple compound or simple compounds united in a repetitious manner are called polymers.
The simple compounds which build up the polymer molecule are called monomers.
Polymerisation : the process in which two or more molecules of a simple compound unite together to form a new compound is called polymerization. 

Types of polymers : 
All polymers are not synthetic; some are found in nature. Proteins, carbohydrates, fats and nucleic acids are some of the natural polymers. They are the essential components of our fodd. The polymers which are available in nature are natural polymers. Some of the commonly used polymers such as nylon, terylene are not found in nature; they are synthesized. They are synthetic polymers. 
Synthetic polymers are classified into 1) addition polymers and 2) condensation polymers. 
Addition polymerization is a process in which several molecules join together to form a giant molecule during the reaction. Theere is no elimination of molecules. They are prepared from unsaturated monomers. Ex. Polythene and polyvinyl chloride (pvc). 
Polymers obtained by the condensation reaction between monomers are called condensation polymers. The polymerization in which several monomers form a polymer with the elimination of some simple molecules during the reaction is called condensation polymerization. 
The condensation involves elimination of molecules like water, methanol etc. Leading to linking of polymers. Nylon-66 and terylene are condensation polymers. 

Some important polymers. Their used and the monomers from which they are formed, are listed below :

Important Polymers and the monomers uses.

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