Poly.chemIV

What is a composite material?The composite materials are generally made by placing the dissimilar materials together in such a manner that they work as a single mechanical unit.

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Composite Steel AluminiumWeight0

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Composite Steel Aluminium

Thermal Expansion

Advantageous Properties of the composites over metals polymers ceramics Higher specific strength. Lower specific gravity. Higher specific stiffness. Lower electrical conductivity. Better corrosion and oxidation

resistance. Can be fabricated easily. Lower specific gravity. They are tough having good

impact and thermal shock resistance.

Constituents of Composites

Matrix Phase is the continuous body constituent which encloses the composite and give it its bulk form. Matrix phase may be metal, ceramics (or) polymers.

Dispersed Phase is the structural constituent which determines the internal structure of composite

Application of composite materials:

Fabrication of roofs and floors.

Communication antennae, electronic circuit boards, sport goods, furniture and turbine engines. They are also extensively used in automobile industries marine applications like propellers, spares, ship parts.

Plywood

Ceramics

Ceramic is an in-organic non-metallic materials that are processed at high temperatures, and subsequent cooling. eg. ceramic wash basin, ceramic tiles etc.

White Pottery

White ware products consist of refractory body and glossy' coating. They are white ceramic materials that are white in colour.

The raw materials used for manufacture of white pottery, are given below.

China Clay

Feldspar (KAlSiO2)

Flint(SiO2)

MANUFACTURE OF WHITE POTTERY

Step I Preparation of body ware

The raw materials Kaoline[Al (OH)4 SiO5] and Feldspar are made into fine powder and mixed with water to form a creamIt is dried and then fired in a 'biscuit' oven to get porous ware called 'Bisque’

Step II Glazing

In order to make the porous ware into watertight article, it is covered with glaze by melting it over the surface of the body.

The constituents of glaze material are quartz, feldspar, little boric acid and little lead oxide.

The bisque is dipped in the glaze slurry and fired again at high temperature until the glaze materials melt to form a smooth glossy surface.

Step-Ill Decoration The article is decorated with paints

before glazing or it is decorated with coloured glass after glazing

Purpose of Glazing

To get decorative effect. To make the surface impervious to

liquids. To improve appearance of the

article. To increase the durability of ceramic

material. To get a smooth glossy appearance. To protect the surface from

atmospheric action.

Salt glazing In salt glazing, common salt

(sodium chloride) is used for getting glossy films over earthenware. The process consists of throwing NaCl into furnace when the article is in red-hot condition.

At high temperature, NaCl melts and reacts with silica of the article to form a glossy and impervious film of 'Sodium Silicate'

Uses Spark plugs

Electrical Insulators

Lab equipments

Crucibles and dishes etc

Refractories Refractories are materials,

which can withstand high temperatures.

mostly used for linings of the furnaces, tanks, converters, kilns, crucibles, ladles etc

Requirements of a good refractory:

Refractoriness: It is the ability to withstand very high temperature without deformation during operation.

Strength or Refractoriness under load (RUL): They mustpossess high mechanical strength even at very high temperature and bear maximum possible load without breakage.

Thermal expansion: A good refractory should have low thermal expansion under normal conditions.

Thermal conductivity: In general a good refractory must have low thermal conductivity to reduce heat losses by radiation. But when heat is to be supplied from outside the refractory must possess good conductivity.

Porosity: A good refractory should have low porosity. In porous refractory the molten metal and slag enters and weaken the structure. But porosity helps in thermal shock-resistance of refractories.

Thermal spalling: It is breaking, cracking, peeling off orfracturing of the refractory under high temperature. A goodrefractory must have low thermal spalling.

Chemical composition: A good refractory must be chemically inert with charge and slag.

Classification:

. Acid refractories

Silica (SiO2

. Basic refractories

Magnesia (MgO)2. Dolomite

. Neutral refractories

Chromite(Cr2O3)

Alumina (Al2O3)

Used in furnaces where the charge and slag are acidic in nature

Used in furnaces where the charge and slag are acidic in nature

Used in furnaces where the charge and slag are acidic in nature

Acid refractories

Lubricants “Lubricants may be

defined as the Substance which reduces the friction between the two moving surfaces”.

Characteristics of Lubricants: It should have a high viscosity

index. It should have flash and fire

points higher than the operating temperature of the machine.

It should have high oiliness. The cloud and pour points of a

good lubricant should always be lower than the operating temperature of the machine

The volatility of the lubricating oil should be low.

It should deposit least amount of carbon during use.

It should have higher aniline point.

It should posses a higher resistance towards oxidation and corrosion.

It should have good detergent quality.

Classification of Lubricants:

Solid Lubricants GraphiteMolybdenum disulphide

Semi – solid Lubricants

GreasesVaseline’s

Liquid Lubricants

Vegetable oils –eg: palm oil & castor oilAnimal oils - eg: Whale oil & lard oil Mineral oils – eg: petroleum fractions

Thank you