Engineering materials

CHEMISTRY OF ENGINEERING CHEMISTRY OF ENGINEERING MATERIALSMATERIALS

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Provides an introduction to the science and engineering of materials (e.g. ceramics, polymers etc)

Develop an awareness of materials and their properties that, as an engineer, you must depend in the future

To introduce basic concepts, nomenclature, testing of materials.

To reveal the relationships between

Processing - Structure - Properties - Performance

To develop ideas behind materials selection and design.

Scope & Objective

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• Some of these have descriptive subclasses.• Classes have overlap, so some materials fit into more than one class.

• Metals

• Ceramics

• Polymers

• Electronic Materials

• Composites

• Biomaterials

Six Major Classes of Materials

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• Ceramics• Structural Ceramics (high-temperature load bearing) • Refractories (corrosion-resistant, insulating) • Whitewares (e.g. porcelains)• Glass • Electrical Ceramics (capacitors, insulators, transducers, etc.)• Chemically Bonded Ceramics (e.g. cement and concrete)

• Polymers• Plastics• Liquid crystals• Adhesives

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• Composites• Particulate composites (small particles embedded in a different material)• Laminate composites (tennis rackets)• Fiber reinforced composites (e.g. fiberglass)

Introduction to Engineering Materials

Materials are used in construction or fabrication

• Include binding or cementing materials such as lime,cement and gypsum plasters;

• Ceramics - Glass, clay products, refractories,abrasives, composites, insulators etc

• Adhesives, lubricants

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Cementing & Binding Materials

Mostly Inorganic materials with characteristic

properties of setting & hardening on mixing with

water to a paste like consistency

These are capable of cementing rigid masses such

as bricks, gravel, tiles etc. to give coherent &

strong structuresSticking together ·

Orderly6

Types of Cementing Materials

Based on the manner in which they set & harden- Canbe classified into two categories

Hydraulic Cementing Materials

These are capable of setting and hardening in air, aboveground, below ground & under water, e.g. PortlandCement

Non-Hydraulic Cementing Materials

These materials set and harden in air only and hence cannot be used under water e.g. Fat Lime

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LIMEA cementing material, has been used since ancient times for the

construction of palaces, bridges, temples, forts, monuments.

Some of these still exist in perfectly good conditions.

• Lime or quick lime is –CaO

• It is obtained by heating of naturally occurring calciumcarbonate (CaCO3) in the form of lime stone, chalk or marbleto about 900° in the presence of limited supply of air(Calcination)

• CaCO3 + Heat → CaO + CO2↑

• This quicklime can be hydrated i.e combined with water

CaO + H2O → Ca (OH)2 + Heat

SLAKED LIME

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Types of Lime

Different types of limes are obtained depending onthe chemical composition of the lime stone used inthe manufacture of quick lime.

Lime stone usually contains MgCO3, Al2O3, Fe2O3, SiO2

• Fat Lime or high-calcium lime

• Hydraulic Lime

• Lean or poor lime

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Types of Lime

Fat Lime or high-calcium lime• It is a non-hydraulic cementing material & setting

occurs only by drying

• It is obtained by calcining limestone of high purity(>95% CaCO3)

• Contains more than 95% CaO and less than 2%oxides of Fe, Al, & Si

• It’s a rapid slaking lime accompanied with theevolution of a large amount of heat & volumeexpansion

• Used for whitewashing10

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Hydraulic Lime• It is obtained from marls (lime stone containing 5-30% clay)

• Silica & alumina combine with CaO to give Ca- aluminate andCa-silicate.

• Exhibits hydraulic properties and sets a hard mass onimmersing in water.

• It slakes with difficulty, doesn’t shrink or crack on setting.

• Hardens by hydrolysis

• Used as a substitute for cement particularly in newfoundation for buildings

Types of Lime

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Lean or poor lime• Contains more than 30% clay

• 70-80% CaO, >5% MgO, smaller proportions of Si &Alumina

• Slakes very slowly, forms a thin paste with water

• Sets or hardens very slowly

• Poor binding material with muddy white color

• Used for plaster finishing

Types of Lime

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• Lime is manufactured by calcining lime stone in vertical kilns usingcoal or producer gas as fuel

(mixture of N, CO and H generated by passing air with steam over burning coal in a furnace)

• A kiln can be like a large cylindrical tower (20-40 m height, 2-3 m indiameter) lined with refractory bricks.

• Limestone is fed from the top and passes slowly down through thetower

• Flame of the burning fuel seeps (flow) from the sides decomposingthe lime stone

• Air is supplied from the bottom of the tower-for cooling of hot lime &for combustion of the fuel

MANUFACTURE OF LIME

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A kiln is a thermally insulated chamber, or oven, which is used forhardening, drying or burning of materials such as clay and other rawmaterials to form ceramics (including pottery, bricks etc)

KILN KILNPOTTERY

KILN

PROPERTIES OF LIME

• Slaking

• Plasticity

• Sand Carrying Capacity

• Setting & hardening

• Hardness

• Absorption of atmospheric CO2

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PROPERTIES OF LIME

• Slaking-– It is the reaction of CaO with water (3:1 ratio)

which produces hydrated (slaked) lime (CaO.H2O).

– The reaction is highly exothermic evolving about280 Kcal heat/kg of the lime and is accompaniedby increase in volume (about 2 times)

– Important property for using lime as a bindingmaterial.

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PROPERTIES OF LIME

• Plasticity-

• Easy workability and ability to spread duringapplication as plaster

– Lime containing MgO has good workability, pure limeis sticky

– Plasticity can be modified by incorporating sand

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• Sand Carrying Capacity-

– Useful in the use of lime as a plaster, it reducesthe shrinkage of lime on setting

– Sand carrying capacity of Ca-Lime is highercompared to dolomite lime [CaMg(CO3)2]

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PROPERTIES OF LIME

• Setting & hardening– It involves the transformation of lime mortar

(sand & lime) into the hard CaCO3 whichserves as a binding material and finishingmaterial

–Brought about by dehydration (loss of waterby evaporation) and carbonation of lime(reaction with atmospheric CO2)

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PROPERTIES OF LIME

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Setting Under Water

Hydraulic limes undergo setting under water due tochemical decomposition of the complex silicates ofCa, Al into simpler compounds of Ca-Silicate,aluminate and hydroxide.

Ca-Silicate, aluminate crystallizes in a hard mass in theinterior while the water soluble Ca(OH)2 diffuses tothe surface & interacts with CO2 to form hard CaCO3

PROPERTIES OF LIME

• Hardness-

Resistance of lime mortar to abrasion andimpact on setting and hardening.

– High Mg limes exhibit better hardness comparedto high Ca limes

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PROPERTIES OF LIME

PROPERTIES OF LIME

• Absorption of atmospheric CO2 by limeresults in its swelling and disintegration to afine powder of CaCO3.

– This air slaked lime can not be used for makingmortar or plaster as it can not set

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