II Semester Question Bank - Chemistry of Industrial Materials

7/28/2019 II Semester Question Bank - Chemistry of Industrial Materials

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UNIT I: FUELS

Part A Questions and Answers

1. Distinguish between GCV and NCV.

Gross or Higher Calorific Value (GCV): The total heat generated when a unit quantity offuel is completely burnt and the products of combustion are cooled to room temperature

Net or Lower Calorific Value (LCV):The net heat produced when a unit quantity of fuel iscompletely burnt and the products of combustion are allowed to escape

2. What is meant by refining of petroleum?

The process involves removal of impurities and separation of various fractions on the basis oftheir boiling points from petroleum.

3. Define cracking. What is the necessity of cracking of petroleum fractions of higherboiling points?

The process of breaking of heavier compounds into more useful lower fractions by theapplication of heat and pressure or by using catalysts is known as cracking.

Crude oil on distillation yields only 16 20% gasoline. This is known as straight run petrol. Itcontains mainly n-paraffins. Presence of n-paraffins produces knocking in SI engines.Hence, in order to improve the quantity and quality, higher fractions are cracked to producehigh quality gasoline.

4. Define octane number of petrol. How can it be improved? (or) What is leaded petrol?What are the advantages and disadvantages of leaded petrol?

Octane number is defined as the percentage of isooctane in isooctane-n-heptane mixture,which has the same amount of knocking as a standard binary mixture when tested instandard engine under standard conditions. It can be improved through the addition of tetraethyl lead and oxygenates.

Petrol containing tetra ethyl lead is called leaded petrol. Leaded petrol prevents knocking inSI engine. But it produces lead bromide in SI engines and causes atmospheric pollution.

5. Define cetane number of diesel. How can it be improved?

Cetane number is defined as the percentage of cetane in cetane - -methyl naphthalenemixture which has same ignition delay as a standard binary mixture when tested in astandard engine under standard conditions. Cetane number of diesel oil can be improvedthrough the addition of Isoamyl nitrite, Ethyl nitrate.

6. What are oxygenates? Give examples.


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Oxygenates are organic compounds rich with oxygen that are added to gasoline in order toboost the gasoline's octane level and to reduce atmospheric pollution associated withautomobile emissions. Examples: Methyl tertiary butyl ether, ethyl tertiary butyl ether.

7. What is CNG? What are its advantages?

CNG is compressed natural gas stored at pressure. It consists of 8090% methane in

gaseous form with small amounts of ethane, propane and butane. CNG is an attractive fueldue to its clean burning characteristics and very low amount of exhaust pollution.

8. Name the reagents used for absorbing CO2, CO and O2 during flue gas analysis byOrsats apparatus.

Reagents AbsorbentsCO2 KOH solutionCO Ammoniacal cuprous chloride solutionO2 Alkaline pyrogallol

9. Calculate the volume of air required for the complete combustion of one litre of CO.

CO + O2 CO21 litre 0.5 litre1 litre of CO requires = 0.5 litre of oxygen for complete combustion

The volume of airrequired

=21

1005.0

= 2.38 litre

10. Write the expression to calculate theoretical quantity of air required for combustion of

1kg of a fuel.

fuelsolidaof1kgburningforrequiredairofquantityminimumThe

+

+= S

8

OH8C67.2

23

100

Part B Questions and Answers

1. Explain a gross and net calorific value? How calorific value of a liquid fuel is

determined by bomb calorimeter?

Determination of calorific value of a solid (or) liquid fuel

Principle:A known weight of the fuel is burnt completely and the quantity of heat liberated isabsorbed in water and measured.

Description:A bomb calorimeter consists of the followings:

(i) A stainless steel bomb: It can withstand a pressure of about 100 atmospheres. It isprovided with two electrodes and an oxygen inlet valve. One of the electrodes acts as supportfor the crucible. It is placed in copper calorimeter.

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(ii)A copper calorimeter: The copper calorimeter contains a known weight of water. It has anarrangement for inserting a thermometer and stirrer. The calorimeter is surrounded by air

jacket and water jacket to prevent the loss of heat.

(iii) A stainless steel crucible: It holds the weighed pellet of fuel sample. The crucibleis fixed in such a way that the fuse wire touches the fuel sample.

Beckmann'sThermometer

Oxygen valve

Electrodes

Stirrer

Copper calorimeter

Magnesium fuse wire

Stainless steelcrucible

Water jacket

Air jacket

6V Battery

Ebonite cover

Stainless steelbomb

Weighed pellet ofgiven fuel sample

Working:A known quantity of fuel (m gm)is taken in the crucible. The bomb is charged withoxygen to a pressure of 30 atmospheres and the oxygen charging valve is closed tightly.Then the bomb is placed carefully in a known amount of water (W gm). The water in the

calorimeter is stirred throughout the experiment and its initial temperature is noted (T 1C).Now the fuel is ignited by passing current through the fuse wire. The heat produced byburning is transferred into the water. The temperature is measured to an accuracy of 0.001Cby a Beckmanns thermometer till the maximum temperature (T2C) is reached.

Calculations:Mass of fuel = m gmMass of water in calorimeter = WgWater equivalent of calorimeter = wgInitial temperature of water = T1CFinal temperature of water = T2C

The water equivalent of the calorimeter is determined by burning a fuel of knowncalorific value (Example: Benzoic acid, CV = 26565 kcal/kg)By heat balance, heat produced by thefuel due to combustion

= Heat absorbed by water andcalorimeter

Ifx is the calorific value of fuel, heatproduced

= (x m) cal

Heat absorbed by water andcalorimeter

= (W + w) (T2 T1)

(x m) (W + w) (T2 T1)

x = cal/g)()( 12

m

TTwW +

For calculating the more accurate calorific value of a fuel, the following corrections

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should be considered. (i) Fuse wire correction (C 1) (ii) Cotton/Thread correction (C2),Acid correction (CA), Cooling correction (TC).

HCV,x ()()( 112

m

CTTTwWC

+++

2. What is meant by crude petroleum? Discuss the principle steps involved in the refiningof crude petroleum?

Definition: Crude Petroleum is a naturally occurring brown to black coloured viscous oil. It isfound under the crust of earth, on shore or off shore. Chemically it is a complex mixture ofparffinic, naphthenic, olifinic and aromatic hydrocarbons. The approximate composition ofpetroleum is: 8087%C + 1115%H + 0.13.5%S + 0.50.9%N + 0.10.9%O

Principle: The process of (i) removing impurities and (ii) separating petroleum into moreuseful fractions with different boiling point ranges is known as refining of petroleum.Removal of impurities:

(i) Modern electrical desalting: This process is used to remove dissolved salts like NaCl,MgCl2 etc from oil.

(ii) Cottrells process: The highly charged electrodes used in this process cause colloidalwater droplets to combine to form bigger drops, and separated easily from oil.(iii) Chemical precipitation: This process involves addition of CuO in order to precipitatesulphur as CuS, which is filtered and removed.

Purified

Petroleum

Oil Heater

450oC

Uncondensed

Gases

Petroleum Ether

Gasoline

Naphtha

Kerosene

Diesel

Heavy Oil

Residual Oil

Cracking Gasoline

Fractionating

Tower

S.S Tray

Chimney with Cap

Oil Vapours

Fractional distillation: Fractional distillation is used to separate out the purified petroleuminto various fractions based on their boiling points.

(i) Pre-heater or Heating still: Here the purified oil is vaporized by heating to a temperature of450C. The hot oil vapours are introduced through the bottom of fractionating tower.

(ii) Fractional distillation tower or Bubble tower: It is a tall cylindrical tower consists of a largenumber of stainless steel trays placed at shorter distances. Each tray is provided with

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chimneys covered with loose caps. The tower is hot at the lower end and comparativelycooler at the top. When the oil vapours go up, high boiling point condense at the bottom trayswhereas low boiling point fractions condense at the top trays. Lower fractions are used afterpurification while the high boiling point fractions are subjected to cracking operation to getmore useful lower fractions.The following table summarizes the various fractions obtained by the fractional distillation ofpetroleum.

S.No. Name of thefraction

Chemicalcomposition

Boilingpointrange

Uses

1. Uncondensed gases C1C4 030C Used as domestic fuelunder the trade nameof LPG

2. Petroleum ether C5C7 3070C Used as solvent for rubbers, varnishes

3. Petrol or Gasoline,CV: 11250kcals/kg

C5C8 40120C Used as fuel for IC-engines

4. Naphtha or SolventSpirit C9C10 120180C Used as solvent fordry cleaning, used as

fuel

5. Kerosene,CV: 11100kcals/kg

C10C16 180250C Used as fuel for domestic heating andJet engines

6. Diesel,CV: 11000kcals/kg

C15C18 250320C Used as fuel for dieselengines, generators

7. Heavy oil C17C30 320400C Used for cracking toproduce gasoline

8. Heavy oil on refractionation yields:Lubricating oils Used as lubricantPetroleum Jelly-Vaseline Used in cosmetics,

medicinesGreases Used as lubricantParaffin wax Used in candles, boot

polishes, wax papers9. Residue on vacuum distillation yields:

Pitch (Asphalt-Bitumen) Used for making tar,waterproofing ofroofs

Petroleum coke Used as fuel,electrode rods

3. What is meant by cracking of heavy oil? Explain fluidized bed catalytic cracking.

Definition: The process of decomposition of less volatile heavier compounds into highlyvolatile lower fractions by the application of heat and pressure or by using catalysts is knownas cracking.

Fluidized-bed or Moving-bed catalytic cracking: The Cat cracker consists of the followingmain parts: Pre-heater, Reactor, Fractional tower, Condenser, Stabilizer and Regenerator.

Name of parts Role in the Cat cracker

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Pre-heater : Here the heavy oil is vaporized by heating to a temperature of 450C.Finely powdered synthetic zeolites or bentonites are used ascatalysts and are suspended in hot oil vapors. The mixture is forcedinto the reactor.

Reactor : The reactor is a slim and tall tower. It is provided with a centrifugalseparator at the top, which allows only cracked vapors to passthrough and not any solid catalyst particles. It is maintained at 500C.

Cracking occurs at the surface of the catalyst particles. About 70% ofhot oil vapors are cracked into gasoline hydrocarbons. Duringcracking catalyst particles are coated with carbon and settle at thebottom of the reactor.

Fractionaldistillation tower

: It is a tall and slim tower. It is used to separate out gasoline and otherlower hydrocarbons from uncracked heavy oil vapors.

Condenser : The gasoline and other lower hydrocarbons are admitted into acondenser, where they get cooled and recovered as a mixture ofliquids.

Stabilizer : It is used to separate out gasoline from the mixture. The lower hydrocarbon liquids are recovered as gas, which is subjected for

polymerization to obtain superior type of petrol.

Regenerator : It is a tall tower maintained at 600C. At this temperature, the carbonis burnt off and the catalyst particles are reactivated. The regeneratoris provided with a centrifugal separator at the top, which allows onlyflue gas (waste gas) to pass through and not any regenerated solidcatalyst particles. The reactivated catalysts are again used for freshbatch of hot oil vapours to continue the process.

Heavy

OilOil Heater

450oC

Reactor500oC

Cracked

Vapours

Condenser

Gas +

Gasoline

Gas for

Polymeris

-ation

Gasoline

Heavy Oil

FractionatingColumn

Stabiliser

------------------

Regenerator600oC

Regenerated

Catalyst

Powderad Catalyst

Spent Catalyst...............

Flue Gas

4. Explain the causes, mechanism and prevention of knocking in I.C. engines?

Definition: Knocking is a kind of mild explosion which occurs in IC engines due to suddenincrease of pressure developed by spontaneous combustion of fuel and air mixture.

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Causes of knocking: Knocking in internal combustion engine causes mechanical damage incylinder and reduction of power output.

Chemical structure and Knocking: The knocking tendency in IC engines depends upon thecompactness of molecules, double bonds and cyclic structure.Knocking tendency in SI engines decreases in the following order while knocking tendencyinCI engines increases in the same order.

n-Paraffins Iso-paraffins Olefins Naphthenes AromaticsIt means that the presence of maximum quantity of aromatics and minimum quantity of n-paraffins in petrolis desirable. It also indicates that the presence of maximum quantity of n-paraffins and minimum quantity of aromatics in dieselis desirable.

Measurement of knocking in SI engines (or) Octane Number: The quality of petrol isexpressed in terms of octane number. It is defined as the percentage of isooctane inisooctane-n-heptane mixture, which has the same amount of knocking as a standard binarymixture when tested in standard engine under standard conditions.

Leaded petrol (or) Octane number Enhancers The octane number of gasoline may be

improved by adding about 1-3ml of ethyl fluid (60% Tetra ethyl lead + 26% Ethylene bromide+ 9% Ethylene chloride + 2% Red dye) to 1 gallon of petrol. Petrol containing TEL is knownas leaded gasoline.

Measurement of knocking in CI engines (or) Cetane Number: The quality of diesel isexpressed in terms of cetane number. It is defined as the percentage of cetane in cetane --methyl naphthalene mixture which has same ignition delay as a standard binary mixturewhen tested in a standard engine under standard conditions.

Improvement of antiknock value (or) Cetane number Enhancers: Cetane number ofdiesel oil can be improved through the addition of Isoamyl nitrite, Ethyl nitrate.

5. What is flue gas? How it is estimated by Orsats method?

Definition: The mixture of gases (CO2, O2, CO etc.,) coming out from the combustionchamber is called flue gas. Usually, the flue gas is estimated by Orsats method.

Significance: Analysis of Flue gas gives an idea about the complete or incompletecombustion process.

The presence of a high % of CO in the flue gas shows incomplete combustion of thefuel and also indicates the short supply of oxygen.

If the flue gas contains considerable amount of oxygen, it indicates an excess supply

of oxygen and the possibility of complete combustion.

Description: The Orsats apparatus consists of four main parts:

(i) A 3-way stop cock: It has provisions: for entry of flue gas into the gas burette; to releaseair present in the burette; to connect the glass horizontal tube.

(ii) Absorption pipettes: The central part of horizontal tube is connected to three absorptionpipettes via 2-way stop cocks.

Pipette-A contains KOH solution to absorb CO2 gas Pipette-B contains alkaline pyrogallol solution to absorb O2 gas Pipette-C contains ammoniacal cuprous chloride solution to absorb CO gas

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(iii) Gas burette (100cc): It is surrounded by a water jacket to maintain gas temperatureconstant throughout the experiment

(iv) Water reservoir: It contains an acidified 25% solution of NaCl and coloured with methylorange. It is connected to the end of gas burette by means of a rubber tube. By raisingthe water reservoir, the gas can be sent to various parts of the apparatus and by loweringthe water reservoir, the gas can be brought back into the gas burette

Determination: The analysis of flue gas generally deals with the determination of CO2, O2and CO by absorbing them in the respective solution of KOH, alkaline pyrogallol andammoniacal cuprous chloride. It is quite necessary to follow the order of absorbing the gases,CO2-first, O2-second and CO-last. This is because the absorbent used for O2 (i.e. alkalinepyrogallol) can also absorb some amount of CO2 and the % of CO2 left would be less.

Liq.NH3

+Cu2

Cl

2

PyrogallicAcid

KOH

Solution

Levelling Bottle

Water + small amount

Gas Burette

Rubber Tube

Three way

Stop-Cockof NaCl

- - -- - -- - -- - -- - -- - -- - -

- - -- - -- - -- - -- - -- - -- - -

- - -- - -- - -- - -- - -- - -- - -

___

___-----

- - - - -- - - - -- - - - -- - - - -- - - - -

Wooden Box

ABC

- - - - -

(i) Determination of CO2gas: To measure the volume of CO2, the flue gas is first passed into

the absorption pipetteA via its 2-way stop cock by raising the water reservoir. ThepipetteA absorbs only CO2 gas present in the flue gas. Then the flue gas is taken backto the gas burette by lowering the water reservoir. This procedure is repeated severaltimes in order to ensure complete absorption of CO2 gas. Now stop cock of pipetteA isclosed. To find the volume of CO2 gas, the volume of residual (remaining) gas ismeasured by equalizing the water level both in the water reservoir and in the burette. Letthe volume of residual gas beXcc.

The percentage by volume of CO2 gas = (100 X) cc

(ii) Determination of O2gas: To measure the volume of O2, stop cock of pipetteB is openedand the flue gas [initial volume = (100X) cc] is passed into it by raising the water

reservoir. The pipetteB absorbs only O2 gas. Then the flue gas is taken back to the gasburette by lowering the water reservoir. This procedure is repeated several times in orderto ensure complete absorption of O2 gas. Now stop cock of pipetteB is closed. To findthe volume of O2 gas, the volume of residual (remaining) gas is measured by equalizingthe water level both in the water reservoir and in the burette. Let the volume of residualgas be Ycc.

The percentage by volume of O2 gas = [(100X) Y] cc

(iii) Determination of CO gas: To measure the volume of CO, stop cock of pipetteC isopened and the flue gas {initial volume = [(100X)Y cc} is passed into it by raising thewater reservoir. The pipetteC absorbs only CO gas present in the flue gas. Then the flue

gas is taken back to the gas burette by lowering the water reservoir. This procedure is

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repeated several times for complete absorption of CO in pipetteC. To find the volume ofCO gas, the volume of residual (remaining) gas is measured by equalizing the water levelboth in the water reservoir and in the burette. Let the volume of residual gas be Z cc.

The percentage by volume of CO gas = [(100X) Y] Zcc

(iv) Determination of N2gas: The residual volume of gas in the gas burette after CO 2, O2 andCO absorption can be taken as the percentage by volume of N2 gas.

UNIT II: LUBRICANTS AND ADHESIVESPart A Questions and Answers

1. Define the terms: Lubricants and lubrication.

Lubricant is a substance, used to reduce the friction between two moving surfaces. Theprocess of reducing friction between two moving surfaces with respect to one another byintroducing a lubricant between them is called lubrication.

2. What are extreme pressure additives? Give examples.

Extreme pressure additives are used to provide adhering power to oil to maintain thick oil film

under extreme pressures

Examples: Organic chlorine and sulphur compounds.

3. What are oiliness improvers? Give examples.

Oiliness improvers are used to increase oiliness or adhering property of lubricants

Examples: Castor Oil; Palmitic acid; Stearic acid; Oleic acid

4. Define aniline point.

It is the lowest temperature at which an equal volume of aniline and oil sample mixes each

other to form a homogeneous solution. It gives a measure of paraffinic and aromatic contentin oil.

5. Distinguish between soda base grease and lime base grease.

Soda based grease: It is an emulsion of mineral oil and sodium soap. It is slightly watersoluble and is used up to 120C.

Lime based grease: It is an emulsion of mineral oil and calcium soap. It is water resistantand used up to 135C.

6. How does graphic differ from molybdenum di sulphide in lubricating action?

Graphite: It can be used only up to 370 C. Adsorbed water and gases are required for

effective lubrication in vacuum.MoS2: It is used up to 800C. It does not require adsorbed water and air for lubrication invacuum.

7. What are adhesives and adherends?

Substances capable of binding two materials together by surface attachment are calledadhesives.

The materials held together by an adhesive are called adherends.

8. What are the advantages of adhesive bonding over other joining methods?

Any two surfaces can be joined together by an adhesive

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Adhesive bonding minimizes the chances of galvanic type corrosion of two dissimilarmetals.

9. What are the defects or limitations or disadvantages of adhesive bonding?

There is no single and general purpose adhesive which can join all types of surfaces

Adhesive strength is generally lower than other joining methods like welding

10. What is meant by specific adhesion?If the attachment of surfaces takes place by either physical or chemical forces of attraction, itis called specific adhesion.


1. Explain the mechanism of lubrication.

(i) Fluid-film lubrication (or) Thick-film lubrication (or) Hydrodynamic lubrication

When two metallic surfaces are perfectly separated by thick fluid film of about 1000 in orderto avoid direct metal to metal contact in turn to reduce friction, then the process is termed as

fluid film lubrication.

Velocity

Thick Layerof Lubricant

Load

Since the frictional force generated in the movement of metal surfaces is only due to internalresistance of the particles of lubricants, its coefficient of friction is as low as 0.001 to 0.003.This type of lubrication depends upon mainly viscosity of lubricants and it must have aminimum viscosity and it must remain in place (a good oiliness).

This type of lubrication is used in machineries working under low load and fair speedconditions. Delicate instruments and light machines like watches, clocks, sewing machinesand scientific equipments are required this type of lubrication.

Examples: Hydrocarbon oils blended with long chain polymers are considered as fluid film

lubricants.(ii) Boundary lubrication (or) Thin-film lubrication

When two metallic surfaces are perfectly separated by an adsorbed thin layer of boundarylubricants of only 2 to 3 molecules thick in order to avoid direct metal to metal contact in turnto reduce friction, then the process is termed as boundary lubrication.

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Velocity

Load

AdsorbedThin Layer

of Lubricant

Since the load is carried by a thin layer of adsorbed lubricant, its coefficient of friction is 0.05to 0.1. This type of lubrication depends upon mainly oiliness of lubricants. It also should havelow viscosity index, high resistance to heat and oxidation.This type of lubrication is used in machines working under heavy load and slow speedconditions. Railway track joints, gears, rollers, tractors are required this type of lubrication.

Examples: Graphite, MoS2 as emulsions are considered as boundary lubricants.

(iii) Extreme pressure lubrication

When two metallic surfaces are separated by an extreme pressure additive in order towithstand heavy load and high temperatures, the process is known as extreme pressurelubrication.

The machines working under extreme conditions (heavy load and high speed) generate veryhigh local temperatures. This causes the lubricants to stick on to the surface and decompose.Hence the lubricating oils are blended with special additives are known as extreme pressureadditives. Extreme pressure lubrication is used in (i) wire drawing (ii) making tough metals.

Examples: Chlorinated esters; sulphurized fats or oils; tricresyl phosphate

2. Explain the following properties of lubricants and give their significances (i) Viscosityindex (ii) Flash and fire point (iii) Cloud and pour point.

(i) Viscosity-index (VI)

Definition:Viscosity index is defined as the average decrease in viscosity per degree rise oftemperature between 100 and 210oF. A good lubricant should have minimum change inviscosity for a wide range of temperature (high VI).

Example (i): Gulf coast oil. This oil mainly consists of naphthenic hydrocarbons and shows alarge change in viscosity with temperature. Thus, its VI value is arbitrarily fixed as zero.

Example (ii):Pennsylvanian oil.This oil mainly consists of paraffinic hydrocarbons and shows

relatively a small change in viscosity with temperature. Thus, its VI value is arbitrarily fixed as100.

Determination of Viscosity-Index:The VI of a test oil is determined by comparing with theabove two standard oils. The viscosity of test oil is compared at 100oF with zero viscosity-index Gulf coast oil and 100 viscosity-index Pennsylvanian oil, both having the same viscosityat 210oF.

where, L is the viscosity (in seconds) at 100oF of the standard oil having VI of zero

U is the viscosity (in seconds) at 100oF of the test oil H is the viscosity index (in seconds) at 100oF of the standard oil having VI of 100.

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Viscosity Index Improvers: Viscosity-index of lubricating oil can be increased by theaddition of linear polymers such as polyalkyl styrene, polyisobutylene, n-hexanol etc.

- - - - - - - - - - - - - - - - - - - - - - - - ---------

Visco

sity

Temperature100oF

L

210oF

U

H

(ii) Cloud point and Pour point

Cloud Point: When petroleum oil is cooled under specified conditions, the temperature atwhich the oil becomes cloudy or hazy is called its cloud-point.

Significance: On cooling the oil, the impurities (wax, asphalt) present in oil crystallize out,and making the oil turbid. Knowledge of the cloud-point is useful in locating the lowesttemperature up to which a machine can be operated without any risk of jamming.

Pour Point: When petroleum oil is cooled without any disturbance, the temperature at whichthe oil just ceases to flow is called its pour point.

Significance: On cooling the oil below the cloud-point, the oil itself crystallizes out andminute crystals of wax become interlocked and the flow is therefore arrested. Knowledge ofpour point is essential for fixing the lowest temperature up to which the flow of lubricant isreliable.

Pour-Point Depressant:A good lubricant must have low cloud-point and pour point.Pourpoint of a lubricant can be lowered by lowering the viscosity of the oil, or by dewaxing, or byadding suitable chemical calledpour-point depressant.Examples:Paraflowand Santapour .

(iii) Flash point and Fire point

Flash Point: It is the lowest temperature at which the oil gives off enough vapours that willflash if a small flame is brought near to it.Fire Point: It is the lowest temperature at which the oil gives off enough vapours that mustburn continuously for at least five seconds when a small flame is brought near to it.

Significance: Knowledge of flash point and fire-point is useful in providing safeguardsagainst fire hazards during use, transport and storage of the lubricating oil.

3. Write a note on greases?

Definition: Grease is a semi-solid lubricant prepared by adding suitable metallic soap topetroleum oil or synthetic oil. The metallic soap is also called as gelling agent.

Grease is used under the following situations:

Where the machine is worked under heavy load and slow speed operations (Rail axle

boxes).

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Where frequent lubrication is not possible (automobile wheel bearings). Where spilling of oil from the bearings is undesirable (in preparing paper, textile etc.). In places where the lubricants have to prevent the entry of dirt or moisture.

(i) Calcium based Grease or Cup-Grease: It is an emulsion of petroleum oil and calciumsoap. It is water-resistant. It can be used only up to 70C. It is used for lubricating pumpsand tractors.

(ii) Soda based Grease: It is an emulsion of petroleum oil and sodium soap. It is slightlysoluble in water. It can be used up to 120C. It is used in ball bearings.

(iii) Lithium soap Grease: It is an emulsion of petroleum oil and lithium soap. It isresistant to both heat and water. It can be used up to 135C. It is used for aircraftlubrication.

(iv) Axle Greases: It is prepared by adding lime to resin and fatty oils. It is waterresistant. It is used for machines working under low loads and high speeds.

4. Write a note on solid lubricants?

Solid lubricants are used in machineries working at high temperatures and under heavy loadconditions, and other environments, which prohibit the use of oils and greases.

(i) Graphite

Structure: The graphite crystal consists of flat layers of covalently bonded carbon atoms.Each carbon atom is bonded to three other carbon atoms to form hexagonal layers. The bondlength in the hexagons is 1.42 . The adjacent layers are joined together by weak vanderWaals forces attraction, the layers slide them one over the other.

------------

--------

----

------------

------------

-----------

-

----------

--

1.42Ao

3.40 Ao

------------

----------

--

------------

------------

----------

--

------------

------------

Properties: Graphite is not effective as a lubricant in vacuum. Adsorbed water and gases areessential for effective lubrication. It can be used as lubricant up to 370 oC, and above thistemperature, it gets oxidized.

Uses: Graphite is used either as powder or as colloidal dispersions. When graphite isdispersed in oil, it is called oildagand when it is dispersed in water, it is called aquadag.Graphite is used in air-compressors, laths, foodstuff industries, railway track joints, internalcombustion engines etc.

(ii) Molybdenum disulphide, MoS2

Structure: MoS2, has a sandwich like structure in which a layer of molybdenum atoms liesbetween two layers of sulphur atoms. The atoms in the layer are held by strong covalentbonds. Presence of intermolecular forces of attraction is responsible for sliding one layer overanother.

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---------------

----------------

---------

------

----------------

---------

------

----------------

--------

-------

--------------

--

3.08 Ao

3.13 Ao

Sulphur atom layer

Molybdenum atom layer

Sulphur atom layer

3.15 Ao

---------------

-----------

-----

Properties: Unlike graphite, it does not require the presence of adsorbed gases for effectivelubrication in vacuum. MoS2 can be used as lubricant up to 800oC, and above thistemperature, it gets oxidized.

Uses: MoS2 can also be used as powder or as colloidal dispersions. It is mainly used inheavy machineries working under heavy load and high temperatures.

5. What are adhesives? Explain the classification of adhesives with suitable examples.

NATURAL ADHESIVES:

S.No. Name of Adhesive Properties and uses

1. Shellac resin It is a natural resin, dissolved in alcohol and usedas adhesive. It is used for making conveyers, beltsetc.

2. Starch It is prepared from corn, potato, wheat flour etc. Itis used for making office paste, postage stamps,wall paper, and for note book bindings etc.

3. Protein glues (i) Casein adhesives, soya protein adhesives areprepared from casein and soya respectively. Theyare widely used in wood work industries.

4. Animal glues Animal glues are derived from hides, tendons or bones of dead animals, which are rich in collagen.They are used for making furniture, labels, paperboxes etc.

5. Silicate based adhesive It is prepared by dissolving sodium silicate inwater. It is used for making paper boxes, plywoodetc.

SYNTHETIC ADHESIVES:

S.No. Name of Adhesive Properties and uses

(i) Thermosetting Resins

1. Phenol formaldehyde resin It is fungus, insect and heat resistant. It is used formaking plywood, laminates etc.

2. Melamine formaldehyde resin It is fungus, insect and heat resistant. It is alsoused for making plywood, laminates etc.

3. Epoxy resin It is used for bonding glasses, metallic andceramic articles. Araldite, the trade name of

epoxy resin used very much in aircraft industry.4. Silicone resin It is water resistant. It can withstand temperature

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up to 2500C. It is used for bonding metals,ceramics, plastics etc

(ii) Thermoplastic Resins

1. Cellulose derivatives Cellulose acetate, cellulose nitrate, and ethylcellulose are the most important water solublecellulose adhesives. Cellulose nitrate mixed withalcohol is the trade name of Collodion. It is used

in cloth and foot-wear industries.2. Acrylics (Plexiglass) Methyl acrylic esters adhesives are used for bonding porous surfaces like paper, cloth, leatheretc.

3. Polyvinyls Polyvinyl acetate, polyvinyl acetal and polyvinylbutyral are used for bonding non-porous surfaceslike glasses, metals etc.

6. Explain the various physical factors and chemical factors influencing adhesive action.

Physical factors influencing adhesive action

(i) Interfacial Tension:The attraction between the liquid adhesive and adherend surfacesis maximum when the interfacial tension between the two is minimum.

(ii) Porosity of contacting surfaces:Presence of pores in adherends sometimes disturbsthe equilibrium between solute and solvent of the adhesives. In such a case, poor bondstrength is formed. But in the case of sodium silicate adhesive, presence of pores helpsto absorb the water quickly to form gel. This enhances bond strength.

(iii) Thickness of adhesive film:Thick adhesives with too many voids have poor cohesiveproperties. Such adhesives develop weak bond strength. However, viscosity of suchadhesives can be reduced by adding suitable solvent, which can develop good bondstrength.

(iv) Physical characteristics of adhesive film:Adhesives with good tensile strength andcompressive strength develop good bond strength. Adhesives with negligible creep makethe bond strong. Good bond strength is obtained when thermal coefficient of expansion ofadhesive and adherend do not vary much with temperature.

(v) Technique of application of adhesives:Whatever may be the method of application ofadhesive (in the form of powder or liquid, pressure and temperature actually determinewhether full curing of adhesive film takes place or not. The bond strength will be weakbefore the proper curing of the adhesive film.

Chemical factors influencing adhesive action

(i) Polar characteristics of adhesives:Adhesives with organic polar groups are used forbonding organic materials together (plastics, rubbers etc). Further, the addition of polarmolecule to non-polar adhesive enhances its the bond strength.

15


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(ii) Degree of polymerization: Partially polymerized semisolid resins develop good bondstrength than the unpolymerized resin or the highly polymerized resin.

(iii) Side chains in adhesive molecule: The bond strength of an adhesive also dependsupon the length of side chain in the adhesive molecule and its structure. In the case ofcellulose esters, maximum bond strength is obtained when fatty acids having side chainsof 6 to 14 carbon atoms are substituted.

(iv) Effect of pH: Protein glues shows better adhesive strength in the presence of limewhereas vulcanized rubber shows better adhesive strength at a lower pH.

UNIT III PHASE RULEPart A Questions and Answers

1. Write mathematical statement of phase rule

Gibbs phase rule is mathematically stated as: F = C = P + 2.Where, P is the number of phases; C is the number of components; F is the number ofdegrees of freedom.

2. How many phases, components and degrees of freedom are available in the followingsystems?(i) CaCO3 (s) CaO (s) + CO2 (g) (ii) NH4Cl (s) NH3 (g) + HCl (g)

(i)P = 3; C = 2; F = 23 + 2 = 1 (ii) P = 2; C = 1; F = 1 2 + 2 = 1

3. State reduced phase rule.

For solid-liquid alloy system, the variable factor pressure is ignored due to the absence ofgaseous phase. For such a system the phase rule equation is reduced to F = C P + 1 andit is known as reduced phase rule.

4. State the conditions under which two substances can form a simple eutectic.

The two solids should be completely miscible in liquid state and completely immiscible insolid state.

They should not react chemically with each other.

5. Mention the differences among melting point, triple point and eutectic point.

Melting point: It is the temperature at which a pure metal starts melting.

Triple point: It is the temperature at which any 3 phases are simultaneously in equilibrium.

Eutectic point: It is the temperature at which a mixture of two solids melts together.

6. Eutectic is a mixture and not a compound. Explain.

Since the two solids are completely miscible in liquid state and are completely immiscible insolid state, eutectic is a mixture of two solids and not a compound.

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7. What are the limitations of phase rule?

The influence of factors such as electric, magnetic, gravitational, surface forces is ignoredin phase rule.

The phase rule is applicable only to heterogeneous equilibrium systems.

8. What are the advantages of phase rule?

The phase rule takes no account of the nature or amount of substances.

Phase rule is applicable only to macroscopic systems .Information about molecularstructure is not required.

9. What is peritectic point?

It is the temperature (1495C) at which the liquid melt of composition 0.53 wt% carbon reactswith ferrite of 0.09 wt% carbon to form austenite of composition 0.17 wt% carbon.

(0.17%C)austenite(0.09%C)ferrite-(0.53%C)meltLiquidC1495

+

10. What is ledeburite?

The temperature (1147C) at which the liquid melt of composition 4.3 wt% carbon transformsinto austenite and cementite. This eutectic mixture is called as ledeburite.

Ledeburite

cementiteaustenite-C)(4.3%meltLiquid

C1147 +

11. What is eutectoid point?

It is the temperature (723C) at which austenite of 0.83 wt% carbon transforms into ferrite and cementite. This mechanical mixture is called as pearlite.

Pearlite

cementiteferrite-(0.83%C)austenite-

C727 +


1. State the phase rule. Explain the terms involved in it with suitable examples.

Gibbs phase rule is mathematically stated as: F = C = P + 2.Where, P is the number of phases; C is the number of components; F is the number ofdegrees of freedom.

Phase:A phase is a homogeneous, physically distinct, and mechanically separable part of asystem, which is separated from other parts of system by definite boundaries.

Examples:

(i) Freezing water system: It consists of three phases namely liquid water, solid ice andwater vapour.

(ii) Gases:A pure gas or a mixture of any number of gases is considered as a single phase.This is because gases are completely miscible in all proportions.

(iii) Liquids: If two liquids are immiscible (Benzene and water), they are considered as twoseparate phases. If two liquids are miscible (alcohol and water), they are considered asone liquid phase only.

(iv) Solids: Each solid is considered as a separate phase. For example, a heterogeneous

mixture of CaCO3 and CaO consists of two phases.

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Components: It is defined as the minimum number of chemical constituents required toexpress the composition of all the phases present in the system.

Examples:

(i) The freezing water system: This system consists of three phases namely ice, water andwater vapour. The chemical composition of all the three phases can be expressed bychemical constituent, water. Hence it is an example of one-component system.

(ii) Thermal decomposition of CaCO3: CaCO3(s) CaO(s) + CO2(g)

This system consists of three phases namely, solid CaCO 3, solid CaO and gaseous CO2.The chemical composition of all the three phases can be expressed by any two of thethree chemical constituents. Hence it is an example of two-component system.

Degree of Freedom (Or) Variance of a System: It is defined as the minimum number ofindependent variable factors such as temperature, pressure and concentration (composition)required to describe the system completely.

Examples:

(i) Consider a one component system consisting of two phases: water water vapour:P = 2; C = 1; and F = C P + 2 = 1 2 + 2 = 1; to define such a system, only onevariable factor (either temperature or pressure) is needed. Hence the system isunivariant.

(ii) Consider a one component system consisting of one phase: water vapour:P = 1; C = 1; and F = C P + 2 = 1 1 + 2 = 2; to define such a system, two variablefactors (temperature and pressure) are needed. Hence the system is bivariant.

(iii) Consider a one component system consisting of three phases: ice water watervapour.P = 3; C = 1; and F = C P + 2 = 3 1 + 2 = 0; to describe this equilibrium system, noneed to specify any variable factors, because all the three phases can occur inequilibrium only at a particular temperature and pressure. Hence this system does nothave any degree of freedom (invariant or zero variant).

2. Draw and explain the phase diagram of ice-waterwater vapour system. How does themelting point of ice change with variation of pressure?

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Temperature

Pre

ss

ure

---------------------------------------------- ----------------

------------------------------

----------------------

-----------------------------------

---------------------------------------

------

-----

Solid Ice

Liquid Water

Water Vapour

O

B A

C

A'

273oC 0.0075

oC 100oC 374

oC

4.58mm

1atm

218atm

Vapo

uriza

tioncurv

e

Subli

matio

ncurv

e

Fusi

onc

urve

0oC

----------------------

The water system is an example of one component system. It consists of three phasesnamely solid ice, liquid water and water vapour.

Salient features of phase diagram of water system:

(i) Curves: The phase diagram consists of three curves OA, OB and OC. Each curveseparates two phases and hence the system is univariant along the curve (F = CP+2 =12+2 = 1).

Curve OA: is the vaporization curve because it separates the liquid region from vapour

region. Along the curve OA, water and water vapour are in equilibrium (water watervapour). The curve OA ends at the point A, which corresponds to the critical temperature(374C) and critical pressure (218.5atm) of water. Beyond which the liquid and vapourphases merge into each other to form a single homogeneous phase.

Curve OB: is the fusion or melting curve because it separates ice and water phases. Thecurve OB is slightly inclined towards pressure axis. This shows that melting point of icedecreases with the application of pressure.

Curve OC: is the sublimation curve because it separates ice and water vapour phases. Atthe lower limit, the curve OCterminates at absolute zero (273C) where no vapour can bepresent and only ice exists.

(ii) Point O (Triple Point):The three curves OA, OB, and OCmeet at a point O, at whichsolid ice, liquid water and water vapour are simultaneously in equilibrium. This is calledtriple point (Solid ice Liquid water Water vapour).

At the triple point, the system is invariant (F = CP+2 = 13+2 = 0). The triple point ofwater system corresponds to a temperature of 0.0075C and a pressure of 4.58mmmercury.

(iii)Areas: The curve is divided into three areasAOB, BOCand COA. Each area represents asingle phase and hence the system is bivariant (F = CP+2 = 11+2 = 2).

(iv) Curve OA' (Meta stable Equilibrium): The curve OA represents the vapour pressure

curve of super cooled water. The process of cooling of water below its freezing point

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without the separation of solid is known as super cooling. The super cooled water is highlyunstable. It can be converted into solid by a slight disturbance. Hence the system alongthe curve OAis said to be in meta stable equilibrium.

3. Explain the construction of eutectic phase diagram by thermal analysis.

Thermal analysis involves the study of cooling curve of various compositions of two solidsduring solidification.

(i) Cooling curve for pure metal

Time

Tem

pe

ratu

re

x

s

a a'

Endof

freezing

Begin

ning

off

reezin

g

s: The point s represents that a pure metal is in molten state.

sa: Along the line sa, the temperature of the liquid melt decreases gradually with time.

a: It is the point at which the molten liquid metal starts freezing on its surface.

aa: Along the line aa, the temperature of liquid melt remains constant until it is completelysolidified into solid metal. This is because the liquid melt and solid metal have samechemical composition.

a: The point a indicates the end of freezing.

ax: Along the line ax, the temperature of solid metal again decreases with time.(ii) Cooling curve for a mixture of solid A and solid B

Time

Tem

pera

ture

s

a

b b'

x

Freezing of eitherA orB starts

End offreezingEutectic

point

20


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22/37

O

Liquid melt

Solid Ag +

Liquid melt

Solid Pb + Solid Ag

100%Pb 100%Ag

Composition wt%

Tempe

rature

A

BSolidPb +

Liquidmelt303oC

961oC

303oC

327oC

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.....

.

.

.

.

.

.

.

.

.

.

.

97.4%Pb

+ 2.6%Ag

a

b

Salient features of phase diagram of lead-silver system:

(i) Curves:

CurveAO: PureAgmelts at 961C. Addition ofPb lowers the freezing point ofAgalong thecurveAO. ThereforeAO is the freezing point curve of silver. Along AO, solidAgand liquidmelt are in equilibrium. Hence the system along the curve is univariant (F = 22+1 = 1).

Curve BO: Pure Pb melts at 3270C. Addition ofAglowers the freezing point ofPb along thecurve BO. Therefore BO is the freezing point curve ofPb. Along BO, solid Pb and liquid meltco-exist and hence the system is univariant (F = 2 2 + 1 = 1).

(ii) Point O (Eutectic Point):The curveAO and BO intersect at O which is called eutectic point.At the eutectic point three phases are in equilibrium (Liquid melt Solid Ag+ Solid Pb ).Hence the system is non-variant (F = CP+1 = 23+1 = 0). Below the point O, both silverand lead exist in the solid state.

Therefore, eutectic point is the lowest temperature at which a mixture of two solids melts(eutectic = easy melting). The eutectic point ofPb-Agsystem corresponds to a temperature303C and composition 97.4%Pb+2.6%Ag.

(iii) Areas:The area aboveAOChas a single phase (molten Pb andAg). Applying the reducedphase rule F = CP+1 = 21+1 = 2, the system is bivariant. The area below AO (solidAg+liquid melt), below BO (solid Pb + liquid melt) and below O (solid Ag+ solid Pb) have two

phases and hence the system is univariant (F = CP+1 = 22+1 = 1).Application of Pb-Ag System (Pattinsons Process): The process of recovery of silver fromargentiferous lead is called as desilverisation. Desilverisation of lead is based on the formation ofeutectic mixture. Argentiferous lead consists of a very small amount of silver (0.1%). The ore isheated to a temperature well above its melting point, so that it exists as liquid melt(point a in Pb-

Ag system). When it is allowed to cool, the temperature of the melt falls along the line ab. Assoon as point b is reached, lead is crystallized out. On repeating the process of melting andcooling, more and more lead is separated along the line BO. At O a eutectic mixture containing2.6%Ag and 97.4%Pb is obtained. The eutectic alloy is then treated for recovery of silver.

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5. Draw and explain iron-carbon phase diagram with different phases and invariantreactions.

Iron-carbon phase diagram consists of: (i) Steel portion:[0.0032.12 wt% C] (ii) Cast ironportion:[>2.12 6.67wt% C]

Ferrite

727oC

wt% Carbon

912oC

Temperature

0.022

0.008

0.83 2.12

1147oC

1495oC

Austenite

1400oC

1538oC

0.090.17

0.53

4.3

Liquid (Fe+C)

Austenite

+ Liquid

Austenite + Cementite

Austenit

e+

Cementite

Austen

ite+Ferrite

A

B

C

D

H

E

F

G

Cementite

+ Liquid

J

MN

I

K

6.67

Cementite + PearliteFerrite+

Pearlite

L

DF+L

DF

DF+A

DF+L:Deltaferrite+L

iquid

DF:Deltaferrite

DF+A:Deltaferrite+A

ustenite

F: Peritectic point

C: Eutectic Point

M: Eutectoid point

4.3

Le

de

bu

rit

e

727oC

1550oC

Salient features of iron-carbon phase diagram:

(i) Curves: The curve ABCD is known as liquidus line. Above this line, only one phase(liquid) exists. When carbon is added to iron, the melting point of iron graduallydecreases along the liquidus line ABC up to 4.3%. On further addition of carbon, themelting point of iron increases along the line CH.

The curve AEFGCH represents solidus line below which only solid phase of variouscompositions of iron and carbon exists

(ii) Areas: The area AEI represents of -ferrite phase. The area IFGMJI represents of -austenite phase and the area JKL represents -ferrite phase.

(iii) Phases (Microconstituents of Fe-C System)

Ferrite: It is an interstitial solid solution of carbon in BCC iron. . ferrite is soft,ductile, and magnetic but has poor strength. At room temperature, the solubility of carbonis limited to 0.008 wt%, because the BCC iron has relatively small interstitial positions.The maximum solubility of carbon in BCC iron is 0.022 wt% at 727C. It transforms into

austenite at 912C Austenite: It is an interstitial solid solution of carbon in FCC iron. austenite is

tough and denser than ferrite. It is non-magnetic. The maximum solubility of carbon in

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iron is 2.12 wt% at 1147C because the FCC iron has relatively more interstitial positions.But the solubility decreases to 0.83 wt% at 727C. It transforms into ferrite at 1400C.

Ferrite: It is the interstitial solid solution of carbon in BCC iron. The maximumsolubility of carbon in iron is 0.09 wt% at 1495C. It is a stable phase between 1400Cand 1538C. It melts at 1538C. It has the softest structure. It has no practicalsignificance in engineering

Cementite (Iron carbide, Fe3C): It is the intermetallic compound of iron and carbon. Themaximum solubility of carbon in iron is 6.67 wt% at 1550C. It is white, extremely hardand brittle phase.

(iv) Invariant Reactions (Critical Points)

Peritectic point:It is the temperature (1495C) at which the liquid melt of composition 0.53wt% carbon reacts with ferrite of 0.09 wt% carbon to form austenite of composition0.17 wt% carbon.

(0.17%C)austenite(0.09%C)ferrite-(0.53%C)meltLiquidC1495

+

Eutectic point:It is the temperature (1147C) at which the liquid melt of composition 4.3wt% carbon transforms into austenite and cementite. This eutectic mixture is called asledeburite.

Ledeburite

cementiteaustenite-C)(4.3%meltLiquid

C1147 +

Eutectoid point:It is the temperature (723C) at which austenite of 0.83 wt% carbontransforms into ferrite and cementite. This mechanical mixture is called as pearlite.

Pearlite

cementiteferrite-(0.83%C)austenite-

C727 +

UNIT IV ALLOYS AND COMPOSITES


24


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1. Write the importance (purpose) of making alloys.

To increase the strength of metals: Pure iron is a weak metal whereas carbon is brittle.When the two are combined, we get a strong and workable alloy called steel.

To increase the hardness of metals: Gold is the soft and ductile metal. When it is alloyedwith copper, we get a hard alloysuitable for making ornaments.

To increase the corrosion resistance of metals: Iron is susceptible to oxidation corrosion.When chromium is added to iron, it forms a coherent oxide film of chromium oxide andimproves its corrosion resistance.

To lower the melting point of base metals: Alloying of lead with tin reduces the meltingpoint of the constituent metals by forming a simple eutectic. Such eutectic mixture isfusible at the lowest temperature and used as solder.

2. What are alloy steels? Why there is a need for alloying steels? What are itsapplications?

Definition: The properties of plain carbon steel can be further improved by adding certainelements like Cr, Ni, Mn, Si, V, W etc. Such admixtures are called alloy steel.

Need (Effect) of Alloying Elements on Steel and Applications:

S.No. Alloying element Properties Applications

1. Chromium, Cr Makes steel stainless,increases strength, hardnessand corrosion resistance.

Shafts, gears, cutlerys,surgical instruments

2. Nickel, Ni Improves strength, hardness Crankshafts, axles3. Manganese, Mn Improves strength, hardness,

deoxidiser

Shafts, gears

4. Silicon, Si Improves strength, deoxidiser Transformer cores

3. Give the composition and the main use of nichrome.

Nichrome has the composition: 70% Fe + 10% Ni + 20% Cr.

Applications: It is used for making boiler parts, gas turbines, heating elements forelectric irons, ovens, room heaters etc.

4. Distinguish between brasses and bronzes.

Brasses are essentially alloys of copper and zinc whereas bronzes are alloys of copperwith any element other than zinc and nickel

Brasses have higher strength than copper while bronzes have higher strength than bothcopper and brasses

Brasses have good resistance to atmospheric corrosion and fair resistance to marinecorrosion. Bronzes, in general, have better corrosion resistance than brasses.

5. What are composites? What are the advantages of composites?

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Composites are hybrid materials formed by integration of two or more materials with superiorstructure and better properties than constituent materials.

Composites possess excellent strength, stiffness and are light weight Composites have high specific modulus Composites are highly resistant to corrosion Composites are recyclable, reliable and consume less energy

6. Mention the applications of composites.

Composite materials are extensively used in:

Manufacturing advanced aerospace structures Light weight construction materials High speed and fuel efficient transport vehicles Electronic components and Sporting goods

7. What are the constituents of composites? Mention their functions.

Matrix phase: The matrix phase is the primary phase. It surrounds and holds the individualreinforcing elements. Examples: Polymers, Metals, Ceramics

Functions:

Matrix phase takes the load and stress and transfers into reinforcements Matrix phase gives shape to composites

Reinforcement phase: The reinforcement phase is the secondary phase. It carries most ofthe loads.

Functions:

Reinforcement phase imparts mechanical properties like light weight, strength, stiffness,toughness and thermal stability Reinforcement phase acts as major load bearing constituent

8. What are ceramic-matrix composites?

Ceramic-Matrix Composite (CMC) is material that consists of a ceramic dispersed in anotherceramic dispersed phase (oxides, carbides).

Examples of ceramic matrix: Alumina (Oxide matrix), SiC (Non-oxide matrix)

Examples of reinforcements: Whiskers (Fine single crystal materials) of SiC, TiB2, AlN,ZrO2.

9. What are Cermets? Mention their applications.

Cermets are the materials composed of ceramic particles dispersed in a refractory metalmatrix. They are characterized with high tensile strength, high thermal shock resistance, highdensity, high modulus, high shape ability etc. Most cermets contain 15-20% metal.

(i) Oxide base cermets are used as high speed cutting tool materials, thermocoupleprotection tubes, molten metal processing equipment parts.

(ii) Carbide base cermets are used for gauges and valve parts.


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1. What are alloys? Write an account on ferrous alloys. (or) Write the chemicalcomposition and uses of (i) heat treatable stainless steel and (ii) non-heat treatablestainless steel.

Definition: An alloy is a homogeneous mixture of two or more metals. In an alloy, the metalwhich is present in excess amount is called base metaland the elements which are present

in least amounts are known as alloying elements.

Ferrous alloys: They contain iron as major component. Common examples areplain carbonsteel and alloy steel.

Plain carbon steel: Plain carbon steel is a binary alloy of iron and carbon.

S.No. Types C (% by Wt) Properties Applications

1. Low carbon steel(Mild steel)

0.1-0.3 Soft, ductile,weldable.

Manufacture of bolts, nuts,and screws.

2. Medium carbon

steel

0.3-0.8 Hard and

tougher thanmild steel,non-weldable.

Manufacture of automotive

engine components, wheels,gears, hydraulic fittings,shafts and axles.

3. High carbon steel 0.8-1.3 Hard, tough. Manufacture of hammers,dies, and razors.

Stainless steel: Stainless steel is otherwise known as corrosion resistant steel. The stainlesssteel is protected against corrosion because of the formation of dense, tough film ofchromium oxide. It is of two types: Heat treatable stainless steel and non-heat treatablestainless steel.

(i) Heat treatable stainless steel

S.No. Types % Composition Properties and Applications

1. Plain chromiumstainless steel

C: 0.1-0.8Cr: 12-18

For making cutlery, scissors, surgicalinstruments

2. High chromium lownickel steel

C: 0.1-0.3Cr: 12-18

Ni: 2%

(ii) Non-heat treatable stainless steel

S.No. Types Composition Properties and Applications

Magnetic type

1. Ferriticstainless steel

C: 0.1-0.8Cr: 12-18

For making surgical instruments,decorative pieces, steam oil pumps.

2. Martensiticstainless steel

C: 0.8-1.3Cr: 12-18

For making utensils, springs, cuttingtools.

Non-magnetic type

1. Austeniticstainless steel

C: 0.5Cr: 18-25Ni: 8-21

For making sinks, utensils, dental andsurgical instruments.

2. What are non-ferrous alloys? Write the composition, properties and uses of variousvarieties of brass and bronze.

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Definition: Non-ferrous alloys do not contain iron as a base metal. Common examples ofnon-ferrous alloys are copper alloys, aluminium alloys, lead alloys, nickel alloys etc.

Copper alloys: Alloys of copper are generally classified into two groups. (i) Brasses (ii)Bronzes.

(i) Brasses: Brasses are alloys of copper and zinc.

S.No. Types %Composition Properties and Applications

1. Gilding metal(or) French gold

Cu: 90Zn: 10

It is stronger and harder than copper.

For making coins, medals, tokens.2. Dutch metal Cu: 80

Zn: 20It is stronger and harder than Gilding metal.

For making cheap jewelry, name plates.3. Cartridge brass Cu: 70

Zn: 30It has good combination of strength andductility.

For making cartridge cases.4. Muntz metal Cu: 60Zn: 40

It is stronger and harder than cartridgebrass.

For making condenser tubes.5. Admirality brass Cu: 70

Zn: 29Sn: 1

It is resistant to sea water corrosion.

For making propellers for ships and boats.

6. Naval brass Cu: 60Zn: 39Sn: 1

It is resistant to corrosion.

For structural applications especially where

they contact with sea water.

(ii) Brasses: Brasses are alloys of copper and zinc.

S.No. Types %Composition Properties and Applications

1. Common bronze Cu: 90Sn: 10

It is soft and ductile.

For making coins, statues, ornaments.

2. Gun metal Cu: 88Sn: 10Zn: 2

It is strong and resistant to corrosion

For handling liquids, steam and oil under

pressure2. Phosphor bronze Cu: 89Sn: 10

P: 1

Phosphorous increases strength andductility

For making gears, bearings, turbineblades.

4. Aluminiumbronze

Cu: 90Al: 10

It has good resistance to corrosion andabrasion.

For making coins, gears, propellers.

3. Discuss the various types of aluminium alloys giving their composition, properties and

uses.

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(1) Wrought Aluminium Alloys: Aluminium alloys, which are shaped by mechanicalworking processes such as extrusion, rolling, drawing, forging are known as wroughtalloys.

(i) Non-Heat Treatable Wrought Aluminium Alloys: Alloys which do not respond to heattreatment are called as non- heat treatable alloys.

AlMn alloys: This alloy possesses very good resistance to corrosion and goodweldability. It is widely used for making utensils, food and chemical handling equipments,gas and oil tanks, pressure vessels etc.

(ii) Heat Treatable Wrought Aluminium Alloys: Alloys which respond to heat treatment arecalled as non- heat treatable alloys.

Duralumin: Duralumin consists of about 95% Al + 4% Cu + 0.5% Mn + 0.5% Mg. Due toits high strength and low density, it is widely used for making aircraft and automobileparts. Due to its high ductility and good electrical conductivity, it is used for makingsurgical instruments, cables etc.

Magnelium: Magnelium consists of about 70-90% Al+10-30% Mg. It is characterized bylight weight, high tensile strength, good machinability and weldability. It is used in aircraftand automobile industries.

(2) Cast Aluminium Alloys: Aluminium alloys, which are shaped by casting processes suchas die casting, investment castings are known as cast alloys.

Al-Si alloys: Aluminium alloy with 10% Si possesses casting properties and goodcorrosion resistance. They are used in automobile gear boxes, radiators etc.

AlMg alloys: Aluminium alloy with 10% Mg possesses high strength and excellent

corrosion resistance. They are used for large tanks carrying milk, petrol.4. What is Fiber reinforced polymers (FRP)? Discuss the various types of FRP (PMC) with

suitable examples.

Definition: FRP are composite materials that typically consist of strong fibers embedded in aresin matrix.

Types of FRP (or Classification of Polymer matrix composites, PMC):

Glass fiber reinforced polymers (GFRP)

Aramid fiber (Kevlar) reinforced polymers (AFRP) Carbon fiber reinforced polymers (CFRP)

(i) Glass Fiber Reinforced Polymers (GFRP)

Definition: GFRP is a kind of PMC reinforced by Glass fibers

Preparation, Properties and Applications: There are basically four varieties of glass fibersused in composites. They are E-glass (electrical grade), S-glass (high strength), AR-glass(alkaline resistant) and Z-glass (zirconia containing glass fibers).

E-glass fibers are used for structural and electrical applications because of their highelectrical insulating properties and good mechanical properties.

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S-glass fibers retain their strength at higher temperatures and have higher fatigue strengthand are used in defence and aeronautical applications.

AR- and Z-glass fibers possess good resistance to alkaline environments and are used forstructural applications.

(ii) Aramid Fiber (Kevlar) Reinforced Polymers (AFRP)

Definition: AFRP is a kind of PMC reinforced by aramid (aromatic polyamides) fibers.

Preparation, Properties and Applications: Kevlar is the trade name of aramid [Poly (para-phenylene-terephthalamide)] fibers. Aramid fibres are synthesized by polycondensation of p-phenylene diamine and terephthaloyl dichloride.

Aramid fibers characterized by high strength and stiffness; light weight and low density; ultrahigh modulus. AFRP are used for manufacturing aerospace, automotive and marineapplications.

(iii) Carbon Fiber Reinforced Polymers (CFRP)

Definition: CFRP is a kind of PMC reinforced by carbon fibers.

Preparation, Properties and Applications: Carbon fibers are prepared by carbonization ofrayon or polyacrylonitrile in an inert atmosphere at high temperatures (1600 to 2200C).

Carbon fibers characterized by high strength to weight ratio; very high modulus of elasticity;light weight; good corrosion resistance; low coefficient of thermal expansion; high electricalconductivity. CFRP are used for manufacturing automotive, marine and aerospace parts etc.

5. What are metal matrix composites (MMC)? Describe MMC with suitable examples.

Definition: MMC is a material that consists either a ceramic or another metal dispersed inmetal matrix.

Examples of matrix: Al, Mg, Ti, Cu etc.,

Examples of reinforcements: Ceramics Oxides (Al2O3), Carbides (SiC, TiC), Borides(TiB2); Metals Pb, W, Mo etc.

Characteristics: MMC are characterized by: High strength at elevated temperatures; Highstiffness; High thermal stability; High thermal conductivity etc.

Types of MMC:

S.No. Types Reinforcement Properties and Applications

1. Al-matrixcomposites

SiC particles,Al2O3 fibers

Used for manufacturing automotive parts,cores for high voltage electrical cables.

2. Mg-matrixcomposites

SiC particles Used for manufacturing components for aircraft parts, gear boxes.

3. Ti-matrixcomposites

TiB2, TiC Used for manufacturing turbine enginecomponents, automotive engine components

UNIT V INTRODUCTION TO NANOMATERIALS

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1. Define nanochemistry.

Nanochemistry is the study of synthesis and analysis of materials in the nanoscale range (1 10nm), including large organic molecules, inorganic cluster compounds, and metallic orsemiconductor particles.

2. What are nanomaterials or nanostructured materials?

Materials, which possess grain size less than 100nm in at least one coordinate (dimension),are known as nanomaterials or nanostructured materials.

3. How are nanomaterials classified on the basis of dimensions?

S.No. Reduction in size indifferent coordinates

Size Examples

1. 3 dimensions


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7. What are nanoparticles? Write the preparation, properties and applications ofnanoparticles.

Definition: Particles or powders with grain size (diameter) less than 100 nm are callednanoparticles.

Synthesis of nanoparticles by chemical reduction method:

Group VI metal halides like MoCl3, WCl4 can be reduced into their corresponding metals byusing NaBEt3H (sodium tri-ethoxy boron hydride) with toluene as solvent at roomtemperature.

Properties:

As the particle size decreases, surface to volume ratio increases. This enhances catalyticactivity of nanoparticles.

Size reduction influences thermal properties like melting point. Melting point decreases

with the particle size reduction.Applications of nanoparticles:

Since Ag nanoparticles have good antibacterial properties, it is used in refrigerators, air-conditioners, water purifiers etc.

ZnO, TiO2 nanoparticles are used as sunscreen cosmetics because they absorb uvandgive protection to skin.

8. What are nanowires? Write the preparation, properties and applications ofnanoparticles.

Definition: Nanowires are cylindrical solid wires with a diameter ranging from 10100nm anda length of few micrometers.

Preparation of nanowires by VLS mechanism: A well accepted mechanism for the growthof nanowires through gas phase reaction is vapour-liquid-solid (VLS) process.

Mechanism: VLS mechanism follows two step processes:

(i) In the first step, diffusion of vapour phase (reactants) takes place into the liquid phase(molten nanoparticle catalyst)

(ii) In the second step, super saturation of reactants occurs in the liquid phase which causesthe precipitation of solid phase (nanowire)

Synthesis of Silicon Nanowire: To grow silicon nanowire, gold nanoparticles is used ascatalyst. The substrate is first covered with a coating of gold nanoparticles and heated to atemperature in a furnace so that it becomes liquid. Simultaneously the precursor (rawmaterial), silane (SiH4) is introduced into the furnace where it vapourises to form siliconvapour. During the reaction, silicon vapour diffuses and dissolves in molten goldnanoparticles. When the concentration of silicon becomes supersaturated, the excessmaterial (silicon) precipitates and grows as nanowires.

Applications:

Nanowires are used in electron devices like field effect transistors, in sensors, and

detectors Nanowires replace copper in computers and in electronics.

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9. Mention the important properties and applications of nanoporous materials.

Nanoporous materials have the surface area of 5001000m2/gm, which enhances thechemical reactivity and catalytic activity of various reactions.

They have very low thermal conductivity and are used as thermal insulators.

10. Write the basic principles of Chemical vapour deposition (CVD) and Physical vapourdeposition (PVD) methods?

CVD method involves a transport of reactant gases towards the substrate kept at sometemperature. The reactants crack into different products and diffuse on the surface andundergo certain chemical reactions. This leads to the growth of thin films, nanowires andnanotubes.

Physical vapour deposition (PVD) is a technique by which a metal, ceramic or a compound isconverted into gaseous form and then deposited on the surface of a substrate.

Examples: Evaporation, Sputtering, Laser ablation


1. Explain plasma arcing method for synthesis of CNTs.

Electric arc discharge method (or) Plasma arcing: Carbon nanotubes are commonlyprepared by striking or producing an arc between graphite electrodes in an inert atmosphere.The following are the conditions required for CNT formation.

Electrodes : Pure graphite rodsDiameter of electrodes : 5 to 20mGap between the electrodes : 1 mmCurrent : 50 to 120 AmperesVoltage : 20 to 25 V

Inert gas pressure : 100 to 500torr Temperature rise during arcdischarge

: 3000 to 3500C

To Vacuum

+

GasInletGraphite Electrodes

In this method, a potential of 2025V is applied across the pure graphite electrodes of 520m diameter and separated by 1mm at 500torr pressure of flowing helium gas. Underthese conditions carbon atoms are ejected as vapour from the positive electrode and formsnanotube on the negative electrode. To produce SWCNT a small amount of Co, Ni, or Fe is

incorporated as catalyst in the central region of the positive electrode. If no catalysts areused, the tubes formed are multi-walled types.

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2. Explain any two important properties of cabon nanotubes.

(i) Electrical properties of CNTs

Carbon nanotubes (CNTs) can be both metallic or semiconducting, depending upon thehelicity (chirality) and diameter of the nanotubes. Helicity refers to rolling of hexagonal chainswith respect to the tube axis. Helicity results in three different kinds of CNTs. They arearmchair, zigzag, and chiral nanotubes.

The general rules for the electrical conductivity of the SWNTs are as follows: Basically, all armchair tubes (n, n) tubes are metallic because of their symmetry.

One out of three zigzag and chiral tubes can be either metallic or semi-conductingdepending upon their chiral vector (n, m).

Metallic properties dominate when 0m-n = or integer.3

m)-(n=

Semi conducting properties dominate when integer.3

m)-(n

Hence, (7,1) and (5,2) tubes would be metallic, whereas (8,0) and (6,1) tubes would be

semiconducting; the (5,5) armchair tube would always be metallic.

In metallic state, the conductivity of CNTs is very high. It is estimated that CNTs can carrybillion amperes of current per square centimeter. The copper wire fails at one million amperesof current per square centimeter because resistive heating melts the wire. One reason forhigh conductivity of CNTs is that they have very few defects to scatter electrons and offer avery low resistance.

armchair zigzag chiral

(ii) Mechanical properties of CNTs

(i) Tensile strength: It is a measure of the amount of stress needed to pull a material. The

tensile strength of CNTs is ~100 times stronger than that of steel of the same diameter. (a)The strength is provided by the interlocking of carbon-to-carbon covalent bonds (b) EachCNT is one large molecule. It means that, it does not have any weak spots like grainboundaries, dislocation etc.

(ii) Youngs modulus: It is a measure of stiffness or flexibility a material. CNTs have Youngsmodulus ranging from 1.28 to 1.80TPa whereas steel has 0.21TPa. It means that Youngsmodulus of CNTs is almost 5 to 10 times of steel.

(iii) Thermal conductivity: CNTs have high thermal conductivity. It has beenpredicted that, thermal conductivity of CNTs is ten times that of silver.

(iv) Density: CNTs are light weight with a density of about that of steel and 1/2 of

that of aluminium. The density of CNTs is 1.331.44gm/cm3.

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3. Discuss the various steps involved in sol-gel process for the synthesis of nanoporousmaterials.

Synthesis of Nanoporous materials by sol-gel process:

Basic principle: Sols are particles in liquid. Gels are nothing but a continuous network ofparticles with porous structure filled with a liquid. A sol-gel process involves the formation ofsols in a liquid and then converting the sol particles into a porous network filled with a liquid.By drying the liquid, it is possible to obtain a thin film or monolithic solid is known as aerogel.

Precursors: The precursors used in sol-gel process for the synthesis of nanoporousmaterials are metal alkoxides, M(OR)4. They readily react with water to form gels. Egs:Tetramethoxy silane, [Si(OCH3)4]; Tetraethoxy silane, [Si(OC2H5)4]

Synthesis of silica aerogel: The process consists of four main steps:

1. Hydrolysis: It occurs through the addition of water and to form silanol, (SiOH) particles.

2. Condensation: The self condensation of silanol groups produces siloxane linkages, (Si

OSi) filled with byproducts of water or alcohol.

3. Polycondensation: The condensation process continues to form poly condensed silica gelwith SiOSi linkages.

SiOSiOSi

SiOSiOSi

SiOSiOSi

O O O

O O O

4. Drying: The gels are subjected to super critical drying in an autoclave. The criticalpressure and critical temperature used are 78bar and 294C respectively in order toremove liquid from silica gel to form the network structure of silica aerogel.

Precursor, M(OR)4

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

.

.

.

. .

.

.

.

.

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

..

.

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ _

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

_ _ _ _ _ _ _ __ _ _ _ _ _ _ _

Hydrolysis

Sol

Gel

Aerogel

Xerogel

Condensation

Polycondensation

Superc

ritical

dryin

g

Rapidevaporation

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4. Explain CVD method for the synthesis of nanotubes.

Chemical vapour deposition (CVD) method:In chemical vapour deposition (CVD) method, carbon nanotubes (CNTs) are grown bydecomposing an organic gas over a substrate covered with metal catalyst nanoparticles.

A thermal CVD reactor is simple and inexpensive to construct. It consists of a quartz tubeenclosed in a furnace. The substrate material may be silica, mica, quartz, or alumina.Thermal CVD can be used to grow SWCNT as well as MWCNT.

Substrate

VacuumPump

C2H2

N2Furnace

Quartz Tube

Thermal CVD uses acetylene (C2H2), ethylene (C2H4), or methane (CH4) gas as the carbonprecursors (feed stock or raw material) and Fe, Co, or Ni nanoparticles as the catalyst. Thegrowth temperature is typically in the range of 500900C. At these temperatures, the carbonatoms dissolve in the metal nanoparticle catalysts, which finally become saturated. Thesaturated carbon then precipitates to form carbon nanotubes at the surface of catalyst coatedsubstrates. The diameter of the tube is determined by the size of nanoparticles, which workas catalyst.

5. Explain the basic principle of any two physical vapour deposition (PVD) techniques.

Definition: PVD is a technique by which a metal, ceramic or a compound is converted intogaseous form and then deposited on the surface of a substrate.

(i) Sputtering:The source materials used in this process are generally an alloy, ceramic ora compound. In sputtering technique, a high energy atom in its ionized form (usually Ar+)is used to hit the surface atoms of the targeted source material. Then the knocked outatoms in vapour form are deposited on the surface of the substrates to produce a uniformcoatings.

(ii) Laser ablation: Laser ablation has several advantages, such as high quality SWNT

production, diameter control and the production of new materials.The laser ablationapparatus consists of a furnace, a quartz tube with a window, a graphite targetdoped with small amount of catalytic metals like cobalt and nickel, flow systems forargon gas to maintain constant pressures and flow rates and a watercooled coppercollector placed somewhat outside the furnace.

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1200oC, Furnace

Graphite Target

Nd:YAG Laser

Water cooledCu-Collector

Ar Gas

Quartz Tube

A laser beam of a pulsed (or continuous) Nd:YAG (Neodymium-doped-yttrium aluminiumgarnet, Nd:Y3Al5O12) or CO2 is introduced through the window by focusing onto the targetlocated in the center of the furnace. The furnace temperature is maintained at 1200 C.Due to the emission of a pulsed (or continuous) laser, the target is vaporized in hightemperature. This leads to the formation of small carbon molecules and atoms. Theargon gas then sweeps the carbon atoms from the high temperature zone to the coldercopper collector where they condense to form carbon nanotubes. The argon flow rateand pressure are typically 1cm.s-1 and 500Torr respectively.

6. Write an account on the applications of nanomaterials.

1. Cabon nanotubes (CNTs) can be used as catalyst supports because they can provide theadvantages of large surface areas, high chemical stability and controlled surfacechemistry.

2. CNTs are used in the development of flat panel displays used in televisions andcomputers

3. Silver nanoparticles have good antibacterial properties, and hence it is used inrefrigerators, air-conditioners, water purifiers etc.

4. ZnO, TiO2 nanoparticles are used as sunscreen cosmetics because they absorb uvandgive protection to skin.

5. Silicon and gallium nitride nanowires are used in electron devices like field effecttransistors, in sensors, and detectors.

6. Nanoporous materials have very low thermal conductivity (presence of air in the poresmakes the porous material less conductive) and are used as thermal insulators.

II Semester Question Bank - Chemistry of Industrial Materials

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