Chemistry for Engineering Materials

                                            


                                                           

                                                                   Fuel

Advantages and disadvantages of liquid fuels?

Advantage and disadvantage of liquid fuels are given below

Advantage:

·        Calorific value is high.

·        They require less space for storge.

·        They are easy to handle.

·        They don’t produce ash.

·        They produce less smoke.

·        Higher combustion efficiency

·        They require less air for combustion.

·        They are easy to transport.

·        They have uniform combustion.

Disadvantage:

·        They are costly.

·        Their production cost is higher.

·        They are given bad odor.

·        Greater risk of fire.

 

What is calorific value? Calorific value of wood?

Calorific value: Colorific value refers to amount of heat produced by unit volume of a substance on complete combustion. [KJ/kg]

Calorific value of wood approximate – [17000 – 22000 KJ/KG]

 

Proximate and unlimited analysis of coal?

Proximate analysis: Proximate analysis of coal is an assay of the coal. The various parameter studied are percentages of moisture, volatile matter, ash and fixed carbon.

 

Moisture

3-30 %

Volatile matter

3-50%

Ash

2-30%

Fixed carbon

16-92%

 

Unlimited analysis: Unlimited analysis of coal is the element analysis of the coal. The various parameter studied are percentages of carbon, hydrogen, Sulphur, nitrogen, ash and oxygen.

Carbon

50-95%

Hydrogen

2.5-5%

Sulphur

0.5-7%

Nitrogen

0.5-3%

Oxygen

2-4%

Ash

2-30%

 

What Is Crude Oil and composition?

Crude oil is a naturally occurring petroleum product composed of hydrocarbon deposits and other organic materials.

Composition of crude oil is

1.     Carbon - 83 to 87%

2.     Hydrogen - 10 to 14%

3.     Nitrogen - 0.1 to 2%

4.     Oxygen - 0.05 to 1.5%

5.     Sulfur - 0.05 to 6.0%

6.     Metals - < 0.1%

 

Water gas and its characteristic?

Water gas: water gas is a kind of fuel gas a mixture of carbon monoxide and hydrogen. It is produced alternately hot blowing a fuel layer with air and gasifying it with steam.

Reaction:

Supplied steam reacts with red hot coke at 900 -1000  to form CO and H  

Composition:

Composition of water gas is

 

Use:

·        A source of hydrogen gas.

·        An illuminating gas.

·        A fuel gasses.

 

Producer Gas and its Characteristics?

Producer Gas:

Producer gas is a mixture of gases that contain carbon monoxide, hydrogen, carbon dioxide, nitrogen. These gases carbon monoxide and hydrogen gas combustible and carbon dioxide and nitrogen gas non-combustible gases.

Composition:

Composition of producer gas is discussed below

Calorific value 1300 Kcal/

Reaction:

The gas production reaction can be divided into four zone as follows

Ash zone: Ash zone the lowermost zone. The ash generated from the producer gas formation is released out from this zone.

Combustion zone: Here burns the carbon and forms  and . The temperature of this zone is about 1100 . The following reaction take place.

 

Reduction Zone: Here carbon dioxide and steam combines with red hot carbon and liberates free hydrogen and carbon monoxide. The reactions are

All these reduction reactors are endothermic, so the temperature in the reduction zone falls to  .

 

Distillation Zone: In this zone  the incoming coal is heated by outgoing gases by given sensible heat to the coal. The heat given by the gases and heat radiated from the reduction zone help to distillate the fuel thereby volatile matter of coal is added to the outgoing gas.

 

Properties of petroleum product?

Flash point: The flash point of a liquid is the lowest temperature at which it will generate sufficient vapor to ignite when it is exposed to a source of ignition.

Fire point: fire point of a fuel is the lowest temperature at which the vapor of that fuel will continue to burn at least 5 seconds after ignition.

Cloud point: Cloud point is the temperature at which wax begins separate when oil chilled to a low temperature.

Pour point: Pour point of a liquid is the temperature below which the liquid loses its flow characteristics.

 

 

What is lubricant and lubricity and its characteristic?

Lubricant: Lubricant is a substance which is applied between two rubbing surfaces for reducing friction.

Lubricity: Lubricity is measure of the reduction in friction by a lubricant.

Characteristic: A good lubricant generally possesses the following characteristic

o   High boiling point and low freezing point.

o   Corrosion preventive.

o   A high viscosity indexes.

o   A high resistance to oxidation.

o   Thermal stability.

o   Hydraulic stability.

 

Rules of a lubricant?

The primary function of a lubricant is to

·        Reduce friction.

·        Prevent wear.

·        Protect the equipment from corrosion.

·        Control temperature.

·        Control contamination.

·        Transmit power.

 

 

Cement

 

What is cement and its composition?

Cement: Cement is a binder, a substance to use construction that sets, hardens and adheres to other materials to bind them together.

Composition: Chemical composition of cement

·      Lime 60-65

·      Silica 17-25

·      Alumina 3-8

·      Iron oxide .5-6

·      Gypsum 01-4

 

What is Portland cement and its raw materials?

Portland cement: Portland cement is the product obtained by pulverizing clinker consisting hydraulic calcium silicates to which some calcium sulfate has usually been provided as an inter ground addition. 

Raw material: Two principal material from which Portland cement is made are

·        A material of high lime content such as lime stone, chalk, shells.

·        A material of high silica and alumina content such as clay, shale, or blast furnace slag.

 

Cement manufacturing process

The manufacturing procedures of Portland cement is described below

·        Mixing and crushing raw materials.

·        Burning.

·        Grinding.

·        Packaging and storage.

 

Mixing and crushing raw materials: Limestone is crushed and stored in silos. Clay is washed with water to remove other organic matter. Both these materials are mixed in grinding mill to form slurry. Slurry contains 38-40  water.

 


Burning: The burning process is done by zone of rotary kiln. There are three zone.

·      Dry zone: The temperature of dry zone about 400 . Most of the water in the slurry gets eliminated.

·        Calcination zone: The temperature of calcination zone about 700-1000 . Lime gets decomposed into  and .

·        Clinkering zone: Lower part have temperature between 1250-1500 . Lime and clay react to form small and hard stone are known as clinker.

 

Grinding: Cooled clinker are received from the cooling pans and sent into mills. The clinker is grinded finely into powder in ball. At final stage of grinding about 2-3  of powdered gypsum is added.

 

Packaging: The grinding cement is stored in silos. From which it is marketed either in container or bags.

 


 

Properties of cement?

Two properties of cement

Physical properties

·        Fineness

·        Soundness

·        Consistency

·        Setting time

·        Heat of hydration

·        Strength of cement

·        Compressibility

Chemical properties

·        Lime

·        Silica

·        Alumina

·        Iron oxide

 

 

Semiconductor

 

What is semiconductor? Properties of semiconductor? Types of semiconductors?

Semiconductor: Semiconductors are materials which have a conductivity between conductors (generally metals) non-conductors (such as ceramic).

Properties: There are four important properties of semiconductors

·      Resistivity:  

·      Conductivity:  

·        Temperature coefficient of resistance: Negative.

·        Current flow: Due to electrons and holes.

 

Types: Semiconductor can be classified as

·        Intrinsic

·        Extrinsic

a)  N-type

b)  P-type

 

 

 


What is N-type and P-type semiconductors?

N-type: When a small amount of pentavalent impurity added to a pure semiconductor its knowns as N-type semiconductor.

 


·        We use pentavalent impurity like Arsenic.

·        Arsenic has five valance electrons.

·        When a small amount of arsenic is added to germanium crystal,

some number of free electrons becomes available in the crystal.

·        Though each arsenic atom provides one free electron.

·        That means small amount of arsenic impurity provides enough atoms to supply millions of free electrons.

 

P-type: When a small amount of trivalent impurity added to a pure semiconductor its knowns as P-type semiconductor.

·        We use trivalent impurity like gallium.

·        Gallium has three valance electrons.

·        When a small amount of gallium is added to germanium crystal there exist large number of holes in the crystal.

·        This missing electron is called a hole. Therefore, for each gallium atom added one hole is created. A small amount of gallium provides millions of holes.

 


 

What is forward and reverse bias.

Forward: Forward is where the external voltage delivered across the P-N junction diode. In a forward bias setup P-side attached to the positive terminal and N-side is fixed to the negative side of the battery. 

 

 


Reverse bias: Reverse bias is where the external voltage delivered across the P-N junction. In a reverse bias setup P-side of the diode is attached negative side and N-side is fixed to the positive side of the battery.

 

What are superconductors and their use and example?

Superconductor: Superconductors are materials that offer no resistance to electrical current

Example: Example of superconductors aluminum, niobium, magnesium diboride.

Use:

·        superconductors mainly used for creating powerful electromagnets in MRI scanners.

·        This conductor is used to transmit power for long distance.

·        Used to memory or storage elements.

·        They can also use separate magnetic and non-magnetic materials.

 

What is a P-N junction diode? What happens to the depletion layer of P-N junction diode when it is?

p-n junction diode: A p-n junction diode is formed when a p-type semiconductor is fused to an n-type semiconductor creating a potential barrier voltage across diode junction.

 




The width of depletion layer of p-n junction decreases when the junction is forward biased.

The width of depletion layer of p-n junction increases when the junction is reverse biased.

 

Energy band description of semiconductor?

For silicon:

 

·        We see that forbidden energy gap is very small valence band to conduction band.

·        Being 1.1ve for silicon.

·        So small energy needed by their valence electron cross over to the conduction band.

·        Even at room temperature some of the valence electrons may acquire sufficient energy to enter into conduction band thus become free electrons.

What is majority and minority carrier?

In an n-type semiconductor the electrons are the majority carriers, whereas the holes are minority carriers.

In the p-type semiconductor material the holes are majority carriers, whereas the electrons are minority carriers.

   

 


Why is Silicon preferred over Germanium for semiconductor?

The reason why silicon is more used than germanium is given below

·        Silicon can be work at higher temperature as compared to germanium.

·        The structure of germanium crystal will be destroyed at higher temperature.

·        Also, silicon has much smaller current leakages than that of germanium.

 

Differences Between Intrinsic and Extrinsic Semiconductors

Intrinsic Semiconductors

Extrinsic Semiconductors

Semiconductor in its purest form.      

Semiconductor in its impure form.

It has low conductivity.

It has a higher conductivity than an intrinsic semiconductor.

The band gap between the conduction and valence bands is quite narrow.

The energy gap is greater than that of an intrinsic semiconductor.

Pure silicon and germanium crystalline forms are example.

Impurities such as As, Sb, In,

P, and other are doped with germanium.