Chemistry - Water Treatment Notes from VIT

1. Water Treatment

2. HARD WATER
Water that contains appreciable quantity
of dissolved minerals (like magnesium
and calcium ions) is called hard water.
Or
Water which does not produce lather
with soap solution
SOFT WATER
Treated water which does not contained
any dissolved minerals except sodium.
Or
Water which produce lather with
soap solution
2

3. Why hard water do not produce lather with soap?
Soap is Na or K salts of long chain fatty acids, C17H35COOH.
When water is hard (i.e. if it contains salts of magnesium and calcium),
the following reaction takes place when it is used with soap.
2C17H35COONa + CaCl2 → (C17H35COO)2Ca↓ + 2NaCl
2C17H35COONa + MgSO4 → (C17H35COO)2Mg↓ + Na2SO4
Hardness of water is due to presence of Calcium and Magnesium salts

5. Test for Hardness- Eriochrome Black-T test
1. Take Two conical flasks and
add 5 ml of ammonium buffer
solution and 2-3 drops of EBT
indicator
2. To one flask add 5 ml of RO
water (soft) and shake well
3. To another flask add 5 ml of
sea water (hard) and shake
well
4. Observe the colour in both
Pure water Hard water
Sodium salt of EBT

6. Estimation of Hardness by EDTA method
• Ca and Mg ions form complex with the chelating agent, ethylene diamine
tetraacetic acid (EDTA).
• When Eriochrome BlackT (EBT) is added to hard water in the presence of
ammonia- ammonium chloride buffer (pH 9-10) EBT forms a Meta stable
wine red coloured complex with the Ca& Mg ions
• On treating the wine red complex with EDTA, a more stable metal –EDTA
complex is formed setting the EBT free.
• This reaction proceeds with a colour change from wine red to steel blue.

7. Dr.V.S.Gayathri
EDTA Sodium salt of EBT
Structure of Metal-EDTA
complex
(here M=Ca2+, Mg2+)

8. Hardness - expression
Hardness is expressed as equivalent amount (equivalents) of CaCO3
i. Molar mass of CaCO3 is exactly 100
ii. It is the most insoluble salt that can be precipitated in water treatment.
Equivalents of CaCO3 is calculated using the formula
Mass of hardness producing substance in mg/L x100
Molecular wt. of hardness producing substance
units – mg/L = ppm
parts of CaCO3 equivalents in hardness in 106 parts of water

9. 9
Softening of hard water

10. 10
II. Zeolite (Permutit) method of Softening of water
Zeolite is a Hydrated Sodium Alumino Silicate (HSAS),
capable of exchanging reversibly its sodium ions for
hardness producing ions in water.
Porous Structure of zeolite
The general chemical structure of zeolite is given
below Na2O.Al2O3.xSiO2.yH2O (x = 2-10 and y = 2-6)
Why synthetic zeolite is better than natural zeolite for the
softening of water?
Micro pores of Zeolite

11. 11
Zeolite softener
Zeolite bed
Gravel
Hard water in
Injector
NaCl storage
Softened water
To
sink
Hard water spray

12. 12
Process of softening by Zeolite method
For the purification of water by the zeolite softener, hard water is passed through the zeolite bed at a
specified rate. The hardness causing ions such as Ca2+, Mg2+ are retained by the zeolite bed as CaZe
and MgZe respectively; while the outgoing water contains sodium salts. The following reactions takes
place during softening process
Na2Ze + Ca(HCO3)2 CaZe + 2NaHCO3
Na2Ze + Mg(HCO3)2 MgZe + 2NaHCO3
To remove temporary hardness
To remove permanent hardness
Na2Ze + CaCl2 CaZe + 2NaCl
Na2Ze + MgSO4 MgZe + Na2SO4
Regeneration of Zeolite Bed
CaZe (or) MgZe + 2NaCl Na2Ze + CaCl2 (MgSO4)
Washings
drained
Regenerated
Zeolite
Used
Zeolite
10% brine
solution
Hardness
water
Scale formation

13. 13
Limitations of Zeolite process
1. If the water is turbid ---- then the turbidity causing particles clogs the pores of the Zeolite and makes
it inactive
2. The ions such as Mn2+ and Fe2+ forms stable complex Zeolite which can not be regenerated that
easily
3. Any acid present in water (acidic water) should be neutralized with soda before admitting the water
to the plant
Advantages of Zeolite process
1. Soft water of 10ppm can be produced by this method
2. The equipment occupies less space
3. No impurities are precipitated, hence no danger of sludge formation in the treated water
4. It does not require more time and more skill
Disadvantages of Zeolite process
1. Soft water contains more sodium salts than in lime soda process
2. It replaces only Ca2+ and Mg2+ with Na+ but leaves all the other ions like HCO3
- and CO3
2- in
the softened water (then it may form NaHCO3 and Na2CO3 which releases CO2 when the water
is boiled and causes corrosion)
3. It also causes caustic embitterment when sodium carbonate hydrolyses to give NaOH

14. 14
III. Ion-Exchange resin (or) deionization (or) demineralization process
Ion exchange resin
Ion exchange resins are insoluble, cross linked, long
chain organic polymers with a microporous structure,
and the functional groups attached to the chain is
responsible for the “ion-exchange” properties.
Cation
exchange Resin
Resin after
treatment

15. 15
In general the resins containing acidic functional groups (-COOH, -SO3H etc) are capable of exchanging
their H+ ions with other cations, which comes in their contact; whereas those containing basic functional
groups ( -NH2, =NH as hydrochlorides) are capable of exchanging their anions with other ions, which
comes in their contact.
Based on the above fact the resins are classified into two types
1. Cation exchange resin (RH+)
2. Anion Exchange resin (ROH-)

16. 16
Structure of Cation and Anoin exchange resins
R = CH3
Cation exchange resin Anion exchange resin

17. 17
Ion exchange purifier or softener
Cation exchange Resin Anion exchange Resin
Gravel
bed
Hard
water
Injector
Injector
Alkaline solution for
regeneration of resin
Soft water
Wastages to
sink
Wastages to
sink
Acid solution
for
regeneration
of resin
pump

18. 18
Process of softening
2 RH+ + Ca2+ (hard water) R2Ca2+ + 2 H+
2 RH+ + Mg2+ (hard water) R2Mg2+ + 2 H+
2 ROH- + SO4
2- (hard water) R2SO4
2+ + 2 OH-
2 ROH- + Cl- (hard water) R2Cl- + 2 OH-
H+ + OH- H2O
Reactions occurring at Cation exchange resin
Reactions occurring at Anion exchange resin
At the end of the process

19. 19
Regeneration of ion exchange resins
R2Ca2+ + 2H+ (dil. HCl (or) H2SO4) 2 RH+ + Ca2+ (CaCl2, washings)
R2SO4
2- + 2OH- (dil. NaOH) 2 ROH- + SO4
2- (Na2SO4, washings)
Advantages
1. The process can be used to soften highly acidic or alkaline waters
2. It produces water of very low hardness of 2ppm. So the treated waters by
this method can be used in high pressure boilers
Disadvantages
1. The setup is costly and it uses costly chemicals
2. The water should not be turbid and the turbidity level should not be more
than 10ppm
Regeneration of Cation exchange resin
Regeneration of Anion exchange resin

20. 20
IV. Softening of water by Mixed Bed deioniser
Description and process of mixed bed deionizer
1. It is a single cylindrical chamber containing a mixture of anion and cation exchange resins bed
2. When the hard water is passed through this bed slowly the cations and anioins of the hard water
comes in to contact with the two kind of resins many number of times
3. Hence, it is equivalent to passing the hard water many number of times through a series of cation
and anion exchange resins.
4. The soft water from this method contains less than 1ppm of dissolved salts and hence more
suitable for boilers
Mixed bed
deionizer
c
c
c
c c
c
a
a
a
a
a
a
Anion exchange
resin
Demineralised
water
Cation exchange
resin
Hard water
Mixed resin
bed

21. • Reverse osmosis filters have a pore size around
0.0001 micron
• After water passes through a reverse osmosis
filter, it is essentially pure water
• In addition to removing all organic molecules and
viruses, reverse osmosis also removes most
minerals that are present in the water
• Reverse osmosis removes monovalent ions, which
means that it desalinates the water
Reverse osmosis

22. Principle of osmosis and reverse osmosis
• When two solutions of unequal concentrations are
separated by a semipermeable membrane, solvent will
flow from lower to higher solute concentration
• This phenomenon can be reversed (solvent flow
reversed) by applying hydrostatic pressure on the
concentrated side

23. Osmosis Reverse Osmosis
Hydrostatic pressure
in excess of osmotic
pressure is applied,
the solvent flow
reverses
➢Cellulose acetate
➢Polysulfone
➢Polysulfone amide
➢Polyamide
➢Poly-acrylonitrile

24. Advantages:
Reverse OSMOSIS
1. Removes ionic, non-ionic, colloidal and high
molecular weight organic matter
2.Removes colloidal silica
3.Low Maintenance cost - Life time (~2 years)
4.Easy membrane replacement
5.Low operating cost, high reliability

25. Module VI
FUELS & COMBUSTION
INTRODUCTION AND SOLID FUELS

26. FUELS
Fuel is a combustible substance which when burnt in
oxygen or air, produces significant amount of heat which
can be economically used for domestic and industrial
purposes for generating power.
In the process of combustion, the chemical energy of
fuel is converted into heat energy.
• Fuel + Air/oxidizer  Products of combustion + Energy

27. Calorific value of fuels
• The most important property of fuel to be taken into
account is its calorific value or the capacity to supply
heat. The calorific value of a fuel can be defined as
"the total quantity of heat liberated when a unit mass
or volume of the fuel is burnt completely".
•Units are Calorie/ Kilocalorie - Calorie is the
amount of heat required to raise the temperature of
one gram of water through one degree centigrade.

28. Determination of Calorific Value
Bomb calorimeter

29. Calculation
m = mass of fuel pellet (g)
W = mass of water in the calorimeter (g)
w = water equivalent of calorimeter (g)
t1 = initial temperature of calorimeter.
t2 = final temperature of calorimeter.
HCV = gross calorific value of fuel.

30. Higher or Gross Calorific Value (HCV or GCV)
• Usually, all fuels contain some hydrogen and when the
calorific value of hydrogen containing fuel is determined
experimentally, the hydrogen is converted to steam.
• If the products of combustion are condensed to room
temperature (15C or 60F), the latent heat of condensation of
steam also gets included in the measured heat, which is then
called "higher or gross calorific value".
• So gross or higher calorific value may be defined as "the total
amount of heat produced when one unit mass/volume of the
fuel has been burnt completely and the products of combustion
have been cooled to room temperature".

31. Lower or Net Calorific Value
• In actual use of fuel, the water vapour and moisture etc are not
condensed and escapes as such along with hot combustion gases.
Hence a lesser amount of heat is available. So, net or lower calorific
value may be defined as "the net heat produced when unit mass /
volume of the fuel is burnt completely and the products are permitted
to escape".
• Net or lower calorific value can be found from GCV value
NCV = GCV - Latent heat of water vapour formed
= GCV - Mass of hydrogen x 9 x latent heat of steam
• 1 part by mass of hydrogen produces 9 parts by mass of water. The
latent heat of steam is 587 k cal / kg or 1060 B. Th. U. / lb of water
vapour formed at room temperature. (ie 15C).

32. Water Equivalent of the calorimeter is determined by
burning a fuel of known calorific value (benzoic acid (HCV
= 6,325 kcal/kg) and naphthalene (HCV = 9,688 kcal/kg)
If H is the percentage of hydrogen in fuel,
the mass of water produced from 1 g of fuel = (9/100)×H
= 0.09 H
Heat taken by water in forming steam = 0.09 H× 587 cal
(latent heat of steam = 587 cal/kg)
LCV = HCV – Latent heat of water formed
32

33. 1. 0.72 gram of a fuel containing 80% carbon, when burnt
in a bomb calorimeter, increased the temperature of water
from 27.3o to 29.1oC. If the calorimeter contains 250
grams of water and its water equivalents is 150 grams,
calculate the HCV of the fuel. Give your answer in KJ/Kg.
Solution. Here x= 0.72 g, W = 250g, t1 = 27.3oC, t2 = 29.1oC.
HCV of fuel (L) = (W + w) (t1 - t2) Kcal/kg
x
= (250 + 150) × (29.1-27.3) kcal/kg = 1,000 × 4.2 kJ/Kg = 4,200 kJ/kg
0.72
33

34. 2. On burning 0.83 of a solid fuel in a bomb calorimeter , the
temperature of 3,500g of water increased from 26.5oC to 29.2oC.
Water equivalent of calorimeter and latent heat of steam are
385.0g of and 587.0 cal/g respectively. If the fuel contains 0.7%
hydrogen, calculate its gross and net calorific value.
Solution. Here wt. of fuel (x) = 0.83 g of ; wt of water (W) = 3,500
g; water equivalent of calorimeter (w) = 385 g ; (t2 - t) = (29.2oC -
26.5oC) = 2.7oC ; percentage of hydrogen (H) = 0.7% ; latent heat
of steam = 587 cal/g
Gross calorific value = (W + w) (t1 - t2) cal/g
x
= (3,500 +385) × 2.7 = 12,638 cal/g
0.83
NCV = [GCV – 0.09 H × 587]
= (12,63 8– 0.09 × 0.7 × 587) cal/g
= (12,638 – 37) cal/g = 12,601 cal/g
34

35. 1. Fuse wire correction
2. Acid correction
3. Cooling correction
35

36. Corrections
Fuse wire correction:
Heat liberated during sparking should be subtracted
from calorific value
36

37. Acid correction:
Fuels containing Sulphur and Nitrogen if oxidized, the heats of formation of H2SO4 and
HNO3 should be subtracted (as the acid formations are exothermic reactions)
37

38. 38

39. Cooling correction:
The rate of cooling of the calorimeter from maximum temperature to room temperature
is noted. From this rate of cooling (i.e., dt°/min) and the actual time taken for cooling (X
min) then correction (dt × X) is called cooling correction and is added to the (t2 . t1)
term.
39

40. (W+w) (t2-t1+Cooling Correction) – (Acid + Fuse Correction)
Mass of the fuel (x)
GCV =
40

41. 3. A sample of coal contains C =93%; H =6% and ash = 1%. The following data were
obtained when the above coal was tested in bomb calorimeter.
Wt. of coal burnt =0.92g
Wt. of water taken =550g
Water equivalent of calorimeter =2,200g
Rise in temperature =2.42 oC
Fuse wire correction =10.0 cal
Acid correction =50.0 cal
Calculate gross and net calorific value of the coal, assuming the latent heat of
condensation of steam as 580 cal/g.
Solution: Wt. of coal sample (x) = 0.92 g; wt. of water (W) =550 g;
water equivalent of calorimeter (w) = 2,200g;
temperature rise (t2-t1) = 2.42 oC;
acid correction = 50.0cal;
fuse wire correction = 10.0 cal;
latent heat of steam = 580 cal/g;
percentage of H =6%
41

42. GCV = (W + w) (t1 - t2) –[acid+fuse corrections]
x
= (550+2,200) × 2.42 – [50+10] cal
0.92g
= 7,168.5 cal/g.
NCV = [GCV – 0.09 H × latent heat steam]
= (7168.5 – 0.09 × 6 × 580) cal/g
= 6855.3 cal/g
42

43. Knocking
• In an internal combustion engine, a mixture of gasoline vapour and air
is used as a fuel.
• After the initiation of the combustion reaction by spark in the cylinder,
the flame should spread rapidly and smoothly through the gaseous
mixture, thereby the expanding gas drives the piston down the cylinder.
• The ratio of the gaseous volume in the cylinder at the end of the
suction-stroke to the volume at the end of compression-stroke of the
piston is known as the 'compression ratio'.
• The efficiency of an internal combustion engine increases with the
compression ratio.

44. • Compression ratio (CR) is defined as the ratio of the cylinder volume
(V1) at the end of the suction stroke to the volume (V2) at the end of
the compression stroke of the piston.
• V1 being greater than V2, the CR is >1.
• The CR indicates the extent of compression of the fuel-air-mixture by
the piston.
• However, successful high compression ratio is dependent on the nature
of the constituents present in the gasoline used.
• In certain circumstances, due to the presence of some constituents in
the gasoline used, the rate of oxidation becomes so great that the last
portion of the fuel-air mixture gets ignited instantaneously producing an
explosive violence, known as 'knocking'.
• The knocking results in loss of efficiency, since this ultimately
decreases the compression ratio.

46. Chemical structure and knocking
• The tendency of fuel constituents to knock is in the
following order. Straight - chain paraffins > branched - chain
paraffins (isoparaffin) > olefins > cyclo paraffins (naphthenes) >
aromatics.
Octane number
• The most common way of expressing the knocking
characteristics of a combustion engine fuel is by 'octane
number', introduced by Edger. It has been found that n-
heptance, knocks very badly and hence, its anti-knock value
has arbitrarily been given zero.

47. • Octane number is equal to the percentage by volume of iso-octane
(2,2,4-trimethyl pentane) in a mixture of n-heptane and iso-octane
having the same knocking tendency compared to the sample of gasoline
being tested;
• Iso-octane has the best antiknocking properties and assigned an octane
number of 100 whereas n-heptane has poor antiknocking property and
assigned an octane number of zero.
• The hydrocarbons present influence the knocking properties of gasoline
which vary according to the series:
straight chain paraffin > branched chain paraffin > olefin >
cycloparaffin > aromatics.
• The fuel which has same knocking tendency with the mixture having
80% iso-octance has octane number 80.
Octane number

48. C C
C
C
C
C C
H H
H H
H
H
H
H
H
H H
H
H
H
H
H
n-heptane
C
CH3
CH3
CH3
CH2
CH3
CH CH3
Isooctane

49. Improvement of anti-knock characteristics of a fuel
• The octane number of many otherwise poor fuels can be raised
by the addition of tetra ethyl lead (C2H5)4Pb or TEL and diethyl
telluride (C2H5)2Te. In motor spirit (Motor fuel) about 0.5ml
and in aviation fuel 1.0 - 1.5ml of TEL is added per litre of
petrol.
• TEL is converted into a cloud of finely divided lead and lead
oxide particles in the cylinder and these particles react with any
hydrocarbon peroxide molecules formed, thereby slowing down
the chain oxidation reaction and thus decreasing the chances of
any early detonation.
• However deposit of lead oxide is harmful to the engine life. In
order to help the simultaneous elimination of lead oxide formed
from the engine, a small amount of ethylene dibromide (or
ethylene dichloride) is also added to petrol.
• The added ethylene dibromide removes lead oxide as volatile
lead bromide along with the exhaust gases. The presence of
sulphur compounds in petrol reduces the effectiveness of the
TEL. TEL is more effective on saturated hydrocarbons than on
unsaturated ones.

50. Other additives
• Oxidation inhibitors - 2,4 - ditertiary butyl - 4 - methyl phenol.
• Rust inhibitors - Organic compounds of phosphorus or
antimony.
• Ignition control additives - tricresyl phosphate which suppresses
pre-ignition of the fuel due to glowing deposits on spark plug or
a hot spot on the cylinder wall.

51. Diesel Engine Fuels
Characteristics of an ideal diesel oil
•It should have low spontaneous ignition
temperature.
•It should have very little sulphur, aromatic and ash
content.
•The ignition lag should be as short as possible.

52. Knocking in Diesel Engines
• In a diesel engine, the fuel is exploded not by a spark, but by the
application of heat and pressure. In the cycle of operations of a diesel
engine, air is first drawn into the cylinder and compressed.
• Towards the end of the compression stroke, the fuel (diesel oil) is
injected as a finely-divided spray into air in the cylinder heated to about
500C by compression.
• The oil absorbs the heat from the air and if it attains its ignition
temperature the oil ignites spontaneously. The pressure of the gases is
further increased by the heat accompanying the ignition of the oil.
• The piston is pushed by the expanding gases and this constitutes the
power stroke.
• Fuel feed and ignition continue during this down stroke. The fuel
injection stops at the exhaust stroke.

53. • Diesel engine fuels consist of longer chain hydrocarbons than internal combustion
engine fuels.
• The main characteristic of diesel engine fuel is that it should easily ignite below
compression temperature.
• There should be as short an induction lag as possible. This means that it is essential
that the hydrocarbon molecules in a diesel fuel should be as far as possible the
straight-chain ones with a minimum admixture of aromatic and side-chain
hydrocarbon molecules.
• The suitability of a diesel fuel is determined by its cetane value, which is the
percentage of hexadecane in a mixture of hexadecane and 2-methyl naphthalene,
which has the same ignition characteristics as the diesel fuel sample, under the same
set of conditions.
• The cetane number of a diesel fuel can be raised by the addition of small quantity of
certain "pre-ignition dopes" like alkyl nitrites such as ethyl nitrite, iso-amyl nitrite,
acetone peroxide.

54. CH3
H H
H
H H
H
H C C
C H
14
2-Methyl naphthalene (Cetane No. = 0)
n-Hexadecane (Cetane No. = 100)

55. Ignition quality decreases among
hydrocarbons is as follows
• n-alkanes > naphthalenes > alkenes > branches
alkanes > aromatics
• Cetane number decreases
• Ignition quality decreases
• Ignition delay increases

56. CORROSION CONTROL

57. Spontaneity of Corrosion
❖Metal has natural tendency to go to Thermodynamically stable
state
❖Metals (thermodynamically unstable) are usually extracted from
ores (thermodynamically stable) through the application of a
considerable amount of energy
Corrosion (oxidation)
Metallurgy (reduction)
❖The energy required to convert ore to metallic state is returned
when the metal corrodes to form the original compound.
❖The tendency of metal to release this energy by corrosion, is
reflected by the relative positions of pure metals in the
electrochemical series.
Metal
(T.D.Unstable)
Ore (metallic compd)
T.D.Stable
Energy

58. 4Fe + 3O2 + 6H2O → 4Fe(OH)3
Rust formation in iron

59. Protective coatings
oProtective coating provide a physical barrier between
the metal and the environment.
oThey not only give corrosion protection but also add to
the decorative value of the article.
oCoatings are broadly divided as:
a) Inorganic coatings : metallic and chemical conversion
coatings
b) Organic coatings : paints, varnishes
59

64. 64
Physical Vapour Deposition
o This is a process of depositing some material by atom by atom or
molecule by molecule or ion by ion.
1. This process is widely used to produce decorative coatings on plastic parts
those are resembling shiny metal.
2. Many automobile parts are plastic with a PVD coating of aluminium.
3. A lacquer coating is applied over the decorative coating to provide corrosion
protection.
4. This process is also used to apply relatively thick (1mm) coatings of heat
resistant materials on jet engine parts, A special alloy of chromium, aluminium
and yttrium is used for this type of coating.
Applications:

65. PVD: – 1. Thermal Evaporation Method
Al and Au are quite usable in thermal evaporation system with heated
crucible, for they can be melt in crucible and generate enough quantity of
vapours.
However, W and Ti are not suitable for their low vapour pressure.
Typical deposition rates in industry is around 0.5 µm/min (~8 nm/s, for Al)
65

66. PVD: 2 – Sputtering Method
Sputtering :
A popular method for adhering thin films onto a substrate.
Sputtering is done by bombarding a target material with a charged gas (typically
argon) which releases atoms in the target that coats the nearby substrate.
It all takes place inside a magnetron vacuum chamber under low pressure.
High technology coatings such as ceramics, metal alloys and organic and inorganic
compounds are applied by sputtering.
The substance to be coated is connected to a high voltage DC power supply.
When the vacuum chamber has been pumped down, a controlled amount of argon or
another gas is introduced to establish a pressure of about 10-2 to 10-3 torr.
On energizing current supply, plasma is established between the work and the material to
be coated.
The sputtering gas is often an inert gas such as argon. For efficient momentum transfer,
the atomic weight of the sputtering gas should be close to the atomic weight of the target,
so for sputtering light elements neon is preferable, while for heavy elements krypton or
xenon are used. Reactive gases can also be used to sputter compounds.
6

67. The gas atoms are ionized and they
bombard the material to be coated.
The energy of imposing ions cause
atoms of the target material to be
sputtered off and they are transported
through the plasma to form a coating.
•The target atom or molecular will be
hit to substrate surface and condense
as a film.
Direct current sputtering is used when
the target is electrically conductive.
Radio-frequency sputtering, which uses
a RF power supply is used when the
target is a non conductor such as
polymer.
Figure : PVD by sputtering process
7
PVD: 2 – Sputtering Method
Sputtering is a process whereby particles are ejected from a solid target material due to
bombardment of the target by energetic particles.
Sputtering is done either using DC voltage (DC sputtering) for metals or using AC voltage
(RF sputtering) for dielectric materials and polymers.

68. Applications of Sputtering method:
o This method is used in VLSI fabrication
(Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by
combining hundreds of thousands of transistors or devices into a single chip)
o Sputtering is used extensively in the semiconductor industry to deposit thin films of
various materials in integrated circuit processing.
o Thin antireflection coatings (MgF2 and Fluoropolymers; mesoporous silica materials;
titanium nitride and niobium nitride) on glass for optical applications are also
deposited by sputtering.
o An important advantage of sputter deposition is that even materials with very high
melting points are easily sputtered while evaporation of these materials in a resistance
evaporator or Knudsen cell is problematic or impossible. Sputter deposited films have
a composition close to that of the source material.
8
PVD: 2 – Sputtering Method

69. Sputtering offers the following advantages over other PVD methods used in
VLSI fabrication:
1) Sputtering can be achieved from large-size targets, simplifying the deposition
of thins with unifrom thickness over large wafers;
2) Film thickness is easily controlled by fixing the operating parameters and
simply adjusting the deposition time;
3) Control of the alloy composition, as well as other film properties such as
step coverage and grain structure, is more easily accomplished than by
deposition through evaporation;
4) Sputter-cleaning of the substrate in vacuum prior to film deposition can be
done;
Sputtering, however, has the following disadvantages too:
1) High capital expenses are required;
2) The rates of deposition of some materials (such as SiO2) are relatively low;
3) Some materials such as organic solids are easily degraded by ionic
bombardment;
4) Sputtering has a greater tendency to introduce impurities in the substrate
than deposition by evaporation because the former operates under a lesser
vacuum range than the latter.

70. 70
Computational chemistry is the use of computers to
solve the equations of a theory or model for the
properties of a chemical system.

71. 71
⮚Simulation is becoming a third pillar of science, along
with theory and experiment.
⮚Using theory, we develop models: simplified
representations of physical systems.
⮚We test the accuracy of these models in experiment,
and use simulation to help refine this feedback loop.
⮚Anything that can be measured can be simulated,
including properties related to energetics, structures,
and spectra of chemical systems.

72. The Nobel Prize in Chemistry 1998
John A. Pople Walter Kohn
The Nobel Prize in Chemistry 1998 was divided equally between
Walter Kohn "for his development of the density-functional
theory" and John A. Pople "for his development of
computational methods in quantum chemistry".
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2013 Nobel Prize In Chemistry
"for the development of multiscale models for complex chemical systems”
• Martin Karplus, Université de Strasbourg, France, and Harvard University,
Cambridge, MA, USA
• Michael Levitt, Stanford University, Los Angeles, CA, USA
• Arieh Warshel, University of Southern California (USC), CA, USA

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Using computational chemistry software you can in particular perform:
o Electronic structure predictions
o Geometry optimizations or energy minimizations
o Conformational analysis and potential energy surfaces (PES)
o Frequency calculations
o Finding transition structures and reaction paths
o Molecular docking: Protein – Protein and Protein-Ligand interactions
o Electron and charge distributions calculations
o Calculations of rate constants for chemical reactions: Chemical
kinetics
o Thermochemistry - heat of reactions, energy of activation, etc.
o Calculation of many other molecular and physical and chemical
properties
o Orbital energy levels and electron density
o Electronic excitation energy

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• Structure of a molecule in general is how atoms are arranged
in the molecule in the three dimensional space.
• Potential energy surface (PES) is a plot of energy with respect
to various internal coordinates of a molecule such as bond
length, bond angle etc.

76. Potential energy for nuclear motion in a diatomic molecule
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77. Potential Energy Surfaces and Mechanism
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Conformational Analysis
⮚Identification of all possible minimum energy structures
(conformations) of a molecule is called conformational analysis.
⮚Conformational analysis is an important step in computational
chemistry studies as it is necessary to reduce time spent in the
screening of compounds for properties and activities.

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⮚The identified conformation could be the local minimum,
global minimum, or any transition state between the
minima.
⮚Out of the several local minima on the potential energy
surface of a molecule, the lowest energy conformation is
known as the global minimum.
Global
minimum
Local minima

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Global minimum
Local minimum
Local minimum

81. Ethane Conformations
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