madhvesh fullerenes

7/31/2019 madhvesh fullerenes

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Fullerenes

Fullerene cages are about 7-15 angstroms in diameter ( 1A = 10-10m). In atomic terms, their sizes are enormous.

But fullerenes are still small compared to many organic molecules.

Chemically, they are quite stable; breaking the balls requires

temperatures of over 10000 C.

At much lower temperatures (a few hundred oC) fullerenes will "sublime

which means vapour will form directly from the solid.

Fullerene-20 (C20) is the smallest number of carbon atoms containing

fullerene. Giant fullerene with at least 600 Carbon atoms have beendiscovered.

What are Fullerenes?Fullerenes are a group of polymorphic formof pure carbon compounds whose discretemolecule consists of hollow spherical clusterof a large number of carbon atoms.

Characteristics of Fullerenes:Each molecule is composed of groups of carbon atoms that are bonded to oneanother to form both hexagon (6-membered ring) and pentagon (5-membered ring) geometrical configurations. But no two pentagons share acommon side.


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Properties of Fullerene- C60 The material composed of 60 carbon atoms is known as

Buckminsterfullerene (C60) as its shape resembles the geodesic domes

designed by R. Buckminster Fuller.

Pure C60 consists of 60 carbon atoms arranged as 12 pentagons and 20

hexagons.

It is a yellow powder, which appears brown to black with increasing filmthickness.

In toluene (1g/L), turns to magenta colored solution.

When exposed to strong ultraviolet light, they polymerize, forming bonds

between adjacent balls. Its crystalline form is cubic.

As a pure solid, it is electrically insulating.

On reaction with good inorganic electron donors (alkali metals), electrical

conductivity is increased several times. Stoichiometry of the alkali fulleridesis M3C60.

On reaction with organic electron donor like tetrakis (dimethyl amino)

ethylene (TDAE), ferromagnetic material is formed.


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Fullerene C60

The rugby-ball shapedC70has 12 pentagons and25 hexagons

Gives red color withdichlorobenzene

Pentagon (C5)

Hexagon (C6)

Fullerene C70

The soccer-ball shaped C60has 12 pentagons and 20hexagons

Gives pink color with

toluene

Comparison between C70 and C60

Applications: (i) preparation of superconductors, (ii)electronic devices, (iii) micro-electronic devices, (iv) preparation offerromagnetic materials, and (v) as charge carriers in batteries.


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Preparation of fullerene by DC-Arc Method

It is basically a DC arc chamber reactorchamber with(a) Reactor chamber,(b) Electrode assembly (anode &cathode),(c) cooling system for the reactor

chamber,(d) cooling system for the electrodeassembly(e) vacuum system,(f) electrical and electronics system.

The operating conditions are:(i) diameter of the electrodes: 6 mm;(ii) discharge voltage: 25 V(iii) current on the electrodes: 60 A(iv) cooling water flow of the discharge

chamber: 300L/h(v) cooling oil flow of the electrodes:60L/h;(vi) control gas pressure(helium): 100to 200 mmHg.


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Composition and separation of the soot from the DC Arc method The soot contains (a) Carbon clusters mixture = 25-30%; and b) C60 and C70

fullerenes = 1.2-2.5%.

Fullerenes can be separated from the carbon mixture by Soxhlet extraction withtoluene followed by separation in a ultrasonicator bath.

The obtained C60+C70 mixture is further separated by column chromatography usingneutral alumina as the stationary phase and hexane as the mobile phase..

Set-up Assembly:

The main part is the extra-pure spectroscopic grade graphite rods of 6 mm

dia and 150 mm length fixed in copper holders. The facing sides of both the graphite rods are parallel.

The arc chamber has a cooling coil attached to remove the heat produced.

The power to the generator is a high current, low voltage power supply.

Working method: The chamber is evacuated to 10-3 torr using a vacuum pump.

The pump is disconnected and the chamber is now filled with 99.99% pureHelium gas to a pressure of 100 to 200 mm Hg.

An arc is strike between two graphite electrodes kept at a distance of 2 mmapart by maintaining a voltage of 25 V.

At the end of the reaction, the chamber is cooled down and the soot iscollected from the inner walls.


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Purification of Fullerenes by Chromatography

The Soot (C60+C70+impurities) extracted withToluene using the Soxhlet method is deep Redin color.

o The column is first filled with carbon granules.

o Toluene is filled into the column until the level of

toluene equals to the height of carbon granules.

o Then the solution containing C60& C70 in toluene is

added into the column through a dropper flask.

o The initial solution coming out of the column is

collected separately in a conical flask and thrown into

waste.

o Color starts to change to magenta after 20 to 25minutes the fraction is collected as C60.

o After 20 to 30 minutes the solution with magenta color

stops coming out.

o At this stage, dichlorobenzene is added to the column.

o A red color separation will be seen for C70 fraction willappear.

o This fraction C70 is collected separately in a flask.

o From both the flasks, the solvent is evaporated to

obtain pure C60 and C70 fractions separately.

o The characterization of purified C60 and C70 are carried

out using XRD, 13C-NMR, Mass spectra and FTIR.

Alumina

Carbon granules

Crude soot solution(in organic solvent)

C70 BandC60 Band

impure band-1

impure band-2

1. pure C60 (magenta) in Toluene

2. pure C70 (Red) in C6H4Cl2


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Applications of fullerene C60

When doped with alkali metals, the solid C60 becomes a superconductor (A3C60 where A = Alkali metal).

Resistance of a substance tends to be zero at the criticaltemperature (Tc). Eg.: for K3C60 the Tc is 18 K.

C60 - Non conducting

K3C60 - Insulating at RTK3C60 - Super conductingat below Tc ~18 K

K3C60 exhibit super conductivity due to thepartial filling of conduction band. It retainsthe basic FCC structure of C

60

and latticeconstants to accommodate the alkali ions.

K3C60 has only a single stable superconductingphase with a Tc of 19 K. RbC60 hasmaximum Tc of 28 K.

Resistance

Temp. (K)

Superconductivity in C60


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Superconductivity of Doped C60When K3C60 is cooled to well below room temperature, its resistivity begins to drop sharplyat about 19 K indicating the onset of superconductivity.

As larger Alkali Metal Cations are incorporated into the C60 lattice,, the superconductingtemperature (Tc) also increases. For example, compared to K3C60 (19 K), Rb3C60 exhibit Tc of28 K. This rise may be related to an increase in the density of states at the Fermi level withincreasing lattice constant. Hence, higher Tc could be obtained by incorporating larger alkalimetal cations into the C60 lattice.


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HIV Protease Inhibition by C60o Derivatives of C60 are currently being

investigated as potential inhibitors ofthe protease enzyme, which is specificto the HIV (virus) generation.

o Active site of the HIV enzyme roughlydescribed as an open-ended cylinderstructure, which is lined almostexclusively by large hydrophobic aminoacids.

o The C60 has approximately the same

radius as the cylinder of the active siteof HIVP.o Since C60 and its derivatives are

primarily hydrophobic, a stronghydrophobic vander Waals interactionbetween the non-polar active-site

surface and the C60 surface which canable to block the active side and hence,reduce the HIV (virus) generation.

o There is also an opportunity to increasethe binding energy by the introductionof specific electrostatic interactions in

the C60.

Hydrophobic sites

Cylind

erical

C60 (as inhibitor)

HIV protease site

Diagram for the C60 HIV

protease inhibition.


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LUBRICANTS

Friction:

Resistance observed between two

moving or sliding surfaces

creating wear and tear.

Lubricant:

Any substance introduced between

two moving or sliding surfaceswith a view to reduce the frictional

resistance between them is know

as a lubricant.

Lubrication:

The process of introducing

lubricant between moving/sliding

parts is known as lubrication


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Functions of Lubricanto To reduce frictional resistance between surfaces and

reduce deformation, wear and tear between moving/sliding

surfaces.

o To reduce loss of energy in the form of heat (Coolant).o To reduce waste of energy i.e., to increase efficiency of

machines.

o To reduce irregular expansion of metals.

o To reduce welding of the two surfaces.o To reduce or avoid rough relative motions of moving /

sliding parts.

o To reduce running and maintenance cost of the machine.o To reduce the leakage of gases under high pressure like a

seal or Teflon.


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Mechanisms of Lubrication1. Fluid-film (or) Thick-film (or)

Hydrodynamic lubrication

2. Boundary lubrication (or)Thin-film lubrication

3. Extreme pressure lubrication


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1. Fluid Film/Thick-Film/HydrodynamicLubrication (~ 1000 )

Characteristics:o The surfaces are separated by a thick-film (at least

1000 thick) and hence there is no direct surface to

surface contact.

o No welding of junctions.

o Since thick film lubricant covers/fills the irregularitieson the both surfaces, there is no direct contact

between material surfaces and so the wear is reduced.


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In Fluid Film Lubrication,the Lubricating properties depend on:

o Viscosity of lubricant (Lubricant should beof low viscosity).

o Thickness of lubricant layer.

o Relative velocity and area of moving/slidingsurfaces.


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Example: Shaft running (Journal bearings)

Lubricant oil covers the irregularities of the shaft as well as the

bearing surfaces.


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o Examples where fluid film lubrication is used are :

i) Sophisticated instruments

ii) Light machines like watches, guns, sewing machines etc.

o Examples for fluid-film lubricants are:

Hydrocarbon oils are considered to be satisfactory lubricants.

To maintain viscosity throughout lifecycles long chain

polymers are used as blenders with normal hydrocarbons

oils.

Small amount of unsaturated hydrocarbons present in

hydrocarbon oils produced from petroleum fractions,

which causes oxidation and produce gummy like products.

Hence, anti-oxidant like aminophenol are used in journal

bearings with lubricant


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Mechanism of fluid film lubrication


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2. Boundary Lubrication/Thin-filmLubrication

Characteristics of thin film lubricationare:

o High viscosity-index.o Resistance to heat and oxidation.

o Good Oiliness.

o Low pour-point.


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Mechanism of Boundary Lubrication/Thin-film

Lubrication

This Lubrication takes place due to:

o Adsorption of lubricating oils to both surfaces by

physical/chemical means.

o The adsorbed layers on the both metal surfaces

carry the applied load.

o Co-efficient of friction, f = 0.05 - 0.15 and distance

between surfaces is to be the order of the distance

of the asperities.


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For boundary lubrication, the lubricantmolecule should have:

(i) Long hydrocarbon chain with polar groups.

(ii) Polar groups promote spreading and orientationover the metallic surfaces at high pressure.

(iii) Lateral attraction between the chains.

(iv) Active groups or atoms, which can formchemical linkages with metal or other surfaces.


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Examples of Boundary lubrication Vegetable and animal oils (glycerides of higher

fatty acids & their soaps).

o These oils either physically adsorbed to metal surfaces or

react chemically at the metal surfaces.

o Although these oils posses greater adhesion property, yet

they tend to breakdown at high temperatures. Hence, fatty

acids are added to improve the oiliness.

Graphite and Molybdenum disulphide alone or oilsuspension may be used because:

o They have Low internal friction

o They can bear/withstand compression

o They are thermally stable


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Mechanism of Boundary Lubrication


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3. Extreme-pressure LubricationWhen moving/sliding surfaces are under very high pressure

and speed, a high local temperature is attained. In such conditions, liquid lubricants fail to stick and may

decompose and even vaporize.

To avoid this, special additives are added to mineral oils. Theseare called extreme-pressure additives.

Mechanism The extreme-pressure additives form on metal surfaces

more durable films, capable of withstanding very high loadsand high temperatures.

Examples:

Organic compounds containing chlorine, sulphur and phosphorus.

o These compounds react with metallic surfaces, at prevailing hightemperatures, to form metallic chlorides, sulphide or phosphides.

o These metallic compounds possess high melting points.


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CLASSIFICATION OF LUBRICANT

Based on Physical state, lubricantsare classified as:

a) Lubricating oils or liquid lubricantsb) Semi solid lubricants or greases

c) Solid lubricants


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1. Lubricating oils or liquid lubricants

Purpose:o Provide a continuous fluid film.

o Provide a cooling between the surfaces.

o Act as a sealing agent.o Act as corrosion preventing materials.

Properties of liquid lubricants:

o Low pressure i.e., high boiling point.o Adequate viscosity for particular service conditions.

o Low freezing point.

o Heat stability.

o Stability to decomposition at the operating terms.

o High oxidation resistance.

o Non-corrosive properties.


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Types of Liquid Lubricants

a) Animal and Vegetable oils:- Usable under very high temperature and heavy load.

Disadvantages of its usages are

1. Costly2. Undergo oxidation easily in contact with air and forms

gummy and acidic products, and get thickened.3. Tendency to hydrolyze in contact with moist-air or aqueous

medium.So, they are used as blending agents with other mineral oils.

b) Mineral oils or petroleum oils:

- They are obtained by distillation of petroleum.o Length of hydrocarbon chain varies between 12 to 50 carbon

atoms.o Shorter- chain oils have lower viscosity than the longer- chain

hydrocarbons.


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Liquid lubricants are most widely used lubricants

because they are1. Cheap

2. Available in abundance

3. Quite stable under service conditions.

o But they havepoor oiliness charactercompared toanimal and vegetable oils.

o So, high molecular weight compounds like oleicacid, stearic acid are used to over come this problem.

c) Blended oils:

o No single oil serves as the most satisfactory lubricantfor many of the modern machines. Hence, additivesare used to improve the properties. These blendedoils give desired lubricating property required for a

machinery.


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Additives used are:a) Oiliness- carriers:

o Coconut oil, caster oil, and palmitic, stearic and oleic acids.

b) Extreme-Pressure additives such as:

o Fatty esters or acids which form oxide film with metal surface.

o Organic materials containing sulphur.

o Organic chlorine compounds.

o Organic phosphorous compounds.

o Some times lead (Pb) compounds could be used as high pressure

lubricants.

c) Pour-point depressing additives:

o Phenol, condensation product of chlorinated wax with

naphthalene.


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d) Viscosity index improvers : hexanol

e) Thickeners : Polystyrene or polystyers

f)Antioxidants or inhibitors : Aromatic phenolic or amino compounds

g) Corrosion preventers : Phosphorous or Antimony organic

compounds

h)Abrasion inhibitors : tricresyl phosphate

i)Antifoaming agents : glycols and glycerol

j) Emulsifiers : sodium salts of sulphonic acid

k) Deposit inhibitors : detergents such as salts of phenol and

carboxylic acids


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2. Semi-Solid Lubricants or Greases

o Semi solid consisting of a soap dispersed throughout

a liquid lubricating oil.

- May be Petroleum oil or synthetic oil with a specific additive.Preparation:

Saponification of fat (such as tallow or fatty acid) with alkali

(like lime, caustic soda etc.,)

Addition to hot lubricating oil under agitation

o To increase the heat resistance of grease, inorganic solid

thickening agents ( like finely divided clay, bentonite, colloidal

silica, carbon block etc.,) are added.

o Have higher shear or frictional resistance than oils and hence

support much heavier load at lower speeds.


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Applications of Greases:

o When oil cannot remain in place due to high load, low

speed, intermittent operation, sudden jerks etc.

o Work at high temperature

o When external contamination may create problem

o When dripping or spurting of oil is undesirable

Types of greases:o Calcium based greases or cup-greases

o Soda-based greases

o Lithium-based greases

o Axle- greases lime with resin and fatty acids

o Graphite greases

o Soap stone


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3. SOLID LUBRICANTSSolid lubricants are used when:

o Other lubricants can not be usedo Contamination undesirable

o Too high temperature or load are involved

o Combustible lubricants not acceptable

Examples of solid lubricants used are:

a) Graphite (or)

b) Molybdenum disulphide


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Examples of Solid Lubricants

1.Graphite:

oVery soapy in touch

o Non inflammable

o Not oxidized in air below 375C

o Oil + graphite oildag

o Water + Graphite aquadag

- Emulsifying agent (tannin)

o Grease + graphite graphite

-greases


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Examples of Solid Lubricants

2. Molybdenum disulphide:o Low coefficient of friction

o Stable in air up to 400 C

Soapstone, talc or mica are also used as solid lubricants.


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Properties of Lubricants1. Viscosity:

The property of a liquid or fluid by virtue of which it offersresistance to its own flow .

- Viscosity should not be too low or too high.(viscosity is inversely proportional to temperature)

2. Flash - Points and Fire - Points :

Flash Point:The lowest temperature at which the oil lubricant gives offenough vapour that ignites for a moment, when a tinyflame is brought near it.

Fire Point:

The lowest temperature at which the vapour of the oil burncontinuously for at least five seconds, when a tiny flame is

brought near it.


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3. Oiliness:

A measure of its capacity to stick on to the surfaces ofmachine parts under conditions of heavy pressure or load.

o For high pressure - high oiliness oil should be used.

o Important for extreme Pressure lubrication

4. Cloud and Pour points:

When an oil is cooled slowly, the temperature at which it

becomes cloudy or hazy in appearance, is calledits CLOUD POINT.

The temperature at which the oil ceases to flow or pour, is

called its POUR POINT.

5. Volatility:

o Good lubricant should have low volatility.

o It is measured by vaporimeter.


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6. Emulsification:o The property of oils to get intimately mixed with water forming

an emulsion.

o Emulsions have a tendency to collect dirt, girt, foreign materialetc., causing abrasion and wearing out of the lubricating partsof the machinery.

o A good lubricating oil should form an emulsion with waterwhich breaks off quickly.

7. Carbon residue:Normally lubricants consist of high % of carbon containingcompounds.

o Lubricants decompose due to raise in temp. and deposit

carbon creating problems to :a) IC engines and b) Air compressors.

o A good lubricant should deposit least amount of the carbon .


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8. Corrosion stability: Corrosion Test:

o A polished copper strip is placed inside a lubricating oil for

a specified time and temperature and then checked for any

tarnishing .

o To prevent or retard corrosion effect of lubricating oils,

additives such as Phosphorous, Arsenic, Antimony,

Chromium, Bismuth or Lead are added.

9. Decomposition stability:o Lubricating oils must be stable to decomposition at the

operating temperatures by :

a. Oxidation: To prevent it anti oxidant or inhibitor are used.

b. Hydrolysis: Moisture in oils causes hydrolysis of esters

c. Pyrolysis : At high temperature


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10. Aniline point: (A.P.)o The minimum equilibrium solution temp. for equal volumes of

aniline and oil sample.

o A good lubricating oil should have higher aniline points (A.P)o Higher A.P means higher % of paraffinic hydrocarbons and

hence lower % of aromatic HC.

(Aromatic HC dissolves natural rubbers and few synthetic

ones)

11. Precipitation Number:

o The percentage of asphalt present in oil.

o Precipitation Number is used to differentiate the different

classes of lubricants.


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12. Specific Gravity:A.P.I. ( American petroleum Institute) degree

A.P.I degree = 141.5/sp. gr. at temp(60F) -131.5

where 141.5 modulus of the A.P.I scale.

13. Ash Point:

o For used oil it is important to get an idea as to how much

abrasion and wear it may cause

14. Saponification number:

o Number of milligrams of KOH required to saponify1g of oil.


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15. Mechanical stability:

o At very high pressures of operation, the stability of a

lubricant is judged by four balls extreme pressurelubricant test.

16. Neutralization Number:

o Is a scale to determine the amount of acidic or basicconstituents of an oil.

o Acid Number: Amount of KOH required in milligrams

to neutralize the fatty acids in 1g of oil.o Good lubricating oil acid number value < 0.1


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C. PropellantsHigh oxygen containing fuels ormixture of fuels + oxidiser

Controlled combustion

Evolution of Huge volume of hot gases(temp= 3000oC & pressure:300kg/cm2)

Gases escape through a jet or nozzleat supersonic velocity.


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Characteristics of a good propellanto Have high specific impulse

o Deposit low molecular weight products( H2, CO2, CO, N2)

o Burn at a slow and steady rate

o Have low ignition delay ( in milliseconds)o Have high density

o Be Stable over a wide range of temperatures

o Be Safe to handle and store at ordinary conditions

i.e., under shock, heat or impact

o Be readily ignitable at predictable burning rate

o Be Non corrosive and non hygroscopic

o Leave no solid residue after ignition

o Not release any toxic products on burning

o Give high temperature on combustion


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Types : Mono propellantsFuel + oxidizer are in the same molecule or in the

same solution.

Properties:o Safe to store

o Burning should be smooth

Examples : H2O2,nitro methane,ethylene oxide,

hydrazine,propyl nitratea mixture of 21.4% MeOH and 78.4%H2O2 solution

Bi ll t


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Bipropellants

Fuel and oxidiser are separate compounds andinjected separately to the combustion chamber from

separate compartments

Fuels: Liquid hydrogen, hydrazine, ethyl alcohol,aniline, kerosene.

Ethanol mixed with 25% of water

Oxidizers: Liquid oxygen, ozone, H2O2, fuming HNO3,liquid fluorine

o Liquid O2 is non toxic but need high pressure insulatedcontainer for storing.

o Liquid O3 is also very good but forms toxic products andcan explode at high concentration

o Liquid fluorine is volatile, toxic, corrosive, very reactive,

difficult to store and handle.

C ti f t f lid d


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Comparative features of solid and

liquid propellantsSolid propellants Liquid propellants

Low specific impulse High

Easily handling and storing Not easy

Simple engine Delicate engine design

More economical Less economical

Not versatile Versatile

Engine calibration difficult Easy

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