Material Characterization -Lecture 22

7/24/2019 Material Characterization -Lecture 22

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Material Characterization MethodsMaterial Characterization Methods

Lecture 22Lecture 22

Carbon Nanotubes



Impact of Nanotechnology



Carbon Nanotube Carbon nanotubes (CNTs) are allotropes of

carbon having diameter of few nanometers.



Carbon nanotube structure Carbon nanotubes are

formed by a layer ofhexagonally-arrangedcarbon atoms rolled into acylinder

Electrons are localised

internally, and some canmove along the length of thetube by ballistic transport.

Carbon nanotube length can

be a million times greaterthan its width. So it can beseen like nearly onedimensional.



Electronic structurec-c bond length 1.43 A.

sp2 bonding like graphite.

Nanotubes naturally align themselves into"ropes" held together by Van der Waalsforces.

CNT : metallic

semiconducting

•The white circles- metallic CNT•The black circles -semiconductor CNT



Types of CNTs

Single-walled

nanotubes (SWNT) Diameter-1~5 nm.

Multi-walled

nanotubes (MWNT) Diameter- 10~80

nm.



Single-walled carbon nanotubes (SWCNT).

SWCNT are made by rolling up a singlegraphite sheet (called graphene ) to a

narrow but long tube closed at both sidesby fullerene-like end caps.

3D model of single-wall carbon nanotube

(SWNT)



Types of SWCNT

Depending on the way the graphene sheet is rolled up



Multi-walled carbon nanotubes (MWCNT)

MWCNT are nanotubes with more thanone graphene cylinder nested one into

another having distance of 3.39 Åbetween two layers .

MWNTs are more chemical resistant thanSWNTs.



3D Model of MWCNT



Synthesis of Carbon Nanotubes

Laser Ablation

Chemical Vapor Deposition



Laser Ablation Method



Process of Laser Ablation

A pulsed or continuous laser is used to vaporize agraphite target placed in an oven at 1200ºC.

The oven is filled with an argon gas which is usedto keep the pressure at 500 Torr.

A very hot vapor plume forms, which then expandsand cools rapidly.

As the vaporized species cools, small carbonmolecules and atoms condense to from largerclusters.



The laser ablation method yields around 70%and produces primarily single-walled carbonnanotubes.

The SWCNTs formed in this case are bundledtogether by Van der Waals forces.

controllable diameter determined by the reactiontemperature.

it is more expensive than chemical vapordeposition.



Chemical Vapor Deposition Method

A typical CVD set-up consists of a targetsubstrate held in a quartz tube placedinside of a furnace.

Typical Parameters:

Pressure: 1atm Temperature: 600 °C - 1000°C

Substrate: Si, mica, quartz, or alumina. Carbon supply: CH4, C2H2 or CO gas Common catalysts: Ni, Fe, or Co.



Process of CVD1. Gas enters chamber at

room temperature .2.

Gas is heated as itapproaches thesubstrate.

3. Gases then react with

the substrate orundergo chemicalreaction in the“Reaction Zone” beforereacting with thesubstrate forming thedeposited material.

4. Gaseous products arethen removed from thereaction chamber.



MWCNT

600-800 °

C

2

H

2

→

2C H

2

SWCNT

900-1000 °

2CO → C CO

2



Mechanism for CNT growth1) Deposit catalyst particles on a substrate.

2) Catalyst dissociates carbon rich gases

(CO, CH4, C2H2) and produces carbonatoms.

3) C atoms dissolve into the catalyst particle.4) Some C atoms precipitate on the surface

when supersaturated.

5) The precipitated C atoms nucleate intocarbon nanotubes.



Advantages of CVD technology

SWNTs / MWNTs

Increased Length andPurity

Relatively cheap

Large-scale Productivity

Lower Temperatures



Unique Properties Of Carbon Nanotubes

Carbon nanotubes are 1000x thinner than anaverage human hair and 200x stronger than

steel.

The first synthetic material to have greater

strength than spider silk.

Excellent conductors of electricity and heat.

Have huge potential for product development.



Properties of CNTs

Mechanical Strongest known material

200 times stronger than steel

MaterialMaterial Young Young’’ss

Modulus (Modulus (EE))

Tensile StrengthTensile Strength

AluminumAluminum 7272 GPaGPa 676676 MPaMPa

SteelSteel 200200 GPaGPa 1,9651,965 MPaMPa

CarbonCarbon NanotubeNanotube 1,2501,250 GPaGPa 300,000300,000 MPaMPa



Thermal 40 times more conductive than aluminum

Thermal conductivity is governed through free electronsinteractions and phonons. Carbon nanotubes have verylow scattering at the boundaries and thus high thermalconductivity.

MaterialMaterial ThermalThermal

ConductivityConductivity

AluminumAluminum 140 W /140 W / mm··KKCopper Copper 400 W /400 W / mm··KK

CarbonCarbon NanotubeNanotube 6,0006,000 W /W / mm··KK



Electrical

Metallic CNTs are more conductive than Cu and Ag Semiconducting to metallic

One-Dimensional Transport

Due to their nanoscale dimensions, electrontransport in carbon nanotubes take placethrough quantum effects and only propagatealong the axis of the tube. Because of this

special transport property, carbon nanotubesare referred to as “one-dimensional”.



Application of Carbon Nanotubes

Energy storage

Field emission devices Transistors AFM tips Nanotweezers Composite materials Nano structures Potential for extremely strong light weight

cables/space elevator Physical memory



Nanotubes In Efficient Solar Cells• Scientists havedeveloped the ‘blackestblack’ colour using carbonnanotubes

• The carbon nanotubesare arranged like bladesof grass in a lawn- they absorb nearly all

light• Use of carbon nanotubes

in solar cells vastlyimprove their efficiency.



Material Characterization MethodsMaterial Characterization Methods

Injection and compression moulding technique to prepare

nanocomposites used for biomedical applications



Ramakrishna et al. (2001),Composite Science andTechnology, 61, 1189



Major cause for primary surgery –

taken from various hip registers

Osteoarthritis, also known as degenerative joint disease, is a group of diseases andmechanical abnormalities entailing degradation of joints



Distribution of Age - THR/TKR

S.M. Kurtz. The UHMWPE Lexicon, School of Biomedical EngineeringScience and Health Systems, Drexel University, and Exponent, Inc.,



Growth rate of THR/TKR

Total hip arthroplasty (THA)



Main reason for revision surgery – taken

from various hip registers



Number of operations and revisions

1997----170,280 THR

1998----173,501 THR----144,133 primary arthroplasties (5%increase over 1994)

No. of revisions --- 28,794 in 1997

--- 29,368 in 1998, representing 17% of total hip replacements and a 7% increase from

the revisions reported in 1994.

4% of the patients were under the age of 40, 6% of the revision patients were under 40, higher risk of revision for

the younger patients



Motivation

Reduction of the number of revised surgeries in total hipreplacement;

Improve mechanical and tribological properties of the UHMWPEby adding CNTs;

Minimize the number of wear particles generation from theacetabular cups;

Development of appropriate techniques and methodologies toproduce and characterize the nanocomposites;

Testing an acetabular cup prototype in a hip joint simulator



CNT were chemically treated with concentrated nitric acid and sulphuricacid mixture which provides many required functional groups on thesurface of the nanotubes in addition to their purification

The chemically treated CNTs were added with deionized water andsonicated for 1 hour to have a homogeneous dispersion of CNTs in water.

Nanofluid is mixed with the required quantity of HDPE pellets. It is heatedand magnetically stirred to have an uniform coating of CNT on HDPE

CNT coated HDPE pellets were used as raw material in an injectionmoulding machine.

HDPE were melted and mixed with CNT at the plasticized unit of theinjection moulding machine and injected into a required specimen.

The test samples were obtained for different weight fraction of the CNT inthe composites.

Sample preparationSample preparation--HDPE/CNTHDPE/CNT



Injection moulding machine



Moulds

Acetabular cup mould

Flat/tensile specimenmould



Moulded samples



Mechanical properties of CNT-HDPE

nano-composites

32.77842.4723.821069109.8622.231.3380.44

22.34776.2718.191020.4106.3817.561.2870.33

19.18756.2413.34978.5106.6712.131.2280.22

17.15743.359.86948.5105.516.741.1690.11

0.00634.530.00863.4105.800.001.0950.00

% increment ofToughness

Toughness(Joules)

%incrementof ε

Strain(ε) atfracture(%)

Ultimatestress(MPa)

% increment ofE

Young’smodulus(GPa)(E)

(%)VolumefractionCNTconcentration



Theoretical prediction of volumetric wear

Wang´s model

Ratner-Lancaster’s correlation

Toughness of the materials is the most important property whichaffects the volumetric wear rate of composites.

12/3 −−∝∆

uuV ε σ

1)( −∝∆

uuV ε σ



Schematic diagram of experimental rig Schematic diagram of experimental rig

SampleCeramic ball

Sample holder Sliding

direction



Comparison of wear volume of HDPE/CNT

0

1

2

3

4

5

90N load

0.500.250

W e a r v o

l u m e ( m m

3 )

Volume fraction of CNT(%)



The chemically treated CNT were added with required quantity ofUHMWPE powder and this mixture was ball milled for optimumperiod of time to have a homogeneous mixing of them.

This mixture was used as raw material in compression mouldingmachine. Optimized processing conditions were followed toprepare compressed sheets of UHMWPE-CNT nanocomposites.

Samples for tensile and tribological studies were cut from thecompressed sheets

The test samples were obtained for different weight fraction of theCNT in the composites.

Sample preparationSample preparation--UHMWPE/CNTUHMWPE/CNT



SEM images of UHMWPE/CNT powder mixturesSEM images of UHMWPE/CNT powder mixtures

with different milling time with different milling time(a) 15min (b) 30min

(c) 45min (d) 60min



Sample preparation-compression moulding technique

Pressure-Temperature-Time cycle



Mould- Acetabular cups



Small punch test



Optical images of the test sample

UHMWPE/CNT-water

SEM i f UHMWPE/CNT i



SEM images of UHMWPE/CNT composites

S i f UHMWP /CNT



Stress-strain curve of UHMWPE/CNT

composites

S t r e s s

( M P a )

Strain (%)



Microparticles from UHMWPE polymer (a & c) CNT/UHMWPE nanocomposites (b & d),a & b – irregular particle shape and c & d - Fibrils shape

(a) (b)

(c) (d)

Material Characterization -Lecture 22

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