[PPT] - Electrospun nanofiber materials for high power target applications PowerPoint Presentation

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Electrospun nanofiber materials for high power target applications

21-22nd Sept., 2017 J-PARC, Tokai, Japan

Sujit Bidhar

FERMILAB-SLIDES-17-017-AD This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office

f Science, Office of High Energy

Physics.

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Outline

Background & Objectives
Electrospinning process
In-house electrospinning unit
Candidate target materials manufacturing
Single nanofiber mechanical characterization
Future plans and summary

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Background- Target material

Demand of multi-MW high performance particle production

targets

– LBNE 2.3MW proton beam, 1.6X1014 p/pulse

Structural integrity over time

– High temperature, thermal stresses, dynamic stresses

Withstand radiation damage

– Embrittlement, radiation corrosion, swelling

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Current Target

ANU/NOvA, 700KWGraphite blocks

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Proton beam Beam spot size<<target dimension Solid continuum high local temperature gradient, thermal stress wave

Water cooling Water cooling

Can it perform satisfactory at higher energy??

Compressive strength 345MPa Tensile strength : 60~140 MPa Endurance Limit : 20 MPa

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HPT Issues -Stress wave

7/12/2018 5 40mm Radial temperature distribution at end of pulse

750kW Spill width: 4.2 µsec Gaussian beam Sigma 4.2mm

Prone to fatigue failure (Mode II) Reduce amplitude, decrease wave speed

T2K window

σ ∆

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Fatigue life

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t T E ∆ ∆ = ∆ . . α ρ σ

Initial stress wave amplitude

ρ E c =

Number stress cycles ~Elastic wave speed Possible by microstructure design temperature gradient

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Sinuous Target -Candidate Microstructure

Design Microstructure to mitigate issues

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Electrospun nano-fiberSinuous target

Electrospun Zirconia nanofiber*

*Journal of Alloys and Compounds 649 (2015) 788e792

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Advantages & Limitations

Advantages:

Local damage of single fiber won’t affect target structural

integrity as a whole

Reduced thermal stress wave

– Reduced temp. gradient – High surface area & gaps  effective local heat removal by passing He gas

Customize material properties by mixing different materials

Limitations:

Widely used for polymer nanofibers
Limited research in ceramics/metal nanofiber
Low density (long target)

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Objective

Fabricate ceramic/metal, composite material nano-fiber with high strength, high density and alloying elements to reduce radiation damage.

Set up in-house electrospun unit
Fabricate ceramic composites nanofiber
Micro-mechanic study single fiber mechanical characterization

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Basic Electrospinning Set up

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10-30 cm 5-10 cm

Process carried out at room temp. and atm. pressure Collector

Fixed type
Rotating drum type

10-30 kV DC

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Electrospinning Principle

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Electrostatic repulsion> surface tension

Droplet is stretched
Jet elongated by

whipping action

Flat needle Taylor cone Slow acceleration Rapid acceleration Ohmic flow Convective flow +/- kV Collector plate Transition liquid to solid Flow direction Solid Liquid

Bending Instability

Jet Initiation stages

solution

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Ceramics Nanofiber Fabrication

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Inorganic precursor(inorganic compound+solvent) Polymer solution(polymer+solvent) Salt additives (surfactants) Solution for electrospinningpolymer-ceramic nanofiber Calcination (Heat treatment)

Vaporize polymer
Promotes crystal growth
Bonding

Representative heating profile

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Lab Set-up

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Electrospinning unit Furnace

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Electrospinning Set-up

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High voltage power supply Syringe pump Collector plate Needle

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Electrospinning Jet

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Stable jet Needle

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Nanofiber Mat – Random Orientation

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Nanofiber

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Nanofiber Mat- Aligned

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C-Channel Reflector plate Needle

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Focused Deposition

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Needle Reflector plate

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Improvised Compact Power Supply

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120 Watt, 120VAC in 4 Watt, 6~12VDC in, +/-20kV DC out

60kV DC out

5kV DC out
Much safe to use (120W4W!)
Mobile compact unit
Can be run on 9 or 12 V battery
20kV

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Candidate electrospun nanofiber-Raw materials

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Polymer solution

PVP+Ethanol+Aceton

Metal/Ceramic

Alumina  Aluminum 2,4-pentadionate+Aceton
Zirconia Zirconium Carbonate +Acetic Acid
WO3  Ammonium meta-tungstate + D.I. Water
TiO2

 Titanium Isopropoxide Carbon-nanotube Composite

CNT-Alumina
CNT-Zirconium

Done Proposed

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Alumina Nanofiber

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As spun After heat treatment

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EDS Mapping Alumina Nanofiber

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As spun After heat treatment Theoretical Al wt% in Al2O3 is 53% Achieved in actual 25%

200 400 600 800 1000 1200 1400 1600 500 1000 1500 2000 2500 3000 3500

Temp, C Time, min

Alumina heating profile

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Titania(TiO2) Nanofiber

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As spun After heat treatment

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EDS Mapping TiO2

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As spun After heat treatment Theoretical Ti wt% in TiO2 is 60% Achieved in actual 51%

100 200 300 400 500 600 700 500 1000 1500 2000 2500

Temp. , C

Time, min

Titanium Heating profile

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Tungsten Oxide (WO3) Nanofiber

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As spun After heat treatment

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Zirconia Nanofiber

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As spun After heat treatment 1.2 gm 0.5 gm

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EDS Mapping- Zirconia Nanofiber

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As spun After heat treatment Theoretical Zr wt% in ZrO2 is 74% Achieved in actual 62%

200 400 600 800 1000 1200 1400 500 1000 1500 2000

Temp., C Time, minute

Zr-heating profile

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Zirconia Nanofiber- Yttrium doped

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Improve thermal shock resistance by Yttrium doping Improve radiation resistance

More grain boundaries blocks dislocation, defect movements,

defect recombination*.

YSZ strong resistance to amorphization

*Sci Rep. 2015; 5: 7746.

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CNT-Ceramics Nanofiber Composites

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SWCNT 1-3 nm Excellent mechanical properties E : 1~5 Tpa Tensile strength : 15-50 Gpa Elongation % : 16% High thermal conductivity (axial), insulator lateral

MIT-research*

Protects Aluminum metal against radiation damage~70 DPA

1-D transport network for He to escape
Reduce embrittlement by 5-10 times.

1~2 Vol% CNT

Bulk not nanofiber!!

*http://news.mit.edu/2016/carbon-nanotubes-improve-metal-longevity-under-radiation-0302

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CNT-Zirconia/Alumina Proposed Nanofiber

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Ceramic(Zirconia) will have high Z value
CNT will enhance mechanical strength, provide protection

against radiation damage

SWNT Surfactant Sonification deionized water Add Alumina +ve charged alumina Nano-particle Add polymer Solution Electrospin Calcination/ Heat treatment CNT filled ceramic nanofiber

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Nano-mechanical mapping – Atomic Force Microscopy

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Tungsten – Polymer nanofiber

Elastic Modulus map

Separation, µm

Tip Deflection in contact mode

Peak Force, nN

340MPa Nanofibers fixed to substrate using double sided tape Soft substrate compared to nanofiber

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Nano-mechanical mapping – Atomic Force Microscopy

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Elastic Modulus map 225GPa Nanofiber solution casted on harder smooth mica substrate Average Elastic modulus ~ 100GPa

200GPa 150GPa 100GPa

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Mechanical characterization

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Macro testing electrospun nanofiber mat

Fracture strength single nanofiber

1. 3 point Bending test on TEM Grid

Set up

Solution cast
Fix to TEM grid using Ion beam (Pt tape)
Press using diamond AFM tip

2. Nano-indentation using AFM tip

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Propose target shape

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Alumina nano-fiber block No major modification to current target holder Customizable Cheaper and scalable

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Physical Properties Characterization (In progress)

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Raman spectroscopy:
disorderness, bond information
Electron energy loss spectrometry (EELS):
sp2/sp3 ratio, atomic composition (low Z)
Wide Angle X-ray Diffraction (WAXD):
lattice parameters, orientation, isotropy.
Thermal analysis:
DSC and DMA :melting and glass transition temperature

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Summary and Future Work

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Installation of a low cost electrospinning set up completed.
Success in fabricating metallic and ceramic nanofiber.
Physical properties of single nanofiber evaluation in progress.

Future work

Expose nanofiber mat to HiRadMat test
Single fiber radiation damage study
Improve ductility of ceramic nanofiber
Fabricate ceramics-CNT composite.
Heat treatment profile
Physical properties before and after radiation.
Damage modeling

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Thank You for Your Attention!!

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Parameters

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Molecular weight of polymer
Solution properties (Viscosity, conductivity, surface tension)
Concentration, electrical potential, flow rate
Distance between needle and collector
Needle gage
Ambient temperature, humidity, air flow

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Problems

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Beading Ribbons Porous globe Cylindrical fiber Troubleshoot

Increase flow rate
Increase polymer concentration or solvent with high evaporation
Salt additives (Surfactant)
Adjust distance between needle and collector
Porosityevaporative characteristic of solvent

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Mass Production-Needleless (In progress)

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HV supply

Solution Rotating screw Rotating drum collector Ground

ve kV

Array of micro-tip needles(10µm )

Corona discharge –ve ion

+ve kV

Charged nanofiber prevents thicker mat formation
Opposite charged ion neutralize nanofiber and promote thicker mat