IFT\P2008-084

Fabrication of HAPL Sized R/F foam Shells

(IFE Target Fabrication Update)

Presented by Reny Paguio1

D. Goodin1, J. Hund, D. Jason, A. Nikroo1, K. Saito1, K. Quan2

1General Atomics, Inertial Fusion Technology, San Diego, CA

2UC San Diego, San Diego, CA

HAPL Meeting, Madison WI, October 22-23, 2008

IFT\P2008-084

Specifications for the HAPL Shell

•Shells need to be uniform− Wall Uniformity (Non Concentricity=NC)− NC Spec. 1-3% (Offset ~10.8m)

•Sphericity-Out of Round (OOR)− OOR Spec is >1% of the shells radius (~23 m)

•Gas tight pinhole free overcoat**J. Hund, et al., HAPL Meeting, Target Fabrication, Talk 3

Foam layer: 0.18 mm thickness Divinyl Benzene (DVB) or Resorcinol-Formaldehyde (RF)

DT Vapor

Foam + DT

Thin (300-1200 Å)High Z coating

~ 2.3 mm rad

10 m CH Overcoat

DTHAPL Target

Coating roughness of 50 nm (RMS)

IFT\P2008-084

Since the last HAPL Meeting we have:

• Improved the Wall uniformity & sphericity of the R/F Shells – NC of 35% to 10%– Out of Round (OOR) spec improved from 75% to 100%

• Improved the surface of the foam shell– Improved the shell’s surface by 50% • (60 nm to 30 nm RMS)

• Improved the solvent exchange process using Soxhlet Extractor– Faster (More efficient)

IFT\P2008-084

• Used in ICF experiments on OMEGA– 2 Step polycondensation reaction*– Foam Is C, H, O– Small Pore size (<0.10 m) -Transparent • Use GDP directly as overcoat• Has been shown to hold gas for HAPL size shells (15 m)

• New Direction from target designers has allowed the possibility to have O in the foam matrix– In the Past: Foam could only be C & H– Has opened the door to use materials such as R/F

R/F was looked as a possible foam, because overcoated DVB shells were not gas retentive

* Pekala, R.W.; et al. J. Mat. Sci., 1989, 24, 3221-3227.

IFT\P2008-084

R/F foam shells are fabricated using a triple orifice droplet generator

3 Steps1. Droplet generation2. Curing3. Solvent exchange &

drying

300-400 Cured shells

Supercritical CO2 dry –

Resulting in a dry R/F foam

shell

Post Cure Process

IFT\P2008-084

HAPL sized R/F shells have been successfully fabricated

• Changed needle & collection tube size

• Optimized the curing step in rotobeaker

• More precise control of density matching between the R/F sol and the outter oil sol− Lead to a high yield of intact shells (~90%)

4500 m

HAPL & OMEGA Sized R/F Shell

OMEGA size

IFT\P2008-084

Initial results show that the wall uniformity of HAPL R/F foam shells needs to be improved

•Looked at ways to improve the wall uniformity−Polymer Additives

Used in the OMEGA R/F shells to improve wall uniformity*

Styrene Butadiene Styrene (SBS) Co-block polymerRaises the Interfacial Tension (IFT) & Viscosity

* Paguio R.R et al., Fusion Sci & Technol, 2006,49,4

0%

25%

50%

75%

100%

0 5 10 15 20 25 30 35% NC

PercentileDVB Shells

R/F shells

NC SpecIFT=20 dynes/cm

IFT=1 dynes/cm

IFT\P2008-084

Modifying the O2 solution changed the viscosity of the oil and the Interfacial Tension (IFT) of the emulsion system

• Surfactant reduces the IFT– Needed to prevent agglomeration of the shells

• Poly Butadiene (PBD) was investigated as a possible SBS replacement– More affect on viscosity than IFT– No dramatic improvement on NC

• Combination of the two leads to a higher IFT & viscosity

0 4 8 12 16

STD(NoSurfactant)

STD

PBD

SBS

SBS/PBD

IFT (dynes/cm)0 10 20 30 40

STD(NoSurfactant)

STD

PBD

SBS

SBS/PBD

Viscosity (Cps.)

IFT\P2008-084

SBS addition has been shown to improve the wall uniformity of HAPL sized R/F foam shells

•Improved from <5% (No Additive) to ~20% with Additive•Wall uniformity not as good as DVB (75%)•Optimizing the SBS:PBD Ratio•Optimize the density matching of the O1 and R/F sol•Investigation of other possible polymer additives

0%

25%

50%

75%

100%

0 5 10 15 20 25 30 35% NC

Percentile DVB ShellsR/F shellsRF-SBSRF-SBS-PBD

NC SPEC

IFT=1dynes/cm

IFT=4dynes/cmIFT=1

dynes/cm

IFT=8dynes/cm20

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The SBS/PBD additive blend to the O2 has also improved the OOR of the shells

• Yield of shells that meet the OOR spec went from 75% to 100%

• IFT increased from 4 to 8 dynes/cm when going to the SBS/PBD blend

0%

25%

50%

75%

100%

0 10 20 30OOR ( )

Percentage SBSSBS/PBD

IFT=4dynes/cm

IFT=8 dynes/cm

( m)

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Acid addition to the Post-Cure removes large isolated defects from the foam’s surface

• Added 0.33M of Acetic Acid to the post cure (PC) process. – Foam structure unchanged

• Surface roughness of the bare foam improved from 60 nm to 30 nm RMS – Wyko Interferometer 50X-400m scan

• Need to optimize the acid concentration to improve the bare foam surface

No Acid Added to PC Acid Added to PC

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Soxhlet Extractor reduced the time needed for solvent exchanging from 2-3 weeks to 3 days

Using the Soxhlet Extractor is a faster more efficient way to solvent exchange

larger shells

Soxhlet Extractor

Traditionally: Once a day exchanged

into IPA

After 2-3 weeks of solvent exchange

Oil still in IPA.

After 3 days in Soxhlet

No oil in IPA.

This has also been extended into OMEGA & NIF R/F foam shell

fabrication

oil

oil

Soxhlet Extractor

Allows a continuous exchange of IPA for the

shells

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Soxhlet Extraction limits surface defects when shells are dried

Dry shell with

Soxhlet

No big dents

Dry shell no Soxhlet

Big dents

•Soxhlet extractor removes nearly all of the oil: No big dents•No Soxhlet : Left over oil which can lead to big dents

IFT\P2008-084

Successfully made improvements on the HAPL sized R/F shells & the fabrication process

•Improved the wall uniformity using polymer additives• Avg. NC went from 35% to 10%

•Improved the OOR • 100% of the shells meet half the HAPL Spec

•Improved the bare surface of the foam with acid addition to PC process• Reduced the surface roughness by 50%

•Made the solvent exchange process more efficient using a Soxhlet Extractor• Shortened Solvent exchange time from 2-3 week to 3 days

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Investigated other organic solvent replacements for the tetrachloroethylene (TCE)

• Looked at two additives– Bromobenzene (IFT went to 9 dynes/cm)– Tri Chlorobenzene (IFT went to 12 dynes/cm)

• Yield of intact shells decreased (~20%)– Emulsion unstable– New to investigate other surfactants

• NC was similar to the SBS/PBD addition with TCE

• Bare foam roughness went up to 120 nm RMS– Due to shell break up during curing process– This is with the acid addition in the PC