2015 NETS

Ying Song1, Joshua Wojcik1, Tim C. Holgate1, Glenn Gaines1, Rob Utz1, Mihaela Nicolau1, Russell Bennett1, Tom Hammel1, Steven Keyser1

Jong-Ai Paik2, Steve Jones2, and Thierry Caillat2

1 Teledyne Energy Systems, Inc. (TESI), Hunt Valley, MD 21031

2 Jet Propulsion Laboratory, Pasadena, CA 91109

2015 NETS Albuquerque, NM

February, 2015

Manufacturability Demonstration And Assessment

Of Aerogel Applicability As An Insulation Replacement For eMMRTG Flight Module

2015 NETS

2

Teledyne Advanced Power Technologies

Thermoelectric systems for space and terrestrial applications

MMRTG Curiosity Rover 100 W

15 W

Radioisotope TE systems

Liquid Fueled TE systems

Electrochemical energy storage Specialty Batteries

FC Replacement for Batteries

Stirling converter systems for terrestrial combustion heated applications

Stirling Converters (Persistent Power)

Fuel cells for space and terrestrial applications

Fuel Cell Flight Systems

Fuel Cell Stacks

Compact Passive FC Systems

Submersible Manned Vehicles

Unmanned Navy Vehicles

2

2015 NETS

Technology Transfer Program

3

Enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG) Concept o Preserve all MMRTG envelope, volume, interfaces and mounting points o Offer significant increases in power –

• >25% at beginning of life (BOL) • >50% at end of 14-year mission (EOM) • Multi-mission capability (vacuum and Mars atmosphere) preserved • 5-year development time

SKD Thermoelectric (TE) Couples

o Substitution of current MMRTG PbTe/TAGS couples with skutterudite (SKD) couples

o Sizing of couples to raise hot junction temperature and increase efficiency

Aerogel Insulation o Technology transfer and further development o Determine suitability for use as TE module insulation

2015 NETS

Silica Aerogel Application for eMMRTG

4

Exceptionally porous material presenting unique properties o High specific surface area o Light weight

Significant sublimation suppression o ~5x10-7 g/cm2.hr rate at 600oC achieved from JPL’s sublimation 4000-hour life

tests

Excellent insulation material o Extremely low thermal conductivity o Comparable mechanical integrity o Thermal stability at higher temperatures

Ambiently dried aerogels eliminate the super-critical drying process

2015 NETS

Silica Aerogel Development at TESI

5

Worked with JPL to transfer aerogel insulation technology o Develop the capability to produce aerogel insulation at TESI o Measure the properties deemed important for the insulation surrounding

thermoelectrics in an RTG o Determine if replacing some, or all, of the current thermoelectric module insulation

with aerogel is feasible

Successfully adapted JPL’s advanced technology to synthesize silica aerogels

Further developed and optimized the manufacturing process for fabricating ambiently dried silica-based aerogels

Characterizing the aerogel materials with the goal of further improvements

2015 NETS

Synthesis of Ambiently Dried Aerogel

6

Lawrence Berkeley Lab

Ambient drying instead of supercritical drying process More practical and operationally feasible Easily replace the existing commercial insulations in the module In situ production using the cast-in ability without exposing T/E

materials to supercritical drying conditions

2015 NETS

Manufacturability Demonstration

7

Baseline Aerogel – Radial Shrinkage Rate Reduced from 70.0% to 8.0%

High Aspect Ratio Aerogel Samples Large Size of Aerogel Sample with Dummy Couples Encapsulated for

Simulation of Module insulation

Demonstrated production capability for multi-couple module bulk insulation

Uniform aerogel with crack-free bulk structure

Modified aerogels increase the mechanical robustness with further shrinkage rate reduction to nearly zero

Effect of the couple leg geometry on aerogel formation and uniformity was examined Chemical compatibility of couple materials to aerogel gel precursor was investigated

2015 NETS

Concept Module Design for Aerogel

8

Direct casting-in technology eliminates additional machining work of fragile insulations

Proper mold design may minimize the effect of skin layer in the module and simplify curing and assembling

Initial trials of 1/3 size of module insulation Ready for scale-up to the full size of module

insulation

Current module insulation

Concept mold designed for module size aerogel insulation

2015 NETS

Combining commercial and aerogel materials together may provide low thermal conductivity with sublimation suppression demonstrated by aerogel Initial trials of simply pouring the gel precursor into the holes in the commercial insulation was successful Additional experiments will be performed

o Investigate particle size and distribution of powders in the gel precursor o Investigate pore size and distribution of the dry aerogel o Evaluate the reinforcement materials and optimize mixing process o Determine if a thin coating can be applied on the surface of the commercial module

insulation that is in contact with aerogel precursor as barrier

Hybrid Insulation in Module

9

Hybrid insulation combines commercial module insulation with aerogel surrounding each SKD element

If aerogel is not suitable as a bulk insulation, hybrid option provides a path forward

Commercial Insulation SKD Elements

Aerogel

2015 NETS

Assessment of Aerogel Applicability

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Evaluation Criteria Established Appearance Uniform structure with no significant defects such as cracks or voids Thermal conductivity No higher than existing insulation under the operating conditions as module bulk insulation Thermal stability Structural integrity with minimal shrinkage and weight loss after exposure to the operating temperature Mechanical Strength

o Compressive strength comparable to the existing insulation o Ability to stand up to dynamic loads

Material compatibility Minimal or no reaction between the aerogel precursor and the couple components

Capability for Characterization at TESI Laser flash system for thermal diffusivity and modulated DSC for heat capacity TGA/DSC for thermal stability and phase transition study High temperature vacuum oven and hot press for thermal stability test SEM/EDS and FT-IR for microstructure and composition analysis BET for surface area and pore size distribution and particle analyzer for particle size and

distribution Couple/module life testers and vibration test instrument Collaboration with other labs for additional analysis

2015 NETS

Aerogel Basic Physical Properties

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Sample Density, mg/cm3 Pure Silica Aerogel 180-200 Modified Aerogel 300-340

Commercial Insulation 1 320-340 Commercial Insulation 2 345-365

Aerogel Density and Comparison to Commercials Hydrophobicity

Microstructure of Aerogels FT-IR Spectra of Aerogels

2015 NETS

Thermal Stability

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Aerogel had little shrinkage (<1%) and a weight loss of 8.5% as temperature increased from RT to 600oC under vacuum and remained stable in dimension and a weight loss of 2.1% at 600oC in 50 hours, comparable to the commercial insulation material

There were no cracks or other defects observed during testing No obvious change in microstructure observed under microscope

2015 NETS

Mechanical Strength

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Mechanical strength is another important property to be addressed for characterizing aerogel materials as alternatives to the commercial insulations Compression Test

o Test methodology for compression testing of the aerogel samples was developed

o High aspect ratio cylindrical samples with flat, parallel faces perpendicular to the long axis were prepared for testing

o Commercial insulations were tested for comparison o Initial test results revealed a relatively lower compressive strength

and elastic modulus o Additional samples were prepared with the reinforcement

materials for higher compressive strength. Being tested Vibration Test

o Small scale Sinusoidal vibration sweep to identify resonance frequency and run sinusoidal vibration test at resonance frequencies o Large scale Test load profile – MMRTG vibration environment

Further modification work for improving mechanical robustness

2015 NETS

Thermal Conductivity

14

Sample preparation, test conditions and methodology successfully developed and optimized for measurement of thermal diffusivity and specific heat capacity of aerogel samples using laser flash system and DSC at TESI

Testing conditions: room temperature to 700oC in argon Initial results showed aerogel had a relatively higher thermal conductivity than the commercial insulation

but is still promising as replacement insulation in the module Further work to modify the structure and composition for lowering thermal conductivity to improve

performance if used as bulk insulation

2015 NETS

Summary and Future Plan

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Comprehensive development of synthesis, structure, thermal properties and characterization of silica aerogel has been done.

Manufacturing capability has been successfully demonstrated. TESI can produced ambiently dried aerogels consistently to meet module size

insulation requirements Process details were refined and test criteria were established for

characterizing and modifying aerogel materials o Crack-free and nearly zero shrinkage rate after ambient drying process o Excellent thermal stability at the module operating temperature o Superhydrophobic surface even after exposure to 600oC

Current and future work o Hybrid insulation o Reinforced aerogel o Finalization of mold design o Scale-up to module size o Dynamic load test

2015 NETS

Contact Information

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Teledyne Energy Systems, Inc.

Ying Song

Ying.song@teledyne.com

10707 Gilroy Road Hunt Valley, MD 21031

410-771-8600 Phone

410-771-8620 Fax www.teledynees.com