www.morganadvancedmaterials.com

The Increasing Importance of the Thermal Conductivity of Ceramics

Ceramics Expo 2017

Richard Clark - Senior Technical Specialistrichard.clark@morganplc.com

Contents

• Overview of Morgan Advanced Materials

• Thermal Conductivity

• Definitions and measurement

• Thermal conductivity of traditional ceramics

• New materials widening the thermal conductivity range

• Applications and market prospects

2“The Increasing Importance of the Thermal Conductivity of Ceramics” Ceramics Expo 2017

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Morgan Advanced Materials

Founded in England in 1856Ticker on LSE: MGAM2016 revenue: GBP989.2 (2015 GBP911.8 million)6 Global Business Units

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Global Business Units

Thermal Ceramics

Molten Metal Systems

Electrical Carbon

Seals and Bearings

Technical Ceramics

Composites and Defense Systems

“The Increasing Importance of the Thermal Conductivity of Ceramics” Ceramics Expo 2017

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Definitions and measurement of thermal conductivity

Thermal conductivity, a transport property frequently referred to as “λ”, is a measurement of the ability of a material to conduct heat, considered to equate to the time rate of heat flow under steady conditions through unit area per unit temperature gradient in the direction perpendicular to the area.

With many assumptions, including “λ” being constant, conductive heat flow is governed by Fourier’s law: Q= - λA(dT/dx) where “Q” is heat flow, “λ” is thermal conductivity, “A” is area, “dT” is temperature difference and “dx” is thickness.

Measurement methods

Steady-state (typically λ < 5 Wm-1K-1 and temperature <650°C except guarded-comparative-longitudinal)

Heat-flow meter

Easy, accurate, quick –primarily for insulation

ASTM C518-15

Guarded heat-flow meter

Slightly higher temperature measurement range

ASTM E1530-11(2016)

Guarded hot-plate

Wider temperature range, absolute method

ASTM C177-13

Guarded-comparative-longitudinal heat flow

λ to 200 Wm-1K-1 and temperature up to 1000°C

ASTM E1225-13

Dynamic (transient)

Hot wire

λ to 20 Wm-1K-1 and temperature to 2000+°C

ASTM C1113 / C1113M-09 (2013)

Laser flash (diffusivity)

λ to 2000+ Wm-1K-1 and temperature to 2000+°C

ASTM E1461-13

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Wide range of thermal conductivity in traditional ceramics

Air

Fused silicaZirconia

Silicon nitride

AluminaSapphire

Aluminum nitrideCVD silicon carbide

Beryllium oxideCopper

Diamond

0.001

0.01

0.1

1

10

100

1000

10000

Ther

mal

con

duct

ivity

(W

/m/K

)

• Many factors control the thermal conductivity of ceramics:

• Grain size and boundaries;• Bonding;• Purity;• Type and structure of impurities;• Porosity

• Main mechanism for heat transfer in ceramics is atomic/lattice vibration

• “Bounded” by fused silica at 1.4 Wm-1K-1

and diamond at 2200 Wm-1K-1 for “traditional” ceramics

AlN with low lattice oxygen % can have λapproaching that of copper

94% alumina λ is about ½ that of 99.5% alumina

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Recent areas of interest in thermal conductivity (high)

• Cubic Boron Arsenide: newly determined to have thermal conductivity similar to that of diamond

• As an electrical insulator this would make it suitable for passive cooling in microelectronics

• Graphene: • For unstrained graphene λ can be up to

5,450 Wm-1K-1 (theoretical, experimentally shown to 5,300 Wm-1K-1)

• For strained graphene λ diverges based on sample size (length in direction of heat flow) so appears to violate many beliefs of λ being an intrinsic material property (and Fourier’s law)

Air

Fused silicaZirconia

Silicon nitride

AluminaSapphire

Aluminum nitrideCVD silicon carbide

Beryllium oxideCopper

Diamond

0.001

0.01

0.1

1

10

100

1000

10000

Ther

mal

con

duct

ivity

(W

/m/K

)

• 2D h-BN: for electronics substrates and packaging4/25/2017

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Recent areas of interest in thermal conductivity (low)

• Silica aerogel λ = 0.0134 Wm-1K-1

(compared to air at 0.026 Wm-1K-1 at room temperature)

• Graphene aerogel λ = 0.053 Wm-1K-1 (at room temperature and as much as an order of magnitude lower at low temperatures(*))

• (Silica based) microporous materials with bulk thermal conductivity ½ that of calm air at operating temperatures for insulation

* Xie et al, Carbon Volume 98, March 2016, Pages 381–390

Air

Fused silicaZirconia

Silicon nitride

AluminaSapphire

Aluminum nitrideCVD silicon carbide

Beryllium oxideCopper

Diamond

0.001

0.01

0.1

1

10

100

1000

10000

Ther

mal

con

duct

ivity

(W

/m/K

)

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Types of high temperature insulation fibers

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High Temperature

Insulation

Amorphous

Alkaline Earth Silicate (AES)

Melt-spun

CaO, MgO, SiO2, ZrO2

Superwool® Plus, Superwool® HT

Aluminosilicate(ASW / RCF)

Melt-spun / blown

Al2O3, SiO2, (ZrO2)

Kaowool®

Crystalline

Polycrystalline (PCW)

Sol-gel

Al2O3

Alphawool®

ASW/RCF invented 1942PCW invented 1969AES invented 1986(Microporous invented 1958)

Key Advantages of Superwool®over RCF:• Low bio-persistence• Low shrinkage up to

classification temperature• Low thermal conductivity

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Thermal conductivity comparison for fiber materials

Thermal conductivity comparison of WDS microporous insulation products vs. other types of insulating products

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Applications where thermal conductivity is key

• “High” Thermal Conductivity• Microelectronics packaging

(passive cooling) (e.g. BeO, AlN, diamond)

• Lasers/photonics (e.g. BeO and AlN) (also YAG in solid-state lasers)

• Aero/defense (e.g. diborides)

• “Low” thermal conductivity• Kiln walls (insulation e.g.

RCF, AES)• Aerospace (insulation e.g.

silica aerogel)• Gas turbines (Thermal

Barrier Coatings e.g. 7YSZ)

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Drivers increasing the need for ceramics –higher temperatures are behind many material changes

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Application Drivers

Electronics / semiconductor Higher temperature / increased need for precision

Automotive Lower vehicle weight (ICE and xEV) / higher engine temperature

Energy / Power Higher temperature / need for improved efficiency

Industrial Higher temperature / higher wear environment

CPI Higher temperature / higher pressure / high corrosion

Medical High corrosion / innovation (new inventions)

Military / Defense Higher temperature / lower weight

Aerospace Higher temperature / lower weight

Largest market segment is electronics. Oxide ceramics are about 60% of the total market and alumina is more than half of that. Market size strongly dependent on definition!

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“The Increasing Importance of the Thermal Conductivity of Ceramics” Ceramics Expo 2017

www.morganadvancedmaterials.com

Questions?