the increasing importance of the thermal …... the increasing importance of the thermal...
TRANSCRIPT
www.morganadvancedmaterials.com
The Increasing Importance of the Thermal Conductivity of Ceramics
Ceramics Expo 2017
Richard Clark - Senior Technical [email protected]
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