Characterization of Inorganic Materials:
Thermal and Thermodynamic Methods
270153 VO, 2 lecture hours, 3 ECTS credits
Klaus Richter
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Common Basics for High Temperature Techniques
Dynamic Methods
Selected Isothermal Methods for Combination
Measurement of Thermodynamic Properties
Estimation and Tabulation of Thermodynamic
Properties
Thermodynamic Modeling
Common Basics
Temperature Scales
0. Law of Thermodynamics:
temperature ⇔ thermal equilibrium
Primary Temperature Scale:
Kelvin scale uses the triple point of water
T = 273.16 K
Secondary Temperature Scale:
ITS90 – International Temperature Scale of 1990
The temperature is defined by a number of secondary fixed
temperatures.
Important for the calibration of all kind of thermometers!
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Common Basics
Fixed Points of the ITS 90
ITS Methods:
• 3.0 - 24.5561K:
He – gas thermometer
• 13.8033 - 1234.93K:
Pt – resistance
thermometer
• more than 1234.93K:
Monochromatic pyrometer
Important Calibration Substances!
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Common Basics
Temperature measurement: Thermocouples
Thermoelectric effect:
“Seebeck effect”
Material A
Type
T max / °C
Fe-CuNi (Typ J)
1150
Ni-CrNi (Typ K)
1350
Pt-PtPh (Typ S)
1650
Pt-EL18 (Typ B)
1800
W-WRe (Typ C)
2300
ΔE
T1
Material B
A
T2
Thermoelectric Voltage ΔE
dependent on T1, T2 and the
“Seebeck coefficient” α
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Tm
B
T0
Cu
Thermocouple Measurement
Arrangement
Common Basics
Temperature Measurement: Resistance Thermometer
Metals:
Pt, Ni, Cu, …..
e.g. “Pt100”
Semiconductors:
Fe3O4, MgAl2O4, …..
R = R0 + Rth (T )
R = R∞ ⋅ e
B
(T + Θ )
PTC Materials
NTC Materials
The temperature-dependence
of R is almost linear
Strong non-linear temperature
dependence of R
ρ ~ 10-5-10-6 Ωcm
ρ ~ 10-2-109 Ωcm
Attention: Ceramic PTC Materials (BaTiO3) have no linear behavior!
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Common Basics
Temperature Measurement: Pyrometry
Black Body Radiation
∞
1. Stefan – Boltzmann:
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I
(
T
,
λ
)
d
λ
=
σ
T
∫
0
2. Wien:
3. Planck:
λMax .T = const .
I (T , λ ) = c1λ
−5
1
e c 2 / λT − 1
Measurement correction by surface
emissivity or use of hollow body radiation
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Common Basics
IR Pyrometer
Monochromatic Pyrometer
Two color Pyrometer
Furnace Construction
Resistance Heating
(Induction Heating)
(Fast Pulse Heating)
Important Construction Principles
for Commercial Instruments:
• Axial Symmetric Tube Furnace
• T-constant zone
• Small heat capacity
• Radiation shielding
• Cooling unit (air or water)
• Separate T-measurement for
controller
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Materials for Heating elements:
• Kanthal Steel (up to 1350°C)
• SiC (up to 1550°C)
• MoSi2 (up to 1700°C)
• Mo wire (up to 1800°C)
• Graphite, W (more than 1800°C)
Materials for Isolation and
Shielding:
• Al2O3 ceramics
• refractory metals
• Graphite
Common Basics
Vacuum and inert gas atmosphere
Measurements in air at high temperatures ⇒ Reaction with oxygen
⇒ Use vacuum or inert gas atmosphere
> 1 mbar
10-3-1 mbar
10-7-10-3 mbar
< 10-7 mbar
Low vacuum
Medium vacuum
High vacuum
Ultra high
Sliding vane pump
Turbo-molecular pump
Oil diffusion pump
(fore-vacuum required)
Inert gas: Ar (N2, He):
e.g. Ar 5.0 (= 99.999 % Ar)
• Subsequent cleaning systems (e.g. Oxisorb®)
• Flushing
• Dynamic flow or static atmosphere
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Common Basics
Pumping Systems
Turbo molecular pump
Sliding vane pump
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Common Basics
Crucible Materials
The selection of a proper crucible material is essential for every hightemperature measurement!
Criteria:
thermal stability ♦ reactivity with the sample ♦ thermal conductivity
♦ permeability for gases ♦ thermal shock resistance
High temperature Materials:
• quartz glass (silica)
• sintered Al2O3 (alumina)
• sintered MgO (magnesia)
• BN
• graphite
• Ta
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Common Basics
~ 1250 °C
~ 1900 °C
~ 2300 °C
~ 1600 °C
~ 3000 °C
~ 2500 °C