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1T. Markus RWTH-Aachen Jan 07
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Investigations of Degradation Phenomena in High Temperature
Discharge Lamps using Thermo chemical Modelling
Torsten Markus and Sarah Fischer
Institute for Energy Research (IEF-2)
Forschungszentrum Jülich GmbH
52425 Jülich
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Content
• Insight into Modern Light Sources
• Corrosion and Chemical Transport
• Calculation Design
• Results
• Conclusion
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PCA-Lamps
Lamp-burner
(PCA)
PCA = Poly Crystalline Alumina
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Aplications for High Intensity Discharge Lamps
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DyI3
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Wall Material Al2O3
Interior with Gaseous Species
e.g. Na, I, Hg, Tl, Dy, Ar, Xe, ...
Tungsten
DepositionMetal Halide Melt
e.g. NaI / TlI / DyI3
Wall Corrosion
1380K
1300K1300K 1310K
1340K 1340K
6000K5000K
3800K 3000K
Alumina
Deposition
Tungsten Electrode
Schematic of a High Pressure Discharge Lamp
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PCA deposition
500µm 500µm
Chemical Transport in Ceramic Discharge Metalhalide
Lamps (CDM)
Cross Section of a Corroded Discharge Vessel
in Horizontal Burning Position (after 9000 h of operation)
Source
Sink
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Explaination of Transport Phenomena
salt meltAl
hot
Salt Melt
Al O (s)2 3 Al O (s)2 3
3 DyI3(l) + 4 Al2O3(s) = Dy3Al5O12(s) + 3 AlI3(g)
DyI3(g) + Al2O3(s) = DyAlO3(s) + AlI3(g)
AlO
Al2O
AlOIAlI3(g)+Al2O3(s)= 3AlOI(g) 3AlOI(g)= AlI3(g)+Al2O3(s)
AlI3
Al
O
Al
O
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From data assessment to an application
calculation
Experimental raw data
(thermodynamic properties and phase equilibria)
Assessment
Programs
Gibbs Energy Database
Application
Programs
Calculations of:
Thermodynamic Data
Phase Equilibria
Process Simulation
Augmented by
Estimation techniques
a) experimental trends
b) ab initio calculations
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„Cooperative Transport Model“R. Gruehn, H.J. Schweitzer, Angew. Chem. 95, 80 (1983)
gas,Z
in
solid,Z
in
p
Komponents i = 1,...N
Iterations Z= 1,...n
Computation
T, V = const
Source
(Condensed Phase)
Sink
(Condensed Phase)
Computation
T, p = const
Thermochemical Database
cp= A + B·T + C·T-1 + D·T-2
T
T
p
f
T
f
T0
0(T)dTcΔHΔH
T
T
p0
T
0
T0
0dT
T
)T(cSS
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SimuSage Modelling
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Equilibrium reactors
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Scheme of the transport program
Sink Source
Phase splitter
Phase splitter
Iteration
Cycle
Frist Step:
Input of the salt meltFirst Step:
Input of Al2O3
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Example: NaI – CeI3 – Mixture
TSink = 1200°C
TSource = 1400°C
V = 0,0285 dm³
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Comparison between experiments and simulations
Composition NaI, CaI2
75% NaI, 25% CaI2 50% NaI, 50% CaI2 25% NaI, 75% CaI2
Simulation [mol Al2O3]: 1,22 · 10-9 < 2,55 · 10-9 < 7,16 · 10-9
Experimental certification:
→ Agreement for NaI – CaI2 – Mixture
NaI – CaI2 - Mixture
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Composition CaI2, CeI3
90,48%, 9,52% 87,1%, 12,9%
Simulation [mol Al2O3]: 5,08 · 10-8 < 5,58 · 10-8
Experimental certification: ≈
What causes this difference?
CaI2 – CeI3 - Mixture
Comparison between experiments and simulations
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SEM – Analysis with 90,48% CaI2 and 9,52% CeI3
1200 °C 1400 °C
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Formation of secondary phases Calculated
Activity
Al2O3_ca(s) 1.0000E+00
CaI2_l(liq) 9.4561E-01
Al2O3_cc(s2) 4.9718E-01
CaI2_ci(s) 2.4571E-01
CeOI_ci(s) 1.1649E-01
CeI3_l(liq) 5.4007E-02
Al2O3_l(liq) 3.5536E-02
CeAlO3_ci(s) 2.0447E-02
CeAl11O18_ci(s) 1.3446E-02
CeI3_ci(s) 1.1285E-02
CeAlO3_l(liq) 5.4999E-03
Ce2Al2O6_ci(s) 4.1199E-03
CeAl11O18_l(liq) 3.4167E-03
CaAl4O7_ci(s) 3.0990E-03
CaAl2O4_ci(s) 7.1260E-04
Al_l(liq) 6.7438E-04
Al_ci(s) 4.0705E-04
CaO_ci(s) 1.4573E-05
AlI3_l(liq) 2.7872E-06
CeO2_ci(s) 1.6025E-06
Al 9.3713E-07
Ce2O3_ci(s) 6.0181E-07
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Example: NaI – CaI2 – CeI3 – Mixture
TSink = 1200°C
TSource = 1400°C
V = 0,0285 dm³
n(CaI2)=0,0008mol
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Experimental Determination of
Thermodynamic Data
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Differential Thermal Analysis (DTA)
Measuring of Phase
Transition
Temperatures
Determination of the
Quantity of Heat
Studies in different
Atmospheres
Thermal Analysis from
RT to 2800 K
T
T
PT
Simultaneous DTA with
Thermogravimetry (TG)
STA 429, Netzsch
Principle of DTA
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Principle of Knudsen Effusion Mass
Spectrometry (KEMS)
Vaporisation studies up to 2800 K
Identification of gaseous species
Determination of partial pressures
(10-8 ... 10 Pa)
Evaluation of thermodynamic data of
gaseous species
condensed phases
Elucidation of corrosion processes
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Mass Spectrometer Knudsen Cell System (CH 5)
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Experiment
II
298rH
Identifiction of
Gaseous Gpecies Pi – partial
pressure
Appearance-Potential
k°p –
Equilibrium Constant
Tr
H
Tr
G
Tr
S
298r
H
298r
S
2nd law
3rd law
Potential of
Knudsen Effusion Mass Spectrometry
ai –
Thermod. Activities
II
298rS
298m ix
HE
mG
i
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0,0
0,2
0,4
0,6
0,8
1,0
0,0 0,2 0,4 0,6 0,8 1,0
0,0
0,2
0,4
0,6
0,8
1,0
0,0 0,2 0,4 0,6 0,8 1,0
0,0
0,2
0,4
0,6
0,8
1,0
0,0 0,2 0,4 0,6 0,8 1,0
0,0
0,2
0,4
0,6
0,8
1,0
0,0 0,2 0,4 0,6 0,8 1,0
a
a
XNaI XNaI
Temperature and Composition dependency
of activity for the NaI – CeI3 system
550 °C 600 °C
625 °C650 °C
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Phase Diagram of the System NaI–CeI3 (DTA)
Binary Excess Polynomial:
GmE=(xNaI
i)(xCeI3j)(A + B*T + C*T*ln(T) + D*T2 + E*T3 + F*T-1)
(calculated)
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Overview of the data to be optimized in the
NaI-CeI3 system
Various experimental data on the binary NaI-CeI3 system have been measured:
– phase diagram data (liquidus points, eutectic points)
– liquid-liquid enthalpy of mixing
– activity of NaI(liq) at different temperatures
OptiSage will be used to optimize the parameters for the liquid Gibbs energy model (XS terms). All other data (G° of the pure stoichiometric solids, as well as the pure liquid components) will be taken from the FACT database (i.e. remain fixed). A polynomial model for the Gibbs energy of the liquid will be used:G = (X1 G°1 + X2 G°2) + RT(X1 ln X1 + X2 ln X2) + GE
where GE = H – TSE
Using the binary excess terms:
H = X1X2 (A1) + X12X2 (B1)
SE = X1X2 (A3) + X12X2 (B3)
Hence:
GE = X1X2 (A1 - A3T) + X12X2 (B1 - B3T)
Where A1, A3, B1 and B3 are the 4
parameters to be optimized.CeI3xCeI3
G
NaI
G°1
G°2
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Summary
Corrosion- and rearrangement – effects of the
wall material limit the life time of High-Energy-
Discharge-Lamps
Cooperative Transport Model was programmed
with SimuSage
Simulations of the corrosion speed of lamp
relevant salt mixtures
Comparison of the experiments and simulations
show remarcable agreement