life time analysis & accelerated aging...
TRANSCRIPT
Chart 1
Life time analysis & accelerated aging tests
SFERA Summer School 16.5.2013
Florian Sutter, Johannes Wette, Arantxa Fernandez (Ciemat)
Contents
Chart 2
Principles of degradation
Outdoor exposure testing
Accelerated aging testing
Conclusions and Outlook
Service life time modeling
Motivation
Chart 3
The cost of corrosion
Goals for improved optical materials
- >30 years lifetime
- >95% specular reflectance (φ = 7.5 mrad)
- specular reflectance loss <1% over life time
- low manufacturing cost < 27 US$/m²
100MW power plant, 40% annual capacity factor
Annual electricity production: 100 MW · 8760 h · 0.4 = 350,400 MWh
1% mirror reflectance loss ≙ 3,504 MWh per year
490,560 US$ / year loss due to degradation (estimated feed-in tariff 0.14 US$/kWh)
[C. Kennedy NREL]
Environmental material stresses during service life
Chart 4
Radiation
Temperature
Mechanical stresses
Environmental pollutants
AbrasionHumidity• ambient relative humidity• dew• rain
• airborne dust or sand• cleaning mechanism
• chemical reactions with dust or sand• pollutants from surrounding industry (e.g. coal plants)• proximity to sea
• wind loads• stresses due to mounting• total solar radiation
• especially UV-A, UV-B
• cyclic day/night temperature changes• frost
R R – O – O – H
R– HR
Photodegradation of paint films
Chart 5
[Zeus; C.Hare, Journal of Protective Coatings and Linings]
• Yellowing• Reduced mechanical strength • Reduced impact resistance• Small surface cracks
– H
UV radiation
+ •HInitiation: Photolisis
Propagation: Autooxidation + O2
Bond cleavage to form free radicals
Peroxy radical formation
– O – O – H +Peroxy radical attack of polymer chain to form hydroperoxide and free radical
– O• + •O – H Fragmentation of hydroperoxide
Termination: Embrittlement
R•R
R• R – O – O•
R – O – O• +
UV radiation
R•
R• •R R R + – Interchain cross linking
Thermal induced cracking and delamination
∆T > 0
Substrate αs
α1
α2
α2 < αS < α1
coating
coatingSubstratecoatingcoating
ET
1
Chart 6
Cracking and delamination
Chart 7
Corrosion of metals
Chart 8
Differential aeration
[U.R. Evans]
[L.Shreir]
0.3VCorrosion pit
M M2+ + 2 e-O2 + 2 H2O + 4e- 4 OH-
Corrosion of metals
Chart 9
Practical galvanic series 2)
Metal VAu +0.24Ag +0.15Cu +0.01X5CrNi18.8 -0.05Ti -0.11Sn -0.19Cr -0.29Pb -0.30Steel 8.8 -0.35Cd -0.52Al (99.5) -0.67Zn -0.80Mg -1.40
2) Potential in artificial sea water with pH 7,5based to the standard hydrogen electrode
Galvanic corrosion appears at potential differences of 0.05 – 0.1 V
Standard electrode potential 1)
Metal VAu +1.5Ag +0.8Cu +0.52Sn +0.15Pb -0.13Fe -0.36Cd -0.40Zn -0.76Cr -0.91Ti -1.21Al (99.5) -1.66Mg -2.36
1) 25 °C; 101,3 kPa; pH=0; effective ion activity= 1based to the standard hydrogen electrode
Galvanic corrosion
Galvanic corrosion of aluminum layer
Galvanic Corrosion
Chart 10
Possible degradation silvered glass mirrors
Chart 11
Glass 4mm
Silver
Low Pb protective lacquer
Pb free top coat
Copper Galvanic dissolution of Cu
UV-light
Embrittlement of lacquer
Delamination of paints
Corrosion of unprotected silver
Examples glass mirror corrosion in the field
Chart 12
Examples glass mirror corrosion in the field
Chart 13
Corrosion can appear <2 years in field
[NREL]
Corrosion of aluminum reflectors
Chart 14
SiO2 sol-gel
Al2O3
SiO2
TiO2
AlCorroded Al-layer
0.5mm
SiO2 - sol-gel protective coating
TiO2SiO2
Al (99.99% purity)
Al2O3
Al-Substrate
3μm
60nm95nm65nm
3μm
Nano-Composite
PVD-layer-system
Anodizing-layer
0.5mm
SiO2 - sol-gel protective coating
TiO2SiO2
Al (99.99% purity)
Al2O3
Al-Substrate
3μm
60nm95nm65nm
3μm
Nano-Composite
PVD-layer-system
Anodizing-layer
Chart 15
Corrosion of aluminum reflectors
O2O2
SiO2
Al
Al2O3
SiO2
SiO2
TiO2
Al
Defect
Al Al3+ + 3 e-
O2 + 2H2O + 4 e- 4OH-
e-
Al2O3
Al Al3+ + 3 e-
e-
Cathodic reaction
Al3+ + 3 H2O Al(OH)3+3H+
2H+ + 2 e- H2
H2-formation
Hydrolysis
O2 + 2H2O + 4 e- 4OH-
Anodic reaction
Crack due to H2-pressure
H2
Differential areation cell
Al-Substrate
Examples aluminum corrosion
Chart 16
PVD reflector in contact with NaCl-solution (50g/l), artificial defect
Chemical reactions dust – polymer coating
Chart 17
Lime rich dust Abu DhabiTransparent polymer coating
Contents
Chart 18
Principles of degradation
Outdoor Exposure Tests
Accelerated aging testing
Conclusions and Outlook
Service life time modeling
Outdoor Exposure Testing
Chart 19
Galvanic separation sample-rack
45° tilt angle
Facing towards equator
+ Covers all environmental stresses
+ Simple
- Requires partners- Sample degradation during handling / shipping
- No acceleration
[Q-lab]
- Various exposure sites needed
Abu Dhabi Tabernas PSACanary Islands Almería
Chart 20
Outdoor exposure testing of aluminum prototype materials
Exposure program without cleaning of samples
Cleaning with pressurized demineralized water
Cleaning with soft tissue and demineralized water
No cleaning
Exposure program to test influence of cleaning on sample degradation
A B C D E F
S099
0A
S099
2
S099
0C
CanariasTabernasAlmeriaAbu Dhabi
-1,0
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
Spec
ular
refle
ctan
ce lo
ss [%
]Specular reflectance losses ∆ρ(660nm,15°,12.5mrad)
Chart 21
Exposure time: 4.6 - 6 months
16.6%12.7%11.6%6.4 %
Total loss per site
9 differently coated aluminum prototype materials
Reflectance – time dependence
Solar weighted hemispherical reflectance of Flabeg mirrors after outdoor exposure at NREL (Colorado), Arizona (APS), Florida (FLA) and accelerated exposure in Ci65 (1 sun / 60°C / 60%RH).
[C. Kennedy NREL]
Annual degradation rate ~ 0.2%/yr
Chart 22
Contents
Chart 23
Principles of degradation
Outdoor Exposure Tests
Accelerated aging testing
Conclusions and Outlook
Service life time modeling
Accelerated aging testing
Chart 24
- Increase temperature to accelerate water diffusion
- Lower wavelengths to accelerate photodegradation (>280nm)
- Increase humidity / condensation cycles / exposure to pollutants (Cl-, S2-, OH-, H+…)
- Extreme temperature cycling to induce cracking, delamination
- Increase mechanical abrasion of coatings
Methods to accelerate degradation:
Accelerated aging tests
Chart 25
IEC 62108 10.7a: Damp heat test 85/85
Chamber temperature: 85 ± 2°CHumidity: 85 ± 5 % relative humidityTesting time: 1000 hours
IEC 62108 10.7b: Damp heat test 65/85
Chamber temperature: 65 ± 2°C Humidity: 85 ± 5 % relative humidityTesting time: 2000 hours
Accelerated aging tests
Chart 26
ISO 11507: UV+Water Test
Chamber temperature: 50 to 60°C Humidity: ambient to 100% relative humidityRadiation: lamp type II, UVA-340; 290-400 nm; peak emission at 340nm;
lamp power matches 1 sunCycle time: 8 hoursTesting time: >1000 hours
Accelerated aging tests
Chart 27
ISO 9227: Neutral salt spray test (NSS)
Chamber temperature: 35 ± 2 °C Humidity: constant 100% relative humiditySprayed solution: demineralized water + 50 g/l NaCl
(pH 6.5 – 7.2)Condensation rate: 1.5 ± 0.5 ml/h on a surface of 80 cm² Sample position: 20 ± 5° respect to vertical Testing time: 480 – 3500 hours
Accelerated aging tests
Chart 28
ISO 9227: Copper accelerated salt spray test (CASS)
Chamber temperature: 50 ± 2 °C Humidity: constant 100% relative humiditySprayed solution: demineralized water + 50 g/l NaCl + 0.26 g/l CuCl2
(pH 3.1 – 3.3)Condensation rate: 1.5 ± 0.5 ml/h on a surface of 80 cm² Sample position: 20 ± 5° respect to vertical Testing time: 120 – 480 hours
CuCl2
Accelerated aging tests
Chart 29
DIN 50018 / ISO 6988: Kesternich Test
Chamber temperature: ambient / 40 ± 3°C Humidity: ambient / 100% relative humidityInitial SO2 concentration: 0.33 or 0.67% of volume of testing chamberCycle time: 24 hoursTesting time: >20 cycles
Accelerated aging tests
Chart 30
ISO 61215: Thermal Cycling
Chamber temperature: -40°C to +85°C Humidity: dryCycle duration: min. 2h 50min, max. 6h Recommended cycle number: >100
Accelerated aging tests
Chart 31
Thermal Cycling with humidity based on ISO 6270-2CH
Chamber temperature: -40°C to +85°C Humidity: ambient to 100% relative humidityCycle duration: 24 hRecommended cycle number: >20
Accelerated aging tests
Chart 32
Humidity Freeze Test IEC 62108
Chamber temperature: -40°C to +65°C Humidity: ambient to 85% relative humidityPrecycling: 400 cyclesCycle duration: 24 hFreeze cycle number: 40Total testing time: ~2000h
400 precycles -40 to 65°C, dry 40 humidity-freeze cycles
Accelerated aging tests
Chart 33
Abrasion testing
Available standards: MIL-STD 810G, ISO 11998, DIN ISO 9211-4
Simulation of windblown dust and sand particles
Simulation of cleaning cycles Scratching of coatings with controlled normal force
Accelerated aging of aluminum - Test comparison
Outdoors (5 months) Salt spray (NSS) Damp heat 85/85 UV+humidity
+ Realistic defect corrosion
- Unrealistic side effects
- Long exposure time >2000 h
Corrosion at coating defects
Corrosion due to diffusion
>600h 1000h 1000h
- Unrealistic cracking for some coatings- Long exposure time
+ Realistic corrosion due to diffusion- Unrealistic degradation due to high acceleration
Chart 34
Accelerated aging of aluminum – Test comparison
70,0
72,0
74,0
76,0
78,0
80,0
82,0
84,0
86,0
0 500 1000 1500 2000 2500 3000
Hours
spec
ular
refle
ctan
ce [%
]NSSUV+humidityDamp HeatOutdoor 6 months
Chart 35
Typical testing program for reflectors
Chart 36
Contents
Chart 37
Principles of degradation
Outdoor Exposure Tests
Accelerated aging testing
Conclusions and Outlook
Service life time modeling
Photodegradation of polymeric glazing materials
[NREL, Köhl et al. / Solar Energy 79 (2005) 618-623]
UV- light concentrator
nm
nmUV dtEtE
385
290
,)(
ttTk
EpUV dteEtEKt B
0
)(
0
E0 = 44.5 W/m²
K (s-1)3.69.6e-5
Chart 38
Life time prediction model for a PVD aluminum reflector
Chart 39
0 0.25 0.49 0.94 2.02 3.12 months
tkfc exp1
k = 6.4 ·10-3 months-0.5
k = 2.9 ·10-3 months-0.5
k = 1.1 ·10-3 months-0.5
k = 5.3 ·10-2 months-0.5
Life time prediction model for a PVD aluminum reflector
Chart 40
tmonths
tktmonths
tkt
%057.0exp%04.0%1.44exp1 00
ρ0 = 86.5 for reflectors without sol gel
ρ0 = 83.5 for reflectors with sol gel
Initial specular reflectance Losses due to corrosion
average reflectance of corroded area
Losses due to abrasion
Correlation of Neutral Salt Spray test to outdoors
Only valid for sol-gel coated PVD aluminum reflectors!
10 years Florida ≙ 2200 h
10 years Golden ≙ 461 h
10 years Tabernas ≙ 67 h
Exposure time outdoors t [months]
Expo
sure
tim
e in
NSS
-test
t NSS
[h]
Chart 41
Chart 42
Conclusions and Outlook
Further research required to
- Understand the degradation mechanisms of the several reflector types
- Improve existing accelerated aging tests (e.g. include reaction with dust)
- Define suited accelerated aging standard for CSP reflectors
- Correlate accelerated aging tests to reference outdoor sites for several materials
- Accelerated aging tests are a useful tool to compare materials under defined laboratory stresses
- Service life time prediction models are semi-empirical. Mechanistic models are aimed at but they are complex.
- At too high stresses unrealistic chemical processes may take place
- Comparison to Outdoor Exposure Tests recommended