Development of novel coatings to resist fireside corrosion ...bf2ra.org/csl/Grant 11 Dominika...
Transcript of Development of novel coatings to resist fireside corrosion ...bf2ra.org/csl/Grant 11 Dominika...
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Development of novel coatings to resist fireside corrosion in biomass-fired
power plants
Supervisors:Dr. Nigel Simms
Prof. John Nicholls(Dr. Tanvir Hussain)
Industrial Supervisor:Colin Davis,
E.ON Technologies (Ratcliffe) Ltd
6th of October 2015
Dominika Orlicka
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Aim
To develop a range of coating compositions resistant to fireside corrosion in biomass-fired power plants using a multi-target magnetron
sputtering technique
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Objectives
Exposure conditions:• To understand stability of salts (KCl, NaCl, K2SO4, Na2SO4) at high
temperatures and chose a deposit for fireside corrosion testing
Coating development:• To use the combinatorial model alloy development methodology
by using two-target magnetron sputtering• To study the influence of Cr, Al and Fe on the coatings properties
and their role in chloride-based corrosion• To investigate the best coating compositions in the fireside
corrosion tests and to understand their behaviour in differentenvironments
• To evaluate the alternative methods of applying the best coatingcompositions on the boiler tubes
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Experimental design
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Mass Flow
Controller
(O2/SO2/N2/HCl/Air)
Vent
NaOH
scrubber
Alumina crucibles
with samplesAlumina
liner
Stainless steel
furnace tube
-5°C
+5°C
-5°C
H
o
t
z
o
n
e
Alumina tube
Safety gas
(N2) N2 vent
Schematic of a controlled atmosphere furnace (for salt stability and coating testing)
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Salt stability tests
Matrix of salt compositions
020406080100
100
80
406080100
0
20
40
60
80
100
806040200
100806040200
020
60
40
20
0
100
40
60
20
20
0
60
0
100
40
80
K2Cl2
Na2Cl2
80
100
Na2SO4
K2SO4
Test 1 Test 2 Test 3 Test 4
Temperature
[°C]600 550 550 550
Gas composition
7% O2, 0.01% SO2,
0.035% HCl,
balance N2
7% O2, 0.01% SO2,
0.035% HCl,
balance N2
0.035% HCl,
balance N2
0.035% HCl,
balance N2
Total flow rate
[cc/min]99.8 99.8 109.5 109.5
Duration
[hour]50 50 50 50
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Electron images of salt crystals
60% KCl + 40% K2SO4
beforea
fter
35% KCl + 20% NaCl+ 15% Na2SO4 + 30% K2SO4 100% K2SO4
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100% KCl 80% KCl + 20% NaCl 100% Na2SO4
beforea
fterElectron images of salt
crystals (1)
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Key issues for deposit stability tests
a) Test 1 (600ºC, HCl + SO2 environment, 22 mixtures, 50 hours)• conversion to sulphates• evaporation of chlorides• only chlorine left was in deposits that started with 50% at of Cl
b) Test 2 (550ºC, HCl + SO2 environment, 22 mixtures, 50 hours)• conversion to sulphates• evaporation of chlorides• only chlorine left was in 40% KCl+60% NaCl mixture and 100% NaCl
c) Test 3 (550ºC, HCl environment, mixtures (pure salts, KCl + NaCl, KCl + K2SO4), 50hours)• chlorides contaminated by sulphates• evaporation of chlorides• chlorine left was in each sample
d) Test 4 (550ºC, HCl environment, mixtures (pure chlorides, KCl + NaCl), 50 hours)• slight evaporation of chlorides• chlorine left was in each sample
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Magnetron sputtering
Target 1
Target 2
Chromium target
Deposition chamber
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Sample holder and substrates
Sample holder
Sapphire disc
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Schematic of a controlled atmosphere furnace (1)
Mass Flow
Controller
(HCl/Air)
Vent
NaOH scrubber
Alumina crucibles
with samples Alumina liner
Stainless steel
furnace tube
-5°C
+5°C
-5°C
H
o
t
z
o
n
e
Alumina tube
Safety gas
(N2) N2 vent
Water pumpDeionised water
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Coating compositions
Cr + Fe30Al
Fe50Cr + Fe20Al
Cr + Fe20Al
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Experimental conditions
Test 1 Test 2 Test 3 Test 4
Temperature[°C]
550 550 550 550
Gas composition
Air315 ppm HCl,balance air
315 ppm HCl,balance air
344 ppm HCl, balance air,
10% H2O
Total flow rate[cc/min]
- 47 47 105
Duration[hour]
Up to 450 Up to 150 150 Up to 300
KCl - - + +
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Techniques used
• SEM/EDX• XRD • FEG-SEM • Cross-section• FIB • IC • TGA• Mass change
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Selected results
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Mass change (Cr + Fe30Al)
Mass change graphs for the test Air + HCl without KCl (left) and with KCl (right) after 150 h
Lowest mass change E, F: 50-80 at.% Cr, 12-29 at.% Fe, 8-22 at.% Al
Lowest mass change F, G: 32-63 at.% Cr, 22-40 at.% Fe, 15-28 at.% Al
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Mass change (Cr + Fe20Al)
Mass change graphs for the test in Air (left) and Air with HCl (right) after 150 h
Lowest mass change E, e, F: 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.% Al
Lowest mass change E, e, F: 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.% Al
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Surface composition (Cr + Fe30Al)
Composition of unexposed coatings
Composition after the test in Air with HCl (with KCl)Composition after the test in Air with HCl (without KCl)
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ESEM images (Cr + Fe30Al, Air with HCl and Air with HCl + KCl)
50 µm
Surface morphology of an as deposited coating (GSE)
Post-exposure surface
morphologies of the coatings (GSE). A4, D4, E4, F4, H4, K4 – without KCl; A3, D3, E3, F3, H3,
K3 – with KCl
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Surface morphologies (Cr + Fe20Al and Fe50Cr + Fe20Al)
Post-exposure surface morphologies of the coating E (GSE) after 150 hours. First picture: Air exposure, followed by Air with HCl, Air with HCl + KCl and Air with HCl + KCl + 10% moisture (last picture)
Post-exposure surface morphologies of the coating A (GSE) after 50 hours. Left picture: Air exposure, right picture: Air with HCl
Cr + Fe20Al
Fe50Cr + Fe20Al
50 µm50 µm 50 µm50 µm
50 µm 50 µm
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XRD analysis for Cr + Fe30Al
XRD spectra of Fe-Cr-Al coatings after 150 h exposure in Air with HCl (left) and Air with HCl (+ KCl) (right)
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Cross-sections and FEG-SEM analysis
(Cr + Fe30Al)Test without KCl Test with KCl
1: low O content2: lower O and higher
Cr content than atthe top
1: high O and Cr content
2: depletion in O and Cr;higher KCl contentthan at the top(exception of sampleF)
3: 61 at% O, 28 at% Cr,9.5 at% Fe, 1 at% Al,0.5 at% KCl
4: 41.5 at% O, 36 at% Cr,7.5 at% Fe, 7 at% Al,8 at% KCl
25 µm
25 µm
25 µm
25 µm
25 µm
D4
E4
F4
D3
E3
sapphire
disc
sapphire
disc
sapphire
disc
2
1
25 µm
F3
1
2 2
1
2
3
2
1
4
1
2
2
11
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FIB-sections (Cr + Fe20Al and Fe50Cr + Fe20Al) -
examples
E2, Cr+Fe20Al, Air, 150h
B3, Fe50Cr+Fe20Al, Air with HCl, 50h
f1, Cr+Fe20Al, Air with HCl, 150h
D2, Fe50Cr+Fe20Al, Air, 50h
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Conclusions
• The magnetron sputtering was successfully used to producea range of Fe-Cr-Al coatings
• The presence of HCl in gas (and no KCl) did not result in any significantchanges compared to air alone
• KCl strongly accelerated the corrosion rate• The weight change data showed the smallest values for samples D – G with a composition range of 32-80 at.% Cr, 12-40 at.% Fe and 8-28
at.% Al for Cr + Fe30Al coatings E – F with a composition range of 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.%
Al For Cr + Fe20Al coatings• XRD analysis showed the presence of Cr2O3 and (Fe, Cr)2O3 oxides• No signs of chromates or chlorides were detected• The investigation of samples is still in progress
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Thank you!