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...
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
Aim
To develop a range of coating compositions resistant to fireside corrosion in biomass-fired power plants using a multi-target magnetron
sputtering technique
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
Experimental design
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)
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
Electron images of salt crystals
60% KCl + 40% K2SO4
beforea
fter
35% KCl + 20% NaCl+ 15% Na2SO4 + 30% K2SO4 100% K2SO4
100% KCl 80% KCl + 20% NaCl 100% Na2SO4
beforea
fterElectron images of salt
crystals (1)
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
Magnetron sputtering
Target 1
Target 2
Chromium target
Deposition chamber
Sample holder and substrates
Sample holder
Sapphire disc
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
Coating compositions
Cr + Fe30Al
Fe50Cr + Fe20Al
Cr + Fe20Al
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 - - + +
Techniques used
• SEM/EDX• XRD • FEG-SEM • Cross-section• FIB • IC • TGA• Mass change
Selected results
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
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
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)
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
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
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)
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
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
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
Thank you!