Long term testing of two ferritic-martensitic steels (P91 and VM12-SHC) with and without slurry deposited aluminide coatings containing 20 wt.% of Al at the surface was carried out by exposing these materials to the Solar Salt, a eutectic mixture composed of 60 % NaNO3 − 40 % KNO3 at 580°C. This salt is currently used in operating thermal solar power plants as heat transfer and storage fluid. Tubes made of expensive Ni based alloys are employed to mitigate corrosion. The tested uncoated ferritic materials exhibited very high corrosion rates developing thick, easily detached scales. IN617 was also tested as a reference and experienced very low corrosion up to 5,000 h, but after 10,000 h a 50 µm thick, mostly NiO scale had developed with Na0.6CoO2 crystals deposited on top. There was also evidence of significant Cr depletion at the alloy surface. Carcinogenic CrVI was found in the Solar Salt melt in which the three uncoated alloys were immersed. In contrast, the two coated ferritic steels did not show evidence of degradation after 10,000 h and the most significant microstructural change was the development of a very thin protective NaAlO2 layer on their surface. An industrial process to deposit these coatings on the inner surfaces of pipes has already been developed.

1.
P.
Audigié
,
V.
Encinas-Sánchez
,
M.
Juez-Lorenzo
,
S.
Rodríguez
,
M.
Gutiérrez
.
F.J.
Pérez
and
A.
Agüero
,
Surf. Coat. Technol.
349
,
1148
1157
(
2018
).
2.
A. S.
Dorcheh
,
R.N.
Durham
and
M.C.
Galetz
,
Sol. Energy Mater. Sol. Cells
144
,
109
116
(
2016
).
3.
G.
McConohy
and
A.
Kruizenga
,
Sol. Energy
103
,
242
252
(
2014
).
4.
M.
Spiegel
and
J.
Mentz
,
Mater. Corros.
65
,
276
281
(
2014
).
5.
P.
Audigié
and
A.
Agüero
, “Comparative Behavior of Fe-based and Ni-based alloys Exposed to Molten Salt Corrosion for Concentrating Solar Power Technologies”, in
International Symposium On High-Temperature Oxidation And Corrosion 2018
, edited by
The Iron and Steel Institute of Japan
,
Matsue, Shimane
(
2018
), pp.
58
61
.
6.
M.
Sarvghad
,
G.
Will
and
T. A.
Steinberg
,
Sol. Energy Mater. Sol. Cells
172
,
220
229
(
2017
)
7.
S.
Khorsand
,
A.
Sheikhi
,
K.
Raeissi
and
M. A.
Golozar
,
Sol. Energy
90
,
169
186
(
2018
).
8.
I.
Terasaki
,
Y.
Sasago
and
K.
Uchinokura
,
Phys. Rev. B
56
,
12685
12687
(
1997
).
9.
H.
Yakabe
,
K.
Kikuchi
,
I.
Terasaki
,
Y.
Sasago
and
K.
Uchinokura
, “
Thermoelectric properties of transition-metal oxide NaCo2O4 system
” in
Proceedings of the 16th International Conference on Thermoelectrics (ICT 97), Dresdesn, Germany
, (
IEEE
,
Piscataway, NJ
,
1997
), pp.
523
527
.
10.
M.
Miclau
,
K.
Bokinala
,
N.
Miclau
,
Mater. Res. Bull.
54
,
1
5
(
2014
).
11.
S. H.
Cho
,
S. C.
Kwon
,
D. Y.
Kim
,
W. S.
Choi
,
Y.
Kim
and
J. H.
Lee
,
Corros. Sci.
151
,
20
26
(
2019
).
12.
13.
A.
Soleimani Dorcheh
and
M.C.
Galetz
,
Sol. Energy Mater. Sol. Cells
146
,
8
15
(
2016
).
14.
Y.
Yang
,
J.
Cheng
,
S.
Liu
,
H.
Wang
and
P.
Dong
,
Mater. Corros.
70
,
120
127
(
2019
).
15.
J.
Liang
,
B.
Guo
,
J.
Tian
,
H.
Liu
,
J.
Zhou
,
W.
Liu
and
T.
Xu
,
Surf. Coat. Technol.
199,
121
126
(
2005
).
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