1. Room temperature electrochemistry results.
Corrosion studies in ethyl-dimethyl-propyl-ammonium bis(trifluoromethylsulfonyl)imide in view of its application as diathermal fluid.
U. Bardi, S. Caporali, A. Lavacchi, I. Perissi Chemistry Department, Università di Firenze, via della Lastruccia, Sesto Fiorentino - Italy
Introduction.
P.M
Density 1.41 g cm-3
Ionic Liquids experienced a rising interest as fluids for heat exchange and storage because they match most the requirements for thermal application fluids. We chose ethyl-dimethyl-propyl-ammonium bis(trifluoromethylsulfonyl)imide, EdMPNTf2N, (viscosity °C, Tdec close to 320 °C) to study the interaction of such IL with several metals and alloys employed in the construction of solar plants: Stainless Steel (AISI 304), Carbon steel (AISI 1018 and S275-J0).
Electrochemistry
Gravimetric method
SEM+EDX
Room temperature electrochemistry results.
Potentiodynamic curves: both AISI 1018 and S275-J0 show tendency to pitting corrosion
OCV curves: a quite stable corrosion potential is reached after s
Tafel plots and Rpol measurements: Low values of corrosion current densities, valuated with Tafel extrapolation and Resistance polarization method, result for all the alloys investigated (<2 A/cm2) with AISI 304 the most performing material.
AISI 1018
Icorr (An)
(A/cm2)
Icorr (Cat)
Rpol
() βa
(mV/dec) βc
Icorr Rpol
1,74
0, 360
27740
133
484
1,63
0,555
0,234
63500
128
450
0,681
1,35
0,124
35900
121
554
1,20
AISI 304
Icorr (An)
(A/cm2)
Icorr (Cat)
Rpol
()
β a
(mV/dec) βc
Icorr Rpol
0,022
0,011
131
257
0,028
146
310
0,026
0,0076
0,021
154
273
0,018
S275-J0
Icorr (An)
(A/cm2)
Icorr (Cat)
Rpol
()
β a
(mV/dec) βc
I corr Rpol
0,0230
0, 201
970000
169
626
0,060
0,0240
0,206
735000
204
420
0,081
0,0590
0,186
663300
313
660
0,139
SEM and EDX analysis
After the 10 days treatment, the IL solution remains yellow-clear and localized corrosion phenomena are detected on both the alloys surfaces.
Comparison of the qualitatively trend of wt% of F and S ,deriving from IL anion, detected by EDX analysis on the specimen surfaces of AISI 304 (*) and AISI 1018 (°) after the immersion in EdMPNTf2N for 48 h and 10 days at 220°C. This behaviour denotes a no pronounced tendency to decomposition also after 10 days respect to imidazolium based ILs.
AISI 304
AISI 1018
The nine points analyzed derive from 3 sites for each sample (3 disks of AISI 1018 and 3 disks for AISI 304, individually immersed in distinct beakers).
SEM image showing localized corrosion on AISI 1018 and AISI 304 after 10 days immersion test at 220°C.
ICP-OES analysis
Alloys Cr
(mg/KgIL) Fe Mn Ni
AISI 304
22,86
71,19 -
23,02
70,83
188,8
56,00
70,49
285,0
11,22
AISI 1018
272,5
4,377
364,2
6,72
146,1
4,490
AISI 1018: wt% 0.14–0.20 C, 0.60–0.90 Mn, P, S, Fe balance
density 7.87 g/cm3
AISI 304: Cr 17-20%, Mn < 2%, Ni 8-11%, C < 800, Fe balance
density 7.93 g/cm3
After 10 days of immersion in the IL at 220 °C no negligible amounts of metals in solution is detected for both the alloys.
Conclusion
If EdMPNTf2N has to be used as fluid for high temperature applications in room atmosphere the surface of the containing vessels will have to be protected against corrosion.