HAL Id: jpa-00216773
https://hal.archives-ouvertes.fr/jpa-00216773
Submitted on 1 Jan 1976HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
MÖSSBAUER SPECTROSCOPY STUDY OF
CORROSION PRODUCTS OF IRON WITH
AMMONIUM NITRATE IN AQUEOUS SOLUTIONS
J. Gancedo, M. Martínez, J. Oton
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplkment au no 12, Tome 37, De'cembre 1976, page C6-297
MOSSBAUER SPECTROSCOPY STUDY OF
CORROSION PRODUCTS
OF IRON WITH AMMONIUM NITRATE IN AQUEOUS SOLUTIONS
J. R. GANCEDO (*), M. L. MARTINEZ and J. M. OTONInstituto de Quimica Fisica Rocasolano D, Serrano 119, Madrid-6, Spain
R6sum6.
-
Au moyen de la spectroscopie Mossbauer, en reflexion et transmission, on a analyse les produits de la corrosion du fer en solutions aqueuses de NH4NO3 a 44 %. On est arrive a identifier les produits de corrosion suivants : magnetite, y-FeOOH, y-Fe20 3, a-FeOOH.Les spectres obtenus A Ia tempQature ordinaire des vert-de-gris (Green Rust) I et I1 sont present& et discutes. On kvalue les relations Fez+/Fe3+ a partir des spectres ajustes par ordinateur, et on les compare avec des resultats antirieurs obtenus par des techniques analytiques conventionnelles.
Abstract. - The corrosion products of iron in 44 % NH4N03 aqueous solutions, either oxygen free or air saturated, were analyzed by Mossbauer spectroscopy, in transmission and scattering modes. Positive identification of the following corrosion products was achieved : magnetite, y-FeOOH, y-Fe20 3 and a-FeOOH.
Room temperature spectra of Green Rust I and I1 are presented and discussed. The FeZC/Fe3+ ratios are evaluated from the computer fitted spectra and compared with previous values from conventional analytical techniques.
1. Introduction.
-
The corrosion reaction of Iron by aqueous solutions of NH4N0, has been previously studied by Smialowski [l-31 and others, but composi- tion of reactions products had not been established. The Mossbauer Spectroscopy finger print techniqueaffords the possibility of identifying such products and, in many cases, of determining the concentrations ratio. The magnetic properties of iron oxides are of great aid for these purposes.
2. Experimental part. - 2.1 EXPERIMENTS IN OPEN ATMOSPHERE.
-
Electrolytic Iron sheet (COMECA,0.15
%
Cu, 0.10%
C+
Si+
P+
Mn+
S impuri- ties) was mechanically polished, cut in discs of 2.5 cm diameter, degreased in benzene and acetone, activated in HCl 1 : 1, and finally immersed in 50 m1 of 44%
NH,N03 water solution. The reaction vessel was thermostatized by means of a silicone oil bath controll- ed with contact thermometer.
2.2 EXPERIMENTS IN OXYGEN-FREE ATMOSPHERE. -
The previously degreased iron discs were introduced into the reactor and evacuated to 10-4 torr, after which hydrogen is allowed to enter until a pressure of 120 torr. Then the specimen is heated during 30 min. (= 400 OC) by means of a 750 W lamp placed in one focus of an elliptic mirror. After cooling and evacua- tion, deaerated [4] 44
%
NH,NO, solution is introduc- ed on the reactor and this is thermostatized as above. The reaction products were separated inside an oxygen- free dry-box.2.3 SPECTRA OF REACTION PRODUCTS.
-
The open atmosphere reaction products yield two different solidphases, one either at the bottom of the reactor o-
attached to the iron disc, and the other forming a super- natant crust. The oxygen-free reaction does not pro- duce crust. Each phase is analyzed separately. An
amount equivalent to 10-20 mg/cm2 of natural iron is placed on a Perspex air-tight sample holder.
The scattering spectra were taken using a toroidal proportional counter after [5]. The spectrograph is constituted by an Intertechnique 400 ch. Multichannel Analyzer, a home-made double symmetrical ramp wave generator and transducer, with a linearity on the calibrated range of 0.15
%,
and a proportional counter. The spectra are fitted in two different ways, the first one is more laborious, and consists of a fit of the expe- rimental points to Lorentzian curves by a computer least squares procedure [6] from which the usual para- meters are obtained. In the second one the peak posi- tions are obtained after a spectrum sharpening by means of a Fourier transform [7] of the experimental spectrum points.2.4 THE MOSSBAUER SPECTRA OF GREEN RUSTS. -
The occasional formation of a green precipitate on the 30 OC experiments at the beginning of the reaction (4-8 hours) and eventual transformation in magnetite and y-FeOOH, opened the possibility of relating this green precipitate to the mixed Fezf -Fe3' hydroxides already described in the literature [S, 91 as Green Rust
I and I1 (G. R.), the M. S. of which have not been published yet.
Both compounds were prepared by us and its identi- fication was accomplished by X-Ray powder difracto- grams [10].
C6-298 J. R. GANCEDO, M. L. MARTINEZ AND J. M. OTON
Q9
.9B
3 2 2 3 2 2
FIG. 1 . - RT spectrum of Green Rust I. FIG. 2.
-
RT spectrum of G r e e ~ Rust 11.The Mossbauer Spectra obtained are shown in figures 1 , 2 and the parameters to which this spectra can be fitted are given in Table I. These calculated para- meters are typical of Fe2+ and Fe3+ in octahedral environment. The X-Ray structure determination is not in the literature.
The intensity absorption ratio Fe2'/Fe3 calculated from the spectra, assuming an identical cc
f
factor for all the species and sites, and equality of areas andwidths in each doublet half, seems to vary slightly from one preparation to another, the effect being more marked for the G. R. I. The degree of precipitate washing or more probably, the existence of variable stoichiometry in both compounds can explain this phenomenon. Our values fit reasonably well with those derived from the formulae, 4 Fe(OH),
.
Fe(OH), to Fe(OH),.
Fe(OH), for G. R. I, and2 Fe(OH)3. 4 Fe(OH),
.
S0,Fe. xH,ORT Green Rust parameters 6 (mmls)
versus Fe
Final reaction products (7 days) in aerated solutions
magnetite mixture y-FeOOH y-FeOOH non-magnetic precipitate magnetite (traces) magnetite
y-FeOOH (traces) a-FeOOH
y-FeOOH lJ-Fe203
magnetite (traces) a-FeOOH nonstoichiometric magnetite nonstoichiometric magnetite
magnetic precipitate -
I y -FeOOH y-FeOOH y-FeOOH
Crust unidentified (traces) magnetite (traces)
for G. R. 11, proposed by Derie and Ghodsi [g]. Our results for G. R. I1 are in disagreement with the Fe2"/Fe3+ ratio proposed by Misawa [8].
2.5 COMPOSITION OF CORROSION PRODUCTS.
-
The found products vary with the corrosion conditions, the results for seven days reaction are summarized on table 11. Typical transmission and scattering spectra are shown in figures 3,4. The scattering measurements do not shown other compounds than those obtained by transmission.A green precipitate which appears at the beginn- ing (4-8 hours) of the 30 OC aerated and deoxygenated
FIG. 3. - RT spectrum of the corrosion products of aerated solutions at 50 "C.
RG. 4. - RT scattering spectrum of the iron disc surface after 7 days reaction with aerated solution at 50 "C.
experiments yields a RT spectrum very similar to that of synthetic Green Rusts ; which excludes the existence of ferrous hydroxide as such on the products. The nature of this compound is under study.
In oxygen free solutions, at 30 OC, 50 OC and 80 OC, the final products are always nonstoichiometric magnetite.
Acknowledgement. - We thank to Dr. Marti Mufioz for the X-Ray powder difractograms and the Ministerio de Educaci6n y Ciencia for financial support to
5. M. 0. and M. L. M.
References
[l] SMIALOWSKI, M. and SZKLARSKA-SMIALOWSKA, Z., Corro- [5] KEISCH, B., J. Physique Colloq. 35 (1974) 151.
sion 18 (1962) 1 t. [6] STONE, A. J., J. Chem. Soc. A (1967) 1971.
[2] FLIS, J., MIELUCH, J. and SMIALOWSKI, M., Corrosion 20 [7] STONE, A. J., Chem. Phys. Lett. 6 (1970) 331.
(1964) 184 t. [S] MISAWA, T., HASHIMOTO, K. and SHIMODAIRA, S., Corros. [3] MIELUCH, 3. and SMIALOWSKI, M., Bull. Acad. Pol. Sci. Ser. Sci. 14 (1974) 131.
Sci. Chim. XI11 (1965) 33. [ g ] DERIE, R. and GHODSI, M., Ind. CChim. Belge 37 (1972) 731.
[41 GILROY, D. and MAYNE, J. E. O., J. Appl. Chem. 12 (1962) [l01 BERNAL, J. D., DASGUPTA, D. R. and MACKAY, A. L. Clay
