Efecto de aleantes e inhibidores sobre la corrosión en rendijas de aleaciones de níquel
2026
| Tesista | Eduardo SAENZ GONZALEZ |
| Director | Dr. Martín A. Rodríguez. CNEA - Argentina |
| Lugar de Realización | Departamento de Corrosión, Gerencia Materiales (CAC-CNEA) |
| Fecha Defensa | 26/03/2026 |
| Jurado | Dr. Ricardo CARRANZA. UNSAM, CNEA - Argentina |
Título completo
Efecto de aleantes e inhibidores sobre la corrosión en rendijas de aleaciones de níquel
Resumen
Las aleaciones de níquel se usan extensamente en la industria nuclear por su elevada
resistencia a la corrosión, aunque siguen siendo vulnerables a la corrosión en rendijas en
medios con cloruros, especialmente a altas temperaturas. Esta tesis estudió la eficiencia y los
mecanismos inhibidores del sulfato, nitrato y molibdato en aleaciones Ni-Cr-Fe y Ni-Cr-Mo,
considerando la posible sinergia entre los inhibidores y la composición química de las
aleaciones. Se utilizaron técnicas electroquímicas PD-GS-PD, junto con caracterizaciones por
microscopía óptica y SEM, perfilometría y análisis EDS. Los ensayos se realizaron en
soluciones de NaCl entre 0,01 y 1 M, a temperaturas de 30–90 °C. A partir del potencial de
repasivación (E R,CREV ) y de la relación molar R = [Inhibidor]/[Cl⁻], se definió una relación
crítica R CRIT que permitió comparar la eficiencia de cada inhibidor en diferentes condiciones.
El mecanismo del molibdato se analizó mediante voltametría cíclica en Pt y DRX, por otro
lado se midió el pH de despasivación (pHd) para relacionarlo con la composición de las
aleaciones y el efecto de los inhibidores. Los resultados mostraron que E R,CREV disminuye al
aumentar la temperatura y crece con el PRE (Pitting Resistance Equivalent). Entre los
inhibidores, el sulfato tuvo un efecto limitado. El nitrato resultó ser el inhibidor más eficaz y
confiable, elevando significativamente el E R,CREV con baja sensibilidad al PRE, la temperatura y
la concentración de cloruros. Su mecanismo se asoció al consumo de protones, favoreciendo
la repasivación dentro de la rendija. El molibdato mostró una eficiencia fuertemente
dependiente de la composición: su acción se intensificó en aleaciones con alto PRE,
particularmente las de Ni-Cr-Mo, donde forma especies poliméricas que precipitan en el
entorno ácido de la rendija y bloquean la disolución anódica. Sin embargo, su efectividad
disminuyó en soluciones con alto contenido de cloruros y en presencia de Fe³⁺, debido a la
formación de especies ricas en molibdeno que reducen la concentración activa del inhibidor.
La correlación entre pHd y R CRIT permitió explicar la sensibilidad del molibdato a la acidez
local y al PRE. Los ensayos a circuito abierto indicaron que los valores de R CRIT obtenidos sin
oxígeno son aplicables en condiciones más reales, donde participan oxidantes como O₂ y Fe³⁺.
Esta investigación aporta bases cuantitativas y mecanísticas para comprender la inhibición de
la corrosión en rendijas y ofrece criterios predictivos para la selección racional de inhibidores
según la composición, la temperatura y los cloruros del medio.
resistencia a la corrosión, aunque siguen siendo vulnerables a la corrosión en rendijas en
medios con cloruros, especialmente a altas temperaturas. Esta tesis estudió la eficiencia y los
mecanismos inhibidores del sulfato, nitrato y molibdato en aleaciones Ni-Cr-Fe y Ni-Cr-Mo,
considerando la posible sinergia entre los inhibidores y la composición química de las
aleaciones. Se utilizaron técnicas electroquímicas PD-GS-PD, junto con caracterizaciones por
microscopía óptica y SEM, perfilometría y análisis EDS. Los ensayos se realizaron en
soluciones de NaCl entre 0,01 y 1 M, a temperaturas de 30–90 °C. A partir del potencial de
repasivación (E R,CREV ) y de la relación molar R = [Inhibidor]/[Cl⁻], se definió una relación
crítica R CRIT que permitió comparar la eficiencia de cada inhibidor en diferentes condiciones.
El mecanismo del molibdato se analizó mediante voltametría cíclica en Pt y DRX, por otro
lado se midió el pH de despasivación (pHd) para relacionarlo con la composición de las
aleaciones y el efecto de los inhibidores. Los resultados mostraron que E R,CREV disminuye al
aumentar la temperatura y crece con el PRE (Pitting Resistance Equivalent). Entre los
inhibidores, el sulfato tuvo un efecto limitado. El nitrato resultó ser el inhibidor más eficaz y
confiable, elevando significativamente el E R,CREV con baja sensibilidad al PRE, la temperatura y
la concentración de cloruros. Su mecanismo se asoció al consumo de protones, favoreciendo
la repasivación dentro de la rendija. El molibdato mostró una eficiencia fuertemente
dependiente de la composición: su acción se intensificó en aleaciones con alto PRE,
particularmente las de Ni-Cr-Mo, donde forma especies poliméricas que precipitan en el
entorno ácido de la rendija y bloquean la disolución anódica. Sin embargo, su efectividad
disminuyó en soluciones con alto contenido de cloruros y en presencia de Fe³⁺, debido a la
formación de especies ricas en molibdeno que reducen la concentración activa del inhibidor.
La correlación entre pHd y R CRIT permitió explicar la sensibilidad del molibdato a la acidez
local y al PRE. Los ensayos a circuito abierto indicaron que los valores de R CRIT obtenidos sin
oxígeno son aplicables en condiciones más reales, donde participan oxidantes como O₂ y Fe³⁺.
Esta investigación aporta bases cuantitativas y mecanísticas para comprender la inhibición de
la corrosión en rendijas y ofrece criterios predictivos para la selección racional de inhibidores
según la composición, la temperatura y los cloruros del medio.
Complete Title
Effect of alloying elements and inhibitors on crevice corrosion of nickel alloys
Abstract
Nickel-based alloys are widely used in the nuclear and other industries. Although they exhibit
high corrosion resistance, they are susceptible to localized attack by crevice corrosion in
chloride-containing environments, particularly at elevated temperatures. This thesis aimed to
determine the efficiency and inhibition mechanisms of sulfate, nitrate, and molybdate species
on the crevice corrosion of nickel alloys, while exploring the possible synergy between these
inhibitors and alloying elements in the Ni-Cr-Fe and Ni-Cr-Mo alloy families. Specific
electrochemical techniques were employed, including the
Potentiodynamic–Galvanostatic–Potentiodynamic (PD-GS-PD) method, complemented by
surface topographical and chemical analyses using optical microscopy, scanning electron
microscopy (SEM), optical profilometry, and energy-dispersive X-ray spectroscopy (EDS).
Experiments were conducted in the temperature range of 30 to 90 °C in 0.01–1 M NaCl
solutions. Based on the analysis of the repassivation potential (ER,CREV) as a function of the
molar ratio R = [Inhibitor]/[Cl⁻], a critical ratio (RCRIT) was defined, which allowed
quantification of the efficiency of each inhibitor under different experimental conditions. The
inhibitory mechanism of molybdate was examined in detail through cyclic voltammetry tests
on an inert platinum (Pt) electrode and X-ray diffraction analysis of deposited products.
Open-circuit potential tests and measurements of the depassivation pH (pHd) were carried out
for each alloy in deaerated chloride solutions, analyzing their relationship with alloy
composition and inhibitor effects. It was found that ER,CREV decreases with temperature
and increases with the Pitting Resistance Equivalent (PRE) of the alloys. Among the
inhibitors, sulfate showed limited action, acting mainly as a supporting electrolyte. Nitrate
was the most efficient and reliable inhibitor, significantly increasing ER,CREV with low
sensitivity to alloy PRE, temperature, and chloride concentration. Its inhibition mechanism
was attributed to a reduction process coupled with proton consumption, which favors
repassivation inside the crevice. Molybdate exhibited an efficiency dependent on alloy
composition: its action improved with increasing PRE, particularly in Ni-Cr-Mo alloys, where
its reduction leads to the formation of polymeric molybdates that precipitate in the acidic
crevice environment, blocking anodic dissolution. However, its effectiveness decreased in
chloride-rich solutions and in the presence of Fe³⁺, due to the formation of Mo-rich species
that reduce the effective inhibitor concentration. The correlation between pHd and RCRIT
provided a unified explanation linking molybdate efficiency with crevice acidity and alloy
PRE. Open-circuit tests confirmed that the RCRIT values determined in oxygen-free
conditions are generally applicable to more realistic service conditions, including
environments containing oxidizing species such as dissolved O₂ and Fe 3+ . This research
established a quantitative and mechanistic basis for understanding how environmental
conditions and alloy composition affect the inhibition of crevice corrosion in Ni-Cr-Fe and
Ni-Cr-Mo alloys. The findings provide predictive criteria for the rational selection of
inhibitors in critical applications, as well as for assessing the influence of naturally occurring
inhibiting species in service environments according to alloy composition, temperature, and
chloride concentration.
high corrosion resistance, they are susceptible to localized attack by crevice corrosion in
chloride-containing environments, particularly at elevated temperatures. This thesis aimed to
determine the efficiency and inhibition mechanisms of sulfate, nitrate, and molybdate species
on the crevice corrosion of nickel alloys, while exploring the possible synergy between these
inhibitors and alloying elements in the Ni-Cr-Fe and Ni-Cr-Mo alloy families. Specific
electrochemical techniques were employed, including the
Potentiodynamic–Galvanostatic–Potentiodynamic (PD-GS-PD) method, complemented by
surface topographical and chemical analyses using optical microscopy, scanning electron
microscopy (SEM), optical profilometry, and energy-dispersive X-ray spectroscopy (EDS).
Experiments were conducted in the temperature range of 30 to 90 °C in 0.01–1 M NaCl
solutions. Based on the analysis of the repassivation potential (ER,CREV) as a function of the
molar ratio R = [Inhibitor]/[Cl⁻], a critical ratio (RCRIT) was defined, which allowed
quantification of the efficiency of each inhibitor under different experimental conditions. The
inhibitory mechanism of molybdate was examined in detail through cyclic voltammetry tests
on an inert platinum (Pt) electrode and X-ray diffraction analysis of deposited products.
Open-circuit potential tests and measurements of the depassivation pH (pHd) were carried out
for each alloy in deaerated chloride solutions, analyzing their relationship with alloy
composition and inhibitor effects. It was found that ER,CREV decreases with temperature
and increases with the Pitting Resistance Equivalent (PRE) of the alloys. Among the
inhibitors, sulfate showed limited action, acting mainly as a supporting electrolyte. Nitrate
was the most efficient and reliable inhibitor, significantly increasing ER,CREV with low
sensitivity to alloy PRE, temperature, and chloride concentration. Its inhibition mechanism
was attributed to a reduction process coupled with proton consumption, which favors
repassivation inside the crevice. Molybdate exhibited an efficiency dependent on alloy
composition: its action improved with increasing PRE, particularly in Ni-Cr-Mo alloys, where
its reduction leads to the formation of polymeric molybdates that precipitate in the acidic
crevice environment, blocking anodic dissolution. However, its effectiveness decreased in
chloride-rich solutions and in the presence of Fe³⁺, due to the formation of Mo-rich species
that reduce the effective inhibitor concentration. The correlation between pHd and RCRIT
provided a unified explanation linking molybdate efficiency with crevice acidity and alloy
PRE. Open-circuit tests confirmed that the RCRIT values determined in oxygen-free
conditions are generally applicable to more realistic service conditions, including
environments containing oxidizing species such as dissolved O₂ and Fe 3+ . This research
established a quantitative and mechanistic basis for understanding how environmental
conditions and alloy composition affect the inhibition of crevice corrosion in Ni-Cr-Fe and
Ni-Cr-Mo alloys. The findings provide predictive criteria for the rational selection of
inhibitors in critical applications, as well as for assessing the influence of naturally occurring
inhibiting species in service environments according to alloy composition, temperature, and
chloride concentration.
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