Stainless Steel In Nitric Acid Research Articles

Influence of the temperature on the reduction mechanism of concentrated nitric acid on a silicon-enriched austenitic stainless steel

Corrosion of silicon-enriched stainless steel in nitric acid strongly depends on the temperature of the electrolyte. Therefore, the reduction reaction of nitric acid on this material was investigated from 40 to 107 °C. For the first time, the autocatalytic reduction mechanism of nitric acid reduction is highlighted by coupling electrochemical measurements (LSW, EIS, Chronoamperometry) with chemical analyses (mass spectrometry, ICP-AES, UV–Vis spectroscopy). This study provides further insights into the nitric acid reduction on an oxidized material compared to that reported earlier on noble metals despite slower kinetics of electrochemical reactions due to the presence of a passivating film. Furthermore, it is shown that HNO2 (or NO+) promotes the autocatalytic reactions in concentrated HNO3 and leads to the formation of NOx species released and detected in the gas phase.

Corrosion of Stellite-6 Overlay Cladding on 304L Stainless Steel in Nitric Acid

Corrosion of Stellite-6 Overlay Cladding on 304L Stainless Steel in Nitric Acid

Electrochemical Corrosion Behavior of Explosively Welded Ti/Type 304L Stainless Steel in Nitric Acid

Two metallurgically incompatible materials, titanium grade 2 and Type 304L stainless steel (SS), were joined through explosive welding for applications in nitric acid service. The morphology and microstructure of the bonded interface were examined using a scanning electron microscope (SEM) and an optical microscope. Typical wavy interfaces along with solidified melted zones at wave vortexes were observed. Various intermetallic phases, having high hardness, were shown to be formed in these solidified melted zones. Elemental distribution in these intermetallic phases was established using SEM coupled with energy dispersive spectroscopy (EDS). Low corrosion rates were observed after exposure of the weld specimens in boiling 14.5 M and 4 M HNO3 solutions. In addition, potentiodynamic polarization tests in 4 M HNO3 solution have been performed at different surfaces at the plane of the welded interface by successive material removal by grinding from 304L SS through weld to titanium. Despite the presence of different intermetallic phases at the test surfaces, it was found that the current densities in the passive regime of potentials were low. The morphological examination of the tested surfaces revealed that corrosion attack was mainly along the boundaries between SS/intermetallic phases, Ti/SS, and along the pre-existing cracks in the intermetallic phases. No corrosion attack was observed along the boundaries between Ti and intermetallic phases.

The kinetics of transpassive dissolution chemistry of stainless steels in nitric acid: The impact of Si

Atomic emission spectroelectrochemistry was used to monitor the elemental dissolution of two stainless steels during transpassive polarization. A 304LN stainless steel (X2 CrNiN 18-10) was compared with a 3.5 wt% Si rich stainless steel (X1 CrNiSi 18-15-4) so as to elucidate the effect of Si on the dissolution mechanism. The enrichment in Si shifted the cathodic reaction to lower potentials explaining that in hot and concentrated nitric acid containing oxidizing species, 304LN SS corrodes more rapidly due to the transpassive break of passivity, while the 3.5 wt% Si SS remains passive. However, when polarized into the transpassive domain, preferential grain boundary corrosion was observed for the 304LN but not for the 3.5 wt% Si SS, despite having similar current densities. Congruent alloy dissolution was observed in the transpassive domain with the stoichiometry of Fe(III), Cr(VI) and Ni(II) yielding a faradaic yield of 100% at early times. For longer times, with the 304LN, the faradaic yield drop to 70% indicative of intergranular dissolution in which the cations released in the intergranular space were not detected by the ICP-AES. Transmission electron microscopy coupled with energy dispersive spectroscopy showed that the interface of the 3.5 wt% Si SS enriches in Cr during a polarization in the transpassive domain of the steel. No similar enrichment was detected for the 304LN.

Transuranic contamination of stainless steel in nitric acid

Stainless steels coupons have been exposed to transuranic species in conditions representative of those found in a spent nuclear fuel reprocessing plant. Stainless steel was prepared to different surface finishes and exposed to nitric acid of varying concentrations containing 237Np, 239Pu or 243Am for one month at 50 °C. Contamination by these transuranics has been observed on all surfaces exposed to the solution through the use of autoradiography. This technique showed that samples held in 4 M HNO3 bind 2–3 times as much radionuclide as those held in 10.5 M HNO3. It was also found that the polished steel surfaces generally took up more transuranic contamination than the etched and “as received” steel finishes. The extent of corrosion on the steel surfaces was found, by scanning electron microscopy, to be greater in solutions containing Np and Pu in comparison to that observed from contact with Am containing solutions, indicating that redox activity of transuranics can influence the mechanism of stainless steel corrosion.

Effect of Heat Treatments on the Electrochemical Behavior of 304L Stainless Steel in Nitric Acid

Effect of Heat Treatments on the Electrochemical Behavior of 304L Stainless Steel in Nitric Acid

A Direct Measurement of the Activation Potential of Stainless Steels in Nitric Acid

The rate of anodic dissolution and the associated activation potential that characterizes the passive-active transition of stainless steels have been measured directly for the first time in nitric acid. The anodic dissolution current under cathodic polarization in pure nitric acid, in absence of chlorides, is masked by intense cathodic hydrogen reduction. In this work, atomic emission spectroelectrochemistry (AESEC) was used to record simultaneously the dissolution rate of the individual alloying elements of stainless steels as well as the overall cathodic current. This methodology has been used to quantify the influence of several parameters on the activation potential: nitric acid concentration, temperature, and the addition of silicon in the steel composition.

Cr（VI）を含む硝酸溶液中におけるSUS310EHPの腐食速度決定因子の検討

Cr（VI）を含む硝酸溶液中におけるSUS310EHPの腐食速度決定因子の検討

Corrosion Behavior of Sensitized 304 SS in Nitric Acid Medium Containing Oxidizing Ions

The corrosion behavior of 304 stainless steel (SS) in the as-received and sensitized conditions has been investigated at room temperature and at 60 °C in the presence of oxidizing ions in 6 and 8 M nitric acid media. Corrosion of 304 SS in nitric acid was far more severe in sensitized condition than in as-received condition. Further, decrease in corrosion resistance was observed with increase in the temperature of nitric acid. The corrosion potential shifted to noble direction with increase in the concentration of nitric acid and the potential shifted further to transpassive potential at 60 °C. Increase in corrosion potential towards transpassive domain led to severe intergranualar attack. Impedance spectra showed two time constant which could be attributed to the redox reaction on the surface of oxide film. However, the effect of oxidizing metal ions was not prominent.

Electrochemical noise resistance evaluation of 304L SS in nitric acid and simulated nuclear high level waste

The paper focuses on corrosion monitoring of 304L stainless steel (SS) (solution annealed, sensitised) in nitric acid (4, 8 and 12M) at 298 and 323 K electrolyte temperatures, and simulated high level waste (HLW, 323 K), using electrochemical noise (EN) measurements. Double loop electrochemical potentiokinetic reactivation test was conducted to assess the degree of sensitisation. Electrochemical noise records revealed passivation process during the monitoring period, under all conditions studied, except for the sensitised specimen in 4M nitric acid (323 K), which showed localised attack. The results showed an inverse relation between EN resistance and corrosion activity. An increase in nitric acid concentration resulted in an increase in corrosion activity, while increasing the electrolyte temperature increased the corrosion activity marginally. A profound increase in corrosion activity occurred for the sensitised specimen in nitric acid when compared to the solution annealed specimen, but the increase was marginal in simulated HLW. The results are detailed in the paper.

Corrosion Behavior of Nitrogen-Containing Stainless Steel in Nitric Acid and Chloride Environments

The corrosion resistance of Type 304LN (UNS S30453) stainless steel containing nitrogen compositions of 0.132 wt%, 0.193 wt%, and 0.406 wt% in nitric acid (HNO3) and chloride medium is investigated in the paper. Increasing the nitrogen content in the steel showed no deleterious effect on corrosion resistance in HNO3. The role of nitrogen in enhancing the pitting corrosion resistance was observed on increasing the nitrogen content from 0.132 wt% to 0.193 wt%. Further increase in nitrogen content to 0.406 wt% was found detrimental, owing to the formation of chromium nitride and manganese-rich precipitates along the grain boundaries. The results are presented in the paper.

Methodology based on potential measurement for predicting corrosion behaviour of SS 304L in boiling nitric acid containing oxidising ions

Austenitic stainless steels like SS 304L are prone to intergranular corrosion (IGC) in boiling nitric acid media. A major cause is sensitisation induced in the heat affected zone of the weldments. Developments in sensitisation resistant materials have lead to the minimisation of degradation due to IGC. Corrosion in nitric acid medium is essentially controlled by oxidising potentials in the transpassive potential regime. The corrosion potential of stainless steel in nitric acid is a function of the concentration of acid, temperature and concentration of specific oxidising ions. In this work, a ‘master curve’ for the dependence of corrosion rates on the applied potentials was generated for type 304L stainless steel (nitric acid grade) in 6M nitric acid at near boiling (95°C) condition. The master curve was validated by measuring the corrosion rates at 48 h exposure in 6M near boiling nitric acid, in which various oxidising ions had been added. It was illustrated that there is a threshold potential (at transition to transpassivity) above which the non-sensitised stainless steel also undergoes IGC. A methodology for the prediction of corrosion rate has thus been proposed that can be applied to austenitic stainless steels at any given operating condition/component in operating plants where nitric acid media are used as process fluid. The effect of the temperature/area ratio of stainless steel on corrosion has been illustrated.

Corrosion Behavior of Type 304L Stainless Steels in Nitric Acid Containing Free and Complexed Fluoride

Abstract The corrosion behavior of Type 304L (UNS S30403) nitric acid grade (NAG) stainless steel in boiling 9 M and 1 M nitric acid (HNO3) and with the addition of 0.03 M sodium fluoride (NaF) and with fluoride complexed with 0.06 M to 0.15 M aluminum nitrate (Al[NO3]3) and 0.015 to 0.0375 M zirconium nitrate (Zr[NO3]4) has been established. The corrosion behavior has also been studied using potentiodynamic polarization in the same environments at room temperature and at near boiling temperature and correlated to the measured corrosion rates. It was shown that the fluoride addition accelerates anodic dissolution. The surface film formed on stainless steel was analyzed using x-ray photoelectron spectroscopy to show that fluorides do not remain attached to the surface. The effect of different ratios of complexing with Al(NO3)3 and Zr(NO3)4 has been studied, showing more effectiveness of zirconium. The corrosion behavior of Types 304L, 304L (welded), 310L (UNS S31000) stainless steels and Alloy 690 (UNS N06...

Corrosion Estimation of Stainless Steel in Nitric Acid by an Optoelectronic Instrument Based on Diffuse Light Scattering Pattern Measurement

This paper presents the design and implementation of an optoelectronic instrument for measuring corrosion of metal surfaces, based on measurement of lightwave scattering pattern. The instrument consists of a thin beam light emitting diode (LED) that illuminates a tiny spot on the metal surface, and an array of photodiodes spread over a hemispherical structure covering the surface to record the light scattering pattern. A mathematical model of light scattering by a corroded metal surface is constructed in which a newly defined corrosion factor is correlated to light scattering pattern. The corrosion factor derived from the scattering pattern gives a measure of the degree of corrosion in a scale from 0 to 100. The temporal behavior of corrosion of stainless steel samples immersed in nitric acid of various concentrations is presented graphically. A semi empirical mathematical model describing the corrosion and dissolution processes in terms of the well-known bilogarithmic laws fits very well with the experimental results. The measured corrosion factor and the corresponding roughness factor as measured by an atomic force microscope are compared to show the relation between the two.

Assessment of Galvanic Corrosion in Galvanic Couples of Sensitized and Nonsensitized AISI Type 304 Stainless Steel in Nitric Acid

Assessment of Galvanic Corrosion in Galvanic Couples of Sensitized and Nonsensitized AISI Type 304 Stainless Steel in Nitric Acid

Correlation between composition of passive layer and corrosion behavior of high Si-containing austenitic stainless steels in nitric acid

Austenitic stainless steels with 18% Cr have a good corrosion behavior in pure nitric acid. However, when oxidizing power of the solution increases, this kind of stainless steels faces a severe intergranular corrosion. Adding a sufficiently high concentration of silicon to the steel avoids this type of corrosion: in oxidizing solutions, those stainless steels exhibit generalized corrosion but their dissolution rate is higher than the one of stainless steels without silicon. To find out the role of silicon on such effects, the corrosion behavior of two different stainless steels with equivalent chromium content but with different silicon content (304L steel and Uranus S1N) has been studied in concentrated nitric acid solutions. Correlations have been evidenced between the passive layer composition investigated by XPS analysis and the corrosion behavior characterized by electrochemical techniques. The presence of silicon in the steel changes neither the oxidation state of chromium or iron, nor the ratio between iron and chromium in the passive layer. Silicon is present in the passive layer in an important content (35 at.%) and thus decreases the chromium content of the passive layer (80 and 50 at.% respectively for 304L steel and Uranus S1N after nitric passivation). Uranus S1N exhibits a less protective passive layer and so its generalized corrosion rate is higher than the one of 304L steel. A selective deposition of platinoïds highlights differences of polarization distribution on the surface between the grain boundaries and grain faces for theses steels. For Uranus S1N, the similar electrochemical behavior of grain boundaries and faces might be connected with the homogeneous silicon distribution.

Corrosion assessment of type 304L stainless steel in nitric acid

AISI type 304L stainless steel (SS) was assessed for its corrosion resistance in nitric acid solution. The effect of variation in nitric acid concentration (1 to 10N) and temperature (298 K, 313 K, 333 K, 348 K) on the corrosion resistance of 304L SS was investigated using potentiodynamic polarisation studies. The corrosion resistance of the alloy was also studied in 1N nitric acid containing different concentrations of chloride ion (1000, 5000, and 10 000 ppm) in order to understand the tendency to pitting corrosion. The results show that the corrosion resistance of the material deteriorated for acid concentrations greater than 4N. The temperature of the acid was found to have a profound effect on the corrosion resistance, with corrosion becoming more prominent at temperatures of 333 K and above. Chloride ions up to a concentration of 10 000 ppm were found to have no effect on the pitting resistance of the material studied.

Effects of Cold Work, Sensitization Treatment, and the Combination on Corrosion Behavior of Stainless Steels in Nitric Acid

Abstract Corrosion behavior of two stainless steels (SS) was investigated in nitric acid (HNO3) for the effect of cold work (CW), sensitization heat treatment (Sens.), and a combination (CW + Sens.). The corrosion rate of the solution-treated type 304 SS (UNS S30400) with extra-low carbon (type 304ELC SS [UNS S30403]) increased with time and reached constant values after 1,000 h of immersion. However, constant corrosion rates were obtained for 25% Cr-20% Ni-Nb (type 310Nb SS [UNS S31040]) from the initial stage of immersion. CW mitigated corrosion of the solution-treated SS. The effect of CW was different on the two types of SS, with the sensitization heat-treated type 304ELC SS showing higher corrosion rates and type 310Nb SS lower corrosion rates by CW. Corrosion resistance of type 310Nb SS was superior to type 304ELC SS after all treatments. Chromium concentration of the sensitization-treated type 304ELC SS was lower in the grain-boundary region than of the solution-treated one, although no chromium ca...

Effect of dissolved chromium species on the corrosionof stainless steel in nitric acid

The effect of Cr(vi) species in HNO3 (concentrations 15–3m) on the corrosion rate of stainless steel has been investigated. The gaseous phase over the HNO3 was carefully controlled using Ar, NO, NO2 or N2 purging. With Ar purging the corrosion rate increased when the Cr(vi) concentrations were above 0.05m. There was evidence that the reduction of Cr(vi) leads to insoluble Cr reduction products on the surface of the steel. Sparging of nitric acid by NO and/or NO2 caused the reduction of any Cr(vi) species present in the solution, to Cr(iii) in a few minutes. However, with no Cr(vi) present, the effect of continuous purging with NO and/or NO2 was to increase the steel corrosion rate when compared with Ar purged solutions, due to catalysis of nitrate reduction by the NOx. The conversion of Cr(iii) to Cr(vi) by nitric acid was shown to require high concentrations of nitric acid, high temperatures and low partial pressures of NO2 over the liquid phase.

酸化性イオンを含む硝酸中におけるステンレス鋼の腐食挙動に及ぼすCrおよびPの影響

酸化性イオンを含む硝酸中におけるステンレス鋼の腐食挙動に及ぼすCrおよびPの影響