Dissolution Of Chromium Research Articles

Corrosion mechanisms of 316L stainless steel in polyphosphoric acid at elevated temperature: Behavior and mechanistic insights

The performance of 316 L stainless steel in polyphosphoric acid (PPA) at high temperature, remains a subject of considerable interest. Through weight-loss tests, electrochemical analyses, SEM, XRD, XPS, and ICP, the corrosion process of 316 L in PPA and the formation of corrosion products are systematically examined. The results elucidate a multi-step corrosion mechanism involving selective dissolution of sulfur and chromium, succeeded by the involvement of additional metallic elements, notably iron, in the construction of the corrosion product layers. This study contributes to a deeper understanding of 316 L stainless steel corrosion in PPA environments, offering insights crucial for corrosion mitigation and material design.

Measurements of UF4/UF3 ratio for redox potential control in u-bearing fluoride salt

Redox potential control is important in mitigating corrosion in molten salt reactors (MSRs) during operation. This study has developed a methodology for establishing the operational boundaries, both upper and lower, of the ratio of UF4 to UF3 (UF4/UF3) for redox potential control in U-bearing fluoride salts by measuring the equilibrium quotient. The upper limit for UF4/UF3 is determined by the potential for chromium dissolution, while the formation of uranium carbides governs the lower limit. By applying the methodology, the research experimentally determined the UF4/UF3 ratio in NaF-KF-UF4 salt at temperatures ranging from 873 K to 1023 K. To determine a stable operational range, the range of the operation temperature of the MSR must be considered, the stable range of the ratio is depicted as a trapezoid, with the upper and lower limits serving as the bases of the trapezoid.

Electrodeposited CrMnFeCoNi Oxy-carbide film and effect of selective dissolution of Cr on oxygen evolution reaction

High entropy compounds were proven to exhibit excellent catalytic activity. Here, a series of amorphous CrMnFeCoNi Oxy-carbide films were successfully synthesized by one-step electrodeposition. As demonstrated, the film presented superior electrocatalytic activity for oxygen evolution reaction (OER) with an overpotential of 295 mV at a current density of 10 mA/cm2. Uniquely, selective dissolution of Chromium (Cr) was observed, which increased the catalytic activity and showed high stability under a large current density of up to 400 mA/cm2. Cr dissolution not only increased the surface area but also improved the conductivity due to newly formed metal-metal bonding, promoting electron transfer and improving OER performance. As revealed by density functional theory (DFT) calculations, Cr-dissolution mediates the bonding of OER intermediates over surface active sites and ultimately reduces OER overpotential. The one-step electrodeposition method and the micro-dissolution mechanism provided a potential way to design and prepare high entropy compound electrodes, aiming to achieve efficient water electrolysis.

The preparation and formation mechanism of ferrochrome slag-based high-strength ceramic aggregate and its impact on the performance of concrete

Solid waste, such as ferrochrome slag (FCS), has been extensively studied for its potential use as a construction material. This research focuses on utilizing FCS as the primary raw material to produce a high-strength ceramic aggregate, referred to as FCS-HSCA. The impact of calcination parameters on the performance of FCS-HSCA was investigated, while the underlying transformation mechanism was comprehensively explored. Subsequently, concrete with FCS-HSCA was prepared, and its influence on the performance of concrete was evaluated. The results reveal that the optimal performance of FCS-HSCA is achieved with a compressive strength of 310.3 MPa, a water absorption of 0.27%, and an apparent density of 2930 kg/m3. These characteristics are associated with specific parameters during the calcination stages, namely a preheating temperature of 1100 ℃, preheating time of 60 min, calcination temperature of 1500 ℃, and calcination time of 180 min. Moreover, the increased crystalline phases promote the solid dissolution of chromium into Mg(Al1.5Cr0.5)O4, and the occurrence state of chromium is stable during the preparation of FCS-HSCA. This results in a decreased leaching value from 0.439 mg/L to 0.188 mg/L, reducing the impact on the environment and human health. Additionally, replacing FCS with FCS-HSCA in concrete enhances its compressive strength from 59.9 MPa to 66.1 MPa. This improvement is attributed to a notable reduction in the diameter of pores on the surface of FCS-HSCA, leading to a denser structure and improved bondability with cementitious composites. Finally, this novel approach maximizes the utilization of material characteristics while enhancing the stability of waste FCS.

Corrosion mechanism of cold forged 316 stainless steel in molten FLiNaK salt

This study examined how cold forging (CF) affects the corrosion of 316 stainless steel (SS) in molten FLiNaK salt at 700 °C for 48 h. CF samples had two corrosion areas: one near the top and another displaying intergranular corrosion (IGC). Samples with lower CF (5–30 %) showed more IGC, while the 50 % CF sample had less IGC but the shallowest corrosion depth. This was due to the increased number of grain boundaries, which raised the potential corrosion initiation sites, and certain grain boundaries promoting chromium dissolution, thus enhancing IGC.

Dissolution of chromium containing oxides by dissolved ozone (DOz) coupled with permanganate: A novel method to decontaminate radioactive surfaces of nuclear facilities

Permanganate-based method for the dissolution of chromium-containing oxide involves a multi-step and multi-cycle procedure, which generates a large volume of waste. In nuclear facilities, the waste will be radioactive and thereby the handling becomes challenging. In the present study, coupling dissolved ozone with permanganate simplifies the procedure and reduces the waste generated. A comparative investigation on the dissolution of chromium substituted nickel/cobalt ferrites by permanganate, dissolved ozone (DOz) and DOz coupled with permanganate have proved the synergistic effect. Further, the percentage of Cr/Fe in the lattice influences the dissolution process. Cr-substituted nickel ferrite dissolved at a higher rate compared to than Cr-substituted cobalt ferrite.

Effect of the Structure of Passive Oxide Films and Surface Temperature on the Rate of Anodic Dissolution of Chromium–Nickel and Titanium Alloys in Electrolytes for Electrochemical Machining: Part 1. Anodic Dissolution of Chromium–Nickel Steel in a Nitrate Solution

Effect of the Structure of Passive Oxide Films and Surface Temperature on the Rate of Anodic Dissolution of Chromium–Nickel and Titanium Alloys in Electrolytes for Electrochemical Machining: Part 1. Anodic Dissolution of Chromium–Nickel Steel in a Nitrate Solution

Excellent high temperature corrosion resistance of 304 stainless steel immersed in purified NaCl–MgCl2 eutectic salts

Corrosion behaviors of 304 stainless steel (304SS) in NaCl–MgCl2 eutectic salts with purification treatment at high temperature were firstly studied by static immersion under Ar. The weight loss of 304SS were 1.61 mg/cm2 at 500°C and 1.80 mg/cm2 at 600°C, respectively. The annual corrosion rate of 304SS was less than 100 μm, indicating that 304SS possessed excellent corrosion resistance at high temperature. The intergranular corrosion of 304SS at high temperature was accompanied by dissolution of active chromium and iron. Its corrosion of 304SS gradually intensified with temperature increase, especially after 600°C, which provided strong data support for materials selection at high temperature in the future. Owing to the compatibility of 304SS with NaCl–MgCl2 salt, 304SS is suitable for use in the container at high temperature.

Corrosion resistance of high nickel alloys in solar salt at 600 °C for up to 4000 h

This study focuses on the time dependent performance of the corrosion resistance of IN625, H230 and 740H alloys in the solar salt (60 wt% NaNO 3 , 40 wt% KNO 3 , at 600 °C) for up to 4000 h. Alloy IN625 showed the lowest mass change with parabolic oxidation kinetics that tends to stabilize with exposure time. Both 740H and H230 alloys deviated from the parabolic oxidation behavior beyond the 3000 h of exposure. Alloy 740H showed the highest mass loss due to the nonuniform surface oxidation and the high chromium dissolution rate. Internal oxidation was noticed with Alloy H230 due to the high tungsten concentrations. • Oxidation of Alloy IN625 was found to follow a parabolic behavior that tends to stabilize with time. • Oxidation of 740H and H230 alloys deviated from the parabolic behavior after 3000 h of exposure. • Alloy 740H showed a nonuniform oxide layer and so has the highest mass loss. • Alloy H230 suffered of internal oxidation due to the high tungsten concentration.

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

It is shown that, in high-rate pulsed galvanostatic anodic dissolution of type CSN17335 and AISI 304 chromium–nickel steels in electrolytes for electrochemical machining (ECM) (chloride, nitrate, and mixed chloride–nitrate solutions with a conductivity of 0.15 S/cm) using microsecond pulses with a duration of 20–2000 μs and current densities in the range of 1–100 A/cm2, a substantial fraction of charge (up to ~40%) is spent on the formation of a passivating oxide film with a semiconducting behavior. The electrochemical treatment therefore directly involves the oxide film, not the alloy. As a consequence, the current efficiency of ECM of these materials is ~60–70%, depending on the alloy composition. When using direct current, the rate of machining increases as a result of the oxide film breakdown due to its thermokinetic instability (“thermal explosion”) caused by a rise in the surface temperature.

High-temperature corrosion behavior of Inconel 625 alloy in a ternary molten salt of NaCl-CaCl2-MgCl2 in air and N2

Chloride molten salt is a promising material for heat transfer and storage under high-temperature conditions. However, the metal materials in pipes and vessels may corrode when exposed to high-temperature molten salts. Corrosion causes serious safety accidents in commercial concentrating solar power systems. In this paper, the corrosion behavior of Inconel 625 (In625) alloy was investigated by immersing In625 alloy in a ternary molten salt of NaCl-CaCl2-MgCl2 with varying contents of MgCl2 and under various atmospheres at 600 °C for up to 21 days. The results show that chromium dissolution is the main corrosion process of In625 when immersed in the ternary molten salt. The corrosion rate was higher at the beginning of the corrosion process but gradually decreased with increasing corrosion time. This study found that MgO and MgCr2O4 were produced in the corrosion layer. MgO and MgCr2O4 play a key role in preventing corrosion in air. However, the corrosion layer cracks in N2. Thus, MgO and MgCr2O4 cannot play an acceptable protective role. Additionally, this study found that O2, H2O and MgOH+ significantly affect the corrosion behavior of In625 in different atmospheric conditions.

Effects of Alkali on Water Soluble Hexavalent Chromium in Ordinary Portland Cement.

Due to the toxicity and mobility of chromium, the disposal of chromium-containing waste is a pressing issue. Co-processing of chromium-containing waste in a cement kiln is currently one of the most effective methods. However, the presence of water-soluble hexavalent chromium (Cr(VI)) in cement limits the use of this method. In this study, Na2CO3 was used to simulate alkali in industrial raw materials to investigate the pattern of influence of alkali content on water-soluble hexavalent chromium. The mechanisms associated with the oxidation and dissolution of chromium were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma emission spectrometry (ICP-OES). The proportion of Cr(VI) in the clinker detected by XPS increased rapidly with increasing alkali content. In the cement slurry system, alkali promotes more hexavalent chromium leaching by influencing pH and other ion concentrations (Ca2+, SO42−). Therefore, the addition of alkali to either the raw meal or to the cement slurry system will favour an increase in the water-soluble Cr(VI) content. This study may provide theoretical guidance for the preparation and use of clinkers containing chromium.

A Closer Look at the Passivity and Transpassive Dissolution of Chromium Using Atomic Spectroelectrochemistry

The dissolution and growth kinetics of the passive film upon chromium (Cr) in 0.1 M NaCl was studied using atomic spectroelectrochemistry. The dissolution rate was independent of applied potential in the passive region, and increased exponentially with increasing potential in the transpassive region. The growth kinetics of the passive film upon Cr in the passive state was consistent with the assumptions of the point defect model. The charge balance analysis established an intermediate potential region whereby the growth rate of Cr2O3 layer was higher than the dissolution rate in the transpassive state. The interdependence of oxidation and dissolution rate of Cr in non-steady state was revealed and its significance to the passivity of Cr-containing alloys was discussed.

Dissolution of Chromium from Steelmaking Slag–Cr-containing Mineral Phases and Synthetic Slags–

Dissolution of Chromium from Steelmaking Slag–Cr-containing Mineral Phases and Synthetic Slags–

In-situ interstitial alloying during laser powder bed fusion of AISI 316 for superior corrosion resistance

• L-PBF of a 316L admixed with 2.5 wt% Cr 2 N enhanced the Cr and N contents as compared to 316L. • A nitrogen content of 0.31 wt% in solid solution was obtained. • The parts were fully austenitic, exhibiting the favorable cellular substructure. • The enhanced nitrogen content improved corrosion resistance and hardness as compared to 316L. • The results show an alternative to manufacturing of high nitrogen steels. The present work explores for the first time additive manufacturing of powder mixtures consisting of Chromium Nitride (Cr 2 N) and AISI 316L with laser powder bed fusion (L-PBF). The addition of 2.5 wt% Cr 2 N to an AISI 316L powder resulted in the successful dissolution of both chromium and nitrogen into a fully austenitic stainless steel microstructure. The nitrogen content was augmented from 0.09 wt% in the as-delivered AISI 316L powder to 0.31 wt% in the L-PBF built part, causing a slight expansion of the austenite lattice. Elongated austenite grains with an internal cellular substructure were obtained in both the Cr 2 N modified 316L and the 316L specimens manufactured by L-PBF. The addition of nitrogen (and chromium) from Cr 2 N resulted in a Vickers hardness increase of about 40 HV 0.1 , mainly by interstitial solid solution strengthening. The modification of 316L by the addition of Cr 2 N significantly improved the corrosion resistance. The improved hardness and corrosion resistance while retaining the manufacturability and cellular microstructure illustrate the potential for modifying the composition and properties of L-PBF 316L with targeted dosing with Cr 2 N powders.

Dealloying Behavior in Ni-Cr-Fe Alloys As a Precursor to SCC in Boiling Caustic Environments

Experiments have shown that the susceptibility of Ni-Cr-Fe Alloys to dealloying, and subsequently stress corrosion cracking (SCC), highly depends on alloy composition and electrochemical potential. Dealloying is defined as the selective dissolution of the more active elements in an alloy (e.g., Cr and Fe in a Ni-based alloy). A dealloying process results in a remnant nano-porous layer on the surface that could be a precursor to SCC by a mechanism known as film-induced cleavage (FIC) where cracks propagate through this layer with sufficient velocity to promote energy transmission into the underlying metal resulting in cleavage fracture. Presence of a threshold amount of a more noble element could theoretically suppress this phenomenon by surface diffusion. This was investigated further by previous researchers, and the percolation theory of materials was hypothesized that states that the more noble element in an alloy creates a percolating mass that would limit the ability to retain a connected pathway of the reactive elements from the surface given it reaches a certain threshold of the mass of the material. This percentage was estimated to be between 50-60% for most alloying systems and termed the parting limit. In this study, percolation theory and dealloying is further explored by exposing several Ni-based and Fe-based alloys with varying percentages of Ni to boiling caustic solutions (50% NaOH) and evaluating their dealloying behavior.As mentioned, dealloying highly depends on electrochemical potential and is believed to occur above a threshold potential known as the dealloying critical potential. The dealloying critical potential is defined as the condition at which a transition occurs from a “passivated” alloy surface to the sustained formation of a bi-continuous porous structure. It can be identified by running an anodic polarization scan and initially matching anodic peaks to a pH-potential diagram (Pourbaix diagram) to evaluate the potential dissolution behavior. Bench-top electrochemical measurements were conducted to find the dealloying critical potential and make a correlation between this potential and alloys’ composition. The figure attached shows the anodic polarization scan results for all alloys included in the study in 50% NaOH at 140°C. It was observed that for the samples with high Ni content (i.e., Alloy 600 and Alloy 690) there was only a single active peak, which indicates transitioning to passivation and inhibition of dealloying. All other materials were susceptible to dealloying. Electron microscopy techniques were used to analyze all the samples used in the figure after exposure to 50% NaOH at 140°C at open circuit potential (OCP) and during a potentiostatic hold at the dealloying critical potential. Scanning electron microscopy (SEM) imaging followed by energy dispersive X-ray spectroscopy (EDS) revealed varying degrees of dealloying, with low Ni-containing alloys showing greater severity.The role of dealloying as a precursor to SCC was also evaluated by utilizing U-bend samples for Alloy 690, Alloy 800, and SS 304. The findings were in-line with previous dealloying result; the alloys with Ni content below the parting limit, SS304 and the Alloy 800, both underwent SCC after 48 hours of exposure to 50% NaOH solution at 135 °C, while the Alloy 690 sample (~60Ni) did not show any signs of cracking. A peculiar phenomenon was also noted for alloys containing Mo where it is seen that their dissolution current is approximately two folds higher than their counterparts with approximately the same Ni content. For example, when comparing SS 304 and SS 316 or Alloy C-276 and Alloy G-35. A possible explanation for that is the electrochemical behavior of Mo in caustic conditions where it is shown in its pourbaix diagram that dissolution occurs over a wider range of pH and potential in comparison to the other alloying elements. This earlier dissolution can possibly create more terrace sites on the surface that could accelerate the dissolution of iron and chromium. However, further studies are needed before a conclusion can be reached. Further work has also been conducted on Alloy 800 under the same conditions to evaluate the possibility of controlling the geometry of the dealloyed layer. The results so far indicate that the time of exposure and the electrochemical potential are critical in controlling the geometry of the dealloyed layer. Parallel studies are being conducted on SS 304 to evaluate the effect of Pb on extending the dealloying regime. The results so far have shown that the addition of Pb would shift the OCP more positively towards a region of passivity. It was also noted that dealloying kinetics is hindered in comparison to pure caustic conditions. However, SCC may still be possible with dissolved Pb present. Figure 1

Environmental degradation of electroplated nickel and copper coated SS316H in molten FLiNaK salt

Corrosion of nickel and copper electroplated coatings on SS316H in molten FLiNaK salt was studied. 500- and 1000-hour static corrosion tests were performed in molten FLiNaK at 700 degrees Celsius. Characterization of the coatings following corrosion indicated that they did not degrade in the molten salt during the corrosion experiment and fully protected the underlying SS316H from chromium dissolution. Interdiffusion between the copper coating and SS316H was extremely limited, interdiffusion between the nickel coating and SS316H. Diffusion modelling revealed that the nickel coatings still significantly reduced chromium dissolution over 60 years despite the interdiffusion.

Influence of sulfate and nitrate ions on kinetics of dissolution of chromium (III) α-CrOOH hydroxide

Chrome is part of many alloyed steels and wear-resistant composite electrochemical coatings. Chromium films are used as firming coatings of metal products and cutting tools in electronic technology. Chromium alloys are used in industry for the manufacture of parts of machines and mechanisms intended for operation in extreme conditions for the formation of durable coatings on metal and other surfaces. Therefore, the question of optimizing the technologies of etching, leaching and enrichment of chromium-containing ores. The paper discusses the kinetic features of the dissolution of chromium hydroxide (III) and proposes the optimal mechanism for the dissolution of chromium hydroxide (III) α-CrOOH in the presence of various ions (sulfate and nitrate) in acidic environments. The influence of various mineral acid ions on the kinetics of dissolution of chromium hydroxide (III) α-CrOOH in acidic environments is considered. The mechanism of dissolution of chromium hydroxide (III) α-CrOOH is proposed from the standpoint of various model representations. The most important direction of research in metallurgy is the selection of effective reagents and determining the main kinetic parameters of dissolution processes. An analysis of data on the influence of the nature of mineral acids on the rate of dissolution of chromium hydroxide (III) α-CrOOH is carried out. To calculate the empirical values of kinetic parameters, the methods of regression analysis were used. In order to select the technological regimes of the selective extraction of valuable metals from raw materials, the following parameters are considered (with acid and anions, T, pH).

Ab-initio investigation of the effect of adsorbed salts on segregation of Cr at the Ni (100) surface

The dissolution and depletion of chromium (Cr) in salt facing nickel (Ni) alloy surfaces is one of the predominant degradation mechanisms of structural components in molten salt technology. In this work, we use density functional theory to investigate the role of electronic level interactions that may underlie the depletion phenomenon of Cr in a Ni 100 surface exposed to various adsorbed salt species. Our results show that, under vacuum, Ni preferentially segregates to the surface layer. Conversely, in the presence of adsorbed anionic salt species (e.g., chlorine (Cl), fluorine (F) or the impurity oxygen (O)) Cr segregation becomes more favorable. In these cases, Cl has the weakest effect on segregation, while O has the strongest effect. Our analysis reveals the strong correlation between Cr segregation and the amount of valence charge transferred between the Cr atom and surface adsorbate: the greater the charge transfer, the lower the segregation energy. We also show that, when considered, secondary cations screen Cr-anion interactions, which in turn reduce the magnitude of the anions effect on segregation. These results shed light on the role of salt impurities likely play in the overall corrosion phenomena in molten salt environments. This work provides insights into the atomic level interactions fundamental to molten salt corrosion and on the importance of maintaining salt purity.