Dissolution Of Chromium Research Articles

Grind hardening: Correlations between surface modifications and applied internal loads

During machining, the machined surface is modified due to the thermal, mechanical and chemical loads applied by the used process. Temperature, temperature gradients, strain and strain gradients lead to a change of the microstructure in the surface zone. Internal material loads are difficult to access by experimental measuring methods during processing. Therefore, this work aims at solving the inverse problem by determining the resulting internal thermal loads during grind hardening based on the characterized surface modifications. During grind hardening, high thermal loads are applied to the workpiece. This leads to a phase transformation in the surface zone. Different electron microscopic investigations like EBSD and EPMA are used to determine the austenite grain size, the resulting grain size, phases and the dissolution and diffusion of carbon and chromium. Based on that, conclusions can be drawn about the heating rate, period of heating time, cooling rate and the achieved maximum temperature. In this work, the steel 42CrMo4 (AISI 4140) was used with a ferrite-pearlite and a quenched and tempered matrix. It was found out, that the microstructure varies depending on the penetration depth and the changing temperature field. Analytically calculated temperature profiles were compared to temperature profiles which were estimated by material modifications in different penetration depths. The acquired data also give a deep insight into the mechanisms of phase transformation for short time heat treatments and the influence of inhomogeneous matrix material on the modified surface zone.

Dissolution of nickel and chromium from Ni-Cr-Fe-O oxide by oxidative treatment with permanganate

Ni-Cr-Fe mixed oxides (NiCrxFe2-xO4) are formed as a corrosion oxide films on structural material surface of coolant or heat transport circuit in water-cooled nuclear reactors. Study on the dissolution behavior of these oxides forms a critical part in development of an efficient chemical decontamination process for the nuclear industry. The present study describes release of Ni and Cr in permanganate medium from the chromium substituted nickel ferrite and also on the mechanistic aspects of oxide dissolution. These oxides were synthesized by combustion method and characterized by the XRD, XPS and Raman spectroscopy. The dissolution kinetics of oxide in permanganate medium was modeled by Shrinking Sphere Model and General Kinetic law Equation. The rate constant for oxide dissolution increased with the Cr substitution in nickel ferrite. Presence of chromium in the oxide lattice affect the release of nickel and also a minimum chromium concentration in the lattice is required for the release of nickel from the oxide lattice during the permanganate treatment. However, when the chromium substitution (x) is increased to 0.6 and above, the nickel release was lowered.

Corrosion of an India produced RAFM steel in flowing lead-lithium eutectic

Reduced Activation Ferritic Martensitic (RAFM) Steel has been specifically developed to serve as a structural material for fusion reactor applications. To establish the corrosion compatibility of an India produced RAFM steel (RAFMS) with Pb-16at.% Li eutectic (Pb-16Li), an electromagnetic pump driven loop has been installed and the compatibility of this RAFMS material has been tested in liquid Pb-16Li at 773K for 5, 000h of exposure at a flow velocity of 0.6–1.5m/s. A corrosion rate of 47–50μm/y was established for the RAFM steel from weight loss measurements and the rate was found to depend on the variation in local flow velocity over the exposed samples. The corrosion attack by liquid Pb-16Li was found to be non uniform in nature which resulted in the formation of undulations over the exposed RAFMS surface. The corrosion mechanism was governed by dissolution of iron and chromium from the RAFMS matrix into the molten Pb-16Li accompanied by enrichment of tungsten near the exposed surface.

Selection of leaching media for metal dissolution from electric arc furnace dust

This study focuses on selective zinc and lead leaching from Electric Arc Furnace (EAF) dust in order to turn this major source of steel plant pollution into a recyclable Fe-rich feed material for the steel manufacturing process. The raw material investigated comprises of engineering steel plant EAF dust that contains zinc 33.2%, iron 17.9%, manganese 2.5%, lead 1.6% and chromium 0.2%. The 16 different leaching media investigated include: (i) acids, - nitric, sulfuric, hydrochloric, aqua regia, citric, acetic, formic, phosphoric, and oxalic; (ii) alkalines - sodium potassium and ammonium hydroxide and (iii) other lixiviants like distilled water, ethanol, ethylene glycol and acetone.The study shows that four media - 10% aqua regia, 1.2 M hydrochloric, 0.94 M citric and 1.5 M nitric acids - resulted in high (>75%) zinc extraction with good Fe selectivity (iron extraction <6% in 1.2 M hydrochloric acid, 10% aqua regia and <15% with 0.94 M citric and 1.5 M nitric acids). Furthermore, these four leaching media showed partial dissolution of manganese (21–35%), chromium (36–65%) and lead (18–60%), although the highest lead removal was achieved with 1.75 M acetic acid. In terms of zinc selectivity, it was found that ammonium outperformed both sodium and potassium hydroxide.

Accelerated corrosion and oxide dissolution in 316L stainless steel irradiated in situ in high temperature water

316L stainless steel samples were irradiated with a proton beam while simultaneously exposed to high temperature water with added hydrogen (320 °C, 3 wppm H2, neutral pH) to study the effect of radiation on stainless steel corrosion. Irradiated samples had thinner and more porous inner oxides with a lower chromium content when compared to unirradiated samples. Observations suggest that depletion of chromium from the inner oxide can be attributed to the dissolution of chromium-rich spinel oxides in irradiated water, leading to an accelerated rate of inner oxide dissolution. Sample areas which were not irradiated, but were exposed to the flow of irradiated water were also found to be porous and deficient in chromium, indicating that these phenomena can be attributed primarily to water radiolysis. A new empirical equation for oxide growth and dissolution is used to describe the observed changes in oxide thickness under irradiation. An experiment in which a stainless steel sample was exposed to high temperature water (320 °C, 3 wppm H2, neutral pH) without irradiation, and then exposed for a second time with irradiation was conducted to observe the effect of irradiation on a pre-formed protective film. After the irradiated exposure, the sample exhibited chromium loss in regions which were directly irradiated, but not on regions exposed only to irradiated water, suggesting that a pre-formed protective oxide may be effective in preventing chromium loss due to irradiated water. Additionally, this observation suggests that enhanced kinetics under irradiation may have accelerated dissolution of chromium from the inner oxide.

Positive current collector for Li||Sb-Pb liquid metal battery

Abstract Corrosion in grid-scale energy storage devices adversely affects service lifetime and thus has a significant economic impact on their deployment. In this work, we investigate the corrosion of steel and stainless steels (SSs) as positive current collectors in the Li||Sb-Pb liquid metal battery. The erosion and formation of new phases on low-carbon steel, SS301, and SS430 were evaluated both in static conditions and under cell operating conditions. The cell performance is not adversely affected by the dissolution of iron or chromium but rather nickel. Furthermore, the in situ formation of a Fe-Cr-Sb layer helps mitigate the recession of SS430.

Role of iron and chromium in the photocatalytic activity of titanium dioxide films on stainless steel

Photocatalytically active titanium dioxide films have been formed on stainless steel grids via sol–gel process followed by heat treatment in the temperature range of 450–550°C. During UV irradiation of the films in an aqueous solution of the Rhodamine B dye and in distilled water we have detected iron and chromium dissolution from uncoated grid regions and the deposition of iron and chromium compounds onto the titanium dioxide surface. The deposition rate of these compounds increases with annealing temperature, which leads to a decrease in the photocatalytic activity of the films.

Conversion of carbon dioxide to methanol through the reduction of formic acid on chromium

BACKGROUND Formic acid (FA) can be produced from CO2 by high rate and high percentage current efficiency (%CE) which exceeds 90% on some metals. This work aims at the electrochemical conversion of formic acid to methanol (MeOH) by a two- step process including the conversion of CO2 to formic acid in the first and the reduction of formic acid to MeOH in the second. RESULTS The main products of the electrochemical reduction of FA in 85% H3PO4, at 80°C on chromium were methyl formate (HCOOMe), MeOH and CH4. The rate of the reduction increased both by increasing the negative potential and the concentration of FA. The total %CE in all experiments exceeded 100% and this was attributed to the cathodic dissolution of chromium which provided an additional reduction capacity. The selectivity to MeOH and HCOOMe was between 89 and 98% and the highest current density was 13 mA cm−2, at –0.95 V. CONCLUSIONS FA is selectively reduced to MeOH and its secondary product HCOOMe on a Cr cathode. The experimental results showed that chromium is the most efficient cathode for the reduction of FA. © 2016 Society of Chemical Industry

Photoelectrochemical monitoring of rouging and de-rouging on AISI 316L

Electrochemical conditions for inducing rouging on surface of AISI 316L in quasi neutral aqueous solution are studied. Potentiostatic polarization at 0.6V vs. SSC at pH∼7 allowed growth of colourless passive films with a band gap slightly lower than that estimated for the oxide grown on the SS surface by air exposure due to chromium dissolution. Under stronger anodic polarization (UE=1.5V vs. SSC) coloured passive films are formed, mainly constituted by iron oxide according to their band gap (Eg=2.0eV). Etching in citric acid at 60°C results to be effective in removing rouging.

Occurrence, Origin and Transformation Processes of Geogenic Chromium in Soils and Sediments

Weathering of ultramafic rocks has been linked to the occurrence of elevated concentrations of hexavalent chromium (Cr(VI)) in soils, sediments, and groundwater. Ultramafic rocks and the derived serpentine soils and sediments are encountered in populated areas around the world and present high Cr concentrations, with an average of 2200 and 2650 mg/kg for rocks and soils, respectively. Groundwater concentrations between 0.2 and 180 μg/L have been reported for Cr(VI) in ultramafic areas, exceeding occasionally the most prevalent drinking water limit of 50 μg/L Crtot, the 5 μg/L Cr(VI) limit established in Italy, and the 10 μg/L Cr(VI) limit proposed in California. Cr release in groundwater occurs through the dissolution of trivalent chromium (Cr(III)) from its mineral hosts, followed by sorption of Cr(III) onto high-valence Mn oxides and oxidation to Cr(VI), which desorbs and is mobile at alkaline pH. Recent findings indicate that hydrogen peroxide and birnessite produced on the surface of Cr(OH)3 by heterogeneous oxidation are two additional potential mechanisms. Thus, groundwater concentrations are controlled by a variety of geoenvironmental factors, including climate, soil mineralogy, pH, organic matter, and others. To provide a basis for the evaluation of Cr mobility in ultramafic environments, this paper presents an overview of the mineralogy and geochemistry of Cr-rich rocks, sediments, and soils, along with the weathering and geochemical processes that control the fate and transport in the subsurface.

Formation of Al2O3 diffusion barrier in cold-sprayed NiCoCrAlY/Ni multi-layered coatings on 304SS substrate

Abstract This work deals with a double-layer coating for the corrosion protection of stainless steel (SS) structures used in molten fluoride salt reactors for energy production. It aims to mitigate the dissolution of chromium from stainless steel structures into the molten salts. On 304SS substrates, three coating layers consisting of NiCoCrAlY, Ni(O), and the nickel layer on the top were deposited by cold spraying. The Ni(O) coating was made by using a powder containing active oxygen and prepared by mechanical-alloyed pure Ni powders in ambient atmosphere. The Al 2 O 3 diffusion barrier was evolved by annealing the cold-sprayed coating system in argon at temperatures ranging from 800 to 1000 °C at the interface between NiCoCrAlY and Ni(O) layers. During the annealing, the Al 2 O 3 layer formed with a growth following a parabolic law, resulting from the reaction of the oxygen in the Ni (O) layer with the aluminium in the NiCoCrAlY layer. The coating test conducted at 900 °C for 100 h in argon showed that the Al 2 O 3 layer changed little during annealing and could effectively prevent the diffusion of Fe and Cr from the SS substrate to the upper Ni layer.

High temperature dissolution of chromium substituted nickel ferrite in nitrilotriacetic acid medium

High temperature (HT) dissolution of chromium substituted nickel ferrite was carried out with relevance to the decontamination of nuclear reactors by way of chemical dissolution of contaminated corrosion product oxides present on stainless steel coolant circuit surfaces. Chromium substituted nickel ferrites of composition, NiFe(2−x)CrxO4 (x ≤ 1), was synthetically prepared and characterized. HT dissolution of these oxides was carried out in nitrilotriacetic acid medium at 160 °C. Dissolution was remarkably increased at 160 °C when compared to at 85 °C in a reducing decontamination formulation. Complete dissolution could be achieved for the oxides with chromium content 0 and 0.2. Increasing the chromium content brought about a marked reduction in the dissolution rate. About 40 fold decrease in rate of dissolution was observed when chromium was increased from 0 to 1. The rate of dissolution was not very significantly reduced in the presence of N2H4. Dissolution of oxide was found to be stoichiometric.

Kinetics of mechanochemical dissolution of chromium in iron

The kinetics of solid Fe–Cr solution formation has been studied during mechanical alloying of Fe and Cr powders taken in an atomic ratio of 80: 20. X-ray diffraction and Mossbauer spectroscopy data have been analyzed within the framework of the energetic approach. It has been established that, in this system, reaction product yield N is related to mechanical energy dose D and specific surface area S of Fe nanograin boundaries in an ideal manner: N ~ D 2 at S ~ D and N ~ D at S = const.

Calculating the thermodynamic characteristics of hydrophobic hydration of chromium(III) and cobalt(III) tris-acetylacetonates in water and regularities of their solvation in aqueous alcoholic solvents

Based on the scaled-particle theory, the Gibbs energy of the formation of cavities in the structure of water and some alcohols are calculated for the processes of dissolution of cobalt(III) and chromium(III) tris-acetylacetonates. The contribution from the hydrophobic hydration of the tris-acetylacetonate molecules in water is calculated. The location of the inversion area is clarified for a number of aqueous alcoholic solvents, and the effect the solvent’s macrophysical parameters have on the patterns of tris-acetylacetonate solvation is analyzed.

Characterization and Sulfuric Acid Leaching of Ferrochrome Converter (CRC) Dust

A ferrochrome converter (CRC) is used for removal of silicon and carbon from ferrochrome in stainless steel production. The raw materials are molten ferrochrome and stainless steel scrap, and the process produces a raw material for argon-oxygen-decarburization (AOD). The zinc content prevents the utilization of CRC dust (CRCD). The objective of this work is characterization and sulfuric acid leaching of CRCD and evaluation of formation mechanisms and the effects of mineralogy and microstructure on the hydrometallurgical treatment. CRCD contains critical (Cr, fluorite) and economically important (Fe, Zn) materials. The mineralogy and microstructure of CRCD are complex. The dust has been formed by many mechanisms. Lime and ferrosilicon prove that take-off of solid particles during charging is important. Also, ejection of liquid droplets is considerable because ferrochrome and slag spheres are common. The highest Zn dissolution is 93–94% and at the same time 5–15% of Cr is leached. The existence of zincite explains the high dissolution of zinc. The encapsulation, e.g., magnesiochromite enclosed into glass, explains the low chromium dissolution. The best selectivity for Zn extraction over iron, chromium, and nickel is achieved with 0.5 M, at 30 and 60 °C with both L:S 10 and L:S 20.

Selective recovery of Cr from stainless steel slag by alkaline roasting followed by water leaching

Selective chromium (Cr) leaching from stainless steel slag (SS slag) by alkali roasting followed by water leaching was investigated. The efficiency of the alkali roasting process for Cr leaching was increased by optimizing the mass ratio of alkaline agents (NaOH, and NaOH–NaNO3) to the slag, roasting temperature and time. At the optimum condition (0.67 mass ratio of NaOH to SS slag, 400°C, 2h) of NaOH roasting, chromium leaching was around 83%, while the matrix material was dissolved only to a limited extent (Si 8.0%). Mechanical activation of the SS slag prior to roasting reduced the optimum NaOH to SS slag mass ratio to 0.4. The addition of NaNO3 as an oxidant to the NaOH salt increased Cr leaching to 89% after roasting at 400°C for 2h. The remaining Cr phases in the residue were almost exclusively FeCr alloys. Further chromium dissolution from these alloys is prevented by a passivation layer of Fe oxides as shown by SEM/EDS images. Based on these results, a SS slag recycling process is suggested in which roasting–water leaching followed by water washing to remove Cr yields a residue which has potential for application as a construction material.

Corrosion of 316 stainless steel in high temperature molten Li2BeF4 (FLiBe) salt

In support of structural material development for the fluoride-salt-cooled high-temperature reactor (FHR), corrosion tests of 316 stainless steel were performed in the potential primary coolant, molten Li2BeF4 (FLiBe) at 700°C for an exposure duration up to 3000h. Tests were performed in both 316 stainless steel and graphite capsules. Corrosion in both capsule materials occurred by the dissolution of chromium from the stainless steel into the salt which led to the depletion of chromium predominantly along the grain boundaries of the test samples. The samples tested in graphite capsules showed a factor of two greater depth of corrosion attack as measured in terms of chromium depletion, compared to those tested in 316 stainless steel capsules. The samples tested in graphite capsules showed the formation of Cr7C3 particulate phases throughout the depth of the corrosion layer. Samples tested in both types of capsule materials showed the formation of MoSi2 phase due to increased activity of Mo and Si as a result of Cr depletion, and furthermore corrosion promoted the formation of a α-ferrite phase in the near-surface regions of the 316 stainless steel. Based on the corrosion tests, the corrosion attack depth in FLiBe salt was predicted as 17.1μm/year and 31.2μm/year for 316 stainless steel tested in 316 stainless steel and in graphite capsules respectively. It is in an acceptable range compared to the Hastelloy-N corrosion in the Molten Salt Reactor Experiment (MSRE) fuel salt.

Influence of Oxygen-Containing Lead Melts on the Fatigue Strength of AISI 409L Steel at Elevated Temperatures

We study the regularities of the influence of lead and lead-bismuth eutectic melts on the fatigue strength of AISI 409L (Fe-11Cr) steel of the ferritic class within the temperature range 500–600°С. It is shown that they reduce the resistance to long-term static loading of steel as compared with its resistance in a vacuum. As temperature increases, the negative influence of the eutectic becomes more pronounced as a result of the corrosive action of lead melts, namely, as a result of the selective dissolution of chromium along grain boundaries and the formation of iron oxides, which rapidly embrittle under loading and, thus, facilitates the fracture processes in the material.

Vanadium-Containing Oil Ash Corrosion of Boilers Under Oxidizing and Syngas Atmospheres

Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low grade fuels. Several iron-based alloys and a nickel-based alloy were studied in order to verify the effect of different Cr and Al contents under conditions typical for the partial oxidation process. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Samples were exposed to H2S-containing syngas atmosphere in order to simulate boiler operating conditions without ash deposition. The prevailing corrosion mechanism under this reducing atmosphere was sulfidation. In order to simulate boiler conditions with oil ash deposits, samples were immersed in 60 mol% V2O5–40 Na2SO4 salt in the same syngas atmosphere. The prevailing corrosion mechanism in this case was sulfidation under a reducing atmosphere and dissolution of iron or chromium from the substrate. The nickel-based substrate showed the best performance under these experimental conditions. In order to simulate air inlet due to shutdowns, samples were immersed in the same salt during exposure in air. The prevailing corrosion mechanism was still sulfidation in the oxidizing atmosphere accelerated by the presence of vanadate salt. This corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of oxides in the molten deposit, and their precipitation near the outer surface of the deposit.

Chemical and electrochemical dissolution of chromium at room and elevated temperatures

Chemical and electrochemical dissolution of chromium at room and elevated temperatures