Dissolution Of Inclusions Research Articles

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Blue sapphire has long been treated with heat to modify its blue color and attain greater value. However, the process of modifying the blue color in sapphire remains not well understood. The color-changing mechanism has traditionally been explained using the Intervalence Charge Transfer (IVCT) (Fe2+-Ti4+ and/or Fe2+-Fe3+) theory, wherein the blue color can be diminished by heat treatment in an oxidizing environment which alters Fe2+ (FeO) to Fe3+ (Fe2O3) and decreases the occurrence of the IVCT process. However, recently, the band gap theory has been proposed, suggesting that iron (Fe) in sapphire is always in the Fe3+ state, the blue color is caused by Fe3+-Ti4+ pair and the heat treatment does not affect Fe oxidation state. Therefore, in this study, eight magmatic sapphires from four localities were investigated for changes in blue color via color analysis, changes in spectra using XANES, and changes in chemical composition using PIXE both before and after heat treatment. The color analysis reveals a slight reduction in saturation (fading of blue) and a noticeable lightening after heat treatment, which corresponds with the high content of solid inclusions or trapiche samples. XANES data analysis using the LCF technique indicated insignificant changes in Fe oxidation state from 2+ to 3+ after heat treatment across all samples. However, when comparing the XANES data with color parameter L*a*b*, it is noted that the percentage of Fe oxidation state changes does not show a positive relationship with changes in blue based on color parameter b* (blue–yellow); rather, it shows a positive relationship with parameter L* (lightness). Microscopic observations also reveal the dissolution of clouds or minute particles around planes of ilmenite needles. It could be suggested that the changes in Fe oxidation state may not be directly related to changes in blue color but could be linked to the partial dissolution of Fe-bearing inclusions.

Effect of Selenium on Dissolution of Manganese Sulfide Inclusions in Stainless Steel

The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. The chemical composition of the inclusions affects the pitting corrosion resistance of stainless steels.1,2 It is known that the inclusion solubility in aqueous solutions affects pitting corrosion resistance. The dissolution of sulfide inclusions produces S species and exposes the bare surface of the steel matrix, resulting in high pitting susceptibility near the inclusions. Selenium is known to improve the machinability of stainless steels. However, the effect of selenium on the dissolution and pit initiation of MnS inclusions in stainless steels remains unclear. In this study, a microelectrochemical technique was applied to analyze the effect of Se on the dissolution and pit initiation of MnS inclusions in stainless steels.Two re-sulfurized stainless steels were prepared by vacuum induction melting: one was Se-free, and the other was Se-added. The specimens were heat-treated at 1373 K for 30 min and quenched in water. After heat treatment, the specimens were polished with 1 µm diamond paste. Polarization curves were measured in 0.1 M NaCl and 0.1 M Na2SO4. An optical microscope and a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy system were used to capture images of the specimen surfaces.

Dissolution of TiO2 and TiN inclusions in CaO–SiO2–B2O3-based fluorine-free mold flux

Dissolution of TiO2 and TiN inclusions in CaO–SiO2–B2O3-based fluorine-free mold flux

Investigation of rare earth (RE) on improving the corrosion resistance of Zr-Ti deoxidized low alloy steel in the simulated tropic marine atmospheric environment

Rare earth (RE) decreased the initial corrosion susceptibility of Zr-Ti deoxidized low alloy steel in a simulated marine environment through modifying the properties of inclusion and pearlite. The localized acidification caused by the dissolution of (RE)2O2S and (RE)xSy inclusions suppressed the hydrolysis of Ca2+ from the environment, inhibiting the deposition of CaCO3 and its participation in the formation of rust layer, which improved the rust layer compactness at first. This inhibition effect was diminished with time, while, the improved inner rust layer by RE effectively blocked the invasion of Cl-, promoting the enrichment of Cl- in the outer rust layer.

Study on the Influence of Non-Metallic Inclusions on the Pitting Corrosion of API 5L X60 Steel

The most economical way to move liquids and gaseous hydrocarbons is by using pipelines. According to several international organizations and oil companies, the use of fossil fuels will continue in the following decades. For this reason, it is important to continue studying different corrosion mechanisms and their origins. One of the mechanisms that provoke small leaks, affecting pipeline hermeticity, is pitting corrosion. It is well-known that non-metallic inclusion dissolution can trigger pit nucleation. As pitting corrosion is recognized to be random in nature, it is also interesting to study the random nature of the inclusions present in API 5L X60 steel. Probability distributions commonly used to describe pitting corrosion characteristics are appropriate for studying inclusion characteristics. The size of inclusions plays a key role in pit nucleation because small inclusions tend to generate more defects, especially when these inclusions are compounds of MnS, and the steel is immersed in a corrosive solution. The results of this research work show that there is a close relationship between the random nature of pitting corrosion and inclusions.

Chemical abrasion: the mechanics of zircon dissolution

Abstract. Chemical abrasion is a technique that combines thermal annealing and partial dissolution in hydrofluoric acid (HF) to selectively remove radiation-damaged portions of zircon crystals prior to U–Pb isotopic analysis, and it is applied ubiquitously to zircon prior to U–Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS). The mechanics of zircon dissolution in HF and the impact of different leaching conditions on the zircon structure, however, are poorly resolved. We present a microstructural investigation that integrates microscale X-ray computed tomography (µCT), scanning electron microscopy, and Raman spectroscopy to evaluate zircon dissolution in HF. We show that µCT is an effective tool for imaging metamictization and complex dissolution networks in three dimensions. Acid frequently reaches crystal interiors via fractures spatially associated with radiation damage zoning and inclusions to dissolve soluble high-U zones, some inclusions, and material around fractures, leaving behind a more crystalline zircon residue. Other acid paths to crystal cores include the dissolution of surface-reaching inclusions and the percolation of acid across zones with high defect densities. In highly crystalline samples dissolution is crystallographically controlled with dissolution proceeding almost exclusively along the c axis. Increasing the leaching temperature from 180 to 210 ∘C results in deeper etching textures, wider acid paths, more complex internal dissolution networks, and greater volume losses. How a grain dissolves strongly depends on its initial radiation damage content and defect distribution as well as the size and position of inclusions. As such, the effectiveness of any chemical abrasion protocol for ID-TIMS U–Pb geochronology is likely sample-dependent. We also briefly discuss the implications of our findings for deep-time (U-Th)/He thermochronology.

In-Situ Observation of Steel/Slag/Inclusion Interaction by Means of High-Temperature Confocal Scanning Laser Microscopy

Non-metallic inclusions (NMIs) in steels have been the focus of various experimental studies due to their detrimental character. While isolated processes, such as agglomeration or dissolution, have been well investigated, holistic in-situ views with high-temperature confocal scanning laser microscopy (HT-CSLM) have been rare. In this work a novel and suitable method is presented to simultaneously observe agglomeration, movement, detachment, and dissolution of non-metallic inclusions by combined the melting of steel and slag with a dual-crucible approach. Therefore, different steel/slag combinations were tested. It is shown that, with transparent that does not become tarnished by the ions stemming from the steel, the steel’s surface and non-metallic inclusions are observable. Furthermore, technological limitations are discussed, including restrictions regarding the melting point of steels and certain steel/slag combinations.

Concept of Inclusion Capacity of Slag and Its Application on the Dissolution of Al2O3, ZrO2 and SiO2 Inclusions in CaO–Al2O3–SiO2 Slag

Concept of Inclusion Capacity of Slag and Its Application on the Dissolution of Al2O3, ZrO2 and SiO2 Inclusions in CaO–Al2O3–SiO2 Slag

Creation of GaMnAs ferromagnetic semiconductor by combined laser method

GaMnAs layers made by pulsed laser deposition in vacuum on semi-insulating GaAs substrates have been studied. During the creation of the structures, the substrate temperature varied in the range from 200 to 350oC, and the thickness of the layers was ~ 50 nm. Samples of the manufactured structures were annealed by pulses of an excimer KrF-laser. The analysis of the Raman scattering spectra of annealed samples using their approximation by Lorentz functions showed, in addition to peaks in the LO- and TO-GaAs modes, the presence of a coupled phonon-plasmon mode. As a result of annealing, a significant increase in the hole conductivity of the layers is observed (the resistance decreases from Rs~107-109 Ω to Rs~ 900-3000 Ω). The type of magnetic field dependence of magnetization at room temperature changes significantly: there is a transition from a nonlinear characteristic with a hysteresis loop for the initial sample (appearing due to the presence of MnAs compound inclusions with a Curie temperature above room temperature) to a linear behavior for the annealed sample. The study of galvanomagnetic properties at temperatures from 10 to 150 K shows the existence of ferromagnetism in GaMnAs layers with a Curie temperature reaching 90 K. The observed effects allow us to conclude that the applied pulsed laser action leads to modification (dissolution) of MnAs inclusions, electrical activation of Mn and, as a consequence, to the formation of a single-phase ferromagnetic semiconductor GaMnAs. Keywords:: pulsed laser deposition, pulsed laser annealing, ferromagnetic semiconductor.

Effect of CaF2 Contents in Slag on Inclusion Absorption in a Bearing Steel

In the current study, laboratory experiments of the slag‐steel reaction are performed to investigate the effect of CaF2 contents in the refining slag on the inclusion absorption of the bearing steel. The increase of the CaO/Al2O3 ratio effectively enhances the absorption of inclusions by slag. The increase of the CaO/Al2O3 ratio enhances the driving force of the inclusion dissolution and lowers the slag viscosity. It is noted that the excessive CaO/Al2O3 ratio led to the formation of solid phases in the slag, lowering the absorption effect of slag. The appropriate addition of CaF2 in the slag is helpful to remove inclusions while aggravating the corrosion of MgO crucibles. The addition of CaF2 mainly reduces the viscosity and melting temperature of slag. The inclusion removal factor is proposed to effectively evaluate the inclusion removal rate in steel during slag steel reaction. As a result, the most recommended composition of slags is 7% CaF2; the CaO/Al2O3 ratio is 2.0.

Discovering the nanoscale origins of localized corrosion in additive manufactured stainless steel 316L by liquid cell transmission electron microscopy

We use liquid cell scanning transmission electron microscopy (STEM) to directly characterize the nanoscale origins of corrosion initiation in Additive manufacturing (AM) 316 L stainless steel. Under applied anodic potentials, we found that the dislocation cellular boundaries were preferentially corroded and that regions of localize corrosion occurred along the cellular boundaries. We directly observed the earliest stages of corrosion by controlling the biasing parameters to decelerate the corrosion processes. The results show that highly localized corrosion occurs via inclusion dissolution along dislocation cell boundaries. More widespread corrosion initiates at the dislocation cell boundaries and spreads throughout the dislocation networks.

Thermodynamic calculations and validation of the competing precipitation behavior of BN and Nb(C,N) in 9CrMoCo heat-resistant steel

In this study, the thermodynamic conditions were calculated for the formation of nitrides in the liquid phase and precipitation in the solid phase of the 9CrMoCo steel matrix. The mutual dependency of BN and Nb(C,N) was demonstrated through thermodynamic calculations and validated experimentally. The equilibrium distribution coefficients for Nb, N, and B at the solid–liquid interface were considered, and the solidification rate (fs) was introduced into the thermodynamic calculation. BN and NbN met the formation conditions when the fs values were 97.96% and 99.04%, respectively. The formation of Nb-containing nitrides was restrained by the formation of BN inclusions in the molten steel, which was confirmed by observing the elemental constituents of the Nb-rich precipitates. N (0.019%) in the solid solution was separated from the BN inclusions at 1523 K and it participated in the precipitation of Nb(C,N) during the subsequent cooling process. Needle-like Nb(C,N) precipitates and particles of Nb(C0.15N0.85) were formed under slow furnace cooling and austempering at 1223 K, respectively. In addition, the secondary precipitation of BN in austenite was restricted by the formation of the Nb(C,N) precipitate during the cooling process after the dissolution of BN inclusions.

TEMPERATURE DEPENDENCES OF THE INITIAL PERMEABILITY OF LITHIUM-TITANIUM FERRITES PRODUCED BY SOLID-STATE SINTERING IN THERMAL AND RADIATION-THERMAL MODES

The paper investigates the features of phase and structural transformations in lithium-titanium ferrites with regard to the time and temperature of solid-state sintering in thermal and radiation-thermal modes. These properties are studied with using the temperature dependence of the initial permeability. It is shown that electron beam exposure during solid-state sintering sharply accelerates the dissolution of impurity inclusions in ferrites. Also phase homogeneity of lithium-titanium ferrites products increase. The obtained results can be used for increasing of thephase homogeneity in ferrite production.

Image Processing Procedure to Evaluate Inclusion Dissolution in a Slag Observed by High-Temperature Confocal Scanning Laser Microscopy

In situ study of the inclusion dissolution behavior in a slag utilizing high-temperature confocal scanning laser microscopy helps to understand the phenomenon of the removal of non-metallic inclusions from liquid steel before the casting process. The current work introduces an image processing procedure to automate and measure the inclusion diameter during its dissolution. Silica and alumina particle dissolution were considered as they appear differently when suspended in the slag (bubble-like transparent and solid-like opaque, respectively). The procedure consists of two parts: (1) morphological isolation and construction of the inclusion, and (2) inclusion diameter calculation. The inclusion diameters could be successfully measured over a series of images and showed good agreement with the manually measured diameters. The image processing procedure has the advantages of significant time saving and standardization compared to manual measurements.

Influence of thermal treatment duration on structure and phase composition of additive Co-Cr-Mo alloy samples

Laser powder bed fusion (LPBF) requires application of powders with specific characteristics. These are near-spherical shape of particles, uniform elemental composition, typical particle size of 5 – 70 µm, etc. Such powders are produced by spheroidization methods. They have such disadvantages as high cost and sale only in large quantities. There are publications describing application in LPBF powders, produced by the methods, alternative to spheroidization. In the current study, powders of pure raw Co, Cr and Mo were used for the production of Co-Cr-Mo powder mixture. Samples of Co-28 wt.% Cr-6 wt.% Mo alloy were produced by LPBF from this powder mixture. Due to the difference between melting temperatures of Co, Cr and Mo, inclusions of Cr and Mo were formed within the bulk of samples. Studies of phase and elemental composition, structure and microhardness of the as-produced samples and after post-treatment with varied duration are represented. As-produced samples have non-uniform elemental composition and are represented by the main Co-based phase. Increasing the annealing duration leads to the sequential dissolution of un-melted Cr and Mo inclusions. Complete dissolution of Cr particles was observed at 10 hours of treatment and complete dissolution of Mo particles was not observed after 20 hours of annealing. Microhardness non-linearly changes with the increasing duration of annealing. This is due to the phase transformations and diffusion processes occurring at such type of post-treatment. Complete dissolution of Mo-particles could be achieved by further increasing the annealing time or by varying the mode of laser powder bed fusion.

Operando electrochemical TEM, ex-situ SEM and atomistic modeling studies of MnS dissolution and its role in triggering pitting corrosion in 304L stainless steel

Insights into the roles of geometry, size, and composition on MnS inclusion dissolution to initiate pits in 304L SS were obtained by combining operando and ex-situ electron microscopy, EDS, and atomistic modeling. The majority of thirty MnS on SS surface did not undergo dissolution even after over a week of exposure, and only a small number caused an attack of SS. Operando TEM during potentiodynamic polarization confirmed that MnS attack was followed by corrosion of the nearby SS substrate. Atomistic modeling revealed that elemental variations in the surface composition may play a role in differentiating pitting initiation by sulfur species.

Pitting corrosion behavior of Cu–P–RE weathering steels

The weathering steels are prone to pitting corrosion in an environment containing chloride ions. The pitting behavior of Cu–P–RE weathering steels and its effect on the corrosion resistance of steels were investigated by multifarious analytical techniques, such as field emission-scanning electron microscopy (FE-SEM), electron probe microanalysis (EPMA), scanning Kelvin probe force microscopy (SKPFM), electrochemical workstation and a series of immersion tests. The results show that the original strip-shaped MnS inclusions and Al2O3 inclusions with sharp angles are modified into the fine spherical rare earth (RE) inclusions with small average size, which are mainly RE oxysulfides after adding appropriate amount of mischmetal (48.9 wt%Ce–42 wt%La–5 wt%Nd–Fe) into the Cu–P weathering steel. In the environment containing Cl–, the pitting corrosion in RE weathering steel is induced by the preferential dissolution of RE inclusions in that the RE inclusions have a more negative potential than steel matrix at the initial corrosion stage. With the increase of corrosion time, the driving force of pitting expansion is weakened as a result of the continuous dissolution of RE inclusions, which makes the pitting tend to propagate horizontally around the RE inclusions. Once the RE inclusions completely dissolve, the open corrosion pits with shallow depth are formed in steel. The dispersed pitting pits with small size and shallow depth induced by RE inclusions are conducive to the formation of uniform and dense corrosion products layer on the steel surface, which reveals that the addition of RE can improve the corrosion resistance of weathering steels.

Ultrafast microstructure modification by pulsed electron beam to enhance surface performance

Pulsed electron beam surface treatment was used to enhance the microstructure and surface mechanical properties. After treatments with different electron beam energy densities, the microstructure and nano-structure of additively manufactured Al-Mg alloys were evaluated by scanning and transmission electron microscopy. At high Es (15 J/cm2) treatment, there is around 30–35 μm melting layer and the new second phase with complex elemental composition (Mn4.6Fe0.4Si3) in the surface modification layer. Thermal stress within different Es has a different effect on the second phase and dislocations, and the thermal stress in high Es improves the dissolution of submicron-sized inclusions presented in the initial state to form new particles. KAM (Kernel Average Misorientation) maps and calculated values prove that the electron beam irradiation increases the degree of local misorientation and surface stress. As Es is up to 15 J/cm2, the value of KAM and stress, as well as the dislocation, is the maximum. The formation of subgrains and precipitates with complex elemental composition after irradiation has comprehensive effects on the nano-hardness, wear rate and friction coefficient. It reveals that the nano-hardness and the friction coefficient of samples irradiated by 15 J/cm2 have the highest and the lowest values, respectively.

Dissolution Behavior of Different Inclusions in High Al Steel Reacted with Refining Slags

Al2O3, Al2O3·TiN, Al2O3·MgO, and CaO·2Al2O3 are four different types of inclusions in high Al steels. To improve the steel cleanness level, the effective removal of such inclusions during secondary refining is very important, so these inclusions should be removed effectively via inclusion dissolution in the slag. The dissolution behavior of Al2O3, Al2O3·TiN, Al2O3·MgO, and CaO·2Al2O3 in CaO-SiO2-Al2O3-MgO slags, as well as the steel-slag reaction, was investigated using laser scanning confocal microscopy (LSCM) and high-temperature furnace experiments, and thermodynamic calculations for the inclusion in steel were carried out by FactSage 7.1. The results showed that Al2O3·TiN was observed to be completely different from the other oxides. The composite oxides dissolved quickly in the slags, and the dissolution time of the inclusions increased as their melting point increased. SiO2 and B2O3 in the slag were almost completely reacted with [Al] in steel, so the slags without SiO2 showed a positive effect for avoiding the formation of Al2O3 system inclusions and promoting inclusions dissolution as compared with SiO2-rich slags. The steel-slag reaction was also found to influence the inclusion types in steel significantly. Because of the rapid absorption of different inclusions in the slag, it was found that the dissolution time of inclusions mainly depends on the diffusion in the molten slag.

Beneficial Effects of Cerium Addition to Sulfide Inclusions on Pitting Corrosion Resistance of Stainless Steels

The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. The chemical composition of the inclusions affects the pitting corrosion resistance of stainless steels. It is known that the inclusion solubility in aqueous solutions affects pitting corrosion resistance. The dissolution of sulfide inclusions produces S species and exposes the bare surface of the steel matrix, resulting in high pitting susceptibility near the inclusions.1 Cerium is expected to be an additive element for insolubilizing water-soluble inclusions because Ce tends to form sulfides and Ce-sulfides exhibit low solubility in aqueous solutions. Additionally, Ce ions have been shown to be effective in the corrosion inhibition of stainless steel. In this study, a microelectrochemical technique was applied to analyze the effect of Ce addition to sulfide inclusions on the pitting corrosion resistance of stainless steels.2,3 To analyze the effect of Ce addition on water solubility of CaS inclusions, spark plasma sintering was used in the facile fabrication of stainless steel specimens containing artificial Ce-added and Ce-free inclusions.3,4,5 The pit initiation resistance at the Ce-added CaS inclusions was higher than that at the Ce-free CaS inclusions. The surface of the Ce-free CaS inclusions largely dissolved during immersion in 0.1 M NaCl, while a large part of the Ce-added CaS inclusions remained undissolved. Thermodynamic calculation showed that CeS is less soluble than CaS.To analyze the effect of Ce ions on pitting at sulfide inclusions, a type 304 stainless steel (Fe-18Cr-8Ni-1.5Mn-0.02S) was prepared by vacuum induction melting. Manganese sulfide inclusions existed in the specimens. Polarization curves were measured in 3 M NaCl and 2.97 M NaCl-0.01 M CeCl3. Pitting occurred at the MnS inclusions in the Ce3+-free solution, whereas no stable pit was generated in the Ce3+-containing solution even when metastable pitting events were observed.It was found that Ce addition inhibits the dissolution of water-soluble inclusions and improved pitting corrosion resistance. Moreover, the Ce3+ ions are expected to inhibit the pitting even after the dissolution of Ce-added inclusions.