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At least 1,801 records · Page 100

Formation Mechanism of Oxide-Sulfide Complex Inclusions in High-Sulfur-Containing Steel Melts

The [S] content in resulfurized steel is controlled in the range of 200 to 800 ppm to ensure good machinability and workability. It is well known that “MgAl{sub 2}O{sub 4}(spinel)+CaS” complex inclusions are formed in molten steel during the ladle refining process, and these cause nozzle clogging during continuous casting. Thus, in the present study, the “Refractory-Slag-Metal-Inclusions (ReSMI)” multiphase reaction model was employed in conjunction with experiments to investigate the influence of slag composition and [S] content in the steel on the formation of oxide-sulfide complex inclusions. The critical [S] and [Al] contents necessary for the precipitation of CaS in the CaO-Al{sub 2}O{sub 3}-MgO-SiO{sub 2} (CAMS) oxide inclusions were predicted from the composition of the liquid inclusions, as observed by scanning electron microscopy–electron dispersive spectrometry (SEM-EDS) and calculated using the ReSMI multiphase reaction model. The critical [S] content increases with increasing content of SiO{sub 2} in the slag at a given [Al] content. Formation mechanisms for spinel+CaS and spinel+MnS complex inclusions were also proposed.

36 MATERIALS SCIENCE↗

Duplex Heterogeneous Nucleation Behavior of Precipitates in C-Mn Steel Containing Sn

The two successive heterogeneous nucleation behaviors of FeSn{sub 2}-MnS-Al{sub 2}O{sub 3} complex precipitates in ultrahigh Sn-bearing steel were investigated. First, Al{sub 2}O{sub 3} was the nucleation site of the MnS at the end of solidification. Then, FeSn{sub 2} nucleated heterogeneously on the MnS particles that nucleated on the Al{sub 2}O{sub 3} particles. The formation sequence of the precipitated phase caused the duplex heterogeneous nucleation to occur consecutively at most twice.

36 MATERIALS SCIENCE↗

Fundamentals of Hydrogen Solubility in Calcium-Alumino-Silicate Molten Fluxes Containing NaF

The effect of the NaF and CaO/SiO{sub 2} ratio (mass percentage ratio) on hydrogen solubility in a CaO-SiO{sub 2}-Al{sub 2}O{sub 3}-NaF system was studied and correlated to the structural units of the molten flux. Fourier transformed infrared, Raman, and X-ray photoelectron spectroscopy analyses were used to evaluate the structural units with NaF additions and various CaO/SiO{sub 2} ratios. At a CaO/SiO{sub 2} ratio of 0.8, the incorporated-hydroxyl dissolution mechanism is dominant, whereas the free-hydroxyl mechanism is pronounced at higher CaO/SiO{sub 2} ratio. At low NaF contents, the hydrogen solubility as a function of the CaO/SiO{sub 2} ratio showed a parabolic trend with a minimum typical of a change from incorporated- to a free-hydroxyl dissolution mechanism. The addition of network-modifying NaF depolymerizes the structural units of the flux, reducing the available sites for incorporated-hydroxyl groups. The hydrogen solubility behavior in the flux system correlates well with the structural analysis, where a high NaF content and CaO/SiO{sub 2} ratio are shown to depolymerize the complex structural units of the molten flux.

36 MATERIALS SCIENCE↗

Thermal Properties of Carbon-Containing Iron Ore Composite Prepared by Vapor Deposition of Tar for Limonite

The optimal conditions for preparing composites, in which tar-derived carbonaceous materials completely fill the pores in Indonesian limonite(IL), were investigated using the vapor deposition (VD) method of tar. Characterization of the composites and their reactivity (reduction/combustion/gasification) during heat treatment was examined. The specific surface area and pore volume of the as-received-IL and dehydrated-IL decreased after the VD treatment for different combinations of tar pyrolysis temperature (TPT) and VD temperature (VDT). It was also noted that the carbon content and crushing strength of the samples increased after the VD treatment, and the optimal values for the TPT-VDT are 700 °C and 350 °C. The C content and the crushing strengths of the composites prepared at TPT-VDT = 700 °C to 350 °C increased with an increase of the VD time to 50 pct carbon content and 10 daN at 240 minutes, respectively. The strength was similar to that of commercial metallurgical coke used in blast furnaces. The reduction of the composite prepared at TPT-VDT = 700 °C to 350 °C for 240 minutes started above 400 °C and was almost completed at 1000 °C. This reduction rate was higher than that of commercial cold-bonded pellets or a coke/IL mixture. The combustion and gasification rates of the composites prepared under different conditions depended on the preparation condition of composites, and the rates were higher than those of commercial metallurgical coke used in blast furnaces.

36 MATERIALS SCIENCE↗

A Study on the Interfacial Reaction Between Liquid Iron and MgO-Based Refractories Containing TiO{sub 2}

The interfacial reactions between liquid iron and MgO-based refractories were investigated based on the TiO{sub 2} concentration values. Substrates comprising MgO, MgO-TiO{sub 2} (MT), MgO-Al{sub 2}O{sub 3} (MA), and MgO-Al{sub 2}O{sub 3}, at loadings of 3, 6, 9, 12, and 15 wt pct TiO{sub 2} (MAT3-15), were reacted with liquid iron at 1823 K by using the sessile drop technique. Microscopic analysis by SEM/EDX and the associated thermochemical calculations by Factsage 7.0™ confirmed the reaction mechanisms of different refractory materials. MgO and MT showed higher resistance against liquid iron penetration compared with MA and MAT3-15, which was attributed to the formation of a magnesiowustite (MO (M = Fe, Mg)) layer formed at the interfaces. Increasing the levels of TiO{sub 2} up to 6 wt pct contributed to the denser microstructure of MA. However, the contact angle was lowest for 9 wt pct of TiO{sub 2} and then gradually increased up to 15 wt pct. Chemical reactions generating a liquid slag phase contributed to the fluctuations in contact angle with respect to TiO{sub 2}.

36 MATERIALS SCIENCE↗

Formulation and Assessment of a Wash-Primer Containing Lanthanum “Tannate” for Steel Temporary Protection

Tannins are polyphenols synthesized by plants and useful for the coating industry as corrosion inhibitors. In addition, lanthanum salts have a great inhibitory effect on steel corrosion. The aim of this study was to obtain lanthanum “tannate” with adequate solubility to be incorporated as the corrosion inhibitor in a wash-primer. The “tannate” was obtained from commercial “Quebracho” tannin and 0.1 M La(NO{sub 3}){sub 3}. The soluble tannin was determined by the Folin–Denis reagent, while the concentration of Lanthanum was obtained by a gravimetric procedure. The protective action of “tannate” on SAE 1010 steel was evaluated by linear polarization curves and corrosion potential measurements. Lanthanum “tannate” was incorporated in a wash-primer formulation and tested by corrosion potential and ionic resistance measurements. The corrosion rate was also determined by the polarization resistance technique. Besides, the primer was incorporated in an alkyd paint system and its anticorrosion performance assessed in the salt spray cabinet and by electrochemical impedance spectroscopy. Results showed that lanthanum “tannate” primer inhibits the development of deleterious iron oxyhydroxides on the steel substrate and incorporated into a paint system had a similar behavior to the primer formulated with zinc tetroxychromate.

36 MATERIALS SCIENCE↗

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO{sub 2}, anatase-TiO{sub 2} and Al{sub 2}TiO{sub 5}. PEO/α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) composite coating only had small micropores and appeared some α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) phase. Besides, the addition of α-Al{sub 2}O{sub 3} (Cr{sub 2}O{sub 3} or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.

36 MATERIALS SCIENCE↗

A Study on the Corrosion Behavior of Carbon Steel Exposed to a H{sub 2}S-Containing NH{sub 4}Cl Medium

NH{sub 4}Cl corrosion failure often occurs in the overhead systems of hydrotreaters, and this failure is always accompanied by the appearance of H{sub 2}S. A combination of electrochemical and surface spectroscopic (SEM/EDS, AFM, XRD) techniques was used to investigate the effect of different factors, including the surface roughness, temperature, dissolved oxygen, pH and H{sub 2}S concentration, on the corrosion behavior of carbon steel in an NH{sub 4}Cl environment with the presence of H{sub 2}S. The effect of H{sub 2}S concentrations (at the ppm level) on the corrosion behavior of carbon steel was systematically revealed. The experimental results clearly indicated that the corrosion rate reached a minimum value at 10 ppm H{sub 2}S. The steel surface was covered by a uniform corrosion product film in a 10 ppm H{sub 2}S environment, and the corrosion product film was tight and protective. The ammonia from NH{sub 4}Cl helped maintaining the protectiveness of the corrosion films in this environment. Dissolved oxygen mainly accelerated the cathodic reaction. The cathodic limiting current density increased with increasing temperature, and the anodic branch polarization curves were similar at different temperatures. The anodic current density decreased as the pH decreased, and the cathodic current density increased as the pH decreased. The absolute surface roughness (R{sub a}) of carbon steel increased from 132.856 nm at 72 h to 153.973 nm at 144 h, and the rougher surface resulted in a higher corrosion rate. The critical innovation in this research was that multiple influential factors were revealed in the NH{sub 4}Cl environment with the presence of H{sub 2}S.

36 MATERIALS SCIENCE↗

Control of Carbon Content in Ultrafine Cemented Carbide by Heat Treatment in Reducing Atmospheres Containing Carbon Oxides

In this work, the method of control of carbon content in the ultrafine-grained cemented carbide alloy was proposed. The treating of the WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} compacts was made in a CO + CO{sub 2} gas mixture at CO concentrations from 0 to 80 vol.% during 50 min at the initial stage of the conventional sintering at a temperature of 700 °C. Conditions for increasing and decreasing the carbon content are CO concentrations of CO in gas mix more than 65 vol.% and less than 35 vol.%, respectively. It is shown that even a small deviation from the stoichiometric carbon content (0.3 wt.%) leads to an increase in porosity and a multiple decrease in the strength of the ultrafine-grained cemented carbide. A comparative analysis with literature data showed that the obtained ultrafine-grained solid alloy WC-8Co-0.4VC-0.4Cr{sub 3}C{sub 2} with stoichiometric composition is not inferior in hardness and toughness to the analogs obtained by hot pressing and electrospark sintering.

36 MATERIALS SCIENCE↗

A Study on Thermal Conductivity and Stability of Nanofluids Containing Chemically Synthesized Nanoparticles for Advanced Thermal Applications

This study presents easy methods of synthesizing silver (Ag) and copper (Cu) nanoparticles through chemical route in an aqueous medium under atmospheric condition at ambient temperature. The synthesized nanoparticles have been characterized with different techniques, such as x-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, UV–visible spectroscopy and dynamic light scattering measurements. Experimental observations have revealed the absence of any metal oxide layer around the nanoparticles which are found to remain stable under ambient conditions. The featured properties, such as narrow size distribution, stability, make these nanoparticles potential candidates for the synthesis of effective nanofluids. The nanofluids have been prepared by dispersing the nanoparticles synthesized through chemical route in a suitable base fluid. The thermal conductivity of nanofluids with different nanoparticles loading has been measured by transient hot-wire method, and the results have shown that the increasing trend of enhancement in thermal conductivity with respect to nanoparticles concentration is attainable only when the nanoparticles concentration is below some limiting value depending on the type of nanofluid. Beyond this limiting value of loading, the thermal conductivity of the nanofluid decreases due to pronounced agglomeration effect. The measurements of thermal conductivity of nanofluids over varying temperatures for a given volume fraction loading of nanoparticles have shown that the thermal conductivity increases markedly with the increase in temperature. Hence, nanofluids are likely to be much more promising at high-temperature applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Oxidation Behavior of Austenitic Steels in Supercritical Water Containing Dissolved Oxygen

Oxidation tests of austenitic steel Super304H and HR3C were conducted at 550-600 °C in supercritical water under 25 MPa with the dissolved oxygen content. The oxidation rate of Super304H rapidly increased with increasing temperature, while the weight change of HR3C at 600 °C is slightly larger than that at 550 °C. A double-layer oxide scale developed on Super304H and HR3C steel, which was made up of an Fe-rich outer layer and a Cr-rich inner layer. The criterion contents of Cr were calculated for Super304H and HR3C. The effect of temperature and the Cr content on oxidation rate and oxide composition were discussed.

36 MATERIALS SCIENCE↗

An Investigation of the Corrosion Mechanisms of Cu-7Ni-3Al-1Fe-1Mn Alloy in Chloride-Containing Environment

The corrosion mechanisms of Cu-7Ni-3Al-1Fe-1Mn (wt.%) alloy in a 3.5% NaCl solution are investigated through a multi-analytical approach. The formation, growth and stable corrosion stage of the stable corrosion layer are reflected by the change of electrochemical response with time. EDS and GI-XRD results show the presence of Cu{sub 2}(OH){sub 3}Cl and Cu{sub 2}O that are the main corrosion products, with the former predominantly present at topmost corrosion layer, and Cu{sub 2}O is mainly located in the inner part, followed by aluminum oxide closer to the alloy substrate.

36 MATERIALS SCIENCE↗

Metal Cationization Extractive Electrospray Ionization Mass Spectrometry of Compounds Containing Multiple Oxygens

Extractive electrospray ionization is an ambient ionization technique that allows real-time sampling of liquid samples, including organic aerosols. Similar to electrospray ionization, the composition of the electrospray solvent used in extractive electrospray ionization can easily be altered to form metal cationized molecules during ionization simply by adding a metal salt to the electrospray solvent. An increase in sensitivity is observed for some molecules that are lithium, sodium, or silver cationized compared with the protonated molecule formed in extractive electrospray ionization with an acid additive. Tandem mass spectrometry of metal cationized molecules can also significantly improve the ability to identify a compound. Tandem mass spectrometry of lithium and silver cationized molecules can result in an increase in the number and uniqueness of dissociation pathways relative to [M + H]{sup +}. These results highlight the potential for extractive electrospray ionization with metal cationization in analyzing complex aerosol mixtures. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Iodine-Containing Mass-Defect-Tuned Dendrimers for Use as Internal Mass Spectrometry Calibrants

Calibrants based on synthetic dendrimers have been recently proposed as a versatile alternative to peptides and proteins for both MALDI and ESI mass spectrometry calibration. Because of their modular synthetic platform, dendrimer calibrants are particularly amenable to tailoring for specific applications. Utilizing this versatility, a set of dendrimers has been designed as an internal calibrant with a tailored mass defect to differentiate them from the majority of natural peptide analytes. This was achieved by incorporating a tris-iodinated aromatic core as an initiator for the dendrimer synthesis, thereby affording multiple calibration points (m/z range 600–2300) with an optimized mass-defect offset relative to all peptides composed of the 20 most common proteinogenic amino acids. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

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