Mol Pct Research Articles

Effect of Al2O3 Concentration on Density and Structure of (CaO-SiO2)-xAl2O3 Slag

The effect of Al2O3 concentration on the density and structure of CaO-SiO2-Al2O3 slag was investigated at multiple Al2O3 mole percentages and at a fixed CaO/SiO2 ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al2O3 content was less than 15 mole pct, density decreased with increasing Al2O3 content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al3+ ion as a network modifier.

The Effect of TiO2 and B2O3 Additions on the Grain Growth of ZnO

The microstructure properties and grain growth kinetics of ZnO-B2O3-TiO2 ceramics with 0.5 and 1 mol pct doping of TiO2 were investigated. The samples were sintered at 1373 K, 1473 K, and 1573 K (1100 °C, 1200 °C, and 1300 °C) for 1, 2, and 3 hours. The bulk density and grain size of ZnO samples increased with the addition of B2O3 and TiO2. The grain size of 0.5 mol pct TiO2-doped ZnO ceramics was larger than the grain size of the 1 mol pct TiO2-doped ZnO ceramics. This is due to the increase in the ZnTi2O4 phase for the 1 mol pct TiO2-doped ZnO ceramics. The value of grain growth kinetic parameters (n and Q) increased when the TiO2 content in ZnO ceramics increased from 0.5 to 1 mol pct. The lowest n and Q values were obtained for the 0.5 mol pct B2O3-doped ZnO samples which showed that the addition of B2O3 has a significant role on the grain growth of ZnO ceramics.

Precipitation of (Zr, Hf)C in FeCrAlYHfZr alloys during electroslag remelting process

Three-dimensional morphology of (Zr, Hf)C in FeCrAlYHfZr alloys during electroslag remelting (ESR) was revealed by the method of non-aqueous solution electrolysis. Two types of (Zr, Hf)C carbides in FeCrAlYHfZr alloys were detected: isolated cubic carbides of (Zr, Hf)C were precipitated in intragranular and dendritic ones were precipitated in the grain boundary. In alloys with sufficient [C], there was a linear relationship between the (mole pct Zr)/(mole pct Hf) in carbides and [mole pct Zr]/[mole pct Hf] in alloys with the slope close to unity, while HfC was easier to be formed than ZrC in alloys with insufficient [C]. Extensive calculations were carried out to predict the composition of (Zr, Hf)C in FeCrAlYHfZr alloys with various concentrations of [Zr], [Hf] and [C].

CeO2-Y2O3-ZrO2 Membrane with Enhanced Molten Salt Corrosion Resistance for Solid Oxide Membrane (SOM) Electrolysis Process

Innovative CeO2-Y2O3-ZrO2 membrane has been successfully developed and used in the solid oxide membrane (SOM) electrolysis process for green metallic materials production. The x mol pct ceria/(8–x) mol pct yttria-costabilized zirconia (xCe(8–x)YSZ, x = 0, 1, 4, or 7) membranes have been fabricated and investigated as the membrane-based inert anodes to control the SOM electroreduction process in molten salt. The characteristics of these fabricated xCe(8–x)YSZ membranes including their corrosion resistances in molten salt and their degradation mechanisms have been systematically investigated and compared. The results show that the addition of ceria in the YSZ-based membrane can inhibit the depletion of yttrium during the SOM electrolysis, which thus makes the ceria-reinforced YSZ-based membranes possess enhanced corrosion resistances to molten salt. The ceria/yttria-costabilized zirconia membranes can also provide reasonable oxygen ion conductivity during electrolysis. Further investigation shows that the newly modified 4Ce4YSZ ceramic membrane has the potential to be used as novel inert SOM anode for the facile and sustainable production of metals/alloys/composites materials such as Si, Ti5Si3, TiC, and Ti5Si3/TiC from their metal oxides precursors in molten CaCl2.

Relationship Between Sulfide Capacity and Structure of MnO-SiO2-Al2O3-Ce2O3 System

Sulfide capacity of the MnO-SiO2-Al2O3-Ce2O3 system was measured at 1873 K (1600 °C), and the structural analysis was carried out using micro-Raman spectroscopy to understand the role of Ce2O3 in the sulfur dissolution behavior. Sulfide capacity of the basic melts (MnO/SiO2 = 2.2(±0.14)) decreased with increasing content of Ce2O3 to approx. 4 mol pct, beyond which it increased. Sulfide capacity continuously decreased in the less basic system (MnO/SiO2 = 1.0(±0.15)), whereas it was hardly affected by Ce2O3 in the relatively acidic composition (MnO/SiO2 = 0.3(±0.05)). There was a significant increase in the intensity of Raman band at 600 cm−1 by Ce2O3 addition in high MnO/SiO2 (=2.2) system, which originated from the transition from [(Al,Mn0.5)O4]-tetrahedron to [(Al,Ce)O6]-octahedron due to strong attraction between Al2O3 and Ce2O3. Combining thermodynamic and structural information, the effect of Ce2O3 on the sulfide capacity of Mn-aluminosilicate melts can be explained by the following factors: (1) Activity of MnO in the melts decreased by addition of Ce2O3; (2) Free oxygen was consumed in the structure modification from [(Al,Mn0.5)O4] to [(Al,Ce)O6] unit by addition of Ce2O3; and 3) When the Ce3+ content was greater than critical value (approx. 4 mol pct) in high MnO/SiO2 (=2.54) melts, excess Ce3+ and Mn2+ ions competitively reacted with S2− ions, resulting in an increase of sulfide capacity.

In Situ Synthesis of 3Y-TZP/MgAl2O4 Nanoparticle Composite Through Co-precipitation

3 Mole pct yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and spinel (MgAl2O4) nanocomposite was synthesized by co-precipitation—calcination method. The powders were made to a composition of 70 vol pct 3Y-TZP and 30 vol pct MgAl2O4. The composite made of 70 pct 3Y-TZP and 30 pct MgAl2O4 is well known for its superplastic ability at high temperatures. Reverse drop method was utilized to precipitate metal ions simultaneously, resulting in a homogenous composition on a molecular scale and crystalline after calcination at 1273 K (1000 °C) for 2 hours. The characterization results showed that the powders were phase pure tetragonal zirconia and spinel, fairly not forming a ternary complex between Spinel and 3Y-TZP. From the TEM and DLS analyses, the average particle size was determined to be about 50 to 100 nm with some level of agglomeration. Raman peaks E g (156 cm−1), E g (274 cm−1), B 1g (332 cm−1), E g (474 cm−1), A 1g (605 cm−1), and B 1g (653 cm−1), due to the tetragonal phase of 3Y-TZP and E g (487 cm−1) due to cubic phase of MgAl2O4, are observed in the sample. HRTEM results show interplanar spacing of (311) of the spinel and (101) of the yttria-stabilized zirconia, which indicates the high-level homogeneity in the nanoparticle composite powders.

Transition Metal Diborides as Electrode Material for MHD Direct Power Extraction: High-temperature Oxidation of ZrB2-HfB2 Solid Solution with LaB6 Addition

Transition metal borides are being considered for use as potential electrode coating materials in magnetohydrodynamic direct power extraction plants from coal-fired plasma. These electrode materials will be exposed to aggressive service conditions at high temperatures. Therefore, high-temperature oxidation resistance is an important property. Consolidated samples containing an equimolar solid solution of ZrB2-HfB2 with and without the addition of 1.8 mol pct LaB6 were prepared by ball milling of commercial boride material followed by spark plasma sintering. These samples were oxidized at 1773 K (1500 °C) in two different conditions: (1) as-sintered and (2) anodized (10 V in 0.1 M KOH electrolyte). Oxidation studies were carried out in 0.3 × 105 and 0.1 Pa oxygen partial pressures. The anodic oxide layers showed hafnium enrichment on the surface of the samples, whereas the high-temperature oxides showed zirconium enrichment. The anodized samples without LaB6 addition showed about 2.5 times higher oxidation resistance in high-oxygen partial pressures than the as-sintered samples. Addition of LaB6 improved the oxidation resistance in the as-sintered condition by about 30 pct in the high-oxygen partial pressure tests.

Erratum to: Recrystallization Behavior of CoCrCuFeNi High-Entropy Alloy

Nokeun Park’s affiliation has been updated as shown in this erratum. The third sentence in the following text has been added to the Experimental Procedures section on page 1482 as clarification regarding the chemical composition of the whole sample: The material used in the current study was an equimolar CoCrCuFeNi alloy (20 mol pct for each element) that was cast with the pseudo float melting process that brings almost homogeneous distribution of each element. An as-cast HEA rod 10 mm in diameter and 60 mm in length was homogenized at 1373 K (1100 C) for 12 hours, followed by water cooling. The chemical composition of homogenized specimen was measured by wavelength-dispersive X-ray spectroscopy, and the atomic percent was Co21Cr22Cu22Fe21Ni14.

Restriction of Phase Transformation in Carbon Nanotube-Reinforced Yttria-Stabilized Zirconia

The present research aims to investigate the effect of multi-walled carbon nanotube (MWNT) reinforcement on the mechanism of transformation toughening in zirconia matrix, and consequently, its fracture toughness. Monoclinic zirconia (un-doped ZrO2), partially stabilized zirconia (3 mol pct yttria-stabilized zirconia (3 mol pct YSZ)), and fully stabilized cubic zirconia (8 mol pct YSZ) with and without 6 vol pct MWNT-reinforced nanocomposites were processed via multi-stage spark plasma sintering. Phase analysis of powders, and sintered and crushed pellets performed using X-ray diffraction reveals the absence of any phase transformation in monoclinic ZrO2, 8 mol pct YSZ and their MWNT-reinforced nanocomposites upon application of stress by means of crushing. However, a significant decrease in the stress-induced phase transformation (81.1 pct metastable tetragonal phase retained with 6 vol pct MWNT reinforcement when compared to that of 68.4 pct tetragonal phase in 3 mol pct YSZ) is observed in the crushed pellet samples of partially stabilized zirconia upon 6 vol pct MWNT reinforcement. Transmission electron microscopy has been utilized for complementary phase analysis. Evaluation of mechanical properties indicates enhancement in fracture toughness (~23.6 to 26.4 pct) with the incorporation of 6 vol pct MWNT. Isolation of the net toughening contribution suggests that MWNT toughening mechanisms are ~3.8 times more effective than transformation toughening in enhancing the fracture toughness of YSZ/MWNT nanocomposites.

Oxidation of Flash-Anodized Al-Mg Alloy in Dry Atmospheres of N2, CO2, and O2 and Humid Atmosphere of Ar

Production of anodized Al alloy is increasing with increased recycling of Al. To study recycling of anodized material, a flash-anodized 3000 series Al alloy containing 0.34 wt pct Mg was remelted in pure atmospheres of CO2, O2, and N2, and Ar with 5 mol pct H2O at 1073 K (800 °C). Hopefully, the results should be of general influence concerning dross formation and scrap remelting in the Al industry. Oxidation studies using a thermogravimetric analyser were performed. Following the treatment, the samples oxide layers were characterized. The highest oxidation rates were observed in atmospheres of O2 and CO2. However, the onset of a break-away oxidation period in O2 is delayed in comparison to CO2. Oxidation in CO2 showed substantially less MgO formation compared to O2. The main source of mass gain can be attributed to the reaction of Mg with oxygen to form MgO and MgAl x O y . Heating in N2 resulted in the lowest mass gain of all atmospheres. Experiments in humid (5 mol pct H2O) Ar atmospheres indicate that there is a minimum threshold of Mg activity to initiate oxidation via H2O. Oxidation kinetics (mechanisms) has been investigated.

On the Densification Behavior of (0.2, 0.5, and 1 Wt Pct) CNT-YSZ Ceramic Composites Processed via Spark Plasma Sintering

Yttria-Stabilized Zirconia (YSZ) is a promising thermal insulating ceramic for high temperature applications due to its stability and chemical inertness. As was demonstrated with other technical ceramics (e.g., Alumina), addition of Single-Wall Carbon Nanotubes (CNTs) to a ceramic matrix may significantly enhance its mechanical properties. In this work, 8 mol pct YSZ with 0.2, 0.5, and 1 wt pct CNT composites were fabricated via the spark plasma sintering process. The densification, Vicker’s microhardness, specific gravity, and microstructure evolution of the composites were investigated. The results suggest that the addition of CNTs to YSZ hindered densification and grain growth during SPS processing leading to inhomogeneous grain size distribution. However, the CNTs had a profound impact on the hardness of the composite ceramics, with an increase from 697 HV (YSZ) to 1195 HV (1 wt pctCNT-YSZ).

Production of Titanium Powder by Sodiothermic Reduction in CaCl2 Molten Salts

A new sodiothermic reduction process of TiO2 in CaCl2 melt was proposed aimed at fine Ti powder preparation. The chemical analysis and direct potentiometric methods were used to investigate the reaction pathway of sodiothermic reduction in CaCl2 melt. The as-prepared samples were characterized by X-ray diffraction and scanning electron microscopy. It was found that when reductant of Na was added into the CaCl2 melt, Ca2+ was reduced to Ca by Na and Ca dissolved in the CaCl2 melt. The whole melt would have the reducing power with dissolved Ca. Using this melt as a reaction medium, fine and uniform Ti powder with a purity of around 99 mass pct was successfully produced at 1173 K (900 °C). In addition, as the CaCl2 melt could dissolve about 20 mol pct CaO, it was found that the molar ratio of TiO2 and CaCl2 should be 1:20 to eliminate the by-product CaO from the reaction interface within the experimental period to continue the reduction.

Formation of omega and Ti2Ni phases in a residual Ti–Ni–Ti multilayer between stainless steel and zirconia after bonding at 1173 K

Stainless steel (316L) and 8 mol pct Y2O3-stabilized zirconia (8Y-ZrO2) were bonded using a Ti–Ni–Ti multilayer at 1173 K (900 °C) for 1 h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular α-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into β-Ti led to the precipitation of the omega (ω) phase with different variants in the residual Ti foil between 316L and Ni. The ω-phase was not found in the residual Ti foil between Ni and 8Y-ZrO2, while Ti2Ni precipitates were precipitated in some α-Ti grains owing to the exclusion of Ni from the β-Ti.

Investigation of Precipitation Behavior in Age-Hardenable Cu-Ti Alloys by an Extraction-Based Approach

We investigated the precipitation processes in Cu-4 mol pct Ti alloy specimens aged at 723 K (450 °C), by means of X-ray diffraction and chemical analyses of the precipitates extracted from the parent alloy specimens. Aging-induced precipitate particles of a spinodally decomposed disorder, α′; those of a metastable order, β′-Cu4Ti; and those of a stable order, β-Cu4Ti, were continuously formed in the aged specimens. The extraction of the precipitate particles from the aged specimens by submergence in a nitric solution allowed for not only the structural analyses of the constituent precipitate phases but also the quantitative evaluation of their chemical compositions and volume fractions. Early during the aging process, the supersaturated Cu solid solution decomposes spinodally in a continuous manner, and an unstable disorder, α′, appears. Then, fine needle-shaped β′-Cu4Ti particles, which have a Ti content of approximately 37.5 mol pct, form in the Cu matrix. During prolonged aging, coarse cellular components composed of the terminal Cu solid solution and stable β-Cu4Ti particles which have a Ti content of 20.5 mol pct nucleate and grow, primarily in the grain boundaries, at the expense of the metastable β′-Cu4Ti particles. The volume fraction of the β′-Cu4Ti particles in the alloy reaches a maximum of approximately 1.7 pct after aging for 24 hours, while that of the β-Cu4Ti particles increases steadily to more than 18 pct after 480 hours. The volume fraction of the fine β′-Cu4Ti particles in the alloy specimens remained constant throughout the age-hardening, indicating that the hardening is primarily owing to the fine dispersion of the β′-Cu4Ti particles and not because of the large volume fraction of coarse β-Cu4Ti particles.

Viscosity Measurements of SiO2-“FeO”-MgO System in Equilibrium with Metallic Fe

The present study delivers the measurements of viscosities in the SiO2-“FeO”-MgO system in equilibrium with metallic Fe. The rotational spindle technique was used for the measurements at the temperature range of 1523 K to 1773 K (1250 °C to 1500 °C). Molybdenum crucibles and spindles were employed in all measurements. The viscosity measurements were carried out at 31 to 47 mol pct SiO2 and up to 18.8 mol pct MgO. Analysis of the quenched sample by Electron probe X-ray microanalysis after the viscosity measurement enables the composition and microstructure of the slag to be directly linked with the viscosity. The replacement of “FeO” by MgO was found to increase viscosity and activation energy of the SiO2-“FeO”-MgO slags. The modified Quasi-chemical Viscosity Model was further optimized in this system based on the current viscosity measurements.

Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-killed Steel

The thermodynamic equilibria between CaO-Al2O3-SiO2-CaF2-MgO(-MnO) slag and Fe-1.5 mass pct Mn-0.5 mass pct Si-0.5 mass pct Cr melt was investigated at 1873 K (1600 °C) in order to understand the effect of slag composition on the concentration of Al2O3 in the inclusions in Si-Mn-killed steels. The composition of the inclusions were mainly equal to (mol pct MnO)/(mol pct SiO2) = 0.8(±0.06) with Al2O3 content that was increased from about 10 to 40 mol pct by increasing the basicity of slag (CaO/SiO2 ratio) from about 0.7 to 2.1. The concentration ratio of the inclusion components, $$ {{X_{{{\text{Al}}_{2} {\text{O}}_{3} }} \cdot X_{\text{MnO}} } \mathord{\left/ {\vphantom {{X_{{{\text{Al}}_{2} {\text{O}}_{3} }} \cdot X_{\text{MnO}} } {X_{{{\text{SiO}}_{2} }} }}} \right. \kern-0pt} {X_{{{\text{SiO}}_{2} }} }} $$ , and the activity ratio of the steel components, $$ {{a_{\text{Al}}^{2} \cdot a_{\text{Mn}} \cdot a_{\text{O}}^{2} } \mathord{\left/ {\vphantom {{a_{\text{Al}}^{2} \cdot a_{\text{Mn}} \cdot a_{\text{O}}^{2} } {a_{\text{Si}} }}} \right. \kern-0pt} {a_{\text{Si}} }} $$ , showed a good linear relationship on a logarithmic scale, indicating that the activity coefficient ratio of the inclusion components, $$ {{\gamma_{{{\text{SiO}}_{2} }}^{i} } \mathord{\left/ {\vphantom {{\gamma_{{{\text{SiO}}_{2} }}^{i} } {\left( {\gamma_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{i} \cdot \gamma_{\text{MnO}}^{i} } \right)}}} \right. \kern-0pt} {\left( {\gamma_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{i} \cdot \gamma_{\text{MnO}}^{i} } \right)}} $$ , was not significantly changed. From the slag-steel-inclusion multiphase equilibria, the concentration of Al2O3 in the inclusions was expressed as a linear function of the activity ratio of the slag components, $$ {{a_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{s} \cdot a_{\text{MnO}}^{s} } \mathord{\left/ {\vphantom {{a_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{s} \cdot a_{\text{MnO}}^{s} } {a_{{{\text{SiO}}_{2} }}^{s} }}} \right. \kern-0pt} {a_{{{\text{SiO}}_{2} }}^{s} }} $$ on a logarithmic scale. Consequently, a compositional window of the slag for obtaining inclusions with a low liquidus temperature in the Si-Mn-killed steel treated in an alumina ladle is recommended.

Synthesis of Nanoscale Nd-Doped Ceria Via Urea-Formaldehyde Combustion Method

Nanocrystalline neodymium-doped ceria solid solutions with Nd3+ concentrations varying from 4 to 20 mol pct have been synthesized by gel combustion method, using urea-formaldehyde as fuel for Nd doping. The combustion reaction is explained through differential scanning calorimetry (DSC)-differential thermogravimetric analysis (TGA), whereas the synthesized materials are characterized through X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The phase obtained from the exothermic reaction contains Nd-substituted CeO2. The deviation of the lattice parameter from Vegard’s law and the decrease in crystallite size with dopant concentration has been explained. The as-synthesized particles are largely nanoporous single crystallites, existing in loosely held spherical-shaped agglomerates. The size of the agglomerates increases with increasing dopant content. High-resolution TEM (HRTEM) reveals the fact that the unit cells are strained.

Solid–Liquid Interfacial Energy of Solid Neopentylglycol Solution in Equilibrium with Neopentylglycol–Aminomethylpropanediol Eutectic Liquid

The grain boundary groove shapes for solid neopentylglycol solution (NPG-40 mol pct AMPD) in equilibrium with the neopentylglycol (NPG)–aminomethylpropanediol (AMPD) eutectic liquid (NPG-42.2 mol pct AMPD) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г) and solid–liquid interfacial energy (σSL) of solid NPG solution have been determined to be (7.4 ± 0.7) × 10−8 K m and (6.4 ± 1.0) × 10−3 J m−2, respectively. The grain boundary energy of solid NPG solution has been determined to be (12.5 ± 1.0) × 10−3 J m−2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution has also been determined to be 0.48.

Measurements of Thermal Conductivity Variations with Temperature for the Organic Analog of the Nonmetal–Nonmetal System: Urea–4-Bromo-2-Nitroaniline

Thermal conductivity variations with temperature for solid phases in the Urea (U)–[X] mol pct 4-bromo-2-nitroaniline (BNA) system (X = 0, 2, 45, 89.9, and 100) were measured using the radial heat flow method. From graphs of thermal conductivity variations with temperature, the thermal conductivities of the solid phases at their melting temperature and temperature coefficients for the U–[X] mol pct BNA system (X = 0, 2, 45, 89.9, and 100) were found to be 0.26, 0.55, 0.46, 0.38, and 0.23 W/Km and 0.007781, 0.005552, 0.002058, 0.002188, and 0.002811 K−1, respectively. The ratios of thermal conductivity of the liquid phase to thermal conductivity of the solid phase in the U–[X] mol pct BNA system (X = 0, 2, 45, 89.9, and 100) were also measured to be 0.30, 0.44, 0.46, 0.49, and 0.51, respectively, with a Bridgman-type directional solidification apparatus at their melting temperature.

Removal of Boron from Silicon-Tin Solvent by Slag Treatment

To eliminate B effectively from Si for its use in a solar cell, a novel process involving the slag refining of molten Si with Sn addition was investigated. The partition ratio of B between CaO-SiO2-24 mol pct CaF2 slag and Si-Sn alloy at 1673 K (1400 °C) was determined by the chemical equilibrium technique. It was found that the partition ratio of B was remarkably increased with the increase in Sn content of alloy, which attributes to the increase in activity coefficient of B as well as the oxygen partial pressure. The partition function was accounted as much as 200 when the alloy composition was Si-82.4 mol pct Sn, which was much higher than the reported values in the range of 1 to 3. The required amounts of slag used for B removal from Si-30, 50, and 70 mol pct Sn melts were only 15.6 pct, 6.5 pct, and 1.2 pct of that used for the removal of B directly from MG-Si without Sn addition in a single slag treatment.