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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
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DOE OSTI2019

Agglomeration Mechanism of Complex Ti-Al Oxides in Liquid Ferrous Alloys Considering High-Temperature Interfacial Phenomenon

This work presents the agglomeration mechanism of complex Ti-Al oxides in the liquid ferrous alloy. Cluster characteristics were investigated using Al and Ti/Al-complex deoxidation method in lab scale. The time-dependent size distribution, total number per volume, average size, and circularity of the clusters were quantitatively analyzed. Furthermore, high-temperature confocal laser scanning microscopy was utilized to directly observe the cluster formation of Ti-Al oxides. A capillary force model including wettability parameters was applied to compare the agglomeration capabilities of different types of non-metallic inclusions. When a low Ti is added into melt, the agglomeration of TiO{sub x}·FeO liquid inclusions is one of the key factors to decrease the frequency of cluster formation. When the Al is added into melt, the heterogeneous precipitation on TiO{sub x}·FeO surfaces is the main reaction process. Ti-Al oxides have lower agglomeration ability than that of Al{sub 2}O{sub 3}, which in turn, contribute to a low agglomeration frequency as well.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Behavior of Ga, In, Sn, and Te in Copper Matte Smelting

The distributions of Ga, In, Sn, and Te between copper-iron mattes and silica-saturated iron silicate slags over a wide range of matte grades 55 to 75 pct Cu were determined at 1300 °C using a gas-phase equilibration-quenching technique and direct phase composition analysis by Electron Probe X-ray Microanalysis and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry. Alumina from aluminum, a typical minor element of electric and electronic copper scrap, and lime were adopted as slag modifiers for increasing the trace element recoveries. Gallium and tin were distributed predominantly in the slag, indium preferred sulfide matte at low matte grades and slag at high, whereas tellurium strongly favored the sulfide matte in particular in high matte grades. The slag modifiers alumina and lime had a minor impact on the distribution coefficients of gallium and tin, but for indium and tellurium the distribution coefficients were more strongly affected by the basic oxides. The strong tendencies of tin and tellurium to vaporize at the experimental temperature were confirmed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study of Cu-Ni-Fe Alloys as Inert Anodes for Al Production in Low-Temperature KF-AlF{sub 3} Electrolyte

Cu-Ni-Fe-based alloys are considered as promising O{sub 2}-evolving anode materials for CO{sub 2}-free Al production. In the present study, biphased (as-cast) and monophased (postcasting homogenized) Cu{sub 65}Ni{sub 20}Fe{sub 15}, alloys, and monophased Ni{sub 65}Fe{sub 25}Cu{sub 10} alloy (in wt pct) are evaluated as O{sub 2}-evolving anodes for Al production in potassium cryolite at 700 °C. The produced Al purity is 99.6 wt pct, and the erosion rate is estimated at 0.4 cm year{sup −1} for both Cu{sub 65}Ni{sub 20}Fe{sub 15} anodes compared to 95.2 wt pct and 3.2 cm year{sup −1} for the Ni{sub 65}Fe{sub 25}Cu{sub 10} anode. The compositions, and morphologies of the surface oxide layer and the metal fluoride layer present at the oxide/alloy interface are compared for the three anodes. The deleterious impact of electrolyte infiltration on the surface oxide building is highlighted.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Cationic Effect of Ferrous Ions on Sulfide Capacity of CaO-Fe{sub t}O-Al{sub 2}O{sub 3}-SiO{sub 2} Slag System

The cationic effect of ferrous ions on the sulfide capacity of CaO-Fe{sub t}O-Al{sub 2}O{sub 3}-SiO{sub 2} slags was studied from the viewpoint of the ionic structure in the slag using micro-Raman spectroscopy. In the cation-excess region (M{sup 2+}/2(Fe{sup 3+} + Al{sup 3+}) > 1.0), the sulfide capacity was directly proportional to the basicity of the slags, owing to the S{sup 2−} stabilizing effect of excess cations. However, in the cation-deficient region (M{sup 2+}/2(Fe{sup 3+} + Al{sup 3+}) < 1.0), the sulfide capacity was independent of the basicity of the slags owing to the deficiency of cations required for charge compensation with Al{sup 3+} and Fe{sup 3+}. The cation-substitution effect on the sulfide capacity of the CaO-rich slags (Fe{sub t}O/(Fe{sub t}O + CaO < 0.5) exhibited a linear relationship with the Fe{sup 2+} content because Fe{sup 2+} had a stronger affinity with S{sup 2−} compared to that with Ca{sup 2+}. However, in the Fe{sub t}O-rich slags (Fe{sub t}O/(Fe{sub t}O + CaO > 0.5), the sulfide capacity decreased with the increase of the Fe{sup 2+} content owing to the Q{sup n} unit affinity of the Fe{sup 2+} ion. The sulfide capacity was determined by the competition between the Q{sup n} unit affinity and stability of the S{sup 2−} ion, depending on the type of cation. Therefore, the partial covalent bonding between the M{sup 2+} cations (M: Ca, Fe) and aluminosilicate affected the ionic interactions with the S{sup 2−} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

New insights into the role of fly ash in mitigating alkali-silica reaction (ASR) in concrete

Alkali-silica reaction (ASR) mitigation mechanisms of fly ash in concrete are still being debated and remain an interesting research topic. This study provides new insights into the role of aluminum oxide (Al{sub 2}O{sub 3}) in fly ash particles on ASR mitigation. A comprehensive test program was conducted and included expansion measurements, dissolution model experiments of exposed and embedded borosilicate glass elements, analyses of pore and immersion solutions, quantification of Ca(OH){sub 2} content, and microstructural analyses. It was found that in addition to the traditionally accepted mitigation mechanisms such as alkali binding, diffusion control and reduction in available Ca(OH){sub 2}, dissolution control of reactive aggregates by aluminum discharged from fly ash particles also contributed to the ASR mitigation. Re-introducing alkalis to fly ash-incorporated concrete prisms which exhibited undeleterious expansion under a long-term ASR exposure triggered and significantly increased the subsequent expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ground-State In-Plane Light-Holes in GaAs/AlGaAs Structures [Book Chapter]

We have performed low-temperature magnetoluminescence, far-infrared cyclotron resonance, and magneto-transport measurements on narrow (4.5 nm) GaAs/Al 0.25 Ga 0.75 As single quantum-wells. The ground state in-plane valence band was found to be light and very nonparabolic, i.e., at zone center, the valence band mass is m v ≈ 0. 1 and for E f ≈ 10 meV, m v ≈ 0.25.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Influences of Mg Ions and Al Ions on Deposition Behavior of Supersaturated Silicic Acid - 20261

Silicic acid can change into various species such as deposit, colloidal, and soluble form under certain conditions: for example, gradual pH changes around geological disposal repositories. In particular, silicic acid deposits narrow groundwater flow paths, thereby restricting the flow of groundwater. Such effects may contribute to a delay in radionuclide migration. Previous studies have reported that silicic acid supersaturated in sodium and calcium ions can narrow the flow paths. This study examined the effect of magnesium (Mg) and aluminum (Al) ions on the deposition of supersaturated silicic acid on the solid phase. The deposition behavior of supersaturated silicic acid on the solid phase was investigated in a batch system while changing the initial supersaturation concentration, the coexisting ion concentration, and the amount of added solid phase. In the presence of Mg ions, silicic acid precipitation increased with increasing Mg ion concentration due to the influence of the electrolyte, and crosslinking reactions. The coexistence of Al ions significantly suppressed silicic acid deposition due to the formation of a covering on the solid surface during Al ion hydrolysis under conditions of high Al concentration (1.4 mM). On the basis of these experimental results, the apparent deposition rate constant of silicic acid was estimated to be in the range from 10{sup -11} to 10{sup -10} m/s. The Damkoehler number (the dimensionless number expressed by the ratio of the characteristic time of mass transfer and the chemical reaction constant) was sufficient to cause the clogging of the host rock by deposition. This suggests that supersaturated silicic acid deposition, regardless of the presence of Mg ions (and Al ions), contributes to improving barrier performance against radionuclide migration in the host rock. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Laser-Induced Plasma as a Method for the Metallic Materials Hardness Estimation: An Alternative Approach

The application of an alternative laser-induced breakdown spectroscopy (LIBS) method based on transversely excited atmospheric (TEA) CO2 laser was investigated for the first time for estimating the hardness of metallic materials. The human eye-safe (TEA) CO2 laser, operating at 10.6 µm, was used for plasma generation. The LIBS spectra were recorded by employing a cost-effective CCD camera for the time-integrated and spatial resolved measurements. The cast iron and aluminum alloys samples with different hardness have been tested. The ratio between the magnesium ionic and neutral lines in LIBS spectra was applied for estimating the material hardness. In addition, the hardness of all samples included in this study was determined using the conventional method for material hardness determination, i.e. Vickers hardness test. The linear dependence of magnesium lines intensity ratio on the sample’s hardness was obtained for both kinds of materials. Profilometric measurements were used to verify that the newly-introduced method is almost nondestructive for the investigated metals. The results obtained in the present work confirmed the potential of using this original LIBS system not only for the fast elemental analysis but also for the direct estimation of the hardness of metals and alloys. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Review of Methodology Development for Controlling Loss of Alloying Elements During the Electroslag Remelting Process

Electroslag remelting (ESR) is an advanced secondary refining technology for the production of clean, fully dense, and homogeneous castings of steels and alloys by removal of undesirable elements and nonmetallic inclusions. However, because of some potential reactions between reactive elements, i.e., Al and Ti, in liquid metal and oxygen as well as weak oxides, such as FeO and SiO{sub 2}, in slag during the ESR process, it is impossible to hold those oxidative elements within specification or to maintain them uniformly from the bottom to top of the resultant ingot. According to a literature survey, recent fundamental research on the oxidation behaviors of Al and Ti in nickel-based alloy by ESR-type slag is scarce. Therefore, summarizing previous knowledge on the controlling loss reactive elements during ESR of Fe- and Ni-based alloys in view of thermodynamics and kinetics is in order to increase the basic understanding of the reaction mechanism between those elements and oxygen and weak oxides in the slag, which can guide the development of a new remelting technique that retards the oxidation of Al and Ti in Inconel 718 alloys during the ESR process. The presence of impurity elements, such as oxygen and sulfur, can also deteriorate the mechanical properties of metal products. Therefore, the inter-related literature about desulfurization during the ESR process is also reviewed in this article.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interfacial Reaction Between High-Al Steel and CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes with Different CaO/Al{sub 2}O{sub 3} Ratios at 1773 K (1500 °C)

The reaction between high-Al steel and CaO-Al{sub 2}O{sub 3}-based mold fluxes with different CaO/Al{sub 2}O{sub 3} ratios was investigated at 1773 K (1500 °C). The increase of CaO/Al{sub 2}O{sub 3} ratio from 1 to 3 accelerated the accumulation of Al{sub 2}O{sub 3} in the flux and reduction of Na{sub 2}O, but had no significant effect on the reduction of SiO{sub 2} and B{sub 2}O{sub 3}. The microstructure of flux-steel interfaces showed that emulsification occurred in the reaction between steel and mold flux. The emulsification was affected by the precipitation of crystals in the flux after the change of flux composition due to the interfacial reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Liquid Inclusion Distortion by Lens Shape Effect: In Situ Observation and Quantification on LCAK Steels Using HT-CSLM

Because of interfacial and surface tension, micron-sized liquid oxide droplets are expected to change from spherical (when fully immersed in liquid steel) to lens shape on top of steel. Inclusion sizes were measured by automated analysis of polished sections of calcium-treated aluminum-killed steel. A sample of the same steel was remelted and observed using confocal scanning laser microscopy. Droplets on the steel surface appear to have approximately twice the diameter of fully immersed spherical inclusions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Accurate Density Calculation for Molten Slags in SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO-‘FeO’-‘Fe{sub 2}O{sub 3}’ Systems

A simple and accurate density calculation model for molten slags containing iron oxides in SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO-‘FeO’-‘Fe{sub 2}O{sub 3}’ systems is established in the present study, by extending a previous model developed for SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO systems. To quantitate the iron oxides in slags, a new method is proposed to recalculate all the iron oxides as ‘FeO’ and ‘Fe{sub 2}O{sub 3},’ which represent the iron oxides in equilibrium with metallic iron and the air atmosphere, respectively. This method is essentially different from most of the other models that dealt with ferrous (FeO) and ferric (Fe{sub 2}O{sub 3}) iron oxides. A total of 860 experimental data points for iron oxide-containing melts are critically collected for the optimization of the model parameters. The model achieves an excellent agreement with literature values with an average error of 1.96 pct and an overall absolute error of 0.092 g/cm{sup 3}. The compositional dependences from unary to multicomponent systems are discussed using the present model. The results show that the densities always increase with the increasing ‘FeO’ or ‘Fe{sub 2}O{sub 3},’ and the substitution of ‘FeO’ by ‘Fe{sub 2}O{sub 3}’ will cause a decrease in density. In the multicomponent systems, SiO{sub 2} tends to have a larger impact on the density of ‘Fe{sub 2}O{sub 3}’-containing systems compared with ‘FeO’-containing systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production

Lower-quality petroleum coke with higher levels of sulfur and metal impurities will have to be used for the manufacturing of anodes for aluminum production in the future. The sulfur and metallic impurities affect the anode properties in the aluminum production process, but the chemical identity of the metal species in the coke is not known. In this study, industrial petroleum cokes with high sulfur levels were analyzed by X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) in order to determine the identity of the V, Ni, and Fe impurities. The XANES spectra were compared with pure-phase standards. EXAFS was used to compare the impurity metal structures with known crystal structures. It was found that V is present mainly as hexagonal V{sub 3}S{sub 4}. Ni is present mainly as hexagonal NiS, and Fe is present as hexagonal FeS. This knowledge of the chemical states of the metal elements in coke, which are known to affect anode performance, is the first step in understanding the mechanism of the action of these elements on anode reactivity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation on the Surface Vortex Formation During Mechanical Stirring with an Axial-Flow Impeller Used in an Aluminum Process

The present study investigated the mechanism of surface vortex formation in an aluminum melt vessel stirred by an axial-flow impeller mechanically. The oxide film is formed at the aluminum melt/air interface, and the movement of the interface entrains the oxide film and inclusions. Hence, the transient movement of melt–air interface is significant. The present study conducted a water model experiment and numerical simulation focusing on the movement of gas–liquid interface. The present study found that the oxide film can be entrained by two phenomena: (1) local surface vortex and (2) sloshing near the vessel wall. The local surface vortex is formed due to the pressure distribution around the impeller, and the sloshing is caused by macroinstabilities, which is generated by the discharged flow of axial-flow impeller. Besides, the shape of gas–liquid interface is dependent on the impeller shape. The axial-flow impeller gives rise to steeply curved shape of gas–liquid interface near the impeller shaft.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Formation Mechanisms and Microstructure Characterization of Al/Al{sub 3}Ni In-situ Composite by Compound Casting

The Compound casting method was used to produce an Al/Ni bimetal composite. The mechanisms of formation of the reinforcing intermetallic phases were studied and the produced bimetal composite’s microstructure was then characterized. The results showed that the Al/Ni interface consisted of two intermetallic layers including Al{sub 3}Ni{sub 2} and Al{sub 3}Ni. It is suggested that the Al{sub 3}Ni reinforcing particles of the composite originated from two sources. (1) Some Al{sub 3}Ni particles detached from the Al{sub 3}Ni layer formed at the interface between the Ni core and the Al melt and dispersed in the liquid Al and (2) Al-Al{sub 3}Ni eutectic phase, which formed during the solidification process. The increase in the temperature led to the formation of more reinforcing particles and extended the depth of dispersion of the particles in the Al matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Remelting Current on Structure, Composition, Microsegregation, and Inclusions in Inconel 718 Electroslag Remelting Ingots

The macro- and microstructures, chemical compositions, microsegregations, and nonmetallic inclusion characteristics at different positions of the as-cast IN718 ingots produced by a laboratory-scale electroslag remelting (ESR) furnace under four remelting currents (150, 200, 250, and 300 A) were compared and investigated comprehensively. The results indicate that the average melting rate increases with the increasing remelting current, and the molten pool tends to be deeper. Thus, at the same position of the ESR ingots, the volume fraction of the segregated phase, the degree of elemental segregation, and the secondary dendrite arm spacing have the same tendency to increase with the increasing remelting current and show an increasing trend from the bottom to the top along the height of each ingot. If the current is set relatively low, the oxygen and nitrogen levels in the ingots increase, the conditions that make the contents and distributions of Al and Ti become unstable. In addition, the major nonmetallic inclusions in the IN718 ESR ingots are MgO·Al{sub 2}O{sub 3} complex oxide inclusions with a three-layer structure and (Nb,Ti)N nitrides. The volume fractions and mean equivalent diameters display a downward trend with the increasing remelting current. The size and quantity of these inclusions are always larger in the upper portions of the ingots than those in the lower portions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

MgAl{sub 2}O{sub 4} Inclusion Agglomeration on the Surface of Liquid Steel

The aggregation, separation, and agglomeration behaviors of MgAl{sub 2}O{sub 4} inclusions were observed by CLSM. From these observations, it was found that the cavity bridge force between two inclusion particles plays a dominant role in the process of agglomeration, and that the action distance of the cavity bridge force is proportional to the radius of the MgAl{sub 2}O{sub 4} inclusion. Once a stable cavity bridge between two MgAl{sub 2}O{sub 4} particles forms, the aggregated MgAl{sub 2}O{sub 4} inclusion cannot be separated again.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Kinetic Study on Alloying Element Transfer During an Electroslag Remelting Process

Experimental and theoretical studies have been carried out to investigate the effects of slag on the alloying elements in ingots during the electroslag remelting (ESR) process with a focus on developing a mass-transfer model to understand the mechanism of slag-metal reaction. Stainless steel 1Cr21Ni5Ti was used as the electrode and remelted with two different kinds of slags using a 50-kg ESR furnace. The contents of sulfur, aluminum, titanium and silicon along the axial direction of the produced ingots were analyzed. On the basis of the penetration and film theories, the theoretical model developed in this work elucidates the kinetics of the slag-metal reaction revealing the mechanism of alloying element transfer during the ESR process. The calculation results obtained from the model agree well with the experimental results. The model indicates that the resultant [O] coming from the desulfurization reaction of (O{sup 2−}) + [S] = (S{sup 2−}) + [O] causes the oxidation of alloying elements in steel by [M] + [O] = (MO). The distribution ratio of sulfur L{sub S} decreases with the increase of slag temperature in the first slag-temperature-rising period, and the concentration of sulfur in the ingot at the beginning of the ESR process is lower than in the rest of the process because of the combination of the large distribution ratio of sulfur L{sub S} and excellent kinetic conditions. The concentration of aluminum along the height of the ingot has an increasing trend in the first slag-temperature-rising period, while it has a decreasing trend in the rest of the process. Two methods can solve this problem: one is starting up the ESR furnace by high temperature molten slag technology and the other is continually adding extra titania into the molten slag in the first slag-temperature-rising period.

36 MATERIALS SCIENCE↗