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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Dissolution Behavior and Phase Evolution During Aluminum Oxide Dissolution in BOF Slag

Basic oxygen furnace (BOF) slag is a byproduct in the steel making process and is produced in considerable amounts. Thus, its valorization is important. Additives such as Al{sub 2}O{sub 3} can be utilized to modify the composition and mineralogy of the slag provided that a fast and effective dissolution of these additives in molten slags can be ensured. With this in mind, the dissolution of Al{sub 2}O{sub 3} particles in molten BOF slag has been investigated between 1500 and 1600 °C. In all cases, a dissolution zone forms around the dissolving particle which limits the dissolution rate in the melt under natural convection conditions. The dissolution in the current system is found to be an indirect process, wherein crystalline reaction products like CaAl{sub 4}O{sub 7} (CA{sub 2}) and CaAl{sub 2}O{sub 4} (CA) form on the surface of the particles. CA forms at 1500 °C and CA{sub 2} at 1600 °C. These reaction products form a continuous layer on the surface of the dissolving particles but the thickness of this reaction layer remains limited. The experimental data have been utilized to evaluate the dissolution paths. Near the Al{sub 2}O{sub 3}/slag interface, the inter-diffusion of Al{sub 2}O{sub 3} and CaO occurs due to which the dissolution path shifts towards the Al{sub 2}O{sub 3}-CaO binary system. A phenomenological model is presented to explain the evolution of the dissolution process in the current system, wherein the kinetics of the process is used to explain the reaction products formed at 1500 °C and 1600 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spatial zonation of a hydrotalcite-like phase in the inner product of slag: New insights into the hydration mechanism

The nano-structural evolution of the inner product of ground granulated blast furnace slag in blended cement at 7, 14, 28 56 and 180d was revealed. Three distinct layered inner hydration product region were observed because of the spatial zonation of hydrotalcite-like phase, C-A-S-H gel and Ca-Al LDH phase. The zonation of inner hydration product explains the presence of the multi-rims features of the slag grains with a relatively high reaction degree at very late ages. Diffusion of dissolved ion from slag grains and the effect of pore space on the reorganization of hydration products play a key role in forming the spatial zonation of inner hydration product. The findings of the zonation of inner region argue that the lack of pore space in the inner region makes the continued dissolution of slag hard to complete.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Influence of CaO/FeO ratio on the formation mechanism and properties of alkali-activated Fe-rich slags

Highlights: • Effect of the CaO/FeO molar ratio in alkali-activated Fe-rich slags is unraveled. • Low CaO/FeO molar ratios enhance the early kinetics and compressive strength. • Reaction extent and strength further increase with higher CaO/FeO ratio after 7 days. • Fe{sup 2+}-trioctahedral layers of the binder are hydroxylated and in a silicate phase. • The final strength is determined by the influence of Ca on the reaction products. In the search for CO{sub 2} mitigating cement technologies, alkali-activated Fe-rich slags present a possible alternative. The influence of the chemical composition of the synthetic Fe-silicate slag on the reaction mechanisms is assessed by varying the CaO/FeO molar ratio. The alkali-activated Fe-rich slags consist of trioctahedral layers that are shown to be hydroxylated and in contact with silicates, in a similar way to phyllosilicate minerals. The formation of this phyllosilicate-like structure is hindered during the first days for samples with high CaO/FeO ratios, because of the partial incorporation of Ca in the trioctahedral layers. At later ages, the samples with higher CaO/FeO ratios gain in reaction extent, to exceed the reaction extent of low CaO/FeO ratios at 28 days and beyond. The increase in compressive strength is even more pronounced than the effect on the reaction extent, which underlines the importance of Ca on the inherent strength of the binding phases.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Pressurized in situ X-ray diffraction insights into super/subcritical carbonation reaction pathways of steelmaking slags and constituent silicate minerals

This study explores mineral carbonation of industrial stainless steelmaking slags and relevant synthetic constituent minerals via in situ pressurized X-ray diffraction, to clarify carbonation reaction pathways and efficiency for carbon storage and waste valorization. The primary mineral phases of Argon Oxygen Decarburization (AOD) and Continuous Casting (CC) slags, namely, åkermanite, bredigite, cuspidine, merwinite, and β- and γ-C 2 S, were reacted in a custom-built beryllium-capped XRD reactor filled with either water-saturated (wet) subcritical CO 2 (g), or wet supercritical CO 2(SC) , in a series of carbonation experiments. Formation of calcite and aragonite was observed for most Ca-bearing minerals, transient precipitation of metastable vaterite was observed, while carbonation of AOD and CC slags in CO 2(SC) resulted in hydrated crystalline calcium carbonates and indirect evidence of amorphous carbonate. Overall, results obtained suggest that low-pressure subcritical carbonation routes are attractive for standalone slag carbonation processes, while high-pressure supercritical carbonation routes are amiable to symbiotic integration with CO 2(SC) -generating green technologies.

42 ENGINEERING↗
DOE OSTI2011

Kinetics of steel slag leaching: Batch tests and modeling

Reusing steel slag as an aggregate for road construction requires to characterize the leaching kinetics and metal releases. In this study, basic oxygen furnace (BOF) steel slag were subjected to batch leaching tests at liquid to solid ratios (L/S) of 10 and 100 over 30 days; the leachate chemistry being regularly sampled in time. A geochemical model of the steel slag is developed and validated from experimental data, particularly the evolution with leaching of mineralogical composition of the slag and trace element speciation. Kinetics is necessary for modeling the primary phase leaching, whereas a simple thermodynamic equilibrium approach can be used for secondary phase precipitation. The proposed model simulates the kinetically-controlled dissolution (hydrolysis) of primary phases, the precipitation of secondary phases (C-S-H, hydroxide and spinel), the pH and redox conditions, and the progressive release of major elements as well as the metals Cr and V. Modeling indicates that the dilution effect of the L/S ratio is often coupled to solubility-controlled processes, which are sensitive to both the pH and the redox potential. A sensitivity analysis of kinetic uncertainties on the modeling of element releases is performed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Determination of the Mode of Occurrence of V, Fe, and Mn in Slags and Charge of Vanadium Production by X-Ray Spectroscopy

Samples of technogenic raw materials are studied by spectroscopic methods. The chemical composition of a roast slag and a charge of vanadium production is analyzed by the X-ray fluorescence method (XRF). The possibilities of X-ray photoelectron spectroscopy are studied for determination of the oxidation state of elements in technogenic raw materials. It is found that ~30% of V occurs in the slag as V(III), whereas, in the charge, the content of V(V) and V(IV) is ~80 and 20%, respectively; no V compounds with the lowest oxidation states are found. Iron in the slag and charge samples is present as Fe{sub 3}O{sub 4}, and Mn mostly occurs as Mn(III). The oxidation state of V in the slag and charge can be determined by the intensity ratio of the K and L lines of the XRF spectra; however, this method is not recommended because of its low accuracy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High Temperature Viscosity Model For Glassy Slags Produced From The Air Products Municipal Waste Gasification Process

Air Products, Inc. (AP) is developing a technology that uses plasma-enhanced gasification to create syngas from Municipal Solid Waste (MSW), for the purpose of generating electricity at a large scale. The process is intended to convert the inorganic components in MSW to a slag that flows easily through and from the gasifier. AP and the Savannah River National Laboratory (SRNL) have established a Cooperative Research and Development Agreement (CRADA) to improve the properties of the slag material produced from MSW gasification. A primary objective for AP is the development of a viscosity model, which can be used to predict the viscosity of the slag produced in the gasification process as a function of its composition in order to ensure that the incoming feeds will ultimately yield slag that can effectively be poured from the gasifier. In addition, the development of such a model could allow AP to determine the type and amount of additives to mix with the incoming MSW to target a specific viscosity range as well as identify waste compositions that could lead to difficulties during processing.

high temperature↗
DOE OSTI2021

Blast furnace slag reactions in various solutions (Interim Report)

Blast furnace slag (BPS) is a critical component of grout formulations for the remediation of low activity nuclear waste. This interim report describes the initial results of a study designed to investigate the fundamental mechanisms of BPS dissolution. The goal of the work is to delineate the physicochemical aspects of the slag that impart beneficial properties to grout formulations to enable the consistent production of a slag-replacement material (“designer slag”) that performs better than what is commercially available. This report documents the dissolution experiments that were conducted using nine different initial solution compositions. Solution measurements for each solution, including pH and solution composition, are given for 1, 7, 14, 28, and 56 day intervals samples. Scanning electron microscopy images are presented for the 56 day samples from each of the solutions. Inferences about reaction mechanisms and 56-day mineralogy are made based on the information collected to date. Some conclusions are made based on the work performed for this interim report, and a path forward including the strategy for making stronger conclusions based on X-ray diffraction (XRD) analyses is presented.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2011

Structural characteristics and hydration kinetics of modified steel slag

This study investigates the structural characteristics and hydration kinetics of modified basic oxygen furnace steel slag. The basic oxygen furnace steel slag (BOFS) was mixed with electric arc furnace steel slag (EAFS) in appropriate ratios and heated again at high temperature in the laboratory. The mineralogical and structural characteristics of both BOFS and modified steel slag (MSS) were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, Raman and Fourier transform infrared spectroscopies. The results show that modification increases alite content in MSS and decreases alite crystal size with the formation of C{sub 6}AF{sub 2}. One more obvious heat evolution peak appears in MSS's heat-flow rate curves in comparison to BOFS, becoming similar to that of typical Portland cement paste. As a result, its cementitious activity is much improved.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The Importance of Slag Structure to Boron Removal from Silicon during the Refining Process: Insights from Raman and Nuclear Magnetic Resonance Spectroscopy Study

Slag structure plays an important role in determining the relative ease of boron removal from silicon. Correlation between slag structure and boron removal thermodynamics was experimentally studied by Raman and nuclear magnetic resonance (NMR) spectroscopy using CaO-SiO{sub 2}-Na{sub 2}O slags with different optical basicities (0.6 to 0.71). Optimization of slag depolymerization leads to efficient removal of boron. The extent of nonbridged oxygen content (NBO/T) and boron removal gradually increased with an increase in optical basicity from 0.6 to 0.66: B{sub 2}O{sub 3} derived from boron oxidation captured nonbridging oxygens of Q{sup 0}(Si), Q{sup 1}(Si), and Q{sup 2}(Si), and was incorporated into the silicate network in the form of Q{sup 3}(Si and B). When optical basicity increased to 0.71, NBO/T rapidly increased and boron removal decreased considerably. Quick depolymerization of Q{sup 3}(Si and B) deteriorated the stability of boron. Various structural forms of boron in the silicate network were successfully detected: the BO{sub 3} trihedrons {sup [3]}B-3Si, {sup [3]}B-2Si-1NBO, and BO{sub 3} (nonring), and the BO{sub 4} tetrahedrons BO{sub 4} (1B, 3Si) and BO{sub 4} (0B, 4Si). BO{sub 4} (1B, 3Si) was the main structure contributing to the increase of boron capacity; BO{sub 3} (nonring), detected under higher optical basicity conditions, may cause deterioration of boron removal by suppressing its oxidation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental Study on the Formation of V-Rich Spinel Phase in CaO-SiO{sub 2}-MgO-FeO{sub t}-Al{sub 2}O{sub 3}-V{sub 2}O{sub 3}-P{sub 2}O{sub 5} Slags at 1573 K (1300 °C)

To concentrate vanadium dissolved in steelmaking slag and to separate the obtained vanadium (V)-concentrating phase by a magnetic method, the mineral phases in a CaO-SiO{sub 2}-MgO-FeO{sub t}-Al{sub 2}O{sub 3}-V{sub 2}O{sub 3}-P{sub 2}O{sub 5} system at 1573 K (1300 °C) were characterized by scanning-electron microscopy-energy-dispersive spectroscopy and X-ray diffractometry. When the samples were equilibrated in a pure iron crucible and argon atmosphere, four phases were identified, namely, orthosilicate, V-bearing spinel, wüstite, and a glass phase. The orthosilicate, V-bearing spinel, and glass phase occurred in all samples, whereas wüstite appeared only in samples with a higher basicity or high FeO{sub t} content. The results indicate that the V-bearing spinel phase, which is analogous to Fe{sub 3}O{sub 4}, is a thermodynamically stable phase that is suitable for the enrichment of vanadium dissolved in slags. Further analysis reveals that the increases in contents of FeO{sub t} and MgO in slag favor spinel-phase formation. When the slags are saturated by the wüstite phase, almost all dissolved vanadium can be concentrated in the spinel phase.

36 MATERIALS SCIENCE↗
DOE OSTI2021

GeoMicro3D: A novel numerical model for simulating the reaction process and microstructure formation of alkali-activated slag

Highlights: • The GeoMicro3D model was innovatively developed for simulating the reaction process and microstructure formation of AAS. • In GeoMicro3D, the dissolution of slag and reactions of aqueous ions are fundamentally described in the local lattice cell. • A novel approach is proposed to speed up the nucleation simulations. • GeoMicro3D was implemented and verified with the relevant experimental data and thermodynamic calculation results. For the first time, this study developed a novel model, named GeoMicro3D, to simulate the reaction process and microstructure formation of alkali-activated slag. The GeoMicro3D model consists of four modules that are designed to simulate, respectively: (i) the initial spatial distribution of real-shape slag particles in alkaline activator, (ii) the dissolution of slag and diffusion of ions via the transition state theory and lattice Boltzmann method, respectively, (iii) the spatial distribution of reaction products using a nucleation probability theory, and (iv) the chemical reactions with thermodynamic modelling. Afterwards the GeoMicro3D model was implemented and verified. The simulation results were discussed and compared with the relevant experimental data and thermodynamic calculation results using GEMS. A good agreement was found in the comparisons, showing the strong simulation capability of GeoMicro3D.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Evaluation of copper slag blast media for railcar maintenance

Copper slag was tested as a blasting substitute for zirconium silicate which is used to remove paint from railroad cars. The copper slag tested is less costly, strips paint faster, is produced near the point of need, provides a good bonding surface for paint, and permits the operator to work in a more comfortable position, i.e., standing nearly erect instead of having to crouch. Outdoor blasting with the tested Blackhawk (20 to 40 mesh) copper slag is also environmentally acceptable to the State of Utah. Results of tests for the surface erosion rate with copper slag blasting are included.

Sagers, N. W.↗
NASA NTRS1995

Space Shuttle solid rocket motor slag expulsion mechanisms

A 13 psi pressure perturbation occurred at approximately 68 seconds on the right Redesigned Solid Rocket Motor (RSRM) during the STS-54 space shuttle mission. While pressure perturbations are a normal characteristic of RSRM operation, the magnitude of the STS-54 perturbation and the resulting thrust imbalance between the left and right motors was outside of flight experience. A joint Marshall Space Flight Center (MSFC) and Thiokol Corporation (RSRM manufacturer) team soon narrowed the probable cause to a temporary nozzle restriction due to slag expulsion. In support of the team, Rockwell Aerospace performed fluid finite element simulations and vehicle flight dynamic correlations to investigate possible slag expulsion mechanisms responsible for pressure perturbations. Results of the simulations and analyses provided evidence that the combination of flight induced accelerations acting on accumulated slag and nozzle vectoring were the most probable cause of RSRM slag expulsion.

Hopson, Charles B.↗
NASA NTRS1996

Correlation of Slag Expulsion with Ballistic Anomalies in Shuttle Solid Rocket Motors

During the Shuttle launches, the solid rocket motors (SRM) occasionally experience pressure perturbations (8-13 psi) between 65-75 s into the motor burn time. The magnitudes of these perturbations are very small in comparison with the operating motor chamber pressure, which is over 600 psi during this time frame. These SRM pressure perturbations are believed to he caused primarily by the expulsion of slag (aluminum oxide). Two SRM static tests, TEM-11 and FSM-4, were instrumented extensively for the study of the phenomena associated with pressure perturbations. The test instrumentation used included nonintrusive optical and infrared diagnostics of the plume, such as high-speed photography, radiometers, and thermal image cameras. Results from all of these nonintrusive observations provide substantial circumstantial evidence to support the scenario that the pressure perturbation event in the Shuttle SRM is caused primarily by the expulsion of molten slag. In the static motor tests, the slag was also expelled preferentially near the bottom of the nozzle because of slag accumulation at the bottom of the aft end of the horizontally oriented motor.

Sambamurthi, Jay K.↗
NASA NTRS2008

The Solid Rocket Motor Slag Population: Results of a Radar-based Regressive Statistical Evaluation

Solid rocket motor (SRM) slag has been identified as a significant source of man-made orbital debris. The propensity of SRMs to generate particles of 100 m and larger has caused concern regarding their contribution to the debris environment. Radar observation, rather than in-situ gathered evidence, is currently the only measurable source for the NASA/ODPO model of the on-orbit slag population. This simulated model includes the time evolution of the resultant orbital populations using a historical database of SRM launches, propellant masses, and estimated locations and times of tail-off. However, due to the small amount of observational evidence, there can be no direct comparison to check the validity of this model. Rather than using the assumed population developed from purely historical and physical assumptions, a regressional approach was used which utilized the populations observed by the Haystack radar from 1996 to present. The estimated trajectories from the historical model of slag sources, and the corresponding plausible detections by the Haystack radar, were identified. Comparisons with observational data from the ensuing years were made, and the SRM model was altered with respect to size and mass production of slag particles to reflect the historical data obtained. The result is a model SRM population that fits within the bounds of the observed environment.

Horstman, Matthew F.↗
DOE OSTI2022

Slag Degassing for Electroslag Remelting Using Cold Start

The effect of slag degassing prior to cold start electroslag remelting (ESR) was investigated using various heat treatments of a commercial 40CaF2 – 30CaO – 30Al2O3 slag. The slag was either degassed in a vacuum heat treatment furnace or in a box furnace in air. Vacuum heat treatment included partial pressure of Ar gas. Several temperatures, ramp rates and/or holding times were investigated for each condition and the pressure was monitored for the heat treatment in the furnace with controlled atmosphere. A research scale 200 kg capacity ESR furnace was used for the experiments along with 1018 steel and 316 stainless steel electrodes. Significant differences in ingot quality were related to the sidewall and the presence of pores which were primarily located near the bottom of the ingot. Adjustments in the heat treatment temperature for heat treatment in air eventually led to an ingot quality near that obtained using slag degassed under vacuum and/or in a controlled atmosphere.

Detrois, Martin↗
DOE OSTI2022

Nitinol Electroslag Remelting: Initial Slag Study

Nitinol’s unique shape memory and super-elastic properties make it attractive for many applications in biomedical, automotive, aerospace, industrial refrigeration, and waste heat reclamation industries. The fatigue performance is limited however, by non-metallic inclusions (NMI) formed during the traditional VIM/VAR or multi-VAR process. ESR is a potential alternative melt process and is commonly used to refine ingot chemistry and enhance the metallurgical structure of many superalloys and specialty steels, but no study on ESR of Nitinol has been reported to date. The key to establishing a successful ESR process is selecting a compatible slag. In this study, several different slag chemistries are evaluated for their compatibility with Nitinol. One slag chemistry is chosen, along with a control, to produce four Nitinol ESR ingots. Pursuit of a novel slag chemistry for adequate Nitinol refinement is discussed.

Fezi, Kyle↗