Oxide Slag Research Articles

Influence of Graphene Oxide and Ground Granulated Blast Furnace Slag on Engineering Properties of High-Performance Concretes

Abstract Concrete structures immersed in sea water suffer severe corrosion, and the application of nanomaterials to concrete presents an innovative approach to enhancing both its physical and mechanical properties. In this paper, the effects of combined admixtures of graphene oxide nanoplatelets (GONPs) and ground granulated blast furnace slag (GGBFS) on concrete were studied, and mechanical and physical tests were performed. It was known that the GGBFS admixture improves the durability of concrete, but in concrete samples containing both GONPs and GGBFS, the compressive strength increased by nearly 43 % and 46 % at 28 and 90 days of curing, respectively, compared with ordinary portland cement (OPC) concretes. The same admixing regime caused an increase in flexural strength of up to 58 % and 59 % during the same time spans. This was accompanied with a significant reduction in chloride permeability, which was appraised by a 64 % drop in electrical conductivity measurements. The GONPs additive, even at the very low concentrations, accelerated the formation of calcium silicate hydrate, thereby enhancing the mechanical and flexural strengths that directly affect the durability and water and chloride absorption. The overall durability and rebar corrosion resistance that were shown through electrochemical tests are consequences of the combined improvements in the physico-mechanical concrete properties. OPC concrete is thus both stronger and significantly more chloride ion resistant with additions of GONPs in the parts per million range and by replacing it with 50 percent by weight GGBFS. The enhanced pozzolanic reactions in concrete help to fill the porosity and significantly contribute to the curtailment mechanism.

Effect of tundish flux on reoxidation behavior of Si-killed 316L stainless steel

The slag-metal reactions between Si-killed 316L stainless steel and the fluxes rice hush ash (RHA), RHA + CaO–SiO2 (flux A), and RHA + CaO–Al2O3 (flux B) were conducted in an induction furnace at 1773 K to investigate the effects of the various fluxes on the reoxidation behavior of the liquid steel. The total oxygen (T.O) content in the liquid steel increased when the steel reacted with RHA and RHA + A fluxes, whereas T.O decreased when the liquid steel reacted with RHA + B flux. The number density of non-metallic inclusion (NMI) in the steel reacted with RHA, RHA + A, and RHA + B fluxes increases, stays constant, and decreases, respectively. The increase in the number density of NMI is due to the reoxidation of the molten steel caused by the dissociation reaction of SiO2. However, the number density of NMI in the steel decreased since B flux has a higher value of physicochemical factor, i.e., log(ΔC/η), where η is slag viscosity and ΔC represents concentration difference between initial content and saturation limit of target oxide in slag. The reoxidation reaction caused by the presence of SiO2 in the fluxes and inclusion absorption (dissolution) reactions are competitive or coupled each other. Higher SiO2 activity in the fluxes (such as RHA) resulted in easier formation of SiO2-rich inclusions. However, the SiO2 activity in Flux A and Flux B is lower than that in RHA, and the MnO–SiO2 and SiO2 inclusions in the Si-killed steel were reduced by Al to form MnO–SiO2–Al2O3(-Cr2O3) system inclusions in the steels reacted with Flux A and B, respectively.

Dual effect of MgO on softing–melting performance of high gangue sinter: changes of slag viscosity and phase composition

ABSTRACT In this paper, through softening–melting test of sinter with high MgO content produced by iron and steel enterprises, the double influence of high MgO concentration on soft melting performance of sinter was researched. The experimental results show that in the sinter melting process, on the one hand, the slag viscosity will gradually decrease from 0.107 to 0.095 Pa·S at 1540°C with the increase in MgO content in the sinter. On the other hand, with the increase in MgO content, the content of solid oxide in sinter slag at 1540°C increases from 2.41% to 15.31%, the separation of slag and iron at high temperature also makes a large number of MgO elements precipitate out in solid phase, which hinders the flow performance of slag. In addition, the influence amplitude of MgO content on the melting performance of sinter mainly depends on gangue content in sinter.

A Study on the History of Advances in Ancient Iron Making Based on Correlation of Oxides in Slag

A lot of slag was produced by ancient production processes such as smelting, melting, and refining. Iron slag has information that can be used to determine the characteristics of the site, the iron-making process and manufacturing date, but there is a limit to reading information through visual observation and nondestructive analysis. Various slag terms have been used depending on the location and characteristics, but it is necessary to use terms that have exact meaning and unity. Although many scientific analyses have been supplemented by archaeological theses, the iron-making trends of each period have not yet been systematically proven. This study reviewed the type of iron-making process used for 100 ancient slags. The slags were analyzed by XRF, revealing when it was formed and some of the detailed processes. XRD analysis was used to define and classify Tap slag, Bloom slag, and Ceramic-rich slag as relative concepts. From the Three Kingdoms Period to the Joseon Dynasty, the amount of temperature variation in the iron-making furnace decreased and the GAS reaction became uniform. It was observed that the amount of iron oxide remaining decreased and the proportion of ceramic-rich slag increased. The change in iron oxide content kept decreasing while the levels of refining, smelting, and melting were maintained, in that order. The results confirmed that advances in ancient iron-making technology can be interpreted based on a comparative review of the relative changes in iron oxide and silicon oxide content in slag.

Effect of P2O5 incorporated in slag on the hydration characteristics of cement-slag system

This paper presents the influence of P2O5 incorporated in slag on the hydration characteristics of cement-slag system. It was found that the gradual addition of phosphorus oxide in slag did not change overall mineralogy of the hydration products. Except hydration retardation in the dormant stage, chemically bound water and portlandite contents, hydration degree of slag, and pore structure at all investigated ages were similar among cement-slag pastes with different P2O5 percentages. Furthermore, significantly higher amount of monosulfate was observed as the P2O5 content in slag increased. In addition, a higher Al/Si atomic ratio was measured in the C-S(A)-H gel phase formed in the cement matrix. However, similar Ca/Si atomic ratio of C-S(A)-H gel phase and Mg/Al atomic ratio of hydrotalcite-like phase were determined in all slag pastes, irrespective of the addition of P2O5. In contrast to magnesium ion which was retained within the original slag boundary, phosphorus ions could migrate into cement matrix. Therefore, P/Si atomic ratio of the C-S-H gel phase increased with the increasing phosphorus oxide content in slag, reaching up to ∼0.08.

Zinc oxide in alkali-activated slag (AAS): retardation mechanism, reaction kinetics and immobilization

The relatively fast setting of alkali-activated slag (AAS) greatly restricts its wide application. ZnO can serve as the retardant for AAS. However, the role of ZnO in AAS is not well understood. This paper investigates the retardation mechanism of ZnO in the AAS system and the effects of ZnO on the reaction and performance of AAS. Results showed that a ZnO dosage of 2 wt% prolonged the setting of AAS paste by 72 min and inhibited the growth of C-(A)-S-H gels within the first 6 h of the reaction. The retardation of ZnO in AAS could be attributed to the ‘nucleation inhibition’, in which Zn2+ inhibits the generation of calcium hydroxide precipitation owing to the preferential incorporation of Ca in the calcium zincate (CZ) phase, thus reducing the nucleation sites and slowing down C-(A)-S-H gels growth, until all Zn ions are transformed into CZ phase or bonded in the AAS framework. ZnO slightly reduced the compressive strength and reaction extent of AAS, and was immobilized in AAS through various physicochemical approaches. This study provides a new look into the interaction between ZnO and AAS systems.

Molten Oxide Electrolysis Using Copper-Containing Carbon-Saturated Molten Iron Anode

This study focused on the use of molten oxide electrolysis (MOE) as a low-cost, clean, continuous separation method suitable for incorporation into actual steelmaking processes. We discussed interfacial behavior from molten iron to slag by anodic polarization of the copper-containing carbon-saturated molten iron (metal phase)–molten oxide (slag phase) interface and investigate the operating mechanism of MOE. The basic constant potential electrolysis between the metal phase (Fe-10 wt% Cu-5.0 wt% C) and slag phase (27 wt% CaO-27 wt% SiO2−45 wt% Al2O3−1.0 wt% CaS) by maintaining 1–2 V vs Pt at 1773 K in an Ar atmosphere is described. When polarized, a high concentration of dispersed Cu-rich phase was detected locally near the metal–slag interface but not in the phase center of the metal. At the metal–slag interface, the energies of the Fe-rich and Cu-rich phase–slag interfaces decreased due to electric capillarity, and the Cu-rich phase distributed near the interface.

Operation and Fundamentals of Direct Anode Copper Production From Matte

Copper matte converting is an essential process in copper pyrometallurgy. Replacing traditional batch converting in Peirce–Smith converters (PSCs), continuous converting is becoming a new trend. In this work, a thermodynamic modeling of the copper matte continuous converting process was carried out under actual production conditions. There were five phases in the process: copper matte, copper, Cu2O, slag, and gas. To directly produce anode copper, the continuous converting process was divided into an oxidation period and a reduction period. The multiphase transformation during converting was investigated. The thermodynamic equilibria of the Cu–Fe–S–O–Si system in the process were evaluated. The results showed that the maximum S and O content dissolved in copper was approximately 1 wt pct. The copper matte appeared when the P(S2) was higher than 1.58 × 10−6 atm at T = 1523 K. When P(O2) was higher than 9.55 × 10−5 atm, the Cu2O phase was produced at T = 1523 K. During the conversion of Cu2S to Cu2O dissolved in copper, P(O2) significantly increased, P(S2) rapidly decreased, and copper loss in the slag increased. Reducing the residual rate of oxidation slag and controlling the flow rate of natural gas could reduce the oxygen content in the anode copper and improve the grade of the anode copper.

Laser Directed Energy Deposition-Based Additive Manufacturing of Fe20Cr5.5AlY from Single Tracks to Bulk Structures: Statistical Analysis, Process Optimization, and Characterization

Laser directed energy deposition (LDED) can be deployed for depositing high-performance materials for various engineering applications. Alumina-forming steel is a high-performance material that possesses excellent corrosion and oxidation resistance, finding application in the power generation sector. In the present work, LDED using powder feeding (LDED-PF) was used to deposit Fe20Cr5.5AlY alloy using single-track, multi-track, and multi-layer deposition on SS 316L substrate. Response surface methodology (RSM)-based optimization was used to optimize the single-track deposition. The relationship between the track geometry parameters and the build rate with the LDED-PF processing parameters was studied. Further, the nonlinear relationship among the major process parameters was developed and an analysis of variance (ANOVA) was utilized to find significant parameters. The multi-track deposition yielded densely clad layers with a columnar grain structure. The presence of complex oxide slag of Y, Al, and Zr on the clad layer was detected. A micro-hardness of 240–285 HV was observed in the clad layer, with a hardness of 1088–1276 HV at the slag layer. The multi-layered structures showed a relative density of 99.7% with columnar growth and an average microhardness of 242 HV. The study paves the way for the deposition of dense alumina-forming steel structures for building components for power generation applications.

Recycled granulates manufacturing from spent refractory wastes and magnesium based binder

This paper analyzes the ability of two Spent Refractory Wastes (SRW) for the manufacturing of recycled granulates for construction applications. A binary magnesium oxide and ground granulated blast furnace slag hydraulic binder was considered as an agglomerating agent for the granulates manufacturing. Influence of curing atmosphere was carried out: in air, 20 % CO2 and 100 % CO2 atmosphere up to 28 days. Granulometry, thermal analysis, particle density, bulk density, water absorption and mechanical strength tests were performed to characterize the granulates. SRW showed their ability for the granulates manufacturing. Results demonstrated the existence of a residual reactivity of the wastes considered. A direct relationship between the CO2 content of the curing atmosphere and the granulates hydration degree was observed. Carbonation process increased from 7 days to 28 days and direct relationships were observed between the CO2 content and the carbonation degree as well as between the binder dosage and the carbonation degree. CO2 curing reduced the water absorption and increased the compressive strength of the granulates.

Extending powder lifetime in additive manufacturing: Chemical etching of stainless steel spatter

• Chemical etching can eliminate most oxides from 316 L spatter. • A reduction in oxide coverage from 7–0.7% was possible. • Removal is thought to occur via initial dissolution of oxide-surrounding metal. • Etched spatter powder performed better in LPBF. • Reduced slag layer, and better wetting was seen for LPBF etched spatter. In laser powder bed fusion, unconsolidated metal powder on the build plate tends to comprise a proportion of oxidised powder after repeated use. This is generally caused by the generation of oxidised spatter particles during processing which can contaminate the powder bed, and be incorporated into future builds, ultimately undermining part integrity. Oxidised metal powder often results in porosity, poor layer-layer bonding and detrimental oxides in the printed part. This work uses a new chemical etching approach to remove oxides from the surface of oxidised stainless steel spatter powder. It was shown that a ten-fold reduction in oxide area coverage on spatter powder was possible through submersion in a solution of heated Ralph's etchant for one hour. Oxide removal is thought to occur mostly via dissolution of the metal surrounding and underneath oxide islands on the powder, allowing more aggressive oxide removal. LPBF processing was performed using spatter, etched and virgin powder sieved to an identical powder size range. Etched spatter showed a reduced oxide slag layer on track surfaces compared to spatter. In addition, incorporation of powder into tracks appeared improved after chemical etching of the powder. This work demonstrates that chemical etching has the potential to be used to increase the re-usability and lifetime of spatter or heavily used powder from widely used and corrosion resistant stainless steel powder.

Consideration of the Competitive Adsorption of Oxygen and Sulfur on the Decarburization Kinetics of Fe–C Droplets in Oxidizing Slag

Consideration of the Competitive Adsorption of Oxygen and Sulfur on the Decarburization Kinetics of Fe–C Droplets in Oxidizing Slag

Investigations on the Interaction Behavior between Direct Reduced Iron and Various Melts.

Since the European Union defined ambitious CO2 emission targets, low-carbon-emission alternatives to the widespread integrated blast furnace (BF)—basic oxygen furnace (BOF) steelmaking strategy—are demanded. Direct reduction (DR) with natural gas as the reducing agent, already an industrially applied technology, is such an alternative. Consequently, the melting behavior of its intermediate product, i.e., direct reduced iron (DRI), in either an electric arc furnace (EAF) or a submerged arc furnace (SAF), is of great interest. Based on the conditions in these aggregates, a test series to experimentally simulate the first few seconds after charging DRI was defined. DRI samples with different carbon contents and hot briquetted iron (HBI) were immersed in high- and low-carbon melts as well as high- and low-iron oxide slags. The reacted samples were quenched in liquid nitrogen. The specimens were qualitatively evaluated by investigating their surfaces and cross sections. The dissolution of carbon-free DRI progressed relatively slowly and was driven by heat transfer. However, carbon, present either in the DRI sample or in the melt, not only accelerated the dissolution process, but also reacted with residual iron oxide in the pellet or the slag.

Study on thermodynamics and dynamics of top slag modification in O5 automobile sheets

Abstract This article presents a new Ruhrstahl–Heraeus top slag modifier with an enhanced modification effect at an enterprise producing O5 automobile sheets. To compare the modification effect of the original and new modifiers, the thermodynamic and dynamic conditions of the top slag modification were studied by thermodynamic calculations and dynamic analysis. The results showed that the utilization of both modifiers reduced the total iron (TFe) content in the top slag. The new modifier controlled the CaO/Al2O3 (C/A) and TFe content of the top slag to approximately 1.22–1.30 and 6.07–7.97%, respectively. The adsorption capacity of top slag for inclusions was stronger than that of the top slag modified with the original modifier. The concentrations of Al2O3-type inclusions, Ti x O·Al2O3 composite inclusions, and oxide inclusions were reduced by 13.4, 21.2, and 3.4 per cm2 with the new modifier compared with the original modifier. The total oxygen content in molten steel was 2.8 ppm lower than that of the original when the new modifier was used. Moreover, the new modifier exhibited a better dynamic condition on the surface of top slag, as determined by R-G-B numerical analysis. Overall, the new modifier improved the dynamic conditions of top slag modification, reduced top slag oxidation, and effectively improved the cleanliness of the molten steel.

Enhanced performance of Al2O3–SiC–C castables via in-situ formation of multi-reinforced phases by introducing surface treated composite metal powders

Al2O3–SiC–C (ASC) castables were prepared with bauxite and silicon carbide as major raw materials and introducing large amount of surface treated composite metal powders (STCMPs) as antioxidant. Their comprehensive properties were greatly improved attributed to the in situ formation of multi-reinforced phases including carbide silicon whiskers and mullite fibers in the matrix. Compared with the corresponding samples without STCMPs, the high temperature modulus of rupture of those with 6 wt% STCMPs calcined in air increased by 47.3% and with 8 wt% STCMPs calcined in reducing atmosphere increased by 220%. The retained CMOR ratio of the sample with 6 wt% STCMPs calcined in reducing atmosphere was high up to 50% after 5 cycles thermal shocks. Moreover, the oxidation index and slag erosion index of samples with 6 wt% STCMPs were decreased by 45% and 74%. This work provides a new perspective for the preparation of ASC castables with excellent high-temperature performance.

Separation of ultrafine uranium oxide particles from zirconium alloys in remelting processes with fluoride and oxide slags: thermodynamic analysis

This paper examines how ultrafine particles of uranium oxide interact with zirconium alloys in the presence of oxide and fluoride slags. The authors analyzed the probability of the components of Zr – 1% Nb alloy contaminated with ultrafine uranium oxide particles transitioning into slag phase during the process of remelting fuel element claddings using different fluxing agents. By means of thermodynamic modelling, the authors looked at the interaction of the cladding material of fuel elements used in thermal reactors (zirconium-niobium alloy) contaminated with traces of nanosized uranium oxide with molten oxide and fluoride fluxes in the temperature range of 1,000 to 2,000 oC. It was found that, for the interaction of Zr – 1% Nb alloy with fluoride and oxide melts, the metal should be slightly dissolved in the slag phase. Analysis of the interactions of ultrafine uranium compounds with slag mixtures for the temperature range of 1,000 to 2,000 oC showed a predominant transition of uranium, when reacting with fluoride fluxes, into the metal phase in its elementary form – U and into slag phase (about 4%) in the form of UF3 and UOF2 compounds. During reactions with oxide fluxes, uranium mainly distributes in the metal in its elementary form — U. At the same time, 18 to 19% of uranium can transition into slag phase in the forms of UO, UO2, and UOF2. It should be noted that that fact that uranium oxide particles have an ultradispersed structure should contribute to their transition into slag and thus help speed up the treatment process.This research was carried out in the framework of the Single Industry-Specific Plan by Rosatom; Project No. EOTP-TTsPM-263. Equipment owned by the shared knowledge centre Ural-M was utilized for this research.The authors would like to thank T.V. Osinkina and A.S. Russkikh, junior researchers at the Laboratory of Rare Refractory Metals of the Institute of Metallurgy at the Ural Branch of the Russian Academy of Sciences, for their contribution.

High temperature corrosion of SiC-CaAl12O19 composite refractory by coal slag

Corrosion processes of SiC-CaAl12O19(CA6) composite refractory were carried out by both static crucible test and rotary drum test at 1500 °C and 1600 °C under a reducing atmosphere, respectively. The corrosion mechanism of the SiC-CA6 refractory was analyzed by means of X-ray diffraction(XRD) and scanning electron microscope(SEM). The results show that the corrosion temperature and condition had significant influence on the slag resistance of the SiC-CA6 refractory. But no matter which corrosion methods and which temperatures under the condition of this experiment, the SiC-CA6 refractory exhibited good penetration resistance even though a little corrosion appeared at a higher temperature. During the corrosion process, most of Fe containing oxide in slag could be reduced by CO in atmosphere and SiC in samples to form Fe-Si metal alloys, which precipitated at the interface between the slag and composites. The penetrated slag could react with the SiO2 produced by SiC oxidation and the CA6 matrix to form CaAl2Si2O8 and corundum, filling the pore inside the samples and causing the densification of the reaction layer. Because of the reaction between infiltrated slag and SiC-CA6 refractory, the composition and properties of local slag changed and inhibited the further penetration.

Optimization of alkali metals discharge performance of blast furnace slag and its extreme value model

Abstract In order to improve the alkali metals discharge capacity of slag, the gas-slag balance method was used to carry out the slag alkali metals discharge experiments, the effect of slag composition on alkali metals discharge performance of slag was studied, some suggestions were put forward to optimize the alkali metals discharge performance of slag and the extreme value model was established. The results show that the alkali metals discharge ratio of slag decreased with the increase in the binary basicity and mass fraction of TiO2, and increased with the increase in the mass fraction of MgO, Al2O3 and MnO. The change in slag composition led to the change in the solubility of alkali metal oxides in liquid slag, decomposition of alkali metal silicates, structure of the slag in liquid state and viscosity of the slag, and then affected the alkali metals discharge performance of slag. The ability of slag to absorb alkali metals was certain under the condition of fixed composition. With the help of slag alkali metals discharge extreme value model, whether the current slag meets the needs of blast furnace alkali metals discharge could be evaluated. The alkali metals discharge capacity of slag could be improved by optimizing the alkali metals discharge performance of slag combined with experiments and actual production.

Equilibrium Phase Relations for a SiO2-Al2O3-FeOx System at 1300 °C and 1400 °C in Air

A long-term fundamental study for the construction of the thermodynamic database of a metallurgical slag system has been proposed. In the present work, the equilibrium phase relations for the key ternary SiO2-Al2O3-FeOx system at 1300 °C and 1400 °C in air were experimentally determined by the equilibrium-quenching technique, followed by X-ray Photoelectron Spectroscopy and Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer analysis. The oxidation states of Fe2O3 and Fe3O4 were confirmed at 1300 °C and 1400 °C, respectively, from both XPS detection and FactSage calculation. Within the high-SiO2 composition range, the solid phases of silica, mullite, magnetite and ferric oxide were confirmed as the equilibrium phases. Based on the equilibrium compositions, the 1300 °C and 1400 °C isotherms were projected onto a SiO2-Al2O3-FeOx quasi-ternary phase diagram; however, obvious discrepancies with about a 20 °C difference were confirmed from further comparison with the predictions given by FactSage, indicating that more efforts are needed for the updating of the current thermodynamic database relating to metallurgical slag oxide systems.

Valorization of nano-PbO as an additive to modify the properties and radiation shielding of alkali-activated slag mortar

In this work, for the first time, the possibility of employing nano-lead oxide (nPbO) in alkali-activated slag (AAS) mortar as a modifier agent for its properties was studied. Different ratios of nPbO (0 wt%, 1 wt%, 3 wt% and 5 wt%) were added to the plain AAS mortar. The effects of these ratios on flowability, mechanical strength, water absorption, total porosity, aging resistance, gamma-ray radiation shielding, crystalline phases, thermal analysis and microstructure were investigated. The gamma-ray attenuation coefficients were determined as a function of the additive percentages of lead oxide for gamma-ray energies of 1332, 1173 and 662 keV using Co-60 and Cs-137 sources. Different techniques were used to analyze the results. The results showed higher flowability of the mixtures with introducing nPbO. The flowability increased with increasing nPbO ratio. The mechanical strength and aging resistance increased with introducing 1% and 3% nPbO, then slightly decreased with including 5% nPbO. Water absorption and total porosity decreased with introducing 1% and 3% nPbO, then slightly increased with including 5% nPbO. Introducing nPbO in the AAS system improved the radiation properties, of which the attenuation coefficients increased with including nPbO. In a word, using suitable ratios of nPbO improved the fresh, hardened, durability and radiation properties of AAS mortar and can provide it for wider applications.