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ISIJ International Vol. 61 (2021), No. 12

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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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ISIJ International Vol. 61 (2021), No. 12

Structure of Aluminosilicate Melts

Bjorn Mysen

pp. 2866-2881

Abstract

In peralkaline and meta-aluminous melts, essentially all Al3+ (>95%) occupy tetrahedral coordination, whereas for peraluminous melts, complex mixtures of aluminum triclusters with 4-fold coordinated Al3+ and Al3+ in 5- and 6-fold coordination with oxygen describe the structure. Aluminum in tetrahedral coordination requires electrical charge-balance. With alkali metals (M+) in this role, the proportions are M+=Al3+. The overall structure is dominated by three-dimensionally interconnected tetrahedra to form 6-membered rings of tetrahedra. The Al/(Al+Si) of these tetrahedra are simple positive functions of the bulk melt Al/(Al+Si). When tetrahedrally-coordinated Al3+ is charge-balanced by divalent cations, the M2+ cation charge-balances 2Al3+ tetrahedrally coordinated cations. This structure is dominated by SiO4, (Si,Al)O4, and AlO4 entities.In peraluminous melts, where there is insufficient proportion of M2+ and M2+ cations for charge-balance, aluminum exists in triclusters with Al3+ in tetrahedral coordination. In peralkaline aluminosilicate melts, there coexist discrete structural units with different degree of silicate polymerization. These units are termed Qn-species where the superscript, n, is the number of bridging oxygen in individual units. Equilibria among these units are of the type, 2Qn = Qn+1 + Qn−1. In these melts, Al3+ is distributed among these units. The Al3+ in peralkaline aluminosilicate melts strong preference Q4 units. This preference is, however, temperature-dependent as reflected in changes in the ΔH of the Qn-species reaction.

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ISIJ International Vol.61(2021), No.12

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Article Title

Structure of Aluminosilicate Melts

Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature

Shota Hatano, Shogo Hayashi, Noritaka Saito, Kunihiko Nakashima

pp. 2904-2914

Abstract

CaO-based slag used in hot metal pretreatment and converters in steelmaking processes typically contains dispersed gas phases. This is called foaming slag, which is known to degrade the quality of slag. The rheological behavior of this slag is dependent on the dispersed part of the gas phase. This gas is generated by the chemical reaction between the hot metal and the slag. In this study, simulated foaming slag was prepared by reacting sodium hydrogen carbonate and oxalic acid in glycerol, which disperses carbon dioxide. Next, we systematically investigated the effects of the volume fraction of the dispersed gas phase and the proportion of glycerol on the viscosity and bubble diameter. According to the model used in this study, the bubbles were smaller than those in the model in which the gas was directly dispersed. The bubble size increased as the gas phase ratio and liquid viscosity increased, likely because the bubble growth is promoted by increase in the gas phase ratio and liquid phase viscosity, and the frequency with which the bubbles contact one other. The increase of the gas phase ratio at low liquid-phase viscosity and low shear rate caused an increase in both apparent viscosity and relative viscosity, which was obtained by dividing the apparent viscosity by liquid-phase viscosity. However, these increases in viscosity were not observed at a high shear rate. This is likely because the mechanism of bubble diffusion and flow is affected by the liquid-phase viscosity and shear rate. We found that the model in this study exemplified a Herschel-Bulkley fluid. In addition, we proposed an equation for measuring viscosity from the gas phase ratio.

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Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature

High Temperature Softening and Melting Interactions Between Newman Blend Lump and Sinter

Mohammad Mainul Hoque, Hamid Doostmohammadi, Subhasish Mitra, Damien O’dea, Xinliang Liu, Tom Honeyands

pp. 2944-2952

Abstract

In this work, the softening and melting (S&M) behaviour and whole blast furnace (BF) performance of Newman Blend Lump (NBLL), plant sinter, and sinter-NBLL mixture were studied using S&M under load test and numerical BF modelling. Both physical and chemical interactions between sinter and lump were confirmed in the S&M process. Significant improvements were found in the S&M behaviour of the sinter-NBLL mixture because of the physical and chemical interaction. The physical interaction was examined using X-ray/Neutron Computed Tomography (CT) scanning on the samples from interrupted S&M under load tests. The void fraction in the ferrous layer of the sinter-NBLL mixture was found to be similar to the sinter and was higher than that for NBLL. The chemical interaction was investigated by analysing the Ca transfer from sinter to NBLL, which indicated that Ca transfer started around 1200°C in the S&M process. FactSage was used to assist in the interpretation of the S&M test results. It was found that the NBLL sample starts to melt at a lower temperature compared to other burdens used in the present study, which also agreed well with the CT scan results. The whole BF performance of different ferrous burdens was studied using the experimental results as inputs. The sinter-NBLL mixture behaved more like the sinter than the NBLL; compared with the sinter only burden with the same total basicity, the sinter-NBLL combination formed a more permeable CZ, had a lower total BF pressure drop, and a higher gas utilization rate.

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High Temperature Softening and Melting Interactions Between Newman Blend Lump and Sinter

Influence of Slag Viscosity and Composition on the Inclusion Content in Steel

Dali You, Christian Bernhard, Alexander Mayerhofer, Susanne Katharina Michelic

pp. 2991-2997

Abstract

Influence of slag viscosity and composition on the inclusion content in the steel is studied using laboratory experiments and modeling simulations. The steel samples are taken during the experimental process to record the inclusion content change. Afterwards the prepared samples are analyzed using automated scanning electron microscope and energy dispersive spectroscopy (SEM/EDS) method. A simple steel/slag reaction model is constructed based on the effective equilibrium reaction zone (EERZ) method. The inclusion content evolution process is discussed by combining the experimental and calculated results. It is found that the inclusion content evolution in the steel is determined by the inclusion generation and removal.

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Influence of Slag Viscosity and Composition on the Inclusion Content in Steel

Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

Tae Sung Kim, Sang-Beom Lee, Joo Hyun Park

pp. 2998-3007

Abstract

The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.

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Article Title

Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

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