84 research outputs found
Dissolution of MgO·Al2O3 spinel and MgO in CaO-Al2O3-MgO-SiO2 slag under forcedconvection
In this work, the dissolution mechanism of dense MgO·Al2O3 spinel and MgO rod into molten CaO-Al2O3-MgO-SiO2 slag was investigated at 1873 K with forced convection. The dissolutionexperiments were carried out by employing a newly developed rotating cylinder method. The effect of rotation speed and reaction time on the dissolution rate was studied. The measured dissolution rates of both spinel and MgO were dependent on the rotation speed, indicating that mass transfer in the slag phase to one of the rate-limiting steps. It was also found that the dissolution rate of spinel in slag was enhanced more rapidly than that of MgO with the increasing reaction time and rotation speed. It was also found that the composition of the slag at the interface was far from equilibrium value between the slag and solid. The results implied that the chemical reaction at the solid-slag interface should be the other important step that jointly controlling the dissolution process.QC 20170918European Union’s Research Fund for Coal and Steel (RFCS) research program under grant agreement No RFSR-CT-2015-0000
Int. J. Mater. Res.
In the present work, the mechanism of nickel coating on BN particles by hydrazine reduction was studied. A nickel sulfate - ammonium sulfate - ammonia - hydrazine hydrate plating system was employed. It was found that Pd on the surface of BN particles acted as an active center for nickel deposition at the initial stage of the process. Thereafter, Ni itself would act as an active center to catch Ni from the solution through the reaction: Ni2+, + 2H(ad)(*) double right arrow Ni + 2H(+). The rate of the process was found to be controlled by the reaction at the interface under the present experimental conditions. A kinetic model was proposed on the basis of the experimental results. The model predictions were found to be in agreement with the experimental data.In the present work, the mechanism of nickel coating on BN particles by hydrazine reduction was studied. A nickel sulfate - ammonium sulfate - ammonia - hydrazine hydrate plating system was employed. It was found that Pd on the surface of BN particles acted as an active center for nickel deposition at the initial stage of the process. Thereafter, Ni itself would act as an active center to catch Ni from the solution through the reaction: Ni2+, + 2H(ad)(*) double right arrow Ni + 2H(+). The rate of the process was found to be controlled by the reaction at the interface under the present experimental conditions. A kinetic model was proposed on the basis of the experimental results. The model predictions were found to be in agreement with the experimental data
The Effect of Al2O3, CaO and SiO2 on the Phase Relationship in FeO-SiO2 Based Slag with 20 Mass% Vanadium
An innovative and sustainable way for production of vanadium (V) is to co-process V titanomagnetite ores with V-bearing steel slag, via reduction. V-slag produced from highly enriched Fe-V melt contains as high as 20 mass% V. The phase relationship in FeO-SiO2 based slag with V fixed at 20.4 mass% was investigated experimentally at 1673 K. The compositions covered the normal production range, viz. Al2O3 from 0 to 6 mass%, CaO from 1 to 5 mass% and SiO2 from 10 to 17 mass%. The content of MnO was fixed at 5.5 mass%. Samples quenched at 1673 K were found to be solid-liquid mixtures, either in a 2-phase region consisting of liquid and a solid spinel phase, or in 3-phase region consisting of liquid, spinel phase and silica phase. Free silica was only found in samples with a composition of 0 mass% Al2O3, 1 mass% CaO and 17 mass% SiO2. Formation of free silica was prohibited in samples with 1 mass% CaO and up to 17 mass% SiO2 by adding 5 mass% Al2O3. Addition of 4 mass% Al2O3 was also sufficient to prevent the presence of free silica in samples with 3 mass% CaO and 13.5 mass% SiO2. Most of the V was kept in the spinel phase, while the solubility of V in the liquid was generally less than 1 mass% as V2O3. Fe, Mn and Al coexisted in both liquid phase and spinel phase. On the other hand, Si and Ca only distributed in the liquid phase. The fraction of solid phase, viz. spinel was found to decrease with increasing SiO2 content.QC 20170613</p
A New Experimental Design to Study the Kinetics of Solid Dissolution into Liquids at Elevated Temperature
A new method was developed to study the dissolution of solid cylinder in liquid under forcedconvection at elevated temperature. In the new design, a rotating cylinder was placedconcentrically in a container fabricated by boring four holes into a blank materials for creatingan internal volume with a quatrefoil profile. A strong flow in radial direction in the liquid wascreated, which was evidently shown by computational fluid dynamic (CFD) calculations andexperiments at both room temperature and elevated temperature. The new setup was able tofreeze the sample as it was at experimental temperature especially the interface between thesolid and the liquid. This freezing was necessary to obtain reliable information forunderstanding the reaction mechanism. This was exemplified by the study of dissolution ofrefractory in liquid slag. The absence of flow in radial direction in the traditional setup using asymmetrical cylinder was also discussed. The difference in the findings by different worksusing the symmetrical cylinder was found to be mostly due to the extent of misalignment of therod in the cylinder.QCR 20170918European Union’s Research Fund for Coal and Steel (RFCS) research program [grant agreement No RFSR-CT-2015-00005]
Dissolution of MgO Based Refractories in CaO-Al2O3-MgO-SiO2 Slag
Dissolution of different types of MgO based refractories into molten CaO-Al2O3-MgO-SiO2 slag was studied at 1873 K. The prepared refractory cubes were dissolved in both stagnant slagand slag stirred with different speeds. Even in a stagnant slag, the decarbonized commercial MgO-carbon refractory dissolved very fast. Formation of micro spinel particles by addition of either colloidal alumina or micro alumina powder in the MgO matrix efficiently reduced the dissolution. The dissolution of MgO refractories into slag was found to be controlled by the slag penetration into the MgO matrix. In the case of stagnant slag, the slag penetration would lead to the final dissociation of the decarbonized commercial MgO-carbon cube in less than 6 minutes. A slag penetrated layer was formed in the cubes with spinel particles formed in situ.The major dissolution took place between the MgO grains and the liquid in this penetrated layer. The increase of the thickness would slow down the dissolution process. In the case of forced convection, the slag penetrated layer was removed at high stirring speeds and partially removed at lower stirring speeds. The removal of the penetrated layer would enhance the dissolution process.QCR 20170918European Union’s Research Fund for Coal and Steel (RFCS) research program [grant agreement No RFSR-CT-2015-00005
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