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- Hjortsberg, Erik, et al.
(författare)
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X-ray microtomography for characterisation of cracks in iron ore pellets after reduction
- 2013
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 40:6, s. 399-406
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a method, based on X-ray microtomography and three-dimensional (3D) image analysis, of characterising and quantifying crack distribution in iron ore pellets. The aims have been to verify the method and to determine to what extent crack propagation contributes to the decrease in compressive strength that occurs during reduction at 500°C as haematite transforms into magnetite. Raw materials known to cause disintegration problems were selected in order to promote crack propagation. Pellets displayed crack lengths of sizes roughly corresponding to half the pellet diameter already before reduction and, during reduction, a further crack propagation of ∼50% occurred. Through estimations by finite element analysis of the crack size and the pellet geometry, it has been possible to determine that this crack growth most likely is a mechanism that contributes to the decrease in compressive strength. The decrease of ∼90% that was experimentally determined to occur after 30 min of reduction is, however, too large to be explained by crack propagation alone. The study shows that the proposed techniques allow 3D imaging of iron ore pellets and characterisation of cracks. The scans are non-destructive and can be carried out repeatedly, which allows a specific sample to be studied at different stages during a process. Through future use of the proposed method, our aim is to reach a deeper understanding of the mechanisms behind low temperature disintegration of iron ore pellets and the performance of LKAB olivine pellets inside the blast furnace.
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- Hryha, Eduard, 1980, et al.
(författare)
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Development of methodology for surface characterization of vanadium containing slag
- 2014
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 46:10-11, s. 984-988
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Tidskriftsartikel (refereegranskat)abstract
- Swedish steel producers are particularly interested in the recovery of vanadium oxide from the steelmaking slag because of its high content in the LD-converter slag. Hence, optimization of the vanadium recovery has strong economic and environmental impact. Solving the problem with vanadium recovery from the slag requires development of reliable technique for assessing the oxidation state of vanadium. This paper summarizes methodology for the robust analysis of the Ca-Si-based slag materials containing vanadium oxide in different oxidation states utilizing XPS. The measurements show that because of high oxygen affinity of vanadium oxides and number of oxidation states, only fracturing of machined specimens in an ultra-high vacuumchamber, connected to XPS, allows accurate evaluation of oxidation state of vanadium in slag. Proper charge compensation, required due to non-conductive nature of the slag specimens, is considered to be the main problem faced during analysis. As neither carbon nor oxygen signals were proven to be appropriate reference point for charge referencing in this material, the calcium 2p peak position at 347.0 eV, characteristic for CaSiO3, shown to be the most stable and reliable binding energy calibration reference and was used during the charge compensation. Results indicated that in the case of the studied slags,vanadium oxides present are formed preferably by mixture of V2O3 and VO2, depending on the reducing potential of the controlled atmosphere applied during the slag synthesis.
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- Hryha, Eduard, 1980, et al.
(författare)
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Stoichiometric Vanadium Oxides Studied by XPS
- 2012
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 44:8, s. 1022-1025
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Tidskriftsartikel (refereegranskat)abstract
- Recovery of vanadium oxide from the steelmaking slag is of great interest for Swedish steel producers and technique for assessing the oxidation state of vanadium is crucial in optimization of the vanadium recovery. There is a large spread in the reported values of the published V2p3/2 binding energy values for various oxidation states of vanadium. Therefore extensive analysis of vanadium oxide standards was performed aiming to obtain reliable data as well as improved methods for preparation of representative oxide standards. Powdered oxide standards of V2O5, VO2, V2O3 and VO of purity better than 99% were chosen. In as-received state all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of XPS spectra for vanadium oxides in lower oxidation states. Therefore different methods for obtaining of representative surface for vanadium oxide standards were tested. The experimental results show high-sensitivity of vanadium oxide standards to argon ion etching. Hence, a method to obtain representative surface chemical compositions of standards by special heat-treatment is proposed. Such approach was developed using preparation chamber (furnace) attached to the XPS instrument. The annealing was performed in vacuum at defined temperatures from 400 to 900ºC for 4-24 hours; the annealing parameters were selected based on thermodynamic equilibrium data for vanadium oxides. Experimental fitting parameters (peak position E and full width of half maximum of the peak FWHM) for vanadium V2p3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides.
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