To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe3O4 and MgFe2O4, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di‐calcium silicate and glass phase, which are Fe3+ ions formed by oxidation. An incorporation of Fe3+ ions into crystal structures has stabilized high temperature polymorph of C2S, β‐C2S, and α’‐C2S, in the treated slag samples. Fe3+ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α’‐C2S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries.
Basic oxygen furnace (BOF) slag contains a significant amount of iron-containing species, which is considered to be iron resources and therefore need to be recovered. In this work, the oxidation behaviour of BOF slag under air (at selected oxidation temperatures and holding time) was investigated to explore the potential of transforming non-magnetic wustite in the BOF slag into magnetic spinel, which may subsequently be recovered by magnetic separation. The experimental results show that the iron-containing spices in the BOF slag can be oxidised into magnetic spinel phases in the investigated temperature range of 1000-1150°C and thereafter be recovered by magnetic separation. The formation of these phases is closely related to the oxidation temperatures and holding time: a higher oxidation temperature and longer holding time lead to a larger amount of formed magnetic species; however, the amount of formed magnetic species decreases at elevated temperature (>1050°C) and with extended holding time (>40 min).
The precipitation behaviors of the topologically close-packed (TCP) phases in the bicrystal DD5 superalloy have been investigated. The results showed that the [001] crystallographic orientations are consistent with that of adjacent grains; however, the direction of the needle-like TCP phases is not consistent with that of the γ phase channels. The angle between needle-like TCP phases and γ phase channels is 45°, but the angle between the needle-like TCP phases of the adjacent grains is equal to the misorientation of the adjacent grains. Furthermore, during long-term aging, the needle-like TCP phases gradually decompose and transform into globular and short rod-like phases. The TCP phases precipitate preferentially in the dendrite. It is difficult to precipitate at the interdendrite/grain boundary, which is caused by the segregation of the constituent elements of the TCP phase to the dendrite.
The industrial solid waste recycling team at North Minzu University has done much research on resource utilization of magnesium slag. This chapter mainly introduces a detailed discussion of resource utilization of magnesium slag. This includes the use of magnesium slag to prepare glass ceramics, porous ceramics, and sulfoaluminate cement clinker, fixing/stabilizing heavy metals in acidic residue generated by lead-zinc smelting, and modifying copper slag. Keywords Slag based glass ceramics • Porous ceramics • Sulfoaluminate cement clinker • Heavy metals Preparation of Glass Ceramics Using Magnesium Slag Preparation Principle of Glass CeramicsGlass ceramics are uniform polycrystalline materials in which glass and crystals coexist. They are commonly prepared via the addition of a crystal nucleating agent, forming crystal nuclei in the glass after proper heat treatment followed by crystal nucleus growth; ultimately, glass ceramics are obtained. Compared with other materials, glass ceramics have properties such as an adjustable thermal expansion coefficient (a zero expansion coefficient can be achieved), high mechanical strength, excellent electrical insulation, low dielectric loss, remarkable wear resistance, corrosion resistance, high temperature resistance, and also good chemical stability [1].Using magnesium slag to prepare glass ceramics can consume and reuse a large amount of industrial waste that is generated by magnesium smelting. Furthermore, the prepared glass ceramics materials have excellent properties. Han Fenglan of North Minzu University prepared glass ceramics via sintering. Magnesium slag, resin ash, and alumina were mixed according to the composition design, and the mixture was melted at high temperature, quenched with water, and ground to fine powder. After the thermal performance was characterized using thermogravimetric analysis and differential scanning calorimetry (TG-DSC), the glass powder was dried, pressed into shape, and then the sample was nucleated (hold time of 1 h) and crystallized (hold times of 0.5, 1, 1.5, 2, and 2.5 h) to prepare glass ceramics [2].
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