Growth behavior of spinel in stainless steel slag during cooling process

Selective elemental concentration during the solidification of stainless steel slags for increased Cr recovery with MnO addition

“…As the temperature decreases, the crystal size seems to slightly increase, where large‐sized MnCr 2 O 4 spinel phases are observed in sample S3 at lower temperatures. However, the diameter of most Cr 2 O 3 and MnCr 2 O 4 crystals is still smaller than 20 μm, which is consistent with the result observed by Cao et al 45 …”

“…As the temperature decreases, the crystal size seems to slightly increase, where large-sized MnCr 2 O 4 spinel phases are observed in sample S3 at lower temperatures. However, the diameter of most Cr 2 O 3 and MnCr 2 O 4 crystals is still smaller than 20 μm, which is consistent with the result observed by Cao et al 45 In samples S1 and S2, the addition of MnO depolymerized the network structure of the slag system, generating some simpler structural units and a lower viscosity, which contributed to the mass transfer during the crystal growth process. For samples S4 and S5, where the primary phase is the MnCr 2 O 4 spinel phase, the nucleation of MnCr 2 O 4 spinel occurred via a process similar to the initial nucleation of Cr 2 O 3 crystal in samples S1 and S2.…”

“…and higher undercoolings or lower viscosities did not significantly promote the growth of the primary crystal in the current experiment. Combined with the growth trend of the primary crystal size at different temperatures, it can be speculated that the growth mechanism of primary crystals (Cr 2 O 3 or MnCr 2 O 4 ) from 1500 to 1300°C is surface‐controlled growth, and this growth rate may be limited by the interfacial reaction rate at the crystal surface 45 . A typical schematic diagram of the crystal nucleation and growth relationship is shown in Figure 11A, where the dotted lines represent the thermodynamic reaction‐controlled region and the solid lines represent the kinetic diffusion‐controlled region for both crystal growth and the nucleation rate 46,47 .…”

“…Combined with the growth trend of the primary crystal size at different temperatures, it can be speculated that the growth mechanism of primary crystals (Cr 2 O 3 or MnCr 2 O 4 ) from 1500 to 1300°C is surface-controlled growth, and this growth rate may be limited by the interfacial reaction rate at the crystal surface. 45 A typical schematic diagram of the crystal nucleation and growth relationship is shown in Figure 11A, where the dotted lines represent the thermodynamic reaction-controlled region and the solid lines represent the kinetic diffusion-controlled region for both crystal growth and the nucleation rate. 46,47 However, the actual situation of nucleation and growth during slag crystallization may be similar to that described in Figure 11B, where a large distance exists between the growth and the nucleation curves, resulting in the inhibition of crystal growth in later stages.…”

Experimental Study on Precipitation Behavior of Spinels in Stainless Steel-Making Slag under Heating Treatment

“…Unit = atom%. Cao et al [12] showed that the size of the spinel crystals increased from 10.8 µm to 24.8 µm during the cooling process from 1350 • C to 1250 • C and the increase reached 129% with respect to the initial size of the spinel crystals. The increase reached 108% (4.25 µm to 8.88 µm), with the silicon content increasing from 5 wt% to 15 wt% [13].…”