No abstract

A combined cellular automaton-finite difference (CA-FD) model has been developed to simulate solute diffusion controlled solidification in continuous steel casting. Constitutional and curvature undercooling were both solved to determine the equilibrium temperature and growth velocity of the solid/liquid interface. Simulations were firstly performed for both the free dendritic growth from an undercooled melt and the columnar dendritic growth in unidirectional solidification. Finally, competitive dendritic growth and columnar to equiaxed transition (CET) occurring in solidification of continuous casting process were reproduced by the present CA-FD model. The effect of the fragmentation of dendrites due to fluid flow induced by EMS in mould on nuclei was taken into consideration by increasing the grain density. The comparison between the simulated and experimentally observed results shows that the present model can be used to simulate solidification structure formation during the continuous casting process of steel. The influence of superheat on solidification structure was also analyzed, and it was found that increasing superheat increases the columnar dendritic growth and reduces the equiaxed ratio, as it is empirical well known.

A 3-D mathematical model has been developed to study the multiphase phenomena of magnetic field, flow field and temperature distribution of molten steel and inclusion behaviour, considering the coupled effects of electromagnetic brake (EMBR) and argon gas injection in the slab continuous casting mold with high casting speed. The effects of EMBR and argon gas injection on the flow and temperature of molten steel and inclusion removal rate have been investigated. Simulation results indicate that EMBR can slow down the flow velocity of molten steel effectively, especially near the meniscus; the areas of upper and lower re-circulation zones are reduced and temperature distribution of molten steel is more uniform and the temperature gradient is reduced; but it has no helpful for the removal of small inclusions. The argon gas injection can increase the molten steel flow up tendency in the upper re-circulation area duo to the buoyancy effect of ascending argon gas bubbles near the submerged entry nozzle (SEN) and be in favour of the floating up of inclusion particles, and temperature in the upper re-circulation zone increases. The increasing of argon gas flow rate results in a stronger vortex flow zone near the free surface, especially near the SEN and easily forms a secondary eddy flow with EMBR, which impacts the fluctuation of free surface and the slag entrapment. The double action of EMBR and argon gas injection can further increase the temperature in the upper re-circulation zone, especially near the meniscus, and the floating up rate of inclusions are also improved and the inclusions to be trapped into solidified shell is reduced.

Layered rare-earth hydroxide (LRH) crystals of (Y0.95Eu0.05)2(OH)5NO3·nH2O with a lateral size of ∼ 300 μm and a thickness of ∼ 9 μm have been synthesized via a hydrothermal reaction of mixed nitrate solutions in the presence of mineralizer NH4NO3 at 200 °C for 24 h. LRH exhibits the ability to undergo intercalation and anion exchange with DS− (C12H25OSO3−) via hydrothermal treatment. Compared with traditional anion exchange at room temperature, hydrothermal processing not only shortens the anion exchange time from 720 to 24 h but also increases the basal spacing. The arrangements of DS− in the interlayer of LRH are significantly affected by the DS− concentration and reaction temperature, and the basal spacing of the LRH-DS sample in the crystal edge is assumed to be larger than that in the crystal center. A higher DS− concentration and reaction temperature both induce more intercalation of DS− anions into the interlayer gallery, thus yielding a larger basal spacing. Unilamellar nanosheets with a lateral size of ≽60 μm and a thickness of ∼ 1.6 nm can be obtained by delaminating LRH-DS in formamide. The resultant unilamellar nanosheets are single crystalline. Transparent (Y0.95Eu0.05)2O3 phosphor films with a uniform [111] orientation and a layer thickness of ∼ 90 nm were constructed with the nanosheets as building blocks via spin-coating, followed by proper annealing. The oriented oxide film exhibits a strong red emission at 614 nm (the 5D0–7F2 transition of Eu3+), whose intensity is ∼ 2 times that of the powder form owing to the significant exposure of the (222) facets.