Fluoride evaporation and crystallization behavior of CaF_2–CaO–Al_2O_3–(TiO_2) slag for electroslag remelting of Ti-containing steels

To elucidate the behavior of slag films in an electroslag remelting process, the fluoride evaporation and crystallization of CaF2–CaO–Al2O3–（TiO2） slags were studied using the single hot thermocouple technique. The crystallization mechanism of TiO2-bearing slag was identified based on kinetic analysis. The fluoride evaporation and incubation time of crystallization in TiO2-free slag are found to considerably decrease with decreasing isothermal temperature down to 1503 K. Fish-bone and flower-like CaO crystals precipitate in TiO2-free slag melt, which is accompanied by CaF2 evaporation from slag melt above 1503 K. Below 1503 K, only near-spherical CaF2 crystals form with an incubation time of less than 1 s, and the crystallization is completed within 1 s. The addition of 8.1wt% TiO2 largely prevents the fluoride evaporation from slag melt and promotes the slag crystallization. TiO2 addition leads to the precipitation of needle-like perovskite（CaTiO3） crystals instead of CaO crystals in the slag. The crystallization of perovskite（CaTiO3） occurs by bulk nucleation and diffusion-controlled one-dimensional growth.

REPLACED SITE OF Eu^(2+) ION IN THE COMPLEX FLUORIDES WITH THE PEROVSKITE CRYSTAL STRUCTURE

The replaced site of Eu^(2+) ion is dependent on the electronegativity difference of the cations in complex fluorides.In the mixed fluoride KMgF_3:Eu^(2+),Eu^(2+) ion occupies K^+ site,its emission spectrum is a sharp line and its valence-state is stable.

Enhanced αγ′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing

Poly（vinylidene fluoride）（PVDF） exhibits pronounced polymorphs. Its γ phase is attractive due to the electroactive properties. The γ-PVDF is however difficult to obtain under normal crystallization condition. In a previous work, we reported a simple melt-recrystallization approach for producing γ-phase rich PVDF thin films through selective melting and subsequent recrystallization. We reported here another approach for promoting the αγ′ phase transition to prepare γ-phase rich PVDF thin films. To this end, a stepwise crystallization and subsequent annealing process was used. The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition. It was found that crystallizing the PVDF melt first at 152 °C for 4 h, then quenching to room temperature and finally annealing the sample at 160 °C for 100 h was the most efficient to produce γ-PVDF rich films. This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 °C, which favors the formation of γ-PVDF crystals for triggering the αγ′ phase transition.

Pulsed laser reshaping and fragmentation of upconversion nanoparticles-from hexagonal prisms to ID nanorods through“Medusa”-like structures

One dimensional(1D)nanostructures attract considerable attention,enabling a broad application owing to their unique properties.However,the precise mechanism of 1D morphology attainment remains a matter of debate.In this study,ultrafast picosecond(ps)laser-induced treatment on upconversion nanoparticles(UCNPs)is offered as a tool for 1 D-nanostructures formation.Fragmentation,reshaping through recrystallization process and bioadaptation of initially hydrophobic(β-Na_(1.5)Y_(1.5_)F_(6):Yb^(3+),Tm^(3+)/β-Na_(1.5)Y_(1.5_)F_(6))core/shell nanoparticles by means of one-step laser treatment in water are demonstrated.“True”1D nanostructures through"Medusa^-like structures can be obtained,maintaining anti-Stokes luminescence functionalities.A matter of the one-dimensional UCNPs based on direction of energy migration processes is debated.The proposed laser treatment approach is suitable for fast UCNP surface modification and nano-to-nano transformation,that open unique opportunities to expand UCNP applications in industry and biomedicine.