2021, Vol.31, No.1

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

ε-Ga2O3, a metastable phase of Ga2O3, has excellent compatibility with substrates having a hexagonal structureor a quasi-hexagonal structure, so that a film having a relatively lower surface roughness and defect density than β-Ga2O3can be obtained easily. Accordingly, we attempted to fabricate a high-quality β-Ga2O3 film with a low surface rough nessand defect density using the property of phase transition to β-Ga2O3 when ε-Ga2O3 is annealed at a high temperature. Forthis, the growth of high-quality ε-Ga2O3 films must be preceded. In this study, the optimal flow rate was investigated byanalyzing the structural and morphological characteristics of the ε-Ga2O3 film according to the supplied precursor ratio. Inaddition, the annealing condition and the effect of β-Ga2O3 mixed in the ε-Ga2O3 film on the crystallinity of β-Ga2O3 afterphase transition were also investigated.

TiO2 has been used in various fields such as solar cells, dental implants, and photocatalysis, because it has high physical and chemical stability and is harmless to the body. TiO2 nanofibers which have a large specific surface area also show a good reactivity in bio-friendly products and excellent photocatalysis in air and water purification. To fabricate TiO2 nanofibers, an electrospinning method was used. To observe the diameter of TiO2 nanofibers with fabrication variables, the fabrication variables was divided into precursor composition variables and process variables and microstructure was analyzed. The concentrations of PVP (Polyvinylpyrrolidone) and TTIP (Titanium(Ⅳ) isopropoxide) were selected as precursor composition variables, and inflow velocity and voltage were also selected as process variables. Microstructure and crystal structure of TiO2 nanofibers were analyzed using FE-SEM (Field emission scanning electron microscope) and XRD (X-ray diffraction), respectively. As-spun TiO2 nanofibers with an average diameter of about 0.27 μm to 1.31 μm were transformed to anatase TiO2 nanofibers with an average diameter of about 0.22 μm to 0.78 μm after heat treatment of 3 hours at 450ºC. Anatase TiO2 nanofibers with an average diameter of 0.22 μm can be expected to improve the photocatalytic properties by increasing the specific surface area. To change the average diameter of TiO2 nanofibers, the control of precursor composition variables such as concentrations of PVP and TTIP is more efficient than the control of electrospinning process variables such as inflow velocity and voltage.

Lithium carbonate recovered from the waste solution generated during the lithium secondary battery manufacturing process contains heavy metals such as cobalt, nickel, and manganese. In this study, the recrystallization of lithium carbonate was performed to remove heavy metals contained in the powder and to increase the purity of lithium carbonate. First, theleaching efficiency of lithium carbonate according to pH in the aqueous hydrochloric acid solution was examined, and the effect on the recrystallization of lithium carbonate according to the equivalent and concentration of sodium carbonate was confirmed. As the equivalent and concentration of sodium carbonate increased, the recovery rate of lithium carbonate improved. And the SEM image showed that the crystal shape was changed depending on the reaction conditions with sodium carbonate. Finally, the high purity lithium carbonate of 99.9% or more was recovered by washing with water.