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구영진,이명현,윤석영,이윤주 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.4
3D printing technology has advanced rapidly over the last decade. However, for ceramic materials, drying and sintering steps are required after printing, and excessive shrinkage that occurs during these steps is a major factor that has hindered the development of the ceramic 3D printing technology. In this study, a non-sintering ceramic 3D printing method was developed using a hydraulic material to overcome the size deformation issue encountered during the post-processing of a scaffold-type printed green body. The deformation characteristics occurring during the curing process were confirmed. Tricalcium silicate (C3S) and tricalcium aluminate (C3A), which are well-known hydraulic materials, were selected. They were prepared into a printable paste by mixing with a viscous hydrophilic oil such as polyethylene glycol and polypropylene glycol, which helped the printout survive without collapse while it was cured. The scaffold was printed by Fused Deposition Modelling (FDM), which is the simplest and most economical printing method, and was cured by immersion in a water bath. The hydrated scaffold of the C3S/C3A mixture exhibited a smaller strain than the scaffold of the single materials, and the deformation amount depended on the printing direction. Remarkably, a scaffold with the smallest deformation, of less than 1%, and the highest compressive strength was obtained with a C3S/C3A mixing ratio of 65/35.
구영진,이윤주,이명현,윤석영 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.9
With the development of additive manufacturing technology, many types of materials are being utilized, and methods of printing the materials and characteristics of their hydration properties are being studied in the fields of construction and biotechnology. Tricalcium silicate (C3S), which is used as a cement material or biomaterial, is a representative hydraulic material. In previous research, scaffolds were printed via fused deposition modeling and the deformation properties during the hydration process of the printed scaffold were investigated. C3S, like ceramic materials, requires post-processing such as curing after printing, and volumetric deformation occurs during this process. Deformation information is very important to ensure the numerical value of the final product, as well as to suppress the possibility of deformation. In this study, silica, hydroxyapatite (HA), and alumina were mixed with three types of fillers to print a C3S support, which was then cured through a two-step process. In this process, HA and silica, which have good hydrophilicity, exhibited high strength due to the suppression of scaffold deformation. It was confirmed that the smaller the particle size, the more effective it was in obtaining a stable hydrated print.
Sol-Gel방법에 의해서 성장시킨PbTiO₃박막의 결정화와 물리적 성질
구영진,강민진,정원태,김태현,김상수 昌原大學校 基礎科學硏究所 2000 基礎科學硏究所論文集 Vol.12 No.-
Ferroelectric PbTiO3 thin films coated on SiO2/Si(100) and ITO glass substrates were prepared by sol-gel processing of metal alkoxide solutions and solvents. The use of sol-gel method for preparing various functional films makes it possible for the homogeneous distribution of elements at the molecular level, precise composition control, lower temperature synthesis, large surface coating and high optical quality. First of all, the XRD investigation shows that perovskite phase of polycrystalline PbTiO3 was formed by four times coating of the concentrated solution and by the heat treatment over 500, 600℃(O2 gas and air) and over 10, 20, 30 min. Surfaces of thin films were crack-free and uniform and the average grain size investigated by SEM was 0.25∼1.00 ㎛. Dielectric constant of PbTiO3/ITO glass thin film were 380 ∼ 5.25 in the region of 1 kHz∼ 10 MHz at room temperature(30℃), respectively. From the hysteresis loop of PbTiO3/ITO glass thin film, a remnant polarization of 0.382 μC/cm2 and a coercive filed of 23.85 kV/cm were obtained. At the frequency(5 kHz), C-V measurements of films in MFIS and MFM configurations showed well-behaved C-V characteristics and an injection type hysteresis. The capacitance of flat band(CFB) was 60 pF. The band gap energies of the thin films depend on the assumption of direct or indirect transition. Using one layer structure model, we calculated refractive index, extinction coefficient, absorption coefficient and band gap energy of thin film in the wavelength range of 300 to 800 nm. The band gap energy, refractive index and extinction coefficient at λ = 6325 Å of the PbTiO3 thin film were 3.7 eV, 1.96 and 0.1 respectively.