This page has only limited features, please log in for full access.
For the removal of pollutants, a modified TiO2 photocatalyst is attracting attention. Fe-doped TiO2 nanofibers were prepared through a combination of electrospinning and calcination. Morphological characterization of the sample was conducted using field-emission scanning electron and transmission electron microscopy. The crystal structure of each sample was analyzed using high-resolution transmission electron microscopy, selected area electron diffraction, and Fast Fourier Transform imaging. The average diameter of the Fe-doped TiO2 nanofibers was measured to be 161.5 nm and that of the pure TiO2 nanofibers was 181.5 nm. The crystal phase when heat treated at 350 °C was anatase for TiO2 nanofibers and rutile for Fe-doped TiO2 nanofibers. The crystal phase of the TiO2 matrix was easily transitioned to rutile by Fe-doping. The photocatalytic performance of each sample was compared via the photodegradation of methylene blue and acid orange 7 under ultraviolet and visible light irradiation. In the Fe-doped TiO2 nanofibers, photodegradation rates of 38.3% and 27.9% were measured under UV irradiation and visible light, respectively. Although other catalysts were not activated, the photodegradation rate in the Fe-doped TiO2 nanofibers was 9.6% using acid orange 7 and visible light. For improved photocatalytic activity, it is necessary to study the concentration control of the Fe dopant.
Kyeong-Han Na; Bo-Sung Kim; Han-Sol Yoon; Tae-Hyeob Song; Sung-Wook Kim; Churl-Hee Cho; Won-Youl Choi. Fabrication and Photocatalytic Properties of Electrospun Fe-Doped TiO2 Nanofibers Using Polyvinyl Pyrrolidone Precursors. Polymers 2021, 13, 2634 .
AMA StyleKyeong-Han Na, Bo-Sung Kim, Han-Sol Yoon, Tae-Hyeob Song, Sung-Wook Kim, Churl-Hee Cho, Won-Youl Choi. Fabrication and Photocatalytic Properties of Electrospun Fe-Doped TiO2 Nanofibers Using Polyvinyl Pyrrolidone Precursors. Polymers. 2021; 13 (16):2634.
Chicago/Turabian StyleKyeong-Han Na; Bo-Sung Kim; Han-Sol Yoon; Tae-Hyeob Song; Sung-Wook Kim; Churl-Hee Cho; Won-Youl Choi. 2021. "Fabrication and Photocatalytic Properties of Electrospun Fe-Doped TiO2 Nanofibers Using Polyvinyl Pyrrolidone Precursors." Polymers 13, no. 16: 2634.
This study examined the effect of adding synthetic fibers, that is, polypropylene (PP) and nylon (Ny), on explosive spalling and residual tensile mechanical properties of high-performance fiber-reinforced cementitious composites (HPFRCCs). Three different matrix strengths (100 MPa, 140 MPa, and 180 MPa), four different volume contents of the synthetic fibers (0%, 0.2%, 0.4%, and 0.6%), and three different exposure time (1 h, 2 h, and 3 h) based on the Internatinoal Organization for Standardization (ISO) fire curve were adopted as variables for this experiment. The experimental results revealed that the addition of synthetic fibers improved the resistance to explosive spalling induced by high-temperature, especially when PP and Ny were mixed together. For a higher matrix strength, greater volume content of the synthetic fibers was required to prevent explosive spalling, and higher residual strengths were obtained after the fire tests. An increase in the volume fraction of the synthetic fibers clearly prevented explosive spalling but did not affect the residual tensile strength. In the case of a higher matrix strength, a reduction in the strength ratio was observed with increased exposure time.
Gang-Kyu Park; Gi-Joon Park; Jung-Jun Park; Namkon Lee; Sung-Wook Kim. Residual Tensile Properties and Explosive Spalling of High-Performance Fiber-Reinforced Cementitious Composites Exposed to Thermal Damage. Materials 2021, 14, 1608 .
AMA StyleGang-Kyu Park, Gi-Joon Park, Jung-Jun Park, Namkon Lee, Sung-Wook Kim. Residual Tensile Properties and Explosive Spalling of High-Performance Fiber-Reinforced Cementitious Composites Exposed to Thermal Damage. Materials. 2021; 14 (7):1608.
Chicago/Turabian StyleGang-Kyu Park; Gi-Joon Park; Jung-Jun Park; Namkon Lee; Sung-Wook Kim. 2021. "Residual Tensile Properties and Explosive Spalling of High-Performance Fiber-Reinforced Cementitious Composites Exposed to Thermal Damage." Materials 14, no. 7: 1608.
This study aims to investigate the relationship between the steel fibers and the electromagnetic wave shielding effectiveness of a high-performance fiber-reinforced cementitious composite (HPFRCC). The distribution characteristics of the steel fibers and the variation of the electrical conductivity of HPFRCC as a function of the fiber content were quantified based on micro computed tomography (CT) and impedance measurements to determine their correlations with the electromagnetic shielding effectiveness. The impedance results showed that no electrical network was formed in the composite by the steel fibers and it is difficult to manufacture HPFRCC with high-electrical conductivity using steel fibers alone without CNTs or other carbon-based materials. For the steel fiber content of greater than 0.5%, the number of contact points between the steel fibers increased significantly, and the relationship between the fiber content and the number of contact points was observed. Despite the improvement of the electrical conductivity owing to the presence of the steel fibers and to the increase in the contact points between the steel fibers, the shielding effectiveness did not increase further for the steel fiber contents equal or above 1.5%. Consequently, it was found that the factor that controls the shielding effectiveness of HPFRCC is not the electrical network of the steel fibers, but the degree of the dispersion of the individual steel fibers.
Namkon Lee; Gijoon Park; Junil Pae; Juhyuk Moon; Sungwook Kim. Relationship between Three-Dimensional Steel Fiber Statistics and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites. Materials 2020, 13, 5125 .
AMA StyleNamkon Lee, Gijoon Park, Junil Pae, Juhyuk Moon, Sungwook Kim. Relationship between Three-Dimensional Steel Fiber Statistics and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites. Materials. 2020; 13 (22):5125.
Chicago/Turabian StyleNamkon Lee; Gijoon Park; Junil Pae; Juhyuk Moon; Sungwook Kim. 2020. "Relationship between Three-Dimensional Steel Fiber Statistics and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites." Materials 13, no. 22: 5125.
Electrospun NiZn ferrite nanofibers have great potential due to their one-dimensional structure and electrical properties, but they have a low reproducibility resulting from many process confounders, so much research effort is needed to achieve optimized process control. For structure control, the viscosity of the precursor solution is a likely parameter. One solution is to use polyvinyl pyrrolidone (PVP) and metal nitrate to obtain the desired viscosity by increasing the nitrate content, even if the polymer content is decreased. Ni0.5Zn0.5Fe2O4 ferrite nanofiber was electrospun with various precursor conditions. Fifteen different precursor solutions, with a content of five polymers and three metal nitrates, were prepared, with precursor solutions composed of Fe(NO3)2·9H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, polyvinyl pyrrolidone (PVP), and N,N-dimethylmethanamide. The fiber diameter changed from the lowest, of 62.41 nm, to 417.54 nm. This study shows that the average diameter can be controlled using the metal nitrate concentration without a difference in crystal structure when PVP is used. In a 24.0 mmol metal nitrate precursor solution, the process yield was improved to 140% after heat treatment. There was also no significant difference in the crystal structure and morphology. This system reduces the cost of raw materials for electrospinning and increases the process yield of NiZn ferrite nanofibers.
Kyeong-Han Na; Wan-Tae Kim; Tae-Hyeob Song; Sung-Wook Kim; Won-Youl Choi. Microstructure of Ni0.5Zn0.5Fe2O4 Nanofiber with Metal Nitrates in Electrospinning Precursor. Nanomaterials 2020, 10, 1344 .
AMA StyleKyeong-Han Na, Wan-Tae Kim, Tae-Hyeob Song, Sung-Wook Kim, Won-Youl Choi. Microstructure of Ni0.5Zn0.5Fe2O4 Nanofiber with Metal Nitrates in Electrospinning Precursor. Nanomaterials. 2020; 10 (7):1344.
Chicago/Turabian StyleKyeong-Han Na; Wan-Tae Kim; Tae-Hyeob Song; Sung-Wook Kim; Won-Youl Choi. 2020. "Microstructure of Ni0.5Zn0.5Fe2O4 Nanofiber with Metal Nitrates in Electrospinning Precursor." Nanomaterials 10, no. 7: 1344.
This study aimed to investigate the potential use of carbon nanotubes (CNTs), which are an innovative construction material preferred by many researchers. Long-term microstructure enhancement and on-site application are major reasons to conduct research on CNT-cement composites; thus, a study on mechanical properties as well as the thermal conductivity of CNT-cement composites was carried out. As the CNT content increased, the thermal conductivity of CNT-cement composites was also enhanced. In addition, a couple of microstructure analyses such as isothermal calorimetry, thermal gravimetric analysis and SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) for observing hydration reaction rate and types of hydration products were conducted to establish the advantage of CNT use in cement composites. Strength development of CNT-cement composites at early ages was slow, although eventually CNTs containing water developed equivalent level of strengths at last as internal curing effects.
Sang-Hwa Jung; Sungwoo Oh; Sung-Wook Kim; Jae-Heum Moon. Effects of CNT Dosages in Cement Composites on the Mechanical Properties and Hydration Reaction with Low Water-to-Binder Ratio. Applied Sciences 2019, 9, 4630 .
AMA StyleSang-Hwa Jung, Sungwoo Oh, Sung-Wook Kim, Jae-Heum Moon. Effects of CNT Dosages in Cement Composites on the Mechanical Properties and Hydration Reaction with Low Water-to-Binder Ratio. Applied Sciences. 2019; 9 (21):4630.
Chicago/Turabian StyleSang-Hwa Jung; Sungwoo Oh; Sung-Wook Kim; Jae-Heum Moon. 2019. "Effects of CNT Dosages in Cement Composites on the Mechanical Properties and Hydration Reaction with Low Water-to-Binder Ratio." Applied Sciences 9, no. 21: 4630.
This study aimed to investigate the effect of multi-walled carbon nanotubes (MWCNTs) and steel fibers on the AC impedance and electromagnetic shielding effectiveness (SE) of a high-performance, fiber-reinforced cementitious composite (HPFRCC). The electrical conductivity of the 100 MPa HPFRCC with 0.30% MWCNT was 0.093 S/cm and that of the 180 MPa HPFRCC with 0.4% MWCNT and 2.0% steel fiber was 0.10 S/cm. At 2.0% steel fiber and 0.3% MWCNT contents, the electromagnetic SE values of the HPFRCC were 45.8 dB (horizontal) and 42.1 dB (vertical), which are slightly higher than that (37.9 dB (horizontal)) of 2.0% steel fiber content and that (39.2 dB (horizontal)) of 0.3% MWCNT content. The incorporation of steel fibers did not result in any electrical percolation path in the HPFRCC at the micro level; therefore, a high electrical conductivity could not be achieved. At the macro level, the proper dispersion of the steel fibers into the HPFRCC helped reflect and absorb the electromagnetic waves, increasing the electromagnetic SE. The incorporation of steel fibers helped improve the electromagnetic SE regardless of the formation of percolation paths, whereas the incorporation of MWCNTs helped improve the electromagnetic SE only when percolation paths were formed in the cement matrix.
Namkon Lee; Sungwook Kim; Gijoon Park. The Effects of Multi-Walled Carbon Nanotubes and Steel Fibers on the AC Impedance and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites. Materials 2019, 12, 3591 .
AMA StyleNamkon Lee, Sungwook Kim, Gijoon Park. The Effects of Multi-Walled Carbon Nanotubes and Steel Fibers on the AC Impedance and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites. Materials. 2019; 12 (21):3591.
Chicago/Turabian StyleNamkon Lee; Sungwook Kim; Gijoon Park. 2019. "The Effects of Multi-Walled Carbon Nanotubes and Steel Fibers on the AC Impedance and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites." Materials 12, no. 21: 3591.
Concrete has high compressive strength, but low tensile strength, bending strength, toughness, low resistance to cracking, and brittle fracture characteristics. To overcome these problems, fiber-reinforced concrete, in which the strength of concrete is improved by inserting fibers, is being used. Recently, high-performance fiber-reinforced cementitious composites (HPFRCCs) have been extensively researched. The disadvantages of conventional concrete such as low tensile stress, strain capacity, and energy absorption capacity, have been overcome using HPFRCCs, but they have a weakness in that the fiber reinforcement has only 2% fiber volume fraction. In this study, slurry infiltrated fiber reinforced cementitious composites (SIFRCCs), which can maximize the fiber volume fraction (up to 8%), was developed, and an experimental study on the tensile behavior of SIFRCCs with varying fiber volume fractions (4%, 5%, and 6%) was carried out through direct tensile tests. The results showed that the specimen with high fiber volume fraction exhibited high direct tensile strength and improved brittleness. As per the results, the direct tensile strength is approximately 15.5 MPa, and the energy absorption capacity was excellent. Furthermore, the bridging effect of steel fibers induced strain hardening behavior and multiple cracks, which increased the direct tensile strength and energy absorption capacity.
Seungwon Kim; Dong Joo Kim; Sung-Wook Kim; Cheolwoo Park. Tensile Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composite with Respect to Fiber Volume Fraction. Materials 2019, 12, 3335 .
AMA StyleSeungwon Kim, Dong Joo Kim, Sung-Wook Kim, Cheolwoo Park. Tensile Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composite with Respect to Fiber Volume Fraction. Materials. 2019; 12 (20):3335.
Chicago/Turabian StyleSeungwon Kim; Dong Joo Kim; Sung-Wook Kim; Cheolwoo Park. 2019. "Tensile Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composite with Respect to Fiber Volume Fraction." Materials 12, no. 20: 3335.
In this study, the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) is examined as a function of fiber length and volume fraction. Straight steel fiber with three different lengths (lf) of 13, 19.5, and 30 mm and four different volume fractions (vf) of 0.5%, 1.0%, 1.5%, and 2.0% are considered. Test results show that post-cracking flexural properties of UHPFRC, such as flexural strength, deflection capacity, toughness, and cracking behavior, improve with increasing fiber length and volume fraction, while first-cracking properties are not significantly influenced by fiber length and volume fraction. A 0.5 vol % reduction of steel fiber content relative to commercial UHPFRC can be achieved without deterioration of flexural performance by replacing short fibers (lf of 13 mm) with longer fibers (lf of 19.5 mm and 30 mm).
Jung-Jun Park; Doo-Yeol Yoo; Gi-Joon Park; Sung-Wook Kim. Feasibility of Reducing the Fiber Content in Ultra-High-Performance Fiber-Reinforced Concrete under Flexure. Materials 2017, 10, 118 .
AMA StyleJung-Jun Park, Doo-Yeol Yoo, Gi-Joon Park, Sung-Wook Kim. Feasibility of Reducing the Fiber Content in Ultra-High-Performance Fiber-Reinforced Concrete under Flexure. Materials. 2017; 10 (2):118.
Chicago/Turabian StyleJung-Jun Park; Doo-Yeol Yoo; Gi-Joon Park; Sung-Wook Kim. 2017. "Feasibility of Reducing the Fiber Content in Ultra-High-Performance Fiber-Reinforced Concrete under Flexure." Materials 10, no. 2: 118.