Ick-Soo Kim

Tensile and Creep Properties of an Oxide Dispersion-Strengthened Ferritic Steel

The tensile and creep properties of two oxide dispersion-strengthened (ODS) steels with nominal compositions of Fe–12Cr–0.25Y2O3 (designated 12Y1) and Fe–12Cr–2.5W–0.4Ti–0.25Y2O3 (12YWT) were investigated. Optical microscopy, transmission electron microscopy, and atom probe field ion microscopy studies indicated that the 12YWT contained a high density of extremely fine Y–Ti–O clusters, compared to the much larger oxide particles in the 12Y1. The fine dispersion of particles gave the 12YWT better tensile and creep properties compared to commercial ODS alloys and ferritic/martensitic steels that would be replaced by the new ODS steel.

Defect and void evolution in oxide dispersion strengthened ferritic steels under 3.2 MeV Fe+ ion irradiation with simultaneous helium injection

Abstract In an attempt to explore the potential of oxide dispersion strengthened (ODS) ferritic steels for fission and fusion structural materials applications, a set of ODS steels with varying oxide particle dispersion were irradiated at 650°C, using 3.2 MeV Fe + and 330 keV He + ions simultaneously. The void formation mechanisms in these ODS steels were studied by juxtaposing the response of a 9Cr–2WVTa ferritic/martensitic steel and solution annealed AISI 316LN austenitic stainless steel under the same irradiation conditions. The results showed that void formation was suppressed progressively by introducing and retaining a higher dislocation density and finer precipitate particles. Theoretical analyses suggest that the delayed onset of void formation in ODS steels stems from the enhanced point defect recombination in the high density dislocation microstructure, lower dislocation bias due to oxide particle pinning, and a very fine dispersion of helium bubbles caused by trapping helium atoms at the particle–matrix interfaces.

Fabrication of nano-hydroxyapatite on electrospun silk fibroin nanofiber and their effects in osteoblastic behavior

In this study, a novel tissue engineering scaffold material of electrospun silk fibroin/nano-hydroxyapatite (nHA) biocomposite was prepared by means of an effective calcium and phosphate (Ca-P) alternate soaking method. nHA was successfully produced on regenerated silk fibroin nanofiber as a substrate within several minutes without any pretreatments. The morphologies of both nonmineralized and mineralized nanofibers were analyzed using a field-emission scanning electron microscopy (FESEM). The crystallographic phases of the nHA were analyzed using X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectrophotometer and thermogravimetry analyses (TGA) were employed to determine the type of functional groups and the amount of nHA presenting in the silk/nHA biocomposite nanofibers, respectively. The osteoblastic activities of this novel nanofibrous biocomposite scaffold were also investigated by employing osteoblastic-like MC3T3-E1 cell line. The cell functionality such as alkaline phosphatase (ALP) activity was ameliorated on mineralized nanofibers. All these results indicated that this silk/nHA biocomposite scaffold material may be a promising biomaterial for bone tissue engineering.

Cationic-cellulose nanofibers: preparation and dyeability with anionic reactive dyes for apparel application.

Continuous effort in research and development of nanofibers for apparel usage has been focused within their functional properties only. We investigated esthetic properties by producing colored cationic-cellulose nanofibers for the very first time for the potential application of apparel use. The cellulose acetate nanofibers were electrospun followed by deacetylation and cationization to produce functional cationic-cellulose nanofibers and then dyed with anionic reactive dyes. The spectrophotometric measurement of dyed samples was carried out to determine color coordinates and color yield values. The cationic-cellulose nanofibers showed enhanced color yield and dye fixation without addition of an electrolyte in comparison to cellulose nanofibers. The cationization of cellulose nanofibers significantly enhanced the color yield values of around 76% at dye concentrations of 5%. Excellent color fastness results demonstrate that these new colored and breathable materials can potentially be considered as future apparel for casual or fashion.

Noble metal/functionalized cellulose nanofiber composites for catalytic applications.

In this study, cellulose acetate nanofibers (CANFs) with a mean diameter of 325 ± 2.0 nm were electrospun followed by deacetylation and functionalization to produce anionic cellulose nanofibers (f-CNFs). The noble metal nanoparticles (RuNPs and AgNPs) were successfully decorated on the f-CNFs by a simple wet reduction method using NaBH4 as a reducing agent. TEM and SEM images of the nanocomposites (RuNPs/CNFs and AgNPs/CNFs) confirmed that the very fine RuNPs or AgNPs were homogeneously dispersed on the surface of f-CNFs. The weight percentage of the Ru and Ag in the nanocomposites was found to be 13.29 wt% and 22.60 wt% respectively; as confirmed by SEM-EDS analysis. The metallic state of the Ru and Ag in the nanocomposites was confirmed by XPS and XRD analyses. The usefulness of these nanocomposites was realized from their superior catalytic activity. In the aerobic oxidation of benzyl alcohol to benzaldehyde, the RuNPs/CNFs system gave a better yield of 89% with 100% selectivity. Similarly, the AgNPs/CNFs produced an excellent yield of 99% (100% selectivity) in the aza-Michael reaction of 1-phenylpiperazine with acrylonitrile. Mechanism has been proposed for the catalytic systems.

Recent Nanofiber Technologies

This article is a perspective that includes a brief introduction to nanofiber production methods, their potential applications, and three review articles in the field of nanofibers. Although the full range of applications that best exploit these new developments are yet to be developed, the emerging innovative applications of nanofibers in biomedical, sensor, electronic, and other areas will likely be enabled or enhanced by these recent advances in several key techniques. Three review articles, distinct but interrelated, discuss technical research and development, and include possible applications for several industries in the polymer nanofiber arena.

The Effects of Laundering on the Mechanical Properties of Mass-produced Nanofiber Web for Use in Wear

Nanofiber web mass produced via electrospinning has many potential applications due to its large specific area, very small pore size, high porosity and so forth. Despite these potentials, the application of nanofiber web has been limited by its poor mechanical properties. To remedy these poor mechanical properties, laminating processes have been applied to its manufacture. For use in clothing, fabric should have not only adequate mechanical properties, but also the durability to withstand laundering. Hence, the purpose of this study was to measure the mechanical properties of mass-produced nanofiber web, and then to investigate the change of these mechanical properties after laundering in order to evaluate the possibility of using such fiber in a breathable fabric for outdoor wear. We concluded that the maintenance of nanofiber web morphology, despite repeated laundering, allowed for the retention of the mechanical properties.

Antibacterial property and characterization of cotton fabric treated with chitosan/AgCl-TiO2 colloid

The antibacterial activity of cotton fabric was studied by using chitosan/AgCl-TiO2 colloid. Different blend ratios of chitosan to AgCl-TiO2 colloid were used to investigate the efficacy of antibacterial activity against Staphylococcus aureus (gram positive) and Escherichia coli (gram negative) and its effect on physical properties of cotton fabric. Our study shows that the combination of chitosan with AgCl-TiO2 colloid produced better antibacterial activity than the fabric treated without chitosan; 100% bacterial reduction against S. aureus and E. coli obtained with chitosan/AgCl-TiO2 colloid at concentrations of 4 g/L and 10 g/L respectively. Moreover, the treated cotton indicates improved tensile strength and wrinkle recovery angle (WRA). Increasing chitosan concentration slightly affected the fabric stiffness and whiteness. The treated cotton fabrics were further characterized by Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), energy dispersive X-ray (EDX) and wide angle X-ray (WAXD). We can expect a direct industrial application of our proposed work because it is simple one go pad-dry-cure method and the low cost commercial grades of chitosan and AgCl-TiO2 are conveniently available in the market.

The Effect of Laundering on the Thermal and Water Transfer Properties of Mass-produced Laminated Nanofiber Web for Use in Wear

Nanofiber web produced via mass production electrospinning has many potential applications due to its large specific area, very small pore size, and high porosity. Despite such potential, the application of nanofiber web has been limited on account of its poor mechanical properties. In our previous study, the mechanical properties of laminated nanofiber web were investigated, and it was found that the mechanical properties of nanofiber web are sufficient for use as cloth in outdoor wear if a laminating process is used in its production. In this study, we focus on the use of nanofiber web as a breathable fabric. The purpose of this study is to measure the functional properties of mass-produced nanofiber web, and then to investigate any change of those functional properties that may occur as a result of laundering. The measured functional properties include the water transfer properties of waterproofness and vapor permeability as well as the thermal transfer properties of warm/cool feeling and thermal conductivity. We conclude that the maintenance of nanofiber web morphology despite repeated laundering allows for the retention of the water and thermal transfer properties of the material.

Zein/cellulose acetate hybrid nanofibers: Electrospinning and characterization

Protein based scaffolds are preferred for tissue engineering and other biomedical applications owing to their unique properties. Zein, a hydrophobic protein, is a promising natural biodegradable polymer. However, electrospun structures prepared from Zein have poor mechanical and wetting properties. Cellulose acetate (CA) is an economical, biodegradable polymer having good mechanical and water retention properties. The aim of present study was to fabricate a novel material by electrospinning Zein/CA blends. A series of Zein/CA hybrid nanofibers were electrospun and characterized. The attenuated total reflectance-Fourier transform infrared spectroscopy (ATRFTIR) spectrum showed the characteristic peaks of both Zein and CA, and was composition dependent. The X-ray photoelectron spectrometry (XPS) curves of Zein/CA blends demonstrated a similar profile to that of pristine Zein nanofibers. Thermogravimetric analyser (TGA) studies confirmed that the Zein/CA hybrid nanofibers have a higher degradation temperature and better thermal stability than pristine Zein nanofibers. The glass transition temperature (Tg) of Zein/CA hybrid nanofibers was also increased in comparison to pure Zein nanofibers as revealed by differential scanning calorimetry (DSC). Zein/CA hybrid nanofibers have hydrophilic surface character as revealed by water contact angle (WCA) analysis. SEM imaging showed bead free morphology of the electrospun nanofibers. The average nanofiber diameter decreased for Zein/CA blends with increasing CA composition. The electrospun Zein/CA hybrid nanofibers may be used for tissue engineering scaffolds and for other biomedical materials.