Kap-Ho Lee

Functional nanofiber mat of polyvinyl alcohol/gelatin containing nanoparticles of biphasic calcium phosphate for bone regeneration in rat calvaria defects†

New biodegradable mats was successfully obtained by functional polyvinyl alcohol (PVA)/Gelatin (GE) blend fiber mats containing different BCP amounts (20, 40, and 50 w/v%) of biphasic calcium phosphate (BCP) nanoparticles for bone regeneration. BCP nanoparticles were loaded and dispersed successfully in the PVA/GE fibrous matrix. The addition of BCP was found to have increased fiber diameter, tensile strength, osteoblast cell adhesion, proliferation, and protein expression. Compared to the others, the 50% BCP-loaded electrospun PVA/GE fibers had the most favorable mechanical properties, cell attachment and growth, and protein expression. In vivo bone formation was examined using rat models, and increased bone formation was observed for the 50% BCP-loaded electrospun PVA/GE blends within 2 and 4 weeks. This result suggests that the 50% BCP-PVA/GE composite nanofiber mat has high potential for use in the field of bone regeneration and tissue engineering.

Microstructural characterization of electroconductive Si3N4–TiN composites

Abstract Electroconductive Si3N4–TiN composites from Si and TiN powders have been fabricated by in situ reaction-bonding and post-sintering under N2 atomosphere. The values of fracture strength and electrical resistivity in the Si3N4–50 wt.% TiN composite were 531 MPa and 2.5×10−2 Ω cm, respectively. The dispersion of TiN particles inhibited the abnormal growth of rod-like Si3N4 grains with large size in diameter. An amorphous phase observed in most grain boundaries and triple points is attributed to liquid phase sintering. Many dislocations formed by the difference of thermal expansion coefficients were observed in Si3N4 and TiN grains.

Stress-Induced Phase Transformation of ZrO2 in ZrO2 (3mol%Y2O3)-25vol%Al2O3 Composite Studied by Transmission Electron Microscopy

To improve mechanical properties, fracture toughness in particular, ZrO{sub 2} ceramic has been widely used not only as a matrix, but also as a toughening agent. Among them, recently, the ZrO{sub 2}-Al{sub 2}O{sub 3} system has received much attention because of the applications to wear and tool materials in the Al{sub 2}O{sub 3}-rich part and superplastic deformation behavior at the high temperature in the ZrO{sub 2}-rich part. Furthermore, recent availability of high pure and fine-grained ZrO{sub 2} and Al{sub 2}O{sub 3} powders makes it possible to synthesize the composites with submicron size grains by pressureless-sintering at the comparatively low temperature of 1,450 C. The purpose of the present work is to investigate the stress-induced t-m phase transformation of ZrO{sub 2} in the ZrO{sub 2}(3mol%Y{sub 2}O{sub 3})-25vol%Al{sub 2}O{sub 3} bulk composite made by the use of micro-indentation. In addition, the fracture characteristic was studied by the observation of fracture surface made by 3-point bending test.

Few-atomic-layer boron nitride nanosheets synthesized in solid thermal waves

In this study, we demonstrate the synthesis of few-atomic-layer hexagonal boron nitride (h-BN) sheets in a solid thermal wave implemented in a B2O3 + (3 + 0.5k)Mg + kNH4Cl exothermic mixture (here, k is the mole number of NH4Cl). The maximum synthesis temperature, developed using a thermal wave, was between 1030 and 1250 °C as k was changed from 5 to 7 moles. The phase content, morphology, and optical properties of the products were characterized. It is shown that BN sheets synthesized at the given k were 1.5–3 nm thick and had a hexagonal structure. The number of atomic layers in one sheet ranged from 5 to 10; the lateral dimension of individual sheets ranged from 50 to 1000 nm. The developed method allowed the synthesis of a large amount of uniform and high quality BN nanosheets (tens of grams in laboratory-scale experiments); this method will reduce the overall production cost.

The influence of point defect on the behavior of oxygen precipitation in CZ-Si wafers

Abstract The effect of heat treatment conditions and point defects on oxygen precipitation was investigated with various grown-in defect region wafers. The behavior of oxygen precipitation depends on the nucleation temperature and the type and the concentration of point defects. The peak temperature of nucleation for oxygen precipitation is 687–734°C in vacancy-rich, oxidation-induced stacking fault ring, interstitial Si-rich and interstitial pure regions. In vacancy-pure region, the peak temperature of nucleation is about 870°C. The vacancy plays an important role in increasing the peak temperature of nucleation for oxygen precipitation.

Size Tailored Nanoparticles of ZrN Prepared by Single-Step Exothermic Chemical Route

Abstract ZrN nanoparticles were prepared by an exothermic reduction of ZrCl 4 with NaN 3 in the presence of NaCl flux ina nitrogen atmosphere. Using a solid-state combustion approach, we have demonstrated that the zirconium nitride nanoparticlessynthesis process can be completed in only several minutes compared with a few hours for previous synthesis approaches. Thechemistry of the combustion process is not complex and is based on a metathesis reaction between ZrCl 4 and NaN 3 . Becauseof the low melting and boiling points of the raw materials it was possible to synthesize the ZrN phase at low combustiontemperatures. It was shown that the combustion temperature and the size of the particles can be readily controlled by tuningthe concentration of the NaCl flux. The results show that an increase in the NaCl concentration (from 2 to 13 M) results ina temperature decrease from 1280 to 750 o C. ZrN nanoparticles have a high surface area (50-70 m 2 /g), narrow pore sizedistribution, and nano-particle size between 10 and 30 nm. The activation energy, which can be extracted from the experimentalcombustion temperature data, is: E = 20 kcal/mol. The method reported here is self-sustaining, rapid, and can be scaled up fora large scale production of a transition metal nitride nanoparticle system (TiN, TaN, HfN, etc.) with suitable halide salts andalkali metal azide.Key wordszirconium nitride, nanoparticles, combustion synthesis, particle size, sodium chloride.

Ammonium fluoride-activated synthesis of cubic δ-TaN nanoparticles at low temperatures

Cubic delta-tantalum nitride (δ-TaN) nanoparticles were selectively prepared using a K2TaF7 + (5 + k) NaN3 + k NH4F reactive mixture (k being the number of moles of NH4F) via a combustion process under a nitrogen pressure of 2.0 MPa. The combustion temperature, when plotted as a function of the number of moles of NH4F used, was in the range of 850°C to 1,170°C. X-ray diffraction patterns revealed the formation of cubic δ-TaN nanoparticles at 850°C to 950°C when NH4F is used in an amount of 2.0 mol (or greater) in the combustion experiment. Phase pure cubic δ-TaN synthesized at k = 4 exhibited a specific surface area of 30.59 m2/g and grain size of 5 to 10 nm, as estimated from the transmission electron microscopy micrograph. The role of NH4F in the formation process of δ-TaN is discussed with regard to a hypothetical reaction mechanism.