• Journal of the Korean Ceramic Society
• /
• v.34 no.4
• /
• pp.406-412
• /
• 1997

Al2O3/SiC hybrid-composite has been fabricated by the conventional powder process. The addition of $\alpha$-Al2O3 as seed particles in the transformation of ${\gamma}$-Al2O3 to $\alpha$-Al2O3 provided a homogeneity of the microstructure. The grain growth of Al2O3 are significantly surpressed by the addition of nano-size SiC particles. Dislocation were produced due to the difference of thermal expansion coefficient between Al2O3 and SiC and piled up on SiC particles in Al2O3 matrix, resulting in transgranular fracture. The high fracture strength of the composite was contributed to the grain refinement and the transgranular fracture mode. The addition of SiC platelets to Al2O3/SiC nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC platelets with nitrides such as BN and Si3N4 enhanced fracture toughness much more than non-coated SiC platelets by enhancing crack deflection.

• Journal of the Korean Ceramic Society
• /
• v.32 no.7
• /
• pp.846-852
• /
• 1995

The multiply reinforced mullite-zirconia composites were prepared with addition of Al2O3 particles, platelets, and fibers. The sinter-HIP specimens (presintered at 1$700^{\circ}C$ and hipped at 1$600^{\circ}C$) showed that the fracture toughness of Al2O3 fiber reinforcement (4.4 MPa.{{{{ SQRT {m} }}) was higher than those of platelet (4.0 MPa.{{{{ SQRT {m} }}) and of particle (3.9MPa.{{{{ SQRT {m} }}) reinforcement, whereas the fracture strength of Al2O3 particle reinforcement (304 MPa) was higher than those of platelet (293MPa) and of fiber (248MPa) reinforcement.

• Safety and Health at Work
• /
• v.2 no.3
• /
• pp.282-289
• /
• 2011

Objectives: We sought to establish a novel method to generate nano-sized carbon black particles (nano-CBPs) with an average size smaller than 100 nm for examining the inhalation exposure risks of experimental rats. We also tested the effect of nano-CBPs on the pulmonary and circulatory systems. Methods: We used chemical vapor deposition (CVD) without the addition of any additives to generate nano-CBPs with a particle size (electrical mobility diameter) of less than 100nm to examine the effects of inhalation exposure. Nano-CBPs were applied to a nose-only inhalation chamber system for studying the inhalation toxicity in rats. The effect on the lungs and circulatory system was determined according to the degree of inflammation as quantified by bronchoalveolar lavage fluid (BALF). The functional alteration of the hemostatic and vasomotor activities was measured by plasma coagulation, platelet activity, contraction and relaxation of blood vessels. Results: Nano-CBPs were generated in the range of 83.3-87.9 nm. Rats were exposed for 4 hour/day, 5 days/week for 4 weeks to $4.2{\times}10^6$, $6.2{\times}10^5$, and $1.3{\times}10^5$ particles/$cm^3$. Exposure of nano-CBPs by inhalation resulted in minimal pulmonary inflammation and did not appear to damage the lung tissue. In addition, there was no significant effect on blood functions, such as plasma coagulation and platelet aggregation, or on vasomotor function. Conclusion: We successfully generated nano-CBPs in the range of 83.3-87.9 nm at a maximum concentration of $4.2{\times}10^6$ particles/$cm^3$ in a nose-only inhalation chamber system. This reliable method can be useful to investigate the biological and toxicological effects of inhalation exposure to nano-CBPs on experimental rats.

• The Korean Journal of Ceramics
• /
• v.7 no.2
• /
• pp.80-84
• /
• 2001

The anisotropic CdS platelets were synthesized in the lamellar bilayer phase region of the octylamine-water binary system. The influence of the synthesis conditions of the system components on morphology and size of the platelets was examined. Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) studies have shown thickness and face size of the synthesized particles. Platelets with face sizes ranging from 50 to 250 nm and thickness from 10 to 30 nm have been synthesized at room temperature. In addition, HRTEM micrographs show that the synthesized platelets are poly crystal.

• Current Optics and Photonics
• /
• v.2 no.6
• /
• pp.623-628
• /
• 2018

Clotting properties of human blood are important clinical information to monitor for patients with platelet and coagulation disorders. Most devices used to diagnose these disorders utilize blood plasma together with tissue factors and $Ca^{{+}{+}}$ additives. In some instruments, magnetic particles were mixed with blood samples and a rotating magnetic field was applied, resulting in the rotation of magnetic particles, which was probed by impinging light. The working principle seems obvious yet had not been investigated in depth. We modeled the collective behavior of light propagating through magnetic needles, aligned in the direction of the rotating external magnetic field, with scattering light analysis software. Simulation results indicated that the scattering pattern undergoes periodic undulations with respect to the slant angle of the magnetic needles. Also provided is a means of extracting meaningful information from the scattering measurement.

• Journal of Periodontal and Implant Science
• /
• v.27 no.1
• /
• pp.45-59
• /
• 1997

Platelet-derived growth factor(PDGF) has been shown to play an important role in periodontal regeneration. The purpose of the present study was to examine the distribution of PDGF in experimentally created periodontal intrabony defects after flap surgery with various bone graft materials. Six healthy mongrel dogs were used in this study. Three-wall bony defects were created in maxillary and mandibular premolars, inflammation induced by wire ligation and injection of impression material into the defects. Eight weeks later, the experimental lesions thus obtained were treated by plain flap surgery(control group), flap surgery plus autogenous bone graft(autogenous bone group), flap surgery plus Biocoral graft(Biocoral group), or flap surgery plus bioglass graft(bioglass group), which were randomly assigned to the defects. After 4, H, and 12 weeks postoperatively, 2 dogs were sacrificed at each time and 1he specimens were taken for histological examinations and immunohistochemical examinations for PDGF. In the control defects the amount of new bone formation was minimal. In the autogenous bone and Biocoral group new bone was deposited around implanted particles and the amount of new bone was increased with time. A large number of bioglass particles exibited a central excabation and bone formation could be observed in the central excabation as well as around the particles. The expression of PDGF was low in the control group. The expression of PDGF in Biocoral group was increased at 1, H week, but decreased at 12 week. The increased PDGF expression in autogenous bone and bioglass group was maintained to the end of the experiment.

• Journal of Ceramic Processing Research
• /
• v.13 no.spc2
• /
• pp.270-273
• /
• 2012

x mol% (x = 0 ~ 20) Na2CO3 excess Bi2.5Na3.5Nb5O18 (BNN) particles were synthesized using molten salt as a flux. The secondary phases were observed at stoichiometric ratio of BNN precursors and their intensity decreased with increasing Na contents. The results of SEM images showed that all particles existed in a platelet shape and the particle increased in size with higher increasing Na contents. Plate-like NaNbO3 particles were developed using BNN precursor obtained by a topochemical microcrystal conversion. XRD analysis of NaNbO3 particles showed that a single perovskite phase and the intensity of (h00) peaks increased with increasing Na contents in BNN precursor. SEM images showed that the size of plate-like NaNbO3 was significantly changed by controlling Na contents in BNN precursors.

• Journal of the Korean Ceramic Society
• /
• v.39 no.10
• /
• pp.1007-1010
• /
• 2002

Alpha alumina platelet particles were synthesized from the powder mixture of ${\gamma}-Al_2O_3and\;Na_2SO_4$ with the use of microwave heating. The characteristics of the particles such as particle size and particle size distribution were compared with those of particles obtained from the same mixture without the use of microwave. Sample with the use of microwave showed small particle size and narrow particle size distribution compared to that without the use of microwave.

• Journal of the Korean Ceramic Society
• /
• v.46 no.3
• /
• pp.288-294
• /
• 2009

The platelet AlO(OH) nano colloids were prepared by hydrothermal reaction of the $\gamma-Al_2O_3$ obtained with dehydration of $\gamma$-AlO(OH) and dilute $CH_3COOH$ solution. In hydrothermal reaction process, reversible reaction was accompanied between $\gamma-Al_2O_3$ and AlO(OH), and hydrothermal reaction temperature, hydrothermal reaction time and $CH_3COOH$ concentration had an effect on the crystal structure, surface chemical property, surface area, pore characteristics and crystal morphology of the AlO(OH) nano colloid particles. In this study, it was investigated to the hydrothermal reaction condition of the AlO(OH) nano colloid for using catalyst support, heat resisting agent, adsorbents, binder, polishing agent and coating agent. The crystal structure, surface area, pore volume and pore size of the platelet AlO(OH) nano colloids were investigated by XRD, TEM, TG/DTA, FT-IR and $N_2$ BET method in liquid nitrogen temperature.

• Journal of the Korean Ceramic Society
• /
• v.32 no.2
• /
• pp.257-269
• /
• 1995

The TiC-Co/Al reaction-sintered products were prepared by the infiltration of various Co/Al metal mixture into the preform, and their microstructure, phases, and mechanical properties were investigated. With increasing the atomic ratio of Co/Al, tiC grain shape was changed from spherical to platelet particles, and the grain size increased. The crystalline phases found in the liquid matrix formed by the infiltration of Co/Al metal mixture were determined to be Al5Co2 and AlCo by EDS and XRD, and the two crystalline phases were located dominantly between TiC grains, when the Co/Al atomic ratio was lower than an unity. There was a tendency that the density, bending strength and fracture toughness increase with Co/Al atomic ratio until the infiltrated metal was 100% Co. The maximum value was achieved by the composition containing 100% Co infiltrated metal. The Vickers hardness decreased as Co/Al atomic ratio increased.