• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.291-292
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• 2006

A steel/cemented carbide couple is selected to generate a tough/hard two layers material. Sintering temperature and composition are deduced from phase equilibria, and experimental studies are used to determine optimal conditions. Liquid migration from the hard layer to the tough one is observed. Microstructure evolution during sintering of the tough material (TEM, SEM, image analysis) evidences coupled mechanisms of pore reduction and WC dissolution. Liquid migration, as well as interface crack formation due to differential densification are limited by suitable temperature and time conditions.

• Journal of Welding and Joining
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• v.14 no.4
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• pp.53-61
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• 1996

It was attempted to improve the wear resistance of Al alloy under the load condition by making a formation of the thicker surface hardening alloy layers. The thicker surface hardening alloy layers were formed on 6061 Al alloys overlayed by MIG and TIG welding process with Cu powders feeding. The characteristics of hardening and wear resistance have been investigated in relation to the microstructures of alloyed layers, with a selection of optimum alloying conditions for formation of overlaying layer. The results obtained were summarized as follows With increasing feeding rate of Cu powders by MIG welding, the hardness and specific wear of the overlay weld alloys were increased. It is considered that these high hardness and specific wear of overlay weld alloys were due to the formation of Θ($Al_2Cu$) phases. With increasing feeding rate of Cu powders by TIG welding, the hardness and specific wear of the overlay weld alloys were increased in feeding rates 12 and 18g/min. However, the hardness and specific wear were decreased in the powder feeding rate 38g/min. It is considered that considered that decrease of hardness and specific wear in the powder feeding rate 38g/min due to formation of ${\gamma}$($Al_4Cu_9$) phases.

• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.120-129
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• 2009

The purpose of this study was to investigate the pulpal response to direct pulp capping with dentin sialoprotein (DSP) -derived synthetic peptide in teeth of dogs, and to compare its efficacy to capping substances $Ca(OH)_2$ and white mineral trioxide aggregate (WMTA). A total of 72 teeth of 6 healthy male beagle dogs were used. The mechanically exposed pulps were capped with one of the following: (1) DSP-derived synthetic peptide (PEP group): (2) $Ca(OH)_2$ (CH group): (3) a mixture paste of peptide and $Ca(OH)_2$ (PEP+CH group): or (4) white MTA (WMTA group). The access cavity was restored with a reinforced glass ionomer cement. Two dogs were sacrificed at each pre-determined intervals (2 weeks, 1 month, and 3 months). After the specimens were prepared for standard histological processing, sections were stained with hematoxylin and eosin. Under a light microscope, inflammatory response and hard tissue formation were evaluated in a blind manner by 2 observers. In the PEP group, only 3 of 17 specimens showed hard tissue formation, indication that the DSP-derived synthetic peptide did not induce proper healing of the pulp. Compared with the CH group, the PEP group demonstrated an increased inflammatory response and poor hard tissue formation. The CH and WMTA groups showed similar results for direct pulp capping in mechanically exposed teeth of dogs.

• Polymer(Korea)
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• v.24 no.2
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• pp.149-158
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• 2000

Oil-absorptive expanded polyurethane (EPU) was prepared with a lypophilic polyol, polypropyleneglycol (PPG) as the soft segment, and toluenediisocyanate (TDI) and $H_2O$ as the hard segment. PPGs haying various average molecular weights ((equation omitted) : 1000, 2000, 3000) were employed to investigate that the soft segment content was consequent on the oil-absorptivity and the mechanical properties of the EPUs. As (equation omitted) of PPG was decreased from 3000 to 1000, the oil-absorptivity and the tensile strength of the EPUs increased from 1460 to 3010% and from 0.26 to 0.55 $kg_{f}$ /$cm^2$ respectively. As the hard segment content ratio, ${\gamma}$ ([NCO]/[OH]) was increased from 1.0 to 1.2, the tensile strength of the EPUs increased from 0.56 to 0.95 $kg_{f}$ /$cm^2$, due to the formation of allophanate and/or biuret bondings. However, as the surfactant (S-A) content was increased from 1.0 to 2.5 pbw, the oil-absorptivity was decreased from 3634 to 3312%, due to the formation of closed cell structures.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.19 no.2
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• pp.75-80
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• 2013

The physicochemical properties of the hydroxypropylated mung bean, sweet potato and water chestnut starches were studied. The blue value and amylose content of mung bean starch were higher than those of sweet potato and water chestnut. Pasting temperature of hydroxypropylated starches were lower than those of native starch and decreased with increasing contents of propylene oxide. Peak viscosity increased with the increase of degree of hydroxypropylation. With increasing contents of propylene oxide, the clarity and swelling power of all starches were increased and those of mung bean were higher. Mung bean starch produced better hard capsules than sweet potato and water chestnut starch. Hydroxypropylated (>6% propylene oxide) water chestnut starch-based capsules completely dissolved, but hydroxypropylated (>12% propylene oxide) mung bean and sweet potato starch-based capsules were dissolved within 10 min. These results showed that hydroxypropylated starch-based capsules have potentials for pharmaceutical applications as a substitute for gelatin hard capsules.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.398-403
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• 1983

In this investigation, the effect of microstructural factors on the impact energy was studied, using dual phase steels with soft phase of ferrite encapsulated by hard phase of martensite. It was found that the effect of the ferrite grain size on the impact energy decreases as the strength ratio increases, these results are due to the micro-brittlefracture facet by the difficulty of cleavage crack formation in the ferrite grain.

• Journal of Powder Materials
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• v.10 no.6
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• pp.374-382
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• 2003

During the sintering of powder materials, many these are microstructural phenomena are caused by atomic diffusion. (1) neck formation and compact densification, (2) grain growth, i.e., growth of matrix grains and dispersed grains, (3) alloying or generation of compound, (4) generations of peculiar and hard layers near sintered compact surface, etc. The studies of the present author and co-workers on these phenomena which were carried out during 40 years are briefly introduced.

• Journal of Powder Materials
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• v.1 no.2
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• pp.119-198
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• 1994

The characteristics of various important microstructural factors of WC-base hard- metals (cemented carbides) such as the amount of Co metal binder phase, the carbide grain size, the microstructural defects acting as a fracture source, the solid solubility of tungsten in the binder phase affected by the carbon content, the precipitation of $Co_3W$, the domain size of binder phase, the formation of ${\beta}-free$ layer or Co-rich layer and CVD or PVD coated layer, and the effects of these factors on the flexural strength of the hardmetals are reviewed.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2002.05a
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• pp.35-35
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• 2002

Atomic force microscopy was applied to study the formation and growth mechanism of thin chrome layers prepared under various pulse plating conditions. The chrome was electro-deposited from an electrolyte bath containing 250 gl-l of chromic acid, 25 gl-l of sulfuric acid using direct current density of $1.6{\;}mA.$\textrm{mm}^{-2} and pulse currents with on-off time from 5 to 900 ms. The higher current density enhanced nucleation rate which resulted in refining grain size. The chrome growth kinetics determining nodule size and shape significantly depends on the duration of on-time rather than duration of off-time and on/off time ratio.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.1
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• pp.16-21
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• 2002

Ti-0 film is a kind of biocompatible surface materials. In this paper, a new method, glow discharge plasma oxidizing, has been used in synthesizing Ti-O gradient films on Ti6A14V substrates. The effects of ion bombardment and process parameters on the structures of titanium oxide layers have been investigated. The results demonstrate that DC glow plasma oxidizing is more efficient in preparation of dense, hard, and high adhesive Ti-O biomedical films on titanium and its alloys. Samples treated by this method show higher hardness values than by others. Especially, in the condition of hollow cathode discharge, the ion bombardment enhances ionization of oxygen, promotes the oxygen permeation and facilitates the formation of the oxide of low valence states of titanium.