• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.43-49
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• 2005

YSZ layer containing nano-sized particles has been deposited on the commercial A1203 substrate by Electron Beam Physical Vapor Deposition (EB-PVD). The role of coating rnjcrostructures of YSZ to indentation damage is studied. The different coating microsouctures are prepared by varying the substrate temperatures from $600^{circ}C$ to $800^{circ}C$ during the deposition. Microhardness test and Hertzian indentation are conducted on the $YSZ/Al_{2}O_{3}$ layered systems. The damage and flilure behaviors have been investigated according to the effect of microstructures and indentation loads. With increasing the substrate temperature during EB-PVD, the overall grain sizes are coarser and more faceted, which microsoucture ultimately influences on the indentation behavior, thus, YSZ/Al_{2}O_{3}$ layered system prepared at the substrate temperature of $800^{circ}C$ shows relatively higher damage tolerance.

• Restorative Dentistry and Endodontics
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• v.22 no.2
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• pp.505-518
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• 1997

The objective of this investigation was to compare the effects of water storage on the aspect of hardness and diametral tensile strengths of four hybrid glass ionomer cements(two compomers and two resin-reinforced glass ionomers) with a resin composite material. One composite resin(Degufill Ultra), two compomers(Dyract, Compoglass Cavifil), and two resin-reinforced glass ionomers(Fuji Duet, Vitremer) were used in this study. Cylindrical specimens were prepared and stored at $36{\pm}1^{\circ}C$ in distilled water for 10 minutes after set, and then tested on an Instron testing machine(No.4467) at 1.0 mm/min displacement rate. Vicker's hardness and diametral tensile strengths as time elapsed were measured after aging in water for 10 minutes, 1 hour, 3 hours, 1 day, 3 days, 5 days and 7 days at $36{\pm}1^{\circ}C$. During the test of diametral tensile strength, stress-strain curves were obtained, from which the compressive modulus were calculated and compared. The structure of four set glass ionomer cement mass was observed on SEM(Hitachi, S-2300) after being etched with 9.6% hydrofluoric acid for 1 minute. The results were as follows; 1. The hardness of the experimental group(compomer and the resin reinforced glass ionomer cement) did not exceed the value of control group(Degufill Ultra). 2. Vicker's hardness of the Fuji Duet tended to increase succeedingly, Dyract was decreased after 3 hours in water, and Vitremer was the lowest. 3. The control group(Degufill Ultra) presented progressively on increased diametral tensile strength with time, Fuji Duet were decreased after 3 days, Compoglass Cavifil and Vitremer were decreased after 5 days in water storage. 4. Compressive modulus of the control group(Degufill Ultra) and Dyract were increased sharply timely, Fuji Duet and Vitremer were increased smoothly by lapse of time in water. Fuji Duet were stronger than Vitremer. On the other hand, Vitremer exhibited the lowest toughness. 5. The microstructure of compomer was similar with that of the composite resin(Degufill Ultra), and the fillers in resin-reinforced glass ionomer cements were noticed. It can be concluded that mechanical properties of hybrid glass ionomer cements is weaker than composite resin, and that the compomers or the resin-reinforced glass ionomers can not substitute the composite resins. A plenty of considerations should be done on the application of them to the area under the loading and high wear has a little adverse effect on the mechanical properties on the water storage for 7 days. The further research should be needed to confirm the advantage of the compomer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.8
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• pp.1783-1788
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• 2009

We newly propose that we may reuse scrap powders ($Z_rO_2$+8 mol%-$Y_2O_3$) as $Y_2O_3$-stabilized zirconia (YSZ) sintered products through sintering process at 1550$^{circ}C$ for 2hrs. We also prepared the reference specimen from fresh $Z_rO_2$+30 mol%-$Y_2O_3$ powder mixture (celluar type with 1㎛-length). The reference sample showed a dense microstructure with grains of $\sim$10㎛ in diameter, while the sintered sample from scrap powder showed irregular grains of 1$\sim$30 ㎛ in diameter. Through XRD analysis, we confirmed that the reference sample has mixed phases of $Y_2O_3$(cubic), $Z_{r0.8}O_{1.9}$(cubic), and $Z_rO_2$(monoclinic), while the sintered YSZ sample from scrap powder has only tetragonal phase. Moreover, the sintered YSZ from scrap powder showed vickers hardness and apparent density more than 70 and 4.11 g/cc, which implies that it can be suitable for structural material application.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.327-332
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• 1999

The recovery activation energy, the order of reaction and the recovery rate constant were detemined by isochronal and isothermal annealing treatment to investigate the recovery behaviors of neutron irradiated Mn-Mo-Ni low alloy steels$(fluence: 2.3\times10^{19}ncm^{-2}, 553K, E\geq1.0 MeV)$. Vickers microhardness tests were conducted to trace the recovery behavior after heat treatments. The results were analyzed in terms of recovery stages, behavior of responsible defects and recovery kinetics. It was shown that recovery occurred through two annealing stages(stage I : 703-753K, stage n : 813-873K) with re$\infty$very activation energies of 2.5 eV and 2.93 eV for each stage I and n, respectively. From the comparison of unirradiated and irradiated isochronal anneal curves, a radiation anneal hardening(RAH) peak was identified at around 813K. Most of recovery have occurred during about 120 min irrespective of isothermal annealing temperatures of 743K and 833K. Recovery rate constants were determined to be $3.4\times10^{-4}min^{-1} and 7.1\times10^{-4}min^{-1}$ for stage I and II, respectively. The order of reaction was about 2 for both recovery stages. Comparing the obtained data with those of previously reported results on neutron irradiated Mn- Mo- Ni steels, the thermal recovery be­havior of the present material seems to occur by the dissociation of point defect clusters formed during irradiation, and by the recombination process of self-interstitials and vacancies from dissociated vacancy clusters.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.190-201
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• 2004

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four esthetic restorative materials in an alkaline solution. The brands studied were Charmfil, Charmfil flow(composite resin), Compoglass F and PrimaFlow(compomer). The results were as follows: 1. The mass loss were not significantly different among the materials(p>0.05). 2. The sequence of the degree of degradation layer depth was in descending order by Compoglass F, PrimaFlow, Charmfil, and Charmfil flow. There were significant differences between Compoglass F and the others(p<0.05). 3. The sequence of the Si loss was in descending order by Charmfil flow, Charmfil, PrimaFlow, and Compoglass F. There were significant differences among these materials(p<0.05). 4. When observed with SEM, destruction of bonding between matrix and filler was observed and when observed with CLSM, the depth of degradation layer of specimen surface was observed. 5. The sequence of maximum wear depth was in descending order by Comfoglass, PrimaFlow Charmal, and Charmfil flow. There were significant differences among these materials(p<0.05). 6. The correlation coefficient between Si loss and degradation layer depth (r=0.602, p<0.05) Vicker's hardness number and maximum wear depth (r=0.501, p<0.05) were relatively high. These results indicate that wear and hydrolytic degradation may be considered to be evaluation factors of composite resins and compomers.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.171-177
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• 2001

The thermal and mechanical properties of amorphous Z $r_{62-x}$N $i_{10}$C $u_{20}$A $l_{8}$ $Ti_{x}$ (x=3, 6, 9at%) alloys were investigated. The crystallization process was confirmed as amorphous longrightarrow amorphous + Z $r_2$A $l_3$+ Zr + (Ni,Ti) longrightarrow Z $r_2$Cu + Al + (Ni,Ti) for 3at%Ti, amorphous longrightarrow amorphous + Al longrightarrow $Al_2$Ti + NiZr + CuTi for 6at%Ti and amorphous longrightarrow amorphous + Zr + Al longrightarrow Zr + $Al_2$Zr + Al $Ti_3$+ CuTi for 9at%Ti. lickers hardness ( $H_{v}$ ) increased with increasing volume fraction( $V_{f}$ ) of pricipitates for all concerned compositions. Tensile fracture strength ($\sigma_{f}$ ) showed a maximum value 1219MPa at $V_{f}$ = 38% for 3at%Ti, 1203MPa at $V_{f}$ = 2% for 6at%Ti and 1350MPa at $V_{f}$ = 5% for 9at%Ti. The $\sigma_{f}$ was rapidly decreased after showing the maximum value. The $V_{f}$ corresponding to rapidly decreased $\sigma_{f}$ coincided with the $V_{f}$ transited from ductile to brittle fracture surface.ace.

• Economic and Environmental Geology
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• v.26 no.2
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• pp.129-134
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• 1993

At the Janggun mine, boulangerite usually occurs as needles or irregularly-shaped grains, up to $500{{\mu}m}$ in longer dimensions, closely associated with galena, minerals of a tetrahedrite-freibergite series and bournonite in the peripheries of South A and B orebodies and the zone of manganoan carbonates surrounding them. In some places, especially at the top of South B orebody, it occures as "feather ore" consisting of its fine needles or "hairs" in small drusy cavities together with fine-grained euhedral galena, pyrite, manganoan carbonates, quartz, etc. In reflected light, it is bluish grey in colour exhibiting moderate bireflectance and is strongly anisotropic without any internal reflections. Reflectance in air is $R_{max}=43.2$, $R_{min}=35.7$ percent at wavelength of 580 nm, and VHN: $146-173\;kg/mm^2$ at a 50 g-load. The chemical composition on the average from 23 complete spot analyses by electron microprobe is, Pb 56.1, Sb 25.1, S 18.5, Total 99.6 (all in weight percent); the corresponding chemical formula calculated on the basis of S=11 is; $Pb_{5.16}Sb_{3.93}S_{11.0}$ which fulfils approximately the ideal formula $Pb_5Sb_4S_{11}$. The strongest reflections on the X-ray diffraction pattern are; $3.73\;{\AA}\;(10)$, $3.22\;{\AA}\;(5)$, $3.03\;{\AA}\;(4)$ and $2.82\;{\AA}\;(5)$ and the pattern is in harmonic with space group $C^5_{2h}-P2_1/a$. From the textural evidence of the microscopic observations, the mineral is considered to have been formed at the latest stage of hydrothermal lead-zinc-silver mineralization.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.557-568
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• 2005

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four esthetic restorative materials in an alkaline solution(0.1N NaOH). The brands studied were MetafilCX(Sun medical, Japan) Solitaire 2(Heraeus Kulzer, USA), Composan LCM(Promedica, Germany), DenFil(Vericom, Korea). The results were as follows: 1. The mass loss of each brand was 0.74~7.94% and highest value in Metafil($7.94{\pm}0.39%$). 2. The sequence of the degree of degradation layer depth was in descending order by Metafil, Solitaire 2, DenFil, Composan LCM. There were significant differences between Metafil and the others(p<0.05). 3. The sequence of the Si loss was in descending order by Metafil, Solitaire 2, Composan LCM, DenFil. There were significant differences among the materials(p<0.05). 4. On SEM, destruction of bonding between matrix and filler and on CLSM, the depth of degradation layer of specimen surface was observed. 5. The sequence of maximum wear depth was in descending order by Metafil, Solitaire 2, Composan LCM and DenFil. There were significant differences among the materials(p<0.05). 6. The correlation coefficient between Si loss and degradation layer depth (r=0.491, p<0.05) and Vicker's hardness number and maximum wear depth (r=-0.942, p<0.05) were relatively high. These results indicate that hydrolytic degradation and wear may consider as a evaluation factors of composite resins.