• Bulletin of the Korean Chemical Society
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• 제33권4호
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• pp.1220-1224
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• 2012

This study examines the photoelectric conversion efficiency of dye-sensitized solar cells (DSSCs) when nanometer-sized Y (0, 0.1, 0.5, and 1.0 mol %)-incorporated $TiO_2$ prepared using a solvothermal method is utilized as the working electrode material. The photoelectric properties of the Y-$TiO_2$ used in DSSCs were studied by frequency-resolved modulated photocurrent/photovoltage spectroscopy. The recombination was much slower in the Y-$TiO_2$-based DSSCs than in the pure $TiO_2$-assembled DSSC. Compared to that using pure $TiO_2$, the energy conversion efficiency was enhanced considerably by the application of Y-$TiO_2$ in the DSSCs to approximately 6.08% for 0.5 mol % Y-$TiO_2$.

• Applied Science and Convergence Technology
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• 제26권5호
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• pp.143-147
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• 2017

Structural studies on the addition characteristics of Nb ions to $BaTiO_3$ solid solutions were performed by XRD and SEM/EDS technique. The X-ray diffraction peaks of the (111), (200) and (002) planes of Nb-doped $BaTiO_3$ solid solutions with different mole% of Nb were analyzed. We also investigated the relationship between the dielectric and structural properties of Nb-doped $BaTiO_3$. The transition temperatures of $BaTiO_3$ solid solution doped with 0.5mole%Nb and 1.0 mole%Nb were ${\sim}116^{\circ}C$ and ${\sim}87^{\circ}C$, respectively, which were found to be shifted to very low temperature from the transition temperature of pure $BaTiO_3$ (about $125^{\circ}C$). As a result of analysis of 1/K versus T and ln[$(1/K)-(1/K_m)$ versus ($T-T_m$)] of the two compositions used in this experiment, the diffusivity slightly differs from that of pure $BaTiO_3$ at temperatures above Curie temperature. And this characteristic was analyzed by applying the modified Curie-Weiss law.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제26권1호
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• pp.59-72
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• 2000

In this study, the rate of bone formation and the pattern of bone to implant contact surface around HA coated implant and pure Ti implant inserted into the irradiated tibia of rabbit were compared. Sixteen mongrel mature male rabbits were used as experimental animal. Each rabbit received 15 Gy of irradiation. Four weeks after irradiation, two holes were prepared on the tibia of each rabbit for placement of HA coated type and pure Ti type implants. Prior to implant placement, one group received steroid irrigation and the control group was similarly irrigated with normal saline. This was immediately followed by placement of the two different types of implants. Postoperatively, tetracycline was injected intramuscularly for 3 days. For fluorescent labelling, 3 days of intramuscular alizarine red injection was given. 2 weeks before sacrifice, followed by intramuscular calcein green on the last 3 days before specimen collection. Each rabbit was sacrificed on the second, fourth, sixth and eighth week after the implantation. The specimens were observed by the light microscope and the fluorescent microscope. The results were as follows; 1. All implants inserted into the irradiated tibia of rabbit were free from clinical mobility and no signs of bony resorption were noted around the site of implant placement. 2. Under the light microscope, new bone formation proceeded faster around implants that received steroid irrigation compared to the control group irrigated with saline. Bone to implant contact surface was greater in the steroid irrigated group than the saline irrigated group. Therefore, better initial stabilization was observed in the group pretreated with steroid irrigation. 3. Under the light microscope. HA coated implants showed broader bone to implant contact surface than pure Ti implants, and HA coated implants had better bone healing pattern than pure Ti implants. 4. In the steroid pretreated group, acceleration of bone formation was demonstrated by fluorescent microscopy around the 2, 4 weeks group and the 6 weeks HA coated implant group. The difference in the rate of bone formation proved to be statistically significant(P<0.05). Faster bone formation was noted in the saline irrigated group in the 6 weeks pure Ti implants and 8 weeks group. The difference was not statistically significant(P<0.05). 5. For the rabbits that were sacrificed on the second and fourth week after the implant placements, the rates of bone formation around HA coated implants proceeded faster than those around pure Ti implants under the fluorescent microscopy. For the rabbits that were sacrificed on the sixth week after the implant placements, the rates of bone formation around pure Ti implants proceeded faster than those around HA coated implants under the fluorescent microscopy. But this result did not show statistical significance (P<0.05) For the rabbits that were sacrificed on the eighth week after the implant placements, the rates of bone formation around HA coated implants proceeded faster than those around pure Ti implants under the fluorescent microscopy. This result was statistically significant (P<0.05).

• Journal of Welding and Joining
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• 제30권2호
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• pp.70-75
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• 2012

In this study, effect of nitrogen volume in the shielding gas of Ar-$N_2$ mixing gas on the bead shape, hardness and microstructure of GTA welds of 3mm thick Commercial Pure Ti was investigated. As the nitrogen volume increased, the welding current for full penetration was reduced and hardness in the fusion zone significantly increased compared with that of the base metal, but there is no difference in the hardness of HAZ. Microstructure in the fusion zone with pure Ar gas changed from equiaxed alpha of the base metal to serrated alpha. On the other hand, microstructure using Ar-$N_2$ mixing gas changed to acicular alpha. With the increasing of nitrogen content, the amount of acicular alpha increased and the size of that was fine.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.215-218
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• 2006

A study was made to investigate microstructural evolution and mechanical properties of ultra-fine grained (UFG) pure-Ti produced by equal channel angular (ECA) pressings. The deformed structures were analyzed by finite element method and transmission electron microscopy with the increment of straining. After 4 isothermal ECA pressings, initial coarse grains ($30{\mu}m$) were significantly refined to ${\sim}0.3{\mu}m$ with homogeneous distribution of microstructure which was resulted from $180^{\circ}$ rotation of the sample between pressings. UFG pure-Ti exhibited the considerable improvement in yield strength while losing strain hardening capacity as compared to coarse grained microstructure at ambient temperature, which was mainly attributed to ultra-fine grain microstructure with non-equilibrium grain boundaries.

• 분석과학
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• 제9권2호
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• pp.192-197
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• 1996

현재 사용되고 있는 생체용 금속재료로 스테인레스강(SUS 316), Co-Cr강, 순수 Ti, Ti-6Al-4V이 많이 사용되고 있으며 그 중에서도 특히 Ti이 각광을 받고 있다. 그러나 순수한 Ti은 생체적합성과 내식성은 좋은 반면 기계적 성질이 합금에 비해 뒤떨어지고, Ti-6Al-4V은 V의 세포독성이 지적되고 있어 이러한 문제를 해결하기 위해 세포독성이 없는 함금원소를 Ti에 첨가한 새로운 합금을 설계하였다. 그 중에서 Ti-20Zr-3Nb-3Ta-0.2Pd-1In과 Ti-5AI-4Zr-2.5Mo은 기계적 성질도 뛰어나고 우수한 전기화학적 부식특성을 가지고 있었다.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3301-3306
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• 2013

This paper aims to address the cellular toxicity of ultra-pure titanium dioxide ($TiO_2$) and zinc oxide (ZnO) nanoparticles (NPs) frequently employed in sunscreens as inorganic physical sun blockers to provide protection against adverse effects of ultraviolet (UV) radiation including UVB (290-320 nm) and UVA (320-400 nm). In consideration that the production and the use of inorganic NPs have aroused many concerns and controversies regarding their safety and toxicity and that microsized $TiO_2$ and ZnO have been increasingly replaced by $TiO_2$ and ZnO NPs (< 100 nm), it is very important to directly investigate a main problem related to the intrinsic/inherent toxicity of these NPs and/or their incompatibility with biological objects. In the present study, we took advantage of the laser-assisted method called laser ablation for generation of $TiO_2$ and ZnO NPs. NPs were prepared through a physical process of irradiating solid targets in liquid phase, enabling verification of the toxicity of ultra-pure NPs with nascent surfaces free from any contamination. Our results show that $TiO_2$ NPs are essentially non-poisonous and ZnO NPs are more toxic than $TiO_2$ NPs based on the cell viability assays.

• 대한치과기공학회지
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• 제33권4호
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• pp.263-270
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• 2011

Purpose: The grindability of binary Ti-X%Zr(X=10,20,40) alloys in order to develop a Ti alloy with better machinability than unalloyed titanium has been evaluated. Methods: Experimental Ti-Zr alloys were made in an argon-arc melting furnace. Slabs of experimental alloys were ground using a SiC abrasive wheel on an electric handpiece at circumferential speeds(12000,18000,25000 or 30000rpm) by applying a force(200gr). Grinding rate was evaluated by measuring the amount of metal volume removed after grinding for 1 minute and the volume ratio of metal removed compared to the wheel material lost, which was calculated from the diameter loss (grinding ratio). Experimental datas were compared to those for cp Ti(commercially pure titanium) and Ti-6%Al-4%V alloy were used controls. Results: It was observed that the grindability of Ti-Zr alloys increased with an increase in the Zr concentration. More, they are higher than cp Ti, particularly the Ti-20%Zr alloy exhibited the highest grindability at all circumferential speeds. There was significant difference in the grinding rate and grinding ratio between Ti-20%Zr alloy and cp Ti at any speed(p<0.05). Conclusion: By alloying with Zr, the Ti exhibited better grindability at all circumferential speeds. the Ti-20%Zr alloy has a great potential for use as a dental machining alloy.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.1017-1020
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• 2002

The pure Ti is taken annealing process for one hour at 90$0^{\circ}C$. The pure Ti is sufficient for ASTM B348 Grade2. The rolling mill roll the Ti-8Ta-3Nb(wt%) which became vacuum melting in arc furnace until the length is about 45mm and the thickness is about 6.05mm. Then it is made 6mm$\times$6mm$\times$44mm by wire cutting with EDM and it is made ∮ 6mm by rough cutting with the general purpose lathe. The machining accuracy of implant parts in the dental and medical science are decided by dimension, shpe, straightness, surface roughness. It is difficult to cut for the Ti alloy. It is caused problems of straight degree and surface roughness to the Ti alloy have many cases which length is smaller than diameter in cutting. Total 24 specimens different kind of 4 alloies are used in experiment to gain a cutting property. According to the cutting velocity, cutting depth, cutting temperature, feed and clearance angle experiments are performed. Conclusively it is expected that cutting depth of 0.5mm, feed velocity of 0.07mm/rev and cutting velocity of 80m/min could make a suitable result.

• 소성∙가공
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• 제27권5호
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• pp.301-313
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• 2018

In this paper, tensile test was performed on pure titanium sheet (CP Ti sheet) with HCP structure in each direction to evaluate mechanical and surface properties and analyze microstructural changes during plastic deformation. We also evaluated forming limits of Ti direction in dome-type punch stretching test using a non-contact three-dimensional optical measurement system. As a result, it was revealed the pure titanium sheet has strong anisotropic property in yield stress, stress-strain curve and anisotropy coefficient according to direction. It was revealed that twinning occurred when the pure titanium sheet was plastic deformed, and tendency depends differently on direction and deformation mode. Moreover, this seems to affect the physical properties and deformation of the material. In addition, it was revealed the pure titanium sheet had different surface roughness changes in 0 degree direction and 90 degree direction due to large difference of anisotropy, and this affects the forming limit. It was revealed the forming limit of each direction obtained through the punch stretching test gave higher value in 90 degree direction compared with forming limit in 0 degree direction.