• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.466-472
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• 2008

Purple Gold is the alloy consisting of 78wt%Au-22wt%Al, and is expressed as a chemical formula, $AuAl_2$. Lately it is being used for the material of accessories or the decorative ornaments, being one of the colored golds having the peculiar purple color, like White Gold and Pink Gold. Purple Gold has the weak point in shaping through casting process due to the bad malleability and castability, being the intermetalic compound of Au and Al. Therefore, it is possible to produce the final product only by the cutting and the grinding process or to use it as a decorative coat with the thin film evaporation. This study implemented two kinds of thin film experiments. One is the case that heat treatment was made after Au and Al deposition evaporated separately with a weight ratio 78:22 on the 200nm$SiO_2$/Si substrate. The other is the case that the surface deposition was made through the vacuum evaporation, keeping the glass substrate temperature remain room temperature, using the bulk $AuAl_2$ as a source. The final film property was measured, focusing on the Purple Gold's color and thickness through the bare eye inspection, the microstructure analysis, the surface resistance analysis, the color difference analysis, and XRD analysis. Purple Gold was not formed, as the excessive surface agglomeration occurred, in case of being produced and treated thermally with 12.5nmAu/40nmAl/200nm$SiO_2$/Si structure. Our results suggest that of Purple Gold films, showing the same purple color as the bulk's, were successfully deposited with the direct thermal evaporation from the $AuAl_2$ bulk source.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.196-196
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• 2016

치과나 기공소로부터 높은 원가로 인한 재료선택에 어려움을 겪고 있어 귀금속 금합금의 물성을 가질 수 있도록 하면서 가격급등으로 인한 문제 해결하기 위한 비귀금속 합금으로 대체가 필요하기에 이에 따른 연구가 이루어져 국산 제품의 상품화를 위해 파라듐을 이용하여 적합한 새로운 합금을 개발하는 것이 필요하다. 치과용 골드합금은 미국치과의사 협회의 구정에 의하면 1형부터 4형까지 분류하고 있으며 3형에 해당하는 강도와 기계적인 특성을 갖도록 파라듐으로 대체하는 연구가 진행중이거나 시판되고 있다. 따라서 본 연구에서는 2형, 3형 및 4형을 대체가능하도록 팔라듐을 기반으로 한 새로운 합금을 설계하고 합금의 성분원 소인 Au(1~5), Pd(20~25), Ag(70~75), In(1.5) 및 Zn(2)등으로 조성을 변화시켜 측량 후 합금을 제조하기 위하여 아르곤 분위기하의 진공아크용해로를 이용하여 용해하였다. 정량된 금속을 진공아크 용해로에 장입하고 용해는 균질한 합금이 되도록 최소한 6회 이상 용융을 실시하며 합금성분의 손실이 발행하지 않도록 보정을 하였다. 합금의 미세조직 관찰을 위하여 샘플을 고속 다이아몬드 정밀 절단기(Acculom-5, STRUERS, Denmark)를 이용하여 절단한 후 2000 grit의 Sic 연마지에서 단계적으로 $0.3{\mu}m$ 알루미나 분말까지 연마한 후 초음파 세척을 하였다. 준비한 시편은 KCN과 $(NH_4)_2S_2O_8$을 1:1로 혼합한 부식액으로 에칭한 후 OM과 SEM을 이용하여 조직을 관찰하였으며 각 샘플의 성분변화는 EDS 분석을 통해 확인하고 결정구조는 XRD를 사용하여 분석하였다. 경도시험은 비커스경도시험기를 이용하여 5kg의 하중을 30초간 작동시켜 압흔을 연결된 micron으로 평균값을 측정하였다. 각 시편의 부식거동은 POTENTIOSTAT(Model PARSTAT 2273, EG&G, USA)을 이용하여 구강 내환경화 유사한 $36.5{\pm}1^{\circ}C$의 0.9% NaCl에서 실시하였다. 인가전위는 -1500mV에서 1000mV까지 1.67 mV/min의 주사속도로 인가하여 시험을 수행하였으며 분극곡선으로부터 부식전위와 부식전류밀도 및 부동태영역의 전류밀도로 금속의 용출거동을 조사하였으며 부식이 끝난 시편은 FE-SEM과 EDS를 사용하여 조사하였다. 기계적인 특성은 Pd-Ag에 3wt%의 Au를 첨가한 합금이 Pd-Ag에 1.5wt%합금을 첨가한 경우에 비하여 기계적인 특성이 증가하고 내식성이 크게 증가하였다. 이들 합금에 Cu를 11wt%를 첨가한 경우는 비커스경도가 200이상으로 높게 나타났지만 내식성이 크게 감소하였다.

• The Journal of Advanced Prosthodontics
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• v.9 no.3
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• pp.170-175
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• 2017

PURPOSE. The aim of the present study was to evaluate the fracture resistances of zirconia, cast nickel-chromium alloy (Ni-Cr), and fiber-composite post systems under all-ceramic crowns in endodontically treated mandibular first premolars. MATERIALS AND METHODS. A total of 36 extracted human mandibular premolars were selected, subjected to standard endodontic treatment, and divided into three groups (n=12) as follows: cast Ni-Cr post-and-core, one-piece custom-milled zirconia post-and-core, and prefabricated fiber-glass post with composite resin core. Each specimen had an all-ceramic crown with zirconia coping and was then loaded to failure using a universal testing machine at a cross-head speed of 0.5 mm/min, at an angle of 45 degrees to the long axis of the roots. Fracture resistance and modes of failure were analyzed. The significance of the results was assessed using analysis of variance (ANOVA) and Tukey honest significance difference (HSD) tests (${\alpha}=.05$). RESULTS. Fiber-glass posts with composite cores showed the highest fracture resistance values ($915.70{\pm}323N$), and the zirconia post system showed the lowest resistance ($435.34{\pm}220N$). The corresponding mean value for the Ni-Cr casting post and cores was reported as $780.59{\pm}270N$. The differences among the groups were statistically significant (P<.05) for the zirconia group, as tested by ANOVA and Tukey HSD tests. CONCLUSION. The fracture resistance of zirconia post-and-core systems was found to be significantly lower than those of fiber-glass and cast Ni-Cr post systems. Moreover, catastrophic and non-restorable fractures were more prevalent in teeth restored by zirconia posts.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.217-221
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• 2018

Selective laser melting (SLM) technique is one of the additive manufacturing processes, in which functional, complex parts can be directly manufactured by selective melting layers of powder. SLM technique has received great attention due to offering a facile part-manufacturing route and utilizing a hard-to-manufacturing material (e.g. Ti6Al4V). The SLM process allows the accurate fabrication of near-net shaped parts and the significant reduction in the consumption of raw materials when compared to the traditional manufacturing processes such as casting and/or forging. In this study, we focus the high-speed additive manufacturing of Ti6Al4V parts in the aspect of manufacturing time, controlling various process parameters.

• Journal of the Korean Magnetics Society
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• v.20 no.4
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• pp.143-148
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• 2010

This study examined the effects of sheet thickness on electromagnetic wave absorption characteristics and internal microstructure in 92.6%Fe-6.5%Si-0.9%Cr (wt%) alloy flakes/polymer composite sheets available for quasi-microwave band. The composite sheets with the thickness of 0.3, 0.4 and 0.5 mm were prepared by tape casting. A significant decrease in transmission parameter $S_{21}$ and a large increase in power loss were observed for the thick composite sheet in the frequency range of 1~5 GHz. However the permeability properties were not affected by thickness variation, while the imaginary part of complex permittivity increased with the increase of sheet thickness at 1~5 GHz. The enhanced electromagnetic wave absorption characteristics in the thicker composite sheets was attributed to the changed microstructure and the higher dielectric loss.

• Journal of Conservation Science
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• v.25 no.4
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• pp.411-420
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• 2009

A series of scientific analyses, including ICP-AES, microstructure, and TIMS, were carried out on 5 bronze spoons among 14 bronze artifacts excavated from the Ok-dong site in Andong, North Gyeongsang Province. The results of analysis showed that the bronze spoons were formed from an alloy of no more than 75% Cu and 21~23% Sn, placing it in the category of brassware, with trace elements such as Pb, Fe, and Zn. In particular, plumbum Pb contents of which traces of 0.04% were found, appears to have been added as an impurity during smelting. The microstructure of the bronze spoons suggests that the casting process involved using a spoon-shaped hollow mold, followed by an ropid-cooling process after the shape was perfected at approximately $586^{\circ}C$. After comparison of data measured from thermal ionization mass spectrometry (TIMS) of galena from Korea, China, and Japan, it appears that the raw materials for the bronze spoons included galena (lead sulfide) produced from the southern part of China.

• The Journal of the Korean dental association
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• v.53 no.11
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• pp.804-816
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• 2015

PURPOSE: The aim of this study was to evaluate the influence of the oxide layer removal process in the Co-Cr-Mo (CCM) abutment after casting procedure on the prosthesis settlement and screw stability. MATERIALS AND METHODS: CCM abutments of four different interface conditions (CCM-M; machined, CCM-O; oxide layer formed, CCM-B; blasted, CCM-P; polished after blasted) and gold abutment (Gold-C; Cast with type III Gold alloy) were used. The initial settling values of abutments were evaluated according to the difference of implant-abutment length when the tightening torques were applied at 5 Ncm and 30 Ncm, and the settling values of abutments caused by loading were evaluated according to the difference of implant-abutment length before and after loading with 250 N, 100000 cycle. The loss ratios of removal torque for abutment screws were evaluated according to the difference in value of removal torques under 30 Ncm tightening torque applied before and after cyclic loading. RESULTS: The CCM-P and CCM-B group showed a higher initial settling value compared with the Gold-C group (P<.05), while the Gold-C group showed the highest settling values caused by loading (P<.05) and no significant differences were observed for between CCM groups (P>.05). The loss ratio of removal torque values for the CCM-B, CCM-P groups did not differ significantly from that of the Gold-C group (P>.05). CONCLUSION: Even though the oxide layer was removed by different methods, CCM abutment with internal conical connection structure showed lower abutment settling and similar screw loosening after cyclic loading compared with gold abutment.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.85-101
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• 1991

The purpose of this study was to determine the optimum range of laser energy density to the enamel surface of permanent incisors when they are irradiated with the pulsed Nd : YAG laser, Laser impacts on each experimental group were made at energy density of $20\sim50J/cm^2$ by 20 pulses of the pulse width 1.2 msec. The author investigated the enamel surface with the sunning electron microscope(SEM) and the surface roughness tester, and measured the shear bond strength between electrolytically etched Ni-Cr-Be alloy casting and composite resin. The obtained results were as follows: 1. The surface roughness of enamel after laser irradiation showed the significant difference level from the energy density $40J/cm^2(P<0.05)$. 2. The mean shear bond strength of etched-metal resin-bonded specimens were $154.23{\pm}33.30kg/cm^2$ at unlased enamel surface and $195.72{\pm}29.56kg/cm^2$ at lased energy density $30J/cm^2$, and showed a significant difference(P<0.05). 8. SEM photographs showed the irregular microcracks and the structural changes of lased enamel surface. 4. SEM photographs of the fracture surface after testing the shear bond strength showed the aspect of interfacial fracture between bonding agent and composite resin at the metal sides.

• The Journal of Advanced Prosthodontics
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• v.6 no.4
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• pp.266-271
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• 2014

PURPOSE. The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS. Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets ($25.0{\times}3.0{\times}0.5mm$) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (${\alpha}=.05$). RESULTS. The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION. In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength.

• Korean Journal of Materials Research
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• v.13 no.12
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• pp.812-818
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• 2003

The aim of this study is to investigate the fabrication processes on the microstructual changes and mechanical properties of large 7175 aluminum die forgings. The billets range from 370 to 720 mm in diameter were homogenized and hot forged after direct chill casting. The strength and elongation of the homogenized cast billets were revealed nearly same level independent of the billet diameter. However, these properties of ø370 mm cast billet were superior to those of $\Pie720$ mm billet under$ T_{6}$ / condition. The tensile strength of die forged specimens under $T_{6}$ condition increased up to 20% than that of solution treatment, however, the elongation was reduced to 50%. The fracture toughness of die forged specimens under $T_{6}$ condition was 35.6∼39.0 MPa$.$$m^{1}$2 irrespective of the billet size and free forging processes, but this property increased up to 10% by$V_{74}$ treatment. The fracture toughness of die forged specimen manufactured with ø370 mm cast billet showed nearly same level of ø720 mm billet which was processed using MF or Cog free forging followed by die forging.