• Advances in nano research
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• 제13권5호
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• pp.437-451
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• 2022

Synthesis approaches usually affect the physical and chemical properties of ferrites. This helps ferrite materials to design them for desired applications. Some of these methods are mechanical milling, ultrasonic method, micro-emulsion, co-precipitation, thermal decomposition, hydrothermal, microwave-assisted, sol-gel, etc. These methods are extensively reviewed by taking example of ZnFe₂O₄. These methods also affect the microstructure and local structure of ferrite which ultimately affect the physical and chemical properties of ferrites. Various spectroscopic techniques such as Raman spectroscopy, Fourier Transform Infrared spectroscopy, Ultra Violet-Visible spectroscopy, Mossbauer spectroscopy, extended x-ray absorption fine structure, and electron paramagnetic resonance are found helpful to reveal this information. Hence, the basic principle and the usefulness of these techniques to find out appropriate information in ZnFe₂O₄ nanoparticles is elaborated in this review.

• 한국세라믹학회지
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• 제34권2호
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• pp.195-201
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• 1997

본 논문은 kaolinite(Al2O3.2SiO2.2H2O)-aluminum trihydroxide(Al(OH3) 혼합물을 소결전에 planetary ball mill을 사용하여 건식 중에서 혼합분쇄한 후, 이 혼합물을 사용하여 소결하는 동안에 mullite의 생성거동을 연구한 것이다. 혼합물의 입자크기 감소는 분쇄 초기에 현저하였으며, 분쇄기간이 증가함에 따라 미립자들이 응집하는 현상을 보였다. 혼합물의 결정구조는 planetary ball milling에 의한 혼합분쇄에 따라 쉽게 비정질화되었으며, 비정질화되는 정도는 분쇄시간이 증가함에 따라 증가하였다. Kaolinite의 초기 분순물로 존재했던 anatase를 제외한 mullite상만이 상대적으로 낮은 소결온도인 1523K에서 혼합분쇄한 혼합물의 소결체에서 나타났다. 한편, 분쇄하지 않은 혼합물의 소결체의 경우는 이 온도에서 mullite 상 이외에 corundum, cristobalite, Al-Si spinel상이 공존하는 형태로 나타났다. 따라서, 혼합분쇄처리는 출발원료의 미소 규모에 있어서 균일혼합 및 분산을 촉진시키며, 또한 결정구조변화에 따른 열분해온도의 변화일으켜, 상대적으로 낮은 온도에서 고순도의 mullite를 직접 생성하는데 효과적이였다.

• 한국표면공학회지
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• 제42권1호
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• pp.41-46
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• 2009

The fit between dental implant fixture and zirconia abutment is affected by many variables during the fabrication process by CAD/CAM program and milling working. The purpose of this study was to evaluate the surface compatibility and electrochemical behaviors of zirconia abutment for prosthodontics. Zirconia abutments were prepared and fabricated using zirconia block and milling machine. For stabilization of zirconia abutments, sintering was carried out at $1500^{\circ}F$ for 7 hrs. The specimens were cut and polished for gap observation. The gap between dental implant fixture and zirconia abutment was observed using field-emission scanning electron microscopy (FE-SEM). The hardness and corrosion resistance of zirconia abutments were observed with vickers hardness tester and potentiostat. The gap between dental implant fixture and zirconia abutment was $5{\sim}12{\mu}m$ for small gap, and $40{\sim}60{\mu}m$ for large gap. The hardness of zirconia surface was 1275.5 Hv and showed micro-machined scratch on the surface. The corrosion potentials of zirconia abutment/fixture was .290 mV and metal abutment/fixture was .280 mV, whereas $|E_{pit}-E_{corr}|$ of zirconia abutment/fixture (172 mV) was higher than that of metal abutment/fixture (150 mV). The corrosion morphology of metal abutment/fixture showed the many pit on the surface in compared with zirconia abutment/fixture.

• 대한치과보철학회지
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• 제54권3호
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• pp.226-233
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• 2016

목적: 본 연구는 수복물의 적합도를 계측하는 두 가지 측정방법을 평가하기 위해 CAD-CAM (computer aided design-computer aided manufacturing)과 열가압 소성법으로 전부 도재관을 제작하고 micro CT와 cross-section technique으로 전부 도재관의 적합도를 비교하고자 하였다. 재료 및 방법: 하악 제 1대구치 레진 치아를 전부 도재관을 위한 지대치를 형성하고 PMMA (polymethylmethacrylate) 레진 블록을 가공하여 10개의 시편을 복제하였다. 복제한 레진 다이의 인상을 채득하고 모형을 제작하여 5개는 열가압 소성법으로 IPS e.max Press (Ivoclar Vivadent, Schaan, Liechtenstein) 도재관을 제작하였다. 다른 5개의 시편은 CAD-CAM 가공법(Ceramil motion 2, Amann Girrbach, Koblach, Austria)을 이용하여 IPS e.max CAD 도재관을 제작하였다. 각 레진 다이에 전부 도재관을 인산아연 시멘트(Fleck's zinc cement, Keystone industries, Gibbstown, NJ, USA)로 손가락 압력에 의해 합착하였다. 변연 및 내면 적합도를 측정하기 위해서 합착된 시편 10개를 먼저 micro CT로 촬영하여 협-설 시상면의 영상정보를 획득하였다. 그 후 절단 시편을 만들어 주사전자현미경으로 micro CT와 동일한 지점의 간극을 측정하였다. SPSS 22.0 프로그램을 이용하여 각 측정 지점에서 제작 방식별, 측정 방식별로 Mann-Whitney 검정 방법을 통해 유의차 검증을 시행하였다. 결과: Micro CT와 주사전자현미경으로 측정한 변연 및 내면 적합도는 유사하였으며, 통계적으로 유의한 차이를 보이지 않았다. 두 가지 제작법의 도재관은 변연 및 내면 적합도에 유의한 차이가 없었다. 결론: CAD-CAM과 열가압소성으로 제작한 전부 도재관은 적합도에 차이를 보이고 있지 않으며, Micro CT와 주사전자현미경을 이용한 측정 방식 모두 임상적으로 이용 가능할 것으로 사료된다.

• 펄프종이기술
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• 제46권4호
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• pp.1-10
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• 2014

In papermaking industry, inorganic fillers are widely used for the purpose of improving opacity, brightness, printability, uniformity and dimensional stability. They are also useful for production costs and energy savings. In the past, inorganic fillers in papermaking industry only focused on micro-scale but recently, new trials on nano-powdered technology are applying. Even nano-powdered fillers are rapidly utilized for improving the optical and surface properties in coating and surface sizing, there still have some problems in wet-end process due to poor dispersibility and retention. In this study, nano-particled calcium carbonate was produced by milling the PCC and its applicability between micro sized and nano sized calcium carbonated was compared in wet-end process, and finally the sheet properties were evaluated. Nano-PCC was not retained in sheet structure without applying retention system, but with retention system nano-powdered PCC was absorbed on fiber surface with expanding the fiber networks. The application of PAM-bentonite system has resulted in high ash retention and bulky structure for copier paper, and good optical properties in brightness and opacity. However, it required to solve the weakness of low tensile property due to interruption of hydrogen bonding by nano fillers.

• 대한기계학회논문집
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• 제17권5호
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• pp.1172-1182
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• 1993

본 연구에서는 버형성중의 파단을 파단전의 소성변형의 과정이 파단에 영향을 미치는 연성파단(ductile fracture)으로 간주하여 McClintock의 연성파단에 관한 모델 을 이용하여 버형성중의 파단변형도를 얻었다. 이 파단변형도가 인장시험으로부터 얻 은 파단변형도와 커다란 오차가 없음을 확인하여 편의상 인장시험에서의 파단변형도를 버형성중의 파단발생 판정기준으로 사용하였다. 버형성이 시작된 이후에 공구인선부 에서의 피삭재의 변위의 발달에 관한 모델이 제시되었고 파단변형도와 최대변형량과의 비교로부터 파단위치와 각도가 결정된다.

• 한국생산제조학회지
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• 제21권3호
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• pp.387-393
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• 2012

It is very difficult to determine suitable cutting conditions in order to obtain accurate cutting profiles because machining errors caused by tool deflection depend upon cutting conditions. In this study the relationship between real cutting profiles (inclined shapes and machining errors) and cutting conditions was modeled in order to fabricate draft angle on micro molds. CCD (Central Composite Design) of DOE (Design Of Experiment) and RSM (Response Surface Method) were applied in order to model the relationship between cutting conditions and machining errors. In order to use CCD the range of radial depth of cut was chosen by $10-90{\mu}m$ and the range of feedrate was chosen by 200-300mm/min, and 9 points of cutting conditions were chosen inside determined ranges. Then, actual cutting processes were carried out as respect to 9 points of cutting conditions, draft angles and real cutting profiles were measured on cutting profiles, each response surface function was determined by conducting response surface analysis and the functions were represented by 3-dimensional graphs, contour lines and $101{\times}101$ matrices. Consequently it is possible to determine suitable cutting conditions in order to obtain arbitrary given draft angles and cutting profiles by using modeling. To validate proposed approach in this study suitable cutting conditions were determined by modeling in order to obtain arbitrary given draft angle and cutting profile, and actual cutting processes were carried out. About 95% of good agreement between predicted and measured values was obtained.

• 한국정밀공학회지
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• 제29권8호
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• pp.813-817
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• 2012

Laser assisted machining (LAM) is machining method that performs a machining for workpieces using laser beam preheating. LAM is in the early stage of its applications and has only been used in limited fields including turning, planning and micro end-milling throughout the world. LAM system should be able to move to the laser radiation direction and to rotate on a tool path for machining of complex shapes. A laser module with two-axis manipulator is designed in this study. It has been performed static structural analysis and shape modification of the manipulator. As the results of shape modification it has been obtained better results than the initial model. These results will be able to use in development of the two-axis manipulator.

• 한국분말재료학회지
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• 제20권5호
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• pp.366-370
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• 2013

The effects of $B_4C$ on the mechanical properties of WC/Ni-Si hardmetal were analyzed using sintered bodies comprising WC(70-x wt.%), Ni (28.5 wt.%), Si (1.5 wt.%), and $B_4C$ (x wt.%), where $$0{\leq_-}x{\leq_-}1.2$$ wt.%. Samples were prepared by a combination of mechanical milling and liquid-phase sintering. Phase and microstructure characterizations were conducted using X-ray diffractometry, scanning electron microscopy, and electron probe X-ray micro analysis. The mechanical properties of the sintered bodies were evaluated by measuring their hardness and transverse rupture strength. The addition of $B_4C$ improved the sinterability of the hardmetals. With increasing $B_4C$ content, their hardness increased, but their transverse rupture strength decreased. The changes of sinterability and mechanical properties were attributed to the alloying reaction between $B_4C$ and the binder metal (Ni, Si).

• 한국기계가공학회지
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• 제19권8호
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• pp.8-14
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• 2020

In the air current pulverizing type grinding method, the blade wings fitted inside a casing are rotated at a high speed to generate a cornering air current, which facilitates the collision of materials with one another, leading to the pulverizing phenomenon. In contrast to mechanical grinding, grit pulverizing leads to fine grinding and less acid waste and degeneration of the material. Moreover, this approach prevents the loss of nutritional value, while allowing the milling grain to have an excellent texture. However, the existing air current pulverizing type machines consist of prefabricated blades, which cannot be rotated at a speed higher than 5,000 rpm. Consequently, the grinding process becomes time consuming with a low productivity. To overcome these problems, in this study, the shape and structure of the air current pulverizing type wings were optimized to allow rapid grinding at more than 8,000 rpm. Moreover, the optimal design for the ripening parts for the air current pulverizing type device was determined by performing a computational fluid dynamics analysis based on airflow analyses to produce machinery that can grinding materials to the order of micrometers.