• 한국세라믹학회지
• /
• 제52권5호
• /
• pp.320-324
• /
• 2015

Optimization of the fabrication process of NiO-yttrium doped barium zirconate (BZY) composite anode substrates using tape-casting for high performance thin-film protonic ceramic fuel cells (PCFCs) is investigated. The anode substrate is composed of a tens of microns-thick anode functional layer laminated over a porous anode substrate. The macro-pore structure of the anode support is induced by micron-scale polymethyl methacrylate (PMMA) pore formers. Thermal gravity analysis (TGA) and a dilatometer are used to determine the polymeric additive burn-out and sintering temperatures. Crystallinity and microstructure of the tape-cast NiO-BZY anode are analyzed after the sintering.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.1345-1346
• /
• 2007

다양한 게이트 절연막의 펜타신 박막 트랜지스터의 전기적 특성을 atomic force microscope (AFM), X-선 회절을 사용하여 분석하였다. 펜타신 박막 트랜지스터는 thermal evaporator 방법을 사용하여 여러 폴리며 기판위에 제작하였다. Hexamethylsilasane (HMDS), polyvinyl acetate (PVA), polymethyl methacrylate (PMMA)등의 폴리머 기판을 사용하여 다양한 온도에서 증착시켰다. 이 때 PMMA위에 증착시킨 펜타신의 경우가 가장 큰 그레인 크기를 보였고, 가장 적은 트랩 농도를 보였다. 그리고 상부 전극 구조를 가진 박막 트랜지스터를 HMDS 처리를 한 $SiO_2$와 PMMA 절연막을 사용하여 제작하고 비교하였다. 이때 PMMA기판 위에 제작한 트랜지스터는 전계효과 이동도가 ${\mu}_{FET}=0.03cm^{2}/Vs$ 이고, 문턱이전 기울기 0.55V/dec, 문턱전압 $V_{th}=-6V$, on/off 전류비 $>10^5$의 전기적 특성을 보였고, $SiO_2$ 기판위에 제작한 트랜지스터는 전계효과 이동도 ${\mu}_{FET}=0.004cm^{2}/Vs$, 문턱이전 기울기 0.518 V/dec, 문턱전압 $V_{th}=5V$, on/off 전류비 $>10^4$의 전기적 특성을 보였다.

• KSTLE International Journal
• /
• 제6권2호
• /
• pp.33-38
• /
• 2005

Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 mm mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribe tester, under reciprocating motion, using a soda lime ball (1 mm diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C$) and relative humidity ($45{\pm}5\%$). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.

• 공업화학
• /
• 제9권5호
• /
• pp.758-762
• /
• 1998

유화중합을 이용하여 중량 평균입자크기가 $0.3{\mu}m{\sim}1.5{\mu}m$인 중공 라텍스 입자를 제조함에 있어 평균입자크기와 고형분 함량에 영향을 미치는 반응 인자를 조사하였다. 실험결과 유화제 (SDS)의 농도가 증가함에 따라 친수성 코어 폴리머의 크기가 작아졌으며, 친유성 스티렌 단량체 (styrene monomer)와 개시제 (SPS)의 첨가량이 증가함에 따라 중공입자의 크기가 커졌다. 한편, 친수성 아크릴산의 첨가속도가 증가함에 따라 중공입자의 크기가 작아졌다. 또한, 스틸렌 단량체의 첨가량이 증가함에 따라 에멀젼 폴리머의 고형분 함량이 선형적으로 증가하였다.

• Geomechanics and Engineering
• /
• 제14권2호
• /
• pp.195-202
• /
• 2018

Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.

• 한국전기전자재료학회논문지
• /
• 제32권1호
• /
• pp.86-92
• /
• 2019

Although perylene bisimide derivatives have advantages such as excellent thermal stability and high luminance efficiency, they have poor solubility characteristics in organic solvents. In this research, in order to improve the solubility characteristics, we prepared perylene bisimide derivatives (1C) and (2C) with swallow-tail substituted imide, which is known to lead to excellent solubility. The structures and properties of swallow-tail perylene bisimide (1C) and (2C) were analyzed by $^1H-NMR$, FT-IR, UV/Vis spectroscopy, and thermogravimetric analysis (TGA). The maximum absorption wavelengths of (1C) and (2C) in the UV/Vis spectrum were 558 nm and 556 nm, respectively, and the maximum emission wavelengths were 602 nm and 600 nm, respectively. In the TGA, (1C) demonstrated good thermal stability with less than 5 wt% weight loss up to $242^{\circ}C$. In the solubility test, (1C) and (2C) exhibited solubilities of more than 5 wt% in chloroform, ethyl acetate, and dimethylformamide, but not in methanol. When the compounds (1C) and (2C) were mixed with PMMA (polymethyl methacrylate), thin films showed peaks at 679 nm and 677 nm, respectively, in the photoluminescence spectra. (1C) was found to be a possible candidate as red organic phosphor for hybrid LEDs.

• The Journal of Advanced Prosthodontics
• /
• 제13권3호
• /
• pp.144-151
• /
• 2021

PURPOSE. The purpose of this in vitro study was to investigate the wear resistance and surface roughness of three interim resin materials, which were subjected to chewing simulation. MATERIALS AND METHODS. Three interim resin materials were evaluated: (1) three-dimensional (3D) printed (digital light processing type), (2) computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and (3) conventional polymethyl methacrylate interim resin materials. A total of 48 substrate specimens were prepared. The specimens were divided into two subgroups and subjected to 30,000 or 60,000 cycles of chewing simulation (n = 8). The wear volume loss and surface roughness of the materials were compared. Statistical analysis was performed using one-way analysis of variance and Tukey's post-hoc test (α=.05). RESULTS. The mean ± standard deviation values of wear volume loss (in mm³) against the metal abrader after 60,000 cycles were 0.10 ± 0.01 for the 3D printed resin, 0.21 ± 0.02 for the milled resin, and 0.44 ± 0.01 for the conventional resin. Statistically significant differences among volume losses were found in the order of 3D printed, milled, and conventional interim materials (P<.001). After 60,000 cycles of simulated chewing, the mean surface roughness (Ra; ㎛) values for 3D printed, milled, and conventional materials were 0.59 ± 0.06, 1.27 ± 0.49, and 1.64 ± 0.44, respectively. A significant difference was found in the Ra value between 3D printed and conventional materials (P=.01). CONCLUSION. The interim restorative materials for additive and subtractive manufacturing digital technologies exhibited less wear volume loss than the conventional interim resin. The 3D printed interim restorative material showed a smoother surface than the conventional interim material after simulated chewing.

• Imaging Science in Dentistry
• /
• 제52권3호
• /
• pp.283-288
• /
• 2022

Purpose: This study was conducted to measure the radiation exposure and image quality of various cone-beam computed tomography (CBCT) machines under common clinical conditions and to analyze the correlation between them. Materials and Methods: Seven CBCT machines used frequently in clinical practice were selected. Because each machine has various sizes of fields of view (FOVs), 1 large FOV and 1 small FOV were selected for each machine. Radiation exposure was measured using a dose-area product (DAP) meter. The quality of the CBCT images was analyzed using 8 image quality parameters obtained using a dental volume tomography phantom. For statistical analysis, regression analysis using a generalized linear model was used. Results: Polymethyl-methacrylate (PMMA) noise and modulation transfer function (MTF) 10% showed statistically significant correlations with DAP values, presenting positive and negative correlations, respectively (P<0.05). Image quality parameters other than PMMA noise and MTF 10% did not demonstrate statistically significant correlations with DAP values. Conclusion: As radiation exposure and image quality are not proportionally related in clinically used equipment, it is necessary to evaluate and monitor radiation exposure and image quality separately.

• 대한치과교정학회지
• /
• 제53권1호
• /
• pp.45-53
• /
• 2023

Objective: This study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets bonded to three-dimensionally (3D)-printed materials after various surface treatments and artificial aging compared with that bonded to computer-aided design/computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA)-milled materials. Methods: Eighty cylindrical specimens were 3D printed and divided into the following four subgroups (n = 20 each) according to the surface treatment and artificial aging procedure. Group A, sandblasted with 50 ㎛ aluminum oxide particles (SA) and aging; group B, sandblasted with 30 ㎛ silica-coated alumina particles (CO) and aging; group C, SA without aging; and group D, CO without aging. For the control group, 20 CAD-CAM PMMA-milled cylindrical specimens were sandblasted with SA and aged. The SBS was measured using a universal testing machine (0.25 mm/min), examined at ×2.5 magnification for failure mode classification, and statistically analyzed (p = 0.05). Results: The retention obtained with the 3D-printed materials (groups A-D) was higher than that obtained with the PMMA-milled materials (control group). However, no significant difference was found between the study and control groups, except for group C (SA without aging), which showed significantly higher retention than the control group (PMMA-SA and thermocycling) (p = 0.037). Study groups A-D predominantly exhibited a cohesive specimen mode, indicating specimen fracture. Conclusions: Orthodontic brackets bonded to 3D-printed materials exhibit acceptable bonding strengths. However, 3D-printed materials are prone to cohesive failure, which may result in crown fractures.

• 한국방재안전학회논문집
• /
• 제16권1호
• /
• pp.91-103
• /
• 2023

본 연구의 목적은 테르밋 반응으로 결정화된 액체혼합물을 순간적으로 기화시켜, 이에 따라 발생되는 증기압을 이용하여 암석 및 콘크리트를 파쇄시키는 Nonex Rock Cracker(NRC) 암석 파쇄제의 동적 파괴 특성을 분석하고 파괴패턴을 예측할 수 있는 해석기법을 개발하기 위함이다. NRC 암석 파쇄제의 순간적의 증기압 발생 특성을 분석하기 위하여 인공취성재료로 알려진 Polymethyl methacrylate(PMMA) 블록을 대상으로 NRC를 장전하여 파쇄시험을 수행하였다. NRC의 증기압 발생순간을 촬영하기 위하여 초고속 카메라를 활용하였으며, 장약실과 연결된 관측공에 동적압력게이지를 부착하여 장약공 압력-시간이력을 계측하였다. 증기압 암석 파쇄제에 의한 PMMA 블록의 파괴패턴을 모사하기 위하여 2차원 동적 파괴 과정 해석 기법인 2D Dynamic Fracture Process Analysis(2DDFPA)가 활용되었으며, 계측된 장약공 압력-시간이력을 고려한 입사압력함수를 결정하였다. 제안된 해석조건을 활용하여 화강암재료와 고성능 폭약에 의하여 발생될 수 있는 파괴패턴에 대하여 고찰하였다.