그래핀 볼의 친환경 제조 및 특성 평가

박수련 ( Su-ryeon Park ),조은희 ( Eun Hee Jo ),김선경 ( Sun Kyung Kim ),장한권 ( Hankwon Chang ),장희동 ( Hee Dong Jang ) 한국화학공학회 2016 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.54 No.6

Spherical graphene balls were fabricated by an aerosol spray drying process after reduced graphene oxide was prepared by the liquid phase reaction using glucose as an environment-friendly reducing agent. Spherical morphol-ogy of the as-fabricated particles was observed by FE-SEM analysis. Diffraction patterns of spherical particles were found as graphene by XRD analysis. Sphericity of GB was controlled by the variation of operating temperature, amount of glucose, and addition of NH₄OH. Higher sphericity of GB was prepared at higher operating temperature in the pres-ence of NH4OH. As the amount of glucose in the liquid phase reaction increased in the presence of NH₄OH, sphericity of GB increased. The highest sphericity of GB was 1.1. GB of higher sphericity showed lower aggregation property than that of lower sphericity. Furthermore, as-prepared GBs were found as a potential electrode material for capacitor.

LPBF용 타이타늄 합금 분말의 유변특성에 대한 입자 구형도의 영향

김태윤,강민혁,김재혁,홍재근,유지훈,이제인 한국분말재료학회 2022 한국분말재료학회지 (KPMI) Vol.29 No.2

Powder flowability is critical in additive manufacturing processes, especially for laser powder bed fusion. Many powder features, such as powder size distribution, particle shape, surface roughness, and chemical composition, simultaneously affect the flow properties of a powder; however, the individual effect of each factor on powder flowability has not been comprehensively evaluated. In this study, the impact of particle shape (sphericity) on the rheological properties of Ti-6Al-4V powder is quantified using an FT4 powder rheometer. Dynamic image analysis is conducted on plasma-atomized (PA) and gas-atomized (GA) powders to evaluate their particle sphericity. PA and GA powders exhibit negligible differences in compressibility and permeability tests, but GA powder shows more cohesive behavior, especially in a dynamic state, because lower particle sphericity facilitates interaction between particles during the powder flow. These results provide guidelines for the manufacturing of advanced metal powders with excellent powder flowability for laser powder bed fusion.

건강인에서의 좌심실 구형지수

최재혁,성지동 한국심초음파학회 2009 Journal of Cardiovascular Imaging (J Cardiovasc Im Vol.17 No.2

Background: Left ventricular (LV) remodeling manifests as an increase in LV end-diastolic and end-systolic volumes, an increase in myocardial mass, and a change in chamber geometry to a more spherical shape, and has been considered to be a consequence of heart failure, myocardial infarction or mitral regurgitation. However, less is known about change of LV geometry, especially LV sphericity, in asymptomatic population according to aging. Methods: We investigated 261 asymptomatic subjects who volunteered for health screening and underwent transthoracic echocardiography. Those with poor echo image, significant coronary artery disease, LV dysfunction, hypertension, and diabetes mellitus were excluded. LV sphericity index is defined as the ratio of the long-axis length divided by LV short-axis length, both during systole and diastole. LV mass was calculated from septal and posterior wall thickness and LV internal dimension at enddiastole and then divided by body surface area to calculate LV mass index. Results: The mean age of subjects was 49.6±6.7 years and the percentage of male was 81%. LV sphericity index at diastole showed significant correlation with age (r=-0.17, p value<0.01), but LV sphericity index at systole did not. Both indices did not showed significant association with aerobic fitness, blood pressure, glucose, insulin resistance and LV function. LV mass index showed significant correlation with age (r=0.14, p value<0.05). Conclusion: Among the parameters of LV geometry, sphericity index showed decrease with aging in healthy population, meaning LV becoming more spherical with aging. Longitudinal follow-up study is needed to determine its usefulness as a predictor of future LV dysfunction in asymptomatic population. 목 적 좌심실 재형성은 많은 심장질환들의 원인과 결과로서 밀접한 연관이 되어 있음이 여러 연구에서 알려졌으며 그 중 좌심실 구 형화는 승모판판막 역류증, 심근 경색 등과 상관 관계가 있다고 알려져 있다. 그러나 건강인의 좌심실 구형화에 대해서는 잘 알 려져 있지 않아 본 연구에선 건강인의 노령화에 따른 좌심실 구 형지수를 조사하고 기타 여려 요인과의 관계를 조사하여 향후 좌 심실 기능 저하의 예측 인자가 될 수 있는지 알아보고자 하였다. 방 법 2005년 3월부터 2005년 7월까지 삼성서울병원에서 건강검진 을 위해 심초음파를 시행한 무증상의 건강인을 대상으로 수축기 및 확장기 시의 구형지수를 구했으며 운동부하 심폐기능검사 및 임상적 특성들과 혈액검사 등의 결과와 비교 분석하였다. 결 과 심초음파를 시행한 대상 인원 중 좌심실 구형지수에 영향을 줄 가능성 있는 환자들을 모두 제외한 261명에서 확장기 시 좌심실 구형지수와 좌심실 질량지수가 연령에 따른 상관 관계를 보여 연 령이 증가할수록 좌심실이 구형이 되는 경향을 보였다. 운동부하 검사를 시행한 209명에서 최고산소섭취량과의 관계는 의미 있는 상관 관계를 보여 주지 않았다. HOMA-IR을 구할 수 있는 182 명에서 평가한 인슐린 저항성과도 의미 있는 연관은 없었다. 결 론 기하학적 척도들 중 좌심실 질량지수 뿐만 아니라 확장기 시 좌 심실의 구형지수 역시 건강인에서 노령화에 따른 심장의 구조적 변화를 보여주는 지표가 될 가능성을 보여주었으나 운동능력의 지표 및 기타 임상적 특징들과의 연관은 뚜렷하지 않았다. 따라 서, 경시적인 추적관찰을 통하여 좌심실 구형지수가 좌심실 부전 의 발병을 예측하는 지표가 될 수 있을 것인지에 대한 검증이 필 요할 것으로 보인다

Sphericity Optimization of Calcium Alginate Gel Beads and the Effects of Processing Conditions on Their Physical Properties

Jin-Wook Woo,Hye-Jin Roh,Hyun-Duck Park,Cheong-Il Ji,Yang-Bong Lee,Seon-Bong Kim 한국식품과학회 2007 Food Science and Biotechnology Vol.16 No.5

In this study, the sphericity of calcium alginate gel beads was optimized using response surface methodology. The optimum conditions for bead sphericity were a concentration of 2.24% sodium alginate, a flow rate of 0.059 mL/sec for the sodium alginate solution, and a 459 rpm rotation for the calcium chloride solution. The predicted and experimental bead sphericities under the optimum conditions were 94.5 and 96.7%, respectively, showing close agreement. We also investigated the processing condition effects for the physical properties of the optimized calcium alginate gel beads. Immersion in hot water slightly decreased bead size and rupture strength. NaCl treatment increased bead size and decreased rupture strength. While the pH of the calcium chloride solution had little effect on bead sphericity, the bead sizes and gel strengths decreased with longer times in each pH solution. The beads coated with pectin and glucomannan showed no significant changes in sphericity, but their sizes decreased with time. The coated beads showed higher rupture strengths than the uncoated beads.

Quantification of bulk form and angularity of particle with correlation of shear strength and packing density in sands

Suh, Hyoung Suk,Kim, Kwang Yeom,Lee, Junhwan,Yun, Tae Sup Elsevier 2017 Engineering Geology Vol.220 No.-

<P><B>Abstract</B></P> <P>The study presents the quantification of shape parameters in sands. Natural sands, crushed sands, and glass beads are subjected to 2D microscopic and 3D X-ray computed tomographic imaging. Parameters of sphericity, elongation and slenderness are selected for analyzing the bulk forms and roundness is selected to quantify the angularity. Relationship among 2D shape parameters confirms that sphericity, elongation and slenderness are independent with roundness. Critical state friction angles are obtained by a direct shear test and void ratio ranges are measured as well. Both sphericity and roundness denote the strong linearity with void ratio range (<I>e</I> <SUB> <I>max</I> </SUB> − <I>e</I> <SUB> <I>min</I> </SUB>) bounded 0.15 and critical state friction angle (<I>ϕ</I> <SUB> <I>cs</I> </SUB>) delineated by 20° at the unity, emphasizing that readily computable sphericity is sufficient to estimate properties of sands even without roundness. The multiple 2D projections of 3D images and their correlation for different orientation support that either bulk form or angularity in 2D images are acceptable enough to establish correlations between shape parameters and properties in sands. It implies that 2D quantification of particle shape is rational and can be used to approximate soil properties without conducting the laboratory experiments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sphericity and roundness are independent with each other while round particles tend to be spherical in sands </LI> <LI> Computing sphericity is sufficient to establish correlation with soil properties rather than hardly quantifiable roundness </LI> <LI> Quantification of particle shape in 2D is rational to comprehend shape-dependent properties </LI> </UL> </P>

Influence of metal powder shape on drag coefficient in a spray jet

S. Kumar,Hyuntaek Na,이창희,V. Selvarajan 한국물리학회 2009 Current Applied Physics Vol.9 No.3

In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 lm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed. In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 lm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed.

Manufacturing and properties evaluation of Al2O3/ZrO2 granules derived from sodium alginate gelation

Lucio Maria Dolores Sosa,Oh Eun-Ji,Ha Jang-Hoon,Lee Jongman,Lee Hong Joo,Jung Seung Hwa,Shin Jun Young,Song In-Hyuck 한국세라믹학회 2024 한국세라믹학회지 Vol.61 No.4

Spherical millimeter-sized ceramics with porous and dense microstructure are materials of interest in approaches related to catalytic supports and milling media. The reliability of these operations depends on key characteristics of these materials, including high sphericity to ensure efficient process designing, ease of handling, facile separation and/or recyclability, abrasion resistance, and uniform packing. This is accompanied by the structural stability and microstructure tailoring to secure its functionality. The Al 2O3/ZrO2 system has been applied in powdered form for catalytic support applications, and in both porous and dense ceramics for structural applications, highlighting the performance and functionality of the Al2O3/ZrO2 system in these approaches. Based on this analysis, the present study explores the optimized preparation of spherical millimeter-sized Al 2O3/ZrO2 granules along with the assessment of their microstructural, mechanical, and pore-related outcomes as a function of the heat treatment conditions. Optimized Al 2O3/ZrO2 granules with high sphericity, processed through sodium alginate gelation at 900 °C and 1100 °C displayed a hierarchical macro/mesoporosity which can provide potential functionality for catalytic supports-related applications. In comparison Al 2O3/ZrO2 granules similarly processed at a sintering temperature of 1600 °C exhibited a tailored mechanical strength and high relative density ensured by a refined microstructure, as well as a high sphericity which are features preferred for milling media applications.

Relationship between the sphericity of femoral head-acetabulum and the low incidence of primary osteoarthritis of the hip joint in Koreans

Kim, Young-Hoo Yonsei University, College of Medicine 1989 Yonsei medical journal Vol.30 No.3

Correlation of Roundness and Sphericity with Complex Fourier Descriptors of 2-Dimensional Projected Images of Soil Particles

김태식,정영훈 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.3

Roundness and sphericity have long been considered as measurements of the basic morphological properties of soil particles. Recent progress in optical image processing and analysis has enabled us to automate and rapidly perform Fourier analysis. Thus, obtaining complex Fourier descriptors describing the outline boundary of a 2-dimensional projected image of a soil particle could be performed. In this regard, we performed correlation analysis with the values of roundness, sphericity, and complex Fourier descriptor coefficients for 115 images of soil particles measured and reported in previous studies. The results of the statistical analysis revealed that roundness was strongly negatively correlated with Fourier descriptors of the order less than -5 or higher than +5. The width-to-length ratio sphericity was strongly correlated with the Fourier descriptor of the order of +2.

AP의 구형도에 따른 고체추진제의 특성 연구

장명욱,홍성파,손현일,이덕범 국방기술품질원 2020 국방품질연구논집 Vol.2 No.2

The viscosity and mechanical property of composite solid propellant are profoundly affected by sphericity of AP. In HTPB/AP propellant fomulated by two mode of AP size such as 190 ~ 200㎛ and 5 ~ 7㎛, the propellant was found to be much less viscose at end of mix when be nearly sphere of large size AP is effected of bearing in propellant.. It was shown that the strand burner test for HTPB/AP propellant with the increased in sphericity of AP. Considering both lower viscosity and stable rate of burning, the optimum sphericity of AP was estimated to be 2.0(measured to specific surface area)