• 한국분말재료학회지
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• 제29권2호
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• pp.99-109
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• 2022

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.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.449-450
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• 2006

This paper described the preparation method for composing high-grade synthetic diamond by water atomizing using FeNi30 powder catalyst. The objective of this article is about powder making process using super high water atomizing in the atmosphere of inert gas, and then corroded the powder with a corrosion inhibitor. Finally, FeNi30 catalyst powder with lower oxygen content and good sphericity is produced. The experiment of making diamonds by using cubic press and the performance of the diamonds are also discussed.

• 한국분말재료학회지
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• 제29권6호
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• pp.459-467
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• 2022

Soft magnetic powder materials are used throughout industries such as motors and power converters. When manufacturing Fe-based soft magnetic composites, the size and shape of the soft magnetic powder and the microstructure in the powder are closely related to the magnetic properties. In this study, Fe-Si-Al-P alloy powders were manufactured using various manufacturing process parameter sets, and the process parameters of the vacuum induction melt gas atomization process were set as melt temperature, atomization gas pressure, and gas flow rate. Process variable data that records are converted into 6 types of data for each powder recovery section. Process variable data that recorded minute changes were converted into 6 types of data and used as input variables. As output variables, a total of 6 types were designated by measuring the particle size, flowability, apparent density, and sphericity of the manufactured powders according to the process variable conditions. The sensitivity of the input and output variables was analyzed through the Pearson correlation coefficient, and a total of 6 powder characteristics were analyzed by artificial neural network model. The prediction results were compared with the results through linear regression analysis and response surface methodology, respectively.

• 한국분말재료학회지
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• 제16권4호
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• pp.254-261
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• 2009

In this study, we investigated the unit process parameters in spherical $UO_2$ kernel preparation. Nearly perfect spherical $UO_3$ microspheres were obtained from the 0.6M of U-concentration in the broth solution, and the microstructure of the $UO_2$ kernel appeared the good results in the calcining, reducing, and sintering processes. For good sphericity, high density, suitable microstructure, and no-crack final $UO_2$ microspheres, the temperature control range in calcination process was $300{\sim}450^{\circ}C$, and the microstructure, the pore structure, and the density of $UO_2$ kernel could be controlled in this temperature range. Also, the concentration changes of the ageing solution in aging step were not effective factor in the gelation of the liquid droplets, but the temperature change of the ageing solution was very sensitive for the final ADU gel particles.

• Korea-Australia Rheology Journal
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• 제13권1호
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• pp.47-54
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• 2001

Prediction of the maximum packing volume fraction with non-spherical particles has been one of the important problems in powder technology. The sphericity of fly ash particles depending on the particle diameter was measured by means of a CCD image processing instrument. An algorithm to predict the maximum packing volume fraction with non-spherical particles is proposed. The maximum packing volume fraction is used to predict the slurry viscosity under well dispersed conditions. For this purpose, Simha's cell model is applied for concentrated slurry with wide particle size distribution. Also, Usui's model developed for aggregative slurries is applied to predict the non-Newtonian viscosity of dense fly ash - water slurry. It is certified that the maximum packing volume fraction for non-spherical particles can be successfully used to predict slurry viscosity. The pressure drop in a pipe flow is predicted by using the non-Newtonian viscosity of dense fly ash-water slurry obtained by the present model. The predicted relationship between pressure drop and flow rate results in a good agreement with the experimented data obtained for a test rig with 50 mm inner diameter tube. Base on the design procedure proposed in this study, a feasibility study of fly ash hydraulic transportation system from a coal-fired power station to a controlled deposit site is carried out to give a future prospect of inexpensive fly ash transportation technology.

• 한국재료학회지
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• 제30권5호
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• pp.223-230
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• 2020

As a case study on aspect ratio behavior, Kaolin, zeolite, TiO₂, pozzolan and diatomaceous earth minerals are investigated using wet milling with 0.3 mm media. The grinding process using small media of 0.3 pai is suitable for current work processing applications. Primary particles with average particle size distribution D₅₀, ~6 ㎛ are shifted to submicron size, D₅₀ ~0.6 ㎛ after grinding. Grinding of particles is characterized by various size parameters such as sphericity as geometric shape, equivalent diameter, and average particle size distribution. Herein, we systematically provide an overview of factors affecting the primary particle size reduction. Energy consumption for grinding is determined using classical grinding laws, including Rittinger's and Kick's laws. Submicron size is obtained at maximum frictional shear stress. Alterations in properties of wettability, heat resistance, thermal conductivity, and adhesion increase with increasing particle surface area. In the comparison of the aspect ratio of the submicron powder, the air heat conductivity and the total heat release amount increase 68 % and 2 times, respectively.

• 한국재료학회지
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• 제29권4호
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• pp.264-270
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• 2019

As a case study on aspect ratio behavior, Kaolin, zeolite, $TiO_2$, pozzolan and diatomaceous earth minerals are investigated using wet milling with 0.3 pai media. The grinding process using small media of 0.3 pai is suitable for current work processing applications. Primary particles with average particle size distribution D50, ${\sim}6{\mu}m$ are shifted to submicron size, D50 ${\sim}0.6{\mu}m$, after grinding. Grinding of particles is characterized by various size parameters such as sphericity as geometric shape, equivalent diameter, and average particle size distribution. Herein, we systematically provide an overview of factors affecting the primary particle size reduction. Energy consumption for grinding is determined using classical grinding laws, including Rittinger's and Kick's laws. Submicron size is obtained at maximum frictional shear stress. Alterations in properties of wettability, heat resistance, thermal conductivity, and adhesion increase with increasing particle surface area. In the comparison of the aspect ratio of the submicron powder, the air heat conductivity and the total heat release amount increase 68 % and 2 times, respectively.

• 한국광물학회지
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• 제20권2호
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• pp.71-81
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• 2007

접촉변성과 열수변질 작용이 중첩되어 형성된 자성 광산의 대리암형 백운석은 대개 98 wt.% 이상의 매우 높은 백운석 함유도를 보이는 고품위백운석으로서 부수적으로 석영, 백운모, 활철석과 같은 불순물을 미량 함유한다. 열수변질 산물로 여겨지는 황철석으로 인해 0.4 wt.% 정도의 상당히 높은 철분 함유 수준을 보이는 것이 특징이다. 대체로 백색을 띠는 이 백운석은 $0.35{\sim}0.46mm$의 결정 입도를 보이며 반자형의 등립상 조직을 이룬다. 이 백운석의 분체 특성은 전형적인 고품위석회석인 풍촌층 석회석에 비해 분쇄 효율, 미분체의 형성 및 입도 분포 면에서는 다소 우수한 것으로 나타난다. 또한 철분 함량을 제외하고는 기타 충전재로서의 품질상의 주요 요소들 즉, 백색도, 흡유율 및 비표면적은 물론 신장비, 형상비, 구형도와 같은 형상 특성 면에서도 결코 뒤떨어지지 않는 분체 특성을 보인다. 이 같은 자성 백운석의 양호한 분체 특성은 원광에서의 기본적으로 높은 백운석 함유도와 비교적 높은 결정도에 기인한 것으로 여겨진다. 이 백운석은 비교적 높은 철분 함량과 황화광물의 혼재로 인해서 금속제련용을 제외한 소성용 용도로는 적합하지 않은 것으로 판단된다. 그렇지만 적절한 선광 공정이 적용된다면 현재 중탄용 석회석이 차지하고 있는 대부분의 충전재 응용 부문에서는 고품위석회석의 대체재로써 충분히 활용이 가능할 것으로 평가된다.

• 한국결정성장학회지
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• 제8권2호
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• pp.356-364
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• 1998

$ZTA:\;Al_2O_3/\;15\;vol{%}\;ZrO_2$ (Zirconia Toughened Alumina : ZTA)를 상압소결에 의해 제조시 분무건조한 granule의 특성에 따른 성형밀도 및 소결밀도의 변화를 고찰하여, 소결밀도의 재현성을 향상시킬 수 있는 성령 공정 조건을 제시하였다. 결합제의 첨가 유무에 따라 granule의 구형도, 평균크기, granule 내의 hollow의 생성정도, 수분함유량 등이 다름을 확인하였다. granule의 물성 차이가 성형거동에 미치는 영향을 성형압(80~120MPa)과 성형방법(일축성형과 정수압 성형)에 따른 성형밀도의 변화를 통하여 조사하였다. granule의 특성 변화에 의한 밀도의 낮은 재현성은 성형압과 성형방법의 최적화를 통하여 극복될 수 있음을 확인하였다. 즉 가능한 낮은 압력(80MPa)에서 일축성형한 후 고압(500MPa)에서 정수압 성형하였을 때 소결후 밀도변화는 1%이내에서 조절되었다.

• 공업화학
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• 제22권6호
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• pp.642-647
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• 2011

회전형 휘발성 산화장치(voloxidizer)와 200 g $U_3O_8$ 분말을 사용하여 초기 미세 입자층의 운동형태, 열처리 온도 및 시간, voloxidizer의 회전속도에 따른 다공성 그래뉼의 회수율과 특성을 분석하였다. 초기 미세 입자층의 운동형태에 따른 1 mm 이상의 그래뉼의 회수율은 rolling 운동 때보다 slumping 운동일 경우에 보다 높았다. 초기 미세 입자층이 rolling 운동형태인 경우에는 미세입자로부터 그래뉼이 생성됨에 따라서 slumping 운동형태로 변하며 slumping 빈도가 매우 높았다. 열처리 온도의 증가 및 10 h까지는 시간의 증가에 따라서 그래뉼의 회수율이 매우 크게 증가하였다. Slumping 운동형태를 보이는 초기 미세 입자층의 경우에 voloxidizer의 회전속도가 증가함에 따라서 그래뉼의 회수율 은 81.5에서 88.7%로 증가하였으나, 그래뉼 특성 측면에서 보면 회전속도가 2 rpm인 경우에 밀도, 파쇄강도, 구형도가 가장 높았다.