소결 기어용 표면치밀화 기술 개발

김기정(Kijung Kim),김기범(Kibum Kim),김성진(Seong Jin Kim),박현달(Hyundal Park) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11

The novel PM (powder metallurgy) steel for automotive power-train gear components were developed to reduce manufacturing cost, while meeting the requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out comparing to the conventional forged steel. The pinion gears for 6-speed auto-transmission were also manufactured by helical pressing, sintering, and external rolling process (selective surface densification). In order to evaluate the durability of the PM parts, the auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable bending and contact fatigue strengths. The PM gears also showed improved gear tooth profile and better performance during the transmission durability tests. In particular, the PM gears manufactured by helical pressing and selective surface densification showed a significant advantage in reducing the manufacturing cost of about 30% as compared to the conventional forged steel gear manufactured by tooth machining (hobbing, shaving, and grinding) process.

Ce³⁺-enriched core-shell ceria nanoparticles for silicate adsorption

Kim, Kijung,Seo, Jihoon,Lee, Myoungjae,Moon, Jinok,Lee, Kangchun,Yi, Dong Kee,Paik, Ungyu Published for the Materials Research Society by th 2017 Journal of materials research Vol.32 No.14

<▼1><B>Abstract</B><P/></▼1><▼2><P>Ce<SUP>3+</SUP> ions in ceria nanoparticles (NPs) play a role as reactive sites in the adsorption of silicate anions. However, the limited concentration of Ce<SUP>3+</SUP> ions in ceria NPs remains a major challenge in this regard. Herein, we report a simple strategy to synthesize Ce<SUP>3+</SUP>-enriched core-shell ceria NPs for enhanced adsorption of silicate anions. To increase the overall Ce<SUP>3+</SUP> concentration, a shell layer is composed of Ce<SUP>3+</SUP>-rich ultrasmall ceria NPs approximately 5 nm in size. The Ce<SUP>3+</SUP> concentration of such core-shell ceria NPs is increased by 12.7-17.1% relative to that of the pristine ceria NPs, resulting in increased adsorption of silicate anions. The Freundlich model fits the observed adsorption isotherm well and the constants of adsorption capacity (<I>K</I>F) and adsorption intensity (1/<I>n</I>) indicate higher adsorption affinity of the core-shell ceria NPs for silicate anions. We attribute these improvements to the increased Ce<SUP>3+</SUP> concentration contributed by the ultrasmall ceria coating. This strategy can be used for enhancing the reactivity of ceria materials.</P></▼2>

An autodriven, solar fuel collection for a highly compact, biomimetic-modified artificial leaf without membrane

Kim, Sangkuk,Han, Kiduk,Kim, Wuseok,Jeon, Sangmin,Yong, Kijung Elsevier 2019 Nano energy Vol.58 No.-

<P><B>Abstract</B></P> <P>Hydrogen fuel generation from water splitting has recently attracted much attention due to its high potential as a clean, renewable energy source. To obtain pure H<SUB>2</SUB> fuel, it is inevitably required to separate the H<SUB>2</SUB>/O<SUB>2</SUB> product gas mixture, mainly relying on a membrane system at the current stage. However, this process has inherent durability and cost issues due to contamination, corrosion and its complex configuration. In our current work, we invented a highly compact gas separation and collection method in a water electrolysis system, which is set onto a biomimetically modified electrode without the use of a membrane or external convective flow. A key idea of this smart, compact and self-driven system is gas bubble manipulation by buoyant force and a slippery liquid infused porous surface (SLIPS). With the critical help of the biomimetic SLIPS wall by blocking bubble leakage, H<SUB>2</SUB> and O<SUB>2</SUB> product gases can be separately collected at the corresponding collection port. As a result, we achieved a remarkably improved H<SUB>2</SUB> collection value of over 90% with high purity using this membrane-free electrolysis system in which the product gases are separated only by their intrinsic buoyancy. This simple but effective gas separation/collection system is also applied to a highly compact, monolithic artificial leaf, in which the solar water splitting is practicably and conveniently conducted in a compact, floatable design.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A membrane-free gas separation method is invented for monolithic artificial leaf. </LI> <LI> Buoyance force and biomimetic surface design is combined for gas bubble manipulation. </LI> <LI> The collection efficiency of H<SUB>2</SUB> gas records over 90% with its high purity. </LI> <LI> O<SUB>2</SUB> gas, counter product of water electrolysis shows very low cross-over with high purity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A membrane-free, compact solar fuel collection system employing the biomimetic SLIPS of the pitcher plant with water splitting electrodes, showing its mechanism and performance in its gas separation/collection.</P> <P>[DISPLAY OMISSION]</P>

Increase in Ce³⁺ Concentration of Ceria Nanoparticles for High Removal Rate of SiO₂ in Chemical Mechanical Planarization

Kim, Kijung,Yi, Dong Kee,Paik, Ungyu The Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.9

<P>Ceria nanoparticles (NPs) are used as abrasives for silicon dioxide (SiO<SUB>2</SUB>) chemical mechanical planarization (CMP) due to the strong chemical bonds between the Ce<SUP>3+</SUP> ions of ceria NPs and the hydrated silicate species on the surface of SiO<SUB>2</SUB> films. However, the limited concentration of Ce<SUP>3+</SUP> ions in ceria NPs remains a major challenge for this application. Herein, we report a simple strategy to synthesize ceria NPs with high concentrations of Ce<SUP>3+</SUP> ions for enhanced adsorption reactions with silicate anions. Three types of ceria NPs approximately 70 nm in size were synthesized via the aggregation of different sized primary NPs. As the particle size of the primary NPs decreased from 70 nm to 5 nm, the Ce<SUP>3+</SUP> concentration of the ceria NPs increased from 15.6 to 24.0%. The adsorption isotherm fits the Freundlich model and the constants of adsorption capacity (K<SUB>F</SUB>) and adsorption intensity (1/n) indicate that the adsorption affinity for silicate anions increased with increasing Ce<SUP>3+</SUP> concentration. The increase in Ce<SUP>3+</SUP> concentration led to an increase in the chemical adsorption between ceria NPs and silicate anions, resulting in a high removal rate of SiO<SUB>2</SUB> during CMP.</P>

Investigations on association schemes with elementary abelian thin residue

Kim, Kijung,Song, Sung-Yell,Xu, Bangteng North-Holland Pub. Co 2017 Discrete mathematics Vol.340 No.12

<P><B>Abstract</B></P> <P>In this paper, we give a new class of association schemes whose thin residues are isomorphic to an elementary abelian p -group of order <SUP> p 2 </SUP> . We then study the automorphism groups of these schemes and determine whether these schemes are schurian.</P>

Morphologically well-defined Gd_0.1Ce_0.9O_1.95 embedded Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ nanofiber with an enhanced triple phase boundary as cathode for low-temperature solid

Kim, Chanho,Park, Hyunjung,Jang, Inyoung,Kim, Sungmin,Kim, Kijung,Yoon, Heesung,Paik, Ungyu Elsevier 2018 Journal of Power Sources Vol.378 No.-

<P><B>Abstract</B></P> <P>Controlling triple phase boundary (TPB), an intersection of the ionic conductor, electronic conductor and gas phase as a major reaction site, is a key to improve cell performances for low-temperature solid oxide fuel cells. We report a synthesis of morphologically well-defined Gd<SUB>0.1</SUB>Ce<SUB>0.9</SUB>O<SUB>1.95</SUB> (GDC) embedded Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3-δ</SUB> (BSCF) nanofibers and their electrochemical performances as a cathode. Electrospun fibers prepared with a polymeric solution that contains crystalline Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3-δ</SUB> particles in ∼200 nm size and Gd(NO<SUB>3</SUB>)<SUB>3</SUB>/Ce(NO<SUB>3</SUB>)<SUB>3</SUB> precursors in an optimized weight ratio of 3 to 2 result in one dimensional structure without severe agglomeration and morphological collapse even after a high calcination at 1000 °C. As-prepared nanofibers have fast electron pathways along the axial direction of fibers, a higher surface area of 7.5 m<SUP>2</SUP> g<SUP>−1</SUP>, and more oxygen reaction sites at TPBs than those of GDC/BSCF composite particles and core-shell nanofibers. As a result, the Gd<SUB>0.1</SUB>Ce<SUB>0.9</SUB>O<SUB>1.95</SUB> embedded Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3-δ</SUB> nanofiber cell shows excellent performances of the maximum power density of 0.65 W cm<SUP>−2</SUP> at 550 °C and 1.02 W cm<SUP>−2</SUP> at 600 °C, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fibrous cathode of SOFC was fabricated <I>via</I> facile electrospinning method. </LI> <LI> GDC/BSCF heterogeneous structure prevents the agglomeration during sintering. </LI> <LI> Ideal morphology was proposed in terms of high TPB density and fast charge transfer. </LI> <LI> GDC/BSCF fibrous cathode shows higher activity than particulate composite. </LI> </UL> </P>

Highly Dispersed Fe³⁺-Substituted Colloidal Silica Nanoparticles for Defect-Free Tungsten Chemical Mechanical Planarization

Kim, Kijung,Seo, Jihoon,Lee, Myeongjae,Moon, Jinok,Lee, Kangchun,Yi, Dong Kee,Paik, Ungyu The Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.7

<P>Silica nanoparticles (NPs) are used as abrasives for tungsten chemical mechanical planarization (CMP) at acidic pH. However, the use of silica NPs at pH near their isoelectric point remains a problem because agglomeration due to low surface charge leads to defects on the tungsten surface during CMP. Herein, we report a simple strategy to increase the surface charge of silica NPs at acidic pH for defect-free tungsten CMP. The isomorphic substitution of Si4+ by Fe3+ ions on the surface of silica NPs by hydrothermal reaction led to a pH-independent permanent negative surface charge, which increased as the concentration of substituted Fe3+ ions increased. At acidic pH, the increased negative surface charge of Fe3+-substituted silica (Fe-silica) NPs resulted in a reduction in the number of agglomerated large particles relative to that of pure silica NPs. As a result, highly negatively-charged Fe-silica NPs showed high performance in the reduction of defect count on the tungsten surface after CMP. (C) 2017 The Electrochemical Society. All rights reserved.</P>

Communication—Reduction of Friction Force between Ceria and SiO₂ for Low Dishing in STI CMP

Kim, Kijung,Lee, Kangchun,Seo, Jihoon,Song, Taeseup The Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.10

<P>We investigated the effect of friction force between ceria abrasive and SiO<SUB>2</SUB> film on dishing in STI CMP. The control of adsorption amount of poly acrylic acid (PAA) on ceria surface led to the reduction of the friction force during CMP. The reduced friction force by a thick surface layer on ceria resulted in the decrease of the dishing in STI structure during over-polishing process. In the patterned wafer, the dishing decreased from 976 to 594 Å/min at 37.5% pattern density (Si<SUB>3</SUB>N<SUB>4</SUB>/SiO<SUB>2</SUB> = 30/50 μm) as a maximum adsorption amount increased from 0.49 to 0.64 mg/m<SUP>2</SUP>.</P>

Fenton-Like Reaction between Copper Ions and Hydrogen Peroxide for High Removal Rate of Tungsten in Chemical Mechanical Planarization

Kim, Kijung,Lee, Kangchun,So, Sounghyun,Cho, Sungwook,Lee, Myeongjae,You, Keungtae,Moon, Jinok,Song, Taeseup The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.3

<P>The Fenton reaction has been used for the tungsten oxidation under acidic conditions in tungsten chemical mechanical planarization (CMP). However, the narrow working pH window required for ideal reaction limits its application. Herein, we report a simple Fenton-like system via the reaction between copper ion and hydrogen peroxide (H2O2) for the tungsten oxidation over a broad pH range. Copper ion was employed as a reactant with H2O2 for the Fenton-like reaction, resulting in high production rates of hydroxyl radicals in the range of acidic to neutral pH, which leads to a high rate of tungsten oxidation. As a result, the Fenton-like reaction between copper ions and H2O2 enables the high removal rates of tungsten films during CMP process in acidic to neutral pH ranges. (C) 2018 The Electrochemical Society.</P>

Communication—Selective Adsorption of PEG on SiO₂ for High Removal Selectivity in Tungsten CMP

Kim, Kijung,Lee, Kangchun,So, Sounghyun,Cho, Sungwook,Lee, Myeongjae,You, Keungtae,Moon, Jinok,Song, Taeseup The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.3

<P>We studied the effect of selective adsorption of polyethylene glycol (PEG) on SiO2 for high removal selectivity of tungsten to SiO2 in tungsten CMP. The hydrogen bonding between PEG and SiO2 increased as the solution pH decreased. At pH 3, the maximum adsorption of PEG on SiO2 occurred due to the low surface charge of SiO2 (near its isoelectric point). The selective adsorption led to the selective reduction of removal rate of SiO2 during CMP process. As a result, the removal selectivity increased from 4.5 to 85.5 as the PEG concentration increased from 0 to 9 wt% at pH 3. (C) 2018 The Electrochemical Society.</P>