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Zr<sub>2</sub>WP<sub>2</sub>O<sub>12</sub> 세라믹스의 합성과 소결거동 연구
김용현,김남옥,이상진,Kim, Yong-Hyeon,Kim, Nam-Ok,Lee, Sang-Jin 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.6
$Zr_2WP_2O_{12}$ powder, which has a negative thermal expansion coefficient, was synthesized by a solid-state reaction with $ZrO_2$, $WO_3$ and $NH_4H_2PO_4$ as the starting materials. The synthesis behavior was dependent on the solvent media used in the wet mixing process. The $Zr_2WP_2O_{12}$ powder prepared with a solvent consisting of D. I. water was fully crystallized at $1200^{\circ}C$, showing a sub-micron particle size. According to the results obtained from a thermal analysis, a $ZrP_2O_7$ was synthesized at a low temperature of $310^{\circ}C$, after which it was reacted with $WO_3$ at $1200^{\circ}C$. A new sintering additive, $Al(OH)_3$, was applied for the densification of the $Zr_2WP_2O_{12}$ powders. The cold isostatically pressed samples were densified with 1 wt% $Al(OH)_3$ additive or more at $1200^{\circ}C$ for 4 h. The main densification mechanism was liquid-phase sintering due to the liquid which resulted from the reaction with amorphous or unstable $Al_2O_3$ and $WO_3$. The densified $Zr_2WP_2O_{12}$ ceramics showed a relative density of 90% and a negative thermal expansion coefficient of $-3.4{\times}10^{-6}/^{\circ}C$. When using ${\alpha}-Al_2O_3$ as the sintering agent, densification was not observed at $1200^{\circ}C$.
폴리머용액법 및 알루미나 seed를 도입한 YAG:Ce<sup>3+</sup> 형광체 분말 합성
김용현,이상진,Kim, Yong-Hyeon,Lee, Sang-Jin 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.1
$YAG:Ce^{3+}$ phosphor powders were synthesized using a $Al_2O_3$ seed (average particle size: 5 ${\mu}m$) by the polymer solution route. PVA solution was added to the sol precursors consisting of the seed powder and metal nitrate salts for homogeneous mixing in atomic scale. All dried precursor gels were calcined at $500^{\circ}C$ and then heated at $1400^{\circ}C{\sim}1500^{\circ}C$ in $N_2/H_2$ atmosphere. The final powders were characterized by using XRD, SEM, PSA, PL and PKG test. All synthesized powders were crystallized to YAG phase without intermediate phases of YAM or YAP. The phosphor properties and morphologies of the synthesized powders were strongly dependent on the PVA content. Finally, the synthesized $YAG:Ce^{3+}$ phosphor powder heated at $1500^{\circ}C$, which is prepared from 12:1 PVA content and has an average particle size of 15 ${\mu}m$, showed similar phosphor properties to a commercial phosphor powder.
김용현,백원계,신완순,여재익,Kim, Yong-Hyeon,Baek, Won-Kye,Sin, Wan-Soon,Yoh, Jai-Ick 한국군사과학기술학회 2011 한국군사과학기술학회지 Vol.14 No.6
The beam-matter interaction with various coating effects has received continued attention in the high power laser community. Previous works suggest that coatings promote target damage when compared to beaming on uncoated surface. Three types of paint coatings(Acrylic urethane, Silicone alkyd and Stealth blend) and a water coat on metals(Al, Ti and STS) are irradiated with a $CO_2$ laser. Both strain and temperature measurements are provided for assessing the instantaneous response characteristics of each coating on different metals. A selective combination of surface coats with metals has proven effective in either preventing or enhancing damage, both thermal and mechanical, associated with focused beaming on a target.
김용현,고성림,Kim, Yong-Hyeon,Go, Seong-Rim 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.3
The Surface, generated by end milling operation, is deteriorated by tool runout, vibration, friction, tool deflection, etc. Especially in cornering cut, surface accuracy is usually determined by varying cutting forces, which causes tool deflections. Cutting conditions like feed rate is usually kept constant during machining a part, which causes dimensional error in severe cutting. Cornering cut is a typical example of deterioration of surface accuracy when constant feed rate is applied. Therefore it becomes important to develop NC post processor module to determine optimal cutting conditions in various cutting situations. In this paper, cutting force is predicted in cornering cut with flat end mill and feed rate is determined by constraining constantly resultant force. Also some control characteristics of CNC machining center are evaluated.
김용현,Kim, Yong-Hyeon 대전대학교 군사연구원 2004 군사학연구 Vol.2 No.-
Development of science technology, computer network and software technology has not only changed various areas of the society, but also brought rapid change in the condition and the way of performing war. Historical lessons learned from the war in Iraq tells that military capabilities corresponding to the new paradigms of war needs to be assured in order to preserve national interest and take victory in future warfare. Thus, the performance in the latest war in Iraq, the estimated performance in future war and the performance of war in the Korean Peninsula has been put together and analyzed to indicate the direction our force should be built and the structure to be improved. Under all circumstances and threats the military must defend our nation and territory. When war breaks out the military must perform it's basic duty to end war by decisive operations. As the saying is "To preserve peace, prepare for war," continuous increase of military strength and improvement of military structure corresponding to the change of national security environment and weapon system is necessary.
북한 내부정치와 남북관계: 7.4, 남북기본합의서, 6.15 비교
김용현 평화문제연구소 2004 統一問題硏究 Vol.16 No.2
This treatise remarked cause what kind of effect paid attention in inside politician of North Korea process to important talks of north and south Korea: that the 7.4 north and south communique of Cold War, the Inter-Korean Basic Agreement of Cold War disband, the June 15 inter-Korean Joint Declaration of Post-Cold War. The results of this study are as follows: North Korea used the inter-Korea relationship to breakthrough. First, the side which applies the relationship the north and south with the crisis breakthrough which North Korea follows in international politic sudden change of world-wide dimension and Northeast Asia dimension was big is point. Second, the relationship of the north and south korea was applied from the North Korea inside politics of crisis or conversion process. Third, it will pay attention that as the breach against the economic crisis situation of North Korea was applied. Forth, It shows the North Korea inside politics change to relate with 7.4 north and south communique since then there is a necessity which will pay attention a point. In conclusion, North Korea is changing that the point is with the direction center from the political side to the economic side.
The Tensile Properties and Wear Behavior of Mixing-reinforced Composites by Squeeze Casting Process
김용현,이광학,Kim, Yong-Hyeon,Lee, Gwang-Hak Materials Research Society of Korea 1999 한국재료학회지 Vol.9 No.4
The tensile strength and water resistance of ADC12 alloy matrix composites reinforced with saffil/ceraklwool and saffil/Si particle prepared by squeeze casting have been investigated in room temperature and $250^{\circ}C$. Adhesive and scuffing wear phenomena was studied when load was changed to 10~40N and wear velocity was 2.0m/s at room temperature and $250^{\circ}C$. Generally, the morphology of tensile fractured surface revealed dimple pattern which implies ductile fracture of the composites. However, cleavage fracture was also observed in case of ADC12 alloy based saffil/Si particle composite. The maximum tensile strength of 320MPa was obtained in ADC12 alloy based composites reinforced by saffil/cerakwool(5:5) preformed fibers. In the results of dry wear test, it was observed that scuffing was occurred at 40N in room temperature and 30N for $250^{\circ}C$.