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자전고온합성법으로 제조한 이규화몰리브덴 발열체의 소결특성에 미치는 소결조건 및 첨가물의 영향
심건주,장대규,서창열,김운백,Sim, Geon-Ju,Jang, Dae-Gyu,Seo, Chang-Yeol,Kim, Un-Baek 한국재료학회 1995 한국재료학회지 Vol.5 No.8
MoSi$_2$heating elements were fabricated using MoSi$_2$, powder prepared by SHS. Their apparent density, electrical resistivity, bending strength and victors hardness were measured as a function of sintering temperature, time and the amount of ceramic additives. The additives were A1$_2$O$_3$, SiO$_2$and bentonite which were added as a plastisizer. The electrical resistivity of MoSi$_2$decreased with the increase in the apparent density as expected. It decreased when the additives were added and the increase was the largest for the case of SiO$_2$. The bending strength and hardness decreased when the grain size becomes larger which is opposite to the expectation from the Hall-Petch type relation. Instead, they showed inverse proportionality with the volume fraction of pores probably in an exponential manner. The strength and hardness also decreased with the additives.
마그네슘 합금의 플라스마전해산화 코팅에 영향을 미치는 제반 요소들에대한 고찰
심건주 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.5
Magnesium alloys, which possess excellent specific strength and castability, are highly susceptible to corrosion. Although anodizing is widely used to resolve this problem, it requires toxic electrolytes and produces relatively thin and weak surface coatings. Recently, plasma electrolytic oxidation (PEO) has emerged as an alternative to anodizing. Although it is derived from conventional anodizing, it uses eco-friendly electrolytes and forms thicker, denser, and harder coatings on the surface of magnesium alloys. However, PEO is a complex process involving physical, chemical, and electrochemical reactions, and it is influenced by various factors such as the alloy substrate composition, electrolyte/additive composition, and the electrical variables including the mode of power supply, applied voltage/current density, frequency, and duty cycle. In this article, the detailed effects of these parameters on the microstructure and properties of the PEO coatings are reviewed, and methods of improving the coatings are proposed.
산소/철분의 함량변화가 티타늄의 기계적 성질에 미치는 영향
심건주,이강인,장대규,서창열 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.1
Using a vacuum consumable arc melting furnace, the methods of adding oxygen and iron to pure titanium and the effects of these additives on the mechanical properties of titanium were studied. The chemical composition and mechanical properties of ASTM grads 1, 3 and 4 were used as targets in the experiments. Addition of oxygen in the form of Ti-10wt% O master alloy gave more consistent results than in the form of TiO₂. Iron was added in the form of powder. Under the pressure employed in the main experiment about 20% and 50% of oxygen and iron were found to be a loss in the process of melting, respectively. As a result oxygen and iron contents of the grades 3 and 4 turned out to be a little higher than expected, giving rise to the much higher ultimate tensile strength and yield strength but slightly higher reduction in area than the lower ASTM limits. The grade 1 to which nothing was added was satisfactory both in the chemical composition and mechanical properties.
심건주(Gun Choo Shim),최국선(Good Sun Choi) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
Titanium diboride and zirconium diboride powders were synthesized with TiO2(ZrO2)-B2O3-Mg by employing a magnesium thermite technique. In place of B2O3, H3BO3 was also tried as a source of boron with limited success. Removing the by-product MgO by acid leaching, metal borides of submicron size with basically spherical shape could be obtained. In the case of TiB2, a small amount of TiN was formed besides MgO during the synthesis reaction due to high temperature exposure of the reactants to air. Though ZrB2 could be similarly synthesized as TiB2 using the same technique, it was difficult to remove residual ZrO2 even after acid leaching. The presence of ZrN was not as apparent as that of TiN. The spark plasma sintering method was used to sinter the synthesized TiB2 without using any additives. At temperatures of 1600℃ and higher, relative density greater than 98% was obtained. The maximum Vickers hardness of the sintered body was 3360(32.9 GPa). Two sets of commercial powders with particle size of 3 and 16 μm respectively were tested at 2000℃ for comparison but they showed relative density less than 80%. The surface conditions of the sintered commercial powders were unfit for the hardness test.
박제신,심건주,Park, Je-Sin,Sim, Geon-Ju 한국재료학회 2001 한국재료학회지 Vol.11 No.9
Molybdenum-based thermal spray powder is widely used for coating the moving parts of the internal combustion engines due to its excellent wear resistance. A composite powder of the $Mo_{40}(Al_{1-x}Si_x)_{60}$ system was synthesized using the SHS method. The synthesized bulk was pulverized and specially treated to produce thermal spray powder. It was found that the synthesis reaction consisted of two-steps: the formation of $Al_8/Mo_3$ and the formation of Mo(Al,Si)$_2$. Both the temperature and the rate of the SHS reaction linearly increased with the increase of the value of x in $Mo_{40}(Al_{1-x}Si_x)_{60}$, The temperature and the rate of the reaction were also affected by the compacting density of the specimens, exhibiting the maximum valves at 62% and 60%, respectively. Since spherical shape is advantageous to the thermal spraying process, shape-control of the powder was attempted with PVA as a binding additive, resulting in the successful production of almost perfectly spherical powder of 80 $\mu\textrm{m}$ Ø$(d_{50})$ mean particle size.
자전고온합성법에 의한 이규화몰리브덴의 제조에 관한 연구
김원백,심건주,장대규,서창열,조통래 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.7
MoSi₂ powders were prepared by the SHS (Self-Propagating High-Temperature Synthesis) Method. The measured reaction temperatures varied from 1600K to 1900K, while the reaction rate varied from 1 to 4 ㎜/sec. More than 50% of major metallic impurities were removed through evaporation during the high-temperature synthesis. The reaction temperature and rate were the highest when the precursor Mo and Si powders were mixed at the stoichiometric ratio(Si/Mo=2). At this composition, the measured temperature at the reaction front was 1853K, slightly lower than the theoretical adiabatic temperature, 1900K. The small discrepancy indicates that the reaction is close to adiabatic but not perfectly so. When the precursor powders contained either Mo or Si in excess, both the reaction temperature and rate were found to decrease, with the decreasing rate steeper in Si-rich composition than in Mo-rich one. the difference was explained in terms of the amounts of MoSi₂ at each composition. The reaction rate increased with the apparent bulk density and decreased with the particle size. The apparent activation energy for the reaction was found to be 40±3 ㎉/㏖. This value corresponds to the activation energy of 43 ㎉/㏖ calculated from the growth of Mo_5Si₃ in Mo_5Si₂-Mo diffusion couple. The interdiffusion of Mo and Si through MoSi₂ controls the synthesis reaction.
김원백,심건주,장대규,서창열,Kim, Won-Baek,Sim, Geon-Ju,Jang, Dae-Gyu,Seo, Chang-Yeol 한국재료학회 1997 한국재료학회지 Vol.7 No.9
이규화몰리브덴 고온발열체의 제조공정을 개발하였다. 원료분말은 상용 MoSi$_{2}$분말이었으며 Bentonite, Si$_{3}$N$_{4}$, B, ThO$_{2}$를 각각 가소제와 첨가제로 사용하였다. 이들은 진공압출, 소결, 단자부 기계가공, U자형 성형, 용접 등의 과정을 거쳐 U자형 발열체로 제조되었다. 사용제품의 분석결과 최근 사용온도가 크게 증가된 것으로 알려진 190$0^{\circ}C$용 발열체는 다량(33wt%)의 W이 Mo을 치환하고 있는 것으로 나타났다. 발열체의 전기비저항은 겉보기 밀도가 증가함에 따라 급격하게 감소하는 경향을 보였으며 첨가물들의 영향은 미미하였다. 1400-1$600^{\circ}C$에서 용접한 경우 용접면에서의 전기비저항은 비용접부보다 낮았으며 용접온도가 증사함에 따라 감소하였다. 발열시험결과 제조된 발열체는 표면온도가 1$700^{\circ}C$이하에서는 문제가 없었으며 175$0^{\circ}C$ 이상의 온도에서는 원형의 융기가 표면에 발생하면서 급속하게 파괴되었다. 이 융기는 X-선 회절분석결과 SiO로 밝혀졌으며 따라서 발열체의 파괴는 MoSi$_{2}$/SiO$_{2}$계면에서의 Si(in MoSi$_{2}$) + SiO$_{2}$=2SiO(g)반응에 으해 일어나는 것으로 판단된다.